Patent Application
20070267594
It is to be understood that certain descriptions of the present disclosure have been simplified to illustrate only those elements and limitations that are relevant to a clear understanding of the present teaching, while eliminating, for purposes of clarity, other elements. Those of ordinary skill in the art, upon considering the present disclosure, will recognize that other elements and/or limitations may be desirable in order to implement the present teaching. However, because such other elements and/or limitations may be readily ascertained by one of ordinary skill upon considering the present description, and are not necessary for a complete understanding of the present disclosure, a discussion of such elements and limitations is not provided herein. For example, as discussed herein, the materials of the present teaching may be incorporated, for example, as core materials for coils or transformers in various power supplies, and the like. Core materials for coils or transformers are understood by those of ordinary skill in the art, and, accordingly, are not described in detail herein.
Furthermore, compositions of the present teaching will be generally described in the form of a manganese-zinc ferrite material that may be incorporated as high frequency core materials. It will be understood, however, that embodiments set forth in the present disclosure may be embodied in forms and applied to end uses that are not specifically and expressly described herein. For example, one skilled in the art will appreciate that embodiments of the present disclosure may be incorporated into high frequency devices other than core materials that are not specifically identified herein.
The terms “pulverizing,” “pulverized,” and the like, as used herein, refer to mechanically dividing, fragmenting, or disintegrating a material (such as zinc, manganese, and iron oxides or compounds thereof) or other material into a powder. In the embodiments of the present disclosure, pulverization may be carried out in a manner that provides the resultant powder particles with a desired particle size as described herein. As used herein, pulverization includes, for example, all forms of mechanically dividing, fragmenting, or disintegrating a larger mass into a powder, including atomization, crushing, milling, grinding, cold stream processing, and the like.
Other than in the operating examples, or unless otherwise expressly specified, all of the numerical ranges, amounts, values and percentages such as those for amounts of materials, times and temperatures of reaction, ratios of amounts, and others in the following portion of the specification may be read as if prefaced by the word “about” even though the term “about” may not expressly appear with the value, amount, or range. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the present disclosure and claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the present disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Furthermore, when numerical ranges of varying scope are set forth herein, it is contemplated that any combination of these values inclusive of the recited values may be used.
Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. The terms “one,” “a,” or “an” as used herein are intended to include “at least one” or “one or more,” unless otherwise indicated.
Any patent, publication, or other disclosure material, in whole or in part, that is identified herein is incorporated by reference herein in its entirety, but is incorporated herein only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material said to be incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.
The present disclosure is directed, generally, to ferrite materials, and more particularly, to manganese-zinc (“Mn—Zn”) magnetic ferrite materials and methods of forming and employing the same that are designed to operate over a wide range of high frequencies and/or high temperatures with low power losses. It has been found that low power losses at high frequency and high temperature may be obtained from Mn—Zn materials that are a combination of major components and minor components, and which may be processed at particular sintering conditions, as set forth herein. The materials set forth in the present disclosure may include oxides or compounds that convert into oxides upon heating. These materials include components of iron, manganese, and zinc, as major components, and components of silicon, calcium, and, optionally, niobium (i.e. columbium), zirconium, and tantalum, as minor components.
As illustrated in the working examples set forth herein, the Mn—Zn ferrite compositions of the present disclosure may contain oxides of iron, such as Fe2O3, manganese, such as MnO, and zinc, such as ZnO, as major components, and combine amounts of oxides of calcium, such as CaO, silicon, such as SiO2, and, optionally, niobium, such as Nb2O5, zirconium, such as ZrO2, and tantalum, such as Ta2O5, as minor components.
The major components may be added such that the iron component may be present in amounts ranging from 51.0 to 59.0 mol % of the final composition, may be present in amounts ranging from 55.0 to 59.0 mol %, and in some embodiments may be present in amounts ranging from 55.0 to 57.0 mol %, calculated as Fe2O3. The manganese component may be present in amounts ranging from 38.0 to 47.0 mol % of the final composition, may be present in amounts ranging from 40.0 to 45.0 mol %, and in some embodiment may be present in amounts ranging from 41.0 to 43.0 mol %, calculated as MnO. The zinc component may be present in amounts ranging from 1.0 to 3.0 mol % of the final composition, may be present in amounts ranging from 1.5 to 22.5 mol %, and in some embodiments may be present in amounts ranging from 1.5 to 2.0 mol %, calculated as ZnO.
With the major components may be present small, but effective, amounts of oxides (or carbonates) of calcium, silicon, and, optionally, niobium, zirconium, and tantalum. The calcium component may be present in amounts ranging from 0.010 to 0.060 wt %, based on the total weight of the ferrite material, may be present in amounts ranging from 0.020 to 0.050 wt %, and in some embodiments may be present in amounts ranging from 0.030 to 0.045 wt %, calculated as CaO. The silicon component may be present in amounts ranging from 0.005 to 0.040 wt %, based on the total weight of the ferrite material, may be present in amounts ranging from 0.010 to 0.030 wt %, and in some embodiments may be present in amounts ranging from 0.015 to 0.025 wt %, calculated as SiO2. The niobium component may be present with the major components in amounts ranging up to 0.040 wt %, may be present in amounts ranging from 0.010 to 0.030 wt %, and in some embodiments may be present in amounts ranging from 0.015 to 0.025 wt %, based on the total weight of the ferrite material, calculated as Nb2O5. The zirconium component may be present with the major components in amounts ranging up to 0.050 wt %, may be present in amounts ranging from 0.020 to 0.050 wt %, and in some embodiments may be present in amounts ranging from 0.035 to 0.040 wt %, based on the total weight of the ferrite material, calculated as ZrO2. The tantalum component may be present with the major components in amounts ranging up to 0.060 wt %, may be present in amounts ranging up to 0.020 wt %, and in some embodiments may be present in amounts ranging from 0.005 to 0.015 wt %, based on the total weight of the ferrite material, calculated as Ta2O5.
It will be appreciated by one of ordinary skill in the art that although specific oxides for each metal component are discussed herein, other suitable oxides (or carbonates) of iron, manganese, zinc, silicon, calcium, niobium, zirconium, and tantalum, if applicable, may be used to form the ferrite materials set forth in the present disclosure. Accordingly, although the particular metal oxides disclosed herein (ZnO, MnO, Fe2O3, CaO, SiO2, Nb2O5, ZrO2, and Ta2O5) have been found to provide good results in certain embodiments, one of skill in the art would understand that the present embodiments need not be limited to the use of the specific oxidation state identified, and that other metal oxides of other oxidation states or their carbonates may be employed as a partial or complete substitute for the particular metal oxide set forth herein. For example, with respect to iron oxide, embodiments set forth herein may employ FeO, Fe2O3, and Fe3O4, and compounds capable of being converted into Fe2O3, such as iron hydroxide, iron oxalate, and the like; with respect to manganese oxide, embodiments of the present disclosure may employ MnO, MnO2, Mn3O4, and compounds capable of being converted into MnO, such as manganese carbonate, manganese oxalate, and the like; with respect to zinc oxide, the embodiments of the present disclosure may employ ZnO, and compounds capable of converting into ZnO, such as zinc carbonate, zinc oxalate, and the like. Accordingly, although specific metal oxides are reported to describe the components set forth in the present disclosure, one of ordinary skill in the art will understand that the scope of the present disclosure need not be limited to only these specific components.
The ferrite materials of the present disclosure and the products that incorporate the same may be formed by mixing oxides or carbonates of iron, manganese, and zinc as starting materials in the amounts discussed above. Raw materials of iron, manganese, and zinc oxides or carbonates may be mixed before or after pulverization in any manner known to those of ordinary skill in the art, such as through dry blending. The raw materials may be pulverized, such as through grinding, for a time sufficient to achieve an average particle size of the raw materials of 0.9 to 1.9 μm. The raw materials often show variations in the contents of the desired components, which must be monitored and adjusted, if necessary, to the appropriate mole or weight percentage discussed above, because the sintering behavior and resultant material properties are affected by the amounts of these components.
Oxides or carbonates of calcium, silicon, niobium, zirconium, and tantalum may be present, such as by adding, at the start of, during, or following formation of the dry blend of raw materials in the amounts discussed above. Because relatively small amounts of each of the minor components may be employed, in certain embodiments, these components may be added in pure (i.e. at least 99.9%) powder oxide form, rather than in the raw bulk form that may be used to form the blend of major components.
A dispersant, such as Lomar®, commercially available from Henkel Corporation, Morristown, N.J., may be added at the start of, during, or following formation of the dry blend along with other constituents, such as water, to form a slurry. Other dispersants known to those skilled in the art may be employed as long as the dispersant employed is relatively pure and the amount of trace impurities that may be added to the ferrite system is limited. When a dispersant is employed, the specific dispersant to raw component ratio can vary widely so long as it provides the requisite or desired viscosity for pulverizing, with amounts typically ranging from 0.8 wt % to 1.2 wt %, such as 1.0 wt %.
Additives such as polyvinyl alcohol and glycerin may be added to the slurry composition prior to milling that act as sacrificial binder materials for the pressed form. Other binder materials known to those skilled in the art may be employed as long as the binding agent chosen satisfies the relatively strict purity standards that limit the amount of trace impurities in the ferrite system. The amount of binder material that may be added to the system can vary widely. When polyvinyl alcohol and glycerin are employed, each binder material may be added in amounts ranging from 1.0 to 2.0 wt %, such as, for example, 1.5 wt %.
The slurry may be milled and spray dried to produce a granulated powder for pressing into core shapes having a predetermined shape, size, and pressed density. In one embodiment employing a milling process, milling may occur for 15 to 120 minutes. Pressed shapes include, for example, toroids, planar E-cores, and pot cores. The density of the pressed shapes may range from 3.1 to 3.3 g/cm3. For example, where the test cores are pressed into the shapes of toroids, each toroid may have an outside diameter of 22 mm, an inside diameter of 13.7 mm, a height of 6.3 mm, and a density of 3.2 g/cm3. The cores may be sintered at temperatures ranging from 1130° C. to 1200° C., such as 1160° C., and then cooled to temperatures ranging from 20° C. to 30° C. to form the sintered core material. The mean grain size of the resultant sintered core material may range from 4 to 8 μm. The oxygen content of the atmosphere may be controlled during the soak and cooling portions of the cycle based on the temperature and rate of cooling, as known to those of ordinary skill in the art.
As illustrated in the Example and Tables 1-3, it has been found that the Mn—Zn ferrite materials that combine components of iron, such as Fe2O3, manganese, such as Mn3O4 and zinc, such as ZnO, as major components, and components of silicon, such as SiO2, calcium, such as CaCO3, and, optionally, niobium, such as Nb2O5, zirconium, such as ZrO2, and tantalum, such as Ta2O5, as minor components, in the amounts discussed above, provide improved properties relative to known ferrite materials. In particular, the compositions of the present teaching have relatively low ZnO content and a high Fe2O3 content compared to typical Mn—Zn ferrites, and further combines amounts of CaO, SiO2, and, optionally, Nb2O5 to control and limit power losses. Amounts of ZrO2 and Ta2O5 may be added to control excessive grain growth during the sintering operation. It has been found that embodiments that include the combination of these components provide a material having improved ferrite properties.
Certain embodiments will be described further by reference to the following examples. The following examples are merely illustrative and are not intended to be limiting. Unless otherwise indicated, all parts are by weight.
Raw materials of Fe, Mn, and Zn oxides were dry blended and ground for 1.5 hours in an attrition mill to an average particle size of approximately 1.40 μm. An addition of 1.0 weight percent Lomar® (Henkel Corporation) was added at the beginning of the grinding operation to act as a dispersant. Oxides or carbonates of Ca, Si, and, where applicable, Nb, Zr and Ta, in amounts as set forth in Table 1 below, were also added at the beginning of the grinding operation. Before the resulting slurry was removed from the mill, 1.5 weight percent polyvinyl alcohol and 1.5 weight percent glycerin were added to the slurry. The slurry was milled for another 15 minutes and then spray dried to produce a granulated powder for pressing.
Test cores were pressed in the shape of toroids having an outside diameter of 22 mm, an inside diameter of 13.7 mm and a height of 6.3 mm.
The pressed density of the cores was 3.20 g/cm3. The test cores were sintered at 1160° C. to 1200° C. for 5 hours. The oxygen content of the atmosphere was controlled during the soak and cooling portions of the cycle to control grain growth and grain size distribution.
Compositions of the present disclosure are listed below in Table 1. For comparison, compositions outside the range of the present teaching are shown in Table 2.
As shown in the Examples, in corresponding Tables 1, 2 and 3, and as discussed herein, the ferrite materials of the present teaching combine components of iron, such as Fe2O3, manganese, such as MnO, and zinc, such as ZnO, as major components, and components of silicon, such as SiO2, calcium, such as CaO, and, optionally, niobium, such as Nb2O5, zirconium, such as ZrO2, and tantalum, such as Ta2O5 as minor components, in specified amounts, to provide improved properties relative to known ferrite materials. In Table 2, compositions 38 through 50 show core properties are degraded when compared to cores made according to embodiments of the present teaching. Most notably, cores made from compositions outside of the ranges set forth herein exhibit higher core loss, lower permeability, and/or minimum waft loss temperature values less than 180° C.
Compositions as described in the present disclosure control and limit power losses and result in a material having a low permeability and a high Curie temperature. The materials as set forth in the present disclosure can limit, or substantially eliminate, the addition of large amounts of Co3O4, SnO2, TiO2, CaO, and the like, or combinations of these components, while achieving exceptionally good material properties. Accordingly, sintering the combination of major and minor components provides ferrite materials having more consistent material properties relative to known compositions because of their lesser degree of sensitivity to firing conditions.
It has been found that embodiments as described herein provide a ferrite material having a low zinc content (3.0 percent by weight or less) and high iron content relative to typical MnZn ferrites that results in a material with improved properties. For example embodiments of the present teaching exhibit a permeability (μ) ranging from 300 to 1600 and more typically ranging from 700 to 800 at 25° C. In addition, it has been found that certain embodiments of the present teaching provide a ferrite material with a Curie temperature of greater than 270° C., may be 290° C. or greater, in some embodiments 300° C. or greater, and in other embodiments 310° C. or greater.
The relatively high Curie temperatures obtained in certain embodiments of the present teaching also improve the flux density versus temperature response of the material allowing it to be used simultaneously at higher flux densities and higher temperatures. Measurements taken of certain embodiments of the present disclosure indicate maximum magnetic flux densities (Bmax) of at least 4000 G, and in some embodiments at least 4200 G, at 100° C. are readily attainable. Test results also indicate that a Bmax of at least 3000 G are exhibited. At 300° C., Bmax of at least 1000 G, and in some embodiments at least 1300 G, are exhibited. These measurements are significantly higher than known Mn—Zn ferrite materials designed for high frequency applications where a Bmax of less than 3500 G at 100° C., and about 1000 G at 200° C. are disclosed.
Power losses of sintered compositions of the present teaching were measured by winding the toroid test samples with the appropriate number of turns of wire and then applying a sine wave voltage at the desired frequency and at an amplitude sufficient to generate the desired flux density in the core. The current (I) required to achieve the set voltage (V) was then measured, as was the phase angle (θ) between the applied voltage and the measured current. Power losses are expressed as: P=VI cos θ. The power in watts is divided by the volume of the test specimen to obtain a normalized power loss in milliwatts per cubic centimeter of material (mW/cm3). This loss measurement includes losses due to the copper windings, which were assumed to be small.
As further illustrated, at the minimum watt loss temperatures listed in Table 3, embodiments of the present teaching limit, or substantially reduce, the power loss at frequencies of 500 kHz at 500 G relative to known ferrite materials. Measurements of embodiments of the present teaching indicate that power losses may be less than 1000 mW/cm3, may be less than 300 mW/cm3, and in some embodiments are less than 100 mW/cm3 at frequencies of 500 KHz at 500 G.
It has been found that the temperature at which the minimum watt loss occurs can be tailored by careful selection of the appropriate composition of Fe2O3 and ZnO and the careful control of the oxygen content of the sintering atmosphere. Minimum loss temperatures between −30° C. and 250° C. have been observed while simultaneously maintaining the Curie temperature above 270° C. Additions of trace, but effective, amounts of CaO, SiO2, and Nb2O5 work together to control power losses.
It has been found that certain embodiments of the present teaching have been successful at simultaneously achieving low power losses at frequencies up to 500 kHz, minimum power loss at a temperature of 100° C. or greater, saturation magnetic flux density greater than 4000 G at 100° C., a Curie temperature greater than 270° C., while providing relative ease of processing. Prior art techniques have not been successful in meeting this combination of the performance criteria. Embodiments of the present teaching meet these requirements and also provide a much simpler composition than other compositions found in the prior art. The end result is a magnetic material with superior performance that is simple and efficient to process.
Compositions as set forth in the present disclosure use the combination of the oxides (or carbonates) described herein, particularly those compositions that employ Nb2O5, ZrO2, and Ta2O5 and relatively low amounts of CaO, result in ferrite materials having improved chemical and physical properties, as illustrated in the Examples and Tables 1-3. Accordingly, improvements to the magnetic flux density, and power loss at high operating frequencies up to 500 kHz allow reduction in the magnetic cross section of the core materials that employ the compositions of the present teaching.
Test results of the materials of the present teaching show that there is another composition region in which Bmax can be increased to near or above 5000 G at 25° C. and increased above 4000 G at 100° C. It has also been found that relative to the materials of the present teaching, prior art materials do not achieve the same level of performance and are more difficult to process. The present teaching demonstrates that fewer additive additions at much lower concentrations are more effective at reducing power losses even though the resistivity of the material may not be increased.
The compositions of the present teaching are unique in that they contain much higher levels of MnFe2O4 and FeFe2O4 than conventional MnZn ferrite materials. Although not intending to be bound by any theory, it is believed that the higher concentrations of these two species in embodiments of the present teaching play, at least, some role in a higher Curie temperature exhibited.
It should be noted that although certain embodiments as set forth in the present disclosure and identified in the Examples are identified as only having components of iron, such as Fe2O3, manganese, such as MnO, and zinc, such as ZnO, as major components, and components of silicon, such as SiO2, calcium, such as CaO, and, optionally, niobium, such as Nb2O5, zirconium, such as ZrO2, and tantalum, such as Ta2O5 as minor components, it is contemplated that the Mn—Zn ferrite materials as provided herein may include these components, ranging in amounts described herein, as well as other minor components know to those skilled in the art that impart desirable properties to the material.
It will be appreciated by those of ordinary skill in the art that the improved properties of the materials as disclosed herein allow these materials to be incorporated into products that require high frequency operation, such as those related to commercial switching power supplies, as well as for household electric appliances, communication and telecommunication equipment, computer and peripheral equipment, electronics finished products, electronic components, down hole oil drilling sensors, automotive applications, and other high frequency electronic circuitry. Certain embodiments of the present teaching provide for high temperature operation of 100° C. or higher, with low power losses at high flux densities and high frequencies that provide increased power performance to be added to products having a limited area, that may allow for miniaturization of the core volume.
It will also be appreciated by those skilled in the art that changes could be made to the embodiments described herein without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications that are within the spirit and scope of the invention, as defined by the claims.
