Magnetic refrigeration material, preparation method thereof and application of magnetic refrigeration material in magnetic refrigeration in extremely low temperature region

Abstract

The invention discloses a magnetic refrigeration material, a preparation method thereof and application of the magnetic refrigeration material in magnetic refrigeration in an extremely low temperature region. The chemical formula of the magnetic refrigeration material is Gd5 (C3N3O3) (OH) 12, the magnetic refrigeration material belongs to a hexagonal system, the space group is # imgabs 0 #, the cell parameter is # imgabs 1 #, the magnetic refrigeration material has relatively high magnetization intensity and a high-thermal-stability magnetic structure, and still shows superparamagnetic characteristics without magnetic phase change at extremely low temperature, and when the temperature T of the material is 2K and the applied magnetic field delta H is 7T, the maximum magnetic entropy change-delta Sm is 58.1 J * kg <-1 > * K <-1 >, and the maximum magnetic entropy change-delta Sm is 58.1 J * kg <-1 > * K <-1 >. The material is an ideal magnetic refrigeration material in an extremely low temperature region.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic refrigeration materials, and more particularly to a magnetic refrigeration material, a preparation method thereof, and an application thereof in magnetic refrigeration in an extremely low temperature region. Background Art

[0002] Magnetic cooling technology uses magnetic materials as the working matrix and achieves the purpose of cooling through the magnetocaloric effect of the material. Compared with traditional refrigeration technology, magnetic cooling technology does not produce greenhouse gases, does not damage the atmospheric ozone layer, has low noise, good operability, safety, and high efficiency. It is a green and environmentally friendly refrigeration technology. Its mechanism of action is that under the action of an external magnetic field, the magnetic moment of a paramagnetic or ferromagnetic material changes from disorder to order, the magnetic entropy of the material decreases, and heat is released to the outside. When the external magnetic field disappears, the magnetic moment of the magnetic material changes from order to disorder, and the magnetic entropy increases, absorbing energy from the external environment. When the system is adiabatic, the temperature of the magnetic material itself decreases. The magnitude of the magnetocaloric effect can be expressed by the maximum magnetic entropy change value (ΔS M ), relative cooling capacity (RCP), adiabatic temperature change (ΔT ad ) to measure.

[0003] Some compounds with low temperature magnetic order have high magnetocaloric effect. For example, Gd3Ga 5-x Al x O 12 (0≤x≤5), EuTiO3, and ErRuSi all exhibit very high maximum magnetic entropy change values ​​at ultra-low temperatures below 10K. Although some magnetocaloric materials that do not contain rare earth elements have been discovered, their application temperature ranges are relatively high, and magnetocaloric materials for the ultra-low temperature range are still primarily based on rare earth elements. The search and preparation of ultra-low temperature magnetocaloric materials with even superior performance remains a crucial research topic in materials science. Summary of the Invention

[0004] To solve the above problems, the first object of the present invention is to provide a magnetic cooling material. The magnetic cooling material has a large magnetization intensity and a high thermally stable magnetic structure, and still exhibits superparamagnetic properties without magnetic phase transition at extremely low temperatures, with a maximum magnetic entropy change of -ΔS m =58.1 J·kg -1 ·K -1 , is an ideal magnetic refrigeration material in the extremely low temperature zone.

[0005] The second object of the present invention is to provide a method for preparing the magnetic cooling material as described above. The synthesis process provided by the present invention is simple, easy to operate, has mild reaction conditions, and uses abundant and inexpensive raw materials, which is expected to achieve large-scale production and use.

[0006] The third object of the present invention is to provide an application of the magnetic refrigeration material as described above in magnetic refrigeration in the ultra-low temperature region.

[0007] In order to achieve the above first object, the present invention adopts the following technical solutions:

[0008] The present invention discloses a magnetic cooling material, the chemical formula of which is Gd5(C3N3O3)(OH) 12 .

[0009] Furthermore, the magnetoresistive material belongs to the hexagonal system, and the space group is The unit cell parameters are

[0010] In order to achieve the above second purpose, the present invention adopts the following technical solutions:

[0011] The present invention discloses a method for preparing the magnetic refrigeration material as described above, comprising the following steps:

[0012] 1) Weigh LiOH·H2O and H3C3N3O3 into water, heat to dissolve, cool to room temperature, and filter to obtain the compound LiH2C3N3O3·H2O;

[0013] 2) Weighing Gd(NO3)3·H2O, LiH2C3N3O3·H2O, LiOH·H2O and water, placing them in a hydrothermal reactor lined with polytetrafluoroethylene for hydrothermal reaction, slowly cooling to room temperature after the reaction, taking out the contents, repeatedly washing, filtering, and drying to obtain the magnetic cooling material.

[0014] Furthermore, the molar ratio of LiOH·H2O and H3C3N3O3 is 1-3:1; illustratively, the molar ratio of LiOH·H2O and H3C3N3O3 can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, etc.

[0015] Further, the molar ratio of Gd(NO3)3·H2O, LiH2C3N3O3·H2O, LiOH·H2O and water is 4-8:1:2-4:45-50; illustratively, the molar ratio of Gd(NO3)3·H2O, LiH2C3N3O3·H2O, LiOH·H2O and water can be 4-8:1:2:45-50, 4-8:1:3:45-50, 4-8:1:4:45-50, 4:1:2:45-50 , 4:1:3:45-50, 4:1:4:45-50, 5:1:2:45-50, 5:1:3:45-50, 5:1:4:45-50, 6:1:2:45-50, 6:1:3:45-50, 6:1:4:45-50, 7:1:2:45-50, 7:1:3:45-50, 7:1:4:45-50, 8:1:2:45-50, 8:1:3:45-50, 8:1:4:45-50, etc.

[0016] Furthermore, the reaction temperature of the hydrothermal reaction is 140-170°C, and the reaction time is 10-60h. For example, the reaction temperature can be 140°C, 150°C, 160°C, 170°C, etc., and the reaction time can be 10h, 20h, 30h, 40h, 50h, 60h, etc., preferably 50h at 150°C. Under these conditions, Gd5(C3N3O3)(OH) can be formed. 12 It can produce pure phase samples, reduce energy consumption and improve the safety of the preparation process.

[0017] Furthermore, the cooling rate in step 2 is less than 5°C / h.

[0018] Furthermore, the capacity of the polytetrafluoroethylene liner used in the hydrothermal reactor is 10-500 mL; illustratively, the capacity of the polytetrafluoroethylene liner can be 10 mL, 15 mL, 20 mL, 30 mL, 40 mL, 50 mL, 60 mL, 70 mL, 80 mL, 90 mL, 100 mL, 150 mL, 200 mL, 250 mL, 300 mL, 350 mL, 400 mL, 450 mL, 500 mL, etc.

[0019] In order to achieve the third object, the present invention adopts the following technical solutions:

[0020] The invention discloses the application of magnetic refrigeration materials in magnetic refrigeration in an extremely low temperature region.

[0021] Furthermore, the temperature range of the extremely low temperature zone is 2-50K.

[0022] The beneficial effects of the present invention are as follows:

[0023] The Gd5(C3N3O3)(OH) disclosed in the present invention 12 The compound is a new type of magnetic refrigeration material that can be used in ultra-low temperature areas. It belongs to the hexagonal system and its space group is The magnetic refrigeration material has a large magnetization intensity and a high thermally stable magnetic structure in terms of performance. It still exhibits superparamagnetic properties at ultra-low temperatures without undergoing magnetic phase transition. Experiments show that the maximum magnetic entropy change -ΔS is measured when the temperature is T = 2K and the external magnetic field ΔH = 7T. m =58.1 J·kg -1 ·K -1 Compared with the traditional common low temperature magnetic refrigeration medium Gd3Ga5O 12 (38.3 J·kg -1 ·K -1 ) significantly improved, thus this material has potential application prospects in the ultra-low temperature range and can be used in a variety of magnetic refrigeration devices in this range, with significant economic and social benefits. Furthermore, the synthesis process provided by this invention is simple and easy to operate, with mild reaction conditions and abundant and inexpensive raw materials, promising large-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0025] Figure 1 Gd5(C3N3O3)(OH) 12 Schematic diagram of the crystal structure.

[0026] Figure 2 Gd5(C3N3O3)(OH) 12 XRD pattern of crystalline powder.

[0027] Figure 3 Gd5(C3N3O3)(OH) 12 Hysteresis loop between -9T and 9T.

[0028] Figure 4 Gd5(C3N3O3)(OH) 12 Curve of magnetic susceptibility changing with temperature under 0.2T magnetic field.

[0029] Figure 5 Gd5(C3N3O3)(OH) 12 MH curve in the temperature range of 2-30K.

[0030] Figure 6 Gd5(C3N3O3)(OH) 12 Magnetic entropy change curve under 1-7T magnetic field. DETAILED DESCRIPTION

[0031] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the following detailed description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0032] Example 1

[0033] Weigh 4.19 g of LiOH·H2O and 12.9 g of H3C3N3O3 into 80 mL of deionized water, heat to 80°C on a magnetic stirring table and stir for 30 min until completely dissolved. Turn off the heating system of the magnetic stirring table and allow the solution system to cool naturally to room temperature. Filter and dry in an 80°C oven for 1 h to obtain 15.29 g of the compound LiH2C3N3O3·H2O.

[0034] 1.3542 g of Gd(NO3)3·H2O, 0.0918 g of LiH2C3N3O3·H2O, and 0.1005 g of LiOH·H2O were weighed and placed in a 15 mL polytetrafluoroethylene-lined hydrothermal reactor. 3 mL of deionized water was added and the reaction mixture was heated to 150°C in an oven and kept at this temperature for 50 h to allow the hydrothermal reaction to proceed. The mixture was then cooled to room temperature at a rate of 3°C / h. The contents were removed, washed repeatedly, filtered, and dried at 80°C for 1 h to obtain Gd5(C3N3O3)(OH) 12 product.

[0035] Figure 1 Gd5(C3N3O3)(OH) 12 Schematic diagram of the crystal structure. According to single crystal diffraction test, Gd5(C3N3O3)(OH) 12 Belongs to the hexagonal system, space group is Its structural parameters are shown in Table 1. The sample obtained in Example 1 was subjected to powder XRD test using a Bruker advance X-ray diffractometer, and the test results were refined using FullProf. The obtained powder X-ray diffraction pattern is shown in Figure 2 , confirming that the product obtained in Example 1 is Gd5(C3N3O3)(OH) 12 single crystal form.

[0036] Table 1 Gd5(C3N3O3)(OH) 12 Structural parameters

[0037]

[0038] Performance Testing

[0039] The magnetic properties measurement system (MPMS) manufactured by Quantum Design was used to measure the Gd5(C3N3O3)(OH) obtained in Example 1. 12 The following magnetic tests were performed on milligram-level powder samples:

[0040] like Figure 3 As shown in Figure 1, a powder sample was encapsulated in a gel capsule attached to a copper rod. The hysteresis loops of the powder sample were measured at constant temperatures of 2K, 5K, 10K, 20K, 30K, 50K, 100K, and 300K under cyclic applied magnetic fields ranging from -9T to 9T. Within the measured temperature range, the material exhibited no hysteresis, meaning the integrated area of ​​the hysteresis loop was close to zero, indicating that the material did not exhibit ferromagnetism at this operating temperature.

[0041] like Figure 4 As shown in the figure, the continuous variation curve of the magnetic susceptibility (χ) of the powder sample was measured between 2 and 300 K under a stable external magnetic field of 0.2 T, and the Curie-Weiss equation was fitted to the inverse magnetic susceptibility curve in the range of 100-280 K using Origin software. The material has a large magnetization intensity in the operating temperature range of 2-50 K, and the inverse magnetic susceptibility curve is in good agreement with the Curie-Weiss equation fitting results, indicating that the material maintains superparamagnetic properties at very low temperatures (2-50 K) and does not undergo a significant magnetic phase transition even at the extremely low temperature of 2 K.

[0042] like Figure 5 As shown in the figure, the MH curve of the powder sample was measured at an interval of 2K in the temperature range of 2-30K under an external magnetic field strength of 0-7T. According to the second law of thermodynamics and Maxwell's equations of thermodynamics, the data was integrated and calculated to obtain the following: Figure 6 The curve of the change of magnetic entropy of the sample with temperature under different external magnetic fields is shown. The experiment shows that the maximum magnetic entropy change of the material is -ΔS when the temperature is T = 2K and the external magnetic field is ΔH = 7T. m =58.1 J·kg -1 ·K -1 Compared with the traditional common low temperature magnetic refrigeration medium Gd3Ga5O 12 (38.3 J·kg -1 ·K -1 ) has been significantly improved.

[0043] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A magnetic refrigeration material, characterized in that: The chemical formula of the magnetic cooling material is Gd5(C3N3O3)(OH) 12 .

2. The magnetic refrigeration material according to claim 1, characterized in that The magnetic cooling material belongs to the hexagonal system, and the space group is The unit cell parameters are 3. The method for preparing a magnetic refrigeration material according to claim 1 or 2, characterized in that: The steps include: 1) Weigh LiOH·H2O and H3C3N3O3 into water, heat to dissolve, cool to room temperature, and filter to obtain the compound LiH2C3N3O3·H2O; 2) Weighing Gd(NO3)3·H2O, LiH2C3N3O3·H2O, LiOH·H2O and water, placing them in a hydrothermal reactor lined with polytetrafluoroethylene for hydrothermal reaction, slowly cooling to room temperature after the reaction, taking out the contents, repeatedly washing, filtering, and drying to obtain the magnetic cooling material.

4. The preparation method according to claim 3, characterized in that The molar ratio of LiOH·H2O to H3C3N3O3 is 1-3:

1.

5. The preparation method according to claim 3, characterized in that The molar ratio of Gd(NO3)3·H2O, LiH2C3N3O3·H2O, LiOH·H2O and water is 4-8:1:2-4:45-50.

6. The preparation method according to claim 3, characterized in that The reaction temperature of the hydrothermal reaction is 140-170° C., and the reaction time is 10-60 hours.

7. The preparation method according to claim 3, characterized in that The reaction temperature of the hydrothermal reaction is 150° C., and the reaction time is 50 h.

8. The preparation method according to claim 3, characterized in that The cooling rate in step 2 is less than 5°C / h.

9. Use of the magnetic refrigeration material according to claim 1 or 2 in magnetic refrigeration in ultra-low temperature regions.

10. The use according to claim 9, characterized in that The temperature range of the extremely low temperature zone is 2-50K.

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