JP4345588B2 - Rare earth-transition metal-nitrogen magnet powder, method for producing the same, and bonded magnet obtained - Google Patents

Description

  The present invention relates to a rare earth-transition metal-nitrogen based magnet powder, a method for producing the same, and a bonded magnet obtained. More specifically, the present invention relates to a rare earth-transition having excellent magnetic properties, capable of suppressing composition shift of rare earth elements during reduction diffusion. The present invention relates to a metal-nitrogen based magnet powder, a method for producing the same, and an obtained bonded magnet.

  In recent years, there has been a demand for downsizing and high efficiency of various devices such as home appliances, acoustic devices, and various automotive devices. Further, downsizing and high performance of permanent magnets indispensable for such devices are desired. Under such circumstances, the demand for rare earth magnets having magnetic characteristics several tens of times higher than that of low characteristic magnets such as ferrite is increasing.

For example, an Nd—Fe—B based sintered magnet has a (BH) _max exceeding 55 MGOe, and is one of the most in demand magnets. Furthermore, nitrogen is introduced into intermetallic compounds having rhombohedral, hexagonal, tetragonal, or monoclinic crystal structures as magnets aligned with Nd-Fe-B magnets due to the magnetic properties of magnet powder. The rare earth-transition metal-nitrogen based magnet powder has been attracting attention because it has excellent magnetic properties as a permanent magnet material.

Such rare earth-transition metal-nitrogen based magnet powder is represented by, for example, Fe-RN (one or two or more selected from the group consisting of R: Y, Th, and all lanthanoid elements). A permanent magnet (see Patent Document 1), or a hexagonal or rhombohedral crystal structure, and R—Fe—N—H (R: at least one of rare earth elements including yttrium). Magnetic anisotropy material represented (see Patent Document 2), R-Fe-MA (R: rare earth metal composed of Y or yttrium, M: V, Ti, Mo, at least one of A: N Or a rare earth magnet material represented by C) (see Patent Document 3). Furthermore, a rare earth magnet material in which nitrogen or the like is contained in a Th ₂ Zn ₁₇ type, TbCu ₇ type, or ThMn ₁₂ type intermetallic compound having a rhombohedral, hexagonal, or tetragonal crystal structure (Patent Literature) 4) has been proposed.

  In addition, in order to improve the magnetic properties and the like of these magnet materials, use of various additives has been studied. For example, this Patent Document 4 discloses R—Fe—N—H—O—M (R: Y-containing at least one kind of rare earth elements including M: Mg) having a hexagonal or rhombohedral crystal structure. , Ti, Zr, Cu, Zn, Al, Ga, In, Si, Ge, Sn, Pb, Bi, and these elements and R oxides, fluorides, carbides, nitrides, hydrides, at least A magnetic material represented by “a kind” is disclosed.

Many of these rare earth-transition metal-nitrogen based magnetic materials are used as powders having an average particle diameter of 1 to 10 μm. If the average particle size exceeds 10 μm, the required coercive force cannot be obtained, or the surface of the bonded magnet becomes rough and the magnetic particles are likely to fall off. On the other hand, if the average particle size is less than 1 μm, heat is generated due to powder oxidation. This is because the magnetic properties are degraded due to decomposition of the main phase having a Th ₂ Zn ₁₇ type crystal structure.

  As for rare earth-transition metal-nitrogen based magnetic materials, rare earth-transition metal based mother alloy powders having an average particle size exceeding 1 to 10 μm are manufactured by a melt casting method, a liquid quenching method, a reduction diffusion method or the like. Then, after obtaining the master alloy powder, in order to introduce nitrogen atoms into the alloy, nitriding treatment is performed by heating to 200 to 700 ° C. in a mixed gas atmosphere of nitrogen, ammonia, or these and hydrogen, Micronized to a predetermined particle size.

  In order to produce the above master alloy powder by the melt casting method, a rare earth metal, a transition metal, and other metals as required are mixed in a predetermined ratio and melted at a high frequency in an inert gas atmosphere. The ingot is subjected to uniform heat treatment and then pulverized to a predetermined particle size by a jaw crusher or the like. In the liquid quenching method, an alloy ribbon is produced from the alloy ingot and is pulverized. In the reduction diffusion method, a rare earth oxide powder, a reducing agent, a transition metal powder, and if necessary, other metal powder and / or metal oxide are used as starting materials.

  However, in the melt casting method, for example, when a molten alloy is solidified, a temperature distribution is generated and a composition shift occurs. Further, the melt casting method and the liquid quenching method are not economical because the rare earth metal used as a raw material is expensive.

  On the other hand, in the reduction diffusion method, the rare earth element at a high temperature is evaporated due to the temperature distribution in the furnace, causing a composition shift. A magnet powder using a mother alloy having a shifted composition contains an alloy phase other than the main phase, so that the magnetic properties are lowered. For this reason, it is actually difficult to manufacture the above-described method with no variation in the composition of the mother alloy.

For this reason, the present applicant has proposed that the raw material powder is previously pressure-molded to limit the movement of the solution formed during the reduction-diffusion reaction and to prevent variations in the master alloy composition (Patent Document). 5).
Although this problem has been solved to some extent, the process becomes more complicated and disadvantageous in cost. In addition, the rare earth-transition metal master alloy powder in the reduction diffusion reaction product is agglomerated and fused. Because there are many deposits and the alloy powders are strongly agglomerated and fused even after nitriding, the orientation (powder orientation) when the powder is oriented in a magnetic field is inferior and the magnetization is low. The problem remains. For this reason, it is possible to use a pulverizer such as a jet mill to pulverize and pulverize the agglomerated / fused part of the alloy powder, but the coercive force is reduced due to the distortion of the crystals generated during the pulverization. A new problem of lowering occurs.

As described above, various attempts have been made to improve the magnetic properties of the rare earth-transition metal-nitrogen based magnet powder, but many problems to be improved still remain. For this reason, there has been a strong demand to develop a method for producing a rare earth-transition metal-nitrogen based magnet powder that solves the above-described problems of the prior art and exhibits excellent magnetic properties without composition deviation.
Japanese Patent Laid-Open No. 60-131949 Japanese Patent Laid-Open No. 2-57663 JP-A-6-279915 JP-A-3-153852 JP 10-280002 A

  In view of the above-mentioned conventional problems, an object of the present invention is to provide a rare earth-transition metal-nitrogen based magnet powder having excellent magnetic properties, a rare earth element composition shift during reduction diffusion, a method for producing the same, and a bond obtained It is to provide a magnet.

  As a result of intensive studies to achieve the above object, the present inventor reduced a raw material containing a rare earth oxide with a reducing agent and diffused it into a transition metal to obtain a master alloy, and then nitrided the master alloy. Then, in the method of producing a rare earth-transition metal-nitrogen based magnet powder, in a place where the temperature in the reaction vessel for reduction diffusion becomes relatively high due to heating and firing during reduction diffusion, in advance than the rare earth element or the raw material mixture By introducing a raw material for adjustment with an increased content of rare earth elements, even if the rare earth elements evaporate in a place where the temperature is high due to the temperature distribution in the furnace, the rare earth elements are not deficient and generated. It has been found that the composition of the alloy before introducing nitrogen can be made more uniform and the characteristics of the rare earth-transition metal-nitrogen based magnet powder after nitriding can be improved, and the present invention has been completed.

  That is, according to the first invention of the present invention, the raw material mixture containing the rare earth oxide powder, the transition metal powder containing iron, and the reducing agent for reducing the rare earth oxide is introduced into the reaction vessel for reducing diffusion. And heating and firing in a non-oxidizing atmosphere to obtain a rare earth-transition metal master alloy, followed by nitriding to obtain a rare earth-transition metal-nitrogen magnet powder in which variation in the content of rare earth elements is suppressed. In the production method, when the raw material mixture is introduced into the reaction vessel for reduction diffusion, the bottom thereof is preliminarily provided with (a) a rare earth metal, (b) a mixture of a rare earth oxide powder and a reducing agent, or ( c) A raw material for adjustment selected from a mixture of rare earth oxide powder, transition metal powder and reducing agent having a rare earth element content of 1 to 30 atomic% higher than the raw material mixture is loaded, and then the raw material mixture is placed thereon. Characterized by loading That the rare earth - transition metal - method for producing nitrogen-based magnetic powder is provided.

  According to the second invention of the present invention, the rare earth-transition metal-nitrogen system according to the first invention, wherein the content of the rare earth element contained in the raw material mixture is 7 to 11 atomic%. A method for producing magnet powder is provided.

  Further, according to the third invention of the present invention, in the first or second invention, the content of the rare earth element contained in the adjustment raw material is relative to the total amount of the rare earth element contained in the raw material mixture and the adjustment raw material. Thus, there is provided a method for producing a rare earth-transition metal-nitrogen based magnet powder characterized by being 2 to 40%.

  On the other hand, according to the fourth aspect of the present invention, there is provided a rare earth-transition metal-nitrogen based magnet powder obtained by the production method of any one of the first to third aspects.

  According to a fifth aspect of the present invention, there is provided a rare earth-transition metal-nitrogen based magnet powder according to the fourth aspect, wherein the rare earth element content is 3 to 20 atomic%. The

  Furthermore, according to the sixth invention of the present invention, the rare earth-transition metal-nitrogen based magnet according to the fourth or fifth invention, wherein the rare earth element content variation is within 0.3 atomic%. A powder is provided.

  On the other hand, according to the seventh invention of the present invention, there is provided a bonded magnet composition obtained by mixing a resin binder with the rare earth-transition metal-nitrogen based magnet powder according to any one of the fourth to sixth inventions. Is done.

  Furthermore, according to the 8th invention of this invention, the bonded magnet formed by shape | molding the composition for bonded magnets of 7th invention by compression molding or injection molding is provided.

  According to the method for producing a rare earth-transition metal-nitrogen magnet powder of the present invention, when the raw material powder is heated and fired in the reaction vessel for reduction diffusion, the rare earth element is dispersed in the mother alloy even if the rare earth element is scattered. Therefore, the rare earth-transition metal master alloy powder having a more uniform composition can be produced. By performing nitriding using the thus obtained mother alloy powder, a rare earth-transition metal-nitrogen magnet powder having high magnetic properties can be obtained, and an excellent bonded magnet can be provided.

  Hereinafter, the rare earth-transition metal-nitrogen based magnet powder of the present invention, its manufacturing method, and the bonded magnet obtained will be described in detail.

1. Method for Producing Rare Earth-Transition Metal-Nitrogen Magnet Powder The method for producing a rare earth-transition metal-nitrogen magnet powder of the present invention comprises (1) rare earth oxide powder, transition metal powder containing iron, and the rare earth oxide. A raw material mixture containing a reducing agent for reduction, and (a) a rare earth metal, (b) a mixture of a rare earth oxide powder and a reducing agent, or (c) a rare earth element content is 1 more than that of the raw material mixture. ~ 30 atomic% more rare earth oxide powder, transition metal powder and a raw material for adjustment selected from a mixture of reducing agents, and introduced into the reaction container for reduction diffusion so that the raw material for adjustment is located at the bottom, 2) A rare earth-transition metal master alloy is obtained by a reduction diffusion method by heating and firing in a non-oxidizing atmosphere, and (3) a rare earth-transition metal-nitrogen magnet powder is produced by nitriding the master alloy. It is.

(1) Arrangement of raw material mixture in reaction container for reduction diffusion In order to produce a rare earth-transition metal-nitrogen based magnet material according to the present invention, first, rare earth oxide powder, reducing agent, transition metal powder, as required A raw material mixture starting from other metal powder and / or metal oxide, and (a) a rare earth metal, (b) a mixture of rare earth oxide powder and a reducing agent, or (c) a rare earth element content. Preparation material selected from a mixture of rare earth oxide powder, transition metal powder and reducing agent 1-30 atomic% more than the mixture, and these powder raw materials in a specific positional relationship to the reaction vessel for reduction diffusion Load as follows.

(Reaction container for reduction diffusion)
In the present invention, a reactor as shown in FIG. 1 is used to reduce the rare earth oxide and diffuse it into the transition metal. This reactor comprises a closed type reduction diffusion container containing a reaction vessel charged with a raw material mixture, means for replacing the atmospheric gas in the inside with a non-oxidizing gas such as argon, and circulating the non-oxidizing gas, A heater 6 for heating the diffusion container to a predetermined temperature is composed of an electric furnace or the like incorporated in the brick 5.

  As the structure of the reaction vessel installed in the reduction diffusion vessel, various shapes such as a cylindrical shape and a rectangular tube shape are adopted, and the material is preferably a corrosion-resistant material such as stainless steel. The bottom shape of the reaction vessel may be any shape such as a hemispherical shape or a rounded cylindrical shape, and is not particularly limited.

(Rare earth oxide powder)
The rare earth oxide powder used in the present invention is not particularly limited, but as the rare earth element, any one or more of lanthanoid elements including Y, for example, Y, La, Ce, Pr, Nd, and Sm And at least one element selected from the group consisting of: By combining at least one of these with at least one element selected from the group consisting of Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb, the magnetic properties can be further enhanced.
Among the rare earth elements, Sm is particularly preferable, and a material having a high coercive force can be obtained when it accounts for 50 atomic% or more of the rare earth elements.

The rare earth element used here may be a purity that can be obtained by industrial production, and elements that cannot be mixed in production, such as O, H, C, Al, Si, F, Na, Mg, Ca, Li, etc. May be included.
In particular, at least one element of Li, Na, K, Rb, Cs, Mg, Ca, Sr or Ba does not exist in the grain boundary of the rare earth-transition metal-nitrogen based magnet alloy powder, but the alloy When 0.001 to 0.1 wt% is contained inside and uniformly dispersed in the alloy, the rare earth-transition metal-nitrogen based alloy powder can be produced in a shorter nitriding time.

(Transition metal powder)
The transition metal constituting the mother alloy is a basic element responsible for the ferromagnetism of the magnet powder, and Fe, Co, Ni, and Mn are generally used, but are not particularly limited. As the transition metal, Fe is particularly preferable, and a part of Fe may be substituted with Co for the purpose of improving the temperature characteristics of the magnet without impairing the magnetic characteristics.

  In addition to Mn, Ca, Cr, Nb, Mo, Sb, Ge, Zr, V, Si, Al, Ta, Cu, etc., in order to improve coercivity, improve productivity, and reduce costs One or more selected from the above may be added. In this case, the addition amount is desirably 7% by weight or less with respect to the total weight of the transition metal. Further, C or B or the like as an unavoidable impurity may be contained in an amount of 5 parts by weight or less.

As the iron powder, for example, reduced iron powder, gas atomized powder, water atomized powder, electrolytic iron powder or the like can be used, and classification is performed so as to obtain the above particle size as necessary. Note that iron oxide powder may be used up to 30% by weight of the iron powder.
Further, as the cobalt powder, in addition to metallic cobalt, for example, cobaltous oxide and tribasic cobalt oxide, a mixture thereof, etc. As nickel powder, in addition to metallic nickel, various nickel oxides, and further, as manganese powder, In addition to manganese metal, for example, manganese oxide, manganese dioxide, and a mixture thereof can be used.

(Reducing agent)
As the reducing agent, Li and / or Ca, or an alkali metal or alkaline earth metal element composed of at least one selected from these elements and Na, K, Mg, Sr, or Ba can be used.
Among the reducing agents, metal Li or Ca is preferable, and Ca is particularly preferable from the viewpoints of handling safety and cost. Since Ca used as a reducing agent is non-magnetic and remains in the crystal grain boundary of the master alloy, the magnetic properties are lowered. As described above, when Ca is contained in the magnet alloy in an amount of 0.001 to 0.1 wt% and is uniformly dispersed in the alloy, the rare earth-transition metal-nitrogen based alloy powder is reduced in a shorter nitriding time. There is an effect that it can be manufactured, and it is not limited to the above.

(Raw material mixture)
In the present invention, the raw material mixture is a mixture of the rare earth oxide powder, transition metal powder, and reducing agent in a predetermined amount. This can be blended with other metal powders and / or metal oxides as required. This mixture is usually used as a starting material simply mixed with each other. However, the mixture may be pre-pressurized and pelletized.

  It is desirable that the raw material mixture contains 7 to 11 atomic% of rare earth elements. By blending at such a ratio, the composition of the obtained alloy powder is theoretically the value around the highest characteristic. Become. Outside the above range, the composition of the resulting alloy powder deviates from a theoretically preferable value, and the magnetic properties of the finally obtained rare earth-transition metal-nitrogen based magnet powder are deteriorated, which is not preferable.

  It is important that the powders are mixed uniformly so as not to separate due to differences in powder characteristics. As a mixing method, for example, a ribbon blender, a tumbler, an S-shaped blender, a V-shaped blender, a Nauter mixer, a Henschel mixer, a super mixer, a high speed mixer, a ball mill, a vibration mill, an attritor, a jet mill and the like can be used.

(Raw material for adjustment)
In the present invention, the adjustment raw material is (a) a rare earth metal, (b) a mixture of rare earth oxide powder and a reducing agent, or (c) a rare earth element content of 1 to 30 atomic% higher than the raw material mixture. A mixture of rare earth oxide powder, transition metal powder and reducing agent (hereinafter also referred to as excess rare earth mixture).
The rare earth oxide powder and the reducing agent do not need to be special, and may be the same as those used in the raw material mixture.

  The raw material for adjustment is to compensate for the partial reduction of the reduced rare earth by evaporation during the reduction diffusion. Either a rare earth metal or a rare earth oxide powder and a reducing agent are mixed to make a transition metal powder. The mixture may be prepared without using or an excess rare earth mixture may be prepared by increasing the amount of rare earth oxide powder and reducing agent relative to the raw material mixture and relatively reducing the amount of transition metal powder.

  The excess rare earth mixture preferably contains 1 to 30 atomic% of rare earth elements more than the raw material mixture. If the difference in the rare earth element content between the excess rare earth mixture and the raw material mixture is less than 1 atomic%, it will be insufficient to compensate for the shortage of rare earth when heated and fired. Will become excessive and lower the magnetic properties.

  Moreover, it is preferable that content of the rare earth element of the adjustment raw material is 2 to 40% with respect to the total amount of the rare earth elements contained in the raw material mixture and the adjustment raw material. If the content of the rare earth element in the adjustment raw material is less than 2%, it is insufficient to compensate for the amount of rare earth that is insufficient by heating and firing. If it exceeds 40%, the rare earth becomes excessive and the magnetic properties are lowered. It is.

  The raw material mixture is introduced by preparing a raw material for adjustment in advance and loading it at the bottom of a reaction container for reduction diffusion, and then mixing a rare earth oxide powder, a transition metal powder containing iron, and a reducing agent. The raw material mixture is charged. That is, the raw material for adjustment is laid on the bottom of the reaction vessel for reduction diffusion so as to form a layer having a substantially uniform thickness, and a layer of the raw material mixture is formed thereon (see FIG. 2).

  Here, the boundary between the layer of the raw material for adjustment and the layer of the raw material mixture is usually a clear two-layer, but depending on the structure of the reaction container for reduction diffusion and its bottom shape, the amount of powder to be charged is It may be changed stepwise or gently. Furthermore, for the purpose of preventing the rare earth from scattering, an inner lid may be put on the raw material mixture, or a drop lid may be provided.

(2) Reduction Diffusion Step of Raw Material Mixture When the raw material mixture is introduced into a reaction vessel for reduction diffusion, heat treatment is performed in this state in a non-oxidizing atmosphere substantially free of oxygen to cause a reduction reaction.

  Since Ca has a melting point of 838 ° C. and a boiling point of 1480 ° C., the treatment temperature is set to 1000 to 1250 ° C., preferably 1100 to 1200 ° C. When the temperature is lower than 1000 ° C., the rare earth element diffuses unevenly with respect to the iron powder, and the coercive force and squareness of the rare earth-transition metal-nitrogen based magnet powder produced using the iron powder decrease. If the temperature exceeds 1250 ° C., the generated master alloy powder undergoes grain growth and sinters with each other, so that uniform nitriding becomes difficult, and the squareness of the magnet powder decreases.

  If it is said temperature conditions, although a reducing agent melt | dissolves, since it does not become a vapor | steam, it can process preferably. As a result, the rare earth oxide is reduced to a rare earth element, and a rare earth-transition metal master alloy in which the rare earth element is diffused in the transition metal powder is synthesized. The reduction diffusion is performed by carefully controlling not only the temperature conditions but also the amount of the reducing agent input, the powder properties of the reducing agent and the rare earth oxide, the mixed state of various powders, and the time of the reduction diffusion reaction.

  After reducing diffusion for 6 to 12 hours, the furnace is cooled, and if necessary, a reaction product containing a rare earth-transition metal alloy (hereinafter sometimes referred to as a reduced product) is treated with hydrogen, and then poured into water. After decantation, pickling is performed and solid-liquid separation is performed to obtain a rare earth-transition metal alloy powder.

(Hydrogen treatment)
The reduced product is so hard that it is difficult to mechanically grind it. In order to improve the pulverization property and further improve the disintegration property in water, the reduced product can be treated with hydrogen to be powdered. In the hydrogen treatment, the reduced product containing the rare earth-transition metal alloy is put in a stainless steel reaction vessel for reduction diffusion or transferred to a special vessel and sealed with argon gas, and then replaced with hydrogen. Continue to flow hydrogen gas for a period of time.

  The hydrogen treatment is usually carried out at a temperature of 500 ° C. or lower, but it is necessary to set the reaction temperature and time so that the particle size of the taken-out collapsed product is 10 mm or less, preferably 1 mm or less. In the state where the collapsed material exceeds 10 mm, uniform nitriding becomes difficult in the nitriding treatment step performed subsequent to the wet treatment, and the squareness of the magnet powder is lowered.

(Washing, decantation, pickling)
Thereafter, the resultant reduced product is put into about 10 liters of water per 1 kg and stirred for 1 hour to collapse the reduced product. Thereafter, the reduced product is disintegrated in water, and the resulting slurry is transferred to a water washing tank through a coarse sieve. At this time, the pH of the slurry is about 11 to 12, there is no lump remaining without collapsing, and the loss remaining on the sieve is very small.

Thereafter, the decantation is repeated about 5 times. The decantation conditions are such that water is poured into the slurry, and, for example, it is discharged once for 1 minute with stirring and 2 minutes for stationary separation.
Thereafter, an acid such as acetic acid is added so that the slurry has a pH of 5 to 6, pickled, solid-liquid separated, and dried to obtain a rare earth-transition metal alloy powder.
When nitriding the obtained rare earth-transition metal alloy powder into a magnet powder, it is usually preferable to use particles of about 100 μm or less in order to efficiently improve nitriding, and if necessary, crushing is performed. Is preferred.

  The obtained rare earth-transition metal alloy powder may be a powder having an average particle diameter of 10 to 100 μm substantially free of agglomerated / fused portions, and the rare earth-transition metal alloy powder having a larger particle diameter is further finely divided ( (Including crushing). If the particle size is smaller than 10 μm, it is easy to ignite and difficult to handle. On the other hand, if the thickness exceeds 100 μm, uniform nitriding cannot be performed and the magnetic properties may be lowered.

The method for finely pulverizing the alloy powder is not particularly limited. For example, ball milling or medium stirring mill pulverization can be used in the wet pulverization method, and jet mill pulverization using an inert gas can be used in the dry pulverization method.
Among these, jet mill pulverization is particularly preferable because of less agglomeration of the powder. In order to further reduce the agglomeration of the powder, for example, in jet mill pulverization, it is possible to introduce 5 vol% or less of oxygen into an inert gas to make fine powder. Fine pulverization can be performed using a pulverized ball or a ceramic pulverized ball of low specific gravity such as zirconia instead of stainless steel.

  In addition, although the method to grind | pulverize before nitriding a mother alloy was explained in full detail, in this invention, it is not limited to this, The means to grind | pulverize after nitriding can also be taken.

(3) Nitriding process of mother alloy The mother alloy thus finely pulverized can be nitrided using a known method.

For nitriding the rare earth-transition metal alloy powder used in the present invention, for example, the rare earth-transition metal alloy powder is charged into a kiln and heated by introducing nitrogen gas or ammonia-hydrogen mixed gas. In particular, nitriding in an ammonia-hydrogen mixed gas is preferable because it can be performed in a short time compared to nitrogen gas, and a kiln can perform nitriding while rotating as compared with the case of nitriding by standing, so uniform nitriding can be performed. The nitriding temperature is preferably in the range of 250 to 650 ° C. If it is lower than 250 ° C., the nitriding rate is slow, and if it exceeds 650 ° C., it is decomposed into a rare earth nitride and a transition metal.
Also, if a large amount of hydrogen remains in the alloy powder after nitriding in a mixed gas of ammonia and hydrogen, the magnetic properties will deteriorate, so it will be necessary to remove it sufficiently by a method such as vacuum heating if necessary. There is.

  In addition, in the alloy powder obtained by pulverizing the rare earth-transition metal master alloy, crystal distortion generated by pulverization remains, and a soft magnetic phase such as α-Fe is generated in the next nitriding step. It may be a cause. When a soft magnetic phase such as α-Fe is generated, the coercive force and the squareness are lowered. Therefore, in order to further improve the magnetic properties, the obtained alloy fine powder is subjected to argon, helium, It is preferable to remove crystal distortion by heat treatment at 600 ° C. or lower in a non-oxidizing and non-nitriding atmosphere such as vacuum. In particular, when heat treatment is performed at 400 to 600 ° C. at the same time as the nitriding treatment, the processing cost can be reduced, which is advantageous. In the case of simultaneous nitriding treatment, if the heat treatment temperature is less than 400 ° C., the effect of removing residual crystal distortion is not sufficient, whereas if it exceeds 600 ° C., the alloy is a rare earth element nitride and transition metal. It is not preferable because it decomposes into

2. Rare earth-transition metal-nitrogen-based magnet powder The rare-earth-transition metal-nitrogen-based magnet powder obtained by the above method has excellent magnetic properties because there is no variation in the composition of rare earth elements in the magnet alloy.

  In the present invention, there is no variation in the composition of rare earth elements in the magnet alloy. The reduced product (mother alloy) is divided into three parts in the height direction, and the upper, middle, and lower reduced products are nitrided into a magnet powder. In this case, a rare earth element is analyzed from each sample, and the difference between the maximum value and the minimum value of the obtained rare earth element amount is within 0.3 atomic%.

  The rare earth element plays an essential role in generating magnetic anisotropy and generating coercive force in the alloy material in the rare earth-transition metal-nitrogen based magnet powder. The rare earth element needs to be at least 3 to 20 atomic% in the magnet powder. If the amount is less than 3 atomic%, a large amount of α-Fe, which is a soft magnetic phase, is present in the magnet alloy, making it difficult to obtain a high coercive force. On the other hand, if it exceeds 20 atomic%, another phase is generated in addition to the magnetic phase as the main phase, the main phase volume is reduced, and the saturation magnetization of the magnet is lowered, which is not preferable. In order to obtain a high-performance magnet powder according to the present invention, it is necessary to bring the rare earth element content close to the theoretically highest characteristic amount. For this purpose, the rare earth element content should be 7 to 11 atomic%. More preferably.

  The transition metal constituting the magnet alloy is a basic element responsible for the ferromagnetism of the magnet powder, and Fe, Co, Ni, and Mn are common, but are not particularly limited. As the transition metal, Fe is particularly preferable, and a part of Fe may be substituted with Co for the purpose of improving the temperature characteristics of the magnet without impairing the magnetic characteristics. Among these, it is necessary to contain at least 30 to 83 atomic% in the magnet powder. If it is less than 30 atomic%, the magnetization is lowered, which is not preferable. If it exceeds 83 atomic%, the proportion of rare earth elements becomes too small, and a high coercive force cannot be obtained, which is not preferable. When the composition range of the transition metal component is 65 to 80 atomic%, a material having a balanced coercive force and magnetization is obtained, and the high-performance magnet powder of the present invention can be obtained, which is particularly preferable.

Nitrogen is an element that plays an important role in the magnet powder. For example, when nitriding Sm ₂ Fe ₁₇ master alloy, if N is up to 3 per Sm ₂ Fe ₁₇ unit cell, it breaks the crystal structure. Instead, it spreads the lattice and dissolves as an intrusive type. Due to the solid solution of nitrogen, strong uniaxial magnetic anisotropy is exhibited, and saturation magnetization and Curie temperature are also increased.

  If necessary, a film can be formed on the surface of the magnet powder with a surface treatment agent such as a phosphoric acid compound or various coupling agents. Thereby, since the weather resistance of magnet powder improves, the performance of the composition for bond magnets and the bond magnet using the same can be made still more excellent.

3. Rare Earth-Transition Metal-Nitrogen Bond Magnet Composition The bond magnet composition of the present invention basically comprises the rare earth-transition metal-nitrogen magnet powder and a binder component as main components, and if necessary, a lubricant. And an additive such as a stabilizer.

(binder)
As binder components, epoxy resin, vinyl ester resin, phenol resin, unsaturated polyester resin, xylene resin, urea resin, melanin resin, thermosetting silicone resin, alkyd resin, furan resin, thermosetting acrylic resin, thermosetting type Thermosetting resins such as fluorine resin, urea resin, diallyl phthalate resin, polyurethane resin, silicon resin; polyamide resin such as 4-6 nylon and 12 nylon, polyolefin resin, polystyrene resin, polyvinyl resin, acrylic resin, acrylonitrile resin Thermoplastics such as resin, polyurethane resin, polyether resin, fluorine resin, polyphenylene sulfide resin, vinyl chloride resin, polycarbonate resin, polysulfone resin, vinyl acetate resin, ABS resin, polyether ether ketone Resin can be used.

  The composition for bonded magnets of the present invention, after blending a binder with the magnet powder, for example, a blender such as a ribbon blender, tumbler, Nauter mixer, Henschel mixer, super mixer, planetary mixer, and Banbury mixer, kneader, It can be obtained by mixing and kneading using a kneader such as a roll, a kneader ruder, a single screw extruder, a twin screw extruder or the like.

4). Bonded magnet The bonded magnet of the present invention can be obtained by a compression molding or injection molding method for forming the above-described bonded magnet composition.

(Molding method)
As a molding method, when a thermosetting resin is used, it is preferable to use compression molding or injection molding. In the case of compression molding, the amount of resin relative to the total weight of the bonded magnet is 1 to 5% by weight. In the case of injection molding, it is necessary to select optimum conditions such as resin viscosity adjustment and mold temperature, but 7 to 15% by weight preferable. Moreover, when using a thermoplastic resin, it is preferable to use injection molding, and as resin amount, 5 to 20 weight% is preferable.

In the case of compression molding, for example, mixing is performed using a pressure kneader at the above mixing ratio, and a press device including an electromagnet for applying a magnetic field to the die is used, and 800 kA / m (10 kOe) or more is applied to the die. Press molding at a pressure of 4 ton / cm ² while applying a magnetic field.

  In injection molding, for example, a cylinder in which the mixture is heated to 210 ° C. or higher by using a press machine equipped with an electromagnet for applying a magnetic field to the mold by mixing with a heating and pressure kneader at the above mixing ratio. It is melted in and injected into a mold to which a magnetic field of 800 kA / m (10 kOe) or more is applied.

  Next, although this invention is further demonstrated using an Example and a comparative example, this invention is not limited at all by these Examples.

<Magnetic properties>
The magnetic properties of the obtained magnet powder sample were measured as follows. First, magnet powder is mixed with paraffin and packed in a sample case, then heated and oriented, cooled and solidified, and a hysteresis loop is drawn using a vibrating sample magnetometer (VSM) (manufactured by Toei Kogyo) (maximum application) Magnetic field 1190 kA / m (15 kOe)).
Regarding the injection-molded bonded magnet, the magnetic properties were measured using a cioffi type self-recording magnetometer (manufactured by Toei Kogyo Co., Ltd.).

Example 1
As raw materials, Sm ₂ O ₃ having a purity of 99.4% (manufactured by Tomen Co., Ltd.), electrolytic iron having a purity of 99.5% (manufactured by Hoganas), and Ca having a purity of 99.3% (manufactured by Mintec Japan Co., Ltd.) Were mixed using a mixer at a rate that would yield an Sm ₂ Fe ₁₇ alloy, and this was used as the raw material mixture. Next, the amount of Sm ₂ O ₃ used was increased from that of the raw material mixture to prepare an excess rare earth mixture (adjusting raw material) having an Sm amount of 5 atomic%. Then, as shown in FIG. 2, this excess rare earth mixture was uniformly placed in the bottom of the reaction container for reduction diffusion, and subsequently, the raw material mixture of Sm ₂ O ₃ , Fe, and Ca was added. The excess rare earth mixture was added so that the Sm amount was 20% of the total including the raw material mixture.
After putting this reaction vessel into a reduction diffusion vessel, it is charged into an electric furnace (reduction diffusion furnace) as shown in FIG. 1 and replaced with argon, and kept at an argon flow rate of 0.5 to 1 L / min and 1200 ° C. for 8 hours. Then, the rare earth oxide was reduced and diffused in Fe to produce an Sm—Fe master alloy (reduced product).
Thereafter, this reduced product was cut at approximately equal intervals so as to form three parts, ie, an upper part, a middle part, and a lower part. And 1 kg of each reduced product was put into a water tank with 10 L of water, and after stirring for 10 minutes, the supernatant was removed, and this operation was repeated 10 times to remove Ca. Then, it decanted with alcohol, and it dried at 100 degreeC in the vacuum for 5 hours, and obtained the Sm-Fe alloy powder. Sm—Fe alloy powders were produced in the same manner using the reduced products in the upper, middle, and lower parts.
Next, the above three types of alloys were sieved with a sieve opening of 104 μm (150 mesh) and subjected to nitriding treatment in an ammonia-hydrogen mixed gas at 480 ° C. for 8 hours to produce an Sm—Fe—N alloy. Further, 1 kg of this alloy was put into an attritor (manufactured by Mitsui Mining Co., Ltd.), and pulverized at 200 rpm for 2 hours using alcohol as a solvent. Then, it filtered and vacuum-heat-dried, stirring with a Henschel mixer (made by Mitsui Mining Co., Ltd.), and manufactured Sm-Fe-N fine powder. Using the reduced product in the upper part, the reduced product in the middle part, and the reduced product in the lower part as samples, the compositions of these magnet alloys were examined, and the magnetic properties were measured with a vibrating sample magnetometer. The results are shown in Table 1.

(Comparative Example 1)
An alloy was produced in the same manner as in Example 1 except that the adjustment raw material was not placed in the bottom of the reaction container for reduction diffusion. Using the reduced product in the upper part, the reduced product in the middle part, and the reduced product in the lower part as samples, the compositions of these magnet alloys were examined, and the magnetic properties were measured with a vibrating sample magnetometer. The results are shown in Table 1.

(Comparative Example 2)
An excess rare earth mixture having an Sm amount increased by 30 atomic% was prepared and placed in the bottom of the reaction vessel for reduction diffusion, and an alloy was produced in the same manner as in Example 1 except for the other conditions. Using the reduced product in the upper part, the reduced product in the middle part, and the reduced product in the lower part as samples, the compositions of these magnet alloys were examined, and the magnetic properties were measured with a vibrating sample magnetometer. The results are shown in Table 1.

"Evaluation"
Example 1 shows that the variation in Sm amount is small and the magnetic characteristics are high. In particular, the sample (1-C) produced with the lower reductant was the same as in the case of the samples (1-c, 2-c) of Comparative Example 1 and Comparative Example 2 produced with the lower reductant as in the examples. In comparison, it can be seen that the amount of Sm is almost the same value as the upper part and the middle part (1-A, 1-B) of Example 1, and the magnetic characteristics are also very high.

(Examples 2 and 3)
As raw materials, Sm ₂ O ₃ having a purity of 99.4% (manufactured by Tomen Co., Ltd.), electrolytic iron having a purity of 99.5% (manufactured by Hoganas), and Ca having a purity of 99.3% (manufactured by Mintec Japan Co., Ltd.) The Sm ₂ Fe ₁₇ alloy was mixed with a mixer at a ratio to obtain the alloy. Similarly, raw materials for adjusting Sm ₂ O ₃ and Ca were prepared, and raw materials for adjusting Sm ₂ O ₃ and Ca were placed in the bottom of the reaction vessel for reduction diffusion. The rare earth element content of the adjustment raw material was 5 atomic% of the total amount of the raw material mixture and the adjustment raw material. Subsequently, a raw material mixture of Sm ₂ O ₃ , Fe, and Ca was added. This reaction vessel was charged into an electric furnace (reduction diffusion furnace), purged with argon, held at an argon flow rate of 0.5 to 1 L / min, 1200 ° C. for 8 hours, reduced rare earth oxides and diffused into Fe, A reduced product of Sm—Fe alloy (Example 2) was produced.
Then, this reduced product was divided into three parts, an upper part, a middle part, and a lower part, and Sm—Fe—N fine powders were produced with each of the upper, middle, and lower reduced substances in the same manner as in Example 1. The composition of the magnetic alloy of these samples was examined, and the magnetic properties were measured with a vibrating sample magnetometer. The results are shown in Table 2.
On the other hand, in place of the raw materials for adjusting Sm ₂ O ₃ and Ca, Sm metal was put at the bottom of the reaction vessel, and other conditions were used to produce an alloy by the same method as in Example 2 to obtain the alloy of Example 3. It was.

"Evaluation"
It can be seen that Examples 2 and 3 have small variations in Sm amount and high characteristics compared to Comparative Example 1. In particular, the samples (2-C, 3-C) produced with the reduced product in the lower part had almost the same Sm amount as the upper part and the middle part, compared with the sample (1-c) in Comparative Example 1 produced with the reduced product in the lower part. The value and the characteristic are very high.

Examples 4 to 6 (Comparative Examples 3 and 4)
The magnet powder (91.3% by weight) prepared in Examples 1 to 3 and Comparative Examples 1 and 2 and a thermoplastic resin (PA12 (manufactured by Ube Industries)) were mixed at a rate of 8.7% by weight. Then, it was kneaded for 1 pass at 190 ° C. using a Nakatani kneader (manufactured by Nakatani), and then injection molded into a shape of φ20 × 13 mm at a cylinder temperature of 210 ° C. and a molding pressure of 1 ton. Table 4 shows the magnetic properties of the obtained injection-molded bonded magnet.

"Evaluation"
Compared with Comparative Examples 3 and 4, Examples 4 to 6 show that the variation due to the vertical position of the container is small and the magnetic characteristics are high. The lower samples (1-C, 2-C, 3-C) of Examples 4 to 6 are similarly compared to the lower samples of Comparative Examples 3, 4 (1-c, 2-c). In addition, it can be seen that the characteristics are as high as those in the upper part and the middle part.

It is the whole reactor which installed the reduction | restoration diffusion container in the electric furnace. It is sectional drawing of the reaction container for reduction | restoration which introduce | transduced the raw material mixture.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction container 2 Lid 3 Rare earth oxide powder, transition metal powder containing iron, and raw material mixture containing reducing agent for reducing rare earth oxide 4 Adjustment raw material 5 Brick 6 Heater

Claims (8)

A raw material mixture containing a rare earth oxide powder, a transition metal powder containing iron, and a reducing agent for reducing the rare earth oxide is introduced into a reaction vessel for reduction diffusion, and then heated and fired in a non-oxidizing atmosphere to form a rare earth. A method of producing a rare earth-transition metal-nitrogen based magnet powder in which variation in the content of rare earth elements is suppressed after obtaining a transition metal based master alloy,
When the raw material mixture is introduced into the reaction container for reduction diffusion, the bottom thereof is previously provided with (a) a rare earth metal, (b) a mixture of rare earth oxide powder and a reducing agent, or (c) a rare earth element content. Is charged with a raw material for adjustment selected from a mixture of rare earth oxide powder, transition metal powder and reducing agent, which is 1 to 30 atomic% higher than the raw material mixture, and then the raw material mixture is loaded thereon. A method for producing a rare earth-transition metal-nitrogen based magnet powder.   The method for producing a rare earth-transition metal-nitrogen magnet powder according to claim 1, wherein the content of the rare earth element contained in the raw material mixture is 7 to 11 atomic%.   2. The rare earth element according to claim 1, wherein a content of the rare earth element contained in the adjustment raw material is 2 to 40% with respect to a total amount of the rare earth element contained in the raw material mixture and the adjustment raw material. A method for producing a transition metal-nitrogen magnet powder.   A rare earth-transition metal-nitrogen based magnet powder obtained by the production method according to claim 1.   The rare earth-transition metal-nitrogen based magnet powder according to claim 4, wherein the rare earth element content is 3 to 20 atomic%.   6. The rare earth-transition metal-nitrogen based magnet powder according to claim 4 or 5, wherein variation in the content of rare earth elements is within 0.3 atomic%.   A bonded magnet composition obtained by mixing a resin binder with the rare earth-transition metal-nitrogen based magnet powder according to any one of claims 4 to 6.   The bonded magnet formed by shape | molding the composition for bonded magnets of Claim 7 by compression molding or injection molding.

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