La-Fe-Si-based magnetic refrigeration material and preparation method thereof

Abstract

The application discloses a La-Fe-Si-based magnetic refrigeration material and a preparation method thereof. The application first prepares an intermediate alloy powder rich in rare earth components, and then mixes the intermediate alloy powder with other raw material powders to prepare a target alloy. Through alloy component optimization design and in combination with a specific powder metallurgy process, a magnetic heat phase is rapidly formed in a very short sintering time, and pores and reinforcing phases exist in the material, so that the material is complete in shape and has certain strength after being filled with hydrogen.

Description

Technical Field

[0001] This invention relates to the field of magnetic refrigeration materials technology, and in particular to a La-Fe-Si based magnetic refrigeration material and its preparation method. Background Technology

[0002] Magnetic refrigeration is a novel refrigeration technology that uses magnetic materials as the solid working fluid. Its principle is based on the magnetocaloric effect of the magnetic refrigeration material; that is, the material releases heat to the outside during isothermal magnetization and absorbs heat from the outside during adiabatic demagnetization, thus achieving the purpose of cooling. Magnetic refrigeration has advantages such as energy efficiency, environmental friendliness, stability, and reliability, and it is expected to replace traditional gas compression refrigeration, making it a refrigeration method with great development potential.

[0003] Magnetic refrigeration materials are one of the core components of magnetic refrigeration technology, directly affecting the performance of the refrigeration unit. Research has found that Gd5(Si,Ge)4, MnFe(P,Si,As), and La(Fe,Si) are effective materials for this purpose. 13 Compounds such as La(Fe,Si) exhibit a large magnetocaloric effect in the room temperature range, and among many magnetic refrigeration materials, La(Fe,Si) stands out. 13 Due to its advantages such as low magnetic field-induced giant magnetocaloric effect, low hysteresis, low price and safe and non-toxic elements, the basic compound has attracted widespread attention and is one of the most promising room temperature magnetic refrigeration materials for practical application.

[0004] Typically, it contains NaZn 13 La(Fe,Si) crystal structure 13 The formation of the basic magnetocaloric compound (denoted as the 1:13 magnetocaloric phase) requires a peritectic reaction: L + Fe → La(Fe,Si). 13 However, traditional casting methods such as induction and arc melting cannot directly obtain this 1:13 magnetocaloric phase. The ingot requires high-temperature heat treatment for seven days or even weeks to form the magnetocaloric phase, which greatly prolongs the production cycle and results in significant energy consumption. Additionally, La(Fe,Si)... 13 The Curie temperature of the basic compound is around 200K, so it cannot be directly applied at room temperature. (The text then abruptly shifts to a seemingly unrelated topic: La(Fe,Si)...) 13 Hydrogenation of the base compound is currently the most effective method to raise the Curie temperature to room temperature while maintaining a large magnetocaloric effect, but La(Fe,Si) 13 The base compound is inherently brittle, and dense alloys are difficult to fill with hydrogen. Furthermore, during the hydrogen absorption process, a large number of cracks are generated due to lattice expansion, causing the alloy to shatter. This makes it difficult to prepare magnetic working fluids with large specific surface areas, which limits the heat exchange efficiency between the working fluid and the fluid, and thus affects the improvement of the efficiency of the magnetic refrigerator.

[0005] To shorten La(Fe,Si) 13To determine the formation time of the 1:13 magnetocaloric phase, researchers have tried various methods, such as: (1) fabricating the material into micron-sized sheets, wires, spheres, etc.; (2) crushing the metal powder into micro- and nano-sized mixed powders; (3) increasing the annealing temperature and using ultra-high temperature annealing; and (4) controlling the rare earth enrichment of the material composition. However, these methods have drawbacks such as complex processes, difficulty in implementation, and high production costs, and they cannot solve the problem of La(Fe,Si). 13 The hydrogenation and pulverization of the basic compound presents challenges, making it difficult to directly apply the resulting material to refrigeration machines. To address this, polymer or metal binders are added, and molding is performed under specific temperature and pressure conditions to improve the material's mechanical properties and molding capacity. However, low pressure results in low composite material density, while high pressure easily leads to the breakage of the brittle magnetocaloric phase, both of which severely diminish the material's magnetocaloric effect.

[0006] In summary, how to efficiently obtain La(Fe,Si) with high magnetocaloric properties is a key question. 13 Finding a suitable base alloy while ensuring stable material forming is a pressing problem that needs to be solved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is how to achieve efficient phase formation of La-Fe-Si based magnetic refrigeration materials while ensuring stable material formation.

[0008] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a La-Fe-Si based magnetic refrigeration material, comprising the following steps:

[0009] S1. Prepare the raw materials according to the set chemical ratio. The chemical formula is (La). 1-x R x ) m Fe 13-n Si n Where R is selected from any one or more of Ce, Pr, and Nd elements, 1≤m≤7, 1≤n≤10, and 0≤x≤0.5;

[0010] S2. Melt the raw materials prepared in step S1 to obtain a La-Fe-Si based master alloy, crush it into powder to obtain La-Fe-Si based master alloy powder; or melt the raw materials prepared in step S1 to directly obtain La-Fe-Si based master alloy powder.

[0011] S3. Using the La-Fe-Si based intermediate alloy powder obtained in step S2, along with Fe powder, Si powder, M powder, or alloy powder as raw materials, according to the chemical formula (La... 1-x R x ) a (Fe 1-b M b ) (13-y)c Siy A z Prepare a mixed powder, wherein M is selected from any one or more of the elements Cr, Mn, Co, Ni, and Al, the alloy powder is a binary or multi-element alloy powder composed of Fe and one or more of the elements Cr, Mn, Co, Ni, Al, B, C, and Si, A is the element B and / or C, 0≤x≤0.5, 1≤y≤2, 0≤z≤0.5, 1≤a≤2, 0≤b≤0.1, and 0.5≤c≤1.5;

[0012] S4. Press the mixed powder prepared in step S3 into a blank;

[0013] S5. Sinter the blank obtained in step S4 to obtain bulk La(Fe,Si). 13 The basic magnetic refrigeration material, namely La(Fe,Si). 13 La(Fe,Si) in basic magnetic refrigeration materials 13 The matrix phase has NaZn 13 Type crystal structure.

[0014] This invention discloses a La-Fe-Si based magnetic refrigeration material and its preparation method. The invention first prepares a rare earth-rich intermediate alloy powder, and then mixes the intermediate alloy powder with other raw material powders to form the target alloy. Through the optimized design of the alloy composition and combined with a specific powder metallurgy process, the magnetocaloric phase is rapidly formed in a very short sintering time. At the same time, the material contains pores and reinforcing phases to ensure that the material has a complete shape and a certain strength after being filled with hydrogen.

[0015] Furthermore, in step S5, the sintering temperature is 1000–1300°C, and the sintering time is within 5 hours, for La(Fe,Si) 13 NaZn in basic magnetic refrigeration materials 13 The volume fraction of the La(Fe,Si) crystal structure phase reaches more than 90% of the maximum formable phase volume fraction, where the maximum formable phase volume fraction refers to La(Fe,Si). 13 Given a limited formulation for the basic magnetic refrigeration material, extending the sintering time can improve the performance of NaZn. 13 The volume fraction of the magnetocaloric phase in a La(Fe,Si) crystal structure when fully formed. The process of this invention can achieve La(Fe,Si) at conventional sintering temperatures. 13 Rapid phase formation of basic magnetic refrigeration materials is beneficial for industrial application. Compared with rare earth-enriched materials prepared by casting, the sintering process can also reduce the content of rare earth-enriched phases, which helps to reduce the adverse effects of brittle rare earth-enriched phases on the mechanical properties of materials.

[0016] Furthermore, in step S4, the density of the green body formed by pressing the mixed powder is 80% to 95%. Pressing gives the green body a certain density, ensuring the strength of the material after sintering.

[0017] Furthermore, in step S5, the La(Fe,Si) obtained by sintering the green body... 13 The porosity of the basic magnetic refrigeration material is 1% to 10%. After sintering, the magnetic refrigeration material has a certain porosity to ensure that it will not break during hydrogen filling.

[0018] Furthermore, in step S2, the particle size of the obtained La-Fe-Si based master alloy powder is <100μm. This invention achieves efficient phase formation even with relatively large powder particle sizes. Larger particles are less prone to oxidation, preventing material performance degradation. Ordinary mechanical crushing methods can meet the particle size requirements, resulting in low demands on processes and production equipment, which is beneficial for industrial production.

[0019] Furthermore, in step S4, the metal sheath is made of pure Fe or an Fe alloy. The metal sheath restricts the powder packed within it, causing the material to undergo greater uniform deformation during deformation due to the constraint of the sheath. This increases the internal density of the microstructure, reduces the porosity formed by powder metallurgy, and gives the material better mechanical properties.

[0020] Furthermore, the preparation method also includes step S6, processing the La(Fe,Si) obtained in step S5. 13 The basic magnetic refrigeration material is subjected to hydrogen purging treatment.

[0021] Furthermore, in step S6, the hydrogen charging conditions are: pressure 0.1–1 MPa, temperature 20–500 °C, and time 1–12 hours. Hydrogen charging can improve the efficiency of La(Fe,Si). 13 The Curie temperature of the basic magnetic refrigeration material allows the material to operate directly at room temperature. The presence of pores and Fe reinforcement phase in the material ensures the integrity of the material's shape after hydrogen filling.

[0022] A second aspect of this invention provides a La-Fe-Si based magnetic refrigeration material, prepared by the above-described method. The La-Fe-Si based magnetic refrigeration material prepared by this invention exhibits an entropy change of 4–16 J / kg K under a magnetic field change of 0–1 T, and an entropy change of 6–22 J / kg K under a magnetic field change of 0–2 T, thus obtaining a room-temperature magnetic refrigeration material with narrow hysteresis and high magnetocaloric performance.

[0023] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The preparation method of the present invention can quickly obtain NaZn 13 La(Fe,Si) with a magnetocaloric phase and a crystal structure 13 The basic magnetic refrigeration material significantly shortens the phase formation time, improves production efficiency, and reduces production costs.

[0025] (2) The preparation method of the present invention can control the element ratio, thereby accurately adjusting the Curie temperature. The control method is simple, has good repeatability, and can obtain room temperature magnetic refrigeration materials with narrow hysteresis, high magnetocaloric performance and high strength.

[0026] (3) The present invention uses a rolling deformation process to obtain complete La(Fe,Si). 13 The substrate-like material exhibits rapid phase formation and excellent mechanical properties during the rolling process, with the powder particles tightly bonded together. Attached Figure Description

[0027] Figure 1 In Embodiment 1 of the present invention (La) 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 Scanning electron micrograph of a magnetic refrigeration material.

[0028] Figure 2 In Embodiment 1 of the present invention (La) 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 H y Thermomagnetic (MT) curves of magnetic refrigeration materials under a 0.05T magnetic field.

[0029] Figure 3 In Embodiment 1 of the present invention (La) 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 H y Isothermal magnetization (MH) curves of magnetic refrigeration materials during rising and falling field processes at different temperatures.

[0030] Figure 4 In Embodiment 1 of the present invention (La) 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 H y The entropy change of magnetic refrigeration materials as a function of temperature.

[0031] Figure 5 In embodiment 2 of the present invention (La) 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 Scanning electron micrograph of a magnetic refrigeration material.

[0032] Figure 6In embodiment 3 of the present invention (La) 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 Scanning electron micrograph of a magnetic refrigeration material.

[0033] Figure 7 It is in embodiment 4 of the present invention (La) 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 Scanning electron micrograph of a magnetic refrigeration material.

[0034] Figure 8 In Embodiment 10 of the present invention (La) 0.7 Ce 0.3 ) 1.4 Fe 13.68 Si 1.6 Scanning electron micrograph of a magnetic refrigeration material. Detailed Implementation

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0036] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art.

[0038] A specific embodiment of the present invention provides a La-Fe-Si based magnetic refrigeration material, which is formed by mixing rare earth-rich La-Fe-Si based intermediate alloy powder with Fe powder and other powders, followed by pressing or rolling and sintering, and can rapidly form NaZn. 13 The La-Fe-Si based magnetic refrigeration material exhibits a large magnetocaloric effect and good mechanical properties. The specific steps for preparing the La-Fe-Si based magnetic refrigeration material are as follows:

[0039] S1. Prepare intermediate alloy raw materials according to the set chemical ratio. The raw materials contain La, Fe, and Si elements, with the chemical formula (La... 1-x R x ) m Fe 13-n Si n , where R is one or more of the elements Ce, Pr and Nd, 1≤m≤7, 1≤n≤10, 0≤x≤0.5.

[0040] S2. Place the prepared intermediate alloy raw material into an electric arc melting or induction melting furnace, evacuate it, clean it with high-purity inert gas, and then melt it under inert gas protection to obtain the La-Fe-Si based intermediate alloy. In a specific embodiment, the vacuum degree during evacuation is 5×10⁻⁶. -2 The pressure is below 100 Pa; the high-purity inert gas used is high-purity He and / or Ar; the intermediate alloy can be in the form of alloy ingots, alloy sheets, alloy particles, etc., and is crushed into powder to obtain La-Fe-Si based intermediate alloy powder. In specific embodiments, the required particle size of the powder is <100 μm, which is crushed mechanically under the protection of high-purity inert gas, and then sieved using a sieve corresponding to the particle size. In some embodiments, the raw materials prepared in step S1 are melted to directly obtain La-Fe-Si based intermediate alloy powder without further crushing.

[0041] S3. Using La-Fe-Si based intermediate alloy powder as raw material, it is mixed with Fe powder, Si powder, and M powder, where M is any one or more combinations of Cr, Mn, Co, Ni, and Al element powders; or, La-Fe-Si intermediate alloy powder is mixed with Fe powder, Si powder, and alloy powder, where the alloy powder is a binary or multi-element alloy powder composed of Fe and one or more elements selected from Cr, Mn, Co, Ni, Al, B, C, and Si. The chemical formula of the mixed powder is (La... 1-x R x ) a (Fe 1-b M b ) (13-y)c Si y A z , where A is an element of B and / or C, 0≤x≤0.5, 1≤y≤2, 0≤z≤0.5, 1≤a≤2, 0≤b≤0.1, 0.5≤c≤1.5.

[0042] S4. Press the mixed powder prepared in step S3 into a billet. In a specific embodiment, the mixed powder can be pressed directly in a mold; alternatively, the mixed powder can be pressed into a metal sleeve with openings at both ends. The metal sleeve is preferably made of pure Fe or an Fe alloy. Then, it is pressed or rolled, and the sleeve is removed to obtain a plate-shaped billet. In a specific embodiment, the pressure at which the mixed powder is pressed into a billet or pressed into a metal sleeve is 500 MPa to 1.5 GPa. High-pressure pressing near-net-shape forming is beneficial for accelerating the formation of the magnetocaloric phase and improving the material strength. If a sleeve pressing or rolling process is used, it can be carried out at room temperature, or at low or high temperature. During the sleeve pressing or rolling process, the powder is tightly bonded, further accelerating phase formation. In this step, the density of the billet is controlled at 80% to 95%, which ensures the strength of the material after sintering while retaining some porosity to prevent breakage during hydrogen charging.

[0043] S5. The obtained green body is sintered to obtain a material with NaZn content. 13 La(Fe,Si) crystal structure phase 13 A basic magnetic refrigeration material. In a specific embodiment, the sintering temperature is controlled at 1000–1300°C to rapidly form NaZn. 13 A magnetocaloric phase with a crystalline structure, sintered within 5 hours, yielded La(Fe,Si). 13 NaZn in basic magnetic refrigeration materials 13 The volume fraction of the La(Fe,Si) crystal structure phase can reach over 90% of the maximum formable phase volume fraction, which refers to the volume fraction of La(Fe,Si). 13 Given a limited formulation for the basic magnetic refrigeration material, extending the sintering time can improve the performance of NaZn. 13 Volume fraction of the magnetocaloric phase in a type-shaped crystal structure when fully formed. La(Fe,Si) obtained by sintering. 13 The porosity of the base magnetic refrigeration material is 1% to 10%, ensuring that the material will not break down during the subsequent hydrogen charging step. The rapid phase formation mechanism achieved by the above steps is as follows: using an improved powder metallurgy process, a magnetocaloric phase preferentially and rapidly forms inside the rare earth-rich intermediate alloy powder, while Si element dissolves into the Fe powder and diffuses and reacts with the remaining rare earth-rich phase, thereby accelerating the phase formation rate.

[0044] S6. The obtained La(Fe,Si) 13 The La(Fe,Si)3-based magnetic refrigeration material undergoes hydrogen charging treatment. In a specific embodiment, the hydrogen charging conditions are: pressure 0.1–1 MPa, temperature 20–500 °C, and time 1–12 hours. Hydrogen charging treatment can increase the Curie temperature of the La(Fe,Si)3-based magnetic refrigeration material. Due to the presence of pores and Fe reinforcing phases in the material, the material retains its shape and possesses a certain degree of mechanical strength after hydrogen charging.

[0045] The above method can accurately control La(Fe,Si).13 The elemental ratio of the basic magnetic refrigeration material allows for precise adjustment of the Curie temperature; specific processes can be used to achieve the production of NaZn. 13 The efficient synthesis of the crystal structure phase can ensure the integrity of the material shape after hydrogen charging and has good mechanical properties.

[0046] The technical solution and effects of the present invention will be illustrated below with specific embodiments.

[0047] Example 1

[0048] The chemical formula of the La-Fe-Si based magnetic refrigeration material in this embodiment is: (La 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 The chemical formula of the La-Fe-Si based master alloy used is: (La 0.7 Ce 0.3 )2Fe 11 Si2. The preparation method of the La-Fe-Si based magnetic refrigeration material in this embodiment includes the following steps:

[0049] 1) Press (La) 0.7 Ce 0.3 )2Fe 11 The Si2 chemical formula is prepared and placed into the crucible of a vacuum induction melting furnace. After evacuation, high-purity argon gas is introduced and the mixture is melted at high temperature. Once the alloy melt has a uniform composition, the molten alloy is poured into a copper mold and cooled to form an alloy ingot.

[0050] 2) The alloy ingot prepared in step 1) is mechanically crushed into powder and sieved in a nitrogen glove box to obtain powder with a particle size ≤38μm.

[0051] 3) The powder sieved in step 2) is mixed with Fe powder and Si powder with a particle size ≤38μm in a nitrogen glove box according to the chemical formula (La). 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 Mix thoroughly according to the specified proportions.

[0052] 4) Mix the (La) thoroughly in step 3) 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 The powder was pressed into a green body at room temperature in a nitrogen glove box at a pressure of 1 GPa, and the density of the green body was approximately 88%.

[0053] 5) Press the (La) material from step 4). 0.7 Ce0.3 ) 1.2 Fe 11.4 Si 1.6 The blank is placed in a quartz tube, evacuated, filled with argon gas, and then sealed.

[0054] 6) Place the quartz tube sealed into the blank in step 5) into a resistance furnace, heat to 1100℃, and sinter for 5 hours to form a structure containing NaZn. 13 The type of magnetic thermal phase of the crystal structure (La) 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 Magnetic refrigeration materials.

[0055] 7) The sintered (La) from step 6) 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 Magnetic refrigeration materials were saturated with hydrogen at 300°C and 0.2 MPa in a hydrogen atmosphere to obtain hydrogenated (La) materials. 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 H y Magnetic refrigeration materials.

[0056] The (La) obtained in step 6 of this embodiment was observed using a scanning electron microscope. 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 Microstructure of magnetic refrigeration materials. For example... Figure 1 As shown, the material consists of a magnetocaloric phase, a non-magnetocaloric phase, and pores, wherein the magnetocaloric phase contains NaZn. 13 The material exhibits a typical crystal structure (gray area) with a volume fraction of approximately 89%. It also contains certain α-(Fe,Si) phases (black area) and rare-earth-rich phases (white area), with the α-(Fe,Si) phase comprising approximately 8% and the rare-earth-rich phase approximately 3%. The rare-earth-rich phase is primarily composed of La and Ce oxides, along with a small amount of (La,Ce)1Fe1Si1 phase and trace amounts of other phases. Considering the internal porosity, the calculated porosity is approximately 7%, and the porous structure effectively ensures the material's integrity after hydrogen purging.

[0057] The hydrogenation (La) obtained in step 7) was measured using a superconducting quantum interference vibrating sample magnetometer (MPMS(SQUID)VSM). 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si1.6 H y The thermomagnetic (MT) curves of the magnetic refrigeration material under a 0.05T magnetic field and its isothermal magnetization (MH) curves at different temperatures. Figure 2 As shown, the Curie temperature (T) of this material C The K value is 313 K, and there is almost no thermal hysteresis. From Figure 3 It can be seen that near the Curie temperature, the magnetization curve of the material exhibits a distinct inflection point and narrow magnetic hysteresis, demonstrating a first-order paramagnetic to ferromagnetic transition. According to Maxwell's relations: Calculate the entropy change under different temperatures and magnetic field variations from the isothermal magnetization curve of the rising field. For example... Figure 4 As shown, the maximum mass entropy change of this material under magnetic field changes of 0–1T and 0–2T are 9.6 J / kgK and 13.3 J / kgK, respectively, and the maximum volume entropy change is 61.5 mJ / cm². 3 K and 85.3 mJ / cm 3 K.

[0058] Example 2

[0059] The chemical formula of the La-Fe-Si based magnetic refrigeration material in this embodiment is: (La 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 .

[0060] The preparation method of the La-Fe-Si based magnetic refrigeration material in this embodiment differs from that in Example 1 above only in that the sintering time in step 6) is 12 hours.

[0061] The (La) prepared in this embodiment 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 The microstructure of magnetic refrigeration materials, such as Figure 5 As shown, the volume fraction of the magnetocaloric phase is approximately 93%, the volume fraction of the α-(Fe,Si) phase is approximately 5%, and the volume fraction of the rare earth-rich phase is approximately 2%. Taking the internal porosity of the material into account, the calculated porosity is approximately 6%. The measured hydrogenation (La)... 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 H yThe thermomagnetic (MT) curves and isothermal magnetization (MH) curves of the magnetic refrigeration material at different temperatures were used to determine the Curie temperature of the material to be 313 K. Based on Maxwell's relations, the entropy change under different temperatures and magnetic field variations was calculated from the isothermal magnetization curves. The maximum mass entropy change of the material in a magnetic field of 0–2 T is 15.1 J / kg K, and the maximum volume entropy change is 96.6 mJ / cm². 3 K.

[0062] Example 3

[0063] The chemical formula of the La-Fe-Si based magnetic refrigeration material in this embodiment is: (La 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 .

[0064] The preparation method of the La-Fe-Si based magnetic refrigeration material in this embodiment differs from that in Example 1 above only in that the sintering time in step 6) is 24 hours.

[0065] The (La) prepared in this embodiment 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 The microstructure of magnetic refrigeration materials, such as Figure 6 As shown, the volume fraction of the magnetocaloric phase is approximately 93%, the volume fraction of the α-(Fe,Si) phase is approximately 5%, and the volume fraction of the rare earth-rich phase is approximately 2%. If the proportion of internal pores is taken into account, the calculated porosity is approximately 6%.

[0066] Comparing the phase formation of the magnetic refrigeration materials in Examples 1-3, it can be seen that the magnetocaloric phase is fully formed after sintering for 12 hours, and the magnetocaloric phase reaches 95.6% of the volume fraction when fully formed after sintering for 5 hours.

[0067] Example 4

[0068] The chemical formula of the La-Fe-Si based magnetic refrigeration material in this embodiment is: (La 0.7 Ce 0.3 ) 1.2 Fe 11.4 Si 1.6 .

[0069] The preparation method of the La-Fe-Si based magnetic refrigeration material in this embodiment differs from that in Example 1 above only in that the sintering temperature in step 6) is 1150℃ and the sintering time is 3 hours.

[0070] The (La) prepared in this embodiment 0.7 Ce0.3 ) 1.2 Fe 11.4 Si 1.6 The microstructure of magnetic refrigeration materials, such as Figure 7 As shown, the volume fraction of the magnetocaloric phase is approximately 92%, the volume fraction of the α-(Fe,Si) phase is approximately 5%, and the volume fraction of the rare earth-rich phase is approximately 3%. Taking into account the proportion of internal pores in the material, the calculated porosity is approximately 6%. By increasing the sintering temperature, the phase formation time of the magnetocaloric phase can be further shortened, reaching the maximum available phase volume fraction in 3 hours.

[0071] The chemical formulas, sintering conditions, and properties of the La-Fe-Si based magnetic refrigeration materials in Examples 5-9 are shown in Table 1.

[0072] The preparation methods of the La-Fe-Si based magnetic refrigeration materials in Examples 5-7 are different from those in Example 1 above, except that they contain more Fe and the proportion of Fe powder is increased when mixing powders in step 3).

[0073] The preparation method of the La-Fe-Si based magnetic refrigeration material in Example 8 differs from that in Example 1 only in that: (La 0.7 Ce 0.3 ) 1.2 Fe 10.4 Co1Si 1.6 In step 3), a portion of Fe was replaced with Co. The powder was mixed in a certain proportion, with the proportion of Fe powder decreasing and the proportion of Co powder increasing.

[0074] The preparation method of the La-Fe-Si based magnetic refrigeration material in Example 9 differs from that in Example 1 only in that: (La 0.7 Ce 0.3 ) 1.2 Fe 11.2 Mn 0.2 Si 1.6 In step 3), a portion of the Fe was replaced with Mn, and the powder was mixed in a specific ratio, with the proportion of Fe powder decreasing and the proportion of Mn powder increasing.

[0075] For the magnetic refrigeration materials in Examples 5-9, the microstructure was observed using a scanning electron microscope, and the content of each phase was calculated; the thermomagnetic (MT) curve and the isothermal magnetization (MH) curve were determined using a superconducting quantum interference vibrating sample magnetometer (MPMS) (SQUID) to determine the Curie temperature and entropy change; and the bending strength was measured using a three-point bending test method.

[0076] Table 1. Chemical formulas, sintering conditions, and properties of the La-Fe-Si based magnetic refrigeration materials in Examples 5-9

[0077]

[0078] Example 10

[0079] The chemical formula of the La-Fe-Si based magnetic refrigeration material in this embodiment is: (La 0.7 Ce 0.3 ) 1.4 Fe 13.68 Si 1.6 The chemical formula of the La-Fe-Si based master alloy used is: (La 0.7 Ce 0.3 )2Fe 11 Si2. The preparation method of the La-Fe-Si based magnetic refrigeration material in this embodiment includes the following steps:

[0080] 1) Press (La) 0.7 Ce 0.3 )2Fe 11 The Si2 chemical formula is prepared and placed into the crucible of a vacuum induction melting furnace. After evacuation, high-purity argon gas is introduced and the mixture is melted at high temperature. Once the alloy melt has a uniform composition, the molten alloy is poured into a copper mold and cooled to form an alloy ingot.

[0081] 2) The alloy ingot prepared in step 1) is mechanically crushed into powder and sieved in a nitrogen glove box to obtain powder with a particle size ≤38μm.

[0082] 3) The powder sieved in step 2) is mixed with Fe powder and Si powder with a particle size ≤38μm in a nitrogen glove box according to the chemical formula (La). 0.7 Ce 0.3 ) 1.4 Fe 13.68 Si 1.6 Mix thoroughly according to the specified proportions.

[0083] 4) Mix the (La) thoroughly in step 3) 0.7 Ce 0.3 ) 1.4 Fe 13.68 Si 1.6 The powder is pressed into a metal sheath with openings at both ends at room temperature, with a pressure of 600 MPa; then the sheath is rolled to obtain a plate-shaped blank with a density of about 95%.

[0084] 5) Roll the (La) material from step 4) 0.7 Ce 0.3 ) 1.4 Fe 13.68 Si 1.6 The plate-shaped blank is placed in a quartz tube, evacuated, filled with argon gas, and then sealed.

[0085] 6) Place the quartz tube sealed into the blank in step 5) into a resistance furnace, heat to 1100℃, and sinter for 5 hours to form a structure containing NaZn. 13 The type of magnetic thermal phase of the crystal structure (La) 0.7 Ce 0.3 ) 1.4 Fe 13.68 Si 1.6 Magnetic refrigeration materials.

[0086] 7) The sintered (La) from step 6) 0.7 Ce 0.3 ) 1.4 Fe 13.68 Si 1.6 Magnetic refrigeration materials were saturated with hydrogen at 300°C and 0.2 MPa in a hydrogen atmosphere to obtain hydrogenated (La) materials. 0.7 Ce 0.3 ) 1.4 Fe 13.68 Si 1.6 H y Magnetic refrigeration materials.

[0087] In step 6 of this embodiment, (La) is obtained. 0.7 Ce 0.3 ) 1.4 Fe 13.68 Si 1.6 The microstructure of magnetic refrigeration materials, such as Figure 8 As shown, La(Fe,Si) 13 The basic magnetic refrigeration material consists of a magnetocaloric phase, a non-magnetocaloric phase, and pores. The magnetocaloric phase comprises approximately 84% by volume, the α-(Fe,Si) phase approximately 12%, and the rare-earth-rich phase approximately 4%. The α-(Fe,Si) phase is arranged in elongated strips along the rolling direction (RD). Considering the proportion of pores within the material, the calculated porosity is approximately 1%. Three-point bending tests were conducted to determine the porosity of hydrogenated (La...)... 0.7 Ce 0.3 ) 1.4 Fe 13.68 Si 1.6 H y The magnetic refrigeration material has a bending strength of 57 MPa.

[0088] Example 11

[0089] The chemical formula of the La-Fe-Si based magnetic refrigeration material in this embodiment is: (La 0.7 Ce 0.3 ) 1.3 Fe 13.68 Si 1.6 .

[0090] The preparation method of the La-Fe-Si based magnetic refrigeration material in this embodiment differs from the preparation method in Example 10 above only in that: (La 0.7 Ce 0.3 ) 1.3 Fe 13.68 Si 1.6 The content of La and Ce was increased. In step 3), the powder was mixed in a certain proportion, and the proportion of Fe powder was reduced. 0.7 Ce 0.3 )2Fe 11 The proportion of Si2 powder is increased.

[0091] The (La) obtained in step 6 of this embodiment was observed using a scanning electron microscope. 0.7 Ce 0.3 ) 1.3 Fe 13.68 Si 1.6 The microstructure of the magnetic refrigeration material was analyzed, and the content of each phase was calculated. The volume fraction of the magnetocaloric phase was approximately 77%, the α-(Fe,Si) phase approximately 19%, and the rare-earth-rich phase approximately 4%. The α-(Fe,Si) phase was arranged in elongated strips along the rolling direction (RD). Considering the internal porosity, the calculated porosity was approximately 2%. The porosity was determined by a three-point bending test (La...). 0.7 Ce 0.3 ) 1.3 Fe 13.68 Si 1.6 The flexural strength of the magnetic refrigeration material is 201 MPa.

[0092] The technical solution of this invention uses powder metallurgy to prepare La-Fe-Si based magnetic refrigeration materials. During the preparation process, rare earth elements inevitably undergo oxidation and volatilization, resulting in loss. Therefore, in each embodiment, the rare earth content is increased slightly during the formulation to compensate for the rare earth loss. However, in Examples 10 and 11, a rolling process is used, which results in more severe rare earth loss, thus requiring a greater amount of rare earth compensation.

[0093] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the scope of protection of this invention.

Claims

1. A method for preparing a La-Fe-Si based magnetic refrigeration material, characterized in that, Includes the following steps: S1. Prepare intermediate alloy raw materials according to the set chemical ratio, with the chemical formula (La). 1-x R x ) m Fe 13-n Si n Where R is selected from any one or more of Ce, Pr, and Nd elements, 1≤m≤7, 1≤n≤10, and 0≤x≤0.5; S2. Melt the raw materials prepared in step S1 to obtain a La-Fe-Si based master alloy, crush it into powder, and obtain La-Fe-Si based master alloy powder with a particle size of <100 μm. S3. Using the La-Fe-Si based intermediate alloy powder obtained in step S2, along with Fe powder, Si powder, M powder, or alloy powder as raw materials, according to the chemical formula (La... 1-x R x ) a (Fe 1-b M b ) (13-y)c Si y A z Prepare a mixed powder, wherein M is selected from any one or more of the elements Cr, Mn, Co, Ni, and Al, the alloy powder is a binary or multi-element alloy powder composed of Fe and one or more of the elements Cr, Mn, Co, Ni, Al, B, C, and Si, A is the element B and / or C, 0≤x≤0.5, 1≤y≤2, 0≤z≤0.5, 1≤a≤2, 0≤b≤0.1, and 0.5≤c≤1.5; S4. Press the mixed powder prepared in step S3 into a green body with a density of 80%~95%. S5. The green body obtained in step S4 is sintered at a temperature of 1000~1300℃ to obtain bulk La(Fe,Si). 13 In the basic magnetic refrigeration material, during the sintering process, a magnetocaloric phase preferentially and rapidly forms inside the rare-earth-rich intermediate alloy powder. Simultaneously, Si element dissolves into Fe powder and diffuses and reacts with the remaining rare-earth-rich phase, accelerating the phase formation rate. The La(Fe,Si) material... 13 La(Fe,Si) in basic magnetic refrigeration materials 13 The basic magnetocaloric phase has NaZn 13 NaZn crystal structure, sintering time within 5 hours 13 The volume fraction of the La(Fe,Si) crystal structure phase reaches more than 90% of the maximum formable phase volume fraction. 13 The porosity of the basic magnetic refrigeration material is 1%~10%; S6. The La-Fe-Si based magnetic refrigeration material obtained in step S5 is subjected to hydrogen charging treatment.

2. The method for preparing the La-Fe-Si based magnetic refrigeration material according to claim 1, characterized in that, In step S4, the billet forming method is to press the mixed powder into a metal sleeve with openings at both ends, roll it, and then remove the sleeve to obtain a plate-shaped billet.

3. The method for preparing the La-Fe-Si based magnetic refrigeration material according to claim 2, characterized in that, In step S4, the metal sheath is made of pure Fe or an Fe alloy.

4. The method for preparing the La-Fe-Si based magnetic refrigeration material according to claim 1, characterized in that, In step S6, the hydrogen charging conditions are: pressure 0.1~1 MPa, temperature 20~500℃, and time 1~12 hours.

5. A La-Fe-Si based magnetic refrigeration material, characterized in that, It is prepared by the preparation method as described in any one of claims 1 to 4.

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