Patent Application
20220189669
The present disclosure relates to an anisotropic magnetic powder, an anisotropic magnet and a method for manufacturing an anisotropic magnetic powder.
In recent years, a TbCu7 type samarium-iron-nitrogen magnet powder has been attracting attention as a raw material for a magnet having higher magnetic properties than those of a neodymium magnet.
The TbCu7 type samarium-iron-nitrogen magnet powder is manufactured by nitriding a TbCu7 type samarium-iron alloy powder. In addition, because the TbCu7 type samarium-iron alloy is in a metastable phase, the TbCu7 type samarium-iron alloy cannot be manufactured by a conventional alloying method by heat melting and cooling, and for example, the TbCu7 type samarium-iron alloy is manufactured by an ultra-rapid quenching method (see Patent Documents 1 and 2).
Patent Document 1: Japanese Patent Application Publication No. 7-118815
Patent Document 2: Japanese Patent Application Publication No. 5-279714
However, when using the ultra-rapid quenching method, only an isotropic magnet powder containing polycrystal particles of TbCu7 type samarium-iron-nitrogen alloy with a random crystal orientation can be manufactured, and consequently, an anisotropic magnet with a high maximum energy product cannot be manufactured.
In order to manufacture an anisotropic magnet with a high maximum energy product, an anisotropic magnet powder containing single-crystal particles of a TbCu7 type samarium-iron-nitrogen alloy needs to be manufactured.
One embodiment of the invention is intended to provide an anisotropic magnet powder containing single-crystal particles of a TbCu7 type samarium-iron-nitrogen based alloy.
One embodiment of the present invention includes a single-crystal particle of a TbCu7 type samarium-iron-nitrogen based alloy in an anisotropic magnet powder.
Another embodiment of the present invention includes a TbCu7 type samarium-iron-nitrogen based alloy in an anisotropic magnet.
Another embodiment of the present invention includes, in a method for manufacturing an anisotropic magnet powder, steps of: producing a samarium-iron based alloy powder by heat treating a composition containing samarium, iron and an alkali metal halide and/or an alkaline earth metal halide at a temperature of a melting point of the alkali metal halide and/or the alkaline earth metal halide or higher; and producing a samarium-iron-nitrogen based alloy powder by nitriding the samarium-iron based alloy powder, wherein the temperature for heat treating is 500 degrees C. or higher and 800 degrees C. or less.
Another embodiment of the present invention includes, in a method for manufacturing a magnetic powder, steps of: producing a samarium-iron based alloy powder by heat treating a composition containing samarium, a samarium oxide and/or a samarium halide, iron, an iron oxide and/or an iron halide, an alkali metal halide and/or an alkaline earth metal halide, and an alkali metal and/or an alkaline earth metal at a temperature of a melting point of the alkali metal halide and/or the alkaline earth metal halide or higher; and producing a samarium-iron-nitrogen based alloy powder by nitriding the samarium-iron based alloy powder, wherein the temperature for heat treating is 500 degrees C. or higher and 800 degrees C. or less.
According to an embodiment of the present invention, an anisotropic magnet powder containing single-crystal particles of a TbCu7 type samarium-iron-nitrogen based alloy can be provided.
Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the contents described in the following embodiments. Also, the components described below include those that can be readily envisioned by a person skilled in the art and those that are substantially the same. In addition, the components described below may be properly combined with each other.
An anisotropic magnet powder of the present embodiment contains single-crystal particles of a TbCu7 type samarium-iron-nitrogen based alloy.
Here, the term “powder” refers to a mass of particles, and the term “single-crystal particle” refers to a solitary particle in which a particle without a crystal grain boundary and with a uniform crystal orientation does not agglutinate with other particles.
An intensity ratio of an X-ray diffraction peak of a (024) plane of a Th2Zn17 type samarium-iron-nitrogen based alloy phase to an X-ray diffraction peak of a (110) plane of a TbCu7 type samarium-iron-nitrogen based alloy phase of an anisotropic magnet powder according to the present embodiment is preferably 0.300 or less, more preferably 0.100 or less, and further preferably 0.001 or less. When an intensity ratio of an X-ray diffraction peak of a (303) plane of the Th2Zn17 type samarium-iron-nitrogen based alloy phase to the X-ray diffraction peak of the (110) plane of the TbCu7 type samarium-iron-nitrogen based alloy phase of the anisotropic magnetic powder according to the present embodiment is 0.300 or less, a proportion of the TbCu7 type samarium-iron-nitrogen based alloy phase with respect to the anisotropic magnetic powder according to the present embodiment is sufficiently high.
A ratio c/a of a lattice constant c to a lattice constant a of the TbCu7 type samarium-iron-nitrogen based alloy phase of the anisotropic magnet powder according to the present embodiment is preferably 0.838 or more, more preferably 0.840 or more, and even more preferably 0.845 or more. When the ratio c/a of the lattice constant c to the lattice constant a of the TbCu7 type samarium-iron-nitrogen based alloy phase of the anisotropic magnetic powder according to the present embodiment is 0.838 or more, a proportion of Fe in the TbCu7 type samarium-iron-nitrogen based alloy phase with respect to the anisotropic magnetic powder according to the present embodiment is sufficiently high. As a result, the magnetic properties of the anisotropic magnet powder in the present embodiment are improved.
An integral width of a (101) plane X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen based alloy phase with respect to the anisotropic magnet powder according to the present embodiment is preferably 0.66 degrees or less, and further preferably 0.54 degrees or less. When the integral width of the (101) plane X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen based alloy phase of the magnetic powder according to the present embodiment is 0.66 degrees or less, the crystallinity of the anisotropic magnetic powder according to the present embodiment is improved.
The coercivity of the anisotropic magnet powder according to the present embodiment is preferably 3.0 kOe or more, and further preferably 8.0 kOe or more.
The particle size of the anisotropic magnet powder according to the present embodiment is preferably 3 μm or less, and further preferably 1 μm or less. Because the particle size of single domain particles of the Th2Zn17 type samarium-iron-nitrogen based alloy is about 3 μm, and because an anisotropic magnetic field is about ⅓ of the Th2Zn17 type samarium-iron-nitrogen based alloy, the particle size of the single-domain particles of the TbCu7 type samarium-iron-nitrogen based alloy is not considered to be beyond 3 μm.
Therefore, when the particle size of the anisotropic magnet powder according to the present embodiment is 3 μm or less, because a magnetic structure of the anisotropic magnet powder according to the present embodiment shifts from a multi-domain structure to a single-domain structure, magnetic properties of the anisotropic magnet powder according to the present embodiment increases. In addition, when the particle size of the anisotropic magnet powder according to the present embodiment is 1 μm or less, because the formation of the nucleation reversed domains can be inhibited, the magnetic properties of the anisotropic magnet powder according to the present embodiment further increase.
A first method for manufacturing an anisotropic magnet powder according to the present embodiment includes steps of: producing a samarium-iron based alloy powder by heat treating a composition containing samarium, iron and an alkali metal halide and/or an alkaline earth metal halide at a temperature of a melting point of the alkali metal halide and/or the alkaline earth metal halide or higher; and producing a samarium-iron-nitrogen based alloy powder by nitriding the samarium-iron based alloy powder.
Here, the heat-treating temperature is 500 degrees C. or higher and 800 degrees C. or less, and is preferably 550 degrees C. or higher and 650 degrees C. or less. Therefore, it is possible to alloy at a temperature significantly lower than the melting point of the metal constituting the samarium-iron based alloy, and as a result, a samarium-iron based alloy powder containing single-crystal particles of the TbCu7 type samarium-iron based alloy can be manufactured. In addition, by nitriding the samarium-iron based alloy powder, an anisotropic magnet powder containing single-crystal particles of the TbCu7 type samarium-iron-nitrogen based alloy can be manufactured.
In the specification and claims, when the alkali metal halide and/or the alkaline earth metal halide is a mixture, the temperature of the melting point of the alkali metal halide and/or the alkaline earth metal halide or higher means a temperature of the eutectic point of the mixture or higher shown in a state diagram.
Examples of the form of samarium include a powder and the like.
Examples of iron forms include a powder and the like. On this occasion, by using an iron powder having a particle size smaller than that of the single-domain particles of a TbCu7 type samarium-iron-nitrogen based alloy, it is possible to manufacture a samarium-iron-based alloy powder containing single-crystal particles of a TbCu7 type samarium-iron based alloy having a particle size smaller than that of the single domain particles of a TbCu7 type samarium-iron-nitrogen based alloy. In addition, by nitriding the samarium-iron-based alloy powder, an anisotropic magnet powder containing single-crystal particles of a TbCu7 type samarium-iron-nitrogen based alloy can be manufactured, and as a result, an anisotropic magnet powder with high crystallinity and excellent coercivity can be obtained.
Halides of alkali metal and/or halides of alkaline earth metal include, for example, a fluoride, a chloride, a bromide, an iodide, and the like.
Examples of alkali metal halides include LiCl, KCl, NaCl, and the like, and two or more kinds thereof may be used together.
Examples of the halides of the alkaline earth metal include CaCl2, MgCl2, BaCl2, SrCl2, and the like, and two or more kinds thereof may be used together.
Forms of alkali metal halides and/or alkaline earth metal halides include, for example, a powder and the like.
The concentration of samarium in the alkali metal halide and/or the alkaline earth metal halide at the heat treatment temperature is preferably 3.2 mol/L or more and 8.2 mol/L or less, and further preferably 5.2 mol/L or more and 6.2 mol/L or less. Thus, for example, the generation of heterophases such as Sm-rich crystal phases (e.g., SmFe2 phase, SmFe3 phase) can be reduced.
A method for nitriding the samarium-iron based alloy powder includes, but is not limited to, a method for heat treating the samarium-iron based alloy powder in an atmosphere such as ammonia, a gas mixture of ammonia and hydrogen, nitrogen, a gas mixture of nitrogen and hydrogen, and the like, at a temperature of 300 to 500 degrees C.
The nitrogen content in single-crystal particles of the TbCu7 type samarium-iron-nitrogen based alloy influences the magnetic properties of the anisotropic magnet powder in the present embodiment. The optimal single-crystal particle composition of the TbCu7 type samarium-iron-nitrogen based alloy for increasing the coercivity of the anisotropic magnet powder in the present embodiment is Sm0.667Fe5.667N1.26. Therefore, it it is important to control the nitrogen content in the single-crystal particles of the TbCu7 type samarium-iron-nitrogen based alloy. When the samarium-iron based alloy powder is nitridated using ammonia, it is possible to nitride the samarium-iron based alloy powder in a short period of time. However, the nitrogen content in the single-crystal particles of the TbCu7 type samarium-iron-nitrogen based alloy may be greater than Sm0.667Fe5.667N1.26. In this case, excessive nitrogen can be discharged from the crystal lattice by heat treating the samarium-iron-nitrogen based alloy powder in hydrogen after nitriding the samarium-iron based alloy powder.
For example, the amount of nitrogen contained in the single-crystal particles of the TbCu7 type samarium-iron-nitrogen based alloy is optimized by first nitriding the samarium-iron based alloy powder in an atmosphere of a mixture of ammonia and hydrogen streams at 350 degrees C. to 450 degrees C. for 10 minutes to 2 hours, subsequently transitioning the atmosphere to an atmosphere of a hydrogen stream at the same temperature, and heat treating the samarium-iron based alloy powder for 30 minutes to 2 hours. Hydrogen is then removed by transitioning the atmosphere to an atmosphere of an argon stream and heat treating the samarium-iron-nitrogen based alloy powder at the same temperature for 10 minutes to 1 hour.
A second method for manufacturing an anisotropic magnet powder according to the present embodiment includes steps of: producing a samarium-iron alloy powder by heat treating a composition containing samarium, samarium oxide and/or samarium halide, iron, iron oxide and/or iron halide, an alkali metal halide and/or an alkaline earth metal halide, and an alkali metal and/or alkaline earth metal at a temperature of a melting point of the alkali metal halide and/or alkaline earth metal halide or higher; and producing a samarium-iron-nitrogen based alloy powder by nitriding the samarium-iron-nitrogen based alloy powder.
Here, the temperature for heat treating is 500 degrees C. or higher and 800 degrees C. or less, and preferably 550 degrees C. or higher and 650 degrees C. or less. Therefore, it is possible to alloy the composition at a temperature significantly lower than the melting point of the metal constituting the samarium-iron based alloy, and as a result, a samarium-iron based alloy powder containing single-crystal particles of the TbCu7 type samarium-iron based alloy can be manufactured. In addition, by nitriding the samarium-iron based alloy powder, an anisotropic magnet powder containing single-crystal particles of the TbCu7 type samarium-iron-nitrogen based alloy can be manufactured.
In the specification and claims, when the alkali metal halide and/or the alkaline earth metal halide is a mixture, a temperature of a melting point of the alkali metal halide and/or the alkaline earth metal halide or higher means a temperature of an eutectic point of the mixture or higher shown in a state diagram.
Forms of samarium, samarium oxide and/or samarium halide include, for example, a powder.
The second method for manufacturing the anisotropic magnet powder according to the present embodiment uses samarium, a samarium oxide and/or a samarium halide, and preferably uses samarium. Therefore, it is possible to inhibit a remaining iron phase that is not alloyed with samarium, and as a result, the coercivity of the anisotropic magnet powder can be improved.
Examples of iron oxides include FeO, Fe3O4, and Fe2O3 and the like.
Examples of iron halides include iron (II) fluoride, iron (III) fluoride, iron (II) chloride, iron (III) chloride, iron (II) bromide, iron (III) bromide, and iron (II) iodide and the like.
Forms of iron, an iron oxide and/or an iron halide include, for example, a powder. On this occasion, by using an iron powder having a particle size smaller than that of a single-domain particle of a TbCu7 type samarium-iron-nitrogen based alloy, it is possible to manufacture a samarium-iron based alloy powder containing single-crystal particles of a TbCu7 type samarium-iron alloy having a particle size smaller than that of the single-domain particles of the TbCu7 type samarium-iron-nitrogen based alloy. In addition, by nitriding the samarium-iron-based alloy powder, an anisotropic magnet powder containing single-crystal particles of a TbCu7 type samarium-iron-nitrogen based alloy can be manufactured, and as a result, an anisotropic magnet powder with high crystallinity and excellent coercivity can be obtained.
Alkali metal halides and/or alkaline earth metal halides include, for example, a fluoride, a chloride, a bromide, an iodide and the like.
Examples of alkali metal halides include LiCl, KCl, NaCl and the like.
Examples of alkaline earth metal halides include CaCl2, MgCl2, BaCl2, SrCl2 and the like.
Forms of alkali metal halides and/or alkaline earth metal halides include, for example, a powder and the like.
Examples of alkali metals include sodium, lithium and the like.
Examples of alkaline earth metals include calcium, magnesium and the like.
Forms of alkali metals and/or alkaline earth metals include, for example, a powder and the like.
In the second method for manufacturing an anisotropic magnet powder according to the present embodiment, an alkali metal and/or an alkaline earth metal is used. Thus, the alkali metal and/or alkaline earth metal can reduce a samarium oxide and/or a samarium halide, an iron oxide and/or an iron halide, or can reduce the oxidized surface of samarium and/or iron. As a result, the generation of a heterophase such as a Sm-rich crystal phase (e.g., SmFe2 phase, SmFe3 phase) can be inhibited.
The concentration of samarium in the alkali metal halide and/or the alkaline earth metal halide at the heat treatment temperature is preferably 3.2 mol/L or more and 8.2 mol/L or less, and further preferably 5.2 mol/L or more and 6.2 mol/L or less. Thus, for example, the generation of a heterophase such as a Sm-rich crystal phase (e.g., SmFe2 phase, SmFe3 phase) can be inhibited.
A method for nitriding the samarium-iron-based alloy powder includes, but is not limited to, a method for heat treating the samarium-iron based alloy powder in an atmosphere of ammonia, a gas mixture of ammonia and hydrogen, nitrogen, a gas mixture of nitrogen and hydrogen and the like, at a temperature of 300 to 500 degrees C.
The nitrogen content in single-crystal particles of a TbCu7 type samarium-iron-nitrogen based alloy influences the magnetic properties of the anisotropic magnet powder in the present embodiment. The optimal composition of single-crystal particles of the TbCu7 type samarium-iron-nitrogen based alloy for increasing the coercivity of the anisotropic magnet powder in the present embodiment is Sm0.667Fe5.667N1.26. Therefore, it is important to control the nitrogen content in the single-crystal particles of the TbCu7 type samarium-iron-nitrogen based alloy. When the samarium-iron based alloy powder is nitridated using ammonia, it is possible to nitride the samarium-iron based alloy powder in a short period of time. However, the nitrogen content in the single-crystal particles of the TbCu7 type samarium-iron-nitrogen based alloy may be greater than Sm0.667Fe5.667N1.26. In this case, excessive nitrogen can be discharged from the crystal lattice by heat treating the samarium-iron-nitrogen based alloy powder in hydrogen after nitriding the samarium-iron based alloy powder.
For example, to begin with, the amount of nitrogen contained in the single-crystal particles of the TbCu7 type samarium-iron-nitrogen based alloy is optimized by nitriding the samarium-iron based alloy powder in an atmosphere of a mixture of ammonia and hydrogen streams at 350 degrees C. to 450 degrees C. for 10 minutes to 2 hours, subsequently transitioning the atmosphere to an atmosphere of a hydrogen stream at the same temperature, and heat treating the samarium-iron-nitrogen based alloy powder for 30 minutes to 2 hours. The hydrogen is then removed by transitioning the atmosphere to an atmosphere of an argon stream, and heat treating the samarium-iron-nitrogen based alloy powder at the same temperature between 0 to 1 hour.
(Washing with Water)
The samarium-iron-nitrogen based alloy powder is preferably washed in water to remove an alkali metal halide and/or an alkaline earth metal halide.
For example, water is added to the samarium-iron-nitrogen based alloy powder, stirred, and then decanted repeatedly.
(Dehydrogenation)
When washing the samarium-iron-nitrogen based alloy powder with water, hydrogen may enter a gap between crystal lattices of a samarium-iron-nitrogen based alloy powder. In this case, the samarium-iron-nitrogen based alloy powder may be dehydrogenated.
A method of dehydrogenating the samarium-iron-nitrogen based alloy powder includes, but is not limited to, a method for heat treating the samarium-iron-nitrogen based alloy powder in a vacuum or in an inert gas atmosphere.
For example, the samarium-iron-nitrogen based alloy powder is heat treated in a vacuum or in an argon stream at 150 degrees C. to 250 degrees C. for 1 to 3 hours.
(Vacuum Drying)
The washed samarium-iron-nitrogen based alloy powder is preferably dried in a vacuum to remove water.
Preferably, the temperature at which the washed samarium-iron-nitrogen based alloy powder is dried in a vacuum is from room temperature to 100 degrees C. Therefore, it is possible to inhibit the oxidation of the samarium-iron-nitrogen based alloy powder.
Further, the washed samarium-iron-nitrogen based alloy powder may be replaced with an organic solvent that has a high volatility such as alcohol and that can mix with water, and then may be dried in a vacuum.
The samarium-iron-nitrogen based alloy powder may be milled.
A jet mill, dry and wet ball mills, a vibration mill, a medium agitation mill and the like may be used to mill the samarium-iron-nitrogen based alloy powder.
The anisotropic magnet of the present embodiment contains a TbCu7 type samarium-iron-nitrogen based alloy, and can be manufactured using the anisotropic magnet powder of the present embodiment.
A degree of anisotropy of an anisotropic magnet according to the present embodiment is preferably 1.0% or more, more preferably 5.0% or more, and even more preferably 10.0% or more. When the anisotropic magnet according to the present embodiment has a degree of anisotropy of 1.0% or more, the magnetic properties of the anisotropic magnet according to the present embodiment are high.
A squareness ratio of the anisotropic magnet according to the embodiment is preferably 0.60 or more, and further preferably 0.67 or more. When the squareness ratio of the anisotropic magnet according to the present embodiment is 0.60 or more, the magnetic properties of the anisotropic magnet according to the present embodiment are high.
The anisotropic magnet of the present embodiment may be an anisotropic bonded magnet or an anisotropic sintered magnet, but is preferably an anisotropic sintered magnet in tams of magnetic properties.
An intensity ratio of a (002) plane X-ray diffraction peak to a (110) plane X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen based alloy phase of a crystal orientation plane of the anisotropic sintered magnet according to the embodiment exceeds 2.115. Magnetic properties of the anisotropic sintered magnet in the present embodiment are enhanced when the intensity ratio of the (002) plane X-ray diffraction peak to the (110) plane X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen based alloy phase exceeds 2.115, which is a value of an isotropic magnetic powder.
When the (002) plane X-ray diffraction peak overlaps the (200) and (111) plane X-ray diffraction peaks, the ratio of the sum of the (002) plane, (200) plane and (111) plane X-ray diffraction peaks to the (110) plane X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen based alloy phase of the anisotropic sintered magnet of the present embodiment exceeds 5.656.
The intensity ratio of the (024) plane X-ray diffraction peak of the Th2Zn17 type samarium-iron-nitrogen based alloy phase to the (110) plane X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen based alloy phase of the anisotropic sintered magnet according to the present embodiment is preferably 0.300 or less, and is further preferably 0.001 or less. When the intensity ratio of the (024) plane X-ray diffraction peak of the Th2Zn17 type samarium-iron-nitrogen based alloy phase to the (110) plane X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen based alloy phase of the anisotropic sintered magnet according to the present embodiment is 0.300 or less, the proportion of the TbCu7 type samarium-iron-nitrogen based alloy with respect to the anisotropic sintered magnet according to the present embodiment is sufficiently high.
The ratio c/a of the lattice constant c to the lattice constant a of the TbCu7 type samarium-iron-nitrogen based alloy phase of the anisotropic magnet according to the present embodiment is preferably 0.838 or more, and is further preferably 0.842 or more. If the ratio c/a of the lattice constant c to the lattice constant a of the TbCu7 type samarium-iron-nitrogen based alloy phase of the anisotropic magnet of the present embodiment is 0.838 or more, the proportion of Fe with respect to the TbCu7 type samarium-iron-nitrogen based alloy phase of the anisotropic magnet of the present embodiment is sufficiently high. As a result, the magnetic properties of the anisotropic sintered magnet according to the present embodiment are improved.
The integral width of the (101) plane X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen based alloy phase of the crystal orientation plane of the anisotropic sintered magnet according to the present embodiment is preferably 0.66 degrees or less, and is further preferably 0.54 degrees or less. When the integral width of the (101) plane X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen based alloy phase of the anisotropic sintered magnet according to the present embodiment is 0.66 degrees or less, the crystallinity of the anisotropic sintered magnet according to the present embodiment is improved.
The coercivity of the anisotropic sintered magnet according to the present embodiment is preferably 3.0 kOe or more, and is further preferably 6.0 kOe or more.
The crystal grain size of the anisotropic sintered magnet according to the present embodiment is preferably 3 μm or less, and is further preferably 1 μm or less.
Here, because the particle size of the single-domain particles of the Th2Zn17 type samarium-iron-nitrogen based alloy is approximately 3 μm and because the anisotropic magnetic field is approximately ⅓ of the Th2Zn17 type samarium-iron-nitrogen based alloy, the particle size of the single-domain particles of the TbCu7 type samarium-iron-nitrogen based alloy is not considered to be beyond 3 μm.
Therefore, when the crystal grain size of the anisotropic sintered magnet according to the present embodiment is 3 μm or less, the magnetic structure of the anisotropic sintered magnet according to the present embodiment shifts from a multi-domain structure to a single-domain structure, thereby increasing the magnetic properties of the anisotropic sintered magnet according to the present embodiment. In addition, when the crystal grain size of the anisotropic sintered magnet according to the present embodiment is 1 μm or less, because the formation of the nucleation reversed domains can be inhibited, the magnetic properties of the anisotropic sintered magnet according to the embodiment further increase.
Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.
The 101.8 g of iron nitrate and 14.9 g of calcium nitrate were dissolved in 819 mL of water, and 441 mL of 1 mol of a potassium hydroxide solution was added dropwise while being stirred, and thus a suspension of iron hydroxide was obtained. Then, the suspension was filtered, washed, and the iron powder was dried overnight at 120 degrees C. in air using a hot air drying oven, and the iron hydroxide powder was obtained. Next, the iron hydroxide powder was reduced in a hydrogen gas stream at 500 degrees C. for 6 hours, and thus an iron powder was obtained.
(Heat Treatment)
After 0.20 g of the iron powder, 0.29 g of a samarium chloride powder, 0.60 g of the lithium chloride powder having a melting point of 605 degrees C., and 0.07 g of a calcium powder were placed in an iron crucible, the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. The concentration of samarium in lithium chloride at 650 degrees C. was 3.2 mol/L.
The concentration of samarium in lithium chloride is determined by the following equation.
[(mass of samarium powder)/(molar mass of samarium)]/[(mass of lithium chloride)/(density of lithium chloride)]
(Nitriding)
The samarium-iron based alloy powder was heated up to 200 degrees C. in a hydrogen stream, then was raised to 320 degrees C. in a 1:2 volume ratio of ammonia-hydrogen mixture and held for 1 hour, and thus a samarium-iron-nitrogen based alloy powder was obtained. Next, a nitrogen content of the samarium-iron-nitrogen based alloy powder was optimized by holding the temperature at 320 degrees C., heat treating the samarium-iron-nitrogen based alloy powder in a hydrogen stream for 1 hour, and then heat treating the samarium-iron-nitrogen based alloy powder in an argon stream for 1 hour.
(Washing with Water)
The samarium-iron-nitrogen based alloy powder was washed with pure water, thereby removing unreacted samarium chloride, lithium chloride, unreacted calcium, and calcium chloride.
(Vacuum Drying)
The samarium-iron-nitrogen based alloy powder washed with pure water was replaced with isopropanol, and then dried in a vacuum at room temperature.
(Dehydrogenation)
The samarium-iron-nitrogen based alloy powder dried in a vacuum was dehydrogenated in a vacuum at 200 degrees C. for 3 hours, and thus a magnet powder was obtained.
A magnetic powder was obtained in the same manner as Example 1, except that the additive amounts of the samarium chloride powder and the calcium powder in the heat treatment were changed to 0.59 g and 0.14 g, respectively. Here, the concentration of samarium in lithium chloride at 650 degrees C. was 5.4 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the additive amounts of the samarium chloride powder and the calcium powder in the heat treatment were changed to 0.90 g and 0.21 g, respectively. The concentration of samarium in lithium chloride at 650 degrees C. was 7.2 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the additive amounts of the samarium chloride powder and the calcium powder in the heat treatment were changed to 1.21 g and 0.28 g, respectively. Here, the concentration of samarium in lithium chloride at 650 degrees C. was 8.4 mol/L.
A magnet powder was obtained in the same manner as Example 1, except that the additive amounts of the samarium chloride powder, the lithium chloride powder, the iron powder, and the calcium powder in the heat treatment were changed to 1.40 g, 1.42 g, 0.49 g, and 0.65 g, respectively. Here, the concentration of samarium in lithium chloride at 650 degrees C. was 5.4 mol/L.
A magnet powder was obtained in the same manner as Example 5, except that the additive amounts of the calcium powder in the heat treatment were changed to 1.31 g, 1.96 g, and 2,62 g, respectively. Here, the concentration of samarium in lithium chloride at 650 degrees C. was 5.4 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.24 g of an iron powder, 0.80 g of a samarium chloride powder, 0.51 g of a lithium chloride powder having a melting point of 605 degrees C., 0.22 g of a potassium chloride powder having a melting point of 770 degrees C., and 0.31 g of a calcium powder were placed in an iron crucible, the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. Here, the concentration of samarium in lithium chloride and potassium chloride at 650 degrees C. was 4.9 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.24 g of an iron powder, 0.80 g of a samarium chloride powder, 0.54 g of a lithium chloride powder having a melting point of 605 degrees C., 0.22 g of a sodium chloride powder having a melting point of 801 degrees C., and 0.29 g of a calcium powder were placed in an iron crucible, the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. Here, the concentration of samarium in lithium chloride and sodium chloride at 650 degrees C. was 5.2 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.24 g of an iron powder, 0.80 g of a samarium chloride powder, 0.47 g of a lithium chloride powder having a melting point of 605 degrees C., 0.31 g of a calcium chloride powder having a melting point of 772 degrees C., and 0.27 g of a calcium powder were placed in an iron crucible, the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. Here, the concentration of samarium in lithium chloride and calcium chloride at 650 degrees C. was 4.5 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.24 g of an iron powder, 0.80 g of a samarium chloride powder, 0.50 g of a lithium chloride powder having a melting point of 605 degrees C., 0.28 g of a magnesium chloride powder having a melting point of 714 degrees C., and 0.29 g of a calcium powder were placed in an iron crucible, the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. Here, the concentration of samarium in lithium chloride and magnesium chloride at 650 degrees C. was 4.8 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.24 g of an iron powder, 0.80 g of a samarium chloride powder, 0.57 g of a lithium chloride powder having a melting point of 605 degrees C., 0.57 g of a barium chloride powder having a melting point of 962 degrees C., and 0.27 g of a calcium powder were placed in an iron crucible, the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. Here, the concentration of samarium in lithium chloride and barium chloride at 650 degrees C. was 4.5 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.24 g of an iron powder, 0.80 g of a samarium chloride powder, 0.44 g of a lithium chloride powder having a melting point of 605 degrees C., 0.58 g of a strontium chloride powder having a melting point of 874 degrees C., and 0.27 g of a calcium powder were placed in an iron crucible, the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. The concentration of samarium in lithium chloride and strontium chloride at 650 degrees C. was 4.5 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.24 g of an iron powder, 0.28 g of a samarium oxide powder, 1.04 g of a lithium chloride powder having a melting point of 605 degrees C., and 0.19 g of a calcium powder were placed in an iron crucible, the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. The concentration of samarium in lithium chloride at 650 degrees C. was 3.2 mol/L.
A magnet powder was obtained in the same manner as Example 15, except that the additive amounts of the samarium oxide powder and the calcium powder in the heat treatment were changed to 0.47 g and 0.33 g, respectively. Here, the concentration of samarium in lithium chloride at 650 degrees C. was 5.4 mol/L.
A magnet powder was obtained in the same manner as Example 15, except that the additive amounts of the samarium oxide powder and the calcium powder in the heat treatment were changed to 0.63 g and 0.43 g, respectively. The concentration of samarium in lithium chloride at 650 degrees C. was 7.2 mol/L.
A magnet powder was obtained in the same manner as Example 15, except that the additive amounts of the samarium oxide powder and the calcium powder in the heat treatment were changed to 0.73 g and 0.50 g, respectively. Here, the concentration of samarium in lithium chloride at 650 degrees C. was 8.4 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.24 g of an iron powder, 0.40 g of a samarium powder, and 1.04 g of a lithium chloride powder having a melting point of 605 degrees C. were placed in an iron crucible, and the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. Here, the concentration of samarium in lithium chloride at 650 degrees C. was 5.4 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.29 g of an iron powder, 0.24 g of a samarium powder, 1.04 g of a lithium chloride powder having a melting point of 605 degrees C., and 0.20 g of a calcium powder were placed in an iron crucible, and the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. The concentration of samarium in lithium chloride at 650 degrees C. was 3.2 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.24 g of an iron powder, 0.40 g of a samarium powder, 1.04 g of a lithium chloride powder having a melting point of 605 degrees C., and 0.20 g of a calcium powder were placed in an iron crucible, and the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. Here, the concentration of samarium in lithium chloride at 650 degrees C. was 5.4 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.20 g of an iron powder, 0.54 g of a samarium powder, 1.04 g of a lithium chloride powder having a melting point of 605 degrees C., and 0.20 g of a calcium powder were placed in an iron crucible, and the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. The concentration of samarium in lithium chloride at 650 degrees C. was 7.2 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.19 g of an iron powder, 0.63 g of a samarium powder, 1.04 g of a lithium chloride powder having a melting point of 605 degrees C., and 0.20 g of a calcium powder were placed in an iron crucible, the iron crucible was heat treated at 650 degrees C. for 6 hours in an argon atmosphere, and thus a samarium-iron alloy powder was obtained. Here, the concentration of samarium in lithium chloride at 650 degrees C. was 8.4 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.24 g of an iron powder, 0.40 g of a samarium powder, 0.35 g of a lithium chloride powder having a melting point of 605 degrees C., 0.71 g of a calcium chloride powder having a melting point of 772 degrees C., and 0.20 g of a calcium powder were placed in an iron crucible, and the iron crucible was heat treated at 600 degrees C. in an argon atmosphere for 6 hours, and thus a samarium-iron alloy powder was obtained. Here, the concentration of samarium in lithium chloride and calcium chloride at 600 degrees C. was 5.4 mol/L.
In the heat treatment, a magnetic powder was obtained in the same manner as Example 24, except that the heat treatment time was changed to 48 hours. The concentration of samarium in lithium chloride at 600 degrees C. was 5.4 mol/L.
A magnetic powder was obtained in the same manner as Example 1, except that the magnetic powder was heat treated as follows.
(Heat Treatment)
After 0.24 g of an iron powder, 0.25 g of a samarium powder, 0.35 g of a lithium chloride powder having a melting point of 605 degrees C., and 0.71 g of a calcium chloride powder having a melting point of 772 degrees C. were placed in an iron crucible, and the iron crucible was heat treated at 600 degrees C. for 6 hours in an argon atmosphere, a samarium-iron alloy powder was obtained. Here, the concentration of samarium in lithium chloride and calcium chloride at 600 degrees C. was 3.2 mol/L.
A magnet powder was obtained in the same manner as Example 26, except that the additive amount of samarium powder in the heat treatment was changed to 0.30 g. Here, the concentration of samarium in lithium chloride and calcium chloride at 600 degrees C. was 4.0 mol/L.
A magnet powder was obtained in the same manner as Example 26, except that the additive amount of samarium powder in the heat treatment was changed to 0.35 g. Here, the concentration of samarium in lithium chloride and calcium chloride at 600 degrees C. was 4.7 mol/L.
A magnet powder was obtained in the same manner as Example 26, except that the additive amount of samarium powder in the heat treatment was changed to 0.40 g. Here, the concentration of samarium in lithium chloride and calcium chloride at 600 degrees C. was 5.4 mol/L.
A magnet powder was obtained in the same manner as Example 24, except that the additive amount of calcium powder in the heat treatment was changed to 0.10 g. Here, the concentration of samarium in lithium chloride and calcium chloride at 600 degrees C. was 5.4 mol/L.
A magnet powder was obtained in the same manner as Example 24, except that the additive amount of calcium powder in the heat treatment was changed to 0.40 g. Here, the concentration of samarium in lithium chloride and calcium chloride at 600 degrees C. was 5.4 mol/L.
A magnet powder was obtained in the same manner as Example 24, except that the additive amount of samarium powder in the heat treatment was changed to 0.25 g. Here, the concentration of samarium in lithium chloride and calcium chloride at 600 degrees C. was 3.2 mol/L.
A magnet powder was obtained in the same manner as Example 24, except that the additive amount of samarium powder in the heat treatment was changed to 0.30 g. Here, the concentration of samarium in lithium chloride and calcium chloride at 600 degrees C. was 4.0 mol/L.
A magnet powder was obtained in the same manner as Example 24, except that the additive amount of samarium powder in the heat treatment was changed to 0.35 g. Here, the concentration of samarium in lithium chloride and calcium chloride at 600 degrees C. was 4.7 mol/L.
Production of a magnetic powder was attempted in the same manner as Example 2, except that the additive amounts of samarium chloride powder and lithium chloride powder in the heat treatment were changed to 0 g and 0.59 g, respectively, but the magnet powder could not be produced.
In a heat treatment, production of a magnetic powder was attempted in the same manner as Example 16, except that a lithium chloride powder was not added, but the magnetic powder could not be produced.
In a heat treatment, production of a magnetic powder was attempted in the same manner as Example 16, except that a calcium powder was not added, but the magnet powder could not be produced.
In a heat treatment, production of a magnetic powder was attempted in the same manner as Example 21, except that a lithium chloride powder was not added, but the magnetic powder could not be produced.
Table 1 shows conditions for a heat treatment.
Next, the presence or absence of single-crystal particles of the TbCu7 type samarium-iron-nitrogen alloy, the intensity ratio of the (024) plane X-ray diffraction peak of the Th2Zn17 type samarium-iron-nitrogen alloy phase to the (110) plane X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen alloy phase (hereinafter referred to as an “intensity ratio of an X-ray diffraction peak”), the ratio c/a of the lattice constant c to the lattice constant a of the TbCu7 type samarium-iron-nitrogen alloy phase (hereinafter referred to as a “lattice constant ratio”), an integral width of a (101) plane X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen alloy phase (hereinafter referred to as an “integral width of an X-ray diffraction peak”), and the coercivity were evaluated.
The magnet powder was embedded in resin, polished, and then processed into a focused ion beam (FIB), and thus a thin section was obtained. Then, a transmission electron microscope (TEM) was used to obtain a selected area diffraction image of the thin section, thereby evaluating the presence or absence of single-crystal particles of the TbCu7 type samarium-iron-nitrogen alloy.
Specifically, the presence or absence of the single-crystal particles of the TbCu7 type samarium-iron-nitrogen alloy was evaluated by checking whether the selected area diffraction image of the thin section is a spot-like diffraction image unique to the single-crystal particles and matches the spatial group P6/mmm, which is a feature of the crystal structure of the TbCu7 type samarium-iron-nitrogen alloy.
The X-ray diffraction spectra of the magnetic powder were measured using an X-ray diffraction device, Empyrean (made by Malvern Panalytical) and an X-ray detector, Pixcel 1D (made by Malvern Panalytical). Specifically, the X-ray diffraction spectrum of the magnet powder was measured using a Co-tube as an X-ray source under the conditions of a tube voltage of 45 kV, a tube current of 40 mA, a measurement angle of 30 to 60 degrees, a measurement step width of 0.013 degrees, and a width scan speed of 0.09 degrees/sec (see
Peak searching and profile fitting were performed using High Score Plus (made by Malvern Panalytical) as the X-ray diffraction pattern analysis software, while setting the least significance difference at 1.00. Specifically, the integral intensity of the diffraction peak at the (110) plane of the TbCu7 type samarium-iron-nitrogen alloy phase near 41.5 degrees and the integral intensity of the diffraction peak at the (024) plane of the Th2Zn17 type samarium-iron-nitrogen alloy phase near 43.2 degrees were obtained, and then the intensity ratio of the diffraction peak was calculated.
From
After measuring the X-ray diffraction spectrum of the magnet powder (see
From
In addition, after measuring the X-ray diffraction spectrum of the magnet powder (see
From
A magnet powder was mixed with thermoplastic resin and then oriented in a 20 kOe magnetic field, thereby producing a bonded magnet.
The bonded magnet was installed in the orientation direction using a vibration sample magnetometer VSM at a temperature of 27 degrees C. and in a maximum applied magnetic field of 90 kOe, and the coercivity was measured.
TABLE 2 shows evaluation results of the presence or absence of single-crystal particles of a TbCu7 type samarium-iron-nitrogen alloy, an intensity ratio of an X-ray diffraction peak, a lattice constant ratio, an integral width of the X-ray diffraction peak, and coercivity.
From Table 2, it can be seen that the magnet powders of Examples 1 to 34 are anisotropic magnet powders containing single-crystal particles of a TbCu7 type samarium-iron-nitrogen alloy.
In contrast, in Comparative Examples 1, 2, and 4, the samarium-iron alloy powder is not produced and the magnet powder cannot be produced because the heat treatment is performed at a temperature below the melting point of calcium.
In Comparative Example 3, because alkali metal or alkaline earth metal is not used, samarium oxide is not reduced, and a magnet powder cannot be produced.
A magnet powder was obtained in the same manner as Example 21 except that the temperature was raised to 270 degrees C. during nitriding.
A magnet powder was obtained in the same manner as Example 21 except that the temperature was raised to 370 degrees C. during nitriding.
A magnet powder was obtained in the same manner as Example 21 except that the temperature was raised to 420 degrees C. during nitriding.
A magnet powder was obtained in the same manner as Example 21 except that the dehydrogenated samarium-iron-nitrogen alloy powder was milled as follows.
(Milling)
One gram of dehydrogenated samarium-iron-nitrogen alloy powder, 20 ml hexane, 100 g of a 0.5 mm diameter zirconia ball was put in a 100 ml plastic container, and then milled at 20 Hz for 1 hour using a vibrating mill apparatus, and thus a magnet powder was obtained.
A magnetic powder was obtained in the same manner as that in Examples 21-4 except that a zirconia ball having a diameter of 1.0 mm was used in the milling process.
A magnetic powder was obtained in the same manner as in Examples 21-4 except that a zirconia ball having a diameter of 1.5 mm was used in the milling process.
From
In addition, because the selected area diffraction image in
A magnetic powder was obtained in the same manner as Example 21-6, except that the milling time was changed to 3 hours.
A magnetic powder was obtained in the same manner as Example 21-6, except that the milling time was changed to 5 hours.
Samarium-iron alloy powder was obtained in the same manner as Example 21 except that the samarium-iron alloy powder was not nitrided.
The iron and samarium were weighed so that the iron content in the samarium-iron alloy was 90 at % and the samarium content in the samarium-iron alloy was 10 at %, and the samarium-iron alloy was obtained by arc dissolution method.
A samarium-iron alloy was melted by filling a quartz tube with a nozzle with the samarium-iron alloy and melting the samarium-iron alloy at high frequency. Next, Ar gas was blown from the upper portion of the quartz tube, and melted water of the samarium-iron alloy was injected from the nozzle to a rotating copper cooling roller, and a quench thin zone of the samarium-iron alloy was obtained. On this occasion, the circumferential speed of the cooling roll was set to 30 m/sec. The obtained quench thin zone was heated to 700 degrees C. for 30 minutes in an Ar atmosphere, and thus a samarium-iron alloy powder was obtained.
The magnet powder was obtained in the same manner as Example 21-3, except that the obtained samarium-iron alloy powder was used.
A magnet powder was obtained in the same manner as Comparative Example 5, except that the dehydrogenated samarium-iron-nitrogen alloy powder was milled as follows.
(Milling)
One gram of dehydrogenated samarium-iron-nitrogen alloy powder, 20 ml hexane, 100 g of a 1.5 mm diameter zirconia ball was put in a 100 ml plastic container, and then milled at 20 Hz for 5 hours using a vibrating mill apparatus, and thus a magnet powder was obtained.
A magnet powder was obtained in the same manner as Example 24 except that the dehydrogenated samarium-iron-nitrogen alloy powder was milled as follows.
(Disintegration)
One gram of dehydrogenated samarium-iron-nitrogen alloy powder, 20 ml hexane, 100 g of 1.5 mm diameter zirconia balls were put in a 100 ml plastic container, and then milled at 20 Hz for 1 hour using a vibrating mill apparatus, and thus a magnet powder was obtained.
A magnet powder was obtained in the same manner as Example 25 except that the dehydrogenated samarium-iron-nitrogen alloy powder was milled as follows.
(Milling)
One gram of dehydrogenated samarium-iron-nitrogen alloy powder, 20 ml of hexane, 100 g of 1.5 mm diameter zirconia balls were put in a 100 ml plastic container, and then milled at 20 Hz for 1 hour using a vibrating mill apparatus, and thus a magnet powder was obtained.
Next, the presence or absence of single-crystal particles of TbCu7 type samarium-iron-nitrogen alloy, an intensity ratio of X-ray diffraction peak, a lattice constant ratio, an integral width of X-ray diffraction peak, coercivity, the presence or absence of anisotropy of bonded magnet, anisotropy, a squareness ratio, and residual magnetization were evaluated.
The magnet powder was mixed with the thermoplastic resin and then oriented in a 20 kOe magnetic field, thereby producing a bonded magnet.
Under the conditions at the temperature of 27 degrees C. and the maximum applied magnetic field of 90 kOe created by using the vibration sample type magnetometer VSM, when the residual magnetization in installing the bonded magnet in the orientation direction is denoted Mr_EASY, and when the residual magnetization in installing the bonded magnet in the direction perpendicular to the orientation direction is denoted Mr_HARD, the degree of anisotropy [%] was determined by the following equation.
(1−Mr_HARD/Mr_EASY)×100
Here, when the degree of anisotropy exceeds 1.0%, it was determined that there was anisotropy of the bonded magnet, and when the degree of anisotropy is 1.0% or less, it was determined that there was no anisotropy of the bonded magnet.
In addition, when a bonded magnet is installed in the orientation direction, and when the magnetization where a magnetic field of 90 kOe is applied is denoted M 90 kOe, the squareness ratio was obtained by the following formula.
Mr_EASY/M 90kOe
TABLE 3 shows the evaluation results of the presence or absence of single-crystal particles of TbCu7 type samarium-iron-nitrogen alloy, an intensity ratio of X-ray diffraction peak, a lattice constant ratio, an integral width of X-ray diffraction peak, coercivity, the presence or absence of anisotropy of bonded magnet, a degree of anisotropy, a squareness ratio, and residual magnetization.
From Table 3, it can be seen that the magnet powders of Examples 21-1 to 21-8, 24-1 and 25-1 are anisotropic magnet powders containing single-crystal particles of a TbCu7 type samarium-iron-nitrogen alloy. Also, it can be seen that the bonded magnets produced using the magnetic powders of Examples 21-1 to 21-8, 24-1, and 25-1 have anisotropy.
In contrast, in Comparative Examples 21-1, a samarium-iron alloy powder having a low coercivity is prepared because the samarium-iron alloy powder is not nitrided.
Because the magnetic powders in Comparative Examples 5 and 5-1 were produced using a quench band of samarium-iron alloy, it is found that the magnetic powder does not contain single-crystal particles of TbCu7 type samarium-iron-nitrogen alloy. In addition, it can be seen that the bonded magnet produced by using the magnet powder of Comparative Example 5 has no anisotropy.
Next, the presence or absence of anisotropy, a degree of anisotropy, a squareness ratio, residual magnetization, and coercivity of the sintered magnet were evaluated.
In a glove box, a 5.5 mm long, 5.5 mm wide carbide rectangular mold (die) was filled with 0.5 g of magnetic powder of Example 25-1, and then oriented in a 20 kOe magnetic field. The die was then placed in a discharge plasma sintering device with a pressurization mechanism by a servo press machine without exposure to air. Next, the magnet powder was electrically charged and sintered for 1 minute at a pressure of 1200 MPa and a temperature of 500 degrees C. under the condition that the inside of the sintering device was maintained at a vacuum (a pressure of 2 Pa or less and an oxygen concentration of 0.4 ppm or less), thereby producing a sintered magnet. Here, after the magnet powder was electrostatically sintered, the pressure was returned to the atmosphere with an inert gas, and the sintered magnet was taken out into the atmosphere after the temperature fell below 60 degrees C.
Under the conditions at the temperature of 27 degrees C. and the maximum applied magnetic field of 90 kOe created by using the vibration sample type magnetometer VSM, when the residual magnetization in installing the bonded magnet in the orientation direction is made Mr_EASY, and when the residual magnetization in installing the bonded magnet in the direction perpendicular to the orientation direction is made Mr_HARD, the degree of anisotropy [%] was determined by the following equation.
(1−Mr_HARD/Mr_EASY)×100
Here, when the degree of anisotropy exceeds 1%, it was determined that there was anisotropy of the sintered magnet, and when the degree of anisotropy is 1% or less, it was determined that there was no anisotropy of the sintered magnet.
In addition, a sintered magnet is installed in the orientation direction, and when the magnetization in applying a magnetic field of 90 kOe is made M 90 kOe, a squareness ratio was obtained by using the following formula.
Mr_EASY/M_ 90 kOe
A bonded magnet was installed in the orientation direction using a vibration sample magnetometer VSM under conditions at a temperature of 27 degrees C. and in a maximum applied magnetic field of 90 kOe, and the coercivity was measured.
The results showed that the sintered magnet had anisotropy with an anisotropy of 18%. The sintered magnet had a squareness ratio of 0.53, a residual magnetization of 500 emu/cm3, and a coercivity of 6.7 kOe.
Next, an intensity ratio of the (002) plane X-ray diffraction peak to the (110) plane X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen alloy phase of the crystal orientation plane (hereinafter referred to as the intensity ratio of the X-ray diffraction peak of the crystal orientation plane), an intensity ratio of the (024) X-ray diffraction peak of the Th2Zn17 type samarium-iron-nitrogen alloy phase to the (110) plane X-ray diffraction peak of the TbCu7 type samarium-nitrogen alloy phase of the amorphous orientation plane (hereinafter referred to as the intensity ratio of the X-ray diffraction peak of the amorphous orientation plane), and a lattice constant ratio c/a of a lattice constant c to the lattice constant a of the TbCu7 type samarium-iron-nitrogen alloy phase of the crystal orientation plane (hereinafter referred to as the lattice constant ratio of the crystal orientation plane), and an integrated width of the (101) X-ray diffraction peak of the TbCu7 type samarium-iron-nitrogen alloy phase of the crystal orientation plane (hereinafter referred to as an integral width of an X-ray diffraction peak of the crystal orientation plane) were evaluated.
The X-ray diffraction spectra of sintered magnets were measured using an X-ray diffractometer, Empyrean (Malvern Panalytical) and an X-ray detector, Pixcel 1D (Malvern Panalytical). Specifically, the X-ray diffraction spectrum of the sintered magnet was measured using a Co-tube as an X-ray source under the conditions of a tube voltage of 45 kV, a tube current of 40 mA, a measurement angle of 30 to 60 degrees, a measurement step width of 0.013 degrees, and a width scan speed of 0.09 degrees/sec (see
Peak searching and profile fitting were performed using High Score Plus (Malvern Panalytical) as the X-ray diffraction pattern analysis software, while setting the minimum significance to 1.00.
Specifically, the X-ray diffraction spectrum of the plane perpendicular to the magnetic field application direction obtained by cutting the sintered magnet, i.e., the crystal orientation plane, was measured, and the intensity ratio of the X-ray diffraction peak of the crystal orientation plane was calculated after the integral intensity of the diffraction peak of the (110) plane of the TbCu7 type samarium-iron-nitrogen alloy phase near 41.5 degrees was obtained, and the integral intensity of the diffraction peak of the (002) plane near 50.1 degrees was obtained.
From
When the (002) plane x-ray diffraction peak overlaps the (200) and (111) plane x-ray diffraction peaks, the ratio of the sum of (002) plane, (200) plane and (111) plane x-ray diffraction peak intensities to the (110) plane x-ray diffraction peak intensity is calculated after calculating the integral intensity of the (200) plane diffraction peak near 48.4 degrees and the (111) plane diffraction peak near 48.9 degrees.
From
In addition, the X-ray diffraction spectrum of the surface perpendicular to the crystal orientation surface obtained by cutting the sintered magnet, i.e., the amorphous orientation surface, was measured, and the integral intensity of the (110) plane diffraction peak of the TbCu7 type samarium-iron-nitrogen alloy phase near 41.5 degrees was obtained, and the integral intensity of the (024) plane diffraction peak of the Th2Zn17 type samarium-iron alloy phase near 43.2 degrees was obtained, and then the intensity ratio of the X-ray diffraction peak of the amorphous orientation surface was calculated.
From
Furthermore, after measuring the X-ray diffraction spectrum of the crystal orientation surface of the sintered magnet (see
From
After measuring the X-ray diffraction spectrum of the crystal orientation plane of the sintered magnet (see
From
This application claims priority to Priority Application No. 2019-044954, filed March 12, 2019 with the Japan Patent Office, the contents of which are hereby incorporated by reference in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-044954 | Mar 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/000734 | 1/10/2020 | WO | 00 |
