A low-temperature magnetic refrigeration material and its preparation method and application

Abstract

The present invention belongs to the technical field of magnetic refrigeration materials, and specifically relates to a low-temperature magnetic refrigeration material and its preparation method and application. The chemical formula of the low-temperature magnetic refrigeration material is Eu 2 MgSi 2 O 7 The material has a magnetic phase transition temperature of <2K and has a large magnetocaloric effect at a temperature of 2.5K. The low-temperature magnetic refrigeration material prepared by the present invention has a strong magnetocaloric effect at low temperatures. At the same time, the preparation process of the low-temperature magnetic refrigeration material is simple, suitable for large-scale industrial production, and has broad application prospects in the field of low-temperature magnetic refrigeration.

Description

Technical Field

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

[0002] Magnetic refrigeration technology is a new type of solid-state refrigeration technology based on the magnetocaloric effect. The magnetocaloric effect is a phenomenon in which the magnetic moment order of a magnetic material changes when the external magnetic field changes, that is, the magnetic entropy changes, causing the material itself to absorb or release heat. The current mainstream low-temperature refrigeration technology is 3 He dilution refrigeration technology, however 3 He is an extremely scarce strategic resource that is almost impossible to extract naturally. 3 Compared with He dilution refrigeration technology, magnetic refrigeration technology uses solid refrigerant and does not require expensive 3 He strategic resources. Moreover, magnetic refrigeration technology has many advantages such as energy saving, high efficiency, stability, reliability, and long life. Therefore, in the field of low-temperature refrigeration, magnetic refrigeration technology has shown great advantages and has attracted the attention of a large number of researchers.

[0003] Magnetic refrigeration materials are the key to the practical application of magnetic refrigeration technology. Rare earth-based compounds have become one of the research focuses in the field of magnetic refrigeration materials due to their large magnetocaloric effect and low magnetic phase transition temperature.

[0004] Patent document CN108840364A discloses an inorganic gadolinium-based complex crystal and its preparation method. The maximum magnetic entropy change of the magnetic refrigeration material under a 0-2T magnetic field change is about 28J / (kg·K), which is a good magnetic refrigeration material. However, the crystal preparation process has problems such as harsh experimental conditions, high energy consumption, and long growth cycle. It not only requires a stainless steel high-pressure reaction vessel with a polytetrafluoroethylene reactor, but also requires crystallization at 180°C for 7 days to obtain crystals with good crystallinity, which is not conducive to industrial production.

[0005] Patent document CN104559944A discloses a magnetic refrigeration material containing rare earth hydroxide and a preparation method thereof. The composition formula of the magnetic refrigeration material is Gd(OH) 8 / 3 Cl 1 / 3 At around 3K, its maximum magnetic entropy change under 0-5T magnetic field changes is 48J / (kg·K), and the maximum magnetic entropy change under 0-7T magnetic field changes is as high as 60J / (kg·K), which has a large low-temperature magnetocaloric effect. However, a large amount of hydrochloric acid and sodium hydroxide are needed in the preparation process of this magnetic refrigeration material. The use of these strong acids and alkalis will inevitably cause pollution to the environment and it is difficult to achieve large-scale production.

[0006] Mater.Today Phys.27(2022)100810 reported a magnetic refrigeration material Gd2GeO5, the magnetic phase transition temperature of which is <2K, the maximum magnetic entropy change under the magnetic field change of 0-8.9T near 3K is 50J / (kg·K), and the adiabatic temperature change is 22.2K. Its magnetocaloric performance is better than most reported traditional magnetocaloric materials, making this magnetic refrigeration material a good alternative to existing commercial magnetic refrigerants. However, the magnetic entropy change of this magnetic refrigeration material under a low magnetic field of 0-2T is only 9J / (kg·K), which indicates that the application of this magnetic refrigeration material requires a higher driving magnetic field and the application cost is high.

[0007] J.Am.Chem.Soc.137(2015)15988-15991 reported a magnetic refrigeration material with excellent performance, which is [Ln 60 ] nanocages assembled with ultra-strong alkali-resistant lanthanide molecular sieves have extremely high stability. These compounds have extremely high stability and still maintain a single crystallinity after being treated in boiling water, hydrochloric acid and sodium hydroxide aqueous solution. Among them, [Gd 60 The maximum magnetic entropy change of the nanocage magnetic refrigeration material under a magnetic field change of 0-7T near 2K is 61J / (kg·K), which is one of the largest values ​​known so far. However, the magnetic entropy of this material under a low magnetic field change of 0-2T is only 10J / (kg·K), and it also requires a higher driving magnetic field, which limits its practical application.

[0008] Therefore, in view of the problems of long preparation cycle, great environmental pollution and small low-field magnetic entropy change in the current preparation process of magnetic refrigeration materials, it is necessary to develop a magnetic refrigeration material with simple process, short preparation cycle and excellent magnetic refrigeration effect. Summary of the invention

[0009] The present invention aims to provide a low-temperature magnetic refrigeration material and its preparation method and application. The low-temperature magnetic refrigeration material prepared by the present invention has a strong magnetocaloric effect at low temperatures. At the same time, the preparation process of the low-temperature magnetic refrigeration material is simple, suitable for large-scale industrial production, and has broad application prospects in the field of low-temperature magnetic refrigeration.

[0010] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a low-temperature magnetic refrigeration material, the chemical formula of which is Eu2MgSi2O7, the magnetic phase transition temperature of which is <2K, and it has a large magnetocaloric effect at a temperature of 2.5K.

[0011] Preferably, the maximum magnetic entropy change of the magnetic refrigeration material at a temperature of 2.5K when the magnetic field changes from 0 to 2T is ≤28 J / (kg·K).

[0012] Preferably, the maximum magnetic entropy change of the magnetic refrigeration material at a temperature of 2.5K when the magnetic field changes from 0 to 5T is ≤54 J / (kg·K).

[0013] Preferably, the maximum magnetic entropy change of the magnetic refrigeration material at a temperature of 2.5K when the magnetic field changes from 0 to 7T is ≤61 J / (kg·K).

[0014] Preferably, the low-temperature magnetic refrigeration material belongs to the tetragonal system, and the space group is The unit cell parameters are α=β=γ=90°.

[0015] The low-temperature magnetic refrigeration material Eu2MgSi2O7 prepared by the present invention is a material with giant magnetocaloric effect. The Eu ions in the magnetic refrigeration material exist in divalent form. 2+ The high ionic magnetic moment can provide a larger magnetic saturation magnetization at a lower temperature. In the low temperature region (<2K), the material exhibits a large magnetocaloric effect. 2+ The quasi-two-dimensional structure of the ions makes the magnetization intensity easy to saturate under the drive of the magnetic field. It has a large magnetic entropy change value under the magnetic fields of 0-2T, 0-5T, and 0-7T, and can achieve a good magnetic refrigeration effect. It is a low-temperature magnetic refrigeration material with excellent performance.

[0016] The present invention also claims a method for preparing the low-temperature magnetic refrigeration material, comprising the following steps:

[0017] Eu2O3, MgO, SiO2 and Si powder are mixed and ground to obtain a mixture, and the mixture is placed in a sintering furnace under an inert atmosphere and sintered twice to obtain the low-temperature magnetic refrigeration material.

[0018] Preferably, the molar ratio of Eu2O3, MgO, SiO2 and Si is 10:10:15:(7-10). It can be understood that the molar ratio of Eu2O3, MgO, SiO2 and Si includes but is not limited to 10:10:15:7, 10:10:15:7.25, 10:10:15:7.31, 10:10:15:7.38, 10:10:15:7.5, 10:10:15:8, 10:10:15:9, 10:10:15:10.

[0019] Preferably, the molar ratio of Eu2O3, MgO, SiO2 and Si is 10:10:15:(7.25-7.5).

[0020] More preferably, the molar ratio of Eu2O3, MgO, SiO2 and Si is 10:10:15:(7.25-7.38).

[0021] Preferably, the first sintering of the two sinterings is carried out at 1025±25°C for 12 hours, and the second sintering is carried out at 1050±50°C for 30 hours. After the first sintering is completed, the mixture is cooled to room temperature, and then the mixture is ground again before the second sintering.

[0022] Preferably, the inert atmosphere comprises argon and / or nitrogen atmosphere.

[0023] Preferably, the sintering furnace comprises a tube furnace or a vacuum furnace.

[0024] The present invention has found through research that Eu2MgSi2O7 can be obtained by adding europium oxide, magnesium oxide, silicon dioxide and silicon in different ratios through a high-temperature solid-phase reaction. Too high or too low a silicon dosage and too low or too high a sintering temperature will affect the preparation of Eu2MgSi2O7. By controlling the four raw materials within a specific ratio range, single-phase Eu2MgSi2O7 can be obtained.

[0025] The present invention also claims protection for an application of the low-temperature magnetic refrigeration material in the field of magnetic refrigeration technology. The low-temperature magnetic refrigeration material of the present invention can be widely used in the fields of low-temperature physics, space exploration, aerospace, etc., and is helpful to promote the high-value utilization of rare earth resources.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The low-temperature magnetic refrigeration material of the present invention has a giant magnetocaloric effect. The maximum magnetic entropy change at 2.5K under a 0-7T magnetic field change is ≤61J / (kg·K), and the maximum magnetic entropy change under a 0-5T and 0-2T magnetic field change is ≤54J / (kg·K) and ≤28J / (kg·K), respectively, which is superior to the materials in the prior art and most low-temperature magnetic refrigeration materials (such as Gd3Ga5O 12 、Gd2GeO5、Gd 60 Nanocages, etc.) are low-temperature magnetic refrigeration materials with excellent performance.

[0028] (2) The method for preparing the low-temperature magnetic refrigeration material of the present invention adopts the Si reduction method for preparation, and does not require hydrogen reduction. The preparation process is simple, the reaction cycle is short, the energy consumption is low, and it is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the X-ray diffraction pattern of the low-temperature magnetic refrigeration material prepared in Examples 1 to 4 of the present invention.

[0030] Figure 2 This is the X-ray diffraction pattern of the low-temperature magnetic refrigeration material prepared in Comparative Examples 1 and 2.

[0031] Figure 3 The thermomagnetic curves of the magnetic refrigeration material prepared in Example 4 of the present invention under zero field cooling (ZFC) and field cooling (FC) in a 0.01T magnetic field.

[0032] Figure 4 It is the first derivative of the field cooling (FC) thermomagnetic curve of the magnetic refrigeration material prepared in Example 4 of the present invention under a 0.01T magnetic field.

[0033] Figure 5 This is an isothermal magnetization curve of the magnetic refrigeration material prepared in Example 4 of the present invention at 2-50K under a 0-7T magnetic field change.

[0034] Figure 6 This is a relationship diagram between the magnetic entropy change and temperature of the magnetic refrigeration material prepared in Example 4 of the present invention under a 1-7T magnetic field change. DETAILED DESCRIPTION

[0035] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0036] In the embodiments and comparative examples, the experimental methods used are conventional methods unless otherwise specified, and the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0037] Example 1

[0038] Eu2O3, MgO, SiO2, and Si are weighed according to the ratio of the amount of substance of 10:10:15:10, and ground to obtain a uniform mixture, and the obtained mixture is placed in a crucible made of corundum and covered with a lid; the corundum crucible is placed in a tube furnace and sintered twice in an argon atmosphere to obtain the low-temperature magnetic refrigeration material. The first sintering condition is to keep the temperature at 1000°C for 12 hours, and after the sintering is completed, wait for the tube furnace to cool to room temperature, grind the mixture again, and then sinter for the second time, and the second sintering condition is to keep the temperature at 1100°C for 30 hours.

[0039] Example 2

[0040] Eu2O3, MgO, SiO2, and Si are weighed according to the ratio of the amount of substance of 10:10:15:7.5, and ground to obtain a uniform mixture, and the obtained mixture is placed in a crucible made of corundum and covered with a lid; the corundum crucible is placed in a tube furnace and sintered twice in an argon atmosphere to obtain the low-temperature magnetic refrigeration material. The first sintering condition is to keep the temperature at 1030°C for 12 hours. After the sintering is completed, wait for the tube furnace to cool to room temperature, grind the mixture again, and then sinter for the second time. The second sintering condition is to keep the temperature at 1050°C for 30 hours.

[0041] Example 3

[0042] Eu2O3, MgO, SiO2, and Si are weighed according to the ratio of the amount of substance of 10:10:15:7.38, and ground to obtain a uniform mixture, and the obtained mixture is placed in a crucible made of corundum and covered with a lid; the corundum crucible is placed in a tube furnace and sintered twice in an argon atmosphere to obtain the low-temperature magnetic refrigeration material. The first sintering condition is to keep the temperature at 1000°C for 12 hours. After the sintering is completed, wait for the tube furnace to cool to room temperature, grind the mixture again, and then sinter for the second time. The second sintering condition is to keep the temperature at 1100°C for 30 hours.

[0043] Example 4

[0044] Eu2O3, MgO, SiO2, and Si are weighed according to the ratio of the amount of substance of 10:10:15:7.25, and ground to obtain a uniform mixture, and the obtained mixture is placed in a crucible made of corundum and covered with a lid; the corundum crucible is placed in a tube furnace and sintered twice in an argon atmosphere to obtain the low-temperature magnetic refrigeration material. The first sintering condition is to keep the temperature at 1050°C for 12 hours. After the sintering is completed, wait for the tube furnace to cool to room temperature, grind the mixture again, and then sinter for the second time. The second sintering condition is to keep the temperature at 1100°C for 30 hours.

[0045] Comparative Example 1

[0046] Compared with Example 4, the only difference in this comparative example is that the molar ratio of Eu2O3, MgO, SiO2, and Si is 10:10:15:6.

[0047] The preparation method is similar to that of Example 4.

[0048] Comparative Example 2

[0049] Compared with Example 4, the only difference in this comparative example is that the molar ratio of Eu2O3, MgO, SiO2, and Si is 10:10:15:3.

[0050] The preparation method is similar to that of Example 4.

[0051] Effect example

[0052] The low-temperature magnetic refrigeration materials prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were subjected to X-ray powder diffraction phase analysis using a Brucker D8A A25 X-ray diffractometer (XRD). Figures 1-2 shown.

[0053] Figure 1 It shows that the X-ray diffraction patterns of the magnetic refrigeration materials in Examples 1 to 4 of the present invention match well with the theoretical patterns, indicating that the magnetic refrigeration materials in Examples 1 to 4 have high purity and are all composed of a single Eu2MgSi2O7 phase, belonging to the tetragonal system, with a space group of

[0054] Figure 2 It is shown that the X-ray diffraction patterns of the magnetic refrigeration materials in Comparative Examples 1 to 2 show obvious impurity peaks, indicating that there are impurity phases in the material and pure phase Eu2MgSi2O7 cannot be obtained.

[0055] The low-temperature magnetic refrigeration material samples prepared in each embodiment were subjected to magnetocaloric performance testing and analysis, and the magnetic entropy change under different magnetic field changes was calculated based on the isothermal magnetization curves at different temperatures using Maxwell's relationship.

[0056] Taking the low temperature magnetic refrigeration material Eu2MgSi2O7 prepared in Example 4 as an example, the test results are shown in the attached Figure 3-6 .

[0057] Depend on Figure 3 and Figure 4 It can be seen that the phase change temperature of the magnetic refrigeration material in Example 4 of the present invention is below 2K, and it is a low-temperature magnetic refrigeration material. The ZFC and FC thermomagnetic curves of the material completely overlap, indicating that the magnetic phase change process is highly reversible and there is no thermal hysteresis phenomenon, which is conducive to the practical application of magnetic refrigeration materials.

[0058] Figure 5 It is the isothermal magnetization curve of the magnetic refrigeration material in Example 4 of the present invention at 2-50K under a 0-7T magnetic field change, wherein the solid curve at 2K is the process of increasing the magnetic field, and the hollow curve at 2K is the process of decreasing the magnetic field. It can be seen from the figure that the magnetic refrigeration material in Example 4 is paramagnetic at a higher temperature (>20K), and the magnetization intensity increases with decreasing temperature; at a temperature of 2K, its magnetization intensity increases rapidly with increasing external magnetic field, and tends to saturation when the magnetic field is 5T, and the rising and falling field magnetization curves almost coincide, further indicating that the magnetic refrigeration material has no obvious thermal hysteresis and hysteresis loss.

[0059] The magnetic entropy change under different magnetic field changes can be calculated based on the isothermal magnetization curves at different temperatures using Maxwell relations. Figure 6 It can be seen that the maximum magnetic entropy change of the magnetic refrigeration material in Example 4 increases monotonically with the increase of the external magnetic field, and under a certain external magnetic field, the maximum magnetic entropy change of the magnetic refrigeration material gradually increases with the decrease of temperature; near the temperature of 2.5K, when the magnetic field changes to 0-2T, 0-5T and 0-7T, the maximum magnetic entropy change values ​​are 28J / (kg·K), 54J / (kg·K) and 61J / (kg·K), respectively.

[0060] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing a low-temperature magnetic refrigeration material, characterized in that: The following steps are involved: Eu2O3, MgO, SiO2 and Si powder are mixed and ground to obtain a mixture, and the mixture is sintered twice under an inert atmosphere to obtain the low-temperature magnetic refrigeration material; The molar ratio of Eu2O3, MgO, SiO2 and Si powder is 10:10:15:(7-10); The two sinterings are performed firstly, and then the mixture is cooled to room temperature after sintering, and then the mixture is ground again, and then the mixture is sintered for the second time. The first sintering is carried out at a temperature of 1000-1050° C. for 12 hours, and the second sintering is carried out at a temperature of 1050-1100° C. for 30 hours.

2. The preparation method according to claim 1, characterized in that: The molar ratio of Eu2O3, MgO, SiO2 and Si is 10:10:15:(7.25~7.5).

3. The preparation method according to claim 1, characterized in that: The inert atmosphere includes argon and / or nitrogen atmosphere.

4. A low-temperature magnetic refrigeration material prepared by the preparation method according to any one of claims 1 to 3, wherein the chemical formula of the low-temperature magnetic refrigeration material is Eu2MgSi2O7, the magnetic phase transition temperature of the material is <2K, and it has a magnetocaloric effect at a temperature of 2.5K.

5. The low-temperature magnetic refrigeration material according to claim 4, characterized in that: At least one of the following (1) to (3): (1) The maximum magnetic entropy change of the magnetic refrigeration material at a temperature of 2.5K when the magnetic field changes from 0 to 2T is ≤28J / (kg·K); (2) The maximum magnetic entropy change of the magnetic refrigeration material at a temperature of 2.5K when the magnetic field changes from 0 to 5T is ≤54J / (kg·K); (3) The maximum magnetic entropy change of the magnetic refrigeration material is ≤61 J / (kg·K) when the magnetic field changes from 0 to 7 T at a temperature of 2.5 K.

6. The low-temperature magnetic refrigeration material according to claim 4, characterized in that: The low-temperature magnetic refrigeration material belongs to the tetragonal crystal system, and the space group is a unit cell parameter of α=β=γ=90°.

7. An application of the low-temperature magnetic refrigeration material according to any one of claims 4 to 6 in the field of magnetic refrigeration technology.

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