A rare earth alkali metal fluorosilicate crystal and its synthesis method and application in magnetic refrigeration

Abstract

The present invention provides a rare earth alkali metal fluorosilicate crystal, a synthesis method thereof, and application in magnetic refrigeration. The crystal has a chemical formula of Na5R4F(SiO4)4, where the metal R is Gd, Tb, Dy, Ho, or Er. The synthesis method comprises: 1) uniformly mixing a Na-containing compound, an R-containing compound, a Si-containing compound, and a B-containing compound; heating the mixture to 300-500°C in an oxygen-containing environment at normal pressure, pre-sintering the mixture at a constant temperature, and cooling the mixture once to obtain a pre-sintered material; 2) grinding the pre-sintered material, placing the mixture again in an oxygen-containing environment at normal pressure, heating it to 1000-1100°C, sintering the mixture at a constant temperature, and cooling the mixture once to obtain Na5R4F(SiO4)4 crystals. The Na-containing compound is selected from a Na-containing fluoride. In the present invention, a high-temperature co-solvent method is used for the first time to synthesize Na5R4F(SiO4)4 crystals. The synthesis method is convenient, fast, easy to operate, and suitable for large-scale industrial production. The maximum magnetic entropy change of the obtained Na5R4F(SiO4)4 crystals can reach 49.6 J kg at 2.6K and Δμ0H=7T. ‑1 K ‑1 , while the cooling capacity and relative cooling capacity are 308.9J·kg ‑1 and 406.7 J·kg ‑1 , showing its potential as a magnetic refrigeration material in the low-temperature region.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic refrigeration materials, and specifically comprises a rare earth alkali metal fluorosilicate crystal, a synthesis method thereof, and application in magnetic refrigeration. Background Art

[0002] Ultra-low temperature environments are essential for high-end fields such as space exploration and quantum computing. Currently, the primary method for achieving ultra-low temperature environments is through helium, including reduced-pressure evaporation of helium or dilution refrigeration. However, as a strategic resource, helium reserves are very limited. Faced with increasingly scarce helium resources, there is an urgent need to find a substitute. The magnetocaloric effect (MCE) refers to the use of magnetic materials as working substances in thermodynamic cycles. Magnetic materials were first discovered in 1917 and quickly developed into an important refrigeration technology. MCE is defined as the change in isothermal magnetic entropy and adiabatic temperature under the application and removal of a magnetic field. Due to its advantages such as high recycling efficiency and the lack of consideration for gravity, magnetic refrigeration has been recognized as a competitive cooling technology for cryogenic applications and is expected to replace helium as the mainstream cryogenic refrigeration method, attracting the attention of various countries.

[0003] During the magnetization process, due to the minimal thermal disturbance at low temperatures, the magnetic moment of the magnetic material can be deflected along the direction of the magnetic field, thereby changing from disorder to order, and the magnetic entropy decreases. At this time, according to the principles of thermodynamics, the magnetic fluid releases heat. During the demagnetization process, the magnetic moment of the magnetic material changes from order to disorder again, and the magnetic entropy increases, at which point the magnetic fluid absorbs heat from the outside. Under adiabatic conditions, there is no heat exchange between the magnetic fluid and the external environment. During the excitation and demagnetization processes, the magnetic field performs work on the material, causing the internal energy of the material to change, and thus the temperature of the material itself to change.

[0004] In low-temperature magnetic refrigeration, paramagnetic salts with weak interactions become potential candidates because the thermal vibration of the lattice can be ignored. The selection of paramagnetic salt magnetic refrigeration materials requires that the magnetic ions have a large spin ground state, small magnetic anisotropy, high magnetic density, suitable magnetic exchange and low-energy excited spin state. Compared with other rare earth ions, Gd 3+ The ions have a large ground state spin (S = 7 / 2) and completely quenched orbital momentum. Therefore, Gd-based oxides tend to exhibit high saturation moments and negligible magnetic anisotropy, resulting in large MCEs.

[0005] For practical applications, magnetic refrigeration materials must first meet two characteristics. First, the magnetic entropy change of the magnetic cooling material must be as large as possible, thereby generating a large adiabatic temperature. Therefore, it is usually selected to contain light ligands (such as BO3 3- 、SiO4 4-) magnetic refrigeration materials, which is conducive to obtaining a large MCE. Secondly, high heat exchange efficiency needs to be obtained in the magnetic refrigeration cycle. In this case, due to the lack of grain boundary scattering, single crystals usually have higher thermal conductivity than polycrystalline, which is beneficial for heat exchangers. Therefore, high Gd 3+ Single crystal compounds with a high ratio of 1:1 to 1:1 have great potential for magnetic refrigeration applications. However, the current methods for preparing Gd-based single crystal compounds containing light ligands are often harsh and require a large number of reaction raw materials, which is not conducive to industrial production. The development of new preparation processes to address this technical problem is urgent. Summary of the Invention

[0006] To address the aforementioned issues with the prior art, the first objective of the present invention is to provide a method for synthesizing rare earth alkali metal fluorosilicate crystals. This method successfully synthesizes Na5R4F(SiO4)4 crystals using a high-temperature co-solvent method. This method features a simple synthesis process, a short synthesis cycle, a limited number of required raw materials, and the elimination of strict control of O2 in the reaction environment, facilitating subsequent large-scale industrial production.

[0007] The second object of the present invention is to provide a Na5R4F(SiO4)4 crystal synthesized using the synthesis method described above.

[0008] The third object of the present invention is to provide an application of the above-mentioned Na5R4F(SiO4)4 crystal in magnetic refrigeration. The application of the Na5R4F(SiO4)4 crystal in magnetic refrigeration proposed by the present invention is innovative. The maximum magnetic entropy change of the crystal reaches 49.6 J kg at 2.6K and Δμ0H=7T. -1 K -1 , while the cooling capacity and relative cooling capacity are 308.9J·kg -1 and 406.7 J·kg -1 , showing its potential as a magnetic refrigeration material in the low-temperature region.

[0009] The fourth object of the present invention is to provide an application of the Na5R4F(SiO4)4 crystal as described above in the preparation of a refrigeration device.

[0010] To achieve the above first purpose, the technical solution adopted by the present invention includes:

[0011] The present invention discloses a method for synthesizing rare earth alkali metal fluorosilicate crystals, wherein the chemical formula of the crystals is Na5R4F(SiO4)4, and the metal R is Gd, Tb, Dy, Ho or Er;

[0012] The synthesis method comprises the following steps:

[0013] 1) Mixing the Na-containing compound, the R-containing compound, the Si-containing compound and the B-containing compound uniformly, raising the temperature to 300-500° C. in an oxygen environment at normal pressure, pre-calcining at a constant temperature, and cooling once to obtain a pre-calcined material;

[0014] 2) After grinding the pre-sintered material, place it in a normal pressure, oxygen environment again, heat it to 1000-1100°C, sinter it at a constant temperature, and obtain Na5R4F(SiO4)4 crystals after secondary cooling;

[0015] Wherein, the Na-containing compound is selected from Na-containing fluorides.

[0016] In the present invention, by introducing suitable co-solvents (i.e., Na fluoride-containing and B-containing compounds) into the raw materials, technicians were able to synthesize Na5R4F(SiO4)4 crystals for the first time using a high-temperature co-solvent method. This synthesis method has a simple process, a short synthesis cycle, requires fewer types of raw materials, has lower requirements for the reaction environment, does not require O2 control, and does not require a high sintering temperature, making it suitable for large-scale industrial production.

[0017] Furthermore, the Na-containing fluoride is a co-solvent of the reaction system and can be further selected from NaF;

[0018] The R-containing compound is selected from R-containing oxides; for example, Gd2O3, Tb4O7, Dy2O3, Ho2O3 or Er2O3, etc.;

[0019] The Si-containing compound is selected from Si-containing oxides; for example, SiO2;

[0020] The B-containing compound is a co-solvent of the reaction system and can be selected from H3BO3 or B2O3.

[0021] It should be noted that the various limiting conditions for the synthesis method of the present invention are applicable to all metal R cases.

[0022] Furthermore, the raw material ratio affects the impurity ratio of the target product. When the Na-containing compound, the R-containing compound, the Si-containing compound and the B-containing compound are mixed according to the molar ratio of Na, R, Si, and B of 8-10:2:1-3:1-3, the impurity ratio of the target product can be reduced; illustratively, the molar ratio of Na, R, Si, and B can be 8-10:2:1:1, 8-10:2:2:2, 8-10:2:3:3, 8:2:1-3:1-3, 9:2:1-3:1-3, 10:2:1-3:1-3, and the like, preferably 9:2:2:2.

[0023] Further, the heating rate in step 1 and step 2 is 40-80°C / h; illustratively, the heating rate in step 1 and step 2 can be 40°C / h, 45°C / h, 50°C / h, 55°C / h, 60°C / h, 65°C / h, 70°C / h, 75°C / h, 80°C / h, and the like.

[0024] Furthermore, the purpose of constant temperature pre-calcination is to remove H2O in the reactants and to carry out a preliminary solid phase reaction. In a specific embodiment, the constant temperature pre-calcination time is 1-3 days.

[0025] Furthermore, the constant temperature sintering time is 1-3 days.

[0026] Furthermore, the reaction of the present invention is carried out in an oxygen environment at normal pressure. Those skilled in the art may understand this as a reaction carried out in an atmospheric environment, or as a reaction carried out by continuously blowing an oxygen atmosphere into a reactor; the oxygen atmosphere may be an air atmosphere or an atmosphere with other oxygen content ratios, which is not specifically limited here.

[0027] Furthermore, the cooling rate of the primary cooling is 40-60°C / h; illustratively, the cooling rate of the primary cooling may be 40°C / h, 45°C / h, 50°C / h, 55°C / h, 60°C / h, and the like.

[0028] Furthermore, during secondary cooling, the temperature is first lowered to 800° C. at a cooling rate of 1-5° C. / h, and then lowered to room temperature at a cooling rate of 40-60° C. / h.

[0029] To achieve the above second purpose, the technical solutions adopted by the present invention include:

[0030] The present invention discloses a Na5R4F(SiO4)4 crystal synthesized by the above-mentioned synthesis method.

[0031] Furthermore, the Na5R4F(SiO4)4 crystal belongs to the tetragonal system and has a space group of I-4. In particular, for the Na5Gd4F(SiO4)4 crystal, its unit cell parameters are: α=β=γ=90°, Z=2.

[0032] To achieve the third objective, the present invention employs the following technical solutions:

[0033] The present invention discloses an application of the Na5R4F(SiO4)4 crystal in magnetic refrigeration.

[0034] To achieve the fourth objective, the present invention employs the following technical solutions:

[0035] The present invention discloses an application of the Na5R4F(SiO4)4 crystal in preparing a refrigeration device.

[0036] Furthermore, the application is specifically: using Na5R4F(SiO4)4 crystals as magnetic refrigeration materials in the preparation of refrigeration devices, especially as low-temperature magnetic refrigeration materials in the preparation of refrigeration devices.

[0037] Beneficial effects of the present invention:

[0038] The present invention successfully synthesized Na5R4F(SiO4)4 crystals for the first time using a high-temperature co-solvent method. The synthesis process is simple, the synthesis cycle is short, fewer types of raw materials are required, and there is no need for strict control of O2 in the reaction environment, which is conducive to subsequent large-scale industrial production.

[0039] The Na5R4F(SiO4)4 crystal prepared by the present invention belongs to a rare earth alkali metal fluorosilicate crystal, belongs to the tetragonal system, has a space group of I-4, and has the following unit cell parameters: α=β=γ=90°,Z=2, is a paramagnetic salt material with negligible hysteresis and thermal hysteresis effects. It has high refrigeration efficiency when used as a magnetic refrigeration material. The maximum magnetic entropy change of the Na5R4F(SiO4)4 crystal can reach 49.6J kg at 2.6K and Δμ0H=7T. -1 K -1 , while the cooling capacity and relative cooling capacity are 308.9J·kg -1 and 406.7 J·kg -1 , showing its potential as a magnetic refrigeration material in the low-temperature zone, and has broad application prospects in the fields of low-temperature physics, space exploration, aerospace and so on. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0041] Figure 1 The following is a comparison diagram of the XRD patterns of the Na5Gd4F(SiO4)4 crystals prepared in Examples 1 to 3 and the theoretical spectrum.

[0042] Figure 2 A comparison diagram of the XRD pattern of the Na5Tb4F(SiO4)4 crystal prepared in Example 4 and the theoretical spectrum is shown.

[0043] Figure 3 The schematic diagram of the structure of the Na5Gd4F(SiO4)4 crystal prepared in Example 1 is shown; wherein, Figure 3 (a) is the Gd4O in the structure 20 Unit F, Figure 3(b) Gd-Gd bond length in Na5Gd4F(SiO4)4.

[0044] Figure 4 The temperature-dependent magnetic susceptibility curve and Curie-Weiss fitting curve of the Na5Gd4F(SiO4)4 crystal prepared in Example 1 are shown.

[0045] Figure 5 The temperature- and field-dependent magnetization intensity diagram of the Na5Gd4F(SiO4)4 crystal prepared in Example 1 is shown.

[0046] Figure 6 The Arrott curve of the Na5Gd4F(SiO4)4 crystal prepared in Example 1 is shown.

[0047] Figure 7 A diagram showing the magnetic entropy change of the Na5Gd4F(SiO4)4 crystal prepared in Example 1 is shown.

[0048] Figure 8 The refrigeration capacity and relative refrigeration capacity of the Na5Gd4F(SiO4)4 crystal prepared in Example 1 are shown. DETAILED DESCRIPTION

[0049] To more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. It should be understood that the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0050] In addition, unless otherwise specified, the raw materials used in the present invention can be obtained commercially, and any range recorded in the present invention includes the end value and any numerical value between the end values ​​and any sub-range formed by the end value or any numerical value between the end values.

[0051] Example 1

[0052] The high temperature co-solvent method is used to prepare Na5Gd4F(SiO4)4 crystals, which includes the following steps:

[0053] Weigh 1.1337 g (27 mmol) of NaF, 1.0875 g (3 mmol) of Gd2O3, 0.3605 g (6 mmol) of SiO2, and 0.3895 g (6 mmol) of H3BO3, mix them evenly, compact them, put them into an open platinum crucible, place them in a muffle furnace, heat them to 400°C at a heating rate of 60°C / h in an air environment, pre-sinter them at a constant temperature for 1 day, and then cool them to room temperature at a rate of 50°C / h. Grind them to obtain a pre-sintered material.

[0054] The pre-sintered material was poured into a platinum crucible, placed in a muffle furnace, heated to 1100°C at a heating rate of 60°C / h, sintered at a constant temperature for 2 days, cooled to 800°C at a rate of 2°C / h, and then cooled to room temperature at a rate of 50°C / h to obtain Na5Gd4F(SiO4)4 crystals.

[0055] The Na5Gd4F(SiO4)4 crystals prepared in this example were subjected to the following tests:

[0056] Structural characterization:

[0057] The Na5Gd4F(SiO4)4 obtained in this example was characterized by XRD. Figure 1 As shown in the figure, Na5Gd4F(SiO4)4 belongs to the tetragonal system, the space group is I-4, and its unit cell parameters are: α=β=γ=90°, Z=2.

[0058] The schematic diagram of the crystal structure of Na5Gd4F(SiO4)4 prepared in this example is shown in Figure 3 shown. Figure 3 As can be seen in (a), in the ab plane, the rare earth Gd 3+ The ions pass through the shared face with two adjacent polyhedra and four Gd 3+ The ionic polyhedra share a vertex (F(1) site) and are arranged into the basic Gd4O 20 Unit F. Figure 3 (b) shows the Gd-Gd bond of Na5Gd4F(SiO4)4. It can be seen that the Gd-Gd nearest neighbor bond length is The larger distance between magnetic ions leads to a high magnetic density, which is obviously conducive to producing a larger MCE.

[0059] Magnetic test:

[0060] The magnetocaloric effect was studied using a superconducting quantum interference device (SQUID) in the range of 1.8-100K and a magnetic field of 0-7T.

[0061] The temperature-dependent magnetic susceptibility and the inverse temperature-dependent magnetic susceptibility curve of Na5Gd4F(SiO4)4 crystal were measured under the conditions of temperature range of 1.8-100K and magnetic field of 0.01T. Figure 4 As shown in Figure 2 , the zero-field cooling and field-cooling curves overlap, indicating negligible thermal hysteresis. A linear fit of the reciprocal temperature-dependent magnetic susceptibility curves according to the Curie-Weiss theorem indicates that the compound is paramagnetic over the test temperature range, with a Weiss constant θ = -1.25K. The negative Weiss constant indicates that Na5Gd4F(SiO4)4 crystals possess extremely weak antiferromagnetic coupling, making them suitable for use as magnetic refrigeration materials.

[0062] The temperature-variable field magnetization intensity diagram of Na5Gd4F(SiO4)4 crystal measured under the conditions of temperature range of 1.8-15K and magnetic field range of 0-7T is as follows: Figure 5 The curve shows that as the magnetic field strength increases, the magnetization intensity of the Na5Gd4F(SiO4)4 crystal gradually increases and reaches a maximum value of 6.64μ at a temperature of 1.8K and a magnetic field of 7T. Β , and the theoretical value 7μ Β Very close.

[0063] According to the Banerjee criterion, the phase transition type of Na5Gd4F(SiO4)4 crystal is determined: the magnetization intensity data of variable temperature and variable field is used to estimate the results. Figure 6 The Arrott curve has a positive slope at each point, indicating that the magnetic phase transition of Na5Gd4F(SiO4)4 crystal belongs to the secondary magnetic phase transition.

[0064] According to Maxwell's relationship, the change of magnetic entropy of Na5Gd4F(SiO4)4 crystal is estimated by using the magnetization intensity data of variable temperature and variable field. The results are as follows: Figure 7 From the magnetic entropy curve, we can see that within the test range, Na5Gd4F(SiO4)4 crystal shows a maximum magnetic entropy change of 49.6J kg at 2.6K and Δμ0H=7T. -1 K -1 .

[0065] The refrigeration capacity and relative refrigeration capacity of Na5Gd4F(SiO4)4 compound can be calculated based on the magnetic entropy change value, as shown in the following example: Figure 8 As shown in the figure, it can be seen that with the increase of magnetic field intensity, the cooling capacity and relative cooling capacity of the Na5Gd4F(SiO4)4 sample gradually increase, and reach a maximum value of 308.9 J·kg when the magnetic field is 7 T. -1 and 406.7 J·kg -1 .

[0066] Example 2

[0067] The high temperature co-solvent method is used to prepare Na5Gd4F(SiO4)4 crystals, which includes the following steps:

[0068] Weigh NaF: 1.1337 g (27 mmol); Gd2O3: 1.0875 g (3 mmol); SiO2: 0.3605 g (6 mmol); B2O3: 0.2089 g (3 mmol), mix them evenly, compact them, put them into an open platinum crucible, put them into a muffle furnace, heat them to 400°C at a heating rate of 60°C / h in an air environment, pre-sinter them at a constant temperature for 1 day, and then cool them to room temperature at a rate of 50°C / h. Grind them to obtain a pre-sintered material.

[0069] The pre-sintered material was poured into a platinum crucible, placed in a muffle furnace, heated to 1100°C at a heating rate of 60°C / h, sintered at a constant temperature for 2 days, cooled to 800°C at a rate of 2°C / h, and then cooled to room temperature at a rate of 50°C / h to obtain Na5Gd4F(SiO4)4 crystals.

[0070] The Na5Gd4F(SiO4)4 crystals obtained in this example were characterized by XRD, and the results were basically consistent with the theoretical spectrum.

[0071] Example 3

[0072] The high temperature co-solvent method is used to prepare Na5Gd4F(SiO4)4 crystals, which includes the following steps:

[0073] Weigh 1.2596 g (30 mmol) of NaF, 1.0875 g (3 mmol) of Gd2O3, 0.3605 g (6 mmol) of SiO2, and 0.3895 g (6 mmol) of H3BO3, mix them evenly, compact them, put them into an open platinum crucible, place them in a muffle furnace, heat them to 400°C at a heating rate of 60°C / h in an air environment, pre-sinter them at a constant temperature for 1 day, and then cool them to room temperature at a rate of 50°C / h. Grind them to obtain a pre-sintered material.

[0074] The pre-sintered material was poured into a platinum crucible, placed in a muffle furnace, heated to 1100°C at a heating rate of 60°C / h, sintered at a constant temperature for 2 days, cooled to 800°C at a rate of 2°C / h, and then cooled to room temperature at a rate of 50°C / h to obtain Na5Gd4F(SiO4)4 crystals.

[0075] The Na5Gd4F(SiO4)4 crystals obtained in this example were characterized by XRD, and the results were basically consistent with the theoretical spectrum.

[0076] Example 4

[0077] The high temperature co-solvent method is used to prepare Na5Tb4F(SiO4)4 crystals, which includes the following steps:

[0078] Weigh 1.1337 g (27 mmol) of NaF, 1.1215 g (1.5 mmol) of Tb4O7, 0.3605 g (6 mmol) of SiO2, and 0.3895 g (6 mmol) of H3BO3, mix them evenly, compact them, put them into an open platinum crucible, place them in a muffle furnace, heat them to 400°C at a heating rate of 60°C / h in an air environment, pre-sinter them at a constant temperature for 1 day, and then cool them to room temperature at a rate of 50°C / h. Grind them to obtain a pre-sintered material.

[0079] The pre-sintered material was poured into a platinum crucible, placed in a muffle furnace, heated to 1100°C at a heating rate of 60°C / h, sintered at a constant temperature for 2 days, cooled to 800°C at a rate of 2°C / h, and then cooled to room temperature at a rate of 50°C / h to obtain Na5Tb4F(SiO4)4 crystals.

[0080] See also Figure 2 The Na5Tb4F(SiO4)4 crystals obtained in this example were characterized by XRD, and the results were basically consistent with the theoretical spectrum.

[0081] Comparative Example 1

[0082] The sample was prepared using a high-temperature co-solvent method, which includes the following steps:

[0083] Weigh 1.5116 g (36 mmol) of NaF, 1.0875 g (3 mmol) of Gd2O3, 0.3605 g (6 mmol) of SiO2, and 0.3895 g (6 mmol) of H3BO3, mix them evenly, compact them, put them into an open platinum crucible, place them in a muffle furnace, heat them to 400°C at a heating rate of 60°C / h in an air environment, keep the temperature constant for 1 day, and then cool them to room temperature at a rate of 50°C / h. After grinding, a preliminary pre-calcined product is obtained.

[0084] The calcined product was poured into a platinum crucible, placed in a muffle furnace, and heated to 1100°C at a heating rate of 60°C / h. After constant temperature reaction for 2 days, it was cooled to 800°C at a rate of 2°C / h, and then cooled to room temperature at a rate of 50°C / h to obtain the sample to be tested.

[0085] The powder sample obtained in this example was characterized by XRD. The results showed that the XRD pattern of the sample in this example did not match the theoretical spectrum, that is, the target product Na5Gd4F(SiO4)4 crystals could not be synthesized.

[0086] Comparative Example 2

[0087] The sample was prepared using a high-temperature co-solvent method, which includes the following steps:

[0088] Weigh 1.1337 g (27 mmol) of NaF, 1.2875 g (6 mmol) of GdF3, 0.3605 g (6 mmol) of SiO2, and 0.9275 g (15 mmol) of H3BO3, mix them evenly, compact them, put them into an open platinum crucible, place them in a muffle furnace, heat them to 400°C at a heating rate of 60°C / h in an air environment, keep the temperature constant for 1 day, and then cool them to room temperature at a rate of 50°C / h. After grinding, a preliminary pre-calcined product is obtained.

[0089] The calcined product was poured into a platinum crucible, placed in a muffle furnace, and heated to 1100°C at a heating rate of 60°C / h. After constant temperature reaction for 2 days, it was cooled to 800°C at a rate of 2°C / h, and then cooled to room temperature at a rate of 50°C / h to obtain the sample to be tested.

[0090] The powder sample obtained in this example was characterized by XRD. The results showed that the XRD spectrum of the powder sample in this example did not match the theoretical spectrum, that is, the target product Na5Gd4F(SiO4)4 crystals could not be synthesized.

[0091] Comparative Example 3

[0092] The sample was prepared using a high-temperature co-solvent method, which includes the following steps:

[0093] Weigh NaF: 0.5668 g (13.5 mmol); Na2CO3: 0.7154 g (6.75 mmol); Gd2O3: 1.0875 g (3 mmol); SiO2: 0.3605 g (6 mmol); H3BO3: 0.3895 g (6 mmol), mix them evenly, compact them, put them into an open platinum crucible, put them into a muffle furnace, heat them to 400°C at a heating rate of 60°C / h in an air environment, keep the temperature constant for 1 day, and then cool them to room temperature at a rate of 50°C / h. After grinding, a preliminary pre-calcined product is obtained.

[0094] The calcined product was poured into a platinum crucible, placed in a muffle furnace, and heated to 1100°C at a heating rate of 60°C / h. After constant temperature reaction for 2 days, it was cooled to 800°C at a rate of 2°C / h, and then cooled to room temperature at a rate of 50°C / h to obtain the sample to be tested.

[0095] The powder sample obtained in this example was characterized by XRD. The results showed that the XRD pattern of the sample in this example did not match the theoretical spectrum, that is, the target product Na5Gd4F(SiO4)4 crystals could not be synthesized.

[0096] Comparative Example 4

[0097] The sample was prepared using a high-temperature co-solvent method, which includes the following steps:

[0098] Weigh NaF: 1.1337 g (27 mmol); Gd2O3: 1.0875 g (3 mmol); SiO2: 0.3605 g (6 mmol); H3BO3: 0.3895 g (6 mmol), mix them evenly, compact them, put them into an open alumina crucible, put them into a muffle furnace, heat them to 400°C at a heating rate of 60°C / h in an air environment, keep the temperature constant for 1 day, and then cool them to room temperature at a rate of 50°C / h. After grinding, a preliminary pre-calcined product is obtained.

[0099] The calcined product was poured into an alumina crucible, placed in a muffle furnace, heated to 1100°C at a heating rate of 60°C / h, reacted at constant temperature for 2 days, cooled to 800°C at a rate of 2°C / h, and then cooled to room temperature at a rate of 50°C / h to obtain the sample to be tested.

[0100] The powder sample obtained in this example was characterized by XRD. The results showed that the XRD pattern of the powder sample in this example did not match the theoretical spectrum, that is, the target product Na5Gd4F(SiO4)4 crystals could not be synthesized.

[0101] Comparative Example 5

[0102] The sample was prepared using a high-temperature co-solvent method, which includes the following steps:

[0103] Weigh 1.1337 g (27 mmol) of NaF, 1.0875 g (3 mmol) of Gd2O3, 0.3605 g (6 mmol) of SiO2, and 0.3895 g (6 mmol) of H3BO3, mix them evenly, compact them, put them into an open platinum crucible, place them in a muffle furnace, heat them to 400°C at a heating rate of 60°C / h in an air environment, keep the temperature constant for 1 day, and then cool them to room temperature at a rate of 50°C / h. After grinding, a preliminary pre-calcined product is obtained.

[0104] The calcined product was poured into a platinum crucible, placed in a muffle furnace, and heated to 1100°C at a heating rate of 60°C / h. After constant temperature reaction for 2 days, it was cooled to 800°C at a rate of 10°C / h, and then cooled to room temperature at a rate of 50°C / h to obtain the sample to be tested.

[0105] The powder sample obtained in this example was characterized by XRD. The results showed that the XRD spectrum of the powder sample in this example did not match the theoretical spectrum, that is, the target product Na5Gd4F(SiO4)4 crystals could not be synthesized.

[0106] Comparative Example 6

[0107] The sample was prepared using a high-temperature co-solvent method, which includes the following steps:

[0108] Weigh 1.1337 g (27 mmol) of NaF, 1.0875 g (3 mmol) of Gd2O3, 0.3605 g (6 mmol) of SiO2, and 0.3895 g (6 mmol) of H3BO3, mix them evenly, compact them, put them into an open platinum crucible, place them in a muffle furnace, heat them to 400°C at a heating rate of 60°C / h in an air environment, keep the temperature constant for 1 day, and then cool them to room temperature at a rate of 50°C / h. After grinding, a preliminary pre-calcined product is obtained.

[0109] The calcined product was poured into a platinum crucible, placed in a muffle furnace, and heated to 900°C at a heating rate of 60°C / h. After constant temperature reaction for 2 days, it was cooled to 800°C at a rate of 2°C / h, and then cooled to room temperature at a rate of 50°C / h to obtain the sample to be tested.

[0110] The powder sample obtained in this example was characterized by XRD. The results showed that the XRD spectrum of the powder sample in this example was inconsistent with that of Example 1, that is, the target product Na5Gd4F(SiO4)4 crystals could not be synthesized.

[0111] 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. Application of Na5R4F(SiO4)4 crystal in magnetic refrigeration, characterized by: Metal R is Gd; The synthesis method of the Na5R4F(SiO4)4 crystal comprises the following steps: 1) Mix the Na-containing compound, the R-containing compound, the Si-containing compound and the B-containing compound uniformly, compact them, put them into an open platinum crucible, raise the temperature to 300-500°C in an oxygen environment at normal pressure, pre-sinter at a constant temperature, and cool them once to obtain a pre-sintered material; 2) After grinding the pre-sintered material, place it in a normal pressure, oxygen environment again, heat it to 1000-1100℃, sinter it at a constant temperature, and obtain Na5R4F(SiO4)4 crystals after secondary cooling; Wherein, the Na-containing compound is selected from Na-containing fluorides; The R-containing compound is selected from R-containing oxides; The Na-containing compound, the R-containing compound, the Si-containing compound and the B-containing compound are mixed according to a molar ratio of Na, R, Si, and B of 8-10:2:1-3:1-3; During secondary cooling, the temperature is first lowered to 800°C at a cooling rate of 1-5°C / h, and then lowered to room temperature at a cooling rate of 40-60°C / h.

2. The application of Na5R4F(SiO4)4 crystal in the preparation of refrigeration equipment is characterized in that: Metal R is Gd; The synthesis method of the Na5R4F(SiO4)4 crystal comprises the following steps: 1) Mix the Na-containing compound, the R-containing compound, the Si-containing compound and the B-containing compound uniformly, compact them, put them into an open platinum crucible, raise the temperature to 300-500°C in an oxygen environment at normal pressure, pre-sinter at a constant temperature, and cool them once to obtain a pre-sintered material; 2) After grinding the pre-sintered material, place it in a normal pressure, oxygen environment again, heat it to 1000-1100℃, sinter it at a constant temperature, and obtain Na5R4F(SiO4)4 crystals after secondary cooling; Wherein, the Na-containing compound is selected from Na-containing fluorides; The R-containing compound is selected from R-containing oxides; The Na-containing compound, the R-containing compound, the Si-containing compound and the B-containing compound are mixed according to a molar ratio of Na, R, Si, and B of 8-10:2:1-3:1-3; During secondary cooling, the temperature is first lowered to 800°C at a cooling rate of 1-5°C / h, and then lowered to room temperature at a cooling rate of 40-60°C / h.

3. The use according to claim 1 or 2, characterized in that The Na-containing fluoride is NaF; The Si-containing compound is selected from silicon-containing oxides; The B-containing compound is H3BO3 or B2O3.

4. The use according to claim 1 or 2, characterized in that The Na-containing compound, the R-containing compound, the Si-containing compound and the B-containing compound are mixed according to a molar ratio of Na, R, Si and B of 9:2:2:

2.

5. The use according to claim 1 or 2, characterized in that: The heating rate in step 1 and step 2 is 40-80°C / h.

6. The use according to claim 1 or 2, characterized in that The constant temperature pre-burning time is 1-3 days; The constant temperature sintering time is 1-3 days.

7. The use according to claim 1 or 2, characterized in that The cooling rate of the primary cooling is 40-60°C / h.

Images