Rare earth chloride borate magnetic refrigeration material, preparation method thereof and application of rare earth chloride borate magnetic refrigeration material in magnetic refrigeration

Abstract

The invention belongs to the technical field of magnetic refrigeration materials, and particularly relates to a rare earth chloride borate magnetic refrigeration material, a preparation method thereof and application of the rare earth chloride borate magnetic refrigeration material in magnetic refrigeration. The chemical formula of the rare earth chloride borate magnetic refrigeration material is Eu5RE (III) (BO3) 4Cl, metal RE is Eu, Gd, Tb, Dy, Ho, Er or Tm and belongs to a hexagonal crystal system, and the space group is P63mc. The rare earth chloride borate magnetic refrigeration material has a magnetothermal effect with low magnetic field drive near the temperature of liquid helium, the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is larger than or equal to 19.6 J.kg <-1 >. K <-1 > at the temperature of 2.5 K when the magnetic field change is 0-1 T, the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is larger than or equal to 31.7 J.kg <-1 >. K <-1 > at the temperature of 3.5 K when the magnetic field change is 0-2 T, and the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is larger than or equal to 31.7 J.kg <-1 >. K <-1 >. The maximum magnetic entropy change is greater than or equal to 52.0 J.kg <-1 >. K <-1 > when the magnetic field change is 0-5 T at the temperature of 3.5 K, the magnetic refrigeration material is obviously superior to many disclosed magnetic refrigeration materials at present, and the magnetic refrigeration material is expected to be applied to a liquid helium temperature region magnetic refrigeration technology on the basis that the magnetic refrigeration material shows excellent magnetocaloric performance near the liquid helium temperature.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magnetic refrigeration materials, and specifically comprises a rare earth chloride borate magnetic refrigeration material, a preparation method thereof, and application thereof in magnetic refrigeration. BACKGROUND

[0002] Since the 20th century, low-temperature refrigeration technology has developed unprecedentedly and has been widely applied, and has become one of the key supporting technologies for modern scientific and technological development. Among them, the liquid helium temperature range (2-10 K) refrigeration is an important part of low-temperature refrigeration, and plays an important technical support role in the fields of low-temperature physics, low-temperature superconductivity, aerospace, military industry, etc. At present, the mainstream way to obtain liquid helium temperature is to use Gifford-McMahon (GM) refrigerator, but its refrigeration efficiency is only about 1% of the Carnot cycle efficiency. Therefore, how to effectively improve the refrigeration efficiency of the GM machine is an important problem to be broken through in the field of low-temperature refrigeration technology.

[0003] Magnetic refrigeration is a new type of solid-state refrigeration technology that uses the magnetic heat effect (MCE) of magnetic materials to achieve refrigeration. The magnetic heat effect is an intrinsic property of magnetic materials, which means that when the external magnetic field changes, the magnetic entropy of the material will change due to the change of the magnetic moment order, resulting in heat absorption or heat release, thereby achieving refrigeration. Magnetic refrigeration technology has many advantages such as energy saving, high efficiency, green environmental protection, small / micro size, and stability and reliability, and is expected to become a new generation of refrigeration technology to replace traditional gas compression refrigeration. As the source of cold energy for magnetic refrigeration systems, magnetic refrigeration materials are the core of magnetic refrigeration technology, so developing magnetic heat effect materials with large magnetic heat effect near liquid helium temperature is the key to the application of liquid helium temperature magnetic refrigeration technology.

[0004] Gd-based oxides have large magnetic moments and complete orbital momentum quenching, and are a promising low-temperature magnetic refrigeration material. For example, CN118343824A discloses a gadolinium-based low-temperature magnetic refrigeration material and a preparation method thereof, which has a chemical formula of NaGdSiO4. The material is prepared by a solid-phase reaction method, which has the advantages of simple process and short cycle, but its maximum magnetic entropy change under a 0-1 T magnetic field change is only about 4 J·kg -1 ·K -1 . CN120496982A discloses a rare earth aluminates low-temperature magnetic refrigeration material, which has a general chemical formula of RE4Al2O9 (RE is at least one of rare earth elements Gd, Dy and Ho), and its isothermal magnetic entropy change under a 0-2 T magnetic field change is only between 9.47-10.32 J·kg -1 ·K -1CN114974772A discloses a rare earth magnetic material with a monoclinic structure, a chemical general formula of which is RESr2TaO6 (RE is one or two of Gd, Dy, Ho, Er), and an isothermal magnetic entropy change thereof is only between 5.1-27.2 J·kg -1 ·K -1 between.

[0005] However, the conventional magnetic refrigeration material has insufficient magneto-caloric performance at a low magnetic field, needs a superconducting magnet to provide a magnetic field, and has a high cost, which has become a key problem hindering practical application.

[0006] Therefore, development of a liquid helium temperature zone magnetic refrigeration material capable of having a large magneto-caloric effect driven by a low magnetic field near a liquid helium temperature is a key to promoting large-scale application of liquid helium temperature zone magnetic refrigeration technology, and has significant economic value and important practical significance. SUMMARY

[0007] In view of the above problems existing in the prior art, a first object of the present application is to provide a rare earth chloride borate magnetic refrigeration material. The rare earth chloride borate magnetic refrigeration material has a magnetic phase transition near a liquid helium temperature, and is accompanied by a large magneto-caloric effect. The maximum magnetic entropy change thereof is ≥19.6 J·kg -1 ·K -1 at a temperature of 2.5 K and a magnetic field change of 0-1 T, the maximum magnetic entropy change thereof is ≥31.7 J·kg -1 ·K -1 at a temperature of 3.5 K and a magnetic field change of 0-2 T, and the maximum magnetic entropy change thereof is ≥52.0 J·kg -1 ·K -1 which is significantly better than many currently disclosed magnetic refrigeration materials.

[0008] A second object of the present application is to provide a preparation method of the rare earth chloride borate magnetic refrigeration material as described above.

[0009] A third object of the present application is to provide an application of the rare earth chloride borate magnetic refrigeration material as described above in preparation of a liquid helium temperature zone magnetic refrigeration material or device.

[0010] To achieve the above-mentioned first object, the technical solution adopted by the present application comprises: The present application discloses a rare earth chloride borate magnetic refrigeration material, and the chemical formula of the rare earth chloride borate magnetic refrigeration material is Eu5RE(III)(BO3)4Cl, wherein the metal RE(III) represents a rare earth metal in a positive trivalent state, and specifically, Eu, Gd, Tb, Dy, Ho, Er or Tm, which is composed of a single phase and belongs to a hexagonal system, and the space group isP6 3 mc Therefore, the chemical formula of the rare earth chloride borate magnetic refrigeration material can be Eu6(BO3)4Cl, Eu5Gd(Ⅲ)(BO3)4Cl, Eu5Tb(Ⅲ)(BO3)4Cl, Eu5Dy(Ⅲ)(BO3)4Cl, Eu5Ho(Ⅲ)(BO3)4Cl, Eu5Er(Ⅲ)(BO3)4Cl or Eu5Tm(Ⅲ)(BO3)4Cl.

[0011] Further, the rare earth chloride borate magnetic refrigeration material has a magnetic phase transition below the liquid helium temperature, and the magnetic phase transition temperature is ≤4.2 K.

[0012] Further, the rare earth chloride borate magnetic refrigeration material comprises at least one of the following features: 1) The maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is ≥19.6 J·kg -1 ·K -1 ; As a preferred embodiment of the present application, the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is 21.2 J·kg -1 ·K -1 ; 2) The maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is 35.1 J·kg -1 ·K -1 ; 3) The maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is ≥31.7 J·kg -1 ·K -1 ; 4) The maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is ≥52.0 J·kg -1 ·K -1 ; As a preferred embodiment of the present application, the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is 55.9 J·kg -1 ·K -1 .

[0013] To achieve the above-mentioned second object, the technical solution adopted by the present application comprises: The present application discloses a preparation method of the rare earth chloride borate magnetic refrigeration material as described above, comprising the following steps: (1) Eu2O3 and NH4Cl powders are weighed according to stoichiometric ratio respectively, mixed uniformly, preheated at 250-350℃ for 1.5-2.5 h, sintered to obtain EuOCl precursor, wherein the stoichiometric ratio is calculated according to EuOCl precursor; (2) EuOCl, Eu2O3, RE2O3, elemental B and B2O3 are weighed according to the molar ratio of 2:4:1:3.73-3.93:2.43-2.48 respectively, mixed uniformly, sieved through 100-200 mesh to obtain mixed powder, tabletted, pre-fired, heated to higher temperature for high-temperature sintering, cooled to room temperature in the furnace to obtain rare earth chloride borate magnetic refrigeration material.

[0014] Further, in step (1), the sintering temperature is 625-675℃, and the sintering time is 5-7 h.

[0015] It should be noted that in the weighing of step (2), elemental B and B2O3 are both in excess, wherein elemental B is in excess by about 12-18%, and B2O3 is in excess by about 4-6%.

[0016] Further, the mixing in step (2) can be achieved by grinding with an agate mortar for 20-40 min or ball milling with a planetary ball mill for 0.5-2 h.

[0017] Further, in step (2), tabletting is achieved by using dry pressing equipment to press the mixed powder obtained in step (2) into a round or round-like sample, the pressure applied during tabletting is 500-1000 MPa, preferably 800 MPa, and the pressure holding time is 1-10 min, preferably 5 min.

[0018] Further, in step (2), pre-firing is carried out in a flowing mixed gas atmosphere containing hydrogen and argon, the pre-firing temperature is 475-525℃, the constant temperature pre-firing time is 4-6 h, and the heating rate is 1-10℃ / min.

[0019] Further, in step (2), high-temperature sintering is carried out in a flowing mixed gas atmosphere containing hydrogen and argon, the high-temperature sintering temperature is 900-950℃, and the constant temperature sintering time is 8-12 h.

[0020] Further, the volume fraction of hydrogen in the mixed gas atmosphere is 1-10%.

[0021] To achieve the third object, the technical solution adopted by the present application includes: The application discloses application of a rare earth chloride borate magnetic refrigeration material in preparation of a magnetic refrigeration material or device in a liquid helium temperature range (2-10 K).

[0022] The application has the following beneficial effects: 1. The rare earth chloride borate magnetic refrigeration material provided by the application has a chemical formula of Eu5RE(III)(BO3)4Cl, wherein the metal RE(III) is Eu, Gd, Tb, Dy, Ho, Er or Tm, and the rare earth chloride borate magnetic refrigeration material has excellent magnetocaloric performance, and the maximum magnetic entropy change is greater than or equal to 19.6 J·kg -1 ·K -1 when the magnetic field changes from 0 T to 1 T at a temperature of 2.5 K, the maximum magnetic entropy change is greater than or equal to 31.7 J·kg -1 ·K -1 when the magnetic field changes from 0 T to 2 T at a temperature of 3.5 K, and the maximum magnetic entropy change is greater than or equal to 52.0 J·kg -1 ·K -1 ·K, which is significantly better than many magnetic refrigeration materials disclosed in prior arts.

[0023] 2. The rare earth chloride borate magnetic refrigeration material has excellent magnetocaloric performance near the liquid helium temperature, and the raw materials used in the rare earth chloride borate magnetic refrigeration material are low in cost, and the preparation method is simple and short in period, so that the rare earth chloride borate magnetic refrigeration material has a potential application prospect in the field of liquid helium temperature magnetic refrigeration technology. BRIEF DESCRIPTION OF DRAWINGS

[0024] The specific embodiments of the application will be further described in detail in combination with the drawings.

[0025] Figure 1 A magnetic refrigeration material structure schematic diagram of a Eu6(BO3)4Cl compound is shown.

[0026] Figure 2 A magnetic refrigeration material structure schematic diagram of a Eu5Gd(BO3)4Cl compound is shown.

[0027] Figure 3 X-ray diffraction (XRD) spectra of rare earth chloride borate samples prepared in Examples 1, 2 and Comparative Examples 1-3 are shown. Figure 4 X-ray diffraction (XRD) spectra of rare earth chloride borate samples prepared in Examples 3, 4 and Comparative Examples 4-6 are shown. Figure 5 A curve graph of the magnetic entropy change of the rare earth chloride borate sample Eu6(BO3)4Cl prepared in Example 1 with respect to temperature under different magnetic field changes is shown. Figure 6Figure 3 shows the magnetic entropy change versus temperature curve of the rare earth chloride borate sample Eu5Gd(BO3)4Cl prepared in Example 3 under different magnetic field changes. DETAILED DESCRIPTION

[0028] In order to more clearly illustrate the present application, the present application will be further described below in conjunction with preferred embodiments and the accompanying drawings. It should be noted that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of the present application.

[0029] In addition, unless otherwise specified, the raw materials used in the present application can be purchased from commercial suppliers, and any range described in the present application includes the end values and any numerical value between the end values and any sub-range formed by any numerical value or between the end values.

[0030] Example 1 The present embodiment provides a preparation method of Eu6(BO3)4Cl magnetic refrigeration material, which specifically comprises the following steps: (1) Eu2O3 and NH4Cl powders are weighed according to the stoichiometric ratio, mixed uniformly, preheated at 300°C for 2 h, and then sintered at 650°C for 6 h to obtain an EuOCl precursor; (2) EuOCl, Eu2O3, elemental B and B2O3 are weighed according to the molar ratio of EuOCl:Eu2O3:B:B2O3=2:5:3.83:2.452, mixed uniformly, and sieved through a 200-mesh sieve to obtain a mixed powder; wherein the amount of elemental B is 15% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material, and the amount of B2O3 is 5% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material; (3) The mixed powder obtained in step (2) is pressed into a round sheet-shaped sample by using a dry pressing equipment under a pressure of 800 MPa for 5 min; (4) The round sheet-shaped sample obtained in step (3) is placed in a graphite crucible, covered with a lid, and then placed in a tube furnace, heated to 500°C at a rate of 2°C / min, and pre-fired for 5 h to obtain a pre-fired body; (5) The pre-fired body in step (4) is heated to 920°C, sintered for 10 h, and then cooled to room temperature in the furnace to obtain Eu6(BO3)4Cl magnetic refrigeration material.

[0031] Example 2 The embodiment provides a preparation method of Eu5Tb(BO3)4Cl magnetic refrigeration material, and the preparation method specifically comprises the following steps: (1) Eu2O3 and NH4Cl powders are respectively weighed according to the stoichiometric ratio, are fully mixed uniformly, are preheated at 300 DEG C for 2 h, and are then sintered at 625 DEG C for 7 h to obtain an EuOCl precursor; (2) EuOCl, Eu2O3, Tb2O3 and elemental B and B2O3 are respectively weighed according to the substance amount ratio EuOCl:Eu2O3:Tb2O3:B:B2O3=2:4:1:3.73:2.428, are fully mixed uniformly, and are sieved through a 100-mesh screen to obtain a mixed powder; wherein the feeding amount of the elemental B is 12% more than the stoichiometric ratio of the Eu6(BO3)4Cl magnetic refrigeration material, and the feeding amount of the B2O3 is 4% more than the stoichiometric ratio of the Eu6(BO3)4Cl magnetic refrigeration material; (3) the mixed powder obtained in the step (2) is pressed into a round tablet sample by adopting a dry pressing forming equipment under the pressure of 500 MPa for 10 min; (4) the round tablet sample obtained in the step (3) is placed in a graphite crucible, is covered with a cover, and then is placed in a tube furnace and heated to 475 DEG C at the rate of 1 DEG C / min, is pre-burned for 6 h, and a pre-burned body is obtained; (5) the pre-burned body in the step (4) is heated to 950 DEG C, is sintered for 8 h, and is cooled to room temperature in the furnace to obtain the Eu5Tb(BO3)4Cl magnetic refrigeration material.

[0032] Embodiment 3 The embodiment provides a preparation method of Eu5Gd(BO3)4Cl magnetic refrigeration material, and the preparation method specifically comprises the following steps: (1) Eu2O3 and NH4Cl powders are respectively weighed according to the stoichiometric ratio, are fully mixed uniformly, are preheated at 300 DEG C for 2 h, and are then sintered at 650 DEG C for 6 h to obtain an EuOCl precursor; (2) EuOCl, Eu2O3, Gd2O3 and elemental B and B2O3 are respectively weighed according to the substance amount ratio EuOCl:Eu2O3:Gd2O3:B:B2O3=2:4:1:3.83:2.452, are fully mixed uniformly, and are sieved through a 200-mesh screen to obtain a mixed powder; wherein the feeding amount of the elemental B is 15% more than the stoichiometric ratio of the Eu6(BO3)4Cl magnetic refrigeration material, and the feeding amount of the B2O3 is 5% more than the stoichiometric ratio of the Eu6(BO3)4Cl magnetic refrigeration material; (3) the mixed powder obtained in the step (2) is pressed into a round tablet sample by adopting a dry pressing forming equipment under the pressure of 800 MPa for 5 min; (4) The disc-shaped sample obtained in step (3) is placed in a graphite crucible, covered with a lid, and then placed in a tube furnace, heated to 500℃ at a rate of 2℃ / min, and pre-fired for 5 h to obtain a pre-fired body; (5) The pre-fired body obtained in step (4) is heated to 920℃, sintered for 10 h, and then cooled to room temperature in the furnace to obtain a Eu5Gd(BO3)4Cl magnetic refrigeration material.

[0033] Example 4 The present embodiment provides a preparation method of a Eu5Ho(BO3)4Cl magnetic refrigeration material, which specifically comprises the following steps: (1) Eu2O3 and NH4Cl powders are weighed according to the stoichiometric ratio, mixed uniformly, preheated at 300℃ for 2 h, and then sintered at 675℃ for 5 h to obtain an EuOCl precursor; (2) EuOCl, Eu2O3, Ho2O3, elemental B and B2O3 are weighed according to the molar ratio of EuOCl:Eu2O3:Ho2O3:B:B2O3=2:4:1:3.93:2.475, mixed uniformly, and sieved through a 100 mesh sieve to obtain a mixed powder; wherein the amount of elemental B is 18% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material, and the amount of B2O3 is 6% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material; (3) The mixed powder obtained in step (2) is pressed into a disc-shaped sample under a pressure of 1000 MPa for 1 min using a dry pressing equipment; (4) The disc-shaped sample obtained in step (3) is placed in a graphite crucible, covered with a lid, and then placed in a tube furnace, heated to 525℃ at a rate of 10℃ / min, and pre-fired for 4 h to obtain a pre-fired body; (5) The pre-fired body obtained in step (4) is heated to 900℃, sintered for 12 h, and then cooled to room temperature in the furnace to obtain a Eu5Ho(BO3)4Cl magnetic refrigeration material.

[0034] Comparative Example 1 The present comparative example is compared with Example 1, and the only difference is that in step (2), elemental B is not excessive, and specifically comprises the following steps: (1) Eu2O3 and NH4Cl powders are weighed according to the stoichiometric ratio, mixed uniformly, preheated at 300℃ for 2 h, and then sintered at 650℃ for 6 h to obtain an EuOCl precursor; (2) EuOCl, Eu2O3, elemental B and B2O3 were weighed according to the molar ratio of EuOCl:Eu2O3:B:B2O3=2:5:3.33:2.452, mixed uniformly, and sieved through a 200-mesh screen to obtain a mixed powder; wherein the amount of B2O3 was 5% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material; (3) The mixed powder obtained in step (2) was pressed into a circular tablet under a pressure of 800 MPa for 5 min using a dry pressing device; (4) The circular tablet obtained in step (3) was placed in a graphite crucible, covered with a lid, and then placed in a tube furnace, and heated to 500℃ at a rate of 2℃ / min, and pre-sintered for 5 h to obtain a pre-sintered body; (5) The pre-sintered body obtained in step (4) was heated to 920℃, sintered for 10 h, and then cooled to room temperature in the furnace to obtain a Eu6(BO3)4Cl magnetic refrigeration material sample.

[0035] Comparative Example 2 This comparative example is different from Example 1 only in that in step (2), the amount of B2O3 is only 2% more than the stoichiometric ratio, and specifically includes the following steps: 1) Eu2O3 and NH4Cl powders were weighed according to the stoichiometric ratio, mixed uniformly, preheated at 300℃ for 2 h, and then sintered at 650℃ for 6 h to obtain an EuOCl precursor; (2) EuOCl, Eu2O3, and elemental B (15% excess) and B2O3 (2% excess) were weighed according to the molar ratio of EuOCl:Eu2O3:B:B2O3=2:5:3.83:2.382, mixed uniformly, and sieved through a 200-mesh screen to obtain a mixed powder; wherein the amount of elemental B was 15% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material, and the amount of B2O3 was 2% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material; (3) The mixed powder obtained in step (2) was pressed into a circular tablet under a pressure of 800 MPa for 5 min using a dry pressing device; (4) The circular tablet obtained in step (3) was placed in a graphite crucible, covered with a lid, and then placed in a tube furnace, and heated to 500℃ at a rate of 2℃ / min, and pre-sintered for 5 h to obtain a pre-sintered body; (5) The pre-sintered body obtained in step (4) was heated to 920℃, sintered for 10 h, and then cooled to room temperature in the furnace to obtain a Eu6(BO3)4Cl magnetic refrigeration material sample.

[0036] Comparative Example 3 The comparative example is compared with example 1, the only difference is that no pre-burning treatment is performed, specifically comprising the following steps: (1) Eu2O3 and NH4Cl powders are weighed according to the stoichiometric ratio, mixed uniformly, preheated at 300°C for 2 h, and then sintered at 650°C for 6 h to obtain EuOCl precursor; (2) EuOCl, Eu2O3, and elemental B (excess 15%) and B2O3 (excess 5%) are weighed according to the molar ratio EuOCl:Eu2O3:B:B2O3=2:5:3.83:2.452, mixed uniformly, and sieved through a 200-mesh screen to obtain a mixed powder; wherein the amount of elemental B is 15% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material, and the amount of B2O3 is 5% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material; (3) The mixed powder obtained in step (2) is pressed into a circular tablet-shaped sample under a pressure of 800 MPa for 5 min using a dry pressing device; (4) The circular tablet-shaped sample in step (3) is placed in a graphite crucible, covered with a lid, and then placed in a tube furnace, heated to 920°C, sintered for 10 h, and then cooled to room temperature with the furnace to obtain a Eu6(BO3)4Cl magnetic refrigeration material sample.

[0037] Comparative Example 4 The comparative example is compared with example 3, the only difference is that the amount of elemental B in step (2) is 20% more, specifically comprising the following steps: (1) Eu2O3 and NH4Cl powders are weighed according to the stoichiometric ratio, mixed uniformly, preheated at 300°C for 2 h, and then sintered at 650°C for 6 h to obtain EuOCl precursor; (2) EuOCl, Eu2O3, Gd2O3, elemental B, and B2O3 are weighed according to the molar ratio EuOCl:Eu2O3:Gd2O3:B:B2O3=2:4:1:4:2.452, mixed uniformly, and sieved through a 200-mesh screen to obtain a mixed powder; wherein the amount of elemental B is 20% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material, and the amount of B2O3 is 5% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material; (3) The mixed powder obtained in step (2) is pressed into a circular tablet-shaped sample under a pressure of 800 MPa for 5 min using a dry pressing device; (4) The circular tablet-shaped sample in step (3) is placed in a graphite crucible, covered with a lid, and then placed in a tube furnace, heated to 920°C, sintered for 10 h, and then cooled to room temperature with the furnace to obtain a Eu6(BO3)4Cl magnetic refrigeration material sample. (5) The pre-sintered body of step (4) is heated to 920℃, sintered for 10 h, and then cooled to room temperature in the furnace to obtain a Eu5Gd(BO3)4Cl magnetic refrigeration material sample.

[0038] Comparative Example 5 This comparative example is compared with Example 3, and the only difference is that the excess of B2O3 in step (2) is 10%, which specifically includes the following steps: (1) Eu2O3 and NH4Cl powders are weighed according to the stoichiometric ratio, mixed uniformly, preheated at 300℃ for 2 h, and then sintered at 650℃ for 6 h to obtain an EuOCl precursor; (2) EuOCl, Eu2O3, Gd2O3, elemental B and B2O3 are weighed according to the molar ratio of EuOCl:Eu2O3:Gd2O3:B:B2O3=2:4:1:3.83:2.569, mixed uniformly, and sieved through a 200 mesh sieve to obtain a mixed powder; wherein the amount of elemental B is 15% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material, and the amount of B2O3 is 10% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material; (3) The mixed powder obtained in step (2) is pressed into a circular tablet shape sample by dry pressing equipment under a pressure of 800 MPa for 5 min; (4) The circular tablet-shaped sample of step (3) is placed in a graphite crucible, covered with a lid, and then placed in a tube furnace, heated to 500℃ at a rate of 2℃ / min, and pre-sintered for 5 h to obtain a pre-sintered body; (5) The pre-sintered body of step (4) is heated to 920℃, sintered for 10 h, and then cooled to room temperature in the furnace to obtain a Eu5Gd(BO3)4Cl magnetic refrigeration material sample.

[0039] Comparative Example 6 This comparative example is compared with Example 3, and the only difference is that the sintering temperature in step (5) is 850℃, which specifically includes the following steps: (1) Eu2O3 and NH4Cl powders are weighed according to the stoichiometric ratio, mixed uniformly, preheated at 300℃ for 2 h, and then sintered at 650℃ for 6 h to obtain an EuOCl precursor; (2) Weigh out the corresponding amounts of EuOCl, Eu2O3, Gd2O3, elemental B, and B2O3 according to the molar ratio EuOCl:Eu2O3:Gd2O3:B:B2O3=2:4:1:3.83:2.452, mix them thoroughly and evenly, and pass them through a 200-mesh sieve to obtain a mixed powder; wherein, the amount of elemental B is 15% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material, and the amount of B2O3 is 5% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material. (3) The mixed powder obtained in step (2) was pressed into a disc-shaped sample by using a dry pressing molding equipment and kept under a pressure of 800 MPa for 5 min. (4) Place the circular sample obtained in step (3) into a graphite crucible, cover it, and then place it in a tube furnace. Heat it to 500°C at a rate of 2°C / min and pre-fire for 5 h to obtain a pre-fired body. (5) The pre-burned body described in step (4) is heated to 850°C and sintered for 10 h. Then it is cooled to room temperature in the furnace to obtain Eu5Gd(BO3)4Cl magnetic refrigeration material sample.

[0040] Example of effect The rare earth chloride borate samples prepared in Examples 1-4 and Comparative Examples 1-6 were subjected to X-ray diffraction (XRD) tests. The XRD patterns of the obtained samples were compared and analyzed with the standard patterns to determine their phase composition.

[0041] Figure 1 and Figure 2 The images show schematic diagrams of the magnetic refrigeration materials of compounds Eu6(BO3)4Cl and Eu5Gd(BO3)4Cl, respectively, belonging to the hexagonal crystal system with space group [missing information]. P 63 mc .

[0042] Figure 3 The X-ray diffraction (XRD) patterns are shown for the rare earth chloride borate samples prepared in Examples 1, 2, and Comparative Examples 1-3. Figure 3 It can be seen that the XRD patterns of the rare earth chloride borate samples prepared in Examples 1 and 2 are highly consistent with the theoretical patterns, with no obvious impurity peaks, indicating that they are all composed of a single phase; however, the XRD patterns of the rare earth chloride borate samples prepared in Comparative Examples 1-3 show obvious impurity diffraction peaks, indicating that there are impurity phases in the samples and they are not composed of a single phase.

[0043] Figure 4 The X-ray diffraction (XRD) patterns are shown for the rare earth chloride borate samples prepared in Examples 3, 4, and Comparative Examples 4-6. Figure 4It can be seen that the XRD patterns of the rare earth chloride borate samples prepared in Examples 3 and 4 are highly matched with the theoretical pattern, and no obvious impurity peak is observed, indicating that the samples are composed of single phase. However, the XRD patterns of the rare earth chloride borate samples prepared in Comparative Examples 4-6 have obvious impurity diffraction peaks, indicating that the samples have impurity phases and are not composed of single phase. Therefore, it can be seen that the selection of technical parameters is very important. Different reactant ratios, sintering temperatures and times can affect the phase composition of the material, resulting in that the single-phase rare earth chloride borate magnetic refrigeration material cannot be obtained.

[0044] The zero-field cooling (ZFC) and field-cooled (FC) thermomagnetic curves of the rare earth chloride borate prepared in Examples 1 and 3 under a magnetic field of 0.01 T were measured, and the magnetic phase transition temperature of the material was obtained by the first derivative of the ZFC curve. Through testing and analysis, the magnetic phase transition temperatures of the rare earth chloride borates prepared in Examples 1 and 3 are 2.5 K and 2.7 K, respectively, which are below the liquid helium temperature (4.2 K), indicating that the rare earth chloride borate is a potential liquid helium temperature magnetic refrigeration material.

[0045] The isothermal magnetization curves of the rare earth chloride borates prepared in Examples 1 and 3 at different temperatures were measured, and the magnetic entropy change under different magnetic field changes was calculated according to the isothermal magnetization curves at different temperatures by using the Maxwell relationship. Figure 5 The magnetic entropy change-temperature curves of the rare earth chloride borate Eu6(BO3)4Cl prepared in Example 1 under different magnetic field changes are shown in the following table: Figure 5 It can be seen that the maximum magnetic entropy change of the material is 19.6 J·kg -1 ·K -1 at 2.5 K under a magnetic field change of 0-1 T, the maximum magnetic entropy change is 31.7 J·kg -1 ·K -1 at 3.5 K under a magnetic field change of 0-2 T, and the maximum magnetic entropy change is 52.0 J·kg -1 ·K -1 . Figure 6 The magnetic entropy change-temperature curves of the rare earth chloride borate Eu5Gd(BO3)4Cl prepared in Example 3 under different magnetic field changes are shown in the following table: Figure 6 It can be seen that the maximum magnetic entropy change of the material is 21.2 J·kg -1 ·K -1 at 2.5 K under a magnetic field change of 0-1 T, the maximum magnetic entropy change is 35.1 J·kg -1·K -1 The maximum magnetic entropy change is 55.9 J·kg-1·K-1 when the magnetic field changes from 0 to 5 T at the temperature of 3.5 K. -1 ·K -1 The results show that the rare earth chloride borate salt disclosed in the application has superior magnetic heat performance near the liquid helium temperature, which is significantly better than the liquid helium temperature magnetic refrigeration materials disclosed in many prior arts (such as NaGdSiO4, Ho4Al2O9 and GdSr2TaO6, etc.), and therefore has a potential application prospect in the field of liquid helium temperature magnetic refrigeration technology.

[0046] Obviously, the above embodiments of the application are only examples for clearly illustrating the application, and are not intended to limit the implementation modes of the application, and any modification or change made on the basis of the above description for those skilled in the art is within the scope of the application. Obviously, the above embodiments of the application are only examples for clearly illustrating the application, and are not intended to limit the implementation modes of the application, and any modification or change made on the basis of the above description for those skilled in the art is within the scope of the application.

Claims

1. A rare-earth chloroborate magnetic refrigeration material, characterized in that, The rare earth chloride borate magnetic refrigeration material has a chemical formula of Eu5RE(III)(BO3)4Cl, wherein the metal RE is Eu, Gd, Tb, Dy, Ho, Er or Tm, belongs to a hexagonal crystal system, and a space group is P63 / mmc P6 3 mc .

2. The rare earth chloride borate magnetic refrigeration material of claim 1, wherein, The rare earth chloride borate magnetic refrigeration material has a magnetic phase transition below liquid helium temperature, and the magnetic phase transition temperature is ≤4.2 K.

3. The rare earth chloride borate magnetic refrigeration material of claim 1, wherein, The rare earth chloride borate magnetic refrigeration material comprises at least one of the following features: 1) The maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is ≥19.6 J·kg -1 ·K -1 at a temperature of 2.5 K and a magnetic field change of 0-1 T. 2) The maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is 35.1 J·kg -1 ·K -1 at a temperature of 2.5 K and a magnetic field change of 0-2 T 3) The maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is greater than or equal to 31.7 J·kg -1 ·K -1 ; 4) The maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is greater than or equal to 52.0 J·kg -1 ·K -1 .

4. The method of producing a rare earth chloride borate magnetic refrigerant material according to any one of claims 1 to 3, wherein The method comprises the following steps: (1) Eu2O3 and NH4Cl powders are weighed according to the stoichiometric ratio, mixed uniformly, preheated at 250-350 ℃ for 1.5-2.5 h, sintered to obtain EuOCl precursor; (2) EuOCl, Eu2O3, RE2O3, elemental B and B2O3 are weighed according to the molar ratio of 2:4:1:3.73-3.93:2.43-2.48, mixed uniformly, sieved through a 100-200 mesh sieve, tabletted, pre-sintered, and then high-temperature sintered, and cooled to room temperature in the furnace to obtain the rare earth chloride borate magnetic refrigeration material.

5. The preparation method according to claim 4, characterized in that, In step (1), the sintering temperature is 625-675 ℃, and the sintering time is 5-7 h.

6. The preparation method according to claim 4, characterized in that, In step (2), the pressure applied during tabletting is 500-1000 MPa, and the pressure holding time is 1-10 min.

7. The preparation method according to claim 4, characterized in that, In step (2), the pre-sintering is performed in a flowing mixed gas atmosphere containing hydrogen and argon, the pre-sintering temperature is 475-525 ℃, the constant temperature pre-sintering is performed for 4-6 h, and the temperature rising rate is 1-10 ℃ / min.

8. The preparation method according to claim 4, characterized in that, In step (2), the high-temperature sintering is performed in a flowing mixed gas atmosphere containing hydrogen and argon, the high-temperature sintering temperature is 900-950 ℃, and the constant temperature sintering is performed for 8-12 h.

9. The production method according to claim 7 or 8, characterized by, The volume fraction of hydrogen in the mixed gas atmosphere is 1-10%.

10. Use of the rare earth chloride borate magnetic refrigeration material according to any one of claims 1-3 in the preparation of a liquid helium temperature range magnetic refrigeration material or device.

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