JP7294836B2 - Method for producing rare earth transition metal magnet powder - Google Patents

Description

The present invention relates to a method for producing rare earth transition metal magnet powder.

Rare earth transition metal magnet powders represented by neodymium iron boron (Nd ₂ Fe ₁₄ B), samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ) or samarium cobalt (Sm ₂ Co ₅ , Sm ₂ Co ₁₇ ) are excellent Due to its magnetic properties, it is used in various industrial products such as motors. Magnet powder is characterized in that coercive force, which is one of the magnetic properties, improves as the particle size decreases. Therefore, in recent years, there is an increasing need to reduce the particle size of the rare earth transition metal magnet powder.

Known methods for producing rare earth transition metal magnet powder include the melting and casting method and the reduction diffusion method. Among these methods, the melting and casting method is a method in which rare earth metals and iron are blended, high-frequency melting is performed in an inert gas atmosphere, and the resulting alloy ingot is subjected to homogenization heat treatment and then pulverized.

On the other hand, the reduction diffusion method is a method of obtaining a product containing a rare earth transition metal alloy by mixing a rare earth oxide, a transition metal and a reducing agent and then heat-treating the mixture in an inert gas atmosphere. In the case of alloy-based magnet powder such as neodymium-iron-boron, the obtained rare-earth-transition-metal alloy can be directly used as the magnet powder. It is also possible to obtain nitride magnet powder by subjecting a rare earth transition metal alloy to a nitriding treatment. For example, after mixing samarium oxide (Sm ₂ O ₃ ) powder, iron (Fe) powder and a reducing agent, heat treatment is performed in an inert gas atmosphere to obtain a rare earth-iron alloy powder having a Sm ₂ Fe ₁₇ composition, Samarium-iron-nitrogen (Sm ₂ Fe ₁₇ N ₃ ) magnet powder can be obtained by nitriding the alloy powder in an atmosphere of ammonia gas (NH ₃ ) or nitrogen gas (N ₂ ). Compared with the melting and casting method, the reduction-diffusion method has a less complicated process and does not require the use of expensive rare earth metals as raw materials.

By the way, since a reducing agent is used when magnetic powder is produced by the reduction-diffusion method, the product after reduction-diffusion contains by-products derived from the reducing agent. Moreover, this product may contain a heterogeneous phase other than the main phase. For example, when metallic calcium (Ca) is used as a reducing agent to produce samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ) magnet powder, the reducing agent (Ca) is oxidized to form calcium oxide (CaO) in the reduction diffusion process. ) is generated. Moreover, the reducing agent that has not been oxidized may remain and become a residue (Ca). Furthermore, a samarium iron compound (SmFe ₃ ) may be generated as a heterophase. Since such by-products (CaO, Ca, etc.) and heterogeneous phases ( _SmFe3, etc.) degrade the magnetic properties of the magnet, it is desirable to remove them as much as possible.

Conventionally, by-products have been removed by washing the product with water. Specifically, the product is put into water and stirred to form a slurry. At this time, the by-product reacts with water and changes to a hydroxide (solid by-product-derived component). For example, calcium oxide (CaO) and metallic calcium (Ca) change to calcium hydroxide (Ca(OH) ₂ ). Since this hydroxylated by-product (Ca(OH) ₂ etc.) has low solubility in water, most of it floats in suspension in water. Therefore, the slurry is left to stand to obtain a supernatant, and the supernatant is decanted (washed with water) to remove hydroxylated by-products. A technique for removing by-products by such decantation is disclosed in Patent Document 1, for example. Patent Document 1 describes a method for producing rare earth-iron-nitrogen based magnet powder by mixing rare earth oxide powder, iron powder and reducing agent powder, followed by reduction diffusion, cooling, nitriding treatment and wet treatment. Since calcium hydroxide (Ca(OH) ₂ ) derived from the reducing agent remains in the treated product, it is disclosed that decantation (washing with water) is repeated about 5 to 10 times during wet treatment. .

JP 2014-122392 A

Thus, in the conventional reduction-diffusion method, decantation (washing with water) was used to remove by-products in the product. However, as the particle size of magnet powder becomes smaller, the technique of removing by-products by decantation has a problem that the yield of the obtained magnet powder decreases and the production cost increases. This is because magnet powder with a small particle size has a slow sedimentation rate in water and flows out together with hydroxylated by-products during decantation. In addition, it is conceivable that the magnet powder with small particle size is precipitated by leaving it to stand for a long time during decantation. By-products are mixed in the magnet powder, degrading the properties. Furthermore, standing still for a long time results in a long cycle time, which is undesirable from the viewpoint of manufacturing cost.

SUMMARY OF THE INVENTION In view of the problems of the prior art, it is an object of the present invention to provide a method for producing high-performance rare-earth-transition-metal-based magnet powder at a high yield while preventing an increase in production costs.

The inventor of the present invention recently found that when producing rare earth transition metal magnet powder by the reduction diffusion method, part or all of the slurry is passed through a gravity separator during the wet treatment to separate the solids derived from the reducing agent. It is possible to obtain high-performance rare earth-transition metal-based magnet powder at a high yield by removing the components derived from the by-products and recovering the rare earth-transition metal alloy components. Arrived.

The present invention includes the following aspects (1) to (13). In this specification, the expression "-" includes both numerical values. That is, "X to Y" is synonymous with "X or more and Y or less".

(1) A method for producing a rare earth transition metal magnet powder, comprising the following steps;
A mixture preparation step of mixing a rare earth oxide powder, a transition metal powder, and a reducing agent containing at least one selected from alkali metals, alkaline earth metals and hydrides thereof to form a raw material mixture;
a reduction diffusion step of heat-treating the raw material mixture in an inert gas atmosphere to obtain a product containing rare earth transition metal alloy components and by-products; It has a wet treatment process for cleaning,
During the wet treatment step, the product put into water is disintegrated to obtain a slurry containing a rare earth transition metal alloy component and a solid byproduct-derived component, and a part or all of the slurry. is passed through a gravity separator to remove solid by-product-derived components and to perform a separation treatment for recovering rare earth transition metal alloy components.

(2) The method of (1) above, wherein in the wet treatment step, the slurry is allowed to stand to obtain a supernatant containing mainly solid by-product-derived components, and the obtained supernatant is passed through a gravity separator.

(3) The method according to (1) or (2) above, wherein in the wet treatment step, a series of treatments of slurrying treatment and separation treatment are repeated multiple times.

(4) The method according to any one of (1) to (3) above, wherein the gravity separator is a hydrocyclone.

(5) The method according to (4) above, wherein the slurry is distributed and passed through a plurality of hydrocyclones connected in parallel during the separation process.

(6) The method according to (4) above, wherein the slurry is sequentially passed through a plurality of hydrocyclones connected in series during the separation treatment.

(7) The method of (6) above, wherein the slurry is sequentially passed through a hydrocyclone having a larger diameter and then a hydrocyclone having a smaller diameter.

(8) The method according to any one of (1) to (7) above, wherein the product is further pickled during the wet treatment step.

(9) The method according to any one of (1) to (8) above, comprising a step of maintaining the product in a hydrogen pressurized atmosphere between the reduction diffusion step and the wet treatment step.

(10) The method according to any one of (1) to (9) above, further comprising a step of nitriding the product after the reduction diffusion step.

(11) The method according to any one of (1) to (10) above, wherein the reducing agent contains calcium (Ca).

(12) The method according to (11) above, wherein the rare earth transition metal magnet powder has a calcium (Ca) content of 0.1% by mass or less.

(13) The method according to any one of (1) to (12) above, wherein the recovery rate, which is the ratio of the amount of product after separation treatment to the amount of product before separation treatment, is 80% by mass or more.

According to the present invention, it is possible to obtain high-performance rare earth-transition metal-based magnet powder at a high yield, and as a result, it is possible to produce high-performance rare-earth-transition metal-based magnet powder at low cost.

It is a figure which shows the conceptual schematic diagram of a two-liquid separation type hydrocyclone. It is a figure which shows an example of the separation process using a hydrocyclone. 4 shows an embodiment in which a plurality of hydrocyclones are connected in series.

Method for Producing Rare Earth Transition Metal Magnet Powder The rare earth transition metal magnet powder of the present invention is a permanent magnet powder containing a rare earth metal (rare earth element) and a transition metal as main phases, that is, a hard magnetic powder. Examples of such rare earth-transition metal-based magnet powders include those made of alloys of rare earth metals and transition metals or nitrides thereof. In addition, in this specification, an alloy is a concept including an intermetallic compound.

The rare earth-transition metal magnet powder is not particularly limited as long as it contains a rare earth metal and a transition metal as main phases. However, one or two selected from the group consisting of samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ), neodymium iron boron (Nd ₂ Fe ₁₄ B) and samarium cobalt (Sm ₂ Co ₅ , Sm ₂ Co ₁₇ ) It is preferable to use the above combination as the main phase, and it is more preferable to use samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ) as the main phase. The main phase means a phase that accounts for 50% by mass or more of the magnet powder, preferably 90% by mass or more, and more preferably 95% by mass or more. Also, the magnet powder may contain additive components in addition to the main phase. Such magnet powder can be kneaded with a resin to form a bond magnet. A sintered magnet can also be obtained by molding and sintering magnet powder.

The method for producing a rare earth transition metal based magnet powder of the present invention includes the following steps; a mixture preparation step of mixing an agent and a raw material mixture, a reduction diffusion step of heat-treating the raw material mixture in an inert gas atmosphere to obtain a product containing a rare earth transition metal alloy component and a by-product, and After the reduction diffusion step, a wet treatment step is provided in which the product is put into water and washed with water. Further, in the production method of the present invention, during the wet treatment step, the product put into water is disintegrated to obtain a slurry containing a rare earth transition metal alloy component and a solid by-product-derived component. and a separation treatment in which a part or all of the slurry is passed through a gravity separator to remove components derived from solid by-products and to recover rare earth transition metal alloy components. Each step will be described in detail below.

<Mixture preparation process>
In the mixture preparation step, rare earth oxide powder, transition metal powder, and a reducing agent containing at least one selected from alkali metals, alkaline earth metals, and hydrides thereof are mixed to form a raw material mixture.

The rare earth oxide powder is a rare earth metal source that constitutes the main phase of the magnet powder. Rare earth metals are not particularly limited as long as magnet powder can be obtained. However, preferably one or two selected from the group consisting of cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), gadolinium (Gd), dysprosium (Dy) and ytterbium (Yb) more than seeds. At least one selected from the group consisting of praseodymium (Pr), neodymium (Nd) and samarium (Sm) is more preferable from the viewpoint of obtaining a magnet powder with extremely high magnetic properties, and the magnet powder is excellent in heat resistance and weather resistance. samarium (Sm) is more preferable.

The rare earth oxide powder is selected according to the desired composition of the magnet powder. For example, when producing samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ) based magnetic powder or samarium cobalt (Sm ₂ Co ₅ , Sm ₂ Co ₁₇ ) based magnetic powder, samarium oxide (Sm ₂ O ₃ ) is selected. However, when manufacturing neodymium-iron-boron (Nd ₂ Fe ₁₄ B) magnet powder, neodymium oxide (Nd ₂ O ₃ ) may be selected. The rare earth oxide powder may be one rare earth metal oxide or a combination of two or more rare earth metal oxides. Although the particle size of the rare earth oxide powder is not limited, it is desirable that the particle size distribution is relatively uniform, for example, the particle size is preferably 2 to 80 μm.

The blending amount of the rare earth oxide powder is preferably 1.0 to 1.5 times, more preferably 1.05 to 1.2 times the amount (equivalent) required for the stoichiometric composition of the main phase. For example, when producing samarium-iron-nitrogen (Sm ₂ Fe ₁₇ N ₃ ) magnet powder, the amount of samarium oxide (Sm ₂ O ₃ ) compounded is required for the stoichiometric composition (Sm ₂ Fe ₁₇ N ₃ ). 1.0 to 1.5 times the amount to be used is preferable. By setting the compounding amount of the rare earth oxide to 1.0 times or more of the equivalent amount, the rare earth metal (rare earth element) is sufficiently diffused into the transition metal powder, and the coercive force and squareness of the finally obtained magnet powder are improved. can increase On the other hand, by setting the content to 1.5 times or less of the equivalent weight, it is possible to suppress the generation of a different phase (SmFe3 _, etc.) and increase the magnetization.

The transition metal powder is used as a raw material for the transition metal that constitutes the main phase of the magnet powder. The transition metal is not particularly limited as long as magnet powder can be obtained. However, iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), molybdenum (Mo), tungsten (W) and/or aluminum (Al) are preferred. The transition metal powder is selected according to the desired composition of the magnet powder. For example, when producing samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ) based magnet powder or neodymium iron boron (Nd ₂ Fe ₁₄ B) based magnet powder, iron (Fe) powder is selected and samarium cobalt (Sm ₂ Co ₅ , Sm ₂ Co ₁₇ ) based magnet powder, cobalt (Co) powder should be selected. As the iron (Fe) powder, reduced iron powder, gas atomized powder, water atomized powder and/or electrolytic iron powder can be used. The transition metal powder is classified so as to have an optimum particle size, if necessary.

The reducing agent is used to reduce the rare earth oxide powder and contains at least one selected from alkali metals, alkaline earth metals and hydrides thereof. The reducing agent is preferably lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba ) is preferable, and lithium (Li) and/or calcium (Ca) are more preferable from the viewpoint of safety in handling and cost. Particularly preferably, the reducing agent contains calcium (Ca). From the viewpoint of miscibility with rare earth oxide powders and transition metal powders, the reducing agent is preferably in the form of particles or powder, and particularly preferably has a particle size of 4 mesh or less. The amount of the reducing agent is preferably 1.0 to 3.0 times, more preferably 1.10 to 2.0 times the amount (equivalent) required to reduce the rare earth oxide powder.

Additional components other than the rare earth oxide powder, the transition metal powder and the reducing agent may be added during the mixture preparation step. Such additive components include, for example, disintegration accelerators that promote disintegration of the reaction product in subsequent wet processing steps. Alkaline earth metal salts and alkaline earth metal oxides such as calcium chloride (CaCl ₂ ) and calcium oxide (CaO) can be used as disintegration accelerators. Also, when cobalt (Co) is used as the transition metal, cobalt oxide (CoO, Co ₃ O ₄ ) or the like can be added. Furthermore, when producing neodymium iron boron (Nd ₂ Fe ₁₄ B) magnet powder, a boron (B) component may be added. Such additive components are uniformly mixed together with the rare earth oxide powder, transition metal powder and reducing agent.

Rare earth oxide powder, transition metal powder, reducing agent and, if necessary, additive components are uniformly mixed. For mixing, a known mixer such as a ribbon blender, a tumbler, an S-shaped blender, a V-shaped blender, a Nauta mixer, a Henschel mixer, a super mixer, a high speed mixer, a ball mill, a vibration mill, an attritor, and a jet mill is used. be able to.

<Reduction diffusion process>
In the reduction diffusion step, the raw material mixture obtained in the mixture preparation step is heat-treated in an inert gas atmosphere to obtain a product (reduction diffusion product). This product (reduced diffusion product) contains rare earth transition metal alloy components and by-products. In this step, the rare earth oxide powder in the raw material mixture is reduced by the action of the reducing agent and then diffused into the transition metal powder to become a rare earth transition metal alloy component. On the other hand, the reducing agent is partly or wholly oxidized to an oxide. Here, the oxides of the reducing agent are oxides of alkali metals and/or alkaline earth metals. By-products thus consist of oxides and/or residues of the reducing agent.

For example, using samarium oxide (Sm ₂ O ₃ ) as the rare earth oxide powder, iron (Fe) powder as the transition metal powder, and metallic calcium (Ca) as the reducing agent, samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ )-based magnet powder, samarium oxide (Sm ₂ O ₃ ) is reduced to samarium (Sm) by the action of a reducing agent (Ca). Then, the reduced samarium (Sm) diffuses into the iron (Fe) powder to form a samarium-iron alloy (Sm ₂ Fe ₁₇ ) having a Th ₂ Zn ₁₇ -type crystal structure. On the other hand, metallic calcium (Ca), which is a reducing agent, is oxidized to become calcium oxide (CaO). However, when the amount of metallic calcium added is more than the equivalent amount, surplus calcium (Ca) remains. This calcium oxide (CaO) and surplus calcium (Ca) constitute by-products. Furthermore, in some cases, a heterophase such as a samarium iron compound (SmFe ₃ ) may be generated in the reduction diffusion process. Therefore, the product after the heat treatment contains rare earth transition metal alloy components (Sm ₂ Fe _17, etc.), by-products derived from the reducing agent (CaO, Ca, etc.), and in some cases further heterophases (SmFe ₃ , etc.). The product after this heat treatment usually consists of a porous ingot.

The heat treatment is carried out at a temperature higher than the temperature at which the reducing agent melts and at a temperature at which the resulting rare earth transition metal alloy component does not melt. Specifically, the heat treatment temperature is preferably 900 to 1180.degree. By setting the temperature to 900° C. or higher, the diffusion of the rare earth metal (rare earth element) into the transition metal powder becomes uniform, and the coercive force and squareness of the finally obtained magnet powder can be enhanced. On the other hand, by setting the temperature to 1180° C. or less, it is possible to suppress grain growth of the rare earth transition metal alloy component and generation of coarse grains. As a result, for example, when nitride-based magnet powder is produced, the rare-earth-transition metal alloy component is uniformly nitrided in the subsequent nitriding treatment step, and the saturation magnetization and squareness of the magnet powder are improved. Also, the lower the heat treatment temperature, the lower the amount of the rare earth metal oxide compounded. This is because evaporation of rare earth metals such as samarium (Sm) is suppressed.

The heat treatment holding time is preferably 3 to 10 hours. Within this range, the primary particle size of the rare earth transition metal alloy component in the reaction product becomes small. Therefore, for example, when nitride-based magnet powder is produced, nitrogen can easily diffuse from the grain boundaries of the rare-earth transition alloy in the subsequent nitriding process, and the nitriding distance can be shortened. Moreover, the atmospheric gas during the heat treatment is preferably an inert gas such as argon gas and/or helium gas.

<Hydrogen treatment process>
If necessary, a hydrogen treatment step may be provided between the reduction-diffusion step and the wet treatment step, which will be described later, to maintain the product (reduction-diffusion product) in a hydrogen-pressurized atmosphere. The product (hydrogenated product) obtained by the hydrogen treatment has improved disintegration properties when water is added in the wet treatment step described later. In the hydrogen treatment, the product (reduction-diffusion product) obtained in the reduction-diffusion process is maintained in a pressurized hydrogen atmosphere to occlude hydrogen and collapse the product due to volume expansion. Specifically, the reduced diffusion product is placed in a stainless steel container equipped with a vacuum pump and sealed. Next, after removing the air in the container with a vacuum pump, hydrogen is enclosed and pressurized. The pressure inside the container is +5 kPa or more with respect to the atmospheric pressure. More preferably, +10 to 50 kPa with respect to the atmospheric pressure. As the product absorbs hydrogen, the progress of hydrogen absorption can be confirmed by the fact that the pressure gradually decreases from the initial pressurized pressure. When the decrease in pressure becomes small, it can be judged that the hydrogen treatment is finished. After removing hydrogen from the container with a vacuum pump, the pressure inside the container is restored to atmospheric pressure with an inert gas such as nitrogen or argon, and the product (hydrogenated product) is taken out from the container.

<Nitriding process>
If necessary, a step of nitriding the product (reduction-diffusion product, hydrogen-treated product) may be further provided after the reduction-diffusion step or the hydrogen treatment step. By providing the nitriding treatment process, nitride magnet powder such as samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ) can be obtained.

In the nitriding treatment, the product (reduced diffusion product, hydrogen treated product) is heated to preferably 350 to 500° C., more preferably 400 to 480° C., while flowing a gas mixture containing ammonia. As a result, the rare earth transition metal alloy component in the resulting product (nitrided product) is nitrided. When the heating temperature is 350° C. or higher, the nitriding reaction takes place in a short time, improving the efficiency. On the other hand, if the nitriding temperature is too high, the main phase may decompose. For example, when producing samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ) magnet powder by nitriding a rare earth transition metal alloy component made of samarium iron (Sm ₂ Fe ₁₇ ), if the nitriding temperature is too high, the main phase samarium iron (Sm ₂ Fe ₁₇ ), which is samarium iron (Sm 2 Fe 17 ), may decompose to produce α-iron (α-Fe). α-iron (α-Fe) is not preferable because it reduces the squareness of the demagnetization curve of the magnet powder. Such decomposition of the main phase can be suppressed by setting the nitriding temperature to 500° C. or lower. The holding time is preferably 5 to 10 hours, although it depends on the amount of material to be treated.

Nitriding gas to be circulated during the nitriding treatment should contain at least nitrogen atoms, and nitrogen gas and ammonia gas are suitable. Moreover, in order to control the reaction, hydrogen, argon, etc. may be contained. When a mixed gas flow of ammonia and hydrogen is used, the mixing ratio (gas flow ratio) is preferably ammonia:hydrogen=10-70:30-90, more preferably 30-60:40-70. Within this range, the flow rate of ammonia becomes sufficient, and the nitriding efficiency is further improved.

<Heat treatment process>
If necessary, the product (nitrided product) obtained by the nitriding treatment may be further heat-treated in an inert gas. Inert gases include, for example, hydrogen gas, nitrogen gas, argon gas, and helium gas. By performing such a heat treatment, the nitrogen distribution in the individual crystal cells constituting the magnet powder in the resulting product (heat-treated product after nitriding treatment) becomes more uniform, and the squareness of the magnet powder is further improved. . The heat treatment temperature is preferably 350 to 500°C, more preferably 400 to 480°C. Also, the holding time is preferably 20 to 200 minutes, more preferably 30 to 150 minutes.

Nitriding treatment and heat treatment may be performed at any timing after the reduction diffusion step. That is, the nitriding treatment or the heat treatment may be performed between the reduction diffusion step and the wet treatment described later, or the nitriding treatment or the heat treatment may be performed after the wet treatment.

<Wet treatment process>
In the wet treatment process, the product (reduction-diffusion product, etc.) subjected to the reduction-diffusion process is put into water and washed with water. Here, it is preferable to use ion-exchanged water as water. Moreover, the product to be washed with water is not limited as long as it is a product subjected to reduction diffusion. Therefore, the reduced diffusion product obtained in the reduction diffusion step may be subjected to a wet treatment. In addition, when the hydrogen treatment is performed after reduction diffusion, the hydrogen treated product may be subjected to a wet treatment. Alternatively, if the nitriding treatment or the heat treatment is performed before the wet treatment, the wet treatment may be applied to the nitrided product or the post-nitriding heat treated product.

During washing with water, the product put into water disintegrates into a slurry. At this time, the reducing agent-derived by-product reacts with water to change into a solid by-product-derived component composed of hydroxide. Accordingly, the solid by-product-derived components include hydroxides of alkali metals and/or alkaline earth metals. For example, when metallic calcium (Ca) is used as the reducing agent, the product after the reduction-diffusion step contains rare earth transition metal alloy components and by-products (CaO, Ca). During water washing, this by-product (CaO, Ca) reacts with water and changes to calcium hydroxide (Ca(OH) ₂ ). Since calcium hydroxide has low solubility in water, most of it becomes a suspension and floats on water. Therefore, the slurry obtained by washing with water is a suspension of the rare earth transition metal alloy component and the solid byproduct-derived component (Ca(OH) ₂ ). By separating the solid by-product-derived component in the slurry from the rare earth transition metal alloy component, it is possible to obtain a magnet powder with high purity and high properties.

In the production method of the present invention, separation treatment is performed during the wet treatment step. In this separation treatment, part or all of the slurry is passed through a gravity separator to remove components derived from solid by-products and recover rare earth transition metal alloy components. As a result, magnet powder with high properties can be obtained at a high yield. This is because the rare earth-transition metal alloy component has a relatively high specific gravity, whereas the solid byproduct-derived component containing an alkaline earth metal or the like has a low specific gravity, and the two can be easily and reliably separated due to the difference in specific gravity. is. For example, when producing samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ) based magnetic powder using metallic calcium (Ca) as a reducing agent, the specific gravity of samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ) is 7.68 g. /cm ³ , the specific gravity of calcium hydroxide (Ca(OH ₂ )) is 2.21 g/cm ³ , and the difference in specific gravity between the two is more than three times.

In the wet processing step, all of the slurry may be passed through the gravity separator, or only a portion of the slurry may be passed. As a method of passing a part of the slurry, for example, a method of allowing the slurry to stand to obtain a supernatant liquid and passing the supernatant liquid through a gravity separator can be mentioned. The solid by-product-derived component (Ca(OH) ₂ ) has a relatively low specific gravity, and most of it is contained in the supernatant while floating. On the other hand, rare earth transition metal alloy components have a large specific gravity and most of them settle. Therefore, the slurry supernatant mainly contains solid by-product-derived components, and by passing this supernatant through a gravity separator, the solid by-product-derived components can be effectively separated and removed. As a technique for passing the supernatant liquid through the gravity separator, there is a mode in which the inlet of the gravity separator is connected to a pipe for sucking the supernatant liquid, and a pump is installed in the middle of the pipe.

In the wet treatment step, a series of slurrying treatment and separation treatment may be repeated multiple times. As a result, it is possible to efficiently remove solid by-product-derived components that could not be completely removed by a single separation treatment, and to increase the yield of the rare earth-transition metal alloy component. In order to repeat the slurrying treatment and the separation treatment multiple times, for example, the reduction diffusion treated product or the hydrogen treated product and water are put into a treatment vessel (tank) and stirred to make slurry, and the obtained slurry is subjected to separation treatment. to recover the rare earth-transition metal alloy component, put the recovered rare earth-transition metal alloy component into the processing container or another processing container together with water to re-slurry, and subject the resulting slurry to separation treatment again. is mentioned. The number of repetitions may be determined from the viewpoint of the balance between yield and production cost, and may be two times, three times, or more.

The specific gravity separator is not particularly limited as long as it is a device for separating slurry by specific gravity, that is, a wet specific gravity separator. However, the specific gravity separator is preferably a hydrocyclone or a centrifugal separator, and more preferably a hydrocyclone from the viewpoint of continuous operation. A hydrocyclone is a device that separates particles in a slurry based on the difference in their specific gravities, and there are two liquid separation types and three liquid separation types depending on the separation mode. A conceptual schematic diagram of a two-liquid separation type hydrocyclone is shown in FIG. As shown in FIG. 1, the hydrocyclone 1 includes a cyclone body 2 tapered toward the bottom, an inlet (raw liquid inlet) 3 provided on the upper side wall of the cyclone body 2, It has a lower outlet (bottom outlet) 4 provided at the bottom of the cyclone body 2 and an upper outlet (top outlet) 5 provided at the center of the upper portion of the cyclone body 2 . When slurry is injected from the inflow port 3 of the hydrocyclone, the injected slurry undergoes rotational motion. Particles in the slurry are separated according to their specific gravities by the centrifugal force of the rotating motion. That is, the high specific gravity particles are arranged on the peripheral wall of the cyclone body 2 by centrifugal force, and the low specific gravity particles are arranged near the center of the cyclone body 2 . A descending flow is generated along the taper of the cyclone on the peripheral wall, and the high specific gravity particles are led to a lower outlet (bottom outlet) 4 by this descending flow and discharged as an underflow liquid 17 . On the other hand, an upward flow is generated in the central portion, and the low specific gravity particles are guided to the upper flow port (top outlet) 5 by this upward flow and discharged as an overflow liquid 18 . In this way, the particles in the slurry can be separated by the difference in specific gravity with the hydrocyclone.

A liquid cyclone is not particularly limited. However, the diameter at the top of the cyclone body 2 (top diameter) is preferably 10 to 300 mm, more preferably 100 to 150 mm. Also, the slurry supply pressure is preferably 0.05 to 0.4 MPa, more preferably 0.05 to 0.3 MPa. By setting the slurry supply pressure to 0.05 MPa or more, the classification performance is improved, and by setting it to 0.4 MPa or less, abrasion of the inner wall of the cyclone main body is suppressed. The material of each member of the hydrocyclone is preferably ceramic, stainless steel, or nylon having alkali resistance.

An example of separation processing using a hydrocyclone is shown in FIG. As shown in FIG. 2, the product after the reduction-diffusion step and water are put into a processing container 12 to form a processing slurry 11 . The product contains rare earth-transition metal alloy components and by-products that react with water to solid by-product-derived components that are hydroxides. A stirrer 14 is attached to the processing vessel 12 . Using the stirrer 14, the treatment slurry 11 is stirred for a certain period of time. The treated slurry is then allowed to stand to separate into a supernatant liquid and a sediment. Although this supernatant liquid mainly contains low specific gravity solid by-product-derived components, it also contains high specific gravity rare earth transition metal alloy components.

Next, the supernatant liquid is pressure-fed by the pump 13 and forced into the inlet of the hydrocyclone 15 . A valve 16 is provided between the pump 13 and the inlet, and the injection pressure of the supernatant can be adjusted by controlling the opening degree of this valve 16 or controlling the capacity of the pump 13 (for example, inverter value). . The liquid cyclone 15 separates the rare earth-transition metal alloy component with a high specific gravity and the solid by-product-derived component with a low specific gravity, and the rare earth-transition metal alloy component is discharged from the lower outlet as an underflow liquid 17, and is solidified. By-product-derived components are discharged and removed as an overflow liquid 18 from the upper outlet. By introducing the discharged underflow liquid 17 into the processing vessel 12 or another vessel, the rare earth transition metal alloy components are recovered. As a method for introducing the underflow liquid 17 into the processing container 12, there is a mode in which the lower outlet of the hydrocyclone and the processing container are connected by a pipe.

Also, a single hydrocyclone may be used, or a plurality of hydrocyclones may be used. When a plurality of hydrocyclones are used, a method of distributing and passing the slurry through a plurality of hydrocyclones connected in parallel or a method of sequentially passing the slurry through a plurality of hydrocyclones connected in series can be used. The number of cyclones is not particularly limited, and may be two, three, or more.

By using hydrocyclones connected in parallel, the throughput per unit time can be increased. Since the classifying ability of the cyclone is greatly affected by the swirl speed of the slurry injected into the cyclone, it is desirable to increase the swirl speed by reducing the diameter of the cyclone. On the other hand, if the diameter of the cyclone is reduced, the amount of slurry that can flow into the cyclone per unit time will decrease, resulting in a decrease in throughput per unit time. Therefore, as a countermeasure, the cyclones are connected in parallel and the slurry is distributed and supplied to each cyclone, thereby making it possible to secure the treatment capacity while maintaining the classification capacity.

On the other hand, the use of series-connected hydrocyclones improves the classifying ability. FIG. 3 shows a mode in which cyclones are connected in series. Here, three cyclones are connected, and while the underflow liquid (rare earth transition metal alloy component) 17 discharged from each cyclone is recovered, the overflow liquid (solid state) discharged from the final stage cyclone is recovered. by-product-derived components) 18 are discharged and removed.

When serially connected hydrocyclones are used, it is preferable to sequentially pass the slurry from the larger diameter hydrocyclone to the smaller diameter hydrocyclone as shown in FIG. This further improves the classification ability. By connecting the cyclones in series from the largest diameter to the smallest diameter, the components of the rare earth-transition metal alloy that could not be recovered by a single cyclone and leaked into the overflow liquid can be recovered by the subsequent smaller diameter cyclone. It is also conceivable to use a single small-diameter cyclone, but in that case, if slurry containing a large amount of metal powder is supplied to the small-diameter cyclone, abnormal wear and clogging of the cyclone, oxidation and destruction due to friction between metal powders will occur. could happen. Therefore, when using a small-diameter cyclone, it is desirable to remove the metal powder within the allowable range of the preceding cyclone. One example is a mode in which three cyclones, a cyclone with a diameter (top diameter) of 100 to 150 mm, a cyclone with a diameter of 60 to 90 mm, and a cyclone with a diameter of 30 to 50 mm, are connected in series.

During wet processing, the product may be further pickled. By performing the pickling treatment, solid by-product-derived components and heterogeneous phases can be removed more effectively. For example, by performing a pickling treatment after the water washing treatment, the foreign phases (SmFe _3, etc.) in the product are removed, and the solid byproduct-derived components (Ca(OH) _2, etc.) that could not be removed by the water washing treatment ) can be removed.

The pickling treatment can be performed, for example, by putting the product into water and adding an acid while stirring. Inorganic acids and organic acids such as hydrochloric acid, acetic acid, nitric acid and sulfuric acid can be used as the type of acid. However, acetic acid is preferred from the viewpoint of cost and the like. The amount of acetic acid used is not limited. However, 1.0 to 5.0 mol/kg of product is preferred, for example when the product consists of samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ). It is also preferable to wash the pickled product with water several times to remove impurities present in the supernatant. The product after washing with water is dried by a technique such as drying under reduced pressure.

Separation treatment using a gravity separator may be performed during the pickling treatment. Thereby, the recovery rate (yield) of the rare earth transition metal alloy component can be further increased. As a technique therefor, there is a method of passing part or all of the slurry of the product obtained by adding water and acid through a gravity separator. At that time, a hydrocyclone may be used as a gravity separator. Alternatively, the slurry may be allowed to stand to obtain a supernatant, and the resulting supernatant may be passed through a gravity separator. Furthermore, the separation process may be performed only once or may be repeated multiple times.

<Fine pulverization process>
If necessary, the product obtained in the final step (wet-processed product, nitriding product, post-nitriding heat-treated product, etc.) may be pulverized. In the fine pulverization step, the product is put into a pulverizer together with a medium and pulverized to an average particle size of 1 to 3 μm. The pulverizer is not particularly limited. However, a wet-type medium agitating mill such as a bead mill is preferable from the viewpoint that the composition and particle size of the powder can be easily made uniform.

As a medium for pulverization, isopropyl alcohol, ethanol, toluene, methanol, hexane, etc. can be used, and isopropyl alcohol is particularly preferred. At this time, when a phosphoric acid compound is added, the powder is surface-treated at the same time as the pulverization. Phosphoric acid compounds include orthophosphoric acid, disodium hydrogen phosphate, pyrophosphoric acid, metaphosphoric acid, manganese phosphate, zinc phosphate, and aluminum phosphate, and orthophosphoric acid is preferred from the viewpoint of cost. The amount of the phosphoric acid compound to be added depends on the particle size and surface area of the fine powder to be obtained, and cannot be generally defined, but is preferably in the range of 0.1 mol/kg to 0.2 mol/kg of the alloy powder to be pulverized. When the concentration is 0.1 mol/kg or more, the formation of the film becomes sufficient, and when the concentration is 0.2 mol/kg or less, the phosphorus-coated portion that does not contribute to the magnetic force increases excessively and the magnetic properties deteriorate. can be prevented. The pulverized powder after pulverization is filtered and vacuum-dried using a filter with a predetermined mesh size.

According to the manufacturing method of the present invention, the high-performance rare earth-transition metal-based magnet powder containing few impurities can be obtained at a high yield by going through such steps. For example, the recovery rate, which is the ratio of the amount of product after separation treatment to the amount of product before separation treatment in the wet treatment step, is 80% by mass or more. Moreover, even when a reducing agent containing calcium (Ca) is used, the calcium (Ca) content of the obtained rare earth transition metal magnet powder is 0.1% by mass or less.

The invention is illustrated below by examples. However, the invention is not limited to these examples.

Example 1
(1) Production of Rare Earth Transition Metal Magnet Powder <Mixture preparation step>
A raw material mixture was prepared by compounding and mixing samarium oxide (Sm ₂ O ₃ ) powder with an average particle size of 5 μm, iron (Fe) powder with an average particle size of 50 μm, and granular calcium (Ca). At this time, the blending amounts were 405 g of samarium oxide, 1000 g of iron powder, and 140 g of granular calcium.

<Reduction diffusion process>
The resulting raw material mixture was subjected to reduction diffusion treatment to obtain a product (reduction diffusion product). The reduction diffusion treatment was performed by heating the raw material mixture at 1150° C. for 10 hours in an argon (Ar) gas atmosphere.

<Hydrogen treatment process>
The reduction-diffusion treated product was placed in a sealed stainless steel (SUS) container and maintained in a hydrogen atmosphere of +40 kPa with respect to atmospheric pressure.

<Nitriding process>
The product (hydrogenated product) obtained by the hydrogen treatment was subjected to nitriding treatment. The nitriding treatment was performed by holding the product at 450° C. for 7 hours in an atmosphere in which 1.5 L/min of ammonia (NH ₃ ) gas and 1 L/min of hydrogen (H ₂ ) gas were flowed.

<Wet treatment process>
The product (nitrided product) obtained by the nitriding treatment was washed with water. First, 1535 g of the product was placed in a processing container, and 3 L of ion-exchanged water was added. By adding ion-exchanged water, the product collapsed into slurry (slurry treatment). At this time, since the slurry contained calcium hydroxide (Ca(OH ₂ )) derived from the reducing agent, it was strongly alkaline with a pH of 12 or higher.

Next, the resulting slurry was subjected to separation treatment. Separation treatment was carried out as follows. First, the slurry was stirred for 5 minutes and then allowed to stand for 1 minute to separate into a precipitate and a supernatant. Only the supernatant liquid was passed through a liquid cyclone (Murata Industries, Ltd., Model T-80CN Superclone) to separate into an overflow liquid containing low specific gravity components and an underflow liquid containing high specific gravity components. Here, the slurry pressure was adjusted to 0.3 MPa by adjusting the opening of the valve when allowing the supernatant liquid to pass through. Next, the overflow liquid was removed, and the underflow liquid was introduced (recovered) into the processing vessel. After that, ion-exchanged water was newly added to the processing vessel to prepare a slurry. The operations of stirring and standing the slurry, treating the supernatant with a hydrocyclone, and adding ion-exchanged water were successively repeated five times.

The water-washed and separated product was subjected to a pickling treatment. First, deionized water and 168 g (2.8 mol) of acetic acid were added to the product slurry (magnetic powder slurry). At this time, the slurry was strongly alkaline with a pH of 12 or higher.

Next, the obtained slurry was subjected to separation treatment again. Separation treatment was carried out as follows. First, the slurry was stirred for 5 minutes and then allowed to stand for 1 minute to separate into a precipitate and a supernatant. Only the resulting supernatant liquid was passed through a hydrocyclone to separate into an overflow liquid containing low specific gravity components and an underflow liquid containing high specific gravity components. While removing the overflow liquid, the underflow liquid containing the high specific gravity component was introduced (recovered) into the processing vessel. After that, ion-exchanged water was newly added to the processing vessel to prepare a slurry. The operations of stirring and standing the slurry, treating the supernatant with a hydrocyclone, and adding ion-exchanged water were successively repeated five times.

The pickled product was dried to obtain a dried product (samarium iron nitrogen magnet powder). Drying was performed by heating the obtained product at 200° C. under vacuum using a vacuum dryer. The mass of the obtained dried product (magnet powder) was 1249 g.

<Fine pulverization process>
The resulting dried material was ground using a medium agitation mill. 1000 g of the dried material, 1500 g of isopropyl alcohol as a grinding solvent, and 17 g (0.15 mol/kg) of orthophosphoric acid as a surface treatment agent were put into the grinding chamber, sealed and ground for 120 minutes to obtain a magnetic powder slurry. The magnet powder slurry thus obtained was placed in a vacuum dryer, and while the inside of the dryer was kept at a negative pressure by a vacuum pump, the inside of the dryer was held at 150° C. for 6 hours by a heater to dry by heating. After drying by heating, after the temperature inside the dryer reached room temperature, it was taken out from the dryer to obtain samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ) magnet powder.

(2) Evaluation Various properties of the obtained magnet powder were evaluated as follows.

<Magnetic properties>
Magnetic properties of the magnet powder were measured as follows. First, magnetic powder was packed in a sample case together with paraffin, and then heated to be oriented and solidified by cooling to prepare a sample for measurement. Next, using a vibrating sample magnetometer (Toei Industry Co., Ltd., VSM), a hysteresis curve was drawn under the condition of a maximum applied magnetic field of 1670 kA / m (21 kOe), and from this hysteresis curve, residual magnetic flux density (Br) and Coercivity (iHc) was read.

<Amount of residual calcium>
The amount of residual calcium (Ca) in the magnet powder was measured by ICP emission spectrometry.

<Yield>
The mass of the product subjected to the wet treatment (W _(RD) ) and the mass of the product obtained by the pickling treatment (W _{(SFN) )} were measured, and the yield Y (%) was calculated using the formula: Y (% )=100×W _(SFN) /W _(RD) .

Example 2
Magnet powder was produced and evaluated in the same manner as in Example 1, except that three hydrocyclones connected in series as shown in FIG. 3 were used. At that time, a cyclone with a diameter of 130 mm, a cyclone with a diameter of 80 mm, and a cyclone with a diameter of 50 mm were connected in series in this order. The mass of the obtained magnet powder (dried matter) was 1305 g.

Comparative example 1
Magnet powder was produced and evaluated in the same manner as in Example 1, except that the supernatant liquid of the slurry was removed by decantation without using a liquid cyclone during the water washing and pickling treatment in the wet treatment process. gone. The mass of the obtained magnet powder (dry matter) was 1164 g.

Comparative example 2
Magnet powder was produced and evaluated in the same manner as in Comparative Example 1, except that the standing time of the slurry was changed to 2 minutes during the water washing and pickling treatment in the wet treatment process. The mass of the obtained magnet powder (dry matter) was 1232 g.

Comparative example 3
Magnet powder was prepared and evaluated in the same manner as in Comparative Example 1, except that the standing time of the slurry was changed to 30 seconds during the water washing and pickling treatment in the wet treatment process. The mass of the obtained magnet powder (dry matter) was 1115 g.

Results Evaluation results obtained for Examples 1 and 2 and Comparative Examples 1 to 3 were as shown in Table 1.

As shown in Table 1, the yield of Example 1 using a single hydrocyclone in the wet treatment process was 81%, and the yield of Example 2 using multiple stages was 85%. Also, the coercive force iHc of the obtained magnet powder was as high as 895.2 and 901.6 kA/m. On the other hand, in Comparative Example 1 in which no hydrocyclone was used, the yield was as low as 76%. This is because the samarium iron nitrogen (Sm ₂ Fe ₁₇ N ₃ ) magnet powder in the supernatant liquid was discharged out of the system together with calcium hydroxide (Ca(OH) ₂ ) because the hydrocyclone was not used. is. In Comparative Example 2, in which the hydrocyclone was not used and the slurry standing time was extended to 2 minutes, the yield was as high as 80%, but the magnetic properties (Br, iHc) were lowered. This is because the magnet powder in the supernatant settled well and the yield increased by extending the standing time, but calcium hydroxide also settled at the same time and was mixed in the magnet powder. It is speculated that This is supported by the fact that the amount of residual calcium (Ca) in the magnet powder was as high as 0.2% by mass. Furthermore, in Comparative Example 3 in which the hydrocyclone was not used and the slurry standing time was shortened to 30 seconds, the yield was as low as 73%. This is because the desired magnet powder was discharged out of the system by shortening the standing time.

From the above results, according to the method for producing a rare earth transition metal magnet powder of the present invention, it is possible to obtain a high quality rare earth transition metal magnet powder with a high yield. It can be seen that the powder can be produced at low cost.

1 liquid cyclone 2 cyclone body 3 inlet (undiluted solution inlet)
4 lower outlet (bottom outlet)
5 upper outlet (top outlet)
REFERENCE SIGNS LIST 11 treated slurry 12 treatment vessel 13 pump 14 agitator 15 hydrocyclone 16 valve 17 underflow liquid 18 overflow liquid

Claims (10)

A method for producing a rare earth transition metal based magnet powder, comprising the following steps;
A mixture preparation step of mixing a rare earth oxide powder, a transition metal powder, and a reducing agent containing at least one selected from alkali metals, alkaline earth metals and hydrides thereof to form a raw material mixture;
a reduction diffusion step of heat-treating the raw material mixture in an inert gas atmosphere to obtain a product containing rare earth transition metal alloy components and by-products; It has a wet treatment process for cleaning,
During the wet treatment step, the product put into water is disintegrated to obtain a slurry containing a rare earth transition metal alloy component and a solid byproduct-derived component, and a part or all of the slurry. is passed through a specific gravity separator to remove solid byproduct-derived components and a separation treatment to recover rare earth transition metal alloy components,
The gravity separator is a hydrocyclone ,
The reducing agent contains calcium (Ca), the calcium (Ca) content of the rare earth transition metal magnet powder is 0.1% by mass or less, and the amount of the product after the separation treatment relative to the amount of the product before the separation treatment. A method in which the recovery rate, which is the ratio of , is 80% by mass or more. 2. The method according to claim 1, wherein in the wet treatment step, the slurry is allowed to stand to obtain a supernatant liquid containing mainly solid by-product-derived components, and the obtained supernatant liquid is passed through a gravity separator. 3. The method according to claim 1 or 2, wherein in the wet treatment step, a series of slurrying treatment and separation treatment are repeated multiple times. The liquid cyclone has a cyclone body that has a tapered shape with a smaller diameter toward the bottom, an inlet provided in the upper side wall of the cyclone body, and a lower outlet provided at the bottom of the cyclone body. , and an upper outlet provided in the upper center of the cyclone body,
In the wet treatment step, the product and water are put into a treatment vessel to obtain a slurry, and the slurry is allowed to stand to obtain a supernatant liquid mainly containing solid by-product-derived components,
The supernatant liquid is pressurized into the inlet of the hydrocyclone, and the hydrocyclone separates the rare earth-transition metal component with a high specific gravity from the solid by-product-derived component with a low specific gravity, and the rare earth-transition metal alloy component is removed from the lower outlet. While discharging as a flow liquid, solid by-product-derived components are discharged and removed from the upper outlet as an overflow liquid, and the discharged underflow liquid is introduced into the processing vessel to recover the rare earth transition metal alloy component. , the method according to any one of claims 1 to 3 . 5. The method according to claim 4 , wherein the slurry is distributed and passed through a plurality of hydrocyclones connected in parallel during the separation process. 5. The method according to claim 4 , wherein the slurry is sequentially passed through a plurality of hydrocyclones connected in series during the separation process. 7. The method of claim 6 , wherein the slurry is passed sequentially from larger diameter hydrocyclones to smaller diameter hydrocyclones. A method according to any one of claims 1 to 7 , wherein the product is further pickled during said wet treatment step. A method according to any one of claims 1 to 8 , comprising maintaining the product in a hydrogen pressurized atmosphere between said reduction diffusion step and said wet treatment step. The method according to any one of claims 1 to 9 , further comprising a step of nitriding the product after said reduction diffusion step.

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