Magnetic oxide and process for producing same

TECHNICAL FIELD
The present invention relates to a magnetic oxide suitable for use in a wide range of technical fields, e.g., those of toners and carriers for electrophotography, electric resistance elements and magnetic fluids, which magnetic oxide is produced by mixing a magnetization control material of Ca, Ti, Sn, Si or Mg with hematite, hematite+magnetite, or magnetite to obtain a mixed powder and sintering the mixed powder so that it exhibits a given saturation magnetization. Also, the present invention relates to a process for producing the above magnetic oxide.
BACKGROUND ART
A single phase magnetite powder as one of the magnetic oxides has been utilized in a wide range of technical fields, e.g., those of magnetic fluids, electric resistance elements and toners and carriers for electrophotography. It is highly desired in the art to mass-produce a single phase magnetite powder exhibiting any predetermined saturation magnetization at a lowered cost.
The following three general methods are known for producing such a magnetite, and it is know that they have respective drawbacks as described below.
(1) Wet Process: an aqueous solution of Fe.sup.2+ +2Fe.sup.+3 is rendered alkaline and coprecipitated.
Drawbacks: production cost is high and it is not suitable for mass production, although fine particles each having a relatively high purity are readily obtained by coprecipitation.
(2) Dry Process: hematite is heated in either hydrogen and carbon monoxide or steam to thereby be reduced.
Drawbacks: the reaction is performed in a relatively highly reducing atmosphere, e.g., either high pressure steam or hydrogen and carbon monoxide, so that danger accompanies the mass production, and that large scale equipment is required.
(3) Process in which natural magnetite is pulverized.
Drawbacks: a natural mineral is used as a starting material, so that it is difficult to stably produce fine quality powder for a prolonged period of time.
The magnetite powders produced by the above conventional processes have a drawback in that their saturation magnetization values are so high as compared with those of the conventional spinel ferrite that it is unfeasible to attain control of the saturation magnetization by composition regulation with the result that the conventional magnetite powders cannot be employed in use in which the saturation magnetization values inherent in magnetite powder are unacceptable. Magnetite powder having a saturation magnetization value inherent therein (fixed value specified in the second experimental example described later, e.g., up to 92 emu/g) has only partly been employed in use in carriers for electrophotographic development and the like. Moreover, the above magnetite powder having the saturation magnetization value inherent therein as it is cannot replace ferrite or the like in uses in which it has been employed, and, when the replacement is to be made, it is required to alter the circuit or device to be employed disadvantageously.
Taking into account the advantages and disadvantages of the above processes, various proposals have been made with respect to the production of magnetite powder for use in magnetic toners for electrophotography, etc.
For example, Japanese Patent Publication Nos. 238,580/1987, 39,498/1990 and 51,505/1990 disclose processes for producing magnetite useful as a carrier component of an electrophotographic developer, especially a two-component developer composed of a toner and a carrier. Each of these processes comprises providing magnetite powder (or globular magnetite particles) as a starting material, granulating the same into globular grains through, for example, mixing with a binder, followed by heating (sintering), and applying a resin coating to the resultant globular magnetite particles according to the conventional technique.
The use of a material called soft ferrite as carrier particles is known (U.S. Pat. No. 3,929,657, etc.). In this connection, it is known that the carrier particles each composed of the above ferrite not only are excellent in magnetic properties but also do not require a resin coating layer, so that their durability is excellent. Nothing that ferrite particles have resistance variations depending on the control of sintering atmosphere, even with the same composition, attempts have been made to enlarge resistance variation ranges by changing the sintering atmosphere. As an example thereof, there can be mentioned an attempt described in Japanese Patent Publication No. 37782/1987. This comprises providing an Mg ferrite as a starting material and increasing the amount of ferric oxide (Fe.sub.2 O.sub.3) to more that 53% by mole so as to enlarge its resistance variation range.
DISCLOSURE OF THE INVENTION
The Inventor's primary object, in view of the above prior art, is to easily mass-produce a magnetic oxide, in particular, a magnetic oxide exhibiting any desired saturation magnetization at a lowered cost by mixing a magnetization control material of Ca, Ti, Sn, Si or Mg with hematite, hematite+magnetite, or magnetite to obtain a mixed powder, further mixing a substance having a carbon-to-carbon single or double bond with the mixed powder and sintering the obtained mixture.
Another object of the present invention is to provide a process for mass-producing the above magnetic oxide of fine quality at a lowered cost and safely by simple equipment and operation, as compared with the above conventional processes.
A further object of the present invention is to provide a process for mass-producing the above magnetic oxide having any desired saturation magnetization value.
According to the present invention, there is provided a magnetic oxide obtained by mixing a given amount ranging from 0.20 to 76.0% by weight of at least one member selected from among Ca, Ti, Sn, Si and Mg magnetization control (regulation) materials with hematite, hematite+magnetite, or magnetite as a starting material to obtain a mixed powder, adding 0.1 to 4.0% by weight of a liquid or powdery substance having a carbon-to-carbon single or double bond to the mixed powder, stirring the mixture to obtain a substantially homogeneous mixture and sintering the obtained mixture in an inert gas at 550.degree. to 1500.degree. C., and also provided is a process for producing the same.
In the above magnetic oxide and the process for producing the same, preferred conditions for embodying the present invention are as set forth below with respect to each magnetization control material.
In the employment of Ca compound
(1) Starting material: hematite or hematite+magnetite
Ca compound: 1.43 to 64.0% by weight (in terms of Ca)
Sintering temperature: 1200.degree. to 1450.degree. C.
(2) Starting material: magnetite
Ca compound: 1.43 to 64.0% by weight (in terms of Ca)
Sintering temperature: 550.degree. to 1450.degree. C.
In the employment of Ti compound
(3) Starting material: hematite+magnetite
Hematite: 0.0 to 79.0% by weight
Magnetite: 9.8 to 98.8% by weight
Ti compound: 1.2 to 52.7% by weight (in terms of Ti) Sintering temperature: 1200.degree. to 1450.degree. C.
(4) Magnetite: 47.3 to 98.8% by weight
Ti compound: 1.2 to 52.7% by weight
Sintering temperature: 550.degree. to 1450.degree. C.
In the employment of Sn compound
(5) Hematite or hematite+magnetite: 24.0 to 99.2% by weight
Sn compound: 0.8 to 76.0% by weight
Sintering temperature: 1200.degree. to 1450.degree. C.
(6) Magnetite: 24.0 to 99.2% by weight
Sn compound: 0.8 to 76.0% by weight
Sintering temperature: 550.degree. to 1450.degree. C.
In the employment of Si compound
(7) Hematite (or hematite+magnetite): 35 to 99.5% by weight
Si compound: 0.5 to 65% by weight
Sintering temperature: 1200.degree. to 1450.degree. C.
(8) Magnetite: 35 to 99.5% by weight
Si compound: 35 to 99.5% by weight
Sintering temperature: 550.degree. to 1450.degree. C.
In the employment of Mg compound
(9) Starting compound: hematite (or hematite+magnetite)
Mg compound: 0.20 to 18.50% by weight
Sintering temperature: 550.degree. to 1500.degree. C.
(10) Starting compound: magnetite
Mg compound: 0.20 to 26.20% by weight
Sintering temperature: 550.degree. to 1500.degree. C.
(11) Starting compound: hematite (or hematite+magnetite)
Addition of manganese: 0.20 to 10.0% by weight
Mg compound: 0.20 to 26.20% by weight
Sintering temperature: 550.degree. to 1500.degree. C.
(12) Starting compound: magnetite
Addition of manganese: 0.20 to 10.0% by weight
Mg compound: 0.20 to 26.20% by weight
Sintering temperature: 550.degree. to 1500.degree. C.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory view of the steps taken in the first embodiment of the present invention;
FIG. 2 is a view of an exemplary heating curve suitable for sintering in the first embodiment;
FIG. 3 is an explanatory view of the saturation magnetization referred to in the present invention;
FIG. 4 is an explanatory view of the steps taken in the second embodiment of the present invention;
FIG. 5 is a view of an exemplary heating-cooling curve suitable for the second embodiment of the present invention;
FIG. 6 is an explanatory view of the steps taken in the third embodiment of the present invention;
FIG. 7 is a view of an exemplary heating-cooling curve suitable for the third embodiment of the present invention;
FIG. 8 is an explanatory view of the steps taken in the fourth embodiment of the present invention;
FIG. 9 is a view of an exemplary heating-cooling curve suitable for the fourth embodiment of the present invention;
FIG. 10 is an explanatory view of the steps taken in the fifth embodiment of the present invention;
FIGS. 11(a), 11(b) and 11(c) are explanatory view of the ranges of saturation magnetization control attained in the fifth embodiment of the present invention;
FIGS. 12(a) and 12(b) are explanatory views of the grain strengths attained in the fifth embodiment of the present invention; and
FIG. 13 is a view of an exemplary heating curve suitable for the fifth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will now be described with reference to the following Experimental Examples.
First Embodiment
Referring to FIG. 1, hematite, hematite+magnetite, or magnetite is blended with 1.43 to 64.0% by weight of Ca to form a mixed powder in the blending step 1. The term "Ca" is employed herein for simplification of the description of the specification, and means the Ca moiety, expressed in % by weight, of organic and inorganic compounds each containing Ca, such as CaO, CaCO.sub.3, Ca(OH).sub.2, CaCl.sub.2 and CaF.sub.2. The sum of the weight percentage of hematite, hematite+magnetite, or magnetite and the 1.43 to 64.0% by weight of this Ca is 100% by weight (that is, for example, the weight percentage of the "O" moiety of CaO is not contained n the value of 100% by weight). The terminology "hematite+magnetite" employed herein means a mixture (mixed powder) of hematite and magnetite. In particular, the magnetite as a starting material may be either of:
(1) magnetite powder (produced in the house or purchased from other companies), and
(2) magnetite powder obtained by pulverizing a product having an off-specification particle size (recovered item) so as for the same to have the given particle size.
The product grains described later are those each composed of, for example, 10.sup.3 to 10.sup.7 starting powder particles (1-3 .mu.m) gathered into a globular form having a diameter of 50 to 100 .mu.m. Thus, any once produced magnetite powder product (off-specification item) can be pulverized to thereby easily obtain the desired starting material powder.
In the mixing step 2, the above mixed powder is mixed with 0.1 to 4.0% by weight of a compound having --C--C-- or --C.dbd.C-- in its molecules (liquid or solid substance). For example, 2% by weight of PVA (polyvinyl alcohol) as a binder and 1% by weight of a polycarboxylate as a dispersant are added to hematite powder as a starting material, and further water is added for granulation into globular grains. The amount of waster added is in the range of 30 to 70% by weight. When the amount of water was less that 30% by weight, the viscosity of a slurry obtained by milling was too high to be granulated into globular grains. On the other hand, when the amount of waster exceeded 70% by weight, the slurry concentration was too low to be granulated into dense globular grains.
In the wet-milling step 3, the mixture obtained in the mixing step 2 is wetly crushed in an attrition mill to thereby prepare a slurry having a mixed powder concentration of about 50% by weight.
In the granulating step 4, globular grains are formed. In this step, the slurry is agitated in an attrition mill for 1 hr, and subjected to hot-air drying by a spray dryer to obtain globular grains.
In the sintering step 5, the grains obtained in the granulating step 4 are heated at 1200.degree. to 1450.degree. C., provided that those of magnetite may be heated at 550.degree. to 1450.degree. C., in an atmosphere of an inert gas such as nitrogen gas for 2 hr to thereby obtain powder in which single phase magnetite and another magnetic and/or nonmagnetic phase are coexistent. The value of saturation magnetization of the powder can be regulated by the amount of Ca added, so that it is feasible to produce a powdery magnetic oxide having any desired saturation magnetization by changing the amount of Ca added (see Tables 1 to 4). When hematite is present in part of the hematite or magnetite powder, during the 1200.degree. to 1450.degree. C. sintering step 5, not only is the thermal transition from hematite to magnetite effected in the inert gas (in weakly reducing atmosphere) but also the organic substance mixed is brought by the heating in the inert gas into the state of incomplete combustion, in which the hematite is deprived of oxygen during the thermal decomposition of the organic substance to thereby be reduced to markedly promote the conversion to magnetite. In particular, with respect to magnetite, a magnetic oxide having any desired saturation magnetization can be obtained by the sintering at temperatures as relatively low as 550.degree. to 1450.degree. C. This is because there is no need for newly making conversion into magnetite (reduction of hematite), so that the strength required for handling, etc. can be obtained by bonding or mild sintering of the starting material magnetite in the form of a vast plurality of grains.
In the disintegration step 6, the powder in which single phase magnetite and nonmagnetic phase are coexistent, obtained in the sintering step 5, is crushed into a product. According to the above steps, hematite, hematite+magnetite, or magnetite is mixed with the above Ca to obtain a mixed powder, and this mixed powder is further mixed with a compound having --C--C-- or --C.dbd.C-- in its molecules (liquid or solid substance) and water, milled well, hot-air dried, granulated into globular grains and sintered in an inert gas at 1200.degree. to 1450.degree. C., provided that the sintering of magnetite is conducted at 550.degree. to 1450.degree. C., so that the powder in which magnetite and nonmagnetic phase are coexistent (magnetic oxide powder) can be produced. Thus, it has become feasible to safely mass-produce the magnetic oxide powder having any desired saturation magnetization at a lowered cost. Descriptions wilt be made in order below.
Table 1 shows sintering experiment results (hematite) of the present invention. In the experiment, Ca was blended with hematite powder in the amount specified in the Table, and mixed with water to obtain a slurry having a powder concentration of 50% by weight. The slurry was agitated in an attrition mill for 1 hr, and dried at 110.degree. C. 1.0% by weight of polyvinyl alcohol was added to the obtained powder. The mixture was mixed in a mortar, and sifted through a 425-.mu.m-mesh standard sieve to obtain grains. 0.5 g of the resultant grains were put in a cylindrical mold having a diameter of 12.5 mm, and shaped under a molding pressure of 1 t/cm.sup.2. The molding was heated at 1100.degree. to 1500.degree. C. for 2 hr in nitrogen gas. The saturation magnetization of each sample after the heating was measured by means of an vibrating sample magnetometer.
(1) When Ca was not added (Sample Nos. 9, 17 and 25) and the conversion to single phase magnetite was effected, the saturation magnetization of each of the samples was 92 emu/g.
(2) When the heating was conducted at 1100.degree. C., the conversion to magnetite was incomplete so as for hematite (.alpha.-Fe.sub.2 O.sub.3) to remain with the result that the saturation magnetization values of Sample Nos. 1 to 8 were 80 emu/g or less to show the inappropriateness of the heating temperature of 1100.degree. C. On the other hand, when the heating was conducted at 1500.degree. C., the conversion to magnetite was incomplete so as to form wustite (FeO) with the result that the saturation magnetization values of Sample Nos. 33 to 40 were as low as 87 emu/g or less to show the inappropriateness of the heating temperature of 1500.degree. C. Therefore, it has been found that the appropriate heating temperature is in the range of 1200.degree. to 1450.degree. C., the amount of Ca added was increased from 0% by weight. Sample Nos. 11, 19 and 27 of Table 1 containing Ca in an amount of 1.43% by weight exhibited a slight change in saturation magnetization as compared with the sample not containing Ca. The above value of 1.43% by weight was taken as the lower limit of the amount of Ca to be added. On the other hand, the upper limit of the amount of Ca to be added was taken as 10.65% by weight at which the saturation magnetization attributed to the nonmagnetic phase formed by the amount of Ca increased from 1.43% by weight was 20 to 10 emu/g or which was just below the value at which melting would occur during the sintering. Therefore, the amount of Ca to be added to hematite was appropriately in the range of 1.43 to 10.65% by weight.
It has been found from the above experimental results that powder (magnetic oxide) having an arbitrary saturation magnetization in which magnetite and nonmagnetic phase are coexistent can be formed by sintering at 1200.degree. to 1450.degree. C. for 2 hr a mixed powder obtained by mixing 1.43 to 10.65% by weight of Ca with hematite.
Table 2 shows sintering experiment results regarding hematite+magnetite. In the experiment, Ca was blended in the amount specified in the Table with powder of 1:1 mixture of hematite and magnetite, and treated and measured in the same manner as described above with respect to Table 1.
(1) When Ca was not added (Sample Nos. 9, 17 and 25), the saturation magnetization of each of the samples was 92 emu/g.
(2) When the heating was conducted at 1100.degree. C., the conversion to magnetite was incomplete so as for hematite (.alpha.-FE.sub.2 O.sub.3) to remain with the result that the saturation magnetization values of Sample Nos. 1 to 8 saturation magnetization values of Sample Nos. 1 to 8 were 67 emu/g or less to show the inappropriateness of the heating temperature of 1100.degree. C. On the other hand, when the heating was conducted at 1500.degree. C., the conversion to magnetite was incomplete so as to form wustite (FeO) with the result that the saturation magnetization values of Sample Nos. 33 to 40 were as low as 87 emu/g or less to show the inappropriateness of the heating temperature of 1500.degree. C. Therefore, it has been found that the appropriate heating temperature is in the range of 1200.degree. to 1450.degree. C.
(3) while the heating was conducted at a temperature ranging from 1200.degree. to 1450.degree. C., the amount of Ca added was increased from 0% by weight. Sample Nos. 11, 19 and 27 of Table 2 containing Ca in an amount of 1.43% by weight exhibited a slight change in saturation magnetization as compared with the sample not containing Ca. The above value of 1.43% by weight was taken as the lower limit of the amount of Ca to be added. On the other hand, the upper limit of the amount of Ca to be added was taken as 10.65% by weight at which the saturation magnetization attributed to the nonmagnetic phase formed by the amount of Ca increased from 1.43% by weight was 20 to 10 emu/g or which was just below the value at which melting would occur during the sintering. Therefore, the amount of Ca to be added to hematite+magnetite was appropriately in the range of 1.43 to 10.65% by weight.
It has been found from the above experimental results that powder (magnetic oxide) having an arbitrary saturation magnetization in which magnetite and nonmagnetic phase are coexistent can be formed by sintering at 1200.degree. to 1450.degree. C. for 2 hr a mixed powder obtained by mixing 1.43 to 10.65% by weight of Ca with hematite+magnetite.
Table 3 shows sintering experiment results regarding magnetite. In the experiment, Ca was blended with magnetite powder in the amount specified in the Table, and treated and measured in the same manner as described above with respect to Table 1.
(1) When Ca was not added (Sample Nos. 13, 25, 37, 49, 61 and 73), the saturation magnetization of each of the samples was 91 to 92 emu/g.
(2) When the heating was conducted at 500.degree. C., the magnetite was converted to hematite (.alpha.-FE.sub.2 O.sub.3) with the result that the saturation magnetization values of Sample Nos. 1 to 12 were as low as 86 emu/g to show the inappropriateness of the heating temperature of 500.degree. C. The cause of the phenomenon of the above conversion has been found to be the partial oxidation of the magnetite to hematite by a trace (for example, on the order of 10 ppm) of inevitable O.sub.2 contained in the inert gas (nitrogen gas in this embodiment). On the other hand, when the heating was conducted at 1500.degree. C., the magnetite was converted to wustite (FeO) with the result that the saturation magnetization values of Sample Nos. 85 to 96 were as low as 86 emu/g or less to show the inappropriateness of the heating temperature of 1500.degree. C. Therefore, it has been found that the appropriate heating temperature is in the range of 550.degree. to 1450.degree. C.
(3) While the heating was conducted at a temperature ranging from 550.degree. to 1450.degree. C., the amount of Ca added was increased from 0% by weight. Sample Nos. 15, 27, 39, 51 63 and 75 of Table 3 containing Ca in an amount of 1,434 by weight exhibited a slight change in saturation magnetization as compared with the sample not containing Ca. The above value of 1.43% by weight was taken as the lower limit of the amount of Ca to be added. On the other hand, the upper limit of the amount of Ca to be added was taken as 64.0% by weight at which the saturation magnetization attributed to the nonmagnetic phase formed by the amount of Ca increased from 1.43% by weight was as low as 20 to 10 emu/g as observed with respect to Sample Nos. 24, 36, 45 and 57 of Table 3 or which was just below the value at which melting would occur during the sintering. Therefore, the amount of Ca to be added to magnetite was appropriately in the range of 1.43 to 64.0% by weight.
It has been found from the above experimental results that powder (magnetic oxide powder) having an arbitrary saturation magnetization in which magnetite and nonmagnetic phase are coexistent can be formed by sintering at 550.degree. to 1450.degree. C. for 2 hr a mixed powder obtained by mixing 1.43 to 64.0% by weight of Ca with magnetite.
FIG. 2 illustrates an exemplary heating curve suitable for the present invention. The curve shows an exemplary course of heating in which heating is conducted at T.degree.C. for 2 hr. In particular, the heating is so performed that the temperature is elevated at a rate of 200.degree. C./hr from room temperature to T.degree.C., which is held for 2 hr. Thereafter, the temperature is lowered to room temperature at a rate of 200.degree. C./hr. Herein, T.degree.C. is the heating temperature specified in Tables 1 to 3.
FIG. 3 illustrates the saturation magnetization referred to in the present invention. In particular, it is an explanatory view of the measurement of the saturation magnetization shown in Table 1 to 3. The axis of abscissa indicates the intensity of applied magnetic field (H Oe) while the axis of ordinate indicates the corresponding intensity of magnetization (M emu). The intensity of magnetization (Ms emu) of powder in which magnetite and nonmagnetic phase are coexistent is measured by the use of an vibrating sample magnetometer while keeping the application of, for example, 15 kOe magnetic field as specified in FIG. 3. The saturation magnetization is calculated by the following formula specified in the figure:
.delta.=Ms/[weight (g) of sample powder][emu/g]
The values calculated by the above formula are shown as the saturation magnetization .delta. s in Tables 1 to 3.
In the above embodiment, the saturation magnetization of magnetite is regulated only through the nonmagnetic phase created by the addition of Ca. In this connection, the saturation magnetization may further finely be regulated by the formation of an oxide phase (hematite, calcium peroxide, etc.), for example, on the surface of the magnetite powder.
Second Embodiment
The production of magnetic oxides having desired saturation magnetization values by mixing Ti compounds with magnetite or magnetite+hematite will now be described referring to FIGS. 4 and 5 and Tables 5 to 7.
______________________________________magnetite 47.3-98.8% by 9.8-98.8% by weight weighthematite none 0.0-79.0% by weightTi compound 1.2-52.7% by 1.2-52.7% by weight weight______________________________________ (Value for Ti compound: in terms of Ti)
In the mixing step 2, the above mixed powder is mixed with 0.1 to 4.0% by weight of a compound having --C--C or --C.dbd.C-- in its molecules (liquid or solid substance). For example, 2% by weight of PVA (polyvinyl alcohol) as a binder and 1% by weight of a polycarboxylate as a dispersant are added to the mixed powder as a starting material, and further water is added for granulation into globular grains. The amount of water added is in the range of 30 to 70% by weight. When the amount of water was less that 30% by weight, the viscosity of a slurry obtained by milling was too high to be granulated into globular grains. On the other hand, when the amount of water exceeded 70% by weight, the slurry concentration was too low to be granulated into dense globular grains.
In the wet-milling step 3, the mixture obtained in the mixing step 2 is wet milled in an attrition mill to thereby prepare a slurry having a mixed powder concentration of about 50% by weight.
In the granulating step 4, globular grains are formed. In thus step, the slurry is agitated in an attrition mill for 1 hr, and subjected to hot-air drying by a spray dryer to obtain globular grains.
In the sintering step 5, the grains obtained in the granulating step 4 are heated at 550.degree. to 1450.degree. C. (with respect to magnetite) in an atmosphere of an inert gas such as nitrogen gas for 2 hr to thereby form magnetite and another magnetic and/or nonmagnetic phase. The ratio of the nonmagnetic phase can be controlled by regulating the amount, in terms of Ti, of Ti compound added, so that it is feasible to produce a magnetic oxide having any desired saturation magnetization by changing the amount of Ti compound added (see FIG. 5). When hematite is present in part of the magnetite powder, during the 1200.degree. to 1450.degree. C. sintering step 5, not only is the thermal transition from hematite to magnetite effected in the inert gas (in weakly reducing atmosphere) but also the organic substance mixed is brought by the heating in the inert gas into the state of incomplete combustion, in which the hematite is deprived of oxygen during the thermal decomposition of the organic substance to thereby be reduced so as to markedly promote the conversion to magnetite.
In the disintegration step 6, the powder in which magnetite and nonmagnetic phase are coexistent, obtained in the sintering step 5, is crushed into a product.
According to the above steps, magnetite or magnetite+hematite is mixed with the Ti compound to obtain a mixed powder, and this mixed powder is further mixed with a compound having --C--C-- or --C.dbd.C-- in its molecules (liquid or solid substance) and water, milled well, hot-air dried, granulated into globular grains and sintered in an inert gas at 550.degree. to 1450.degree. C. (for only magnetite as the starting material) or 1200.degree. to 1450.degree. C. (for magnetite+hematite), so that the powder in which magnetite and another magnetic and/or nonmagnetic phase are coexistent (magnetic oxide powder) can be produced. Thus, it has become feasible to safely mass-produce the magnetic oxide powder having any desired saturation magnetization at a lowered cost.
Table 4 shows sintering experiment results (TiO.sub.2 : 0% by weight). PVA (polyvinyl alcohol) was added as a binder in the amount specified in Table 4 to hematite powder, and 1% by weight of a polycarboxylate as a dispersant and further water were added and agitated for granulation into grains. The resultant grains were sintered at the temperature specified in the Table, and the qualitative analysis thereof by powder X-ray diffractometry was conducted. Results are shown in Table 4. The following has been found from the results.
(1) No single phase magnetite was obtained from only hematite powder without the addition of PVA (Sample Nos. 1 to 8), even if the heating temperature was changed. The X-ray diffraction pattern shows the presence of the phase of .alpha.-FE.sub.2 O.sub.3 or FeO.
(2) When the amount of PVA added was set at 2% by weight and the heating temperature was varied, single phase magnetite (Fe.sub.3 O.sub.4 only) (Sample Nos. 13 to 15) was obtained at heating temperatures ranging from 1200.degree. to 1450.degree. C. .alpha.-FE.sub.2 O.sub.3 was coexistent at heating temperatures of 1150.degree. C. or below (Sample Nos. 9 to 12) and FeO was coexistent at heating temperatures of 1500.degree. C. or above (Sample No. 16). Therefore, it is requisite that the heating temperature be in the range of 1200.degree. to 1450.degree. C. (Sample Nos. 13 to 15).
(3) At a heating temperature of 1300.degree. C., the amount of PVA added was varied between 0.1 and 3.0% by weight. Single phase magnetite was obtained without exception (Sample Nos. 17 to 22).
It has been found from the above experimental results that single phase magnetite is formed as long as the amount of PVA added to hematite powder is 0.1% by weight (4% by weight) and the sintering is conducted at temperatures ranging from 1200.degree. to 1450.degree. C.
Tables 5 and 6 show experimental example results (magnetite plus Ti) of the present invention. In this experimental example, 0.0 to 84.4% by weight, in terms of Ti of powdery titanium oxide (TlO.sub.2) was mixed with magnetite powder, 1.0% by weight of polyvinyl alcohol was added, and further water was added and mixed to obtain a slurry having a powder concentration of 50% by weight. The slurry was agitated in an attrition mill for 1 hr, and granulated by means of a spray dryer. The thus obtained grains were heated at 400.degree. to 1500.degree. C. in nitrogen gas for 2 hr. The oxygen concentration of the nitrogen gas was measured by means of a zirconia oxygen concentration meter. The saturation magnetization of each heated sample was measured by means of the vibrating sample magnetometer (see FIG. 3 relating to the first embodiment). The material phase was identified by the powder X-ray diffractometry. The collapse test of each sample was conducted by the use of a microcompression tester (MCTM-500 manufactured by Shimadzu Corp.), and the corresponding grain strength was calculated according to the following Hiramatsu's formula.
(Grain strength)={2.8.times.(Breaking load of grains)}/{.pi..times.(Diameter of grain).sup.2 }
(1) Heating temperature range
As shown in Table 5, the formation of hematite (.alpha.-FE.sub.2 O.sub.3) attributed to the oxidation by trace O contained in nitrogen gas was not detected when the heating was performed at 500.degree. C. (Sample Nos. 1 to 12). However, the grains strength Pa was on the order of E6 (meaning 10.sup.6), so that the strength of globular grains formed by joining of a vast plurality of magnetite powder particles was weak to a practical disadvantage. On the other hand, it was found that, when the heating was performed at 1500.degree. C. (Sample Nos. 85 to 96), wustite (FeO) was formed, so that the single phase magnetite (Fe.sub.3 O.sub.4 only) cannot be obtained. Further, it was found that, when a Ti compound is mixed with magnetite as a starting material and the saturation magnetization is arbitrarily regulated by the formation of magnetite and another magnetic and/or nonmagnetic phase, the assurance of a strength required for actual handling by joining or mild sintering is satisfactory because it is not necessary to newly reduce the concerned magnetite for conversion to magnetite, so that desirable saturation magnetization regulation can be made even if the heating is performed at a temperature as low as 550.degree. C.
The above demonstrates that the suitable heating temperature range is from 550.degree. to 1450.degree. C.
(2) Amount of Ti added (% by weight)
Upon noting the amount, in terms of Ti, of powdery titanium oxide added (Sample Nos. 13 to 84) within the heating temperature range of 550.degree. to 1450.degree. C. set in section (1) above, it was found that the saturation magnetization was continuously decreased from 90 to 0 emu/g as the above amount was increased from 1.2 to 52.7% by weight. When the amount of Ti added exceeded 52.7% by weight, the saturation magnetization was decreased to about 0 emu/g to thereby cause the magnetic oxide to lose practicability.
Therefore, it has been found that the suitable amount, in terms of Ti, of Ti compound added is in the range of 1.2 to 52.7% by weight.
The above demonstrates that desirable single phase magnetite and another magnetic and/or nonmagnetic phase can be formed by mixing 1.2 to 52.7% by weight, in terms of Ti, of a Ti compound with magnetite and effecting the heating at 550.degree. to 1450.degree. C. (provided that 0.2 to 4.0% by weight of a substance having a carbon-to-carbon single or double bond is also added).
FIG. 5 shows exemplary saturation magnetization curves as functions of the amount of Ti added. The saturation magnetization curves are drawn in a graph in which the axis of abscissa indicates the weight percentage, in terms of Ti, of a Ti compound added while the axis of ordinate indicates the corresponding saturation magnetization value. They represent experimental example results shown in Table 3. In particular, the saturation magnetization curves are line segments formed by plotting data shown in Table 3 with respect to each of the heating temperature range of 550.degree. to 600.degree. C., heating temperature of 800.degree. C. and heating temperature range of 1100.degree. to 1450.degree. C. in a graph in which the axis of abscissa indicates the weight percentage of Ti added while the axis of ordinate indicates the corresponding saturation magnetization value emu/g and connecting the plots.
Once the saturation magnetization curves of FIG. 5 have been established, therefore, not only can the weight percentage of Ti to be added for obtaining the desired saturation magnetization emu/g be determined but also the saturation magnetization emu/g can contrarily be determined with respect to any certain weight percentage of Ti, to thereby ensure production of a magnetic oxide powder having a desired saturation magnetization.
Table 6 shows results of another experimental example (1:1 mixture of magnetite and hematite, Ti) according to the present invention. It shows experimental data obtained by varying the amount of Ti added as specified in the Table while the proportion of magnetite powder to hematite powder was kept at 1:1. In practice, 0.0 to 84.4% by weight, in terms of Ti, of titanium oxide (TiO.sub.2) was mixed with a mixture of magnetite and hematite powders whose proportion was kept at 1:1, and granulated in the same manner as specified in Table 5. The resultant grains were heated at 1100.degree. to 1500.degree. C. in nitrogen gas for 2 hr. After the heating, the samples were measured in the same manner as specified in Table 5, and results are shown in Table 6.
(1) Heating temperature range
Table 6 demonstrates that the heating at 1100.degree. C. (Sample Nos. 1 to 12) causes hematite (.alpha.-FE.sub.2 O.sub.3) to remain while the heating at 1500.degree. C. (Sample Nos. 37 to 48) forms wustite (FeO), so that the single phase magnetite (Fe.sub.3 O.sub.4 only) cannot be obtained.
Therefore, it has been found that the suitable heating temperature range is from 1200.degree. to 1450.degree. C.
(2) Amount of Ti added (% by weight)
Upon noting the amount, in terms of Ti, of powdery titanium oxide added (Sample Nos. 13 to 36) within the heating temperature range of 1200.degree. to 1450.degree. C. set in section (1) above, it was found that the saturation magnetization was continuously decreased from 87 to 0 eum/g as the above amount was increased from 1.2 to 52.7% by weight. When the amount of Ti added exceeded 52.7% by weight, the saturation magnetization was decreased to about 0 emu/g to thereby cause the magnetic oxide to lose practicability.
Therefore, it has been found that the suitable amount, in terms of Ti, of Ti compound to be added is in the range of 1.2 to 52.7% by weight.
The above demonstrates that desirable single phase magnetite and another magnetic and/or nonmagnetic phase can be formed by mixing 1.2 to 52.7% by weight, in terms of Ti, of a Ti compound with a 1:1 mixture of magnetite and hematite and effecting the heating at 1200.degree. to 1450.degree. C. (provided that 0.1 to 4.0% by weight of substance having a carbon-to carbon single or double bond is also added).
Table 7 shows results of an additional experimental example (1:3 mixture of magnetite and hematite, Ti). It shows experimental data obtained by varying the amount of Ti added as specified in the Table while the proportion of magnetite powder to hematite powder was kept at 1:3. In practice, 0.0 to 84.4% by weight, in terms of Ti, of powdery titanium oxide (TiO.sub.2) was mixed with a mixture of magnetite and hematite powders whose proportion was kept at 1:3 in the same manner as specified in Table 6, and granulated in the same manner as specified in Table 5. The resultant grains were heated at 1100.degree. to 1500.degree. C. in nitrogen gas for 2 hr. After the heating, the samples were measured in the same manner as specified in Table 5, and results are shown in Table 7.
(1) Heating temperature range
Table 7 demonstrates that the heating at 1100.degree. C. (Sample Nos. 1 to 12) causes hematite (.alpha.-FE.sub.2 O.sub.3) to remain while the heating at 1500.degree. C. (Sample Nos. 37 to 48) forms wustite (FeO), so that the single phase magnetite (Fe.sub.3 O.sub.4 only) cannot be obtained.
Therefore, it has been found that the suitable heating temperature range is from 1200.degree. to 1450.degree. C.
(2) Amount of Ti added (% by weight)
Upon noting the amount, in terms of Ti, of powdery titanium oxide added (Sample Nos. 13 to 36) within the heating temperature range of 1200.degree. to 1450.degree. C. set in section (1) above, it was found that the saturation magnetization was continuously decreased from 87 to 0 emu/g as the above amount was increased from 1.2 to 52.7% by weight. When the amount of Ti added exceeded 52.7% by weight, the saturation magnetization was decreased to about 0 emu/g to thereby cause the magnetic oxide to lose practicability.
Therefore, it has been found that the suitable amount, in terms of Ti, of Ti compound to be added is in the range of 1.2 to 52.7% by weight.
The above demonstrates that desirable single phase magnetite and another magnetic and/or nonmagnetic phase can be formed by mixing 1.2 to 52.7% by weight, in terms of Ti, of a Ti compound with a 1:3 mixture of magnetite and hematite and effecting the heating at 1200.degree. to 1450.degree. C. (provided that 0.1 to 4.0% by weight of a substance having a carbon-to-carbon single or double bond is also added).
Table 8 shows results of a further experimental example (1:4 mixture of magnetite and hematite, Ti). It shows experimental data obtained by varying the amount of Ti added as specified in the Table while the proportion of magnetite powder to hematite powder was kept at 1:4. In practice, 0.0 to 84.4% by weight, in terms of Ti, of powdery titanium oxide (TiO.sub.2) was mixed with a mixture of magnetite and hematite powders whose proportion was kept at 1:4 in the same manner as specified in Table 6, and granulated in the same manner as specified in Table 5. The resultant grains were heated at 1100.degree. to 1500.degree. C. in nitrogen gas for 2 hr. After the heating, the samples were measured in the same manner as specified in Table 5, and results are shown in Table 8.
(1) Heating temperature range
Table 8 demonstrates that the heating at 1100.degree. C. (Sample Nos. 1 to 12) causes hematite (.alpha.-FE.sub.2 O.sub.3) to remain while the heating at 1500.degree. C. (Sample Nos. 37 to 48) forms wustite (FeO), so that the single phase magnetite (Fe.sub.3 O.sub.4 only) cannot be obtained.
Therefore, it has been found that the suitable heating temperature range is from 1200.degree. to 1450.degree. C.
(2) Amount of Ti added (% by weight)
Upon noting the amount, in terms of Ti, of powdery titanium oxide added (Sample Nos. 13 to 36) within the heating temperature range of 1200.degree. to 1450.degree. C. set in section (1) above, it was found that the saturation magnetization was continuously decreased from 87 to 0 emu/g as the above amount was increased from 1.2 to 52.7% by weight. When the amount of Ti added exceeded 52.7% by weight, the saturation magnetization was decreased to about 0 emu/g to thereby cause the magnetic oxide to lose practicability.
Therefore, it has been found that the suitable amount, in terms of Ti, of Ti compound to be added is in the range of 12 to 52.7% by weight
Therefore, it has been found that the suitable amount, in terms of Ti, of Ti compound to be added is in the range of 1.2 to 52.7% by weight.
The above demonstrates that desirable single phase magnetite and another magnetic and/or nonmagnetic phase can be formed by mixing 1.2 to 52.7% by weight, in terms of Ti, of a Ti compound with a 1:4 mixture of magnetite and hematite and effecting the heating at 1200.degree. to 1450.degree. C. (provided that 0.1 to 4.0% by weight of a substance having a carbon-to-carbon single or double bond is also added).
Detailed descriptions on the heating curves and the saturation magnetization measurements are omitted in view of the similarity to and obviousness from those for FIGS. 2 and 3 relating to the first embodiment of the present invention.
Third Embodiment
The production of magnetic oxides having desired saturation magnetization values by mixing Sn compounds with hematite, hematite+magnetite, or magnetite will now be described referring to FIG. 6 and Tables 9 to 11.
Referring now to FIG. 6, hematite, hematite+magnetite or magnetite and an Sn compound are weighed and blended in the following proportions in the blending step 1.
______________________________________hematite 24.0-99.2% by weighthematite + magnetite 24.0-99.2% by weight, ormagnetite 24.0-99.2% by weighttogether with 0.8-87.6% by weight.Sn compound (in terms of Sn)______________________________________
Thus, a mixed powder is obtained.
In the mixing step 2, the above mixed powder is mixed with 0.1 to 4.0% by weight of a compound having --C--C-- or --C.dbd.C-- in its molecules (liquid or solid substance). For example, 2% by weight of PVA (polyvinyl alcohol) as a binder and 1% by weight of a polycarboxylate as a dispersant are added to the mixed powder as a starting material, and further water is added for granulation into globular grains. The amount of water added is in the range of 30 to 70% by weight. When the amount of water was less than 30% by weight, the viscosity of a slurry obtained by milling was too high to be granulated into globular grains. On the other hand, when the amount of water exceeded 70% by weight, the slurry concentration was too low to be granulated into dense globular grains.
In the wet-milling step 3, the mixture obtained in the mixing step 2 is wet crushed in an attrition mill to thereby prepare a slurry having a mixed powder concentration of about 50% by weight.
In the granulating step 4, globular grains are formed. In this step, the slurry is agitated in an attrition mill for 1 hr, and subjected to hot-air drying by a spray dryer to obtain globular grains.
In the sintering step 5, the grains obtained in the granulating step 4 are heated at 1200.degree. to 1450.degree. C. (with respect to hematite or hematite+magnetite) or 550.degree. to 1450.degree. C. (with respect to magnetite) in an atmosphere of an inert gas such as nitrogen gas for 2 hr to thereby form magnetite and another magnetic and/or nonmagnetic phase. The ratio of the nonmagnetic phase can be controlled by regulating the amount, in terms of Sn, compound added, so that it is feasible to produce a magnetic oxide having any desired saturation magnetization by changing the amount of Sn compound added. When hematite is present in part of the magnetite powder, not only is the thermal transition from hematite to magnetite effected in the inert gas (in weakly reducing atmosphere) but also the organic substance mixed is brought by the heating in the inert gas into the state of incomplete combustion, in which the hematite is deprived of oxygen during the thermal decomposition of the organic substance to thereby be reduced so as to markedly promote the conversion to magnetite.
In the crushing step 6, the powder in which magnetite and another magnetic and/or nonmagnetic phase are coexistent, obtained in the sintering step 5, is crushed into a product.
According to the above steps, hematite, hematite+magnetite, or magnetite is mixed with the Sn compound to obtain a mixed powder, and this mixed powder is further mixed with a compound having --C--C-- or --C.dbd.C-- in its molecules and water, milled well, hot-air dried, granulated into globular grains and sintered in an inert gas at 550.degree. to 1450.degree. C. (with respect to magnetite) to 1200.degree. to 1450.degree. C. (with respect to magnetite) or 1200.degree. to 1450.degree. C. (with respect to hematite or hematite+magnetite), so that the magnetic oxide powder in which magnetite and another magnetic and/or nonmagnetic phase are coexistent can be produced. Thus, it has become feasible to safely mass-produce the magnetic oxide powder having any desired saturation magnetization at a lowered cost. Descriptions will be made in order below.
Table 9 shows experimental example results (hematite, Sn) according to this embodiment. In this experimental example, 0.8 to 87.6% by weight, in terms of Sn of powdery tin oxide was mixed with hematite powder, 1.0% by weight of polyvinyl alcohol was added, and further water was added and mixed to obtain a slurry having a powder concentration of 50% by weight. The slurry was agitated in an attrition mill for 1 hr, and granulated by means of a spray dryer. The thus obtained grains were heated at 1100.degree. to 1500.degree. C. in nitrogen gas for 2 hr. The oxygen concentration of the nitrogen gas was measured by means of the zirconia oxygen concentration meter. The saturation magnetization of each heated sample was measured by means of the vibrating sample magnetometer. The material phase was identified by the powder X-ray diffractometry.
(1) Heating temperature range
Table 9 demonstrates that the heating at 1100.degree. C. (Sample Nos. 1 to 10) causes hematite (.alpha.-FE.sub.2 O.sub.3) to remain while the heating at 1500.degree. C. (sample Nos. 41 to 50) forms wustite (FeO), so that the single phase magnetite (Fe.sub.3 O.sub.4 only) cannot be obtained.
Therefore, it has been found that the suitable heating temperature range is from 1200.degree. to 1450.degree. C.
(2) Amount of Sn added (% by weight)
Upon noting the amount, in terms of Sn of powdery tin oxide added (Sample Nos. 11 to 40) within the heating temperature range of 1200.degree. to 1450.degree. C. set in section (1) above, it was found that the saturation magnetization was continuously decreased from 91 to 8 emu/g as the above amount was increased from 0.8 to 87.6% by weight. When the amount of Sn added exceeded 76.0% by weight, the saturation magnetization became extremely low to thereby cause the magnetic oxide to lose practicability.
Therefore, it has been found that the suitable amount, in terms of Sn, of Sn compound to be added is in the range of 0.8 to 76.0% by weight.
The above demonstrates that desirable single phase magnetite and another magnetic and/or nonmagnetic phase can be formed by mixing 0.8 to 76.0% by weight, in terms of Sn, of an Sn compound with hematite and effecting the heating at 1200.degree. to 1450.degree. C. (provided that 0.1 to 4.0% by weight of a substance having a carbon-to-carbon single or double bond is also added). FIG. 7 shows an exemplary saturation magnetization curve as a function of the amount of Sn added. The saturation magnetization curve is drawn in a graph in which the axis of abscissa indicates the weight percentage, in terms of Sn, or Sn compound added while the axis of ordinate indicates the corresponding saturation magnetization value. It represents experimental example results shown in Table 9. In particular, the saturation magnetization curve is a line segment formed by plotting data shown in Table 9 with respect to the heating temperature range of 1200.degree. to 1450.degree. C. in a graph in which the axis of abscissa indicates the weight percentage of Sn added while the axis of ordinate indicated the corresponding saturation magnetization value emu/g and connecting the plots.
Once the saturation magnetization curve of FIG. 7 has been established, therefore, not only can the weight percentage of Sn to be added for obtaining a desired saturation magnetization emu/g be determined but also the saturation magnetization emu/g can contrarily be determined with respect to any given weight percentage of Sn, to thereby ensure production of a magnetic oxide powder having a desired saturation magnetization.
Table 10 shows results of another experimental example (1;1 mixture of hematite and magnetite, Sn) according to this embodiment. It shows experimental data obtained by varying the amount of Sn added as specified in the Table while the proportion of hematite powder to magnetite powder was kept at 1:1. In practice, 0.0 to 87.6% by weight, in terms of Sn, of powdery tin oxide was mixed with a 1:1 mixture of hematite and magnetite powders, and granulated in the same manner as specified in Table 9. The resultant grains were heated at 100.degree. to 1500.degree. C. in nitrogen gas for 2 hr. After the heating, the samples were measured in the same manner as specified in Table 9, and results are shown in Table 10.
(1) Heating temperature range
Table 10 demonstrates that the heating at 1100.degree. C. (Sample Nos. 1 to 10) causes hematite (.alpha.-FE.sub.2 O.sub.3) to remain while the heating at 1500.degree. C. (Sample Nos. 41 to 50) forms wustite (FeO), so that the single phase magnetite (Fe.sub.3 O.sub.4 only) cannot be obtained.
Therefore, it has been found that the suitable heating temperature range is from 1200.degree. to 1450.degree. C.
(2) Amount of Sn added (% by weight)
Upon noting the amount, in terms of Sn, of powdery tin oxide added (Sample Nos. 11 to 40) within the heating temperature range of 1200.degree. to 1450.degree. C. set in section (1) above, it was found that the saturation magnetization was continuously decreased from 91 to 9 emu/g as the above amount was increased form 0.8 to 87.6% by weight. When the amount of Sn added exceeded 76.0% by weight, the saturation magnetization became extremely small to thereby cause the magnetic oxide to lose practicability.
Therefore, it has been found that the suitable amount, in terms of Sn, of Sn compound to be added is in the range of 0.8 to 76.0% by weight.
The above demonstrates that desirable single phase magnetite and another magnetic and/or nonmagnetic phase can be formed by mixing 0.8 to 76.0% by weight, in terms of Sn, of a Sn compound with a 1:1 mixture of hematite and magnetite and effecting the heating at 1200.degree. to 1450.degree. C. (provided that 0.1 to 4.0% by weight of a substance having a carbon-to-carbon single or double bond is also added).
Table 11 shows results of an additional experimental example (magnetite, Sn) according to this embodiment. In this experimental example, 0.0 to 87.6% by weight, in terms of Sn, of powdery tin oxide was mixed with magnetite powder, and granulated in the same manner as specified in Table 9. The thus obtained grains were heated at 500.degree. to 1500.degree. C. in nitrogen gas for 2 hr. After the heating, the samples were measured in the same manner as specified in Table 9, and results are shown in Table 11.
(1) Heating temperature range
Table 11 demonstrates that, during the heating at 500.degree. C. (Sample Nos. 1 to 10), the magnetite is oxidized by trace amount of O.sub.2 contained in nitrogen gas to form hematite (.alpha.-FE.sub.2 O.sub.3) while the heating at 1500.degree. C. (Sample Nos. 81 to 90) forms wustite (FeO), so that the single phase magnetite (Fe.sub.3 O.sub.4 only) cannot be obtained. When an Sn compound is mixed with magnetite as a starting material and magnetite and another magnetic and/or nonmagnetic phase is formed to attain arbitrary regulation of the saturation magnetization, there is no need for newly reducing the magnetite to achieve conversion to magnetite, so that it is satisfactory to obtain the strength required for handling, etc., by bonding or mild sintering. Thus, it has been found that desirable saturation magnetization regulation can be achieved at a temperature as low as 550.degree. C.
(2) Amount of Sn added (% by weight)
Upon noting the amount, in terms of Sn, of powdery tin oxide added (Sample Nos. 11 to 80) within the heating temperature range of 550.degree. to 1450.degree. C. set in section (1) above, it was found that the saturation magnetization was continuously decreased from 91 to 8 emu/g as the above amount was increased from 0.8 to 87.6% by weight. When the amount of Sn added exceeded 76.9% by weight, the saturation magnetization became extremely low to thereby cause the magnetic oxide to lose practicability.
Therefore, it has been found that the suitable amount, in terms of Sn, of Sn compound to be added is in the range of 0.8 to 76.0% by weight.
The above demonstrates that desirable single phase magnetite and another magnetic and/or nonmagnetic phase can be formed by mixing 0.8 to 76.0% by weight, in terms of Sn, of an Sn compound with magnetite and effecting the heating at 550.degree. to 1450.degree. C. (provided that 0.1 to 4.0% by weight of a substance having a carbon-to-carbon single or double bond is also added).
As described above, in the second and third embodiments, Ti and Sn compounds are individually mixed with magnetite, magnetite+hematite or hematite, and the resultant mixed powder is mixed with a substance having a carbon-to-carbon single or double bond and sintered to thereby produce a powder comprising magnetite and another magnetic and/or nonmagnetic phase and having an arbitrary saturation magnetization value. Therefore, a magnetic oxide having any desired saturation magnetization can easily be mass-produced at a lowered cost. In particular, a magnetic oxide comprising magnetite and another magnetic and/or nonmagnetic phase and having an arbitrary saturation magnetization value can easily be produced at a lowered cost by a simple process in which a large volume of magnetite, magnetite+hematite or hematite is mixed with a Ti or Sn compound, further mixed with an organic substance and directly brought into the sintering step 5.
Fourth Embodiment
As shown in FIG. 8, 0.5 to 65% by weight, in terms of Si, of a powdery Si compound was weighed and mixed with a member selected from among hematite, hematite+magnetite and magnetite powders in the blending step 1.
In the mixing step 2, the thus mixed powder is mixed with 0.1 to 4.0% by weight of a compound having --C--C-- or --C.dbd.C-- in its molecules (liquid or solid). For example, 2% by weight of polyvinyl alcohol as a binder and 1% by weight of a polycarboxylate as a dispersant are added to the mixed powder, and further water is added for granulation into globular grains. The amount of water added is in the range of 30 to 70% by weight. When the amount of water was less that 30% by weight, the viscosity of a slurry obtained by milling was too high to be granulated into globular grains. On the other hand, when the amount of water exceeded 70% by weight, the slurry concentration was too low to be granulated into dense globular grains.
In the wet-milling step 3, the mixture obtained in the mixing step 2 is wet crushed in an attrition mill to thereby prepare a slurry having a mixed powder concentration of about 50% by weight.
In the granulating step 4, globular grains are formed. In this step, the slurry is agitated in an attrition mill for 1 hr, and hot-air dried by a spray dryer to obtain globular grains.
In the sintering step 5, the grains obtained in the granulating step 4 are heated at 1200.degree. to 1450.degree. C. or 550.degree. to 1450.degree. C. in an atmosphere of an inert gas (such as nitrogen gas) for 2 hr to thereby form magnetite and another magnetic and/or nonmagnetic phase. The value of the saturation magnetization can be controlled by regulating the amount, in terms of Si, of Si compound added, so that it is feasible to produce a magnetic oxide having any desired saturation magnetization by changing the amount of Si compound added (see Tables 13 to 15). When hematite is present in part of the hematite or magnetite powder, not only is the thermal transition from hematite to magnetite effected in the inert gas (in weakly reducing atmosphere) but also the organic substance mixed is brought by the heating in the inert gas into the state of incomplete combustion, in which the hematite is deprived of oxygen during the thermal decomposition of the organic substance to thereby be reduced so as to markedly promote the conversion to magnetite,
In the crushing step 6, the powder in which magnetite and another magnetic and/or nonmagnetic phase are coexistent, obtained in the sintering step 5, is crushed into a product.
According to the above steps, 35 to 99.5% by weight of hematite, hematite+magnetite, or magnetite is mixed with 0.6 to 65% by weight, in terms of Si, of an Si compound to obtain a mixed powder, and this mixed powder is further mixed with 0.1 to 4.0% by weight of a compound having --C--C-- or --C.dbd.C-- in its molecules and still further water, milled well, hot-air dried, granulated into globular grains and sintered in an inert gas at 1200.degree. to 1450.degree. C. (with respect to hematite or hematite+magnetite) or 550.degree. to 1450.degree. C. (with respect to magnetite only), so that the magnetic oxide powder in which magnetite and another magnetic and/or nonmagnetic phase are coexistent can be produced. Thus, it has become feasible to safely mass-produce the magnetic oxide powder having any desired saturation magnetization at a lowered cost. Descriptions will be made below.
Table 12 shows sintering experiment results (SiO.sub.2 : 0% by weight) According to this embodiment. In this experiment, PVA (polyvinyl alcohol) was added as a binder in an amount specified in the Table to hematite powder, and further 1% by weight of a polycarboxylate as a dispersant and water were added and mixed. The mixture was granulated, and sintered at a temperature T specified in the Table. After the sintering, a qualitative analysis by powder X-ray diffractometry was conducted. Results are shown in the Table. The following has been found from the results.
(1) No single phase magnetite was obtained even with the changed heating temperatures from only hematite powder having no PVA added thereto (Sample Nos. 1 to 8). The X-ray diffractometry showed the presence of the phase of hematite (.alpha.-FE.sub.2 O.sub.3) or wustite (FeO).
(2) When the amount of PVA added was set at 2% by weight and the heating temperature was varied, single phase magnetite (Fe.sub.3 O.sub.4 only) was obtained at heating temperatures ranging from 1200.degree. to 1450.degree. C. (Sample Nos. 9 to 12), and wustite (FeO) was coexistent at heating temperatures of 1500.degree. C. or above (Sample Nos. 16).
Therefore, it is requisite that the heating temperature be in the range of 1200.degree. to 1450.degree. C. (Sample Nos. 13 to 15).
(3) At a fixed heating temperature of 1300.degree. C., the amount of PVA added was varied between 0.1 and 3.0% by weight. In any case, single phase magnetite was obtained (Sample Nos. 17 to 22).
From the above experimental results, it has been found that completely single phase magnetite can be obtained whenever PVA is added to hematite powder in an amount of 0.1 to 3% by weight (4% by weight) and whenever the sintering performed by heating at 1200.degree. to 1450.degree. C.
Table 13 shows experimental example results (hematite) according to this embodiment. In this experimental example, 0.0 to 79.5% by weight, in terms of Si, of powdery silicon oxide was mixed with hematite powder, and further mixed with water to obtain a slurry having a powder concentration of 50% by weight. The slurry was agitated in an attrition mill for 1 hr, and dried at 110.degree. C. 1.0% by weight of polyvinyl alcohol was added to the obtained pellet. The mixture was mixed in a mortar, and sifted through a 425-.mu.m-mesh standard sieve to obtain grains. 0.5 g of the resultant grains were put in a cylindrical mold having a diameter of 12.5 mm, and shaped under a molding pressure of 1 t/cm.sup.2. The molding was heated at 1100.degree. to 1500.degree. C. for 2 hr in nitrogen gas. The oxygen concentration of the nitrogen gas was measured by the use of a zirconia oxygen concentration meter. The saturation magnetization of each sample after the heating was measured by means of a vibrating sample magnetometer (see FIG. 3 of the first embodiment). Results are shown in Table 13.
(1) Heating temperature range
Table 13 demonstrates that the heating at 1100.degree. C.(Sample Nos. 1 to 10) causes hematite (.alpha.-FE.sub.2 O.sub.3) to remain while the heating at 1500.degree. C. (Sample Nos. 41 to 50) forms wustite (FeO), so that the single phase magnetite (Fe.sub.3 O.sub.4 only) cannot be obtained.
Therefore, it has been found that the suitable heating temperature range is from 1200.degree. to 1450.degree. C.
(2) Amount of Si added (% by weight)
Upon noting the amount, in terms of Si, of powdery silicon oxide added (Sample Nos. 11 to 40) within the heating temperature range of 1200.degree. to 1450.degree. C. set in section (1) above, it was found that the saturation magnetization was continuously decreased from 91 to 20 emu/g as the above amount was increased from 0.5 to 65.0% by weight (see FIG. 9 referred to later). When the amount of Si added exceeded as small as 20 emu/g or less to thereby cause the magnetic oxide to lose practicability.
Therefore, it has been found that the suitable amount, in terms of Si, of Si compound to be added is in the range of 0.5 to 65% by weight.
The above demonstrates that desirable single phase magnetite+nonmagnetic phase can be formed by mixing 0.5 to 65% by weight, in terms of Si, of an Si compound with hematite and effecting the heating at 1200.degree. to 1450.degree. C. (provided that 0.1 to 4.0% by weight of a substance having a carbon-to-carbon single or double bond is also added).
FIG. 9 shows an exemplary saturation magnetization curve as a function of the amount of Si added in this embodiment. The saturation magnetization curve is drawn in a graph in which the axis of abscissa indicates the weight percentage, in terms of Si, of Si compound added while the axis of ordinate indicates the corresponding saturation magnetization value. It represents experimental example results shown in Table 13. In particular, the saturation magnetization curve is a line segment formed by plotting data shown in Table 18 with respect to the heating temperature range of 1200.degree. to 1450.degree. C. in a graph in which the axis of abscissa indicates the weight percentage of Si added while the axis of ordinate indicates the corresponding saturation magnetization value emu/g and connecting the plots.
Once the saturation magnetization curve of FIG. 9 has been established, therefore, not only can the weight percentage of Si to be added for obtaining a desired saturation magnetization emu/g be determined but also the saturation magnetization emu/g can contrarily be determined with respect to any given weight percentage of Si, to thereby ensure production of a magnetic oxide powder having a desired saturation magnetization.
Table 14 shows results of another experimental example (hematite+magnetite) according to this embodiment. In the experimental example, 0.0 to 79.5% by weight, in terms of Si, of powdery silicon oxide was mixed with a 50% by weight: 50% by weight mixture of hematite and magnetite powders (hematite+magnetite), and the resultant mixed powder was mixed with water, milled, granulated, molded and heated in the same manner as specified in Table 13 to thereby obtain samples. The samples were measured, and results are shown in Table 14.
(1) Heating temperature range
Table 14 demonstrates that the heating at 1100.degree. C. (Sample Nos. 1 to 10) causes hematite (.alpha.-FE.sub.2 O.sub.3) to remain while the heating at 1500.degree. C. (Sample Nos. 41 to 50) forms wustite (FeO), so that the single phase magnetite (Fe.sub.3 O.sub.4 only) cannot be obtained.
Therefore, it has been found that the suitable heating temperature range is from 1200.degree. to 1450.degree. C.
(2) Amount of Si added (% by weight)
Upon noting the amount, in terms of Si, of powdery silicon oxide added (Sample Nos. 11 to 40) within the heating temperature range of 1200.degree. to 1450.degree. C. set in section (1) above, it was found that the saturation magnetization was continuously decreased from 91 to 20 emu/g as the above amount was increased from 0.5 to 65.0% by weight. When the amount of Si added exceeded 65% by weight, the saturation magnetization became as small as 20 emu/g to thereby cause the magnetic oxide to lose practicability.
Therefore, it has been found that the suitable amount, in terms of Si, of Si compound to be added is in the range of 0.5 to 65% by weight.
The above demonstrates that desirable single phase magnetite and another magnetic and/or nonmagnetic phase can be formed by mixing 0.5 to 65% by weight, in terms of Si, of a Si compound with hematite+magnetite and effecting the heating at 1200.degree. to 1450.degree. C. (provided that 0.1 to 4.0% by weight of a substance having a carbon-to-carbon single or double bond is also added).
Table 15 shows results of a further experimental example (magnetite) according to this embodiment. In this experimental example, 0.0 to 79.5% by weight, in terms of Si, of powdery silicon oxide was mixed with magnetite powder and further mixed with water in the same manner as specified in Table 13 to obtain a slurry having a powder concentration of 50% by weight. The slurry was agitated in an attrition mill for 1 hr, and dried at 110.degree. C. 1.0% by weight of polyvinyl alcohol was added to the obtained pellet. The mixture was mixed in a mortar, and sifted through a 425-.mu.m-mesh standard sieve to obtain grains. 0.5 g of the resultant grains were put in a cylindrical mold having a diameter of 12.5 mm, and shaped under a molding pressure of 1 t/cm.sup.2. The molding was heated at 500.degree. to 1500.degree. C. for 2 hr in nitrogen gas. The oxygen concentration of the nitrogen gas was measured by the use of a zirconia oxygen concentration meter. The saturation magnetization of each sample after the heating was measured by means of a vibrating sample magnetometer (see FIG. 3 of the first embodiment). Results are shown in Table 15.
(1) Heating temperature range
Table 15 demonstrates that, during the heating at 500.degree. C. (Sample Nos. 1 to 10), the magnetite is oxidized by trace O.sub.2 contained in nitrogen gas to form hematite (.alpha.-FE.sub.2 O.sub.3) while the heating at 1500.degree. C. (Sample Nos. 81 to 90) forms wustite (FeO), so that the single phase magnetite (Fe.sub.3 O.sub.4 only) cannot be obtained. When an Si compound is mixed with magnetite as a starting material and magnetite and another magnetic and/or nonmagnetic phase is formed to attain arbitrary regulation of the saturation magnetization, there is no need for newly reducing the magnetite to achieve conversion to magnetite, so that it is satisfactory to obtain the strength required for handling and other practical operation by bonding or mild sintering. Thus, it has been found that desirable saturation magnetization regulation can be achieved at a temperature as low as 550.degree. C.
Therefore, it has been found that the suitable heating temperature range is from 550.degree. to 1450.degree. C.
(2) Amount of Si added (% by weight)
Upon noting the amount, in terms of Si, of powdery silicon oxide added (Sample No. 11 to 80) within the heating temperature range of 550.degree. to 1450.degree. C. set in section (1) above, it was found that the saturation magnetization was continuously decreased from 91 to 16 emu/g as the above amount was increased from 0.5 to 65.0% by weight. When the amount of Si added exceeded 65% by weight, the saturation magnetization became as small as 16 emu/g or less to thereby cause the magnetic oxide to lose practicability.
Therefore, it has been found that the suitable amount, terms of Si, of Si compound to be added is in the range of 0.5 to 65% by weight.
The above demonstrates that desirable single phase magnetite and another magnetic and/or nonmagnetic phase can be formed by mixing 0.5 to 65% by weight, in terms of Si, of an Si compound with magnetite and effecting the heating at 550.degree. to 1450.degree. C. (provided that 0.1 to 4.0% by weight of a substance having a carbon-to-carbon single or double bond is also added).
Detailed descriptions on the heating curbed for 2-hr heating at the heating temperature T.degree.C. (heating temperature specified in Tables 12 to 15) and the saturation magnetization relating to the above embodiment are omitted in view of the similarity to and obviousness from those form FIGS. 2 and 3 relating to the first embodiment of the present invention.
Besides the above embodiment, it has been found that the saturation magnetization may further finely be regulated by controlling the sintering conditions so as to form an oxide phase (hematite calcium peroxide, etc.), for example, on the surface of the powder. This is applicable according to necessity although additional operation is required.
As described above, in the forgoing embodiment, an Si compound and a substance having a carbon-to-carbon single or double bond are mixed with hematite, hematite+magnetite, or magnetite, and sintered to thereby produce a powder comprising magnetite and another magnetic and/or nonmagnetic phase and having an arbitrary saturation magnetization value. Therefore, a magnetic oxide having any desired saturation magnetization can easily be mass-produced at a lowered cost. In particular, a powder (magnetic oxide) comprising magnetite and another magnetic and/or nonmagnetic phase and having an arbitrary saturation magnetization value can easily be produced at a lowered cost by a simple process in which a mixed powder comprising a large volume of hematite, hematite+magnetite, or magnetite, an Si compound and a substance having a carbon-to-carbon single or double bond is directly brought into the sintering step 5.
Fifth Embodiment
Referring to FIG. 10, hematite or hematite+magnetite is blended with 0.20 to 18.50% by weight of Mg or alternatively magnetite is blended with 0.20 to 26.20% by weight of Mg, optionally together with 0.20 to 10.00% by weight of Mn (the upper limit of the total of the former two is 18.50% by weight while that of the latter is 26.20% by weight) to thereby form a mixed powder in the blending step 1. The term "Mg" means the Mg moiety, expressed in % by weight, of organic and inorganic compounds each containing Mg, such as MgCO.sub.3, Mg(OH).sub.2, MgCl.sub.2 nH.sub.2 O and MgO. Likewise, the term "Mn" means the Mn moiety expressed in % by weight of organic and inorganic compounds each containing Mn, such as MnO.sub.2, Mn.sub.3 O.sub.4, MnOOH, MnCO.sub.3, Mn.sub.2 O.sub.3 and MnO. The terms "Mg" and "Mn" are employed for brevity in this specification. 0.20 to 18.50% by weight or 0.20 to 26.20% by weight of Mg optionally together with 0.20 to 10.00% by weight of Mn is blended with the balance (q.s. ad 100%) of hematite, hematite+magnetite, or magnetite (that is, for example, the weight percentage of the "O" moiety of MgO is not contained in the value of 100% by weight). The terminology "hematite+magnetite" employed herein means a mixture (mixed powder) of hematite and magnetite. In particular, the magnetite as a starting material may be either of:
(1) magnetite powder (produced in the house or purchased from other companies), and
(2) magnetite powder obtained by pulverizing a product having an off-specification particle size (recovered item) so as for the same to have the given particle size.
The product grains described later are those each composed of, for example, 103 to 107 starting powder particles (1-3 .mu.m) gathered into a globular form having a diameter of 50 to 100 .mu.m. Thus, any once produced magnetite powder product (off-specification item) can be pulverized to thereby easily obtain the desired starting material powder.
In the mixing step 2, the above mixed powder is mixed with 0.1 to 4.0% by weight of a compound having --C--C-- or --C.dbd.C-- in its molecules (liquid or solid). For example, 2% by weight of polyvinyl alcohol as a binder and 1% by weight of a polycarboxylate as a dispersant are added to the mixed powder, and further water is added for granulation into globular grains. The amount of water added is in the range of 30 to 70% by weight. When the amount of water was less than 30% by weight, the viscosity of the slurry obtained by milling was too high to be granulated into globular grains. On the other hand, when the amount of water exceeded 70% by weight, the slurry concentration was too low to be granulated into dense globular grains.
In the wet-milling step 3, the mixture obtained in the mixing step 2 is wet crushed in an attrition mill to thereby prepare a slurry having a mixed powder concentration of about 50% by weight.
In the granulating step 4, the powder is formed into globular grains. In this step, the slurry is agitated in an attrition mill (attritor) for 1 hr, and hot-air dried by a spray dryer to obtain globular grains.
In the sintering step 5, the grains obtained in the granulating step 4 are heated at 550.degree. to 1500.degree. C. in an atmosphere of an inert gas (such as nitrogen gas) for 2 hr to thereby obtain powder in which single phase magnetite and nonmagnetic phase are coexistent. The value of saturation magnetization of the powder can be regulated by the amount of Mg added, so that it is feasible to produce a powdery magnetic oxide having any desired saturation magnetization by changing the amount of Mg added (see Tables 16 to 18). When hematite is present in part of the hematite or magnetite powder, during the 550.degree. to 1500.degree. C. sintering step 5, not only is the thermal transition from hematite to magnetite effected in the inert gas (in weakly reducing atmosphere) but also the organic substance mixed is brought by the heating in the inert gas into the stage of incomplete combustion, in which the hematite is deprived of oxygen during the thermal decomposition of the organic substance to thereby be reduced to markedly promote the conversion to magnetite. The mixing of Mn improves the grain strength of the powder (see Table 10 and FIG. 12).
In the disintegration step 6, the powder in which magnetite and another magnetic and/or nonmagnetic phase are coexistent, obtained in the sintering step 5, is disintegrated into a product.
According to the above steps, hematite, hematite+magnetite, or magnetite is mixed with the above Mg, optionally together with Mn for improving the grain strength of the powder, to obtain a mixed powder, and this mixed powder is further mixed with a compound having --C--C-- or --C.dbd.C-- in its molecules and water, milled well, hot-air dried, granulated into globular grains and sintered in an inert gas at 550.degree. to 1500.degree. C., so that the magnetic oxide powder in which magnetite and nonmagnetic phase are coexistent can be produced. Thus, it has become feasible to safely mass-produce a magnetic oxide powder having any desired saturation magnetization and a satisfactory grain strength at a lowered cost. Descriptions will be made below.
Table 16 shows sintering experiment results (hematite+Mg) according to this embodiment. In the experiment, 0.00 to 40.00% by weight, in terms of Mg, of powder of magnesium oxide (MgO) was blended with hematite powder, and mixed with water to obtain a slurry having a powder concentration of 50% by weight. 1.0% by weight of polyvinyl alcohol was added to the slurry, and agitated in an attrition mill for 1 hr. The slurry was spray dried by the use of a spray dryer to obtain grains. The thus obtained grains were heated at 500.degree. to 1500.degree. C. in nitrogen gas for 2 hr. After the heating, the saturation magnetization of each sample was measured by means of a vibrating sample magnetometer. The grain strength of each sample was determined by measuring with the use of a micro-compression tester (MCTM-500 manufactured by Shimadzu Corp.) and calculating according to the following Hiramatsu's formula.
(Grain strength)={2.8.times.(Breaking load of grain)}/{.rho..times.(Diameter of grain).sup.2 }
(1) When the heating temperature was 500.degree. C., the grain strength was as small as less than 1E7 Pa to thereby cause the magnetic oxide to fall to serve practical use. Thus, 500.degree. C. is unacceptable. On the other hand, when the heating temperature was 550.degree. C., the grain strength was not smaller than 1E7 Pa, so that the magnetic oxide would serve practical use. Therefore, it has been determined that 550.degree. C. is an appropriate lower limit of the heating temperature.
(2) When the heating temperature was 1500.degree. C., the conversion to magnetite was so incomplete as to form wustite (FeO) with the result that the saturation magnetization began to become as small as 86 emu/g or less as noted with respect to Sample No. 91. Although satisfactory saturation magnetization can be obtained at higher temperatures, it has been determined that 1500.degree. C. is an appropriate upper limit of the heating temperature from the viewpoint of the practical heating limit of electric furnaces.
(3) When the amount of Mg added was 0.20% by weight (Sample Nos. 13, 23, 33, 43, 53, 63, 73, 83 and 93) at which the saturation magnetization began to decrease within the heating temperature range of 550.degree. to 1500.degree. C., a saturation magnetization of 90 to 82 emu/g was obtained at 550.degree. to 1100.degree. C.
Thus, it has been determined that 0.20% by weight is an appropriate lower limit of the amount of Mg added. On the other hand, the amount of Mg added at which the saturation magnetization was at least 10 emu/g was 18.50% by weight (Sample Nos. 18, 28, 38, 48, 58, 68, 78, 88 and 98) at 550.degree. to 1500.degree. C. Thus, it has been determined that 18.50% by weight is an appropriate upper limit of the amount of Mg added.
It has been found from the above experimental results that a powder (magnetic oxide) comprising magnetite and another magnetic and/or nonmagnetic phase admixed together and having an arbitrary saturation magnetization as indicated by the hatched portion in FIG. 11(a) described later can be formed by mixing 0.20 to 18.50% by weight of Mg with hematite and sintering the resultant mixed powder at 550.degree. to 1500.degree. C. for 2 hr.
Table 17 shows results of another sintering experiment (hematite+magnetite+Mg) according to this embodiment.
In the experiment, 0.00 to 40.0% by weight, in terms of of powder of magnesium oxide (MgO) was blended with a 1:1 mixture of hematite and magnetite powders, treated in the same manner as specified in Table 16, and measured.
(1) When the heating temperature was 500.degree. C., the grain strength was as small as less that 1E7 Pa to thereby cause the magnetic oxide to fall to serve practical use. Thus, 500.degree. C. is unacceptable. On the other hand, when the heating temperature was 550.degree. C., the grain strength was not smaller than 1E7 Pa, so that the magnetic oxide would serve practical use. Therefore, it has been determined that 550.degree. C. is an appropriate lower limit of the heating temperature.
(2) When the heating temperature was 1500.degree. C., the conversion to magnetite was so incomplete as to form wustite (FeO) with the result that the saturation magnetization began to become as small as 86 emu/g or less as noted with respect to Sample No. 91. Although satisfactory saturation magnetization can be obtained at higher temperatures, it has been determined that 1500.degree. C. is an appropriate upper limit of the heating temperature from the viewpoint of the practical heating limit of electric furnaces.
(3) When the amount of Mg added was 0.20% by weight (Sample Nos. 13, 23, 33, 43, 53, 63, 73, 83 and 93) at which the saturation magnetization began to decrease within the heating temperature range of 550.degree. to 1500.degree. C., a saturation magnetization of 61 emu/g was obtained at 550.degree. to 1100.degree. C. while a saturation magnetization of 90 to 82 emu/g was obtained at 1200.degree. to 1500.degree. C. Thus, it has been determined that 0.20% by weight is an appropriate power limit of the amount of Mg added. On the other hand, the amount of Mg added at which the saturation magnetization was at least 10 emu/g was 18.50% by weight (Sample Nos. 18, 28, 38, 48, 58, 68, 78, 88 and 98) at 550.degree. to 1500.degree. C. Thus, it has been determined that 18.50% by weight is an appropriate upper limit of the amount of Mg added.
It has been found from the above experimental results that a powder (magnetic oxide) comprising magnetite and another magnetic and/or nonmagnetic phase admixed together and having an arbitrary saturation magnetization as indicated by the hatched portion in FIG. 11(b) described later can be formed by mixing 0.20 to 18.50% by weight of Mg with hematite+magnetite and sintering the resultant mixed powder at 550.degree. to 1500.degree. C. for 2 hr.
Table 18 shows results of a further sintering experiment (magnetite+Mg) according to this embodiment. In the experiment, 0.00 to 40.0% by weight, in terms of Mg, of powder of magnesium oxide (MgO) was blended with magnetite, treated in the same manner as specified in Table 16, and measured.
(1) When the heating temperature was 500.degree. C., the grain strength was as small as less than 1E7 Pa to thereby cause the magnetic oxide to fail to serve practical use. Thus, 500.degree. C. is unacceptable. On the other hand, when the heating temperature was 550.degree. C., the grain strength was not smaller than 1E7 Pa, so that the magnetic oxide would serve practical use. Therefore, it has been determined that 550.degree. C. is an appropriate lower limit of the heating temperature.
(2) When the heating temperature was 1500.degree. C., the conversion to magnetite was so incomplete as to form wustite (FeO) with the result that the saturation magnetization began to become as small as 86 emu/g or less as noted with respect to sample No. 91. Although satisfactory saturation magnetization can be obtained at higher temperatures, it has been determined that 1500.degree. C. is an appropriate upper limit of the heating temperature from the viewpoint of the practical heating limit of electric furnaces.
(3) When the amount of MK added was 0.20% by weight (Sample Nos. 13, 23, 33, 43, 53, 63, 73, 83 and 93) at which the saturation magnetization began to decrease within the heating temperature range of 550.degree. to 1500.degree. C., a saturation magnetization of 91 to 82 emu/g was obtained at 550.degree. to 1500.degree. C. Thus, it has been determined that 0.20% by weight is an appropriate lower limit of the amount of Mg added. On the other hand, the amount of Mg added at which the saturation magnetization was at most about 10 emu/g was 26.20% by weight (Sample Nos. 19, 29, 39 and 49) at 550.degree. to 1100.degree. C. and 19.50% by weight (Sample Nos. 58, 68, 78, 88 and 98) at 1200.degree. to 1500.degree. C. It has been determined, taking the above two values into account, that 26.20% by weight is an appropriate upper limit of the amount of Mg added.
It has been found from the above experimental results that a powder (magnetic oxide) comprising magnetite and another magnetic and/or nonmagnetic phase admixed together and having an arbitrary saturation magnetization as indicated by the hatched portion in FIG. 11(a) described later can be formed by mixing 0.20 to 26.20% by weight of Mg with magnetite and sintering the resultant mixed powder at 550.degree. to 1100.degree. C. for 2 hr.
FIGS. 11(a), 11(b) and 11(c) are explanatory vies of the scope of variation of saturation magnetization by regulation. These are summaries of the above-mentioned experimental results of Tables 16 to 18, made for easy understanding. The axis of abscissa indicates the heating temperature, the axis of ordinate the saturation magnetization by regulation.
FIG. 11(a) shows the scope of variation of saturation magnetization by regulation, based on Table 16 relating to hematite+Mg.
(1) When the heating temperature is in the range of 550.degree. to 1100.degree. C., the magnetic oxide can have an arbitrary saturation magnetization ranging from 40 to 10 emu/g as indicated by the hatched portion in the figure by changing the amount of Mg added within the range of 0.20 to 18.50% by weight, as described with respect to Table 16.
(2) When the heating temperature is in the range of 1200.degree. to 1500.degree. C., the magnetic oxide can have an arbitrary saturation magnetization ranging from 90 to 10 emu/g as indicated by the hatched portion in the figure by changing the amount of Mg added within the range of 0.20 to 18.50% by weight, as described with respect to Table 16.
FIG. 11(b) shows the scope of variation of saturation magnetization by regulation, based on Table 17 relating to hematite+magnetite+Mg.
(1) When the heating temperature is in the range of 550.degree. to 1100.degree. C., the magnetic oxide can have an arbitrary saturation magnetization ranging from 60 to 10 emu/g as indicated by the hatched portion in the Figure by changing the amount of Mg added within the range of 0.20 to 18.50% by weight, as described with respect to Table 17.
FIG. 11(c) shows the scope of variation of saturation magnetization by regulation, based on Table 18 relating to magnetite+Mg.
(1) When the heating temperature is in the range of 550.degree. to 1100.degree. C., the magnetic oxide can have an arbitrary saturation magnetization ranging from 90 to 10 emu/g as indicated by the hatched portion in the Figure by changing the amount of Mg added within the range of 0.20 to 26.20% by weight, as described with respect to Table 18.
Table 19 shows results of a still further sintering experiment (hematite+Mg+Mn) according to this embodiment. In the experiment, 3.60% by weight, in terms of of powder of magnesium oxide (MgO) was blended with hematite powder, and further 0.00 to 10.00% by weight, in terms of Mn, of manganese oxide (Mn.sub.3 O.sub.4)was added thereto. The resultant mixture was treated under the same conditions as specified in Table 16.
(1) When the heating temperature was 550.degree. C., the grain strength was gradually increased from 13E8 Pa of Sample No. 16 of Table 16 not containing Mn to 17E8 Pa in accordance with the increase of the amount of Mn added as shown in Table 19, thus demonstrating the contribution of the addition of Mn to the grain strength. The saturation magnetization was also increased from 27 emu/g to 39 emu/g in accordance with the increase of the amount of Mn added. The increase of the saturation magnetization is caused by the incorporation of Mn which itself is magnetized.
(2) When the heating temperature was 1300.degree. C., the grain strength was gradually increased from 36E9 Pa of Sample No. 66 of Table 16 not containing Mn to 52E9 Pa in accordance with the increase of the amount of Mn added as shown in Table 19, thus demonstrating the contribution of the addition of M to the grain strength. The saturation magnetization was also increased from 67 emu/g to 80 emu/g in accordance with the increase of the amount of Mn added. The increase of the saturation magnetization is caused by the incorporation of Mn which itself is magnetized.
FIGS. 12(a) and 12(b) are explanatory views of the effect of the addition of Mn on the grain strength of the Mg blend according to this embodiment. These are graphs of the results of sintering experiment shown in Table 19, prepared for easy understanding. The axis of abscissa indicates the amount of Mn added, % by weight, while the axis of ordinate indicates the grain strength Pa.
FIG. 12 (a) shows the relationship between the amount of Mn added and the grain strength with respect to the magnetic oxide produced by sintering a powder obtained by mixing hematite with 3.60% by weight of Mg and further with Mn at 550.degree. C. in N.sub.2 for 2 hr as specified in Table 19. This graph demonstrates the effect of the addition of Mn in increasing the grain strength of the sintered magnetic oxide.
FIG. 12(b) shows the relationship between the amount of Mn added and the grain strength with respect to the magnetic oxide produced by sintering a powder obtained by mixing hematite with 3.60% by weight of Mg and further with Mn at 1300.degree. C. in N.sub.2 for 2 hr as specified in Table 19. This graph demonstrates the effect of the addition of Mn in increasing the grain strength of the sintered magnetic oxide.
FIG. 13 shows an exemplary heating temperature curve according to this embodiment. The curve is employed in the experiments relating to the above-mentioned Table 16 and FIGS. 12(a) and 12(b). In the sintering, the heating is conducted in an atmosphere of N.sub.2 at a rate of 200.degree. C./hr to a given temperature, which is held for 2 hr. Thereafter, the cooling is conducted at a rate of 200.degree. C./hr.
As described above, in the foregoing embodiment, an Si compound and a substance having a carbon-to-carbon single or double bond are mixed with hematite, hematite+magnetite, or magnetite, and sintered to thereby produce a powder comprising magnetite and nonmagnetic phase admixed together and having an arbitrary saturation magnetization value. Therefore, a magnetic oxide having any desired saturation magnetization can easily be mass-produced at a lowered cost. In particular, a powder (magnetic oxide) comprising magnetite and another magnetic and/or nonmagnetic phase admixed together and having an arbitrary saturation magnetization value can easily be produced at a lowered cost by a simple process in which a mixed powder comprising a large volume of hematite, hematite+magnetite, or magnetite, an Si compound and a substance having a carbon-to-carbon single or double bond is directly brought into the sintering step 5.
TABLE 1__________________________________________________________________________Firing Experiment Results (Hematite) of the Present Invention Amt. of Ca Heating Satn.Sample added temp. Atmo- magnetization Results of powder X-ray diffractometryNo. (wt %) T (.degree.C.) sphere .delta.s (emu/g) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.3 O.sub.4 FeO__________________________________________________________________________1 0.00 1100 N.sub.2 80 found found none2 0.71 " " 82 found found none3 1.43 " " 80 found found none4 3.55 " " 75 found found none5 4.97 " " 72 found found none6 7.10 " " 68 found found none7 10.65 " " 64 found found none8 14.30 " " 60 found found none9 0.00 1200 N.sub.2 92 none found none10 0.71 " " 88 none found none11 1.43 " " 88 none found none12 3.55 " " 86 none found none13 4.97 " " 80 none found none14 7.10 " " 77 none found none15 10.65 " " molten immeasurable immeasurable immeasurable16 14.30 " " " " " "17 0.00 1300 N.sub.2 92 none found none18 0.71 " " 88 none found none19 1.43 " " 87 none found none20 3.55 " " 86 none found none21 4.97 " " 81 none found none22 7.10 " " 77 none found none23 10.65 " " molten immeasurable immeasurable immeasurable24 14.30 " " " " " "25 0.00 1450 N.sub.2 92 none found none26 0.71 " " 88 none found none27 1.43 " " 87 none found none28 3.55 " " 85 none found none29 4.97 " " 80 none found none30 7.10 " " 76 none found none31 10.65 " " molten immeasurable immeasurable immeasurable32 14.30 " " " " " "33 0.00 1500 N.sub.2 85 none found found34 0.71 " " 85 none found found35 1.43 " " 87 none found found36 3.55 " " 80 none found found37 4.97 " " 77 none found found38 7.10 " " molten none found found39 10.65 " " " immeasurable immeasurable immeasurable40 14.30 " " " " " "__________________________________________________________________________
TABLE 2__________________________________________________________________________Firing Experiment Results (Hematite + Magnetite) of the PresentInvention Amt. of Ca Heating Satn.Sample added temp. Atmo- magnetization Results of powder X-ray diffractometryNo. (wt %) T (.degree.C.) sphere .delta.s (emu/g) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.3 O.sub.4 FeO__________________________________________________________________________1 0.00 1100 N.sub.2 67 found found none2 0.71 " " 66 found found none3 1.43 " " 65 found found none4 3.55 " " 64 found found none5 4.97 " " 61 found found none6 7.10 " " 56 found found none7 10.65 " " 51 found found none8 14.30 " " 47 found found none9 0.00 1200 N.sub.2 92 none found none10 0.71 " " 89 none found none11 1.43 " " 88 none found none12 3.55 " " 86 none found none13 4.97 " " 80 none found none14 7.10 " " 77 none found none15 10.65 " " molten immeasurable immeasurable immeasurable16 14.30 " " " " " "17 0.00 1300 N.sub.2 92 none found none18 0.71 " " 88 none found none19 1.43 " " 88 none found none20 3.55 " " 86 none found none21 4.97 " " 81 none found none22 7.10 " " 75 none found none23 10.65 " " molten immeasurable immeasurable immeasurable24 14.30 " " " " " "25 0.00 1450 N.sub.2 92 none found none26 0.71 " " 88 none found none27 1.43 " " 88 none found none28 3.55 " " 85 none found none29 4.97 " " 82 none found none30 7.10 " " 76 none found none31 10.65 " " molten immeasurable immeasurable immeasurable32 14.30 " " " " " "33 0.00 1500 N.sub.2 87 none found found34 0.71 " " 85 none found found35 1.43 " " 86 none found found36 3.55 " " 80 none found found37 4.97 " " 77 none found found38 7.10 " " molten none found found39 10.65 " " " immeasurable immeasurable immeasurable40 14.30 " " " " " "__________________________________________________________________________
TABLE 3__________________________________________________________________________Firing Experiment Results (Magnetite) of the Present Invention Amt. of Ca Heating Satn.Sample added temp. Atmo- magnetization Results of powder X-ray diffractometryNo. (wt %) T (.degree.C.) sphere .delta.s (emu/g) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.3 O.sub.4 FeO__________________________________________________________________________1 0.00 500 N.sub.2 86 found found none2 0.71 " " 85 found found none3 1.43 " " 84 found found none4 3.55 " " 83 found found none5 4.97 " " 80 found found none6 7.10 " " 77 found found none7 10.65 " " 72 found found none8 14.30 " " 69 found found none9 21.30 " " 60 found found none10 35.50 " " 44 found found none11 56.80 " " 18 found found none12 64.00 " " 9 found found none13 0.00 550 N.sub.2 91 none found none14 0.71 " " 90 none found none15 1.43 " " 90 none found none16 3.55 " " 87 none found none17 4.97 " " 85 none found none18 7.10 " " 82 none found none19 10.65 " " 77 none found none20 14.30 " " 74 none found none21 21.30 " " 65 none found none22 35.50 " " 45 none found none23 56.80 " " 19 none found none24 64.00 " " 10 none found none25 0.00 600 N.sub.2 92 none found none26 0.71 " " 90 none found none27 1.43 " " 90 none found none28 3.55 " " 87 none found none29 4.97 " " 84 none found none30 7.10 " " 83 none found none31 10.65 " " 76 none found none32 14.30 " " 74 none found none33 21.30 " " 65 none found none34 35.50 " " 45 none found none35 56.80 " " 20 none found none36 64.00 " " 10 none found none37 0.00 800 N.sub.2 91 none found none38 0.71 " " 91 none found none39 1.43 " " 89 none found none40 3.55 " " 86 none found none41 4.97 " " 85 none found none42 7.10 " " 77 none found none43 10.65 " " 60 none found none44 14.30 " " 47 none found none45 21.30 " " 20 none found none46 35.50 " " 2 none found none47 56.80 " " 1 none found none48 64.00 " " 0 none found none49 0.00 1100 N.sub.2 91 found found none50 0.71 " " 91 found found none51 1.43 " " 89 found found none52 3.55 " " 87 found found none53 4.97 " " 84 found found none54 7.10 " " 76 found found none55 10.65 " " 62 found found none56 14.30 " " 45 found found none57 21.30 " " 19 found found none58 35.50 " " 2 found found none59 56.80 " " 1 found found none60 64.00 " " 0 found found none61 0.00 1200 N.sub.2 92 none found none62 0.71 " " 91 none found none63 1.43 " " 90 none found none64 3.55 " " 87 none found none65 4.97 " " 85 none found none66 7.10 " " 74 none found none67 10.65 " " molten immeasurable immeasurable immeasurable68 14.30 " " " " " "69 21.30 " " " " " "70 35.50 " " " " " "71 56.80 " " " " " "72 64.00 " " " " " "73 0.00 1450 N.sub.2 92 none found none74 0.71 " " 90 none found none75 1.43 " " 90 none found none76 3.55 " " 87 none found none77 4.97 " " 84 none found none78 7.10 " " 75 none found none79 10.65 " " molten immeasurable immeasurable immeasurable80 14.30 " " " " " "81 21.30 " " " " " "82 35.50 " " " " " "83 56.80 " " " " " "84 64.00 " " " " " "85 0.00 1500 N.sub.2 86 none found none86 0.71 " " 86 none found none87 1.43 " " 84 none found none88 3.55 " " 80 none found none89 4.97 " " 78 none found none90 7.10 " " molten immeasurable immeasurable immeasurable91 10.65 " " " " " "92 14.30 " " " " " "93 21.30 " " " " " "94 35.50 " " " " " "95 56.80 " " " " " "96 64.00 " " " " " "__________________________________________________________________________
TABLE 4______________________________________Firing Experiment Results (TiO.sub.2 : 0 wt. %)of the Present Invention Amt. Results of qual.Sam- of PVA Heating anal. of powderple added temp. X-ray diffractometryNo. (wt. %) T (.degree.C.) Fe.sub.3 O.sub.4 .alpha.-Fe.sub.2 O.sub.3 FeO______________________________________Comp. Ex. 1 0 800 -- .smallcircle. --" 2 " 1000 -- .smallcircle. --" 3 " 1100 -- .smallcircle. --" 4 " 1150 .smallcircle. .smallcircle. --" 5 " 1200 .smallcircle. .smallcircle. --" 6 " 1400 .smallcircle. .smallcircle. --" 7 " 1450 .smallcircle. .smallcircle. --" 8 " 1470 .smallcircle. -- .smallcircle.Comp. Ex. 9 2.0 800 .smallcircle. .smallcircle. --" 10 " 1000 .smallcircle. .smallcircle. --" 11 " 1100 .smallcircle. .smallcircle. --" 12 " 1150 .smallcircle. .smallcircle. --Invention 13 " 1200 .smallcircle. -- --" 14 " 1400 .smallcircle. -- --" 15 " 1450 .smallcircle. -- --Comp. Ex. 16 " 1500 .smallcircle. -- .smallcircle.Invention 17 0.1 1300 .smallcircle. -- --" 18 0.2 " .smallcircle. -- --" 19 0.5 " .smallcircle. -- --" 20 1.0 " .smallcircle. -- --" 21 2.0 " .smallcircle. -- --" 22 3.0 " .smallcircle. -- --______________________________________
TABLE 5__________________________________________________________________________Experimental Examples of the Present Invention (Magnetite, Ti) Amt. of Ti Heating Satn. Grain Results of powder X-raySample added temp. Atmo- magnetization strength diffractometryNo. (wt %) T (.degree.C.) sphere .delta.s (emu/g) (Pa) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.3 O.sub.4 FeO__________________________________________________________________________1 0.00 500 N.sub.2 86 15E6 none found none2 0.60 " " 85 15E6 none found none3 1.20 " " 84 17E6 none found none4 3.00 " " 83 12E6 none found none5 6.20 " " 80 13E6 none found none6 9.50 " " 77 14E6 none found none7 13.00 " " 72 13E6 none found none8 16.70 " " 69 12E6 none found none9 28.60 " " 60 11E6 none found none10 37.50 " " 44 12E6 none found none11 52.70 " " 28 13E6 none found none12 84.40 " " 9 11E6 none found none13 0.00 550 N.sub.2 91 15E8 none found none14 0.60 " " 91 15E8 none found none15 1.20 " " 90 17E8 none found none16 3.00 " " 86 12E8 none found none17 6.20 " " 81 13E8 none found none18 9.50 " " 75 14E8 none found none19 13.00 " " 70 13E8 none found none20 16.70 " " 64 12E8 none found none21 28.60 " " 45 11E8 none found none22 37.50 " " 36 12E8 none found none23 52.70 " " 20 13E8 none found none24 84.40 " " 1 11E8 none found none25 0.00 600 N.sub.2 92 23E8 none found none26 0.60 " " 91 25E8 none found none27 1.20 " " 90 25E8 none found none28 3.00 " " 86 22E8 none found none29 6.20 " " 81 22E8 none found none30 9.50 " " 74 24E8 none found none31 13.00 " " 70 24E8 none found none32 16.70 " " 64 22E8 none found none33 28.60 " " 47 21E8 none found none34 37.50 " " 35 20E8 none found none35 52.70 " " 20 25E8 none found none36 84.40 " " 1 21E8 none found none37 0.00 800 N.sub.2 92 45E8 none found none38 0.60 " " 91 48E8 none found none39 1.20 " " 85 47E8 none found none40 3.00 " " 78 42E8 none found none41 6.20 " " 66 41E8 none found none42 9.50 " " 58 44E8 none found none43 13.00 " " 51 49E8 none found none44 16.70 " " 42 42E8 none found none45 28.60 " " 21 45E8 none found none46 37.50 " " 3 43E8 none found none47 52.70 " " 1 40E8 none found none48 84.40 " " 1 41E8 none found none49 0.00 1100 N.sub.2 91 15E9 none found none50 0.60 " " 91 16E9 none found none51 1.20 " " 87 17E9 none found none52 3.00 " " 77 14E9 none found none53 6.20 " " 58 13E9 none found none54 9.50 " " 35 14E9 none found none55 13.00 " " 20 13E9 none found none56 16.70 " " 2 11E9 none found none57 28.60 " " 2 11E9 none found none58 37.50 " " 2 12E9 none found none59 52.70 " " 1 13E9 none found none60 84.40 " " 0 12E9 none found none61 0.00 1200 N.sub.2 92 25E9 none found none62 0.60 " " 91 25E9 none found none63 1.20 " " 86 23E9 none found none64 3.00 " " 78 22E9 none found none65 6.20 " " 57 22E9 none found none66 9.50 " " 37 25E9 none found none67 13.00 " " 20 24E9 none found none68 16.70 " " 1 23E9 none found none69 28.60 " " 0 21E9 none found none70 37.50 " " 0 20E9 none found none71 52.70 " " 0 26E9 none found none72 84.40 " " 0 21E9 none found none73 0.00 1450 N.sub.2 92 23E9 none found none74 0.60 " " 91 24E9 none found none75 1.20 " " 87 25E9 none found none76 3.00 " " 78 22E9 none found none77 6.20 " " 56 26E9 none found none78 9.50 " " 37 24E9 none found none79 13.00 " " 21 23E9 none found none80 16.70 " " 1 22E9 none found none81 28.60 " " 0 21E9 none found none82 37.50 " " 0 26E9 none found none83 52.70 " " 0 25E9 none found none84 84.40 " " 0 21E9 none found none85 0.00 1500 N.sub.2 85 20E9 none found found86 0.60 " " 82 21E9 none found found87 1.20 " " 80 21E9 none found found88 3.00 " " 69 20E9 none found found89 6.20 " " 49 19E9 none found found90 9.50 " " 30 22E9 none found found91 13.00 " " 14 21E9 none found found92 16.70 " " 1 22E9 none found found93 28.60 " " 0 18E9 none found found94 37.50 " " 0 16E9 none found found95 52.70 " " 0 17E9 none found found96 84.40 " " 0 19E9 none found found__________________________________________________________________________
TABLE 6__________________________________________________________________________Experiment Examples of the Present Invention (1:1 Magnetite + Hematite,Ti) Amt. of Satn. mag- Amt. of Amt. magnet- netite hematite of Ti Heating ization Grain Results of powder X-raySample added added added temp. Atmo- .delta.s strength diffractometryNo. (wt %) (wt %) (wt %) T (.degree.C.) sphere (emu/g) (Pa) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.2 O.sub.4 FeO__________________________________________________________________________1 50.00 50.00 0.00 1100 N.sub.2 91 15E9 found found none2 49.70 49.70 0.60 " " 91 16E9 found found none3 49.40 49.40 1.20 " " 87 17E9 found found none4 48.50 48.50 3.00 " " 77 14E9 found found none5 46.90 46.90 6.20 " " 58 13E9 found found none6 45.25 45.25 9.50 " " 35 14E9 found found none7 43.50 43.50 13.00 " " 20 13E9 found found none8 41.70 41.70 16.60 " " 2 11E9 found found none9 35.70 35.70 28.60 " " 2 11E9 found found none10 31.30 31.30 37.40 " " 2 12E9 found found none11 23.70 23.70 52.60 " " 1 13E9 found found none12 7.80 7.80 84.40 " " 0 12E9 found found none13 50.00 50.00 0.00 1200 N.sub.2 92 25E9 none found none14 49.70 49.70 0.60 " " 91 25E9 none found none15 49.40 49.40 1.20 " " 86 23E9 none found none16 48.50 48.50 3.00 " " 78 22E9 none found none17 46.90 46.90 6.20 " " 57 22E9 none found none18 45.25 45.25 9.50 " " 37 25E9 none found none19 43.50 43.50 13.00 " " 20 24E9 none found none20 41.70 41.70 16.60 " " 1 23E9 none found none21 35.70 35.70 28.60 " " 0 21E9 none found none22 31.30 31.30 37.40 " " 0 20E9 none found none23 23.70 23.70 52.70 " " 0 26E9 none found none24 7.80 7.80 84.40 " " 0 21E9 none found none25 50.00 50.00 0.00 1450 N.sub.2 92 23E9 none found none26 49.70 49.70 0.60 " " 91 24E9 none found none27 49.40 49.40 1.20 " " 87 25E9 none found none28 48.50 48.50 3.00 " " 78 22E9 none found none29 46.90 46.90 6.20 " " 56 26E9 none found none30 45.25 45.25 9.50 " " 37 24E9 none found none31 43.50 43.50 13.00 " " 21 23E9 none found none32 41.70 41.70 16.60 " " 1 22E9 none found none33 35.70 35.70 28.60 " " 0 21E9 none found none34 31.30 31.30 37.40 " " 0 26E9 none found none35 23.70 23.70 52.60 " " 0 25E9 none found none36 7.80 7.80 84.40 " " 0 21E9 none found none37 50.00 50.00 0.00 1500 N.sub.2 85 20E9 none found found38 49.70 49.70 0.60 " " 82 21E9 none found found39 49.40 49.40 1.20 " " 80 21E9 none found found40 48.50 48.50 3.00 " " 69 20E9 none found found41 46.90 46.90 6.20 " " 49 19E9 none found found42 45.25 45.25 9.50 " " 30 22E9 none found found43 43.50 43.50 13.00 " " 14 21E9 none found found44 41.70 41.70 16.60 " " 1 22E9 none found found45 35.70 35.70 28.60 " " 0 18E9 none found found46 31.30 31.30 37.40 " " 0 16E9 none found found47 23.70 23.70 52.60 " " 0 17E9 none found found48 7.80 7.80 84.40 " " 0 19E9 none found found__________________________________________________________________________
TABLE 7__________________________________________________________________________Experiment Examples of the Present Invention (1:3 Magnetite + Hematite,Ti) Amt. of Satn. mag- Amt. of Amt. magnet- netite hematite of Ti Heating ization Grain Results of powder X-raySample added added added temp. Atmo- .delta.s strength diffractometryNo. (wt %) (wt %) (wt %) T (.degree.C.) sphere (emu/g) (Pa) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.2 O.sub.4 FeO__________________________________________________________________________1 25.00 75.00 0.00 1100 N.sub.2 91 15E9 none found none2 24.90 74.50 0.60 " " 91 16E9 none found none3 24.70 74.10 1.20 " " 87 17E9 none found none4 24.25 72.75 3.00 " " 77 14E9 none found none5 23.45 70.35 6.20 " " 58 13E9 none found none6 22.63 67.87 9.50 " " 35 14E9 none found none7 21.75 65.25 13.00 " " 20 13E9 none found none8 20.83 62.47 16.70 " " 2 11E9 none found none9 17.85 53.55 28.60 " " 2 11E9 none found none10 15.63 46.87 37.50 " " 2 12E9 none found none11 11.83 35.47 52.70 " " 1 13E9 none found none12 3.90 11.70 84.40 " " 0 12E9 none found none13 25.00 75.00 0.00 1200 N.sub.2 92 25E9 none found none14 24.90 74.50 0.60 " " 91 25E9 none found none15 24.70 74.10 1.20 " " 86 23E9 none found none16 24.25 72.75 3.00 " " 78 22E9 none found none17 23.45 70.35 6.20 " " 57 22E9 none found none18 22.63 67.87 9.50 " " 37 25E9 none found none19 21.75 65.25 13.00 " " 20 24E9 none found none20 20.83 62.47 16.70 " " 1 23E9 none found none21 17.85 53.55 28.60 " " 0 21E9 none found none22 15.63 46.87 37.50 " " 0 20E9 none found none23 11.83 35.47 52.70 " " 0 26E9 none found none24 3.90 11.70 84.40 " " 0 21E9 none found none25 25.00 75.00 0.00 1450 N.sub.2 92 23E9 none found none26 24.90 74.50 0.60 " " 91 24E9 none found none27 24.70 74.10 1.20 " " 87 25E9 none found none28 24.25 72.75 3.00 " " 78 22E9 none found none29 23.45 70.35 6.20 " " 56 26E9 none found none30 22.63 67.87 9.50 " " 37 24E9 none found none31 21.75 65.25 13.00 " " 21 23E9 none found none32 20.83 62.47 16.70 " " 1 22E9 none found none33 17.85 53.55 28.60 " " 0 21E9 none found none34 15.63 46.87 37.50 " " 0 26E9 none found none35 11.83 35.47 52.70 " " 0 25E9 none found none36 3.90 11.70 84.40 " " 0 21E9 none found none37 25.00 75.00 0.00 1500 N.sub.2 85 20E9 none found found38 24.90 74.50 0.60 " " 82 21E9 none found found39 24.70 74.10 1.20 " " 80 21E9 none found found40 24.25 72.75 3.00 " " 69 20E9 none found found41 23.45 70.35 6.20 " " 49 19E9 none found found42 22.63 67.87 9.50 " " 30 22E9 none found found43 21.75 65.25 13.00 " " 14 21E9 none found found44 20.83 62.47 16.70 " " 1 22E9 none found found45 17.85 53.55 28.60 " " 0 18E9 none found found46 15.63 46.87 37.50 " " 0 16E9 none found found47 11.83 35.47 52.70 " " 0 17E9 none found found48 3.90 11.70 84.40 " " 0 19E9 none found found__________________________________________________________________________
TABLE 8__________________________________________________________________________Experiment Examples of the Present Invention (1:4 Magnetite + Hematite,Ti) Amt. of Satn. mag- Amt. of Amt. magnet- netite hematite of Ti Heating ization Grain Results of powder X-raySample added added added temp. Atmo- .delta.s strength diffractometryNo. (wt %) (wt %) (wt %) T (.degree.C.) sphere (emu/g) (Pa) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.2 O.sub.4 FeO__________________________________________________________________________1 20.00 80.00 0.00 1100 N.sub.2 91 15E9 found found none2 19.90 79.50 0.60 " " 91 16E9 found found none3 19.80 79.00 1.20 " " 87 17E9 found found none4 19.40 77.60 3.00 " " 77 14E9 found found none5 18.80 75.00 6.20 " " 58 13E9 found found none6 18.10 72.40 9.50 " " 35 14E9 found found none7 17.40 69.40 13.00 " " 20 13E9 found found none8 16.70 66.60 16.70 " " 2 11E9 found found none9 14.30 57.10 28.60 " " 2 11E9 found found none10 12.50 50.00 37.50 " " 2 12E9 found found none11 9.50 37.80 52.70 " " 1 13E9 found found none12 3.10 12.50 84.40 " " 0 12E9 found found none13 20.00 80.00 0.00 1200 N.sub.2 92 25E9 none found none14 19.90 79.50 0.60 " " 91 25E9 none found no)ne15 19.80 79.00 1.20 " " 86 23E9 none found none16 19.40 77.60 3.00 " " 78 22E9 none found none17 18.80 75.00 6.20 " " 57 22E9 none found none18 18.10 72.40 9.50 " " 37 25E9 none found none19 17.40 69.40 13.00 " " 20 24E9 none found none20 16.70 66.60 16.70 " " 1 23E9 none found none21 14.30 57.10 28.60 " " 0 21E9 none found none22 12.50 50.00 37.50 " " 0 20E9 none found none23 9.50 37.80 52.70 " " 0 26E9 none found none24 3.10 12.50 84.40 " " 0 21E9 none found none25 20.00 80.00 0.00 1450 N.sub.2 92 23E9 none found none26 19.90 79.50 0.60 " " 91 24E9 none found none27 19.80 79.00 1.20 " " 87 25E9 none found none28 19.40 77.60 3.00 " " 78 22E9 none found none29 18.80 75.00 6.20 " " 56 26E9 none found none30 18.10 72.40 9.50 " " 37 24E9 none found none31 17.40 69.40 13.00 " " 21 23E9 none found none32 16.70 66.60 16.70 " " 1 22E9 none found none33 14.30 57.10 28.60 " " 0 21E9 none found none34 12.50 50.00 37.50 " " 0 26E9 none found none35 9.50 37.80 52.70 " " 0 25E9 none found none36 3.10 12.50 84.40 " " 0 21E9 none found none37 20.00 80.00 0.00 1500 N.sub.2 85 20E9 none found found38 19.90 79.50 0.60 " " 82 21E9 none found found39 19.80 79.00 1.20 " " 80 21E9 none found found40 19.40 77.60 3.00 " " 69 20E9 none found found41 18.80 75.00 6.20 " " 49 19E9 none found found42 18.10 72.40 9.50 " " 30 22E9 none found found43 17.40 69.40 13.00 " " 14 21E9 none found found44 16.70 66.60 16.70 " " 1 22E9 none found found45 14.30 57.10 28.60 " " 0 18E9 none found found46 12.50 50.00 37.50 " " 0 16E9 none found found47 9.50 37.80 52.70 " " 0 17E9 none found found48 3.10 12.50 84.40 " " 0 19E9 none found found__________________________________________________________________________
TABLE 9__________________________________________________________________________Other Experimental Examples of the Present Invention (Hematite, Sn) Satn. Amt. magnet- of Sn Heating ization Results of powderSample added temp. .delta.s X-ray diffractometryNo. (wt %) T (.degree.C.) Atmosphere (emu/g) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.3 O.sub.4 FeO__________________________________________________________________________1 0.00 1100 N.sub.2 86 found found none2 0.80 " " 85 found found none3 1.58 " " 84 found found none4 3.98 " " 83 found found none5 8.04 " " 75 found found none6 16.44 " " 69 found found none7 44.04 " " 41 found found none8 64.74 " " 26 found found none9 76.00 " " 16 found found none10 87.60 " " 8 found found none11 0.00 1200 N.sub.2 92 none found none12 0.80 " " 91 none found none13 1.58 " " 90 none found none14 3.98 " " 87 none found none15 8.04 " " 82 none found none16 16.44 " " 76 none found none17 44.04 " " 47 none found none18 64.74 " " 28 none found none19 76.00 " " 21 none found none20 87.60 " " 9 none found none21 0.00 1300 N.sub.2 92 none found none22 0.80 " " 91 none found none23 1.58 " " 90 none found none24 3.98 " " 86 none found none25 8.04 " " 82 none found none26 16.44 " " 74 none found none27 44.04 " " 47 none found none28 64.74 " " 25 none found none29 76.00 " " 21 none found none30 87.60 " " 8 none found none31 0.00 1450 N.sub.2 92 none found none32 0.80 " " 91 none found none33 1.58 " " 90 none found none34 3.98 " " 87 none found none35 8.04 " " 85 none found none36 16.44 " " 75 none found none37 44.04 " " 47 none found none38 64.74 " " 29 none found none39 76.00 " " 21 none found none40 87.60 " " 9 none found none41 0.00 1500 N.sub.2 86 none found found42 0.80 " " 85 none found found43 1.58 " " 84 none found found44 3.98 " " 83 none found found45 8.04 " " 75 none found found46 16.44 " " 68 none found found47 44.04 " " 39 none found found48 64.74 " " 22 none found found49 76.00 " " 15 none found found50 87.60 " " 2 none found found__________________________________________________________________________
TABLE 10__________________________________________________________________________Other Experimental Examples of the Present Invention(1:1 Hematite + Magnetite, Sn) Satn. Amt. magnet- of Sn Heating ization Results of powderSample added temp. .delta.s X-ray diffractometryNo. (wt %) T (.degree.C.) Atmosphere (emu/g) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.3 O.sub.4 FeO__________________________________________________________________________1 0.00 1100 N.sub.2 86 found found none2 0.80 " " 85 found found none3 1.58 " " 84 found found none4 3.98 " " 83 found found none5 8.04 " " 75 found found none6 16.44 " " 69 found found none7 44.04 " " 39 found found none8 64.74 " " 22 found found none9 76.00 " " 16 found found none10 87.60 " " 4 found found none11 0.00 1200 N.sub.2 92 none found none12 0.80 " " 91 none found none13 1.58 " " 90 none found none14 3.98 " " 87 none found none15 8.04 " " 85 none found none16 16.44 " " 75 none found none17 44.04 " " 47 none found none18 64.74 " " 29 none found none19 76.00 " " 21 none found none20 87.60 " " 9 none found none21 0.00 1300 N.sub.2 92 none found none22 0.80 " " 91 none found none23 1.58 " " 90 none found none24 3.98 " " 87 none found none25 8.04 " " 85 none found none26 16.44 " " 74 none found none27 44.04 " " 47 none found none28 64.74 " " 29 none found none29 76.00 " " 20 none found none30 87.60 " " 9 none found none31 0.00 1450 N.sub.2 92 none found none32 0.80 " " 91 none found none33 1.58 " " 90 none found none34 3.98 " " 86 none found none35 8.04 " " 85 none found none-36 16.44 " " 74 none found none37 44.04 " " 46 none found none38 64.74 " " 29 none found none39 76.00 " " 20 none found none40 87.60 " " 10 none found none41 0.00 1500 N.sub.2 86 none found found42 0.80 " " 85 none found found43 1.58 " " 84 none found found44 3.98 " " 83 none found found45 8.04 " " 75 none found found46 16.44 " " 69 none found found47 44.04 " " 39 none found found48 64.74 " " 22 none found found49 76.00 " " 16 none found found50 87.60 " " 4 none found found__________________________________________________________________________
TABLE 11__________________________________________________________________________Other Experimental Examples of the Present Invention(Magnetite, Sn) Satn. Amt. magnet- of Sn Heating ization Results of powderSample added temp. .delta.s X-ray diffractometryNo. (wt %) T (.degree.C.) Atmosphere (emu/g) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.3 O.sub.4 FeO__________________________________________________________________________1 0.00 500 N.sub.2 86 found found none2 0.80 " " 85 found found none3 1.58 " " 84 found found none4 3.98 " " 83 found found none5 8.04 " " 75 found found none6 16.44 " " 70 found found none7 44.04 " " 39 found found none8 64.74 " " 22 found found none9 76.00 " " 14 found found none10 87.60 " " 3 found found none11 0.00 550 N.sub.2 92 none found none12 0.80 " " 91 none found none13 1.58 " " 90 none found none14 3.98 " " 87 none found none15 8.04 " " 85 none found none16 16.44 " " 75 none found none17 44.04 " " 47 none found none18 64.74 " " 29 none found none19 76.00 " " 21 none found none20 87.60 " " 9 none found none21 0.00 600 N.sub.2 92 none found none22 0.80 " " 91 none found none23 1.58 " " 90 none found none24 3.98 " " 87 none found none25 8.04 " " 85 none found none26 16.44 " " 74 none found none27 44.04 " " 47 none found none28 64.74 " " 29 none found none29 76.00 " " 20 none found none30 87.60 " " 9 none found none31 0.00 800 N.sub.2 92 none found none32 0.80 " " 91 none found none.33 1.58 " " 90 none found none34 3.98 " " 86 none found none35 8.04 " " 85 none found none36 16.44 " " 74 none found none37 44.04 " " 46 none found none38 64.74 " " 29 none found none39 76.00 " " 20 none found none40 87.60 " " 10 none found none41 0.00 1100 N.sub.2 92 none found none42 0.80 " " 91 none found none43 1.58 " " 90 none found none44 3.98 " " 87 none found none45 8.04 " " 83 none found none46 16.44 " " 75 none found none47 44.04 " " 47 none found none48 64.74 " " 28 none found none49 76.00 " " 20 none found none50 87.60 " " 9 none found none51 0.00 1200 N.sub.2 92 none found none52 0.80 " " 91 none found none53 1.58 " " 90 none found none54 3.98 " " 87 none found none55 8.04 " " 82 none found none56 16.44 " " 74 none found none57 44.04 " " 47 none found none58 64.74 " " 26 none found none59 76.00 " " 21 none found none60 87.60 " " 8 none found none61 0.00 1300 N.sub.2 92 none found none62 0.80 " " 91 none found none63 1.58 " " 90 none found none64 3.98 " " 87 none found none65 8.04 " " 85 none found none66 16.44 " " 74 none found none67 44.04 " " 47 none found none68 64.74 " " 29 none found none69 76.00 " " 20 none found none70 87.60 " " 9 none found none71 0.00 1450 N.sub.2 92 none found none72 0.80 " " 91 none found none73 1.58 " " 90 none found none74 3.98 " " 87 none found none75 8.04 " " 82 none found none76 16.44 " " 74 none found none77 44.04 " " 47 none found none78 64.74 " " 26 none found none79 76.00 " " 21 none found none80 87.60 " " 8 none found none81 0.00 1500 N.sub.2 86 none found found82 0.80 " " 85 none found found83 1.58 " " 84 none found found84 3.98 " " 83 none found found85 8.04 " " 75 none found found86 16.44 " " 69 none found found87 44.04 " " 39 none found found88 64.74 " " 22 none found found89 76.00 " " 16 none found found90 87.60 " " 4 none found found__________________________________________________________________________
TABLE 12______________________________________Firing Experiment Results (SiO.sub.2 : O wt. %)of the Present Invention Amt.Sam- of PVA Heating Results of powderple added temp. X-ray diffractometryNo. (wt. %) T (.degree.C.) Fe.sub.3 O.sub.4 .alpha.-Fe.sub.2 O.sub.3 FeO______________________________________Comp. Ex. 1 0 800 -- .smallcircle. --" 2 " 1000 -- .smallcircle. --" 3 " 1100 -- .smallcircle. --" 4 " 1150 .smallcircle. .smallcircle. --" 5 " 1200 .smallcircle. .smallcircle. --" 6 " 1400 .smallcircle. .smallcircle. --" 7 " 1450 .smallcircle. .smallcircle. --" 8 " 1470 .smallcircle. -- .smallcircle.Comp. Ex. 9 2.0 800 .smallcircle. .smallcircle. --" 10 " 1000 .smallcircle. .smallcircle. --" 11 " 1100 .smallcircle. .smallcircle. --" 12 " 1150 .smallcircle. .smallcircle. --Invention 13 " 200 .smallcircle. -- --" 14 " 1400 .smallcircle. -- --" 15 " 1450 .smallcircle. -- --Comp. Ex. 16 " 1500 .smallcircle. -- .smallcircle.Invention 17 0.1 1300 .smallcircle. -- --" 18 0.2 " .smallcircle. -- --" 19 0.5 " .smallcircle. -- --" 20 1.0 " .smallcircle. -- --" 21 2.0 " .smallcircle. -- --" 22 3.0 " .smallcircle. -- --______________________________________
TABLE 13__________________________________________________________________________Experimental Examples of the Present Invention (Hematite) Amt. of Si Heating Satn.Sample added temp. Atmo- magnetization Results of powder X-ray diffractometryNo. (wt %) T (.degree.C.) sphere .delta.s (emu/g) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.3 O.sub.4 FeO__________________________________________________________________________1 0.00 1100 N.sub.2 86 found found none2 0.50 " " 85 found found none3 0.90 " " 84 found found none4 2.40 " " 83 found found none5 4.90 " " 75 found found none6 10.40 " " 69 found found none7 31.50 " " 39 found found none8 51.20 " " 22 found found none9 65.00 " " 16 found found none10 79.50 " " 4 found found none11 0.00 1200 N.sub.2 92 none found none12 0.50 " " 91 none found none13 0.90 " " 90 none found none14 2.40 " " 87 none found none15 4.90 " " 83 none found none16 10.40 " " 75 none found none17 31.50 " " 47 none found none18 51.20 " " 28 none found none19 65.00 " " 20 none found none20 79.50 " " 9 none found none21 0.00 1300 N.sub.2 92 none found none22 0.50 " " 91 none found none23 0.90 " " 90 none found none24 2.40 " " 87 none found none25 4.90 " " 82 none found none26 10.40 " " 74 none found none27 31.50 " " 47 none found none28 51.20 " " 26 none found none29 65.00 " " 21 none found none30 79.50 " " 8 none found none31 0.00 1450 N.sub.2 92 none found none32 0.50 " " 91 none found none33 0.90 " " 90 none found none34 2.40 " " 87 none found none35 4.90 " " 85 none found none36 10.40 " " 74 none found none37 31.50 " " 47 none found none38 51.20 " " 29 none found none39 65.00 " " 20 none found none40 79.50 " " 9 none found none41 0.00 1500 N.sub.2 86 none found found42 0.50 " " 85 none found found43 0.90 " " 84 none found found44 2.40 " " 83 none found found45 4.90 " " 75 none found found46 10.40 " " 69 none found found47 31.50 " " 39 none found found48 51.20 " " 22 none found found49 65.00 " " 16 none found found50 79.50 " " 4 none found found__________________________________________________________________________
TABLE 14__________________________________________________________________________Experimental Examples of the Present Invention (Hematite + Magnetite) Amt. of Si Heating Satn.Sample added temp. Atmo- magnetization Results of powder X-ray diffractometryNo. (wt %) T (.degree.C.) sphere .delta.s (emu/g) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.3 O.sub.4 FeO__________________________________________________________________________1 0.00 1100 N.sub.2 86 found found none2 0.50 " " 85 found found none3 0.90 " " 84 found found none4 2.40 " " 83 found found none5 4.90 " " 75 found found none6 10.40 " " 69 found found none7 31.50 " " 39 found found none8 51.20 " " 22 found found none9 65.00 " " 16 found found none10 79.50 " " 4 found found none11 0.00 1200 N.sub.2 92 none found none12 0.50 " " 91 none found none13 0.90 " " 90 none found none14 2.40 " " 87 none found none15 4.90 " " 85 none found none16 10.40 " " 75 none found none17 31.50 " " 47 none found none18 51.20 " " 29 none found none19 65.00 " " 21 none found none20 79.50 " " 9 none found none21 0.00 1300 N.sub.2 92 none found none22 0.50 " " 91 none found none23 0.90 " " 90 none found none24 2.40 " " 87 none found none25 4.90 " " 85 none found none26 10.40 " " 74 none found none27 31.50 " " 47 none found none28 51.20 " " 29 none found none29 65.00 " " 20 none found none30 79.50 " " 9 none found none31 0.00 1450 N.sub.2 92 none found none32 0.50 " " 91 none found none33 0.90 " " 90 none found none34 2.40 " " 86 none found none35 4.90 " " 85 none found none36 10.40 " " 74 none found none-37 31.50 " " 46 none found none38 51.20 " " 29 none found none39 65.00 " " 20 none found none40 79.50 " " 10 none found none41 0.00 1500 N.sub.2 86 none found found42 0.50 " " 85 none found found43 0.90 " " 84 none found found44 2.40 " " 83 none found found45 4.90 " " 75 none found found46 10.40 " " 69 none found found47 31.50 " " 39 none found found48 51.20 " " 22 none found found49 65.00 " " 16 none found found50 79.50 " " 4 none found found__________________________________________________________________________
TABLE 15__________________________________________________________________________Experimental Examples of the Present Invention (Magnetite) Amt. of Si Heating Satn.Sample added temp. Atmo- magnetization Results of powder X-ray diffractometryNo. (wt %) T (.degree.C.) sphere .delta.s (emu/g) .alpha.-Fe.sub.2 O.sub.3 Fe.sub.3 O.sub.4 FeO__________________________________________________________________________1 0.00 500 N.sub.2 86 found found none2 0.50 " " 85 found found none3 0.90 " " 84 found found none4 2.40 " " 83 found found none5 4.90 " " 75 found found none6 10.40 " " 70 found found none7 31.50 " " 39 found found none8 51.20 " " 22 found found none9 65.00 " " 14 found found none10 79.50 " " 3 found found none11 0.00 550 N.sub.2 92 none found none12 0.50 " " 91 none found none13 0.90 " " 90 none found none14 2.40 " " 87 none found none15 4.90 " " 85 none found none16 10.40 " " 75 none found none17 31.50 " " 47 none found none18 51.20 " " 29 none found none19 65.00 " " 21 none found none20 79.50 " " 9 none found none21 0.00 600 N.sub.2 92 none found none22 0.50 " " 91 none found none23 0.90 " " 90 none found none24 2.40 " " 87 none found none25 4.90 " " 85 none found none26 10.40 " " 74 none found none27 31.50 " " 47 none found none28 51.20 " " 29 none found none29 65.00 " " 20 none found none30 79.50 " " 9 none found none31 0.00 800 N.sub.2 92 none found none32 0.50 " " 91 none found none33 0.90 " " 90 none found none34 2.40 " " 86 none found none35 4.90 " " 85 none found none36 10.40 " " 74 none found none37 31.50 " " 46 none found none38 51.20 " " 29 none found none39 65.00 " " 20 none found none40 79.50 " " 10 none found none41 0.00 1100 N.sub.2 92 none found none42 0.50 " " 91 none found none43 0.90 " " 90 none found none44 2.40 " " 87 none found none45 4.90 " " 83 none found none46 10.40 " " 75 none found none47 31.50 " " 47 none found none48 51.20 " " 28 none found none49 65.00 " " 20 none found none50 79.50 " " 9 none found none51 0.00 1200 N.sub.2 92 none found none52 0.50 " " 91 none found none53 0.90 " " 90 none found none54 2.40 " " 87 none found none55 4.90 " " 82 none found none56 10.40 " " 74 none found none57 31.50 " " 47 none found none58 51.20 " " 26 none found none59 65.00 " " 21 none found none60 79.50 " " 8 none found none61 0.00 1300 N.sub.2 92 none found none62 0.50 " " 91 none found none63 0.90 " " 90 none found none64 2.40 " " 87 none found none65 4.90 " " 85 none found none66 10.40 " " 74 none found none67 31.50 " " 47 none found none68 51.20 " " 29 none found none69 65.00 " " 20 none found none70 79.50 " " 9 none found none71 0.00 1450 N.sub.2 92 none found none72 0.50 " " 91 none found none73 0.90 " " 90 none found none74 2.40 " " 87 none found none75 4.90 " " 82 none found none76 10.40 " " 74 none found none77 31.50 " " 47 none found none78 51.20 " " 26 none found none79 65.00 " " 21 none found none80 79.50 " " 8 none found none81 0.00 1500 N.sub.2 86 none found found82 0.50 " " 85 none found found83 0.90 " " 84 none found found84 2.40 " " 83 none found found85 4.90 " " 75 none found found86 10.40 " " 69 none found found87 31.50 " " 39 none found found88 51.20 " " 22 none found found89 65.00 " " 16 none found found90 79.50 " " 4 none found found__________________________________________________________________________
TABLE 16______________________________________Firing Experiment Results (Hematite + Mg)of the Present Invention Amt. of Mg Heating Satn. GrainSample added temp. Atmos- magnetization strengthNo. (wt %) (.degree.C.) phere .delta.s (emu/g) (Pa)______________________________________1 0.00 500 N.sub.2 40 12E62 0.10 " " 41 15E63 0.20 " " 41 14E64 0.80 " " 35 13E65 1.60 " " 29 13E66 3.60 " " 27 12E67 13.20 " " 16 14E68 18.50 " " 10 14E69 26.20 " " 5 12E610 40.00 " " 1 11E611 0.00 550 N.sub.2 40 12E812 0.10 " " 41 13E813 0.20 " " 41 12E814 0.80 " " 35 13E815 1.60 " " 29 14E816 3.60 " " 27 13E817 13.20 " " 16 15E818 18.50 " " 10 14E819 26.20 " " 5 15E820 40.00 " " 1 13E821 0.00 600 N.sub.2 40 15E822 0.10 " " 41 15E823 0.20 " " 41 16E824 0.80 " " 35 15E825 1.60 " " 28 14E826 3.60 " " 27 16E827 13.20 " " 16 15E828 18.50 " " 11 16E829 26.20 " " 5 15E830 40.00 " " 1 17E831 0.00 800 N.sub.2 40 25E832 0.10 " " 41 26E833 0.20 " " 41 26E834 0.80 " " 35 26E835 1.60 " " 29 25E836 3.60 " " 26 28E837 13.20 " " 16 26E838 18.50 " " 10 25E839 26.20 " " 4 27E840 40.00 " " 1 23E841 0.00 1100 N.sub.2 40 16E942 0.10 " " 41 15E943 0.20 " " 40 16E944 0.80 " " 35 16E945 1.60 " " 29 17E946 3.60 " " 24 17E947 13.20 " " 16 17E948 18.50 " " 10 16E949 26.20 " " 5 17E950 40.00 " " 1 17E951 0.00 1200 N.sub.2 92 23E952 0.10 " " 92 24E953 0.20 " " 90 25E954 0.80 " " 87 26E955 1.60 " " 81 25E956 3.60 " " 67 26E957 13.20 " " 32 26E958 18.50 " " 21 23E959 26.20 " " 6 25E960 40.00 " " 1 27E961 0.00 1300 N.sub.2 92 30E962 0.10 " " 92 34E963 0.20 " " 90 34E964 0.80 " " 87 35E965 1.60 " " 81 35E966 3.60 " " 67 36E967 13.20 " " 32 37E968 18.50 " " 21 36E969 26.20 " " 6 36E970 40.00 " " 1 35E971 0.00 1400 N.sub.2 92 33E972 0.10 " " 92 34E973 0.20 " " 90 34E974 0.80 " " 87 35E975 1.60 " " 82 35E976 3.60 " " 67 36E977 13.20 " " 31 37E978 18.50 " " 20 36E979 26.20 " " 6 36E980 40.00 " " 1 35E981 0.00 1450 N.sub.2 92 36E982 0.10 " " 92 37E983 0.20 " " 90 36E984 0.80 " " 87 37E985 1.60 " " 81 37E986 3.60 " " 66 36E987 13.20 " " 32 37E988 18.50 " " 20 36E989 26.20 " " 6 37E990 40.00 " " 1 37E991 0.00 1500 N.sub.2 86 40E992 0.10 " " 85 42E993 0.20 " " 82 40E994 0.80 " " 77 41E995 1.60 " " 70 42E996 3.60 " " 65 41E997 13.20 " " 25 43E998 18.50 " " 16 43E999 26.20 " " 3 41E9100 40.00 " " 1 40E9______________________________________
TABLE 17______________________________________Firing Experiment Results (Hematite + Magnetite + Mg)of the Present Invention Amt. of Mg Heating Satn. GrainSample added temp. Atmos- magnetization strengthNo. (wt %) (.degree.C.) phere .delta.s (emu/g) (Pa)______________________________________1 0.00 500 N.sub.2 60 11E62 0.10 " " 61 12E63 0.20 " " 61 15E64 0.80 " " 55 12E65 1.60 " " 49 11E66 3.60 " " 37 11E67 13.20 " " 26 15E68 18.50 " " 20 12E69 26.20 " " 7 14E610 40.00 " " 3 14E611 0.00 550 N.sub.2 62 15E812 0.10 " " 62 15E813 0.20 " " 61 14E814 0.80 " " 52 15E815 1.60 " " 45 17E816 3.60 " " 40 16E817 13.20 " " 31 13E818 18.50 " " 18 13E819 26.20 " " 7 16E820 40.00 " " 3 17E821 0.00 600 N.sub.2 62 17E822 0.10 " " 62 15E823 0.20 " " 61 16E824 0.80 " " 52 14E825 1.60 " " 44 15E826 3.60 " " 40 17E827 13.20 " " 31 15E828 18.50 " " 20 15E829 26.20 " " 6 14E830 40.00 " " 3 15E831 0.00 800 N.sub.2 62 30E832 0.10 " " 62 36E833 0.20 " " 61 35E834 0.80 " " 53 36E835 1.60 " " 44 34E836 3.60 " " 40 38E837 13.20 " " 32 35E838 18.50 " " 20 36E839 26.20 " " 7 37E840 40.00 " " 3 33E841 0.00 1100 N.sub.2 62 17E942 0.10 " " 62 15E943 0.20 " " 61 16E944 0.80 " " 55 16E945 1.60 " " 44 17E946 3.60 " " 41 17E947 13.20 " " 32 17E948 18.50 " " 21 16E949 26.20 " " 7 17E950 40.00 " " 2 17E951 0.00 1200 N.sub.2 92 22E952 0.10 " " 92 24E953 0.20 " " 90 25E954 0.80 " " 87 25E955 1.60 " " 81 25E956 3.60 " " 67 26E957 13.20 " " 32 24E958 18.50 " " 21 25E959 26.20 " " 6 25E960 40.00 " " 1 28E961 0.00 1300 N.sub.2 92 31E962 0.10 " " 92 33E963 0.20 " " 90 34E964 0.80 " " 87 35E965 1.60 " " 81 34E966 3.60 " " 67 35E967 13.20 " " 32 37E968 18.50 " " 21 36E969 26.20 " " 6 36E970 40.00 " " 1 35E971 0.00 1400 N.sub.2 92 33E972 0.10 " " 92 34E973 0.20 " " 90 34E974 0.80 " " 87 35E975 1.60 " " 82 35E976 3.60 " " 67 36E977 13.20 " " 31 37E978 18.50 " " 20 36E979 26.20 " " 6 36E980 40.00 " " 1 35E981 0.00 1450 N.sub.2 92 38E982 0.10 " " 92 36E983 0.20 " " 90 36E984 0.80 " " 87 37E985 1.60 " " 81 37E986 3.60 " " 66 36E987 13.20 " " 32 37E988 18.50 " " 20 36E989 26.20 " " 6 37E990 40.00 " " 1 36E991 0.00 1500 N.sub.2 86 41E992 0.10 " " 85 40E993 0.20 " " 82 40E994 0.80 " " 77 41E995 1.60 " " 70 42E996 3.60 " " 65 41E997 13.20 " " 25 43E998 18.50 " " 16 40E999 26.20 " " 3 41E9100 40.00 " " 1 41E9______________________________________
TABLE 18______________________________________Firing Experiment Results (Magnetite + Mg)of the Present Invention Amt. of Mg Heating Satn. GrainSample added temp. Atmos- magnetization strengthNo. (wt %) (.degree.C.) phere .delta.s (emu/g) (Pa)______________________________________1 0.00 500 N.sub.2 65 11E62 0.10 " " 64 12E63 0.20 " " 64 11E64 0.80 " " 58 11E65 1.60 " " 50 13E66 3.60 " " 44 11E67 13.20 " " 34 14E68 18.50 " " 25 15E69 26.20 " " 10 11E610 40.00 " " 6 14E611 0.00 550 N.sub.2 92 15E812 0.10 " " 92 15E813 0.20 " " 91 16E814 0.80 " " 89 15E815 1.60 " " 82 18E816 3.60 " " 72 16E817 13.20 " " 34 17E818 18.50 " " 25 17E819 26.20 " " 10 16E820 40.00 " " 6 17E821 0.00 600 N.sub.2 92 14E822 0.10 " " 92 15E823 0.20 " " 91 15E824 0.80 " " 89 14E825 1.60 " " 82 16E826 3.60 " " 72 17E827 13.20 " " 34 15E828 18.50 " " 25 16E829 26.20 " " 10 15E830 40.00 " " 6 16E831 0.00 800 N.sub.2 92 22E832 0.10 " " 92 26E833 0.20 " " 91 25E834 0.80 " " 88 26E835 1.60 " " 82 24E836 3.60 " " 72 26E837 13.20 " " 33 25E838 18.50 " " 25 28E839 26.20 " " 11 27E840 40.00 " " 6 23E841 0.00 1100 N.sub.2 92 17E942 0.10 " " 92 15E943 0.20 " " 91 16E944 0.80 " " 88 16E945 1.60 " " 83 18E946 3.60 " " 72 17E947 13.20 " " 33 17E948 18.50 " " 25 17E949 26.20 " " 11 17E950 40.00 " " 7 17E951 0.00 1200 N.sub.2 92 23E952 0.10 " " 92 24E953 0.20 " " 90 26E954 0.80 " " 87 25E955 1.60 " " 81 26E956 3.60 " " 67 27E957 13.20 " " 33 24E958 18.50 " " 21 25E959 26.20 " " 7 25E960 40.00 " " 1 28E961 0.00 1300 N.sub.2 92 35E962 0.10 " " 92 33E963 0.20 " " 90 34E964 0.80 " " 87 35E965 1.60 " " 81 34E966 3.60 " " 65 35E967 13.20 " " 32 37E968 18.50 " " 21 35E969 26.20 " " 6 36E970 40.00 " " 1 35E971 0.00 1400 N.sub.2 92 33E972 0.10 " " 92 34E973 0.20 " " 90 34E974 0.80 " " 87 35E975 1.60 " " 82 35E976 3.60 " " 65 36E977 13.20 " " 31 37E978 18.50 " " 20 37E979 26.20 " " 6 36E980 40.00 " " 1 35E981 0.00 1450 N.sub.2 92 38E982 0.10 " " 92 36E983 0.20 " " 90 36E984 0.80 " " 87 37E985 1.60 " " 81 36E986 3.60 " " 66 36E987 13.20 " " 33 36E988 18.50 " " 21 37E989 26.20 " " 6 38E990 40.00 " " 1 37E991 0.00 1500 N.sub.2 86 40E992 0.10 " " 85 40E993 0.20 " " 82 40E994 0.80 " " 76 41E995 1.60 " " 70 42E996 3.60 " " 65 41E997 13.20 " " 23 43E998 18.50 " " 16 40E999 26.20 " " 2 41E9100 40.00 " " 1 41E9______________________________________
TABLE 19______________________________________Firing Experiment Results (Hematite + Mg + Mn)of the Present Invention Mg = 3.60 wt % Amt. of Mn Heating Satn. GrainSample added temp. Atmos- magnetization strengthNo. (wt %) (.degree.C.) phere .delta.s (emu/g) (Pa)______________________________________1 0.00 550 N.sub.2 27 14E82 0.10 " " 27 14E83 0.20 " " 27 14E84 0.50 " " 28 16E85 1.00 " " 29 17E86 2.00 " " 31 17E87 3.00 " " 32 17E88 4.00 " " 33 17E89 6.00 " " 35 17E810 8.00 " " 37 17E811 10.00 " " 39 17E812 0.00 1300 N.sub.2 67 36E913 0.10 " " 67 36E914 0.20 " " 67 37E915 0.50 " " 68 40E916 1.00 " " 69 45E917 2.00 " " 71 48E918 3.00 " " 72 50E919 4.00 " " 73 51E920 6.00 " " 75 52E921 8.00 " " 77 52E922 10.00 " " 80 52E9______________________________________

Number	Date	Country
5-215873	Aug 1993	JPX
5-262223	Oct 1993	JPX
5-262224	Oct 1993	JPX
5-018758	Feb 1994	JPX

Number	Date	Country
62-37782	Jan 1987	JPX
62-238580	Jan 1987	JPX
63-184764	Jan 1988	JPX
2-51505	Jan 1990	JPX
2-39498	Jan 1990	JPX

Magnetic oxide and process for producing same

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