JP2014080653A - Production method of rare earth-transition metal-nitrogen system alloy powder, and obtained rare earth-transition metal-nitrogen system alloy powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method that can efficiently produce a rare earth-transition metal-nitrogen system alloy powder that has excellent magnetic properties as a permanent magnet, and the obtained rare earth-transition metal-nitrogen system alloy powder.SOLUTION: A production method includes: a first process in which an alkali solution is added with a solution including a rare earth compound and a transition metal compound, a generated precipitate is aged while being agitated; a second process in which an aged precipitate is cleaned being added with water, decantation is performed until a supernatant fluid becomes at most specific electric conductivity, then performed by dehydration to obtain a precursor of a complex oxide comprising a rare earth element and a transition metal element; a third process in which the precursor is heat-treated under the oxidizability atmosphere to obtain a complex oxide; a fourth process in which the complex oxide is heat-treated under the reduction property atmosphere, and thereby one part of a complex oxide is reduced to a rare earth-transition metal system alloy to make a part reduction complex oxide; a fifth process in which the part reduction complex oxide is mixed with a reduction agent, heat-treated in the specific inert gas atmosphere to obtain a rare earth-transition metal system alloy powder; and a sixth process in which the alloy powder is performed by nitriding.

Description

  The present invention relates to a method for producing a rare earth-transition metal-nitrogen based alloy powder and the obtained rare earth-transition metal-nitrogen based alloy powder, and more particularly, a rare earth-transition metal having excellent magnetic properties for permanent magnets. The present invention relates to a method capable of efficiently producing a nitrogen-based alloy powder and the obtained rare earth-transition metal-nitrogen-based alloy powder.

A permanent magnet having at least one rare earth element as a constituent component is a rare earth element-iron-nitrogen ("R-Fe-N") permanent magnet, which is widely used as a material for bond magnets. This R—Fe—N permanent magnet is known to exhibit a large coercive force when in the R ₂ Fe ₁₇ N ₃ phase.
An R—Fe—N alloy powder is used as a raw material for the R—Fe—N permanent magnet, and there are a melting method and a reduction diffusion method as a method for producing this alloy powder.

  As described in Patent Documents 1 to 3, the melting method is to prepare a constituent metal or mother alloy into a target composition and dissolve it, and pulverize the resulting alloy ingot to a predetermined particle size with a jaw crusher or the like. To do. However, these methods require a pulverization step, and since rare earth metals are highly active against oxidation, oxidation proceeds in the pulverization process or strain is generated, resulting in a decrease in alloy quality. is there.

  On the other hand, the reduction diffusion method mixes rare earth oxide powder, metal powder such as iron, nickel, cobalt or iron oxide powder and alkaline earth metal as a reducing agent, and heats to reduce the raw material oxide, Alloying rare earth metal and transition metal by diffusion reaction, then nitriding, then wet or wet treatment, then nitriding to obtain alloy powder. Compared with melting method, raw material is cheaper and heat treatment temperature Therefore, the alloy powder having a uniform composition can be obtained, the alloy structure is dense, and the composition can be easily adjusted.

As a method for producing an alloy by such a reduction diffusion method, for example, Patent Documents 4 to 6 include the following description.
In Patent Document 4, in a method for producing a rare earth Fe-based alloy powder having a step of reducing and diffusing a mixed raw material of metal Fe powder and oxide powder containing a rare earth element with metal Ca, the tap density of the mixed raw material is 1 In the range of 0.5 to 2.0 g / ml, metal Ca is added in an amount of 1.0 to 3.0 times the equivalent of the mixed raw material and heated at a temperature in the range of 600 to 1300 ° C. A production method for obtaining an alloy powder is described.

Further, Patent Document 5 discloses a process of obtaining a reactant by reducing diffusion and nitriding a raw material obtained by mixing Sm component raw material, Fe component raw material, and granular metal calcium at a predetermined ratio, and treatment with water. Solid-liquid separation to obtain solid content, vacuum heat treatment of the solid content to obtain alloy powder, and treatment of the alloy powder in an atmosphere containing CO ₂ gas. A method for producing -N-based alloy powder is described.

  Furthermore, in Patent Document 6, after mixing iron oxide particle powder and samarium oxide particle powder, the mixture is subjected to a reduction reaction to obtain a mixture of iron particles and samarium oxide particles, and then at a temperature of 30 to 150 ° C. After forming a 1 to 15 wt% oxide film on the surface of the iron particles by performing a stabilization treatment in a range, oxygen-containing atmosphere, Ca is mixed to a temperature range of 800 to 1200 ° C., an inert gas atmosphere A method for producing an Sm—Fe—N based magnetic powder for bonded magnets is described in which a reduction diffusion reaction is performed under the conditions below, followed by a nitriding reaction in a temperature range of 300 to 600 ° C.

The present applicant also performs a reduction diffusion method in which a mixture comprising a rare earth oxide powder, a transition metal powder, and a reducing agent is heated in a non-oxidizing atmosphere to cause a reduction reaction, and the rare earth metal is diffused into the transition metal powder. , R is a general formula R _α Fe _{(100-α-β-γ)} M _β N _y (wherein R is one or more of rare earth elements, M is Cu, Mn, Co, Cr, Ti, Ni And one or more selected from the group consisting of Zr, α, β, and γ are atomic% and satisfy 3 ≦ α ≦ 20, 0.1 ≦ β ≦ 25, and 17 ≦ γ ≦ 25. Has been proposed (Patent Document 7).
According to this method, a rare earth-transition metal-nitrogen based alloy powder in which particles having an amorphous phase, a fine ferromagnetic phase, and a grain boundary are sintered is pulverized, and the pulverization is performed by the rare earth-transition metal-nitrogen. When the sintered part, the grain boundary, or the amorphous phase part of the alloy is crushed and the crystal part is not substantially crushed, the average grain size of the amorphous phase and the fine ferromagnetic phase aligned in the crystal direction is 10 μm. An alloy powder containing 80% by volume or more of the above alloy particles can be obtained.
However, although the reduction diffusion method has the advantages as described above, as with the dissolution method, since there are many coarse particles having an average particle size of 10 μm or more, mechanical grinding by an attritor or a bead mill is essential. Moreover, the coercive force was around 10 kOe, which was not sufficient.

On the other hand, Patent Document 8 discloses a method for producing a magnetic particle having a Th ₂ Zn ₁₇ structure represented by a general formula R _x T _100-xyz N _{y Mz} , which has R ions and T ions. After adding a precipitating agent capable of forming an insoluble salt to the solution, the first step of subsequently adding the M component, calcining the resulting precipitate, A method for producing a magnetic powder having a second step to be obtained and a third step in which a reduction diffusion reaction is performed with metallic calcium having a particle size of 10 mm or less (where R is at least one of rare earth elements including Y, M Is at least one element or oxide thereof having a standard Gibbs energy in the range of −80 kcal to −300 kcal at 300 ° C. to 1200 ° C., and 3 <x <30, 5 <y <15, 0.001 <z <5 It is. ) Is described.
However, since a precipitating agent capable of generating an insoluble salt is added to a solution having R ions and T ions, the particle size of magnetic particles generated by repeating precipitation by dissolution until the supersaturation is generated. As a result, the magnetic properties were not satisfactory.

  For this reason, rare earth-transition metal-nitrogen based alloy powders with uniform particle size and good magnetic properties are required without the need for mechanical pulverization of the alloy powder as in the conventional melting method and reduction diffusion method. A method that can be manufactured in an efficient manner has been desired.

JP-A-3-153852 Japanese Patent Laid-Open No. 60-131949 Japanese Unexamined Patent Publication No. 60-34005 Japanese Patent No. 3567742 Japanese Patent No. 3931458 Japanese Patent No. 4296379 Japanese Patent No. 4127083 Japanese Patent No. 4590920

  In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a method capable of efficiently producing a rare earth-transition metal-nitrogen based alloy powder having excellent magnetic properties for permanent magnets, and the obtained rare earth-transition metal-nitrogen It is to provide an alloy powder.

  As a result of intensive studies to solve the above problems, the present inventor added a solution containing a rare earth compound and a transition metal compound to an alkaline solution and stirred to obtain a precipitate, and then the precipitate The decantation is repeated until the conductivity of the supernatant reaches a specific value, and then the washed precipitate is dried to form a precursor of a complex oxide composed of rare earth elements and transition metal elements. To obtain a composite oxide composed of a rare earth element and a transition metal element, and at least a part of the obtained composite oxide is subjected to a reduction treatment to include a partially reduced composite oxide containing a rare earth-transition metal alloy After that, when this was used as a raw material for the reduction diffusion method, it was found that a rare earth-transition metal alloy powder having a relatively small particle size and a uniform composition could be stably produced. Which resulted in the completion of the invention.

That is, according to the first invention of the present invention, a first step of adding a solution containing a rare earth compound and a transition metal compound to an alkaline solution and aging the resulting precipitate with stirring;
The aged precipitate is washed with water, and decantation is repeated until the supernatant has a conductivity of 1 mS / cm or less, and then dried to obtain a precursor of a composite oxide composed of a rare earth element and a transition metal element. A second step of obtaining a body;
A third step of heat-treating the precursor of the composite oxide in an oxidizing atmosphere at 500 to 1400 ° C. to obtain a composite oxide composed of a rare earth element and a transition metal element;
The complex oxide composed of the rare earth element and the transition metal element is heat-treated in a reducing atmosphere at 300 to 1000 ° C., and a part of the complex oxide is reduced to a rare earth-transition metal alloy, and partially reduced complex oxidation A fourth step of making a product,
The partially reduced composite oxide is mixed with at least one reducing agent selected from granular or powdery alkali metals, alkaline earth metals and hydrides thereof, and the mixture is heated in an inert gas atmosphere to 900 ° C to A fifth step of obtaining a rare earth-transition metal alloy powder by heat treatment at 1200 ° C .;
A sixth step of obtaining a rare earth-transition metal-nitrogen based alloy powder by nitriding heat treatment of the rare earth-transition metal based alloy powder at 300 ° C. to 600 ° C. in a gas atmosphere containing nitrogen or ammonia and hydrogen;
A seventh step of washing the alloy powder containing the rare earth-transition metal nitride with water and drying after the acid washing, and a method for producing the rare earth-transition metal-nitrogen alloy powder is provided. Is done.

  According to the second invention of the present invention, in the first invention, the alkaline solution in the first step is sufficient for the pH of the solution containing the rare earth compound and the transition metal compound to be 7.5 or more. A method for producing a rare earth-transition metal-nitrogen based alloy powder characterized in that the concentration is low.

  According to the third invention of the present invention, in the first or second invention, the alkaline solution in the first step is mixed uniformly with the rare earth compound and the transition metal compound, A method for producing a rare earth-transition metal-nitrogen based alloy powder characterized in that it is added over a sufficient time is provided.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, the rare earth-transition metal-nitrogen system characterized in that the solution temperature in the first step is 100 ° C. or lower. A method for producing an alloy powder is provided.

  According to the fifth invention of the present invention, in any one of the first to fourth inventions, the impurity content contained in the precursor of the composite oxide comprising the rare earth element and the transition metal element in the second step Is a rare earth-transition metal-nitrogen-based alloy powder, characterized in that, in terms of element, is 1.5% by weight or less.

  According to the sixth aspect of the present invention, there is provided a rare earth-transition metal-nitrogen based alloy powder obtained by the method of any one of the first to fifth aspects.

  According to a seventh aspect of the present invention, there is provided a rare earth-transition metal-nitrogen based alloy powder characterized in that, in the sixth aspect, the maximum energy product (BH) max is 40 MGOe or more.

According to the method for producing a rare earth-transition metal-nitrogen based alloy powder of the present invention, a solution containing a rare earth compound and a transition metal compound is added to an alkaline solution and stirred to obtain a precipitate, and then the precipitate is obtained. The decantation is repeated until the electrical conductivity of the supernatant liquid reaches a specific value, so that impurities are sufficiently reduced, and when this is dried, it becomes a precursor of a complex oxide composed of a rare earth element and a transition metal element, The composite oxide precursor is heat-treated to obtain a composite oxide composed of a rare earth element and a transition metal element, and at least a part of the obtained composite oxide is reduced to form a rare earth-transition metal alloy. Since this is used as a raw material for the reduction diffusion method after the partial reduction composite oxide is contained, mechanically pulverizing the alloy powder is not required unlike the conventional dissolution method and reduction diffusion method, and the particle size is uniform. To become.
Moreover, when it is nitrided, a rare earth-transition metal-nitrogen alloy powder having good magnetic properties can be produced efficiently and with high productivity.

  Since this rare earth-transition metal-nitrogen based alloy powder has a particularly high maximum energy product (BH) max, it is formed into a bonded magnet or a sintered magnet, and is required to have high magnetic properties. It can be applied to various uses such as motors for products including acoustic equipment, medical equipment, and general industrial equipment.

Hereinafter, embodiments of the present invention will be specifically described.
1. Method for producing rare earth-transition metal-nitrogen based alloy powder The method for producing rare earth-transition metal-nitrogen based alloy powder according to the present invention is produced by adding a solution containing a rare earth compound and a transition metal compound to an alkaline solution. A first step of aging the precipitate to be stirred;
The aged precipitate is washed with water, and decantation is repeated until the supernatant has a conductivity of 1 mS / cm or less, and then dried to obtain a precursor of a composite oxide composed of a rare earth element and a transition metal element. A second step of obtaining a body;
A third step of heat-treating the precursor of the composite oxide in an oxidizing atmosphere at 500 to 1400 ° C. to obtain a composite oxide composed of a rare earth element and a transition metal element;
The complex oxide composed of the rare earth element and the transition metal element is heat-treated in a reducing atmosphere at 300 to 1000 ° C., and a part of the complex oxide is reduced to a rare earth-transition metal alloy, and partially reduced complex oxidation A fourth step of making a product,
The partially reduced composite oxide is mixed with at least one reducing agent selected from granular or powdery alkali metals, alkaline earth metals and hydrides thereof, and the mixture is heated in an inert gas atmosphere to 900 ° C to A fifth step of obtaining a rare earth-transition metal alloy powder by heat treatment at 1200 ° C .;
A sixth step of obtaining a rare earth-transition metal-nitrogen based alloy powder by nitriding heat treatment of the rare earth-transition metal based alloy powder at 300 ° C. to 600 ° C. in a gas atmosphere containing nitrogen or ammonia and hydrogen;
And a seventh step of washing the alloy powder containing the rare earth-transition metal nitride with water and drying after the acid washing.

  Hereinafter, the production of the rare earth-transition metal-nitrogen based alloy powder according to the present invention will be described for each step, and the rare earth-transition metal-nitrogen based alloy powder will be described together.

(1) Step of generating precipitate from alkaline solution containing raw material compound In the present invention, first, a solution containing a rare earth compound and a transition metal compound as raw material compounds is added to the alkaline solution and continuously stirred. Aged to obtain a precipitate.

  In the present invention, the rare earth compound is one or more of lanthanoid elements including Y, for example, one or more nitrates, sulfates, chlorides selected from the group of Y, La, Ce, Pr, Nd and Sm. And acetate. Examples of the transition metal compound include one or more nitrates, sulfates, chlorides, and acetates containing Fe as an essential component from the group of Fe, Cu, Mn, Co, Cr, Ti, Ni, and Zr. . Although oxides can also be used, nitrates, sulfates, chlorides, acetates and the like are preferred because they are easier to dissolve in water.

  The rare earth compound and the transition metal compound may be dissolved in water so that the atomic ratio of the metal element is 2 to 2.8: 17 from the viewpoint of magnetic properties. Further, even when an aqueous solution of a rare earth compound and an aqueous solution of a transition metal compound are mixed, they are mixed so as to have the above ratio. The temperature of the solution is not particularly limited, but is preferably maintained at 100 ° C. or lower in order to obtain a stable precipitate.

  Furthermore, in the present invention, if desired, one or more selected from Si, Al, Ti, Zr, Zn, or Cu compounds (hereinafter also referred to as M element) is added in addition to the rare earth compound and the transition metal compound prepared in the above step. can do. Here, each content of the Si, Al, Ti, Zr, Zn, and Cu compounds is sufficient for the rare earth-transition metal alloy powder formed in the subsequent heat treatment of the composite oxide to suppress particle growth. It is preferable to make it an amount. Specifically, it can be 0.01 to 10% by weight, preferably 0.05 to 8% by weight, based on the transition metal compound.

On the other hand, the alkaline solution is not particularly limited as long as it can make the rare earth compound and the transition metal compound alkaline with a pH of 8 or more. Examples thereof include alkaline solutions such as ammonium hydrogen carbonate, ammonium hydroxide, sodium hydroxide, potassium hydroxide, and urea. The concentration of the alkaline solution may be higher than the chemical equivalent necessary for each salt to become a hydroxide as a precursor, but the washing time when removing the residual alkali in the subsequent steps is shortened and the productivity is increased. From a viewpoint, it is preferable to set it as the range of equivalent-3 times the equivalent.
Here, the addition time of the solution containing the rare earth compound and the transition metal compound to the alkaline solution is not particularly limited, but is 60 minutes or less, preferably 50 minutes or less from the viewpoint of productivity.

  The temperature of the solution containing the alkaline solution, the rare earth compound, and the transition metal compound is 100 ° C. or lower, preferably 80 ° C. or lower, more preferably 50 ° C. or lower. The reason why the solution temperature is set to 100 ° C. or less is to avoid the evaporation of water from the solution and the change of the component concentration in the system. The lower limit of the solution temperature is not particularly limited, but is usually room temperature from the viewpoint of productivity. In particular, when the liquid temperature is set to room temperature or lower, a cooling device or the like is newly required. Therefore, it is preferable that the liquid temperature does not require such a device.

  After adding a solution containing a rare earth compound and a transition metal compound to the alkaline solution, the solution is aged with continuous stirring in order to make the system uniform. The aging temperature is preferably about the same as the above temperature, that is, room temperature to 100 ° C. The aging time is not particularly limited, but 30 minutes or less is sufficient from the viewpoint of productivity. By maintaining the pH of the solution at 7.5 or higher, preferably 8 or higher, re-dissolution of the generated precipitate can be avoided and a good yield can be maintained.

(2) Decantation of precipitate After that, the precipitate is washed with water, and impurities are removed from the precipitate by decantation.
In the present invention, it is important to repeat the decantation until the supernatant has a conductivity of 1 mS / cm or less. That is, the precipitate is sufficiently washed to remove impurities such as chlorine ions, nitrate ions, sulfate ions, and acetate ions remaining in the precipitate as much as possible. A preferable conductivity is 0.7 mS / cm or less, and a more preferable conductivity is 0.5 mS / cm or less.

In addition, the present applicant, if the amount of impurities remaining in the washed precipitate is 1.5 wt% or less, does not affect the magnetic properties of the rare earth-transition metal alloy powder described above, and the washing As a result of examining the relationship between the amount of impurities remaining in the subsequent precipitate and the conductivity of the supernatant liquid, if decantation is repeated until the conductivity of the washing liquid becomes 1 mS / cm or less, It has been found that the amount of remaining impurities can be 1.5% by weight or less.
Based on the above findings, the amount of impurities is preferably 1.5% by weight or less, and more preferably 1% by weight or less. When the impurity content is more than 1.5% by weight, the magnetic properties of the rare earth-transition metal alloy powder are affected, and desired magnetic properties cannot be obtained.

  Next, the washed precipitate is dried by heating to 80 ° C. or higher, for example, in a non-oxidizing atmosphere. The drying temperature is preferably a temperature at which moisture can be efficiently removed, for example, 100 ° C. or more and 400 ° C. or less. The higher the temperature, the shorter the drying time. At this time, the pressure can be reduced or the drying gas can be circulated. Thereby, the dried product becomes a precursor of a complex oxide composed of a rare earth element and a transition metal element.

(3) Formation of Composite Oxide Consisting of Rare Earth Element and Transition Metal Element The obtained composite oxide precursor is subjected to heat treatment in an oxidizing gas atmosphere to form a composite oxide composed of a rare earth element and a transition metal element. To do.

  The heat treatment temperature at this time is preferably 500 ° C. or higher and 1400 ° C. or lower, and more preferably 700 ° C. or higher and 1200 ° C. or lower. When the temperature is lower than 500 ° C., the composite oxide precursor is not completely oxide, and when the temperature exceeds 1400 ° C., grain growth becomes significant. Although heating time is based also on a processing amount and heating temperature, 1 to 10 hours are preferable and 3 to 8 hours are more preferable. Further, as the oxidizing gas, it is necessary to supply a gas containing 10% or more of oxygen, but it may be appropriately selected from air, a mixture of air and nitrogen, an inert gas, or the like.

(4) Preliminary reduction treatment of composite oxide In the present invention, a part of the composite oxide obtained as described above is reduced to obtain a partially reduced powder composite oxide containing a rare earth-transition metal alloy. The reducing gas species is not particularly limited, and examples thereof include H ₂ and CO. If the heating temperature at this time is too low, the reduction does not proceed only partially, and conversely if it is too high, the grain growth becomes remarkable. Moreover, although heating time is based also on a processing amount and heating temperature, 0.5 to 10 hours are preferable and 1 to 7 hours are more preferable.

  By this reduction treatment, a part of the composite oxide, that is, 10% or more is reduced to a rare earth-transition metal alloy to form a partially reduced composite oxide. In the present invention, 30% or more, more preferably 50% or more of the composite oxide is preferably reduced to the rare earth-transition metal alloy.

(5) Reduction diffusion step Subsequently, Li and / Ca, or these elements and Na, K as a reducing agent are added to the obtained composite oxide mixture (partial reduction composite oxide) including the rare earth-transition metal alloy. , Rb, Cs, Mg, Sr or Ba are mixed with at least one alkali metal or alkaline earth metal element, and heated to a predetermined temperature to reduce and diffuse the partially reduced composite oxide.

  When these reducing agents are used, it is necessary to carefully control the input amount and powder properties of the partially reduced composite oxide, the mixing state of the reducing agent powder, and the temperature and time of the reduction diffusion reaction. Among the reducing agents, metal Li or Ca is preferable from the viewpoint of handling safety and cost, and Ca is particularly preferable.

  The particle size distribution of the partially reduced composite oxide powder and the raw material powder mixture composed of the reducing agent is desirably a distribution close to the particle size of the target product. This mixture is heated and heated to a temperature at which the reducing agent does not evaporate in a non-oxidizing atmosphere in which an inert gas such as argon gas flows.

Since the melting point of Ca is 838 ° C. (boiling point 1480 ° C.), the heat treatment is performed in a temperature range of 900 ° C. to 1200 ° C. Under these conditions, the reducing agent dissolves but does not become vapor, so that it can be processed efficiently. By this heat treatment, the rare earth oxide and the transition metal oxide constituting the partially reduced composite oxide are reduced to the rare earth element and the transition metal, and the reduced rare earth element diffuses into the transition metal to cause the rare earth-transition metal system. An alloy (also called a fired product in an alloy lump) is synthesized.
When the heat treatment is less than 900 ° C., the diffusion becomes insufficient. Conversely, when it exceeds 1200 ° C., the grain growth becomes remarkable. As a result, in any case, an alloy powder having desired magnetic properties cannot be obtained. In addition, although heat processing time changes with processing amount, heating temperature, etc., it is desirable to set it as 1 to 15 hours.

  Thereafter, the obtained alloy containing rare earth and transition metal is cooled to 300 ° C. or lower, preferably 250 ° C. or lower in an inert gas atmosphere. If the supply temperature of the inert gas exceeds 300 ° C., the nitridation reaction performed thereafter may proceed rapidly and the Fe-rich phase may be increased. This is presumably because at a temperature exceeding 300 ° C., the active reaction product is rapidly nitrided and thus decomposed into an Fe-rich phase and SmN.

In the present invention, the fired product can be treated with hydrogen for the purpose of improving the disintegration property in water as described below, if necessary. As a hydrogen treatment method, a rare earth-transition metal alloy powder is charged into a sealed container that does not substantially contain oxygen, the inside of the container is evacuated to 10 ⁻³ Pa or less, and then filled with hydrogen. It is preferable to set the pressure to 09 to 0.11 MPa and further supply hydrogen by applying pressure of 0.005 to 0.02 MPa from the outside. By sealing the alloy and hydrogen in a sealed container, the reaction product spontaneously starts to store hydrogen, and the reaction is accelerated by self-heating, so that it is not necessary to heat from the outside. After filling with hydrogen to 0.01 to 0.11 MPa, further pressurizing 0.005 to 0.02 MPa from the outside, and supplying hydrogen in the amount occluded by the reaction product is always If the amount is less than the range, the hydrogen occlusion reaction cannot be promoted, and if it is more than the range, the heat of reaction becomes too high.

(6) Nitriding treatment of rare earth-transition metal alloy powder Next, the rare earth-transition metal alloy powder obtained above is nitrided. The rare earth-transition metal alloy powder is nitrided in an atmosphere of nitrogen or a mixed gas of ammonia and hydrogen by putting the alloy powder into a kiln. Hereinafter, an example of nitriding with a mixed gas of ammonia and hydrogen will be described in detail.

  In the nitriding step, the atmosphere gas during the reduction diffusion is changed from an inert gas to a mixed gas containing at least ammonia and hydrogen, and then heated to 350 ° C. to 500 ° C., preferably 400 ° C. to 480 ° C. To do. If it is less than 350 ° C., the nitriding rate is slow, and if it exceeds 500 ° C., it decomposes into rare earth nitride and iron, so that the temperature range is set.

The holding time of the nitriding heat treatment may be appropriately selected according to the nitriding temperature and the amount of alloy powder processed, but is 200 to 600 minutes, preferably 300 to 550 minutes. If it is less than 200 minutes, nitriding becomes insufficient. On the other hand, if it exceeds 600 minutes, nitriding proceeds excessively, which is not preferable.
The mixing ratio of ammonia and hydrogen is not particularly limited, but is preferably 10 to 70:30 to 90, preferably 30 to 60:40 to 70. If the ammonia is out of this range and the amount of ammonia is too small, the nitriding efficiency is lowered. On the other hand, if the proportion of ammonia is too large, nitriding proceeds partially and uniform nitriding cannot be performed. If a large amount of hydrogen remains in the alloy powder after nitriding, even if this alloy powder is magnetized, the magnetic properties will deteriorate, so in some cases it may be sufficiently dehydrogenated by methods such as vacuum heating. It is necessary to keep.

(7) Washing with water, decantation, pickling After that, the nitrided alloy powder is put into, for example, about 1 liter of water per 1 kg of alloy powder, and stirred for 0.1 to 3 hours to collapse the reaction product. Then, the obtained 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, washing by decantation is repeated until the pH of the slurry becomes 10 or less. Although the decantation conditions are not particularly limited, in the present invention, since the impurities contained in the precursor of the composite oxide are extremely small, the number of decantations can be significantly reduced as compared with the conventional case.

  Thereafter, a mineral acid such as acetic acid is added so that the slurry has a pH of 5 to 7, and after washing with deacidified water, the slurry is substituted with an organic solvent such as alcohol and dried, thereby rare earth-transition metal. -A nitrogen-based alloy powder is obtained. The drying conditions are preferably 150 to 400 ° C. in a non-oxidizing gas atmosphere.

(8) Crushing The particle diameter of the rare earth-transition metal-nitrogen alloy powder obtained above is 3 μm or less on average, and can be 1 μm or less on average if the production conditions are optimized. This is sufficiently smaller than that obtained by the conventional method, but can be crushed as needed.

  When crushing, it is important to crush in as short a time as possible without applying excessive stress to the powder under mild conditions. For example, it can be pulverized by using a pulverizer such as an attritor, a medium stirring mill using beads, or a jet mill. When crushing with an attritor, crushing is performed for the purpose of the present invention by reducing the amount of media, increasing the amount of solvent, increasing the amount of crushing, and reducing the number of revolutions. It can be performed. The crushing time varies depending on the type of apparatus, the processing amount, etc., but is preferably 60 minutes or less.

2. Rare earth-transition metal-nitrogen-based alloy powder The rare-earth-transition metal-nitrogen-based alloy powder produced by the above method has high magnetic properties such as residual magnetic flux density, coercive force, and maximum energy product (BH) max. . In the present invention, in particular, the maximum energy product (BH) max is as high as 40 MGOe or more.

  Since the surface of the magnet alloy powder of the present invention is easily oxidized, it is desirable to perform a surface treatment with phosphoric acid or the like, or a coating treatment with a Ti coupling agent, a Si coupling agent or the like so as to have sufficient oxidation resistance. . Surface treatment with phosphoric acid or the like can be performed while dispersing the obtained rare earth-transition metal-nitrogen alloy powder in a solvent, or can be performed simultaneously by using a pulverizing solvent containing phosphoric acid during the pulverization. it can.

  Examples of the present invention will be specifically described below together with comparative examples. However, the present invention is not limited to the following examples.

  The conductivity of the supernatant liquid after washing by decantation of the precipitate is measured by a conductivity meter (trade name ES-51, manufactured by Horiba, Ltd.), and chlorine ions, nitrate ions, sulfate ions remaining in the precipitate, The degree of removal of impurities such as acetate ions was confirmed by the rate of decrease in conductivity.

  The magnetic properties of the powder were measured with a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd., VSM-3) having a maximum applied magnetic field of 1200 kA / m. In this measurement, a sample was prepared by applying an orientation magnetic field of 1600 kA / m according to the Japan Bond Magnet Industry Association Bond Magnet Testing Method Guide Book BMG-2005, and evaluation was performed after magnetizing with a magnetic field of 4000 kA / m. .

[Example 1]
A solution prepared by dissolving 246.68 g of Sm (NO ₃ ) ₃ 6H ₂ O and 1717 g of Fe (NO ₃ ) ₃ 9H ₂ O in 2.5 L of water was added to 2.25 L of 2 mol / L NaOH aqueous solution over 15 minutes. After generating the precipitate, stirring was continued for another 10 minutes to age the precipitate. The solution temperature at this time was 20 ° C., and the pH was 9.

  Next, the produced precipitate was washed by decantation. The washing by decantation was repeated until the conductivity of the supernatant after washing was 0.5 mS / cm or less. This confirmed that impurities such as chloride ions, nitrate ions, sulfate ions, and acetate ions remaining in the precipitate were removed. After the washing, the precipitate was collected and dried at 105 ° C.

  Next, the dried precipitate was placed in an electric furnace and baked at 900 ° C. for 5 hours in an air atmosphere, and then reduced at 750 ° C. for 2 hours in a hydrogen atmosphere. The obtained reduction product was added with 38.38 g of granular metal Ca and mixed, and this mixture was put in an iron crucible, and then held at 1180 ° C. for 5 hours in an argon gas atmosphere to carry out a reduction diffusion reaction.

Next, after cooling to room temperature, hydrogen was occluded, and then put into a kiln and maintained at 450 ° C. for 8 hours while feeding NH ₃ 31.5 L / min and hydrogen 10.2 L / min to perform a nitriding reaction It was. The powder after the nitriding reaction was added to water and crushed, and after washing with water was repeated 6 times, acetic acid was added to a pH of 5. After completion of the addition, stirring was continued for 10 minutes, and washing by decantation, which was deoxidized water washing, was performed three times. Then, it substituted by 2-propanol, filtered, and dried at 200 degreeC by nitrogen gas atmosphere, and obtained the alloy powder a whose average particle diameter is 1.1 micrometers.

As a result of powder X-ray diffraction measurement, the obtained alloy powder a was a single phase of Sm ₂ Fe ₁₇ N ₃ . When the magnetic properties of the powder were measured, the residual magnetic flux density Br was 14.53 kG, the coercive force iHc was 11.89 kOe, and the maximum energy product (BH) max was 43.36 MGOe. The results of Example 1 are shown in Table 1.

[Example 2]
In Example 1, an alloy powder b according to Example 2 was obtained in the same manner as in Example 1 except that 2.63 L of 2 mol / L NaOH aqueous solution was used. The solution temperature was 20 ° C., and the pH during precipitation aging was 10.2.

Next, the X-ray diffraction measurement of the alloy powder b of Example 2 was performed. As a result, it was a Sm ₂ Fe ₁₇ N ₃ single phase. When the magnetic properties of the alloy powder were measured, the residual magnetic flux density Br was 14 kG or more, the coercive force iHc was 11.6 kOe or more, and the maximum energy product (BH) max was 40 MGOe or more. The results of Example 2 are shown in Table 1 above.

[Examples 3 to 7]
Moreover, the alloy powder c which concerns on Example 3 was obtained like Example 1 except the baking temperature of the precipitate after drying at 105 degreeC in Example 1 having been 800 degreeC. An alloy powder d according to Example 4 was obtained in the same manner as in Example 1 except that the firing temperature of the precipitate after drying at 105 ° C. in Example 1 was 1000 ° C. Further, an alloy powder e according to Example 5 was obtained in the same manner as in Example 1 except that the reduction diffusion temperature was set to 1150 ° C. in Example 1. An alloy powder f according to Example 6 was obtained in the same manner as in Example 1 except that the reduction diffusion temperature in Example 1 was changed to 1060 ° C. for 8 hours. Further, an alloy powder g according to Example 7 was obtained in the same manner as in Example 1 except that the drying temperature after deacidified water washing, substitution with 2-propanol and filtration in Example 1 was 250 ° C.

Next, X-ray diffraction measurement of the alloy powders cf of Example 3 to Example 7 was performed. As a result, all were Sm ₂ Fe ₁₇ N ₃ single phases. When the magnetic properties of each alloy powder were measured, the residual magnetic flux density Br was 14 kG or more, the coercive force iHc was 11.6 kOe or more, and the maximum energy product (BH) max was 40 MGOe or more. The results of Example 3 to Example 7 are collectively shown in Table 1.

[Examples 8 to 9]
Further, in Example 1, the repetition of cleaning by decantation was terminated when the supernatant liquid conductivity reached 0.2 mS / cm, in the same manner as in Example 1, except that the alloy according to Example 8 was terminated. Powder h was obtained. Further, in Example 1, the repetition of washing by decantation was terminated when the supernatant liquid conductivity reached 0.07 mS / cm, and the alloy powder according to Example 9 was the same as Example 1. i was obtained. In all cases, it was confirmed that impurities such as chlorine ions, nitrate ions, sulfate ions and acetate ions remaining in the precipitate were removed.

Next, X-ray diffraction measurement of the alloy powders h to i of Examples 8 to 9 was performed. As a result, all were Sm ₂ Fe ₁₇ N ₃ single phases. When the magnetic properties of each alloy powder were measured, the residual magnetic flux density Br was 14 kG or more, the coercive force iHc was 11.6 kOe or more, and the maximum energy product (BH) max was 40 MGOe or more. The results of Examples 8 and 9 are collectively shown in Table 1.

[Example 10 to Example 13]
Furthermore, an alloy powder j according to Example 10 was obtained in the same manner as in Example 1, except that 202.47 g of SmCl ₃ 6H ₂ O was used instead of Sm (NO ₃ ) ₃ 6H ₂ O in Example 1. In Example 1, to obtain an alloy powder k according to Fe _{(NO 3) 3} 9H ₂ instead of O FeCl ₃ 6H ₂ Example 11 in the same manner as in Example 1 except for using the O1148.63G. Further, in Example 1, an alloy powder l according to Example 12 was obtained in the same manner as in Example 1 except that 1181.54 g of FeSO ₄ 7H ₂ O was used instead of Fe (NO ₃ ) ₃ 9H ₂ O. Furthermore, an alloy powder m according to Example 13 was obtained in the same manner as in Example 1 except that NH ₄ HCO ₃ was used instead of NaOH in Example 1. In all cases, the pH at the time of precipitation ripening was 9.1.

Next, X-ray diffraction measurement of the alloy powders j to m of Examples 10 to 13 was performed. As a result, all were Sm ₂ Fe ₁₇ N ₃ single phases. When the magnetic properties of each alloy powder were measured, the residual magnetic flux density Br was 14 kG or more, the coercive force iHc was 11.6 kOe or more, and the maximum energy product (BH) max was 40 MGOe or more. The results of Example 10 to Example 13 are summarized in Table 1 above.

[Comparative Example 1]
In Example 1, except that 2 mol / L NaOH aqueous solution was added to 2.5 L of a mixed solution containing 246.68 g of Sm (NO ₃ ) ₃ 6H ₂ O and 1717 g of Fe (NO ₃ ) ₃ 9H ₂ O. In the same manner as in Example 1, an alloy powder n according to Comparative Example 1 was obtained.

As a result of X-ray diffraction measurement of the alloy powder n, it was a single phase of Sm ₂ Fe ₁₇ N _{3. When} the magnetic properties were measured, the residual magnetic flux density Br was 13.90 kG and the coercive force iHc was 11. At 55 kOe, the maximum energy product (BH) max was 39.85 MGOe. The results of Comparative Example 1 are shown in Table 1 above.

[Comparative Examples 2 to 7]
In Example 1, an alloy powder o according to Comparative Example 2 was obtained in the same manner as in Example 1 except that the repetition of washing by decantation was terminated when the supernatant liquid conductivity reached 2 mS / cm. . It was confirmed that impurities such as chloride ion, nitrate ion, sulfate ion and acetate ion were present in the precipitate without being removed.

  Further, an alloy powder p according to Comparative Example 3 was obtained in the same manner as in Example 1 except that the nitriding heat treatment temperature was set to 300 ° C. in Example 1. An alloy powder q according to Comparative Example 4 was obtained in the same manner as in Example 1 except that the nitriding heat treatment temperature was 530 ° C. in Example 1. An alloy powder r according to Comparative Example 5 was obtained in the same manner as in Example 1 except that the temperature of the reduction diffusion reaction was set to 800 ° C. in Example 1. Further, an alloy powder s according to Comparative Example 6 was obtained in the same manner as in Example 1 except that the temperature of the reduction diffusion reaction in Example 1 was 1300 ° C. Furthermore, an alloy powder t according to Comparative Example 7 was obtained in the same manner as in Example 1 except that the drying temperature after deacidified water washing, substitution with AP-2 and filtration in Example 1 was 50 ° C.

As a result of X-ray diffraction measurement of the alloy powders o to t of Comparative Examples 2 to 7, the alloy powders o to q, s, and t were Sm ₂ Fe ₁₇ N ₃ single phase, but the alloy powder r In addition to Sm ₂ Fe ₁₇ N ₃ , unreacted Fe and Sm ₂ O ₃ heterogeneous phases were observed. Further, when the magnetic properties of the powder were measured, the alloy powders o to t of Comparative Examples 2 to 7 had a residual magnetic flux density Br of less than 14 kG, a coercive force iHc of less than 11.6 kOe, and a maximum energy product (BH). The max was less than 40 MGOe. The results of Comparative Examples 2 to 7 are collectively shown in Table 1.

[Comparative Example 8]
In the same manner as in Example 1 described in JP-A-9-143636, the amounts of raw materials and reducing agent are adjusted so that an alloy composition equivalent to that in Example 1 is obtained by the reduction diffusion method. Manufactured. Since the obtained alloy powder was as coarse as 20 μm in average particle size, it was mechanically pulverized by a ball mill.

As a result of X-ray diffraction measurement of the alloy powder u of Comparative Example 9, it was Sm ₂ Fe ₁₇ N ₃ single phase, but when the magnetic properties of the powder were measured, the residual magnetic flux density Br was less than 14 kG, The magnetic force iHc was less than 11.6 kOe, and the maximum energy product (BH) max was less than 40 MGOe. The results of Comparative Example 8 are shown in Table 1 above.

[Evaluation]
As apparent from Table 1 above, in Examples 1 to 13 according to the method for producing rare earth-transition metal-nitrogen based alloy powder of the present invention, alloy powders a to m are produced by the process and conditions of the present invention. Therefore, it is an Sm ₂ Fe ₁₇ N ₃ single phase, the residual magnetic flux density Br is 14 kG or more, the coercive force iHc is 11.6 kOe or more, and the maximum energy product (BH) max is 40 MGOe or more. Had.

On the other hand, in Comparative Examples 1 to 7, the conditions in which the alloy powder n of Comparative Example 1 to the alloy powder q of Comparative Example 4, the alloy powder s of Comparative Example 6, and the alloy powder t of Comparative Example 7 deviate from the method of the present invention. Are both Sm ₂ Fe ₁₇ N ₃ single phase, but the residual magnetic flux density Br is less than 14 kG, the coercive force is less than 11.6 kOe, and the maximum energy product (BH) max is less than 40 MGOe. As a result, sufficient magnetic properties could not be obtained. In addition, since the alloy powder r of Comparative Example 5 has a temperature during reduction diffusion that is too high, other phases of Fe and Sm ₂ O ₃ are mixed in addition to Sm ₂ Fe ₁₇ N ₃ , and the residual magnetic flux density Br is less than 14 kG. Thus, the coercive force was less than 11.6 kOe and the maximum energy product (BH) max was less than 40 MGOe, and sufficient magnetic properties could not be obtained.

  Since the alloy powder of Comparative Example 8 was obtained by the conventional reduction diffusion method, mechanical pulverization was required, and not only processing time and cost were required, but also sufficient magnetic properties were not obtained.

  Unlike the alloy powder obtained by the conventional method, the alloy powder obtained by the method for producing the rare earth-transition metal-nitrogen based alloy powder of the present invention has excellent magnetic properties. Therefore, it can be used as an alloy powder for magnets of motors of products including general home appliances, communications, automobiles, acoustic equipment, medical equipment, and general industrial equipment, and its industrial value is extremely high.

Claims (7)

A first step of adding a solution containing a rare earth compound and a transition metal compound to an alkaline solution and aging the resulting precipitate while stirring;
The aged precipitate is washed with water, and decantation is repeated until the supernatant has a conductivity of 1 mS / cm or less, and then dried to obtain a precursor of a composite oxide composed of a rare earth element and a transition metal element. A second step of obtaining a body;
A third step of heat-treating the precursor of the composite oxide in an oxidizing atmosphere at 500 to 1400 ° C. to obtain a composite oxide composed of a rare earth element and a transition metal element;
The complex oxide composed of the rare earth element and the transition metal element is heat-treated in a reducing atmosphere at 300 to 1000 ° C., and a part of the complex oxide is reduced to a rare earth-transition metal alloy, and partially reduced complex oxidation A fourth step of making a product,
The partially reduced composite oxide is mixed with at least one reducing agent selected from granular or powdery alkali metals, alkaline earth metals and hydrides thereof, and the mixture is heated in an inert gas atmosphere to 900 ° C to A fifth step of obtaining a rare earth-transition metal alloy powder by heat treatment at 1200 ° C .;
A sixth step of obtaining a rare earth-transition metal-nitrogen based alloy powder by nitriding heat treatment of the rare earth-transition metal based alloy powder at 300 ° C. to 600 ° C. in a gas atmosphere containing nitrogen or ammonia and hydrogen;
A seventh step of washing the alloy powder containing the rare earth-transition metal-based nitride with water and drying after the acid cleaning, and a method for producing the rare earth-transition metal-nitrogen based alloy powder.   The rare earth-transition metal- according to claim 1, wherein the alkaline solution has a concentration sufficient for the pH of the solution containing the rare earth compound and the transition metal compound to be 7.5 or more in the first step. A method for producing nitrogen-based alloy powder.   3. The alkali solution according to claim 1, wherein the alkali solution is added to the rare earth compound and the transition metal compound over a sufficient period of time so that the two are uniformly mixed. A method for producing a rare earth-transition metal-nitrogen alloy powder.   The method for producing a rare earth-transition metal-nitrogen alloy powder according to any one of claims 1 to 3, wherein in the first step, the solution temperature is 100 ° C or lower.   In the second step, the impurity content contained in the precursor of the composite oxide composed of the rare earth element and the transition metal element is 1.5% by weight or less in terms of element. A method for producing a rare earth-transition metal-nitrogen-based alloy powder according to any one of the above.   A rare earth-transition metal-nitrogen based alloy powder obtained by the method according to claim 1.   The rare earth-transition metal-nitrogen based alloy powder according to claim 6, wherein the maximum energy product (BH) max is 40 MGOe or more.