Rare earth metal spherical particles and preparation method and application thereof

Abstract

The invention discloses rare earth metal spherical particles and a preparation method and application thereof. The preparation method of the rare earth metal spherical particles comprises the following steps that a plasma rotating electrode atomization method is adopted for a base material to prepare the rare earth metal spherical particles, the base material comprises one or more kinds of rare earth metal, and the mass percentage content of the rare earth metal in the base material is larger than or equal to 10%; according to parameter setting of the plasma rotating electrode atomization method, the rotating speed of the base material ranges from 500 rpm to 30000 rpm; and the working current is 300A to 4000A. The preparation method is simple and rapid in process and low in cost, and the prepared spherical particles are regular in size and high in yield.

Description

Technical Field

[0001] The present invention specifically relates to rare earth metal spherical particles, a preparation method thereof, and applications thereof. Background Art

[0002] Magnetic refrigeration technology is a new type of solid-state refrigeration technology based on the magnetocaloric effect of magnetic materials, which has the advantages of high efficiency, energy saving, environmental friendliness, and strong reliability, and can be used in fields such as cryophysics, medical equipment, and household appliances. However, there are still some technical problems in the preparation, processing, and use of magnetic refrigeration working fluid materials. For example, a high-speed and efficient heat transfer / heat exchange process requires materials to have a high specific surface area and heat exchange area, and the materials need to be processed into shapes such as microspheres or thin plates. The material purity should be high, and the recycled use should have high stability and a long service life. Therefore, it is necessary to develop an effective method for preparing and processing magnetic refrigeration materials to solve problems such as high forming and processing difficulties, low stability, and short service life while maintaining excellent magnetocaloric effects and heat transfer / heat exchange effects.

[0003] Rare earth metal spherical particles are an important material. Due to their excellent physical and chemical properties, such as high melting point, high hardness, high strength, and high corrosion resistance, these properties enable rare earth metals and alloy balls to be widely used in fields such as aerospace, automobiles, electronics, and medicine.

[0004] In the prior art, the preparation methods of rare earth metal spherical particles mainly include mechanical methods, chemical methods, physical methods, etc. These methods have some problems and defects. For example, the rare earth metal spherical particles prepared by mechanical methods have irregular shapes and uneven size distributions; a large amount of organic solvents and toxic substances need to be used in the chemical preparation process, causing environmental pollution; expensive equipment and materials need to be used in the physical preparation process, resulting in high costs.

[0005] The plasma rotating electrode atomization method (PREP method) is a metal powder preparation method based on the principle of high-speed rotation and centrifugal atomization of electrode rod materials. This method can prepare metal powders with low oxygen content, no adhesion, and high sphericity. Using the plasma rotating electrode atomization method to prepare rare earth metal and its alloy spherical working fluid materials required for magnetic refrigeration technology has excellent magnetocaloric effects, high specific surface areas, and high heat exchange effects, and at the same time solves problems such as high forming and processing difficulties, poor material stability, and short cycle service life.

[0006] However, there are many influencing factors in the process of preparing metal powders by the plasma rotating electrode atomization method. How to reasonably design parameters to prepare rare earth metal spherical particles with regular shapes and uniform sizes through a simple preparation process and low costs is an urgent problem to be solved. Summary of the Invention

[0007] In order to overcome the defect of uncontrollable particle size in the process of preparing metal powder by the plasma rotating electrode atomization method in the prior art, the present invention provides rare earth metal spherical particles, a preparation method thereof and an application. The preparation method of the present invention has a simple, fast and low-cost process, and the obtained spherical particles have regular sizes, controllable particle diameters and high yields.

[0008] The particle size and yield of rare earth metal spherical particles are affected by many factors, such as the diameter of the substrate, the gas flow pressure and temperature of the plasma gun head, the feeding speed of the substrate, as well as the rotation speed of the plasma rotating atomization equipment, the quality of the substrate, the stability of the gas flow of the plasma gun head, the design of the collector, the oxygen content in the equipment, the consumption of the substrate, the gas flow direction of the plasma gun head, and the efficiency of the collector. Among these many factors, to solve the technical problems of the present invention, through a large amount of creative work by researchers, by reasonably designing parameters, the preparation of rare earth metal spherical particles with controllable sizes, high purity and high yields has been achieved.

[0009] The present invention provides a method for preparing rare earth metal spherical particles, which comprises the following steps: preparing rare earth metal spherical particles from a substrate by the plasma rotating electrode atomization method, wherein,

[0010] the substrate comprises one or more rare earth metals, and the mass percentage content of the rare earth metals in the substrate is ≥ 10%;

[0011] The parameter settings of the plasma rotating electrode atomization method include: the rotation speed of the substrate is 500 rpm - 30000 rpm, and the working current is 300 A - 4000 A.

[0012] In the present invention, the working current is the total current of the plasma rotating electrode atomization equipment during operation.

[0013] In the present invention, the working current can vary along the radial direction of the cross-section of the substrate.

[0014] In some embodiments, at the central position of the cross-section of the substrate, the working current can be 500 A - 2800 A, such as 600 A, 1300 A, 1400 A, 1800 A or 2600 A.

[0015] In some embodiments, at the position one-fourth of the diameter of the cross-section of the substrate, the working current is 300 A - 3000 A, such as 400 A, 600 A, 700 A, 900 A or 1200 A. In the present invention, the "position one-fourth of the diameter of the cross-section" starts from the edge of the cross-section.

[0016] In the present invention, the rotational speed of the substrate can be 1000 rpm - 30000 rpm, such as 1500 rpm, 2500 rpm, 4000 rpm, 12000 rpm or 26000 rpm.

[0017] In the present invention, the feed rate of the substrate can be 1 - 10 mm / s, preferably 1 - 5 mm / s, such as 1.5 mm / s.

[0018] In the present invention, the mass percentage of the rare earth metal in the substrate can be ≥25%.

[0019] In the present invention, the relative purity of the rare earth metal can be ≥99 wt%, preferably ≥99.5 wt%.

[0020] In the present invention, the substrate is a rare earth metal; the rare earth metal is one or more of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).

[0021] In some specific embodiments, the substrate is lanthanum, gadolinium, terbium, erbium, "lanthanum and cerium" or "praseodymium and neodymium".

[0022] In some specific embodiments, the substrate is lanthanum and cerium, the mass percentage of lanthanum is 0 - 100%, and is not 0 or 100%, the mass percentage of cerium is 0 - 100%, and is not 0 or 100%; for example, the mass percentage of lanthanum is 70%, the mass percentage of cerium is 30%, and the percentage is the mass percentage of each rare earth metal in the total mass of the substrate.

[0023] In some specific embodiments, the substrate is praseodymium and neodymium, the mass percentage of praseodymium is 0 - 100%, and is not 0 or 100%, the mass percentage of neodymium is 0 - 100%, and is not 0 or 100%; for example, the mass percentage of praseodymium is 20%, the mass percentage of neodymium is 80%, and the percentage is the mass percentage of each rare earth metal in the total mass of the substrate.

[0024] In the present invention, the substrate can also be an alloy comprising a rare earth metal and a transition group element; the transition group element is preferably one or more of iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), titanium (Ti), vanadium (V) and chromium (Cr).

[0025] In some embodiments, the substrate is an alloy comprising a rare earth metal, a transition group element and a silicon element. For example, the substrate is an alloy comprising lanthanum, iron and silicon.

[0026] In some embodiments, the substrate is an alloy comprising a rare earth metal, a transition element, and an aluminum element. For example, the substrate is an alloy comprising lanthanum, iron, and aluminum.

[0027] In the present invention, the substrate may also be an alloy comprising a rare earth metal and a Group IVA element; the Group IVA element is preferably one or more of silicon, germanium, and tin.

[0028] In the present invention, the substrate can be commercially obtained or prepared by conventional methods in the art; the preparation method may include the following steps: melting the raw materials and casting them into an ingot, and then machining the ingot to obtain the desired size and shape. The substrate is placed as an electrode in a plasma rotating electrode atomization device during the preparation process.

[0029] Among them, the melting preparation method can be a vacuum intermediate frequency induction melting preparation process.

[0030] Among them, the casting mold can be a copper mold or a cast iron mold; the shape of the mold can be selected according to requirements, such as square or cylindrical.

[0031] In the present invention, the shape of the substrate can be a shape suitable for a plasma rotating electrode atomization device, preferably a rod; the diameter of the rod is preferably 5 mm - 150 mm, more preferably 20 mm - 80 mm, such as 30 mm, 50 mm, or 75 mm; the rod is preferably also thread - processed.

[0032] In the present invention, the surface roughness Ra of the substrate is ≤ 1.6 μm.

[0033] In the present invention, according to the cooperation requirements of the feeding mechanism, corresponding threads can be processed on a part of the substrate.

[0034] In the present invention, the plasma rotating electrode atomization device used in the plasma rotating electrode atomization method includes an electrode rotating and its sealing device, a pushing device, a plasma gun head, an atomization chamber, an inert gas environment, and a collector.

[0035] Among them, the rotating device is used to rotate the substrate at a certain speed, and by the action of centrifugal force, the melted droplets naturally form spherical particles during the flight in the air. The rotating device also includes a sealing device, and the sealing device can ensure that the electrode can rotate at a high speed, with smooth feeding, and at the same time ensure the sealing effect of the cavity.

[0036] Among them, the plasma gun head melts and splashes out a part of the surface of the substrate by its own high temperature to form spherical droplets. The cross-section of the substrate corresponding to the center of the plasma gun head is continuously adjustable from the center of the circle to the edge position. For example, the center of the plasma gun head corresponds to the center position of the cross-section of the substrate or the position of one-fourth of the diameter of the cross-section of the substrate corresponding to the center of the plasma gun head. When the position of the plasma gun head corresponding to the cross-section of the substrate is different, the required current size is different. When the center of the plasma gun head corresponds to the center of the cross-section of the substrate, the arc flame needs to cover the entire cross-section of the substrate, so a larger current is required; when the center of the plasma gun head corresponds to the position of one-fourth of the diameter of the cross-section of the substrate, only the arc flame needs to cover the cross-section of one-fourth of the radius, and a smaller current is required, but it is necessary to ensure that the flame temperature can melt.

[0037] An arc is continuously generated by the discharge between the plasma gun head and the substrate. The arc and the high temperature generated by the arc melt the end face part of the substrate and splash out with the rotation of the electrode to form spherical droplets, and naturally cool into spherical particles during the flight; as the electrode rotates, the end face melts, the droplets splash, and the feeding device continuously feeds, so that the atomization process continues. For the sake of protecting the equipment device, the rod electrode will not be completely consumed, and the atomization stops when a section of the stock head remains.

[0038] Among them, the feeding device is used to feed the substrate into the equipment cavity at a certain feeding speed, form a continuous arc with the plasma gun head and be in the air flow of the arc. The feeding device can be single-piece feeding or a continuous feeding device, and continuous feeding can be achieved through the threaded connection of the bar.

[0039] Among them, the shape of the collector is preferably cylindrical or conical; the width of the chamber of the collector is preferably 100 - 2000 mm; the diameter of the chamber is preferably 1000 - 4000 mm; the inner wall of the collector is preferably made of a non-sticky material; an outlet is provided at its bottom for collecting spherical rare earth metal particles.

[0040] In the present invention, the vacuum degree in the atomization chamber is < 1×10 -2 Pa.

[0041] In the present invention, the oxygen content in the atomization chamber is < 50 ppm, preferably < 5 ppm.

[0042] In the present invention, the preparation can be carried out in an inert gas environment. The inert gas environment is beneficial to arc ignition. The spherical droplets fly and solidify in the inert gas environment. The inert gas environment can protect the spherical droplets from being oxidized. At the same time, through the heat transfer and heat exchange of the inert gas, the speed of solidifying into balls during the flight of the droplets is accelerated, the flight distance is shortened, and spherical rare earth metal particles are formed. The inert gas environment is beneficial to reducing the volume, weight and cost of the equipment.

[0043] Among them, the oxygen content in the inert gas environment is preferably < 10 ppm.

[0044] Among them, the pressure of the inert gas environment is preferably maintained at 0.05 MPa - 0.5 MPa; more preferably 0.1 MPa - 0.3 MPa, such as 0.12 MPa. The pressure of the inert gas environment refers to the pressure of filling the inert gas in the atomization chamber, which will affect the formation and solidification of metal droplets during atomization, and thus affect the morphology and properties of the powder. Generally speaking, the higher the pressure, the better the atomization effect, and the better the indexes such as the sphericity, purity, and oxygen content of the powder. However, the pressure cannot be too high, otherwise the particle size of the powder will be too small and the yield of fine powder will decrease.

[0045] Among them, the inert gas is preferably argon and / or helium.

[0046] In the present invention, the center of the plasma gun head can correspond to any position of the cross-section of the substrate, such as the center position of the cross-section of the substrate or the position of one-fourth of the diameter of the cross-section of the substrate.

[0047] In some specific embodiments, the center of the plasma gun head corresponds to the center position of the cross-section of the substrate, the diameter of the substrate is 50 - 80 mm, the rotation speed of the substrate is 20000 rpm - 30000 rpm, the working current is 2000 A - 3000 A, and the D 50 average particle size of the rare earth metal spherical particles is 10 μm - 100 μm.

[0048] In some specific embodiments, the center of the plasma gun head corresponds to the position of one-fourth of the diameter of the cross-section of the substrate, the diameter of the substrate is 50 - 80 mm, the rotation speed of the substrate is 20000 rpm - 30000 rpm, the working current is 1000 A - 1500 A; the D 50 average particle size of the rare earth metal spherical particles is 10 μm - 100 μm

[0049] In some specific embodiments, the center of the plasma gun head corresponds to the center position of the cross-section of the substrate, the rotation speed of the substrate is 10000 rpm - 20000 rpm; the working current is 1500 A - 3000 A; the D 50 average particle size of the rare earth metal spherical particles is 100 μm - 300 μm.

[0050] In some specific embodiments, the center of the plasma gun head corresponds to the position of one-fourth of the diameter of the cross-section of the substrate, the rotation speed of the substrate is 10000 rpm - 20000 rpm; the working current is 800 A - 1500 A, and the D 50The average particle size is 100 μm - 300 μm.

[0051] In some specific embodiments, the center of the plasma gun head corresponds to the center position of the cross-section of the substrate, and the rotation speed of the substrate is 2000 rpm - 10000 rpm; the working current is 1000 A - 3000 A, and the D of the rare earth metal spherical particles 50 The average particle size is 300 μm - 800 μm.

[0052] In some specific embodiments, the center of the plasma gun head corresponds to the one-fourth diameter position of the cross-section of the substrate, and the rotation speed of the substrate is 2000 rpm - 10000 rpm; the working current is 500 A - 1500 A; the D of the rare earth metal spherical particles 50 The average particle size is 300 μm - 800 μm.

[0053] In some specific embodiments, the center of the plasma gun head corresponds to the center position of the cross-section of the substrate, and the rotation speed of the substrate is 500 - 2000 rpm; the working current is 1000 - 3000 A; the D of the rare earth metal spherical particles 50 The average particle size is above 800 μm.

[0054] In some specific embodiments, the center of the plasma gun head corresponds to the one-fourth diameter position of the cross-section of the substrate, the rotation speed of the substrate is 500 - 2000 rpm, and the working current is 500 A - 1500 A. The D of the rare earth metal spherical particles 50 The average particle size is 800 μm - 1000 μm.

[0055] The present invention also provides rare earth metal spherical particles prepared by the preparation method as described above.

[0056] In the present invention, the average particle size of the rare earth metal spherical particles can be 10 μm - 1000 μm, such as 32 μm, 114 μm, 324 μm, 509 μm or 980 μm.

[0057] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention.

[0058] The reagents and raw materials used in the present invention are all commercially available.

[0059] The positive and progressive effects of the present invention are as follows:

[0060] The present invention provides a new method for preparing spherical particles of rare earth metals and alloys. This method has a simple process, without the need for complex equipment and operations; the prepared spherical rare earth metal particles have a smooth surface and no obvious defects; the product yield is high, reaching over 75%, without the need for additional separation and purification operations; the particle size is controllable and the distribution is uniform, and the particle size of the spherical rare earth metal particles can be controlled by adjusting the parameters of the plasma rotating atomization equipment to meet different application requirements, and it can be widely applied in the fields of aerospace, automotive, electronics, medical treatment, etc.

[0061] In some preferred embodiments, the prepared gadolinium alloy particles not only have the advantages of controllable and uniform particle size, smooth surface without defects and high yield, but also have good magnetocaloric properties. Brief Description of the Drawings

[0062] Figure 1 Photographs of the gadolinium metal rod before and after threading for Example 4 (Figure A is before threading; Figure B is after threading).

[0063] Figure 2 Physical diagram of the gadolinium spherical particles prepared in Example 4.

[0064] Figure 3 Metallographic picture of the gadolinium spherical particles prepared in Example 4.

[0065] Figure 4 Metallographic picture of the gadolinium spherical particles prepared in Example 4.

[0066] Figure 5 Particle size distribution diagram of the gadolinium spherical particles prepared in Example 4.

[0067] Figure 6 Measured result of the temperature difference between the hot and cold ends after the gadolinium spherical particles prepared in Example 4 are operated on a magnetic refrigeration prototype.

[0068] Figure 7 Sphericity of the gadolinium spherical particles prepared in Example 4. Detailed Description of the Embodiments

[0069] The present invention will be further illustrated by the following examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0070] In step (2) of the following Examples 1 - 9, first, the ingot is prepared into a rod-like structure, then it is machined to form a threaded rod, and then the subsequent processes are carried out. Taking Example 4 as an example, the rod-like structure without threads prepared before machining is as shown in Figure A in Figure 1 and the threaded rod prepared after machining is as shown inFigure 1 as shown in Figure B of

[0071] Example 1

[0072] Preparation of spherical particles of rare earth metal lanthanum (La) includes the following steps:

[0073] (1) Using a vacuum induction melting and casting method to prepare a metal lanthanum ingot from lanthanum raw materials with a relative purity of over 99 wt%. The casting mold is a cast iron mold, and the mold shape can be selected as a cylindrical shape according to actual size requirements;

[0074] (2) Machining the ingot into a metal lanthanum rod with a diameter of 30 mm through mechanical processing, and the surface roughness Ra is not greater than 1.6 μm;

[0075] (3) Fixing the metal lanthanum rod to the rotating device of a plasma rotating electrode device as an electrode, aligning the center position of the cross-section at one end of the rod with the center of the plasma gun head. The sealing device of the electrode not only ensures the high-speed rotation function, but also enables smooth feeding and ensures a good sealing effect;

[0076] (4) Evacuating the chamber of the plasma rotating electrode device, with the vacuum degree below 1×10 -2 Pa. Monitoring the oxygen content in the chamber to ensure that the oxygen content in the chamber is less than or equal to 5 ppm;

[0077] (5) Closing the valve between the vacuum pump and the chamber, opening the valve of the inert gas, and filling the vacuum chamber of the plasma rotating electrode device with high-purity argon gas to keep the air pressure in the chamber at 0.12 MPa;

[0078] (6) Turning on the power supply and adjusting the parameters of the plasma rotating electrode device. The feeding speed of the rod is 1.5 mm / s; the rotation speed of the rotating device is 26,000 rpm; the working current of the device is 600 A;

[0079] (7) After the plasma gun head and the electrode are arced, spraying a plasma gas flow from the plasma gun onto the metal lanthanum rod electrode to melt the end face part of the metal rod and splash it out with the rotation of the electrode to form droplets of metal lanthanum;

[0080] (8) Making the droplets naturally form spheres during flight through the centrifugal force of the rotating device and the surface tension of the droplets. The electrode rotates while the end face melts and the droplets splash, and the feeding device continuously feeds to make the atomization process continue;

[0081] (9) Rapidly solidifying the droplets during flight through the cooling effect of the inert gas to form metal lanthanum spheres. The inert gas also helps with arcing;

[0082] (10) Collecting the metal lanthanum spheres through a collector.

[0083] The lanthanum spherical particles prepared in this example have high sphericity, a smooth surface, no obvious defects, controllable particle size and uniform distribution, D50 is 32 μm, the yield is 77 wt %, and the purity of the lanthanum spherical particles is ≥99.5%.

[0084] Example 2

[0085] Rare earth metal alloy La 0.7 Ce 0.3 The preparation of spherical particles comprises the following steps:

[0086] (1) preparing lanthanum and cerium raw materials with a relative purity of more than 99 wt% in a mass ratio of 7:3, and preparing a lanthanum-cerium alloy ingot by vacuum induction melting and casting. The casting mold is a cast iron mold, and the mold shape can be cylindrical according to actual size requirements;

[0087] (2) machining the ingot into a lanthanum-cerium alloy rod with a diameter of 50 mm and a surface roughness Ra of no more than 1.6 μm;

[0088] (3) Fixing the lanthanum-cerium alloy rod to the rotating device of the plasma rotating electrode equipment as an electrode, aligning the center position of the cross section of one end of the alloy rod with the center of the plasma gun head, and the sealing device of the electrode not only ensures the high-speed rotation function, but also makes the feeding smooth and ensures a good sealing effect;

[0089] (4) Evacuate the chamber of the plasma rotating electrode equipment to a vacuum degree of 1*10 -2 Pa, monitor the oxygen content in the chamber to ensure that the oxygen content in the chamber is less than or equal to 5ppm;

[0090] (5) Close the valve between the vacuum pump and the chamber, open the inert gas valve, and fill the vacuum chamber of the plasma rotating electrode equipment with high-purity argon gas to maintain the gas pressure in the chamber at 0.12 MPa;

[0091] (6) Turn on the power and adjust the parameters of the plasma rotating electrode equipment. The feeding speed of the rod is 1.5 mm / s, the speed of the rotating device is 12000 rpm; the working current of the equipment is 1800 A;

[0092] (7) After the plasma gun head and the electrode strike an arc, a plasma gas flow is sprayed toward the lanthanum-cerium alloy rod electrode through the plasma gun, so that the end surface of the alloy rod partially melts and splashes out with the rotation of the electrode to form droplets of lanthanum-cerium alloy;

[0093] (8) The centrifugal force of the rotating device and the surface tension of the droplets make the droplets naturally form a spherical shape during the flight process. The electrode rotates while the end surface melts and the droplets splash. The pushing device continuously feeds, so that the atomization process continues;

[0094] (9) The droplets are rapidly solidified during flight through the cooling effect of the inert gas to form lanthanum-cerium alloy spheres, and the inert gas also helps to initiate the arc;

[0095] (10) The lanthanum-cerium alloy spherical particles are collected by a collector.

[0096] The spherical lanthanum-cerium alloy particles prepared in this example have a high sphericity, a smooth surface, no obvious defects, a controllable particle size and a uniform distribution. The D50 is 114 μm, the yield of the spherical lanthanum-cerium alloy particles is 78 wt%, and the purity is above 99.5%.

[0097] Example 3

[0098] Metal alloy Pr 0.2 Nd 0.8 Preparation of spherical particles includes the following steps:

[0099] (1) Praseodymium and neodymium raw materials with a relative purity of more than 99 wt% are proportioned according to a mass ratio of 2:8, and a praseodymium-neodymium alloy ingot is prepared by vacuum induction melting and casting. The casting mold is a cast iron mold, and the mold shape can be selected as a cylindrical shape according to actual size requirements;

[0100] (2) The ingot is machined into a praseodymium-neodymium alloy rod with a diameter of 75 mm by mechanical processing, and the surface roughness Ra is not more than 1.6 μm;

[0101] (3) The praseodymium-neodymium alloy rod is fixed to the rotating device of the plasma rotating electrode equipment as an electrode, so that the center position of one end cross-section of the alloy rod is aligned with the center of the plasma gun head. The sealing device of the electrode not only ensures the high-speed rotation function, but also makes the feeding smooth and ensures a good sealing effect;

[0102] (4) The chamber of the plasma rotating electrode equipment is evacuated to a vacuum degree of below 1*10 -2 Pa, and the oxygen content in the chamber is monitored to ensure that the oxygen content in the chamber is less than or equal to 5 ppm;

[0103] (5) The valve between the vacuum pump and the chamber is closed, the valve of the inert gas is opened, and high-purity argon is filled into the vacuum chamber of the plasma rotating electrode equipment to keep the air pressure in the chamber at 0.12 MPa;

[0104] (6) The power is turned on, and the parameters of the plasma rotating electrode equipment are adjusted. The feeding speed of the rod is 1.5 mm / s, the rotation speed of the rotating device is 4000 rpm; the working current of the equipment is 2600 A;

[0105] (7) After the plasma gun head and the electrode are arced, a plasma gas stream is sprayed from the plasma gun onto the praseodymium-neodymium alloy rod electrode, melting the end face part of the alloy rod and splashing it out with the rotation of the electrode to form praseodymium-neodymium alloy droplets;

[0106] (8) The droplets naturally form spheres during flight due to the centrifugal force of the rotating device and the surface tension of the droplets. As the electrode rotates, its end face melts, the droplets splash, and the feeding device continuously feeds, enabling the atomization process to continue.

[0107] (9) The droplets rapidly solidify during flight through the cooling effect of the inert gas, forming praseodymium-neodymium alloy spheres. The inert gas also helps to initiate the arc.

[0108] (10) The praseodymium-neodymium alloy spherical particles are collected by a collector.

[0109] The praseodymium-neodymium alloy spherical particles prepared in this example have a high sphericity, a smooth surface, no obvious defects, a controllable particle size and a uniform particle size distribution, with D50 being 324 μm. The recovery rate of the praseodymium-neodymium alloy spherical particles is 78 wt%, and the purity is above 99.5%.

[0110] Example 4

[0111] Preparation of spherical particles of rare earth metal gadolinium (Gd), including the following steps:

[0112] (1) The raw material of gadolinium metal with a relative purity of more than 99 wt% is proportioned, and a gadolinium metal ingot is prepared by vacuum induction melting and casting. The casting mold is a cast iron mold, and the mold shape can be selected as a cylindrical shape according to actual size requirements.

[0113] (2) The ingot is machined into a gadolinium metal rod with a diameter of 50 mm by mechanical processing, and the surface roughness Ra is not greater than 1.6 μm.

[0114] (3) The gadolinium metal rod is fixed to the rotating device of the plasma rotating electrode equipment as an electrode, so that the center position of one end cross-section of the rod is aligned with the center of the plasma gun head. The sealing device of the electrode not only ensures the high-speed rotation function, but also enables smooth feeding and ensures good sealing effect.

[0115] (4) The chamber of the plasma rotating electrode equipment is evacuated, and the vacuum degree reaches below 1×10 -2 Pa. The oxygen content in the chamber is monitored to ensure that the oxygen content in the chamber is less than or equal to 5 ppm.

[0116] (5) The valve between the vacuum pump and the chamber is closed, the valve of the inert gas is opened, and high-purity argon is filled into the vacuum chamber of the plasma rotating electrode equipment to keep the air pressure in the chamber at 0.12 MPa.

[0117] (6) The power is turned on, and the parameters of the plasma rotating electrode equipment are adjusted. The feeding speed of the rod is 1.5 mm / s, the rotation speed of the rotating device is 2500 rpm, and the working current of the equipment is 1400 A.

[0118] (7) After the plasma gun head and the electrode generate an arc, a plasma gas flow is sprayed onto the gadolinium metal rod through the plasma gun, melting the end face part of the metal rod and splashing it out with the rotation of the electrode to form droplets of gadolinium metal;

[0119] (8) Due to the centrifugal force of the rotating device and the surface tension of the droplets, the droplets naturally form spheres during flight. The electrode rotates while its end face melts, and the droplets splash while the feeding device continuously feeds, enabling the atomization process to continue;

[0120] (9) The droplets are rapidly solidified during flight through the cooling effect of the inert gas to form gadolinium metal spheres. The inert gas also helps to generate an arc;

[0121] (10) The gadolinium spherical particles are collected by a collector.

[0122] The physical picture of the gadolinium spherical particles prepared in this embodiment is as shown in Figure 2 shown, and the metallographic picture is as shown in Figure 3 and Figure 4 shown. The sphericity data is as shown in Figure 7 shown. It can be seen from Figure 7 that 95% of the particles have a sphericity greater than 0.9, indicating that the spherical particles prepared by the present invention have a high sphericity. Through the characterization of the above pictures, it can be seen that the gadolinium spherical particles prepared in this embodiment have a high sphericity, a smooth surface, and no obvious defects; Figure 5 The particle size distribution diagram of the gadolinium spherical particles prepared in Example 4 is as shown. It can be seen that D50 is 509 μm, the particle size is controllable and the distribution is uniform. The yield of the gadolinium spherical particles is 79 wt%, and the purity is above 99.5%.

[0123] In addition, the gadolinium spherical particles prepared in this embodiment are also operated on a magnetic refrigeration prototype to test the temperature difference between the hot and cold ends. The results are as shown in Figure 6 shown. As a magnetic refrigeration working medium, the gadolinium spherical particles in this embodiment reach a temperature span of 18.3 °C between the hot and cold ends under the condition that the initial temperature is 20 °C. The relatively high temperature span indicates that the rare earth metal particles prepared by the preparation method of the present invention have high intrinsic properties, good heat exchange and heat transfer performance, and good performance under actual working conditions.

[0124] Example 5

[0125] Preparation of spherical particles of rare earth metal terbium (Tb), including the following steps:

[0126] (1) The raw material of metal terbium with a relative purity of more than 99 wt% is proportioned, and a metal terbium ingot is prepared by vacuum induction melting and casting. The casting mold is selected as a cast iron mold, and the mold shape can be selected as a cylindrical shape according to actual size requirements;

[0127] (2) The ingot is machined into a terbium metal rod with a diameter of 50 mm by mechanical processing, and the surface roughness Ra is not greater than 1.6 μm;

[0128] (3) The terbium metal rod is fixed to the rotating device of the plasma rotating electrode equipment as an electrode, so that the center position of the cross-section of one end of the rod is aligned with the center of the plasma gun head. The sealing device of the electrode not only ensures the high-speed rotation function, but also makes the feeding smooth and ensures a good sealing effect;

[0129] (4) The chamber of the plasma rotating electrode equipment is evacuated, and the vacuum degree is below 1×10 -2 Pa. The oxygen content in the chamber is monitored to ensure that the oxygen content in the chamber is less than or equal to 5 ppm;

[0130] (5) Close the valve between the vacuum pump and the chamber, open the valve of the inert gas, and fill the vacuum chamber of the plasma rotating electrode equipment with high-purity argon gas to keep the air pressure in the chamber at 0.12 MPa;

[0131] (6) Turn on the power supply and adjust the parameters of the plasma rotating electrode equipment. The feeding speed of the rod is 1.5 mm / s, the rotation speed of the rotating device is 1500 rpm; the working current of the equipment is 1300 A;

[0132] (7) After the plasma gun head and the electrode are arced, a plasma gas stream is sprayed onto the terbium metal rod through the plasma gun, so that the end face part of the metal rod melts and splashes out with the rotation of the electrode, forming droplets of terbium metal;

[0133] (8) Due to the centrifugal force of the rotating device and the surface tension of the droplets, the droplets naturally form spherical shapes during flight. The electrode rotates, the end face melts, the droplets splash, and the feeding device continuously feeds, so that the atomization process continues;

[0134] (9) The droplets are rapidly solidified during flight through the cooling effect of the inert gas to form terbium metal spheres. The inert gas also helps to initiate the arc;

[0135] (10) The terbium spherical particles are collected by a collector.

[0136] The terbium spherical particles prepared in this example have a high sphericity, a smooth surface, no obvious defects, controllable particle size and uniform distribution, and D50 is 980 μm. The yield of the terbium spherical particles is 78 wt%, and the purity is above 99.5%.

[0137] Example 6

[0138] Compared with Example 4, the difference is only that the position of the plasma gun head corresponding to the cross-section of the rod is adjusted, so that the center of the plasma gun head is aligned with the quarter position of the diameter of the cross-section of the rod, and the working current of the equipment is correspondingly adjusted to 700 A.

[0139] Example 7

[0140] Compared with Example 5, the only difference is that the position of the plasma gun head corresponding to the cross-section of the bar is adjusted so that the center of the plasma gun head is aligned with the quarter position of the diameter of the cross-section of the bar, and the working current of the corresponding adjustment equipment is 600A.

[0141] Example 8

[0142] Compared with Example 4, the only difference is that the rotation speed is 500 rpm.

[0143] Example 9

[0144] Compared with Example 4, the only difference is that the feed rate is 6 mm / s.

[0145] Table 1

[0146]

[0147] Table 2

[0148]

[0149]

[0150] Effect Example

[0151] (1) Test method for yield

[0152] Yield of rare earth metal and its alloy balls = total mass of rare earth metal and its alloy balls / mass of base material.

[0153] (2) Test method for magnetothermal performance

[0154] The test method is active regenerative, and the conditions are an ambient temperature of 20 °C. After starting up and running, the thermocouples arranged at the hot and cold ends directly measure the real-time temperature values at the hot and cold ends. The temperature difference between the hot and cold ends refers to the hot end temperature minus the cold end temperature.

[0155] The preparation method of the present invention can select different rotation speeds and feed rates according to the required particle size in the application process, and cooperate with the selection of materials. The prepared rare earth metal spherical particles have high purity, good sphericity and a yield of more than 75%. Good sphericity, purity and appropriate particle size can make the heat exchange more sufficient, which is conducive to obtaining a larger refrigeration temperature difference.

[0156] In Examples 1-5, rare earth metal spherical particles with different particle sizes were prepared by using different rare earth metals, setting different rotation speeds and feed rates, and cooperating with specific working currents.

[0157] The above are only several embodiments of the present invention and do not impose any form of limitation on the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention shall be covered within the protection scope of the present invention.

Claims

1. A method for preparing rare earth metal spherical particles, characterized in that, Prepare spherical rare earth metal particles on a substrate by the plasma rotating electrode atomization method, wherein, The substrate includes one or more rare earth metals, and the mass percentage of the rare earth metal in the substrate is ≥10%; The parameter settings of the plasma rotating electrode atomization method include: the rotation speed of the substrate is 500 rpm - 30,000 rpm, and the working current is 300 A - 4,000 A.

2. The method for preparing rare earth metal spherical particles according to claim 1, wherein The rotation speed of the substrate is 1,000 rpm - 30,000 rpm, such as 1,500 rpm, 2,500 rpm, 4,000 rpm, 12,000 rpm or 26,000 rpm; And / or, the working current varies in the radial direction of the cross-section of the substrate. Preferably, at the central position of the cross-section of the substrate, the working current is 500 A - 2,800 A, such as 600 A, 1,300 A, 1,400 A, 1,800 A or 2,600 A; at the one-quarter diameter position of the cross-section of the substrate, the working current is 300 - 3,000 A, such as 400 A, 600 A, 700 A, 900 A or 1,200 A; And / or, the feeding speed of the substrate is 1 - 10 mm / s, preferably 1 - 5 mm / s, such as 1.5 mm / s; And / or, the mass percentage of the rare earth metal in the substrate is ≥25%; And / or, the relative purity of the rare earth metal is ≥99%, preferably ≥99.5%.

3. The method for preparing rare earth metal spherical particles according to claim 1, wherein, The substrate is a rare earth metal, and the substrate is preferably lanthanum, gadolinium, terbium, erbium, "lanthanum and cerium" or "praseodymium and neodymium"; Optionally, the substrate is lanthanum and cerium, the mass percentage of lanthanum is 0 - 100% and is not 0 or 100%, the mass percentage of cerium is 0 - 100% and is not 0 or 100%; for example, the mass percentage of lanthanum is 70%, and the mass percentage of cerium is 30%. The percentage is the percentage of the mass of each rare earth metal in the total mass of the substrate; Optionally, the substrate is praseodymium and neodymium, the mass percentage of praseodymium is 0 - 100% and is not 0 or 100%, the mass percentage of neodymium is 0 - 100% and is not 0 or 100%; for example, the mass percentage of praseodymium is 20%, and the mass percentage of neodymium is 80%. The percentage is the percentage of the mass of each rare earth metal in the total mass of the substrate.

4. The preparation method of the rare earth metal spherical particles according to claim 1, characterized in that, The substrate is an alloy including rare earth metals and transition group elements; the transition group elements are preferably one or more of iron, manganese, cobalt, nickel, copper, titanium, vanadium and chromium; Or, the substrate is an alloy including rare earth metals and Group IVA elements; the Group IVA elements are preferably one or more of silicon, germanium and tin.

5. The preparation method of the rare earth metal spherical particles according to claim 1, characterized in that, The shape of the substrate is a bar; the diameter of the bar is preferably 5 mm - 150 mm, more preferably 20 mm - 80 mm, such as 30 mm, 50 mm or 75 mm; the bar is preferably also processed with threads; And / or, the surface roughness Ra of the substrate ≤1.6 μm.

6. The method for preparing rare earth metal spherical particles according to claim 1, characterized in that, The plasma rotating electrode atomization method satisfies one or more of the following conditions a - d: a. The plasma rotating electrode atomization equipment used in the plasma rotating electrode atomization method includes an electrode rotation and its sealing device, a feeding device, a plasma gun head, an atomization chamber, an inert gas environment, and a collector; wherein, the chamber of the collector is preferably circular or conical; the width of the chamber of the collector is preferably 100 - 2000 mm; the diameter of the chamber is preferably 1000 - 4000 mm; b. The vacuum degree in the atomization chamber is < 1×10 -2 Pa; the oxygen content in the atomization chamber is < 50 ppm, preferably < 5 ppm; c. The preparation is carried out in an inert gas environment, wherein the oxygen content in the inert gas environment is preferably < 10 ppm, and the pressure of the inert gas environment is preferably maintained at 0.05 MPa - 0.5 MPa; more preferably 0.1 MPa - 0.3 MPa, such as 0.12 MPa; the inert gas is preferably argon and / or helium; d. The center of the plasma gun head corresponds to any position of the cross-section of the substrate, such as the center position of the cross-section of the substrate or the position of one-fourth of the diameter of the cross-section of the substrate.

7. The method for preparing rare earth metal spherical particles according to claim 1, characterized in that, The preparation method of the substrate includes the following steps: melting the raw materials to obtain an ingot, and then machining the ingot; the melting method is preferably a vacuum intermediate frequency induction melting preparation process.

8. The preparation method of the rare earth metal spherical particles according to claim 1, characterized in that, The center of the plasma gun head corresponds to the center position of the cross-section of the substrate. The diameter of the substrate is 50 - 80 mm, the rotation speed of the substrate is 20000 rpm - 30000 rpm, the working current is 2000 A - 3000 A, and the D of the rare earth metal spherical particles 50 average particle size is 10 μm - 100 μm; Alternatively, the center of the plasma gun head corresponds to the position of one-fourth of the diameter of the cross-section of the substrate. The diameter of the substrate is 50 - 80 mm, the rotation speed of the substrate is 20000 rpm - 30000 rpm, and the working current is 1000 A - 1500 A; the D 50 average particle size of the rare earth metal spherical particles is 10 μm - 100 μm; Alternatively, the center of the plasma gun head corresponds to the center position of the cross-section of the substrate, and the rotational speed of the substrate is 10,000 rpm - 20,000 rpm; the working current is 1,500 A - 3,000 A; the D 50 average particle size of the rare earth metal spherical particles is 100 μm - 300 μm; Alternatively, the center of the plasma gun head corresponds to the position of one-fourth of the diameter of the cross-section of the substrate, and the rotation speed of the substrate is 10,000 rpm - 20,000 rpm; the working current is 800 A - 1500 A, and the D 50 average particle size of the rare earth metal spherical particles is 100 μm - 300 μm; Alternatively, the center of the plasma gun head corresponds to the center position of the cross-section of the substrate, and the rotational speed of the substrate is 2000 rpm - 10000 rpm; the working current is 1000 - 3000 A, and the D 50 average particle size of the rare earth metal spherical particles is 300 μm - 800 μm; Alternatively, the center of the plasma gun head corresponds to the position of one-fourth of the diameter of the cross-section of the substrate, the rotational speed of the substrate is 2000 rpm - 10000 rpm; the working current is 500 A - 1500 A; the D of the rare earth metal spherical particles 50 average particle size is 300 μm - 800 μm; Alternatively, the center of the plasma gun head corresponds to the center position of the cross-section of the substrate, the rotation speed of the substrate is 500 - 2000 rpm; the working current is 1000 - 3000 A; the D of the rare earth metal spherical particles 50 average particle size is 800 μm or more; Alternatively, the center of the plasma gun head corresponds to the position of one-fourth of the diameter of the cross-section of the substrate, the rotation speed of the substrate is 500 - 2000 rpm, and the working current is 500 A - 1500 A; the D 50 average particle size of the rare earth metal spherical particles is 800 μm - 1000 μm.

9. A rare earth metal spherical particle, characterized in that, It is obtained by the preparation method of rare earth metal spherical particles described in any one of claims 1 - 8.

10. The rare earth metal spherical particles according to claim 9, wherein, The D of the rare earth metal spherical particles 50 The average particle size is 10 μm - 1000 μm, such as 32 μm, 114 μm, 324 μm, 509 μm or 980 μm.

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