Novel rare earth magnetic refrigeration material and preparation method thereof

Abstract

The invention belongs to the technical field of magnetic refrigeration materials, and particularly relates to a novel rare earth magnetic refrigeration material and a preparation method thereof. The material is composed of a metal oxide phase, the chemical general formula of the material is R3CrGa3FeO12, and R is a rare earth element and is one or two of Ho, Tb, Dy and Gd; the preparation method of the novel rare earth magnetic refrigeration material comprises the following steps: (1) ball-milling and mixing R oxide, Cr oxide, Ga oxide and Fe oxide, drying, pre-sintering, crushing and sieving to obtain a pre-sintered material; and (2) carrying out secondary ball milling on the pre-sintered material, carrying out compression molding, and sintering. The novel rare earth magnetic refrigeration material with a stable and good magnetic refrigeration effect is obtained by adopting an R oxide, a Cr oxide, a Ga oxide and an Fe oxide through a simple solid-phase reaction.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic refrigeration materials, and in particular relates to a novel rare earth magnetic refrigeration material and a preparation method thereof. Background Art

[0002] In modern society, refrigeration technology has become an indispensable part, involving all aspects of daily life, industrial and agricultural production, scientific research, science and technology, and national defense. The commonly used refrigeration technology is traditional vapor compression refrigeration, which uses the refrigerant to absorb and release heat during the compression and relaxation process in the compressor, and transfers heat from a low-temperature environment to a high-temperature environment, thereby achieving the purpose of refrigeration. However, this refrigeration technology has problems such as high energy consumption and unfriendly to the environment. During the operation of the compressor, a large amount of heat and noise will be generated, and refrigerants that are harmful to the atmosphere will be emitted.

[0003] Magnetic refrigeration technology, as a new type of refrigeration technology developed based on the magnetocaloric effect of magnetic materials, has received widespread attention and attention in recent years. The magnetocaloric effect is an intrinsic property of magnetic materials, usually defined as the physical phenomenon of magnetic materials releasing or absorbing heat when the magnetic field is strengthened or weakened. By changing the external magnetic field, the magnetic moment of the magnetic material undergoes orderly or disordered changes, thereby inducing the heat absorption and heat release of the magnet, realizing the refrigeration cycle.

[0004] Compared with traditional refrigeration technology, magnetic refrigeration technology has obvious advantages. First, magnetic refrigeration technology is a green and environmentally friendly refrigeration method. Its refrigeration process does not involve any harmful substances and has no negative impact on the environment. Secondly, magnetic refrigeration technology is energy-saving and efficient, which can greatly reduce energy consumption and save resources. Finally, magnetic refrigeration technology operates stably and reliably, and the refrigeration effect is long-lasting, which greatly reduces the maintenance cost and repair frequency of equipment. The development and application of magnetic refrigeration technology are closely related to the performance of magnetic refrigeration materials. At present, high-performance magnetic refrigeration materials mainly include Gd-Si-Ge, Gd-Al-Co and other material systems, but these materials are generally high in cost, poor in stability, limited in refrigeration temperature range and complex in process, which limits their commercial application to a certain extent. Therefore, in-depth research on magnetocaloric effect, especially the exploration of new magnetic refrigeration materials, is still the focus and hot spot in the current scientific research field. Summary of the invention

[0005] The purpose of the present invention is to provide a new type of rare earth magnetic refrigeration material in view of the above technical problems, which is composed of a metal oxide phase and has a stable and good magnetic refrigeration effect.

[0006] The new rare earth magnetic refrigeration material in the technical solution of the present invention is composed of a metal oxide phase, and the general chemical formula is R3CrGa3FeO 12 , where R is a rare earth element.

[0007] Metal oxides are inexpensive and corrosion-resistant magnetic refrigeration materials. Due to the large atomic distance, they can easily produce huge magnetic entropy changes at extremely low temperatures, making them the best magnetic refrigeration materials in the temperature range below 20K.

[0008] Furthermore, R is one or two of Ho, Tb, Dy, and Gd.

[0009] Furthermore, the maximum magnetic entropy change value of the new rare earth magnetic refrigeration material can reach 8-10 JK at 12K and ΔH=5T. -1 mol -1 .

[0010] The present invention also provides a method for preparing the novel rare earth magnetic refrigeration material, comprising the following steps:

[0011] (1) ball-milling and mixing R oxide, Cr oxide, Ga oxide and Fe oxide, drying, pre-calcining, crushing and sieving to obtain a pre-calcined material;

[0012] (2) The pre-sintered material is ball-milled for a second time, pressed into shape, and then sintered.

[0013] Secondary ball milling and sintering after pre-sintering can better control the particle size distribution and phase purity of the magnetic refrigeration material, reduce the impurity content of the pre-sintered powder, and form a relatively narrow particle size and regular grain morphology.

[0014] Furthermore, the R oxide is one or two of Gd2O3, Tb4O7, Dy2O3, and Ho2O3, the Cr oxide is Cr2O3, the Ga oxide is Ga2O3, and the Fe oxide is Fe2O3.

[0015] Furthermore, in step (1), the pre-firing temperature is 800-1200° C., and the holding time is 1-10 hours.

[0016] Furthermore, the heating rate during pre-firing is 1 to 10°C / min.

[0017] Furthermore, in step (1), the pre-firing temperature is 860-940° C., and the holding time is 1-8 hours.

[0018] Preferably, the crushing is performed by breaking up the particles with a wall breaking machine and then grinding the particles.

[0019] Furthermore, in step (1), the mesh size of the sieve is 80 to 120 meshes.

[0020] Furthermore, in step (1) and step (2), the ball milling speed is 200 to 500 rpm / min, and the ball milling time is 6 to 15 hours.

[0021] Furthermore, during ball milling, water in an amount of 1.5 to 5.0 times the mass of the solid material is added as a ball milling medium.

[0022] Furthermore, the material-ball ratio during ball milling is 1:3-6.

[0023] Furthermore, in step (1), the drying temperature is 80 to 150° C. and the drying time is 6 to 20 hours.

[0024] Furthermore, in step (2), the pressure of the pressing molding is 10 to 50 MPa, and the time is 10 to 60 min.

[0025] Furthermore, in step (2), the sintering temperature is 1000-1500° C. and the sintering time is 1-10 h.

[0026] Furthermore, the heating rate during sintering is 1 to 10°C / min.

[0027] Furthermore, in step (2), the sintering temperature is 1240-1350° C. and the sintering time is 1-8 hours.

[0028] Furthermore, both pre-firing and sintering are performed in an air atmosphere.

[0029] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0030] (1) Using R oxide, Cr oxide, Ga oxide and Fe oxide, a new rare earth magnetic refrigeration material (R3CrGa3FeO 12 );

[0031] (2) Metal oxides (R3CrGa3FeO 12 ) As a magnetic refrigeration material, it is cheap and corrosion-resistant, and the atomic distance is large, which can easily produce huge magnetic entropy changes at extremely low temperatures. It is the best magnetic refrigeration material in the temperature range below 20K;

[0032] (3) After pre-sintering, secondary ball milling and sintering can better control the particle size distribution and phase purity of the magnetic refrigeration material, reduce the impurity content of the pre-sintered powder, and form a relatively narrow particle size and regular grain morphology;

[0033] (4) The new rare earth magnetic refrigeration material obtained exhibits a large magnetic entropy change value of 9.12 JK at 12K and ΔH = 5T - 1 mol -1 , has great application potential in magnetic refrigerants;

[0034] (5) The preparation method of the new rare earth magnetic refrigeration material has a simple process, concise steps and is easy to operate, which not only improves production efficiency but also reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The X-ray diffraction spectra of the novel rare earth magnetic refrigeration materials obtained in Example 1 and Example 2;

[0036] Figure 2 The ZFC magnetic susceptibility (χ, main figure) and the inverse of the magnetic susceptibility (χ) of the new rare earth magnetic refrigeration materials obtained in Example 1 and Example 2 under a magnetic field of 200 Oe are shown in FIG. -1 , illustration) Figure;

[0037] Figure 3 Isothermal magnetization (MH) curves of the novel rare earth magnetic refrigeration materials obtained in Example 1 and Example 2 at different temperatures: (a) Example 1, (b) Example 2;

[0038] Figure 4 -ΔS of the new rare earth magnetic refrigeration material obtained in Example 1 under different magnetic field changes m -T curve: (a) Example 1, (b) Example 2;

[0039] Figure 5 ΔS of the new rare earth magnetic refrigeration materials obtained in Example 1 and Example 2 in a 2T magnetic field m Temperature variation curve. DETAILED DESCRIPTION

[0040] The technical scheme of the present invention is further described below by specific examples and accompanying drawings. It should be understood that the specific examples described herein are only used to help understand the present invention and are not used for specific limitations of the present invention. The accompanying drawings used herein are only for better illustrating the disclosure of the present invention and do not have a limiting effect on the scope of protection. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0041] Example 1

[0042] The preparation method of the novel rare earth magnetic refrigeration material of this embodiment comprises the following steps:

[0043] (1) According to Gd3CrGa3FeO 12 The molar ratio of elements is , Gd2O3, Cr2O3, Ga2O3 and Fe2O3 are put into a ball mill, and deionized water of 1.5 times the mass of the above components is added, and the ball milling is carried out at a speed of 300rpm / min and a ball-to-material ratio of 1:4 for 6h, and after drying at 100℃ for 10h, the temperature is increased to 880℃ at a rate of 5℃ / min, and pre-calcined for 3h in an air atmosphere, cooled with the furnace, and then broken up by a wall breaking machine and ground, and sieved by a 100-mesh sieve to obtain a pre-calcined material;

[0044] (2) Add deionized water 1.5 times the mass of the pre-burned material, ball mill the pre-burned material for a second time at 300 rpm / min and a ball-to-material ratio of 1:4 for 8 h, press at a pressure of 20 MPa for 15 min, heat to 1250 °C at a rate of 5 °C / min, sinter for 2 h in an air atmosphere, and cool to room temperature with the furnace.

[0045] Example 2

[0046] The preparation method of the novel rare earth magnetic refrigeration material of this embodiment comprises the following steps:

[0047] (1) According to Ho3CrGa3FeO 12 The molar ratio of elements is , Ho2O3, Cr2O3, Ga2O3 and Fe2O3 are put into a ball mill, and deionized water of 1.5 times the mass of the above components is added, and the ball milling is carried out at a speed of 300rpm / min and a ball-to-material ratio of 1:5 for 6h, and after drying at 95℃ for 10h, the temperature is increased to 900℃ at a rate of 5℃ / min, and pre-calcined for 3h in an air atmosphere, cooled with the furnace, and then broken up by a wall breaking machine and ground, and sieved by a 100-mesh sieve to obtain a pre-calcined material;

[0048] (2) Deionized water (2.0 times the mass of the pre-burned material) was added, and the pre-burned material was ball-milled for a second time at 280 rpm / min and a ball-to-material ratio of 1:5 for 8 h, pressed at a pressure of 30 MPa for 20 min, heated to 1300 °C at a rate of 5 °C / min, sintered in an air atmosphere for 2 h, and cooled to room temperature with the furnace.

[0049] Example 3

[0050] The preparation method of the novel rare earth magnetic refrigeration material of this embodiment comprises the following steps:

[0051] (1) According to Gd3CrGa3FeO 12 The molar ratio of elements is 1:1, Gd2O3, Cr2O3, Ga2O3 and Fe2O3 are put into a ball mill, and deionized water of 2.0 times the mass of the above components is added, and the ball milling is carried out at a speed of 280rpm / min and a ball-to-material ratio of 1:5 for 6h, and after baking at 100℃ for 12h, the temperature is increased to 920℃ at a rate of 6℃ / min, and pre-calcined for 3h in an air atmosphere, cooled with the furnace, and then broken up by a wall breaking machine and ground, and sieved by a 120-mesh sieve to obtain a pre-calcined material;

[0052] (2) Deionized water (1.5 times the mass of the pre-burned material) was added, and the pre-burned material was ball-milled for a second time at 300 rpm / min and a ball-to-material ratio of 1:5 for 8 h, pressed at a pressure of 25 MPa for 20 min, heated to 1350 °C at a rate of 6 °C / min, sintered in an air atmosphere for 2 h, and cooled to room temperature with the furnace.

[0053] Example 4

[0054] The preparation method of the novel rare earth magnetic refrigeration material of this embodiment comprises the following steps: 12 The molar ratio of elements, Gd2O3, Cr2O3, Ga2O3 and Fe2O3 were put into a ball mill, and deionized water 1.5 times the mass of the above components was added, and the ball milling was carried out at a speed of 300 rpm / min and a ball-to-material ratio of 1:4 for 6 hours. After baking at 100°C for 10 hours, the temperature was increased to 880°C at a rate of 6°C / min, and pre-calcined for 5 hours in an air atmosphere. The mixture was cooled with the furnace, broken up with a wall breaker, and then ground. The mixture was sieved with a 100-mesh sieve.

[0055] Example 5

[0056] The preparation method of the novel rare earth magnetic refrigeration material of this embodiment comprises the following steps: 12 The molar ratio of elements, Gd2O3, Cr2O3, Ga2O3 and Fe2O3 were put into a ball mill, and deionized water 1.5 times the mass of the above components was added, and the mixture was ball-milled at a speed of 300 rpm / min and a ball-to-material ratio of 1:4 for 6 hours. The mixture was dried at 100°C for 10 hours and then pressed into shape. The mixture was heated to 1250°C at a rate of 6°C / min, sintered in an air atmosphere for 5 hours, cooled with the furnace, broken up with a wall breaker, and then ground. The mixture was sieved with a 100-mesh sieve.

[0057] Example 6

[0058] The difference between this embodiment and embodiment 1 is that step (1) is carried out according to Gd3CrGa3FeO 12 The molar ratio of elements, Gd2O3, Cr2O3, Ga2O3 and Fe2O3 were put into a ball mill, and deionized water 1.5 times the mass of the above components was added, and the ball milling was carried out at a speed of 300 rpm / min and a ball-to-material ratio of 1:4 for 6 hours. After baking at 100°C for 10 hours, the temperature was raised to 750°C at a rate of 5°C / min, and pre-calcined for 3 hours in an air atmosphere. The mixture was cooled with the furnace, broken up by a wall breaking machine, and then ground. The pre-calcined material was sieved with a 100-mesh sieve.

[0059] Example 7

[0060] The difference between this embodiment and embodiment 1 is that step (1) is carried out according to Gd3CrGa3FeO 12The molar ratio of elements, Gd2O3, Cr2O3, Ga2O3 and Fe2O3 were put into a ball mill, and deionized water 1.5 times the mass of the above components was added, and the ball milling was carried out at a speed of 300 rpm / min and a ball-to-material ratio of 1:4 for 6 hours. After baking at 100°C for 10 hours, the temperature was raised to 1050°C at a rate of 5°C / min, and pre-calcined for 3 hours in an air atmosphere. The mixture was cooled with the furnace, broken up by a wall breaking machine, and then ground. The pre-calcined material was sieved with a 100-mesh sieve.

[0061] Example 8

[0062] The only difference between this embodiment and embodiment 1 is that in step (2), deionized water 1.5 times the mass of the pre-burned material is added, the pre-burned material is ball-milled for a second time at 300 rpm / min and a ball-to-material ratio of 1:4 for 8 h, pressed at a pressure of 20 MPa for 15 min, heated to 1050° C. at a rate of 5° C. / min, sintered for 2 h in an air atmosphere, and cooled to room temperature with the furnace.

[0063] Example 9

[0064] The difference between this embodiment and embodiment 1 is that in step (2), deionized water 1.5 times the mass of the pre-burned material is added, the pre-burned material is ball-milled for a second time at 300 rpm / min and a ball-to-material ratio of 1:4 for 8 h, pressed at a pressure of 20 MPa for 15 min, heated to 1450° C. at a rate of 5° C. / min, sintered for 2 h in an air atmosphere, and cooled to room temperature with the furnace.

[0065] Comparative Example 1

[0066] The preparation method of the novel rare earth magnetic refrigeration material of this comparative example comprises the following steps:

[0067] (1) According to Gd3CrGa4O 12 The molar ratio of elements is 1:1, Gd2O3, Cr2O3 and Ga2O3 are put into a ball mill, and deionized water of 1.5 times the mass of the above components is added, and the ball milling is carried out at a speed of 300 rpm / min and a ball-to-material ratio of 1:4 for 6 hours, and after drying at 100°C for 10 hours, the temperature is increased to 880°C at a rate of 5°C / min, and pre-calcined for 3 hours in an air atmosphere, cooled with the furnace, and then broken up by a wall breaking machine and ground, and sieved with a 100-mesh sieve to obtain a pre-calcined material;

[0068] (2) Add deionized water 1.5 times the mass of the pre-burned material, ball mill the pre-burned material for a second time at 300 rpm / min and a ball-to-material ratio of 1:4 for 8 h, press at a pressure of 20 MPa for 15 min, heat to 1250 °C at a rate of 5 °C / min, sinter for 2 h in an air atmosphere, and cool to room temperature with the furnace.

[0069] According to the X-ray diffraction spectrum ( Figure 1), Example 1 and Example 2 respectively obtained pure Gd3CrGa3FeO 12 and Ho3CrGa3FeO 12 ;like Figure 2 As shown in the χ-T curve, Gd3CrGa3FeO 12 and Ho3CrGa3FeO 12 At low temperatures, it exhibits a ferromagnetic state. As the temperature increases, the magnetization intensity decreases sharply near the Curie temperature, which means that a phase transition from ferromagnetism (FM) to paramagnetism (PM) occurs. -1 -T curve shows that Gd3CrGa3FeO 12 and Ho3CrGa3FeO 12 In the paramagnetic region, the inverse of the magnetic susceptibility is linearly related to the temperature, which conforms to the Curie-Weiss law. Figure 3 As shown in Figure 2, with the increase of magnetic field strength, Gd3CrGa3FeO 12 and Ho3CrGa3FeO 12 The magnetization intensity gradually increases and approaches the saturation value at a temperature of 5K and a magnetic field of 5T, which is very close to the theoretical value; Figure 4 As shown, Gd3CrGa3FeO 12 and Ho3CrGa3FeO 12 -ΔS m The -T curve has a peak value near 12K, and with the increase of ΔH, the magnetic entropy change value also gradually increases. When the external magnetic field is 5T, Gd3CrGa3FeO 12 and Ho3CrGa3FeO 12 Maximum magnetic entropy change -ΔS m max 9.12JK respectively -1 mol -1 and 8.98JK -1 mol -1 ;like Figure 5 As shown, the Gd3CrGa3FeO obtained in Example 1 and Example 2 12 and Ho3CrGa3FeO 12 , having similar magnetic refrigeration effect; Example 4 was only pre-fired at 880°C without secondary ball milling and sintering, and Example 5 was only sintered at 1250°C without pre-fired, and the obtained Gd3CrGa3FeO 12The particle size distribution is uneven, the impurity content is also increased, and the magnetic refrigeration effect is deteriorated; Example 6 is pre-fired at a lower temperature, Example 7 is pre-fired at a higher temperature, Example 8 is sintered at a lower temperature, and Example 9 is sintered at a higher temperature. The rare earth magnetic refrigeration materials obtained in Examples 6-9 have impurity peaks such as RCrO3, and the magnetic refrigeration effect is deteriorated; the magnetic refrigeration material of Comparative Example 1 does not contain iron elements, the peak value of magnetic entropy change is reduced, and the magnetic refrigeration effect is significantly deteriorated.

[0070] Finally, it should be noted that the specific embodiments described herein are merely examples of the spirit of the present invention, and are not intended to limit the implementation methods of the present invention. Those skilled in the art of the present invention may make various modifications or supplements to the described embodiments or replace them in similar ways. It is not necessary and impossible to provide all examples of all implementation methods here. However, these obvious changes or modifications derived from the essential spirit of the present invention still fall within the scope of protection of the present invention, and interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. A new type of rare earth magnetic refrigeration material, characterized in that: The novel rare earth magnetic refrigeration material is composed of a metal oxide phase, and its general chemical formula is R3CrGa3FeO 12 , where R is a rare earth element.

2. The novel rare earth magnetic refrigeration material according to claim 1, characterized in that: R is one or two of Ho, Tb, Dy, and Gd.

3. The novel rare earth magnetic refrigeration material according to claim 1, characterized in that: The new rare earth magnetic refrigeration material has a maximum magnetic entropy change value of 8-10 J K at 12 K and ΔH=5 T. -1 mol -1 .

4. A method for preparing the novel rare earth magnetic refrigeration material according to claim 1, characterized in that: The following steps are involved: (1) ball-milling and mixing R oxide, Cr oxide, Ga oxide and Fe oxide, drying, pre-calcining, crushing and sieving to obtain a pre-calcined material; (2) The pre-sintered material is ball-milled for a second time, pressed into shape, and then sintered.

5. The preparation method according to claim 4, characterized in that: The R oxide is one or two of Gd2O3, Tb4O7, Dy2O3, and Ho2O3, the Cr oxide is Cr2O3, the Ga oxide is Ga2O3, and the Fe oxide is Fe2O3.

6. The preparation method according to claim 4, characterized in that: In step (1), the pre-firing temperature is 800-1200° C. and the holding time is 1-10 hours.

7. The preparation method according to claim 4, characterized in that: The mesh size of the sieve during sieving in step (1) is 80 to 120 meshes.

8. The preparation method according to claim 4, characterized in that: In step (1) and step (2), the ball milling speed is 200 to 500 rpm / min, and the ball milling time is 6 to 15 hours.

9. The preparation method according to claim 8, characterized in that: During ball milling, add 1.5 to 5.0 times the mass of the solid material as water as the ball milling medium.

10. The preparation method according to claim 4, characterized in that: In step (2), the sintering temperature is 1000-1500° C. and the sintering time is 1-10 hours.

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