Rare earth aluminate low-temperature magnetic refrigeration material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of rare earth functional materials, and particularly relates to a rare earth aluminate low-temperature magnetic refrigeration material and a preparation method and application thereof.The preparation method comprises the following steps that 1, rare earth metal nitrate and aluminum nitrate are added into water to be mixed, and a mixed solution is prepared; adding ammonia water into the mixed solution to prepare a precipitate; (2) carrying out annealing treatment on the precipitate to prepare a metal oxide; and (3) calcining the metal oxide to obtain the rare earth aluminate low-temperature magnetic refrigeration material. The rare earth aluminate which has the characteristics of stable structure, low preparation cost, strong mechanical property, high magnetic density and the like and is prepared by adopting a coprecipitation method and combining a high-temperature sintering technology has more excellent magnetocaloric properties in a low-temperature region.

Description

Technical Field

[0001] The present invention belongs to the technical field of rare earth functional materials, and in particular relates to a rare earth aluminate low-temperature magnetic refrigeration material and a preparation method and application thereof. Background Art

[0002] In recent years, with the increasing shortage of helium resources and the widespread application of cryogenic refrigeration in high-tech fields such as deep space exploration, superconductivity, and national defense, the importance of new cryogenic refrigeration technologies has continued to grow. Magnetic refrigeration is a new refrigeration technology that achieves refrigeration based on the magnetocaloric effect of materials. Compared with traditional gas compression refrigeration, it offers advantages such as high efficiency, zero pollution, low noise, and a simple structure, making it expected to become one of the most promising new refrigeration methods in the future. Magnetic refrigeration works by using an external magnetic field to induce ordered and disordered changes in the magnetic moment of a magnetic fluid, causing the magnet to absorb and release heat, thereby achieving the purpose of cooling. The application of low-temperature magnetic refrigeration technology is inseparable from the development of excellent magnetocaloric materials. This requires that magnetocaloric materials not only exhibit a large magnetic entropy change under certain magnetic field changes but also have a wide refrigeration temperature range to ensure strong magnetic refrigeration capabilities.

[0003] In recent decades, heavy rare earth (HRE)-based magnetic materials have become a research hotspot in the field of low-temperature magnetocaloric materials due to their high magnetic moment, low ordering temperature, structural stability, and low production cost. While HRE-based magnetic materials, including HRE alloys and HRE oxides, exhibit promising low-temperature magnetic refrigeration performance, most suffer from complex preparation processes, poor mechanical properties (fragility), long production cycles, or high production costs, limiting their potential for practical application. Summary of the Invention

[0004] The purpose of the present invention is to provide a rare earth aluminate low-temperature magnetic refrigeration material and its preparation method and application, so as to overcome the shortcomings of the existing technology, and to prepare a rare earth aluminate with the characteristics of stable structure, low preparation cost, strong mechanical properties and high magnetic density by using a co-precipitation method combined with high-temperature sintering technology. RE 4Al2O9 exhibits more excellent magnetocaloric properties in the low temperature region.

[0005] In order to achieve the above object, the technical solution of the present invention is: In a first aspect, the present invention provides a method for preparing a rare earth aluminate low-temperature magnetic refrigeration material, comprising the following steps: (1) adding rare earth metal nitrate and aluminum nitrate into water and mixing them to prepare a mixed solution; adding ammonia water to the mixed solution to prepare a precipitate; (2) annealing the precipitate to obtain a metal oxide; (3) The metal oxide is calcined to obtain rare earth aluminate low-temperature magnetic refrigeration material.

[0006] In some other embodiments, in step (1), the molar ratio of rare earth metal ions to aluminum ions in the rare earth metal nitrate and aluminum nitrate is 2:1; The rare earth metal nitrate is at least one of gadolinium nitrate, dysprosium nitrate and holmium nitrate.

[0007] In some other embodiments, in step (1), the total molar ratio of rare earth metal ions and aluminum ions in the mixed solution to the molar ratio of ammonia water is 1:(3.2-4.0); The concentration of the ammonia water is 10-15 mol / L; Optionally, in step (1), the total molar ratio of the rare earth metal ions to the aluminum ions in the mixed solution to the molar ratio of the ammonia water is 1:3.5; and the concentration of the ammonia water is 12 mol / L. Within this ratio range, it is possible to ensure that the rare earth metal ions and the aluminum ions in the mixed solution fully react.

[0008] In some other embodiments, in step (2), the annealing temperature is 560-760°C and the time is 3-6 hours; optionally, the annealing temperature is 600°C and the time is 5 hours; this is beneficial for converting the metal hydroxide into the metal oxide.

[0009] Alternatively, before the precipitate is annealed, the precipitate is pretreated, and the pretreatment comprises aging, filtering, washing and drying the precipitate in sequence; the aging time is 10-24 h, the solvent used for washing is water and / or ethanol, and the drying temperature is 80-120° C. and the time is 10-15 h.

[0010] Optionally, the drying temperature is 100°C and the drying time is 12 hours. Within this ratio range, it is possible to ensure that the moisture in the precipitate is completely dried.

[0011] In some other embodiments, in step (3), the calcination temperature is 1200-1500 °C, the time is 6-18 h, and the atmosphere is air atmosphere; optionally, the calcination temperature is 1400 °C, and the time is 12 h. Within this ratio range, it can ensure complete conversion to generate rare earth aluminate low-temperature magnetic refrigeration material.

[0012] Alternatively, the metal oxide may be pretreated before calcining, wherein the metal oxide is ground into powder and then tabletted; the particle size of the ground metal oxide is 150-250 mesh, and the tabletting is performed at 15-20°C for 3-5 minutes.

[0013] Optionally, the particle size of the metal oxide after grinding is 200 mesh, and the tableting is performed by pressing at 18°C for 5 minutes.

[0014] In a second aspect, the present invention provides a rare earth aluminate low-temperature magnetic refrigeration material prepared by the preparation method of the rare earth aluminate low-temperature magnetic refrigeration material described in the first aspect.

[0015] In some other embodiments, the chemical formula of the rare earth aluminate low temperature magnetic refrigeration material is RE 4Al2O9, wherein RE is at least one of the rare earth elements Gd, Dy and Ho.

[0016] For example, the RE 4Al2O9 is Gd4Al2O9, Dy4Al2O9, Ho4Al2O9, (Gd 0.5 Dy 0.5 )4Al2O9、(Gd 0.5 Ho 0.5 )One of the 4Al2O9.

[0017] described RE 4Al2O9 has the following properties: Under the magnetic field variation of 0-2 T, the isothermal magnetic entropy change is 9.47-10.32 J / kg K, and the relative magnetic cooling capacity is 72.23-92.18 J / kg; Under the magnetic field variation of 0-5 T, the isothermal magnetic entropy change is 16.26-27.94 J / kg K, and the relative magnetic cooling capacity is 279.41-341.38 J / kg; Under the magnetic field variation of 0-7 T, the isothermal magnetic entropy change is 18.46-33.12 J / kg K, and the relative magnetic cooling capacity is 430.59-498.48 J / kg.

[0018] In a third aspect, the present invention provides an application of the rare earth aluminate low-temperature magnetic refrigeration material described in the second aspect in low-temperature magnetic refrigeration.

[0019] In some other embodiments, the application is in low temperature physics, deep space exploration, and military aerospace.

[0020] In a fourth aspect, the present invention provides a method for using a rare earth aluminate low-temperature magnetic refrigeration material, comprising applying the rare earth aluminate low-temperature magnetic refrigeration material described in the second aspect on a substrate.

[0021] Beneficial effects of the present invention: (1) The present invention provides a co-precipitation method for successfully preparing rare earth-transition metal oxide low-temperature magnetic refrigeration materials RE 4Al2O9. This preparation method has simple steps, a short reaction cycle, and uses common chemical reagents as the main raw materials, which are in sufficient supply in the market. The cost is much lower than that of rare earth alloys or special oxide precursors, making it more suitable for large-scale industrial production.

[0022] (2) The present invention prepares RE 4Al2O9 compound is a paramagnetic material and a secondary magnetic phase change material. As can be seen from the lack of bifurcation in the ZFC and FC diagrams, it has negligible hysteresis and thermal hysteresis effects. Therefore, as a low-temperature magnetic refrigeration material, it has a high refrigeration efficiency.

[0023] (3) Prepared by the present invention RE 4Al2O9 has a stable structure. The selected heavy rare earth ions have the characteristics of high magnetic moment. The high magnetic moment ions are densely packed, laying the foundation for high magnetic density. The compact unit cell of the monoclinic system further improves the magnetic moment density. It shows better magnetic refrigeration performance in the low temperature range. Among them, Ho6MoO 12 The compound's maximum relative magnetic refrigeration capacity reached 498.48 J / kg when ∆H was 7 T, demonstrating a large low-temperature magnetic refrigeration capacity. It has broad application prospects in low-temperature physics, deep space exploration, military aerospace, and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0025] Figure 1 XRD refined patterns of samples prepared in Examples 1-3 of the present invention; Figure 2 The XRD pattern of the sample prepared in Example 4-5 of the present invention; Figure 3 This is the XRD pattern of the sample prepared in Comparative Example 1 of the present invention; Figure 4 This is the XRD pattern of the sample prepared in Comparative Example 2 of the present invention; Figure 5 This is the XRD pattern of the sample prepared in Comparative Example 3 of the present invention; Figure 6 This is the XRD pattern of the sample prepared in Comparative Example 4 of the present invention; Figure 7 The ZFC and FC thermomagnetic curves of the samples prepared in Examples 1-3 of the present invention under a 0.1 T magnetic field; Figure 8 Isothermal magnetization curves of the samples prepared in Examples 1-3 of the present invention at different temperatures; Figure 9 The curves of magnetic entropy change versus temperature for the samples prepared in Examples 1-3 of the present invention under different magnetic field changes are shown; Figure 10The ZFC and FC thermomagnetic curves of the sample prepared in Example 5 of the present invention under a 0.1 T magnetic field, the isothermal magnetization curves at different temperatures, and the magnetic entropy change curve with temperature under different magnetic field changes are shown, wherein (a) is the ZFC and FC thermomagnetic curves under a 0.1 T magnetic field, (b) is the isothermal magnetization curve at different temperatures, and (c) is the magnetic entropy change curve with temperature under different magnetic field changes; in, Figure 1 、 Figure 7-9 In the figures, (a) is the sample prepared in Example 1, (b) is the sample prepared in Example 2, and (c) is the sample prepared in Example 3. DETAILED DESCRIPTION

[0026] Those skilled in the art will appreciate that the following examples are intended to illustrate the present invention only and should not be construed as limiting the scope of the invention. Unless otherwise specified, the examples were performed under conventional conditions or manufacturer's recommended conditions. Components used without manufacturer's indication are commercially available conventional products.

[0027] In view of the problems of existing low-temperature magnetic refrigeration materials such as complex preparation process, poor mechanical properties (fragile), long production cycle or high preparation cost, a rare earth aluminate with the characteristics of stable structure, low preparation cost, strong mechanical properties and high magnetic density is prepared by co-precipitation method combined with high temperature sintering technology. RE 4Al2O9( RE is at least one of the rare earth elements Gd, Dy and Ho). The preparation method has simple steps, strong repeatability, short production cycle and low preparation cost. RE 4Al2O9 material exhibits more excellent magnetocaloric properties in the low temperature region.

[0028] In order to better understand the specific scheme, the present invention is further explained through the following specific examples: Example 1 A method for preparing a rare earth aluminate low-temperature magnetic refrigeration material comprises the following steps: Step 1: Prepare 0.1 mol / L gadolinium nitrate and 0.05 mol / L aluminum nitrate solution, mix the prepared gadolinium nitrate solution and aluminum nitrate solution in equal volumes to form a mixed solution (Gd 3+ :Al 3+ molar ratio of 2:1), and then 5.6 ml of concentrated ammonia water (concentration of 12 mol / L) was dropwise added to the mixed solution under continuous stirring (the total molar ratio of rare earth metal ions and aluminum ions to the molar ratio of ammonia water was 1:3.5) until no more precipitation was produced to obtain a precipitate; Step 2: The precipitate was aged for 12 hours, filtered using a Buchner funnel, and washed once with deionized water and alcohol to obtain a filter cake; Step 3: After drying the filter cake in an oven at 100 °C for 12 hours, the dried filter cake was placed in a crucible and annealed at 600 °C for 5 hours to form a metal oxide; Step 4: Grind the metal oxide into powder and use a tablet press to form tablets (after sieving the powder through 200 mesh, take 2 g and place it in a mold with a diameter of 1.8 cm. Press it under a pressure of 18 t for 5 minutes). Then put it into a corundum crucible, heat it to 1400°C in a muffle furnace, sinter it in an air atmosphere for 12 hours, and cool it to room temperature at 5°C / min to obtain the finished product Gd4Al2O9, which is marked as sample (a).

[0029] Measurement of isothermal magnetic entropy change: According to the formula Calculate the magnetic entropy change; where, is the magnetic entropy change value, T is the temperature, H is the magnetic field strength, M is the magnetization intensity; it can also be measured using a vibrating sample magnetometer (VSM) or a physical property measurement system (MPMS-XL). The powder sample is placed in a sample holder and fixed at the magnetic field center of the measuring device. At the selected temperature, the magnetic field intensity ( H ), the range is selected as 0-7 T. The isothermal magnetization curve (MH) curve of the sample is measured and recorded at different temperatures, where M represents the magnetization intensity, H Represents the magnetic field strength.

[0030] Relative refrigeration capacity (RCP) is measured by the maximum magnetic entropy change. Multiply by the half-height width δ T FW HM It is found that the larger the RCP value is, the stronger the cooling capacity of the corresponding material is.

[0031] For the sample prepared in Example 1, the isothermal magnetic entropy change is 10.31 J / kg K under a magnetic field variation of 0 to 2 T, and the relative magnetic cooling capacity is 72.23 J / kg; the isothermal magnetic entropy change is 27.94 J / kg K under a magnetic field variation of 0 to 5 T, and the relative magnetic cooling capacity is 279.41 J / kg; the isothermal magnetic entropy change is 33.12 J / kg K under a magnetic field variation of 0 to 7 T, and the relative magnetic cooling capacity is 430.59 J / kg.

[0032] Example 2 A method for preparing a rare earth aluminate low-temperature magnetic refrigeration material comprises the following steps: Step 1: Prepare 0.1 mol / L dysprosium nitrate and 0.05 mol / L aluminum nitrate solution, mix the prepared dysprosium nitrate solution and aluminum nitrate solution in equal volumes to form a mixed solution (Dy 3+ :Al 3+ molar ratio of 2:1), and then 5.6 ml of concentrated ammonia water (concentration of 12 mol / L) was added dropwise to the mixed solution under continuous stirring (the total molar ratio of rare earth metal ions and aluminum ions to the molar ratio of ammonia water was 1:3.5) until no more precipitation was produced, thereby obtaining a precipitate; Step 2: The precipitate was aged for 12 hours, filtered using a Buchner funnel, and washed once with deionized water and alcohol to obtain a filter cake; Step 3: After drying the filter cake in an oven at 100 °C for 12 hours, the dried filter cake was placed in a crucible and annealed at 600 °C for 5 hours to form a metal oxide; Step 4: Grind the metal oxide into powder and use a tablet press to form tablets (after sieving the powder through 200 mesh, take 2 g and place it in a mold with a diameter of 1.8 cm. Press it for 5 minutes under a pressure of 18 t). Then put it into a corundum crucible, heat it to 1400°C in a muffle furnace, sinter it in an air atmosphere for 12 hours, and cool it to room temperature at 5°C / min to obtain the finished product Dy4Al2O9, which is marked as sample (b).

[0033] Referring to the measurement method of Example 1, it was measured that the isothermal magnetic entropy change of the finished product was 9.47 J / kg K under a magnetic field change of 0 to 2 T, and the relative magnetic cooling capacity was 85.21 J / kg; under a magnetic field change of 0 to 5 T, the isothermal magnetic entropy change was 18.59 J / kg K, and the relative magnetic cooling capacity was 316.15 J / kg; under a magnetic field change of 0 to 7 T, the isothermal magnetic entropy change was 20.69 J / kg K, and the relative magnetic cooling capacity was 496.76 J / kg.

[0034] Example 3 A method for preparing a rare earth aluminate low-temperature magnetic refrigeration material comprises the following steps: Step 1: Prepare 0.1 mol / L holmium nitrate and 0.05 mol / L aluminum nitrate solution, mix the prepared holmium nitrate solution and aluminum nitrate solution in equal volumes to form a mixed solution (Ho 3+ :Al 3+ molar ratio of 2:1), and then 5.6 ml of concentrated ammonia water (concentration of 12 mol / L) was added dropwise to the mixed solution under continuous stirring (the total molar ratio of rare earth metal ions and aluminum ions to the molar ratio of ammonia water was 1:3.5) until no more precipitation was produced, thereby obtaining a precipitate; Step 2: The precipitate was aged for 12 hours, filtered using a Buchner funnel, and washed once with deionized water and alcohol to obtain a filter cake; Step 3: After drying the filter cake in an oven at 100 °C for 12 hours, the dried filter cake was placed in a crucible and annealed at 600 °C for 5 hours to form a metal oxide; Step 4: Grind the metal oxide into powder and use a tablet press to form tablets (after sieving the powder with 200 mesh, take 2 g and place it in a mold with a diameter of 1.8 cm. Press it for 5 minutes under a pressure of 18 t). Then put it into a corundum crucible, heat it to 1400°C in a muffle furnace, sinter it in an air atmosphere for 12 hours, and cool it to room temperature at 5°C / min to obtain the finished product Ho4Al2O9, which is marked as sample (c).

[0035] Referring to the measurement method of Example 1, it was measured that the isothermal magnetic entropy change of the finished product was 10.24 J / kg K under a magnetic field change of 0 to 2 T, and the relative magnetic cooling capacity was 92.18 J / kg; under a magnetic field change of 0 to 5 T, the isothermal magnetic entropy change was 16.26 J / kg K, and the relative magnetic cooling capacity was 341.38 J / kg; under a magnetic field change of 0 to 7 T, the isothermal magnetic entropy change was 18.46 J / kg K, and the relative magnetic cooling capacity was 498.48 J / kg.

[0036] Example 4 The difference from Example 1 is that in step 1, 0.1 mol / L gadolinium nitrate, 0.1 mol / L dysprosium nitrate, and 0.05 mol / L aluminum nitrate solution are prepared, and the prepared gadolinium nitrate solution, dysprosium nitrate solution, and aluminum nitrate solution are mixed in a volume ratio of 0.5:0.5:1 to form a mixed solution (Gd 3+ :Dy 3+ :Al 3+ The mixture was stirred at a molar ratio of 1:1:1, and then 5.6 ml of concentrated ammonia water (concentration of 12 mol / L) was added dropwise to the mixed solution (the total molar ratio of rare earth metal ions and aluminum ions to the molar ratio of ammonia water was 1:3.5) under continuous stirring until no more precipitation was produced to obtain a precipitate; the other preparation steps were the same as those in Example 1. The finished product (Gd 0.5 Dy 0.5 )4Al2O9.

[0037] Example 5 The difference from Example 1 is that in step 1, 0.1 mol / L gadolinium nitrate, 0.1 mol / L holmium nitrate, and 0.05 mol / L aluminum nitrate solution are prepared, and the prepared gadolinium nitrate solution, holmium nitrate solution, and aluminum nitrate solution are mixed in a volume ratio of 0.5:0.5:1 to form a mixed solution (Gd 3+:Ho 3+ :Al 3+ molar ratio of 1:1:1), and then 5.6 ml of concentrated ammonia water (concentration of 12 mol / L) was added dropwise to the mixed solution under continuous stirring (the total molar ratio of rare earth metal ions and aluminum ions to the molar ratio of ammonia water was 1:3.5) until no more precipitation was produced to obtain a precipitate; the other preparation steps were the same as those in Example 1. The finished product (Gd 0.5 Ho 0.5 )4Al2O9.

[0038] Comparative Example 1 The difference from Example 1 is that in step 2, the total molar ratio of gadolinium nitrate and aluminum nitrate to the molar ratio of ammonia water is 1:3.1; the remaining steps are consistent with Example 1.

[0039] Ammonia, as a precipitant, needs to react with metal ions to generate hydroxide precipitates. The reduction of ammonia dosage results in incomplete precipitation of metal ions, and unreacted Gd remains in the mixed solution. 3+ and Al 3+ The final product is a mixture of Gd2O3 and GdAlO3, which does not meet the requirements, so magnetic testing was not performed.

[0040] Comparative Example 2 The difference from Example 1 is that in step 2, ammonia water is replaced by NaOH, and the molar ratio of the total amount of gadolinium nitrate and aluminum nitrate to NaOH is 1:3.1; the remaining steps are consistent with Example 1.

[0041] After replacing ammonia with NaOH, NaOH is completely ionized and the local pH rises suddenly. Excessive NaOH will cause the dissolution of Al(OH)3 precipitate, destroying the Gd 3+ :Al 3+ =2:1 ratio, resulting in the presence of impurities such as Gd2O3, GdAlO3 and Al2O3 in the final product, which reduces the refrigeration capacity. In addition, it is difficult to remove NaOH in the later stage when using NaOH as a precipitant. + , affecting product purity.

[0042] In Example 1, ammonia as a precipitant can form a uniform and stable hydroxide precipitate, and excess ammonia can maintain a weak alkaline environment without dissolving Al(OH)3; the residual NH4OH can be removed by washing, annealing and calcining. 4+ , convenient and efficient.

[0043] Comparative Example 3 The difference from Example 1 is that in step 3, the annealing temperature is 400° C. and 600° C. for 6 h; the remaining steps are consistent with Example 1.

[0044] If the annealing temperature is lowered, undecomposed impurities will remain in the mixture. These impurities will release gas during the subsequent calcination and dehydration process, forming pores inside the product, ultimately leading to a loose product structure; some alumina precipitation will occur, and the product will be impure.

[0045] Comparative Example 4 The difference from Example 1 is that in step 4, the temperature is heated to 1100, 1200, 1300, 1400 and 1500° C. respectively and sintered for 20 h in an air atmosphere; the other steps are consistent with Example 1.

[0046] When the calcination temperature drops to 1100 ℃, the atomic diffusion rate decreases significantly. Even if the sintering time is extended to 20 h and the total heat is close to the original conditions, it is still difficult to completely generate Gd4Al2O9. A mixture of Gd2O3 and Al2O3 remains in the product, affecting the product purity. When the sintering temperature is lowered, a mixture of Gd2O3 and Al2O3 remains in the product, the interatomic bonding force is reduced, and it is difficult to fill the pores between the particles, affecting the densification effect, resulting in a porous and loose structure of the product that is loose and brittle.

[0047] The samples prepared in the examples and comparative examples were subjected to a magnetic field variation of 0 to 7 T. By using the measurement method in Example 1, it was found that the samples prepared in Examples 1-3 had a higher isothermal magnetic entropy change and relative magnetic cooling capacity, which means that the magnetic structure of the material is more stable, the relative magnetic cooling capacity is stronger, and the cooling efficiency is higher. The performance difference between Examples 1-3 is due to the different magnetic moment sizes and magnetocrystalline anisotropy of the rare earth ions. The isothermal magnetic entropy changes in Examples 4 and 5 were between 18.46 and 33.12 J / kg K, respectively, and the relative magnetic cooling capacity was between 430.59 and 498.48 J / kg.

[0048] In Comparative Example 1, the total molar ratio of rare earth metal ions to aluminum ions to the molar ratio of ammonia water was 1:2.8. Ammonia water is a weak base, and the amount of ammonia water added was insufficient, making it impossible to completely convert the rare earth metal ions and aluminum ions into precipitates, resulting in poor performance of the prepared material. In Comparative Example 2, the total molar ratio of rare earth metal ions to aluminum ions to the molar ratio of NaOH was 1:3.1. NaOH is a strong base, and the amount of NaOH added was excessive. Excessive NaOH would react with the already formed precipitate, such as aluminum hydroxide, resulting in a low purity of the final product, which in turn reduced the performance of the prepared material. The annealing temperature in Comparative Example 3 was low, making it difficult to completely convert the precipitate into oxides, resulting in poor performance of the prepared material. The calcination temperature in Comparative Example 4 was low, making it difficult to completely convert the oxides into rare earth aluminate low-temperature magnetic refrigeration materials with a specific structure, resulting in poor performance of the prepared material.

[0049] In order to further explore the differences in the rare earth aluminate low-temperature magnetic refrigeration performance of the prepared samples, more performance tests were conducted on the samples prepared in Examples 1-3. The specific test results are as follows: Performance Characterization 1.XRD test The samples prepared in Examples 1-3 were subjected to XRD tests, and the test results were as follows: Figure 1 and as shown in Table 1.

[0050] Table 1. ( RE = Crystal structure parameters of Gd, Dy and Ho)

[0051] from Figure 1 It can be seen that the samples prepared in Examples 1-3 RE 4Al2O9 materials all belong to the monoclinic system, and the space group is P 21 / c. The diffraction peaks of all samples are consistent with the standard pattern of monoclinic system (space group P21 / c), indicating that RE The 4Al2O9 material was successfully synthesized with a consistent crystal form. The sharp diffraction peaks and narrow half-width (FWHM) indicate high crystallinity, the absence of significant impurities, and good controllability of the preparation process.

[0052] The samples prepared in Example 4-5 were subjected to XRD test, and the test results were as follows: Figure 2 As shown in the figure. The ionic radius of Gd is similar to that of Dy and Ho, and after doping, it can ensure the stability of the crystal structure and reduce the probability of impurity phase generation caused by the large difference in ionic radius. Figure 2 It can be seen that the diffraction peak positions and quantities of the two samples are highly matched, and RE It corresponds to the standard crystal form of 4Al2O9 system and the product has high purity.

[0053] The sample of Comparative Example 1 (the total molar ratio of gadolinium nitrate and aluminum nitrate to the molar ratio of ammonia water is 1:3.1) was subjected to XRD test, and the test results are as follows: Figure 3 As shown. Figure 3 It can be seen that the spectrum shows the presence of mixed diffraction peaks of GdAlO3 and Gd2O3, indicating that the reduction in the amount of ammonia water will lead to the incomplete precipitation of metal ions, and the residual metal ions will cause the formation of impurities in the product.

[0054] The comparative example 2 (where ammonia water is replaced by NaOH and the molar ratio of the total amount of gadolinium nitrate and aluminum nitrate to NaOH is 1:3.1) was subjected to XRD test. The test results are as follows: Figure 4When sodium hydroxide is used as a precipitant in excess, mixed diffraction peaks of GdAlO3, Gd2O3 and Al2O3 appear in the XRD test spectrum of the product. The product is a mixture, so the magnetic properties of this product are not studied.

[0055] The comparative example 3 (annealing temperature is reduced to 400 ° C) is subjected to XRD test, and the test results are as follows Figure 5 The diffraction peak intensity of the sample annealed at 400 °C is lower than that of the sample annealed at 600 °C, indicating that insufficient temperature during the annealing process will cause residual hydroxide, resulting in a loose and porous structure and a decrease in density during the subsequent tableting process.

[0056] The comparative example 4 (calcination temperature was changed) was subjected to XRD test, and the test results were as follows: Figure 6 As shown. Figure 6 It can be seen that the samples calcined below 1100℃ have mixed peaks of Gd2O3 and Al2O3, indicating that when the calcination temperature is insufficient, the product has mixed phases and cannot be completely generated. RE 4Al2O9; The target product can be generated at 1200℃, but the purity is low; The diffraction peaks of the samples calcined at 1200-1500℃ are single and sharp, which verifies the effect of high temperature on the formation of pure phase. RE The importance of 4Al2O9.

[0057] The ZFC and FC tests under a 0.1 T magnetic field are measured using a superconducting quantum interference device (SQUID) or a vibrating sample magnetometer (VSM). The specific test conditions are as follows: cooling from 100 K to 2 K in the absence of a magnetic field, and then heating from 2 K to 100 K with a 0.1 T magnetic field (ZFC test); cooling from 100 K to 2 K in a 0.1 T magnetic field, and then heating from 2 K to 100 K (FC test).

[0058] The ZFC and FC thermomagnetic curves of the samples prepared in Examples 1-3 under different magnetic fields are as follows: Figure 7 As shown, from Figure 7 It can be seen that the ZFC and FC curves basically coincide in the low temperature region (no bifurcation), indicating that the material is a paramagnetic material, the magnetic moment can be freely oriented under an external magnetic field, and its hysteresis and thermal hysteresis effects can be ignored.

[0059] 3.Isothermal magnetic properties The isothermal magnetization test method is usually to use a vibrating sample magnetometer (VSM) or a physical property measurement system (MPMS-XL), both of which have the function of measuring the magnetization intensity at different temperatures and magnetic fields. The isothermal magnetization curves of the samples prepared in Examples 1-3 at different temperatures are shown in Figure 1. Figure 8 As shown, from Figure 8It can be seen that within the low to medium magnetic field range (0-7 T), the magnetization increases approximately linearly with increasing magnetic field, indicating that the material is a weak paramagnet with no saturation magnetization. Under the same magnetic field, the magnetization increases with lower temperature, consistent with the characteristics of paramagnetic materials.

[0060] 4. Magnetic entropy change with temperature The test method for the curve of magnetic entropy change with temperature is vibrating sample magnetometer (VSM) or physical property measurement system (MPMS-XL). The curve of magnetic entropy change with temperature of the samples prepared in Examples 1-3 under different magnetic field changes is as follows: Figure 9 As shown, from Figure 9 It can be seen that An obvious peak appears in the low temperature region (about 5-20 K), and the peak value increases with the increase of the magnetic field, indicating that the material has excellent magnetocaloric effect in the low temperature region; the temperature range corresponding to the peak value is relatively wide, combined with the relative magnetic cooling ability, indicating that the material has practical refrigeration potential in a wide temperature range.

[0061] 5.(Gd 0.5 Dy 0.5 )4Al2O9 sample related characteristics test diagram Figure 10 These are the ZFC and FC thermomagnetic curves of the sample prepared in Example 5 of the present invention under a 0.1 T magnetic field, the isothermal magnetization curves at different temperatures, and the magnetic entropy change curve with temperature under different magnetic field changes, wherein (a) is the ZFC and FC thermomagnetic curves under a 0.1 T magnetic field, (b) is the isothermal magnetization curve at different temperatures, and (c) is the magnetic entropy change curve with temperature under different magnetic field changes.

[0062] Depend on Figure 10 Figure (a) shows the ZFC (zero-field cooling) and FC (field cooling) thermomagnetic curves under a 0.1 T magnetic field. The ZFC and FC curves essentially overlap in the low-temperature range (2-50 K), with no significant bifurcation. This overlap indicates that the material is paramagnetic, with negligible magnetic and thermal hysteresis effects. This confirms the material's magnetic stability at low temperatures, making it suitable for high-efficiency refrigeration.

[0063] Depend on Figure 10 As shown in (b), within the 0-7 T magnetic field range, the magnetization increases approximately linearly with increasing magnetic field, consistent with the typical characteristics of paramagnetic materials. The magnetization increases with lower temperatures, indicating a higher degree of magnetic order at low temperatures, consistent with the characteristics of paramagnetic materials.

[0064] Depend on Figure 10It can be seen from (c) in that the peak value of magnetic entropy change appears in the low temperature region (5-25 K) and increases significantly with the increase of magnetic field intensity. Referring to the measurement method of Example 1, it was measured that the isothermal magnetic entropy change of the finished product under the magnetic field change of 0-2 T was 7.83 J / kg K, and the relative magnetic cooling capacity was 72.23 J / kg; under the magnetic field change of 0-5 T, the isothermal magnetic entropy change was 21.79 J / kg K, and the relative magnetic cooling capacity was 305.07 J / kg; under the magnetic field change of 0-7 T, the isothermal magnetic entropy change was 30.48 J / kg K, and the relative magnetic cooling capacity was 457.19 J / kg. The temperature range corresponding to the peak is relatively wide (5-25 K), and combined with the relative magnetic cooling capacity (RCP) data, it shows that the material has practical refrigeration potential in a wide temperature range. This result is consistent with Figure 9 The magnetic entropy change trend of single rare earth aluminates is consistent, indicating that the Gd-Ho doped system retains the high magnetic entropy change characteristics and may even improve the magnetic refrigeration performance due to the ion synergistic effect.

[0065] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a rare earth aluminate low-temperature magnetic refrigeration material, characterized in that: The following steps are involved: (1) adding rare earth metal nitrate and aluminum nitrate into water to prepare a mixed solution; adding ammonia water into the mixed solution to prepare a precipitate; (2) annealing the precipitate to obtain a metal oxide; (3) The metal oxide is calcined to obtain rare earth aluminate low-temperature magnetic refrigeration material.

2. The method for preparing the rare earth aluminate low-temperature magnetic refrigeration material according to claim 1, characterized in that: In step (1), the molar ratio of rare earth metal ions to aluminum ions in the mixed solution is 2:1; The rare earth metal nitrate is at least one of gadolinium nitrate, dysprosium nitrate and holmium nitrate.

3. The method for preparing the rare earth aluminate low-temperature magnetic refrigeration material according to claim 1, characterized in that: In step (1), the total molar ratio of rare earth metal ions and aluminum ions in the mixed solution to the molar ratio of ammonia water is 1: (3.2-4.0); The concentration of the ammonia water is 10-15 mol / L.

4. The method for preparing the rare earth aluminate low-temperature magnetic refrigeration material according to claim 1, characterized in that: In step (2), the annealing treatment temperature is 560-760 ° C and the time is 3-6 h; Alternatively, before the precipitate is annealed, the precipitate is pretreated, and the pretreatment comprises aging, filtering, washing and drying the precipitate in sequence; the aging time is 10-24 h, the washing solvent is water or ethanol, and the drying temperature is 80-120° C. and the drying time is 10-15 h.

5. The method for preparing the rare earth aluminate low-temperature magnetic refrigeration material according to claim 1, characterized in that: In step (3), the calcination temperature is 1200-1500 ° C, the time is 6-18 h, and the atmosphere is air; Alternatively, the metal oxide may be pretreated before being calcined, wherein the pretreatment comprises grinding the metal oxide into powder and then subjecting the powder to tableting. The particle size of the metal oxide after grinding is 150-250 mesh, and the tableting is performed at 15-20°C for 3-5 minutes.

6. A rare earth aluminate low-temperature magnetic refrigeration material prepared by the method for preparing a rare earth aluminate low-temperature magnetic refrigeration material according to any one of claims 1 to 5.

7. The rare earth aluminate low-temperature magnetic refrigeration material according to claim 6, characterized in that: The general chemical formula of the rare earth aluminate low-temperature magnetic refrigeration material is: RE 4Al2O9, wherein RE is at least one of the rare earth elements Gd, Dy and Ho; described RE 4Al2O9 has the following properties: Under the magnetic field variation of 0-2 T, the isothermal magnetic entropy change is 9.47-10.32 J / kg K, and the relative magnetic cooling capacity is 72.23-92.18 J / kg; Under the magnetic field variation of 0-5 T, the isothermal magnetic entropy change is 16.26-27.94 J / kg K, and the relative magnetic cooling capacity is 279.41-341.38 J / kg; Under magnetic field changes of 0-7 T, the isothermal magnetic entropy change is 18.46-33.12 J / kg K, and the relative magnetic cooling capacity is 430.59-498.48 J / kg.

8. Use of the rare earth aluminate low-temperature magnetic refrigeration material according to claim 6 or 7 in low-temperature magnetic refrigeration.

9. The use according to claim 8, characterized in that The applications are in low temperature physics, deep space exploration and military aerospace.

10. A method for using a rare earth aluminate low-temperature magnetic refrigeration material, characterized in that: The rare earth aluminate low-temperature magnetic refrigeration material according to claim 6 or 7 is applied on a substrate.

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