Rare earth metal magnetic refrigerants and their preparation methods

Abstract

This invention discloses a rare-earth metal magnetic refrigerant and its preparation method. The preparation method includes the following steps: smelting rare-earth metal raw materials and casting them into a mold to obtain a perforated rare-earth metal preform. The wall thickness of the perforations in the perforated rare-earth metal preform is 0.05-0.8 mm, the porosity is 30%-70%, and the pores are uniformly distributed. This invention provides a method for the large-scale, low-cost preparation of high-purity rare-earth metal and alloy magnetic refrigerants. It can prepare perforated refrigerants with different porosities and granular refrigerants with different particle sizes. The process is simple, and the prepared magnetic refrigerant has low processing loss, high yield, and high material utilization.

Description

Technical Field

[0001] This invention relates to a rare earth metal magnetic refrigerant and its preparation method. Background Technology

[0002] Currently, mainstream magnetic refrigeration materials can be broadly divided into two categories: one is rare earth metals and alloys, such as Gd and its alloys, as well as other alloys; the other is compounds, such as LaFe. 13-× Si x (and its hydrogen-absorbing, carburizing, and other rare earth, Co, Mn, and other elemental substitute compounds). Since magnetic refrigeration utilizes the inherent functionality (magnetism) of the material, the higher the material purity, the higher the performance.

[0003] Rare earth metals (including elemental La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and Y) or rare earth alloys (alloys of two or more of the aforementioned rare earth elements) are important magnetic refrigeration working fluids. They can be processed into spherical / granular, flat, and other shapes and are widely used in the development of magnetic refrigeration technology. However, the following challenges still exist:

[0004] For flat working fluids, the thickness is usually less than 0.5 mm. The difficulty of processing thinner materials, the loss of materials during processing, and the difficulty of assembly all affect the application of the materials.

[0005] For spherical / particulate working fluids, the excellent toughness and ductility of rare earth metals and alloys make it very difficult to prepare granular or spherical working fluids using conventional crushing methods. Taking granular working fluids as an example, pure rare earth metal ingots or rare earth metal alloy ingots are typically crushed by hydrogen absorption, followed by dehydrogenation to obtain metal or alloy powder. Spherical working fluids, on the other hand, require atomization of the rare earth metal or alloy (such as gas atomization or rotating electrode methods). These methods suffer from drawbacks such as difficult crushing, numerous processes, high raw material consumption, low powder yield, low production rate, high cost, easy oxidation, and difficulty in large-scale production. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defects in the preparation of magnetic refrigerants from rare earth metals or alloys in the prior art, such as difficulty in crushing, many process steps, large raw material consumption, low powder yield, low yield, easy oxidation, difficulty in large-scale preparation, and high cost. The present invention provides a rare earth metal magnetic refrigerant and its preparation method.

[0007] This invention provides a novel process for preparing high-purity rare-earth metal or alloy magnetic refrigeration materials with porous and permeable structures. This process retains the high-purity magnetic refrigeration performance of rare-earth metals or alloys while overcoming the drawbacks of current rare-earth metal and alloy magnetic refrigeration preparation methods, such as difficulties in crushing, numerous processes, high raw material consumption, low powder yield, low production rate, easy oxidation, difficulty in large-scale production, and high cost. Compared to porous magnetic refrigeration materials made of composite materials in existing technologies, this invention offers higher purity. Compared to spherical working fluids (which have good heat exchange but large pressure drop) and plate-shaped working fluids (which have small pressure drop but lower heat exchange than spherical working fluids), the rare-earth metal magnetic refrigeration material of this invention achieves an optimized balance between heat exchange performance and pressure drop, with a lower pressure drop than spherical working fluids and a higher heat exchange than plate-shaped working fluids. Furthermore, in the prior art, the processing loss of granular working fluid materials is very high, and the material loss is also very high if the flat plate is cut. If it is rolled / calendered, although the material loss can be very low, the assembly is not easy. The rare metal magnetic refrigeration working fluid material of the present invention can achieve very low processing loss and is relatively easy to assemble.

[0008] Currently, there are no reports on the preparation of pure porous rare earth metals and alloy magnetic refrigerants.

[0009] The present invention solves the above-mentioned technical problems through the following technical solution:

[0010] A method for preparing a rare earth metal magnetic refrigerant includes the following steps: after melting rare earth metal raw materials, casting them into a mold to obtain a perforated rare earth metal preform, wherein the wall thickness of the perforated rare earth metal preform is 0.05-0.8 mm, the porosity is 30%-70%, and the pores are uniformly distributed.

[0011] In this invention, the rare earth metal raw materials generally include rare earth metal elements or rare earth alloys.

[0012] In this invention, the rare earth metal raw material is generally selected from one or more of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y.

[0013] Preferably, the rare earth metal raw material is a magnetic rare earth metal or rare earth alloy, and the rare earth metal or rare earth alloy includes two or more rare earth elements selected from Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb.

[0014] In this invention, the rare earth metal raw materials can be industrial-grade or high-purity rare earth metal raw materials. The rare earth alloy can be a commercially available rare earth alloy, or it can be obtained by batching and smelting according to the specified composition ratio.

[0015] In this invention, preferably, the melting is carried out under vacuum or argon protection conditions.

[0016] In this invention, the smelting equipment can be conventional smelting equipment in the art, such as a vacuum induction furnace.

[0017] In this invention, the smelting process generally includes the following steps: vacuuming, heating to degas, filling with protective gas, and heating until the raw materials melt.

[0018] Preferably, the vacuum is drawn to a vacuum pressure of no more than 2.5 Pa, for example, 2 Pa.

[0019] Preferably, the temperature of the heating and degassing process is not higher than 700°C, for example, not higher than 600°C.

[0020] Preferably, the vacuum level reaches a value higher than 2 × 10⁻⁶ before the protective gas is introduced. -3 Pa (pa) level.

[0021] Preferably, the protective gas is filled to a vacuum degree of 4×10⁻⁶. 4 pa.

[0022] In this invention, preferably, the smelting temperature is 50°C to 250°C higher than the melting point of the rare earth metal raw material, for example, the smelting temperature can be between 849°C and 1683°C.

[0023] In this invention, refining is preferably included after smelting and before casting.

[0024] Preferably, the refining temperature is 100°C higher than the melting temperature.

[0025] When the rare earth metal raw material is Gd, the smelting temperature is preferably 1363°C and the refining temperature is preferably 1463°C.

[0026] After refining, a heat preservation step is also included. The heat preservation time can be adjusted according to the amount of furnace charge, for example, 5 minutes.

[0027] In this invention, preferably, the casting is carried out under vacuum or inert atmosphere conditions.

[0028] The inert atmosphere can be a conventional inert gas in the art, such as argon.

[0029] In this invention, preferably, the mold is a porous mold or a mold containing filler particles.

[0030] More preferably, the porous mold is selected from copper molds, plaster molds, graphite molds or Al2O3 molds; more preferably, it is selected from copper molds or plaster molds.

[0031] More preferably, the filler particles are selected from Al2O3, quartz (SiO2), silicon carbide particles, gypsum or magnesia; more preferably from gypsum, magnesia, Al2O3 or quartz (SiO2).

[0032] Theoretically, the sum of the porosity of the porous mold and the filler particles and the porosity of the rare earth metal magnetic refrigerant is equal to 1.

[0033] In this invention, preferably, the casting temperature is 10-250°C higher than the melting point of the rare earth metal molten metal, for example, 200°C higher than the melting point of the rare earth metal molten metal. For example, when the rare earth metal raw material is Gd, the casting temperature is 1363°C or 1450°C.

[0034] In this invention, preferably, the mold is preheated before casting.

[0035] The preheating temperature is preferably 1 / 4 to 3 / 4 of the casting temperature of the rare earth metal molten metal. For example, when the rare earth metal raw material is Gd, the preheating temperature is preferably about 800°C.

[0036] More preferably, the preheating includes the following steps: when the molten metal flows through a preheated porous mold or filler particles, the preheating temperature is 1 / 4 to 3 / 4 of the casting temperature of the rare earth metal molten metal.

[0037] When the flow path of the molten metal is short or the pressure difference is large, preheating of the porous mold or filler particles is not required, or they can be directly water-cooled.

[0038] In this invention, preferably, after the casting, the following steps are further included:

[0039] When under vacuum conditions, pressure is applied to the upper surface of the mold, or when under argon protection conditions, air is extracted from its bottom, creating a large pressure difference between the two ends of the mold. This overcomes the viscous resistance of the molten metal, allowing it to flow better through the pores and completely fill the preform, ensuring that the molten metal can smoothly enter the pores of the preform.

[0040] For example, blow casting or suction casting of porous molds or filler particles can create a large pressure difference across the two ends of the molds or filler particles. Preferably, the pressure difference is greater than one atmosphere, such as two atmospheres.

[0041] Magnetic refrigerants have specific requirements regarding pore size, porosity, and metal wall thickness. Ideally, the wall thickness should be between 50 and 800 micrometers, the porosity between 30% and 70%, and the pores should be uniformly distributed. Such relatively small pores make successful metal casting very difficult. When there is no pressure difference, the mold thickness cannot be too large, otherwise the molten metal cannot flow smoothly through the mold; with a pressure difference, it can be thicker. Whether the mold is preheated also affects casting success. If not preheated, the molten metal may solidify too quickly, making casting difficult; and if the mold is not preheated, its thickness cannot be too large. Ideally, there should be a pressure difference exceeding one atmosphere to help the molten metal flow and complete the casting process.

[0042] In this invention, preferably, after obtaining the perforated rare earth metal preform, the method further includes a step of removing impurities, thereby obtaining the rare earth metal magnetic refrigerant.

[0043] Preferably, the method for removing impurities includes the following steps: cutting, tapping, soaking in ultrasonic waves, high-pressure water treatment, and high-pressure air treatment of the cooled precast blocks to physically remove the impurities.

[0044] Preferably, after removing impurities, mechanical, electrical discharge, or laser drilling is performed on individual unthrough holes.

[0045] In this invention, preferably, after obtaining the rare earth metal magnetic refrigerant, the method further includes a step of modifying the rare earth metal magnetic refrigerant.

[0046] The modification treatment preferably includes the following steps: placing the obtained rare-earth metal magnetic refrigerant in a nitric acid or hydrochloric acid solution. This further modifies and controls the size and shape of the pores, while also activating the surface and removing the interfacial oxide layer, which is beneficial for enhancing the heat exchange effect. Furthermore, nitric acid or hydrochloric acid is readily available, and the corrosion rate and thickness are controllable.

[0047] The volume fraction of the nitric acid or hydrochloric acid solution can be 1%-10%.

[0048] In this invention, preferably, the wall thickness of the through hole of the rare earth metal magnetic refrigerant is 0.05-0.5 mm, for example, 0.1 mm, 0.2 mm or 0.5 mm.

[0049] In this invention, preferably, the porosity of the rare earth metal magnetic refrigerant is 40%-70%, for example 50% or 60%.

[0050] In this invention, the uniform pore distribution can be understood as the uniform pore distribution of the rare earth metal magnetic refrigerant as is conventional in the art. For example, when the rare earth metal magnetic refrigerant is divided into two area regions, the pore density of the two area regions and the overall pore density of the rare earth metal magnetic refrigerant do not deviate by more than 10%. Uniform pore distribution can be controlled by molds or filler particles. From a usage perspective, uniform pore distribution contributes to controllable performance and design, and is beneficial to the heat exchange effect of the magnetic refrigerant.

[0051] In this invention, the through hole refers to a conventional through hole in the art. In the subsequent use of the rare earth metal magnetic refrigerant, the heat exchange gas or fluid medium can flow through the through hole for heat exchange and heat transfer.

[0052] In this invention, the wall thickness and porosity of the through hole can be controlled by selecting different molds.

[0053] In this invention, the rare earth metal magnetic refrigerant prepared can be directly used as a refrigerant.

[0054] In this invention, the rare earth metal magnetic refrigerant has a shape including through holes or granules.

[0055] The granular rare earth metal magnetic refrigerant can be obtained by crushing the rare earth metal magnetic refrigerant.

[0056] The crushing method can be a conventional crushing method in the art, such as: direct mechanical crushing, or ball milling after direct mechanical crushing, or crushing into granular rare earth metal magnetic refrigerant by absorbing hydrogen and then dehydrogenating the rare earth metal magnetic refrigerant.

[0057] For example, the crushing process includes the following steps: absorbing hydrogen and then dehydrogenating the porous magnetic refrigerant, wherein the temperature during hydrogen absorption is 300°C and the absorption time is 4 hours; and the temperature during hydrogen dehydrogenation is 1000°C and the dehydrogenation time is 4 hours.

[0058] The present invention also provides a rare earth metal magnetic refrigerant, which is prepared by the aforementioned preparation method.

[0059] The present invention also provides a rare earth metal magnetic refrigerant, wherein the rare earth metal magnetic refrigerant is in the form of through holes or granules. When the rare earth metal magnetic refrigerant is in the form of through holes, the wall thickness of the through holes is 0.05-0.8 mm, the porosity is 30%-70%, and the pores are uniformly distributed.

[0060] The positive and progressive effects of this invention are as follows:

[0061] (1) This invention provides a novel method for the large-scale, low-cost preparation of high-purity rare-earth metal and alloy magnetic refrigeration working fluids. This method enables the preparation of porous working fluids with varying porosities and particulate working fluids with different particle sizes. It has the following characteristics:

[0062] ① Solving the existing problem of difficult crushing: There are several types of magnetic refrigerant materials, including granular / spherical, flat, and porous foam-like materials. The present invention prepares a porous rare earth metal or alloy that can be directly used as a refrigerant. It can also be used to prepare rare earth metal or alloy powder through direct mechanical crushing and ball milling, or to obtain granular refrigerant by hydrogen absorption crushing and then dehydrogenation of the porous metal. This is easier than the existing methods of preparing it from rare earth metal ingots or alloy ingots. For actual rare earth metals, the toughness and ductility are very good, making it difficult to crush them into very fine particles. Foam-like raw materials are much better, but they are still affected by the good toughness and ductility. The same applies to hydrogen absorption crushing. Large metal blocks must first be made into smaller blocks to increase the contact area and reduce the atomic diffusion / penetration distance, which is a complex process. The porous structure (especially the through-pore structure) prepared by the present invention can not only be used directly as a refrigerant, but is also very beneficial to the hydrogen absorption process. Theoretically, it is faster, more uniform, and easier to crush.

[0063] ② Significantly improved raw material utilization, high yield, and low processing loss: As a magnetic refrigerant material, the granules need to have a uniform particle size (e.g., several hundred micrometers, with some fluctuation). However, existing methods, such as metal atomization, produce near-normally distributed particles. The target particle size typically accounts for only a few percent to about thirty percent of the total, depending on the particle size range; the rest are unusable, resulting in low yield. Furthermore, the atomized powder cannot be directly melted and then atomized; it must be purified, cast into rods, and then atomized, which is time-consuming and wasteful. It is evident that the material yield and utilization are low, and other crushing methods also result in particle size distribution. Once the porous molding of this invention is successfully achieved, it can be directly used as a magnetic refrigerant material, resulting in a very high material utilization rate and a huge difference in yield.

[0064] ③ Not easily oxidized: Rare earth elements such as La and Ce are highly oxidizable, and medium and heavy rare earth elements are also affected by oxidation. Due to the very fine requirements for particle size (on the order of hundreds of micrometers), a long preparation process is required at this particle size, which greatly increases the contact time with oxygen under high temperature conditions (relatively speaking, the temperature rise is caused by crushing friction). Many coarse crushing processes do not have inert gas protection. This invention is completed entirely under vacuum and inert gas protection, and is not easily oxidized after molding and cooling.

[0065] (2) The process of the present invention allows for control over the pore size and wall thickness, thereby providing a certain degree of control over the particles and resulting in relatively high particle size uniformity. In contrast, existing technologies rely entirely on crushing and grinding (such as ball milling). The natural grinding process is relatively less controllable (the time and ball ratio are also somewhat controllable), and the particle size is completely naturally distributed. Attached Figure Description

[0066] Figure 1 This is a schematic diagram of the preparation process.

[0067] Figure 2 This is a schematic diagram of casting and suction casting (A: The mold uses filler particles; B: The mold uses a porous mold). Detailed Implementation

[0068] The present invention will be further illustrated by way of embodiments below, but the present invention is not limited to the scope of the embodiments described herein.

[0069] Example 1

[0070] The preparation method and process of rare earth metal magnetic refrigerants are as follows: Figure 1 Specifically, it includes the following steps:

[0071] (1) Smelting: Rare earth metal Gd is smelted using a vacuum medium-frequency induction furnace. Gd raw material is placed in a Ta crucible or corundum crucible, and a vacuum of ~2 Pa is applied. The crucible and casting mold are then heated to degas the material; the degassing temperature should not exceed 600℃. The casting mold can be a gypsum mold or a mold filled with gypsum / magnesia filler particles, with the porosity controlled at 30% and the pore wall thickness controlled at 0.8 mm. When the vacuum degree inside the induction furnace exceeds 2×10⁻⁶, the smelting process continues. -3 The pressure is in the Pa range; after turning off the vacuum pump, argon gas is introduced to a level of 4 × 10⁻⁶. 4 Pa, mold preheating temperature ~800℃, further heating the crucible to melt the raw material ingot, refining temperature 1463℃, and holding for 5 minutes (adjusted according to the amount of furnace charge).

[0072] (2) Casting: Cool to 1450℃, pour the molten metal into the mold, and immediately open the vacuum valve at the bottom of the mold to allow the molten metal to quickly seep into the porous structure of the mold. See [link to relevant documentation]. Figure 2 Schematic diagram of casting and suction casting.

[0073] (3) Remove impurities: Slice the solidified metal block and then remove the mold material by soaking in ultrasound, high-pressure water, high-pressure air, etc., to obtain a transparent porous Gd magnetic refrigerant material.

[0074] During the preparation process, the final porosity of the magnetic refrigerant can be controlled between 30% and 70% and the pore wall thickness between 0.05 and 0.8 mm through molds and filler particles, and the pores are evenly distributed.

[0075] Examples 2-5

[0076] Except for the features listed in Table 1 below, Examples 2-5 are the same as Example 1.

[0077] Example 2 Gd 1363 1463 1363 40％ 0.5 Example 3 Gd 1363 1463 1363 50％ 0.2 Example 4 Gd 1363 1463 1363 60％ 0.1 Example 5 Gd 1363 1463 1363 70％ 0.05

[0078] Example 6

[0079] The porous Gd magnetic refrigerant material obtained in Examples 1-5 was placed in a hydrogen decomposition furnace. The furnace was evacuated to below 6 Pa, heated to 300°C, and the valves of the chamber and vacuum pump were closed. Hydrogen was introduced until the hydrogen pressure reached 0.098 MPa. If the pressure dropped below 0.068 MPa, hydrogen was automatically replenished to 0.098 MPa. Hydrogen absorption continued for 4 hours, and then the hydrogen valve was closed. The valves of the chamber and vacuum pump were then opened, and evacuation continued while the temperature was raised to 1000°C. Hydrogen removal continued for 4 hours. The heating was then turned off, and the material was allowed to cool naturally or by air to room temperature. The vacuum pump was turned off, and argon or nitrogen was introduced until the pressure reached approximately 1 atmosphere. The furnace was then opened, and the material was removed to obtain a granular working fluid material.

[0080] The porous magnetic refrigerant prepared by the process of this invention can theoretically achieve zero material loss, or control it within 1-2%. Existing flat working fluids have two processing methods: one is to process them into single sheets and then assemble them, with processing losses of approximately 20% or more per sheet; the second method is to process them into a grating-like structure, where the porosity equals the material loss rate, reaching over 30%. For existing atomized particles, the material yield is 5-10%, and even at a 40% material yield, the material loss rate will reach 60%, with even lower yields resulting in greater losses. In contrast, the magnetic refrigerant prepared by the process of this invention can be directly used as a magnetic refrigerant material, offering advantages such as low processing loss and high material utilization.

[0081] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing a rare-earth metal magnetic refrigerant, characterized in that, It includes the following steps: after the rare earth metal raw material is smelted, it is cast into a mold to obtain a through-hole rare earth metal preform. The wall thickness of the through hole of the through-hole rare earth metal preform is 0.05-0.8mm, the porosity is 30%-70%, and the pores are uniformly distributed. The melting is carried out under vacuum or argon protection conditions; The smelting temperature used in the process is 50°C to 250°C higher than the melting point of the rare earth metal raw materials. After the smelting and before the casting, the process also includes refining, wherein the refining temperature is 100°C higher than the smelting temperature. The casting temperature is 10-250°C higher than the melting point of rare earth metal molten metal; Before the casting, the mold is preheated; the mold is a porous mold or a mold containing filler particles; the preheating includes the following steps: when the molten metal flows through the preheated porous mold or filler particles, the preheating temperature is 1 / 4 to 3 / 4 of the casting temperature of the rare earth metal molten metal. After obtaining the porous rare earth metal preform, the process also includes a step of removing impurities, thereby obtaining the rare earth metal magnetic refrigerant.

2. The preparation method of the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, The rare earth metal raw materials include elemental rare earth metals or rare earth alloys. And / or, the rare earth metal raw material is selected from one or more of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Y; And / or, the wall thickness of the through-hole of the rare earth metal magnetic refrigerant is 0.05-0.5 mm; And / or, the porosity of the rare earth metal magnetic refrigerant is 40%-70%.

3. The method for preparing the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, The rare earth metal raw material is a magnetic rare earth metal or rare earth alloy, and the rare earth metal or rare earth alloy includes two or more rare earth elements selected from Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb.

4. The method for preparing the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, The wall thickness of the through-hole of the rare earth metal magnetic refrigerant is 0.1 mm, 0.2 mm or 0.5 mm; And / or, the porosity of the rare earth metal magnetic refrigerant is 50% or 60%.

5. The method for preparing the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, The smelting process includes the following steps: vacuuming, heating to degas, filling with protective gas, and heating until the raw material melts. And / or, the melting temperature is 849~1683℃; And / or, after refining, a heat preservation step is also included.

6. The method for preparing the rare earth metal magnetic refrigerant as described in claim 5, characterized in that, The vacuuming process involves evacuating the vacuum to a pressure not exceeding 2.5 Pa. And / or, the temperature of the heating and degassing process does not exceed 700°C; And / or, before filling with protective gas, the vacuum degree is ≥2×10 -3 Pa; And / or, fill with protective gas to a vacuum degree of 4 × 10⁻⁶. 4 Pa.

7. The method for preparing the rare earth metal magnetic refrigerant as described in claim 6, characterized in that, The vacuuming process involves evacuating the vacuum to a pressure of 2 Pa. And / or, the temperature of the heating and degassing process does not exceed 600°C.

8. The method for preparing the rare earth metal magnetic refrigerant as described in claim 2, characterized in that, When the rare earth metal raw material is Gd, the smelting temperature is 1363℃ and the refining temperature is 1463℃.

9. The method for preparing the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, The casting is carried out under vacuum or inert atmosphere conditions.

10. The method for preparing the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, The porous mold is selected from copper molds, plaster molds, graphite molds or Al2O3 molds; And / or, the filler particles are selected from Al2O3, quartz, silicon carbide particles, gypsum or magnesia.

11. The method for preparing the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, The casting temperature is 200°C higher than the melting point of the rare earth metal molten metal.

12. The method for preparing the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, When the rare earth metal raw material is Gd, the casting temperature is 1363℃ or 1450℃.

13. The method for preparing the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, When the rare earth metal raw material is Gd, the preheating temperature is 800℃.

14. The method for preparing the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, After the casting, the process further includes the following steps: blow casting or suction casting of the porous mold or filler particles to create a pressure difference at both ends of the porous mold or filler particles.

15. The method for preparing the rare earth metal magnetic refrigerant as described in claim 14, characterized in that, The pressure difference is more than one atmosphere.

16. The method for preparing the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, After obtaining the rare earth metal magnetic refrigerant, the process further includes a step of modifying the rare earth metal magnetic refrigerant.

17. The method for preparing the rare earth metal magnetic refrigerant as described in claim 16, characterized in that, The method for removing impurities includes the following steps: cutting, tapping, soaking in ultrasonic waves, high-pressure water treatment, and high-pressure air treatment of the cooled precast blocks to physically remove impurities; The modification process includes the following steps: placing the obtained rare earth metal magnetic refrigerant in a nitric acid or hydrochloric acid solution to further modify and control the size and shape of the pores.

18. The method for preparing the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, After removing impurities, mechanical, electrical discharge, or laser drilling is performed on individual unsealed holes.

19. The method for preparing the rare earth metal magnetic refrigerant as described in claim 17, characterized in that, The volume fraction of the nitric acid or hydrochloric acid solution is 1%-10%.

20. The method for preparing the rare earth metal magnetic refrigerant as described in claim 1, characterized in that, The rare earth metal magnetic refrigerant can be in the form of through holes or granules.

21. The method for preparing the rare earth metal magnetic refrigerant as described in claim 20, characterized in that, The granular rare earth metal magnetic refrigerant is obtained by crushing the rare earth metal magnetic refrigerant; the crushing method is direct mechanical crushing, or ball milling after direct mechanical crushing, or crushing the rare earth metal magnetic refrigerant into granular rare earth metal magnetic refrigerant by absorbing hydrogen and then dehydrogenating it.

22. A rare earth metal magnetic refrigerant, which is prepared by the method for preparing the rare earth metal magnetic refrigerant as described in any one of claims 1-21.

23. A rare-earth metal magnetic refrigerant, characterized in that, The rare earth metal magnetic refrigerant is perforated, with a wall thickness of 0.05-0.8 mm, a porosity of 30%-70%, and uniform pore distribution.

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