A rare earth chloride borate magnetic refrigeration material, its preparation method, and its application in magnetic refrigeration.

Abstract

This invention belongs to the field of magnetic refrigeration materials technology, specifically including a rare earth chloride borate magnetic refrigeration material, its preparation method, and its application in magnetic refrigeration. The chemical formula of the rare earth chloride borate magnetic refrigeration material is Eu5RE(Ⅲ)(BO3)4Cl, wherein the metal RE is Eu, Gd, Tb, Dy, Ho, Er, or Tm, belonging to the hexagonal crystal system, and the space group is [missing information]. P6 3 mc This rare-earth chloride borate magnetic refrigeration material exhibits a large magnetocaloric effect driven by a low magnetic field near liquid helium temperatures. Its maximum magnetic entropy change at 2.5 K with a magnetic field change of 0–1 T is ≥19.6 J·kg. ‑1 ·K ‑1 The maximum magnetic entropy change at 3.5 K temperature and a magnetic field change of 0–2 T is ≥31.7 J·kg. ‑1 ·K ‑1 The maximum magnetic entropy change at 3.5 K temperature and a magnetic field change of 0–5 T is ≥52.0 J·kg. ‑1 ·K ‑1 It is significantly superior to many publicly available magnetic refrigeration materials. Based on its excellent magnetocaloric properties near the liquid helium temperature, it is expected to be applied to magnetic refrigeration technology in the liquid helium temperature range.

Description

Technical Field

[0001] This invention belongs to the field of magnetic refrigeration materials technology, specifically including a rare earth chloride borate magnetic refrigeration material, its preparation method, and its application in magnetic refrigeration. Background Technology

[0002] Since the 20th century, cryogenic refrigeration technology has achieved unprecedented development and widespread application, becoming one of the key supporting technologies for modern scientific and technological development. Among these, liquid helium temperature range (2-10 K) refrigeration is an indispensable and crucial component of cryogenic refrigeration, playing a vital technical support role in fields such as low-temperature physics, low-temperature superconductivity, aerospace, and military applications. Currently, the mainstream method for achieving liquid helium temperatures is the use of the Gifford-McMahon (GM) cryostat, but its refrigeration efficiency is only about 1% of the Carnot cycle efficiency. Therefore, how to effectively improve the refrigeration efficiency of the GM cryostat is a critical challenge that urgently needs to be overcome in the field of cryogenic refrigeration technology.

[0003] Magnetic refrigeration is a novel solid-state refrigeration technology that utilizes the magnetocaloric effect (MCE) of magnetic materials to achieve cooling. The magnetocaloric effect is an intrinsic property of magnetic materials, meaning that when an external magnetic field changes, the magnetic entropy changes due to the alteration of the magnetic moment's order, leading to heat absorption or release and thus cooling. Magnetic refrigeration technology boasts numerous advantages, including energy efficiency, environmental friendliness, miniaturization, and stability, and holds promise as a next-generation refrigeration technology to replace traditional gas compression refrigeration. As the source of cooling capacity in a magnetic refrigeration system, the magnetic refrigeration material is the core of the technology; therefore, developing magnetocaloric materials with a large magnetocaloric effect near liquid helium temperatures is crucial for realizing the application of magnetic refrigeration technology in the liquid helium temperature range.

[0004] Gd-based oxides possess large magnetic moments and completely quenched orbital momentum, making them promising cryogenic magnetic refrigeration materials. For example, CN118343824A discloses a gadolinium-based cryogenic magnetic refrigeration material and its preparation method, with the chemical formula NaGdSiO4. This material is prepared using a solid-state reaction method, which has the advantages of simple process and short cycle time. However, its maximum magnetic entropy change under a magnetic field change of 0-1 T is only about 4 J·kg. -1 ·K -1 CN120496982A discloses a rare-earth aluminate low-temperature magnetic refrigeration material with the general chemical formula RE4Al2O9 (RE being at least one of the rare earth elements Gd, Dy, and Ho). Under a magnetic field change of 0–2 T, its isothermal magnetic entropy change is only between 9.47 and 10.32 J·kg. -1 ·K -1CN114974772A discloses a rare-earth magnetic material with a monoclinic structure, whose general chemical formula is RESr2TaO6 (RE is one or two of Gd, Dy, Ho, and Er). Under a magnetic field variation of 0-5 T, its isothermal magnetic entropy change is only between 5.1-27.2 J·kg. -1 ·K -1 between.

[0005] However, traditional magnetic refrigeration materials have insufficient magnetocaloric performance under low magnetic fields, requiring superconducting magnets to provide the magnetic field, which is costly and has become a key problem hindering their practical application.

[0006] Therefore, developing a liquid helium temperature-range magnetic refrigeration material that can have a large magnetocaloric effect driven by a low magnetic field near the liquid helium temperature is the key to promoting the large-scale application of liquid helium temperature-range magnetic refrigeration technology, and has significant economic value and important practical significance. Summary of the Invention

[0007] To address the aforementioned problems in the existing technology, the first objective of this invention is to provide a rare-earth chloride borate magnetic refrigeration material. This rare-earth chloride borate magnetic refrigeration material undergoes a magnetic phase transition near the liquid helium temperature, accompanied by a large magnetocaloric effect. Its maximum magnetic entropy change at 2.5 K with a magnetic field change of 0-1 T is ≥19.6 J·kg. -1 ·K -1 The maximum magnetic entropy change at 3.5 K and a magnetic field change of 0-2 T is ≥31.7 J·kg. -1 ·K -1 The maximum magnetic entropy change at 3.5 K temperature and a magnetic field change of 0-5 T is ≥52.0 J·kg. -1 ·K -1 It is significantly superior to many currently available magnetic refrigeration materials.

[0008] The second objective of this invention is to provide a method for preparing the rare earth chloride borate magnetic refrigeration material as described above.

[0009] A third objective of this invention is to provide an application of the rare earth chloride borate magnetic refrigeration material described above in the preparation of magnetic refrigeration materials or devices in the liquid helium temperature range.

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

[0011] This invention discloses a rare earth chloride borate magnetic refrigeration material, the chemical formula of which is Eu5RE(Ⅲ)(BO3)4Cl, wherein the metal RE(Ⅲ) represents a rare earth metal in a trivalent state, specifically Eu, Gd, Tb, Dy, Ho, Er, or Tm, and is composed of a single phase, belonging to the hexagonal crystal system, with space group . P6 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.

[0012] Furthermore, the rare earth chloride borate magnetic refrigeration material undergoes a magnetic phase transition below the liquid helium temperature, with a magnetic phase transition temperature ≤ 4.2 K.

[0013] Furthermore, the rare earth chloride borate magnetic refrigeration material includes at least one of the following features:

[0014] 1) At a temperature of 2.5 K and a magnetic field change of 0–1 T, the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is ≥19.6 J·kg. -1 ·K -1 ;

[0015] In a preferred embodiment of the present invention, the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material at 2.5 K temperature and a magnetic field change of 0-1 T is 21.2 J·kg. -1 ·K -1 ;

[0016] 2) At a temperature of 2.5 K and a magnetic field change of 0–2 T, the maximum magnetic entropy change of the rare-earth chloride borate magnetic refrigeration material is 35.1 J·kg⁻¹. -1 ·K -1 ;

[0017] 3) At a temperature of 3.5 K and a magnetic field change of 0–2 T, the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is ≥31.7 J·kg. -1 ·K -1 ;

[0018] 4) At a temperature of 3.5 K and a magnetic field variation of 0–5 T, the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is ≥52.0 J·kg. -1 ·K -1 ;

[0019] In a preferred embodiment of the present invention, the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material at 3.5 K temperature and a magnetic field change of 0-5 T is 55.9 J·kg. -1 ·K -1 .

[0020] To achieve the second objective mentioned above, the technical solution adopted by the present invention includes:

[0021] This invention discloses a method for preparing the rare earth chloride borate magnetic refrigeration material as described above, comprising the following steps:

[0022] (1) Weigh Eu2O3 and NH4Cl powders according to the stoichiometric ratio, mix them thoroughly, preheat at 250-350℃ for 1.5-2.5 h, and sinter to obtain EuOCl precursor, wherein the stoichiometric ratio is calculated based on EuOCl precursor;

[0023] (2) Weigh the corresponding amounts of EuOCl, Eu2O3, RE2O3, elemental B and B2O3 according to the molar ratio of EuOCl, Eu2O3, RE2O3, elemental B and B2O3 as 2:4:1:3.73-3.93:2.43-2.48, mix them thoroughly and evenly, pass them through a 100-200 mesh sieve to obtain mixed powder, press them into tablets, pre-calcine them, and then heat them to a higher temperature for high-temperature sintering. Cool them to room temperature with the furnace to obtain rare earth chloride borate magnetic refrigeration material.

[0024] Furthermore, in step (1), the sintering temperature is 625-675℃ and the sintering time is 5-7 h.

[0025] It should be noted that during the weighing in step (2), both elemental B and B2O3 are in excess, with elemental B being in excess by about 12-18% and B2O3 being in excess by about 4-6%.

[0026] Furthermore, the mixing in step (2) can be achieved by grinding in an agate mortar for 20-40 min or by ball milling in a planetary ball mill for 0.5-2 h.

[0027] Further, in step (2), the tableting is performed by using a dry pressing molding equipment to press the mixed powder obtained in step (2) into a disc or near-disc disc sample. The pressure applied during tableting is 500-1000 MPa, preferably 800 MPa, and the holding time is 1-10 min, preferably 5 min.

[0028] Furthermore, in step (2), the pre-burning is carried out in a flowing mixed atmosphere containing hydrogen and argon, the pre-burning temperature is 475-525℃, the pre-burning is constant for 4-6 h, and the heating rate is 1-10℃ / min.

[0029] Furthermore, in step (2), the high-temperature sintering is carried out in a flowing mixed atmosphere containing hydrogen and argon, the high-temperature sintering temperature is 900-950℃, and the constant temperature sintering is 8-12 h.

[0030] Furthermore, the volume fraction of hydrogen in the mixed atmosphere is 1-10%.

[0031] To achieve the third objective mentioned above, the technical solution adopted by the present invention includes:

[0032] This invention discloses the application of rare earth chloride borate magnetic refrigeration material as described above in the preparation of magnetic refrigeration materials or devices in the liquid helium temperature range (2-10 K).

[0033] Beneficial effects of this invention:

[0034] 1. The rare earth chloride borate magnetic refrigeration material provided by this invention has the chemical formula Eu5RE(Ⅲ)(BO3)4Cl, wherein the metal RE(Ⅲ) is Eu, Gd, Tb, Dy, Ho, Er, or Tm. It exhibits excellent magnetocaloric properties, with a maximum magnetic entropy change ≥19.6 J·kg at 2.5 K temperature and a magnetic field change of 0-1 T. -1 ·K -1 At 3.5 K, the maximum magnetic entropy change is ≥31.7 J·kg when the magnetic field changes by 0-2 T. -1 ·K -1 At 3.5 K, the maximum magnetic entropy change is ≥52.0 J·kg⁻¹ when the magnetic field changes by 0.05 T. -1 ·K -1 It is significantly superior to many magnetic refrigeration materials disclosed in the prior art.

[0035] 2. Due to the excellent magnetocaloric effect of this rare earth chloride borate magnetic refrigeration material near the liquid helium temperature, and the low cost of the raw materials used in this rare earth chloride borate magnetic refrigeration material, as well as the simple and short preparation method, it has potential application prospects in the field of magnetic refrigeration technology in the liquid helium temperature range. Attached Figure Description

[0036] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0037] Figure 1 A schematic diagram of the magnetic refrigeration material structure of Eu6(BO3)4Cl compound is shown.

[0038] Figure 2 A schematic diagram of the magnetic refrigeration material structure of Eu5Gd(BO3)4Cl compound is shown.

[0039] Figure 3The X-ray diffraction (XRD) patterns of the rare earth chloride borate samples prepared in Examples 1, 2 and Comparative Examples 1-3 are shown.

[0040] Figure 4 The X-ray diffraction (XRD) patterns of the rare earth chloride borate samples prepared in Examples 3, 4 and Comparative Examples 4-6 are shown.

[0041] Figure 5 The graph shows the magnetic entropy change of the rare earth chloride borate sample Eu6(BO3)4Cl prepared in Example 1 under different magnetic field changes as a function of temperature.

[0042] Figure 6 The graph shows the magnetic entropy change of the rare earth chloride borate sample Eu5Gd(BO3)4Cl prepared in Example 3 under different magnetic field changes as a function of temperature. Detailed Implementation

[0043] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the invention. It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0044] In addition, unless otherwise specified, all raw materials used in this invention can be obtained commercially available. Any range described in this invention includes the end value and any value between the end values, as well as any subrange formed by the end value or any value between the end values.

[0045] Example 1

[0046] This embodiment provides a method for preparing Eu6(BO3)4Cl magnetic refrigeration material, the preparation method specifically including the following steps:

[0047] (1) Weigh Eu2O3 and NH4Cl powders according to the stoichiometric ratio, mix them thoroughly, preheat at 300℃ for 2 h, and then sinter at 650℃ for 6 h to obtain EuOCl precursor;

[0048] (2) Weigh out the corresponding amounts of EuOCl, Eu2O3, elemental B, and B2O3 according to the molar ratio EuOCl:Eu2O3:B:B2O3=2:5:3.83:2.452, 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.

[0049] (3) The mixed powder obtained in step (2) was pressed into a disc-shaped sample by holding it under a pressure of 800 MPa for 5 min using a dry pressing molding equipment;

[0050] (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.

[0051] (5) The pre-burned body described in step (4) is heated to 920°C and sintered for 10 h. Then it is cooled to room temperature in the furnace to obtain Eu6(BO3)4Cl magnetic refrigeration material.

[0052] Example 2

[0053] This embodiment provides a method for preparing Eu5Tb(BO3)4Cl magnetic refrigeration material, the preparation method specifically including the following steps:

[0054] (1) Weigh Eu2O3 and NH4Cl powders according to the stoichiometric ratio, mix them thoroughly, preheat at 300℃ for 2 h, and then sinter at 625℃ for 7 h to obtain EuOCl precursor;

[0055] (2) Weigh out the corresponding amounts of EuOCl, Eu2O3, Tb2O3, elemental B, and B2O3 according to the molar ratio EuOCl:Eu2O3:Tb2O3:B:B2O3=2:4:1:3.73:2.428, mix them thoroughly and evenly, and pass them through a 100-mesh sieve to obtain a mixed powder; wherein, the amount of elemental B is 12% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material, and the amount of B2O3 is 4% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material.

[0056] (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 500 MPa for 10 min.

[0057] (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 475°C at a rate of 1°C / min and pre-fire for 6 h to obtain a pre-fired body.

[0058] (5) The pre-burned body described in step (4) is heated to 950°C and sintered for 8 h. Then it is cooled to room temperature in the furnace to obtain Eu5Tb(BO3)4Cl magnetic refrigeration material.

[0059] Example 3

[0060] This embodiment provides a method for preparing Eu5Gd(BO3)4Cl magnetic refrigeration material, the preparation method specifically including the following steps:

[0061] (1) Weigh Eu2O3 and NH4Cl powders according to the stoichiometric ratio, mix them thoroughly, preheat at 300℃ for 2 h, and then sinter at 650℃ for 6 h to obtain EuOCl precursor;

[0062] (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.

[0063] (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.

[0064] (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.

[0065] (5) The pre-burned body described in step (4) is heated to 920°C and sintered for 10 h. Then it is cooled to room temperature in the furnace to obtain Eu5Gd(BO3)4Cl magnetic refrigeration material.

[0066] Example 4

[0067] This embodiment provides a method for preparing Eu5Ho(BO3)4Cl magnetic refrigeration material, the preparation method specifically including the following steps:

[0068] (1) Weigh Eu2O3 and NH4Cl powders according to the stoichiometric ratio, mix them thoroughly, preheat at 300℃ for 2 h, and then sinter at 675℃ for 5 h to obtain EuOCl precursor;

[0069] (2) Weigh out the corresponding amounts of EuOCl, Eu2O3, Ho2O3, elemental B, and B2O3 according to the molar ratio EuOCl:Eu2O3:Ho2O3:B:B2O3=2:4:1:3.93:2.475, mix them thoroughly and evenly, and pass them 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.

[0070] (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 1000 MPa for 1 min.

[0071] (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 525°C at a rate of 10°C / min and pre-fire it for 4 hours to obtain a pre-fired body.

[0072] (5) The pre-burned body obtained in step (4) is heated to 900°C and sintered for 12 h. Then it is cooled to room temperature in the furnace to obtain Eu5Ho(BO3)4Cl magnetic refrigeration material.

[0073] Comparative Example 1

[0074] The only difference between this comparative example and Example 1 is that in step (2), elemental B is not in excess. Specifically, it includes the following steps:

[0075] (1) Weigh Eu2O3 and NH4Cl powders according to the stoichiometric ratio, mix them thoroughly, preheat at 300℃ for 2 h, and then sinter at 650℃ for 6 h to obtain EuOCl precursor;

[0076] (2) Weigh out the corresponding amounts of EuOCl, Eu2O3, elemental B and B2O3 according to the molar ratio EuOCl:Eu2O3:B:B2O3=2:5:3.33:2.452, mix them thoroughly and evenly, and pass them through a 200-mesh sieve to obtain a mixed powder; wherein, the amount of B2O3 fed is 5% excess compared to the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material;

[0077] (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.

[0078] (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.

[0079] (5) The pre-burned body described in step (4) is heated to 920°C and sintered for 10 h. Then it is cooled to room temperature in the furnace to obtain Eu6(BO3)4Cl magnetic refrigeration material sample.

[0080] Comparative Example 2

[0081] The only difference between this comparative example and Example 1 is that in step (2), B2O3 is used in excess by only 2%, specifically including the following steps:

[0082] 1) Weigh Eu2O3 and NH4Cl powders according to the stoichiometric ratio, mix them thoroughly, preheat at 300℃ for 2 hours, and then sinter at 650℃ for 6 hours to obtain EuOCl precursor;

[0083] (2) Weigh out the corresponding amounts of EuOCl, Eu2O3, elemental B (15% excess) and B2O3 (2% excess) according to the molar ratio of EuOCl:Eu2O3:B:B2O3=2:5:3.83:2.382, 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% excess of the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material, and the amount of B2O3 is 2% excess of the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material.

[0084] (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.

[0085] (4) Place the circular sample described in step (3) in 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 it for 5 h to obtain a pre-fired body.

[0086] (5) The pre-burned body described in step (4) is heated to 920°C and sintered for 10 h. Then it is cooled to room temperature in the furnace to obtain Eu6(BO3)4Cl magnetic refrigeration material sample.

[0087] Comparative Example 3

[0088] The only difference between this comparative example and Example 1 is that no pre-firing treatment was performed. Specifically, it includes the following steps:

[0089] (1) Weigh Eu2O3 and NH4Cl powders according to the stoichiometric ratio, mix them thoroughly, preheat at 300℃ for 2 h, and then sinter at 650℃ for 6 h to obtain EuOCl precursor;

[0090] (2) Weigh out the corresponding amounts of EuOCl, Eu2O3, elemental B (15% excess) and B2O3 (5% excess) according to the molar ratio of EuOCl:Eu2O3:B:B2O3=2:5:3.83:2.452, 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% excess of the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material, and the amount of B2O3 is 5% excess of the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material.

[0091] (3) The mixed powder obtained in step (2) was pressed into a disc-shaped sample by holding it under a pressure of 800 MPa for 5 min using a dry pressing molding equipment;

[0092] (4) Place the circular sample described in step (3) in a graphite crucible, cover it, and then place it in a tube furnace. Heat it to 920°C and sinter for 10 h. Then cool it to room temperature with the furnace to obtain the Eu6(BO3)4Cl magnetic refrigeration material sample.

[0093] Comparative Example 4

[0094] The only difference between this comparative example and Example 3 is that elemental B is in excess by 20% in step (2), specifically including the following steps:

[0095] (1) Weigh Eu2O3 and NH4Cl powders according to the stoichiometric ratio, mix them thoroughly, preheat at 300℃ for 2 h, and then sinter at 650℃ for 6 h to obtain EuOCl precursor;

[0096] (2) Weigh out the corresponding amounts of EuOCl, Eu2O3, Gd2O3, elemental B, and B2O3 according to the molar ratio EuOCl:Eu2O3:Gd2O3:B:B2O3=2:4:1:4:2.452, 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 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.

[0097] (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.

[0098] (4) Place the circular sample described in step (3) in 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 it for 5 h to obtain a pre-fired body.

[0099] (5) The pre-burned body described in step (4) is heated to 920°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.

[0100] Comparative Example 5

[0101] The only difference between this comparative example and Example 3 is that B2O3 is in excess by 10% in step (2), which specifically includes the following steps:

[0102] (1) Weigh Eu2O3 and NH4Cl powders according to the stoichiometric ratio, mix them thoroughly, preheat at 300℃ for 2 h, and then sinter at 650℃ for 6 h to obtain EuOCl precursor;

[0103] (2) Weigh out the corresponding amounts of EuOCl, Eu2O3, Gd2O3, elemental B, and B2O3 according to the molar ratio EuOCl:Eu2O3:Gd2O3:B:B2O3=2:4:1:3.83:2.569, 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 10% more than the stoichiometric ratio of Eu6(BO3)4Cl magnetic refrigeration material.

[0104] (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.

[0105] (4) Place the circular sample described in step (3) in 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-sinter for 5 h to obtain a pre-sintered body.

[0106] (5) The pre-burned body described in step (4) is heated to 920°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.

[0107] Comparative Example 6

[0108] The only difference between this comparative example and Example 3 is that in step (5), the sintering temperature is 850°C, which specifically includes the following steps:

[0109] (1) Weigh Eu2O3 and NH4Cl powders according to the stoichiometric ratio, mix them thoroughly, preheat at 300℃ for 2 h, and then sinter at 650℃ for 6 h to obtain EuOCl precursor;

[0110] (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.

[0111] (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.

[0112] (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.

[0113] (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.

[0114] Example of effect

[0115] 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.

[0116] 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 .

[0117] 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.

[0118] Figure 4The 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 4 It can be seen that the XRD patterns of the rare earth chloride borate samples prepared in Examples 3 and 4 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 4-6 show obvious impurity diffraction peaks, indicating that the samples contain impurity phases and are not composed of a single phase. Therefore, the selection of technical parameters in this invention is of great importance. Different reactant ratios, sintering temperatures, and times will all affect the phase composition of the material, making it impossible to obtain a single-phase rare earth chloride borate magnetic refrigeration material.

[0119] The thermomagnetic curves of the rare earth chloride borates prepared in Examples 1 and 3 under zero-field cooling (ZFC) and field-cooled cooling (FC) in a 0.01 T magnetic field were measured by way of example. The magnetic phase transition temperature of the material can be obtained by taking 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 were found to be 2.5 K and 2.7 K, respectively, both below the liquid helium temperature (4.2 K), indicating that the rare earth chloride borate is a potential magnetic refrigeration material in the liquid helium temperature range.

[0120] The isothermal magnetization curves of rare earth chloride borates prepared in Examples 1 and 3 were measured at different temperatures. The magnetic entropy change under different magnetic field changes can be calculated based on the isothermal magnetization curves at different temperatures using Maxwell's relation. Figure 5 The curves showing the magnetic entropy change of the rare earth chloride borate Eu6(BO3)4Cl prepared in Example 1 of this invention as a function of temperature under different magnetic field variations are presented. Figure 5 It can be seen that the maximum magnetic entropy change of this material at 2.5 K temperature with a magnetic field change of 0-1 T is 19.6 J·kg. -1 ·K -1 At 3.5 K, the maximum magnetic entropy change when the magnetic field changes by 0-2 T is 31.7 J·kg. -1 ·K -1 At 3.5 K, the maximum magnetic entropy change is 52.0 J·kg⁻¹ when the magnetic field changes by 0–5 T. -1 ·K -1 . Figure 6 The curves showing the magnetic entropy change of the rare earth chloride borate Eu5Gd(BO3)4Cl prepared in Example 3 of this invention under different magnetic field variations with temperature are presented. Figure 6 It can be seen that the maximum magnetic entropy of this material at 2.5 K temperature, with a magnetic field change of 0-1 T, is 21.2 J·kg⁻¹. -1 ·K-1 At 2.5 K, the maximum magnetic entropy change when the magnetic field changes by 0-2 T is 35.1 J·kg⁻¹. -1 ·K -1 At 3.5 K, the maximum magnetic entropy change is 55.9 J·kg⁻¹ when the magnetic field changes by 0–5 T. -1 ·K -1 The results show that the rare earth chloride borate of this invention exhibits superior magnetocaloric properties near the liquid helium temperature, significantly outperforming many existing liquid helium temperature magnetic refrigeration materials (such as NaGdSiO4, Ho4Al2O9, and GdSr2TaO6), thus demonstrating its potential application prospects in the field of liquid helium temperature magnetic refrigeration technology.

[0121] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All embodiments falling under the scope of the present invention...

[0122] Obvious variations or modifications derived from the technical solution are still within the scope of protection of this invention.

Claims

1. A rare earth chloride borate magnetic refrigeration material, characterized in that, The rare earth chloride borate magnetic refrigeration material has the chemical formula Eu5RE(Ⅲ)(BO3)4Cl, where the metal RE is Gd, Tb, Dy, Ho, Er, or Tm, belongs to the hexagonal crystal system, and has the space group [missing information]. P6 3 mc .

2. The rare earth chloride borate magnetic refrigeration material according to claim 1, characterized in that, The rare earth chloride borate magnetic refrigeration material undergoes a magnetic phase transition below the liquid helium temperature, with a magnetic phase transition temperature ≤ 4.2 K.

3. The rare earth chloride borate magnetic refrigeration material according to claim 1, characterized in that, The rare earth chloride borate magnetic refrigeration material includes at least one of the following characteristics: 1) At a temperature of 2.5 K and a magnetic field change of 0–1 T, the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is ≥19.6 J·kg. -1 ·K -1 ; 2) At a temperature of 2.5 K and a magnetic field change of 0–2 T, the maximum magnetic entropy change of the rare-earth chloride borate magnetic refrigeration material is 35.1 J·kg⁻¹. -1 ·K -1 ; 3) At a temperature of 3.5 K and a magnetic field change of 0–2 T, the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is ≥31.7 J·kg. -1 ·K -1 ; 4) At a temperature of 3.5 K and a magnetic field variation of 0–5 T, the maximum magnetic entropy change of the rare earth chloride borate magnetic refrigeration material is ≥52.0 J·kg. -1 ·K -1 .

4. A method for preparing a rare earth chloride borate magnetic refrigeration material, characterized in that, The rare earth chloride borate magnetic refrigeration material has the chemical formula Eu5RE(Ⅲ)(BO3)4Cl, wherein the metal RE is Eu, Gd, Tb, Dy, Ho, Er, or Tm, and its preparation method includes the following steps: (1) Weigh Eu2O3 and NH4Cl powders according to the stoichiometric ratio, mix them thoroughly, preheat at 250-350℃ for 1.5-2.5 h, and sinter to obtain EuOCl precursor; (2) Weigh the corresponding amounts of EuOCl, Eu2O3, RE2O3, elemental B and B2O3 according to the molar ratio of EuOCl, Eu2O3, RE2O3, elemental B and B2O3 as 2:4:1:3.73-3.93:2.43-2.48, mix them thoroughly and evenly, pass them through a 100-200 mesh sieve to obtain mixed powder, press them into tablets, pre-fire them, and then sinter them at high temperature. Cool them to room temperature in the furnace to obtain 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 tablet compression 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-burning is carried out in a flowing mixed atmosphere containing hydrogen and argon. The pre-burning temperature is 475-525℃, and the pre-burning is carried out at a constant temperature for 4-6 hours. The heating rate is 1-10℃ / min.

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

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

10. The application of the rare earth chloride borate magnetic refrigeration material as described in any one of claims 1-3 in the preparation of magnetic refrigeration materials or devices in the liquid helium temperature range.

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