Low curie temperature iron-based magnetocaloric material, preparation method, deicing material and coating

Abstract

The application relates to the technical field of magnetocaloric materials, and discloses a low-curie-temperature iron-based magnetocaloric material, a preparation method, a deicing agent and a coating. The magnetocaloric material takes iron as the main body, introduces rare earth elements, transition group elements and metalloid elements to form a synergistic component system, and has the characteristics of adjustable curie temperature and high saturation magnetic induction intensity. The preparation method comprises the following steps: alloy smelting and high-temperature homogenization heat treatment, block pretreatment, segmented parameter control hydrogen crushing, and gradient temperature rising high-vacuum dehydrogenation. Through the hydrogenation process combining low-temperature permeation, high-pressure crushing and heat preservation and refinement, the uniform and controllable crushing of the alloy is realized, and the residual hydrogen content is effectively reduced in the multi-stage dehydrogenation process. The application can significantly improve the problems of serious oxidation, uneven particle size and magnetic performance attenuation existing in the traditional mechanical crushing or conventional hydrogen crushing process. The obtained magnetocaloric material shows high saturation magnetic induction intensity and stable magnetocaloric performance in the low curie temperature interval.

Description

Technical Field

[0001] This invention belongs to the field of magnetocaloric materials technology, specifically relating to a low Curie temperature iron-based magnetocaloric material, its preparation method, de-icing agent, and coating. Background Technology

[0002] Low Curie temperature magnetocaloric materials refer to functional materials with a low Curie temperature that can produce significant magnetic entropy changes or adiabatic temperature changes under the influence of an applied magnetic field. Their magnetocaloric effect can be used to achieve energy conversion and temperature control. Compared with traditional refrigeration and thermal control methods based on gas compression or phase change media, the magnetocaloric effect has the advantages of good reversibility, high energy efficiency, low operating noise, and environmental friendliness. Therefore, it has attracted widespread attention in the fields of cryogenic refrigeration, precision temperature control, and thermal management in special environments. Especially in applications that require stable operation in the near-room temperature or low-temperature range, low Curie temperature magnetocaloric materials are considered one of the important basic materials for realizing related functional devices.

[0003] In practical applications, magnetocaloric materials often need to be further shaped or composited in powder form to meet the requirements of different structures and service conditions. Therefore, the preparation quality of magnetocaloric material powder has a significant impact on its subsequent molding performance, service reliability, and the stable performance of the magnetocaloric effect. Existing research shows that the uniformity of the powder's chemical composition, particle size distribution, oxygen content, residual hydrogen content, and crystal structure integrity all have a direct or indirect impact on the material's magnetic and magnetocaloric properties. If the powder undergoes severe oxidation, component segregation, or structural damage during preparation, it will inevitably lead to damage to the ordered arrangement of magnetic moments, thereby weakening the magnetic entropy amplitude and reducing the material's practical application value.

[0004] Currently, the preparation of low Curie temperature magnetocaloric alloy powders mainly employs processes such as mechanical crushing, ball milling, or traditional hydrogen crushing. Among these, mechanical crushing and ball milling rely on external mechanical force to pulverize the alloy blocks, making the process relatively simple. However, they easily introduce metallic wear impurities during crushing, and the powder's specific surface area increases significantly, making it more susceptible to oxidation reactions in air. Furthermore, these methods often struggle to effectively control particle size distribution, resulting in a high proportion of fine powder and significant agglomeration, which is detrimental to the consistency and stability of subsequent forming processes.

[0005] In contrast, hydrogen crushing, which induces lattice expansion and internal stress in alloys after hydrogen absorption, causing fracture along grain boundaries or weak bonding interfaces, is considered a relatively mild powder preparation method. However, existing hydrogen crushing processes still face several challenges in practical applications. For example, uneven hydrogen atom penetration within the alloy during hydrogen charging can lead to excessively high or low local hydrogen concentrations, resulting in incomplete crushing or significant particle size variations. Improper control of the dehydrogenation process can result in high residual hydrogen content, which, when occupying interstitial spaces, can negatively impact the magnetic structure. Furthermore, under certain process conditions, excessively high hydrogen absorption or dehydrogenation temperatures can induce grain growth or changes in crystal structure, thereby affecting the material's magnetic stability.

[0006] On the other hand, low Curie temperature magnetocaloric materials typically involve multi-component alloy systems, and their magnetic properties are highly sensitive to compositional ratios and microstructure. During powder preparation, insufficient matching between process parameters and alloy composition characteristics can easily lead to problems such as compositional segregation and unstable phase structures, making it difficult to simultaneously achieve both a low Curie temperature and high saturation magnetic induction. Furthermore, safety and process controllability during powder preparation are also crucial factors for engineering applications, especially when dealing with reactive gases such as hydrogen, which places higher demands on equipment sealing, process stability, and repeatability.

[0007] Therefore, in the field of low Curie temperature magnetocaloric materials, how to obtain magnetocaloric material powders with low oxygen content, low residual hydrogen, reasonable particle size distribution, and suitability for large-scale applications while ensuring the stability of material composition and structure has always been a technical problem that has been continuously focused on and researched by those skilled in the art. The existence of these problems, to some extent, restricts the further promotion and engineering application of low Curie temperature magnetocaloric materials in related application fields.

[0008] Applying low Curie-point ferromagnetic materials to the exterior of transmission line conductors for de-icing is an automatic, uninterrupted de-icing method. It offers the technical advantage of actively preventing icing in response to changes in ambient temperature. Ferromagnetic materials can be manufactured into various forms of devices, such as ferromagnetic wire, pre-stranded wire, or anti-icing self-heating rings / sleeves, depending on the specific anti-icing requirements. These typically consist of a ferromagnetic core and a conductive coating. When the ambient temperature is below the Curie temperature of the ferromagnetic core material, the core exhibits ferromagnetism and high magnetic susceptibility, inducing a high magnetic flux density in the conductor's magnetic field. This allows it to heat the conductor through heat loss for de-icing. Conversely, when the ambient temperature is above the Curie temperature, the core material exhibits paramagnetism, making it difficult to magnetize and generate heat, thus failing to function and incurring losses. Therefore, using ferromagnetic materials with low Curie temperatures and high saturation magnetic induction as the core material can achieve automatic anti-icing: under normal weather temperatures, the core material is minimally affected by the conductor's magnetic field, and the anti-icing device consumes almost no electrical energy; only when the temperature drops to the freezing point, which is conducive to icing, does the anti-icing device begin to generate significant heat, raising the conductor's temperature and preventing icing. This method enables active anti-icing based on changes in the service temperature of the transmission line, and its key lies in developing magnetic materials with Curie temperatures close to the freezing point and high saturation magnetic induction. Summary of the Invention

[0009] The purpose of this invention is to solve the problems of easy oxidation, high residual hydrogen, uneven particle size distribution, and difficulty in maintaining stable magnetocaloric properties in the preparation process of low Curie temperature magnetocaloric material powders in the prior art.

[0010] The objective of this invention is achieved through the following technical solution: A low Curie temperature iron-based magnetocaloric material, wherein the chemical composition of the iron-based magnetocaloric material is expressed as Fe in atomic percentage. a RE b TM c Si d B e ;in, RE represents any one or more combinations of the rare earth elements lanthanum (La), praseodymium (Pr), neodymium (Nd), and cerium (Ce); TM represents any one or more combinations of transition elements nickel (Ni), cobalt (Co), zirconium (Zr), chromium (Cr), and manganese (Mn); a, b, c, d, e are the atomic percentages of the corresponding elements, and satisfy the following conditions: , , , , , .

[0011] Preferably, the Curie temperature is in the range of -50°C to 50°C.

[0012] Preferably, the material has a saturation magnetic induction intensity greater than 0.6T at a temperature 20°C below the Curie temperature.

[0013] Preferably, the material retains a single low Curie temperature magnetic phase structure after the hydrogen absorption-dehydrogenation treatment, and the grain size is no greater than 30 μm.

[0014] Preferably, the residual hydrogen content of the material is no more than 50 ppm.

[0015] Preferably, the material exists in powder form, and the powder particle size is mainly distributed in the range of 50 to 300 μm.

[0016] Based on the same inventive concept, the present invention also provides a method for preparing a low Curie temperature iron-based magnetocaloric material, comprising the following steps: According to Fe a RE b TM c Si d B e The raw materials are prepared according to the specified component ratio, and then smelted at high temperature and subjected to high temperature homogenization heat treatment to obtain alloy ingots. The alloy ingot is cut into block raw materials, which are then cleaned and vacuum dried to obtain pretreated raw materials. The pretreated raw material is placed into a closed hydrogen crushing equipment and subjected to segmented hydrogen charging treatment with stepped parameter control under vacuum conditions to cause hydrogenation and crushing of the pretreated raw material to obtain hydrogen crushed alloy powder. The hydrogen-rich alloy powder was subjected to dehydrogenation treatment under gradient heating and high vacuum conditions, and then cooled and sieved to obtain the low Curie temperature iron-based magnetocaloric material.

[0017] Preferably, when preparing raw materials, considering that lanthanum, praseodymium, neodymium, and cerium are easily oxidized and burned, the theoretically calculated amount of each rare earth element is increased by 10wt% as a smelting compensation.

[0018] Preferably, the high-temperature homogenization heat treatment is performed at a temperature of 1000–1500°C and a holding time of 120–720 hours to eliminate as-cast component segregation and form a stable low Curie temperature phase.

[0019] Preferably, the size range of the block raw material is 5 to 20 mm.

[0020] Preferably, the cleaning is performed using ultrasonic cleaning with ethanol.

[0021] Preferably, the vacuum drying temperature is 60~80℃ and the drying time is 2~4 hours.

[0022] Preferably, the vacuum condition is a vacuum degree ≤ 5 × 10⁻⁶. -3Pa, and maintain for 30-60 minutes.

[0023] Preferably, the segmented hydrogen charging process includes a low-temperature infiltration stage, a high-pressure crushing stage, and a heat preservation and refining stage performed sequentially. By controlling the hydrogen pressure and temperature in a stepwise manner, uniform infiltration and controllable crushing of hydrogen atoms inside the alloy are achieved.

[0024] Preferably, the hydrogen pressure in the low-temperature permeation stage is 0.3~1.0MPa, the temperature is 150~250℃, and the holding time is 2~4h; wherein, the hydrogen purity is ≥99.999%.

[0025] Preferably, in the high-pressure crushing stage, hydrogen gas is pressurized to 1.0~2.5MPa at a rate of no more than 0.2MPa / min, and then kept at this pressure for 4~8h to cause the alloy to fracture along the grain boundaries.

[0026] Preferably, the closed hydrogen crushing equipment is a closed hydrogen crushing furnace with a furnace rotation speed of 10~30 rpm.

[0027] Preferably, the heat preservation and refinement stage includes: after hydrogen absorption, maintaining the hydrogen pressure at 1.0~2.5MPa, reducing the temperature to 100~150℃, and maintaining the temperature for 2~3 hours.

[0028] Preferably, the dehydrogenation process includes a low-temperature dehydrogenation stage and a deep dehydrogenation stage; The cryogenic dehydrogenation stage is evacuated to 1×10⁻⁶. -2 Pa, heat to 100~200℃, and keep warm for 3~5 hours; The deep dehydrogenation stage continues to raise the temperature to 200~350℃ and increase the vacuum level to ≤5×10⁻⁶. -3 Pa, keep warm for 6~10 hours.

[0029] Preferably, the cooling includes: after dehydrogenation is completed, stopping heating, introducing argon gas with a purity of ≥99.999% into the furnace 3 to 5 times to purge, maintaining the argon gas pressure at 0.1 to 0.2 MPa, and then cooling the furnace to room temperature.

[0030] Preferably, the sieving includes classifying the alloy powder using a 40-200 mesh vibrating screen.

[0031] Based on the same inventive concept, the present invention also provides a de-icing device for power transmission lines, comprising: a ferromagnetic core and a conductive coating covering the outer surface of the ferromagnetic core; the device configuration is any one of an anti-icing self-heating ring, an anti-icing sleeve, pre-twisted wire, or ferromagnetic wire, used for fixed installation on the outside of the power transmission conductor; the ferromagnetic core is made of the low Curie temperature iron-based magnetocaloric material; when the ambient temperature is lower than the Curie temperature of the iron-based magnetocaloric material, the device can generate hysteresis loss and heat generation under the action of the alternating magnetic field of the power transmission conductor, thereby achieving anti-icing and de-icing.

[0032] Based on the same inventive concept, the present invention also provides a magnetothermal anti-icing coating, the coating being composed of functional fillers, a film-forming matrix, and additives; the functional filler is the low Curie temperature iron-based magnetothermal material, which is dispersed in the film-forming matrix in powder form; the coating is applied to the surface of a power transmission line or power fitting and cured to form a magnetothermal anti-icing coating; when the ambient temperature is lower than the Curie temperature of the iron-based magnetothermal material, the coating utilizes the alternating magnetic field around the power transmission line to generate heat to achieve active anti-icing and de-icing.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention achieves synergistic technical effects in terms of material microstructure stability, magnetocaloric performance retention, and powder engineering applicability through a systematic design of the material composition system and powder preparation process. Its core lies in the fact that the various process parameters are not set in isolation, but rather matched and controlled around the physicochemical behavior of the magnetocaloric material during hydrogen absorption and dehydrogenation, thereby ensuring the feasibility and repeatability of the final performance at the mechanistic level.

[0034] Firstly, regarding the material composition, this invention employs a multi-element alloy system with iron as the main component and incorporating rare earth elements, transition elements, and metalloid elements. Iron provides the primary source of magnetic moment, forming the basis for the magnetocaloric effect. Rare earth elements, due to their large atomic radii and unique electronic structures, help stabilize specific crystal structures and regulate the intensity of magnetic exchange interactions, shifting the Curie temperature towards a lower temperature range. Transition elements achieve precise adjustment of the Curie temperature by altering local magnetic moments and exchange coupling constants. Metalloid elements, by filling lattice interstices or participating in bonding, enhance structural stability and suppress abnormal grain growth. In principle, this multi-element composition design allows the alloy to maintain phase structure stability during hydrogen absorption and dehydrogenation, avoiding magnetic phase decomposition or irreversible transformation, thus macroscopically manifesting as a stable Curie temperature and a high level of saturation magnetic induction.

[0035] Secondly, in the alloy pretreatment stage, high-temperature melting and prolonged high-temperature heat treatment eliminate as-cast segregation, enabling various elements to fully diffuse at the atomic scale and form a stable phase structure. Mechanistically, homogenization heat treatment significantly reduces compositional gradients and interfacial energies, making the diffusion path of hydrogen atoms in the crystal lattice more consistent during subsequent hydrogen absorption, thus reducing local stress concentration. The resulting technical effect is that the material fracture behavior during hydrogen fragmentation is more uniform, avoiding excessive local fragmentation or large residual fragments, thereby improving the consistency of powder particle size distribution from the source.

[0036] Furthermore, in the hydrogen crushing process, this invention employs a segmented hydrogen charging strategy of "low-temperature infiltration—high-pressure crushing—thermal refinement," supplemented by a controlled pressurization rate and furnace rotation. The physical principle is as follows: under low temperature and low pressure conditions, hydrogen atoms gradually diffuse into the interstitial spaces of the crystal lattice, forming a relatively uniform hydrogen concentration field. Subsequently, under higher pressure, the formation of alloy hydrides induces lattice volume expansion, and internal stress concentrates at grain boundaries, causing the material to fracture along weak bonding interfaces. Finally, under lower temperature and stable hydrogen pressure conditions, the material's brittleness is further enhanced, achieving secondary refinement of the initial particles. This step-by-step mechanism effectively avoids uneven hydrogen atom infiltration and non-uniform crushing caused by instantaneous high stress, thus achieving, in terms of technical effect, a magnetocaloric powder with concentrated particle size distribution, controlled fine powder ratio, and regular particle morphology.

[0037] In the dehydrogenation stage, this invention employs a multi-stage dehydrogenation method combining gradient heating and high vacuum. The principle lies in distinguishing the different binding energy characteristics of surface-adsorbed hydrogen and interstitial hydrogen. The low-temperature stage primarily removes weakly bound surface hydrogen, creating channels for lattice hydrogen diffusion. The high-temperature, high-vacuum stage increases the chemical potential difference, driving lattice hydrogen to gradually migrate to the surface and be extracted. This stepwise dehydrogenation mechanism avoids structural damage or incomplete dehydrogenation caused by single high-temperature treatment, significantly reducing residual hydrogen content. The corresponding technical effect is: effectively preventing hydrogen atoms from occupying interstitial spaces for extended periods and interfering with the ordered arrangement of magnetic moments, thereby ensuring the stability and repeatability of magnetocaloric performance.

[0038] Furthermore, by controlling the entire process in a closed environment, replacing the powder with high-purity protective gas, and providing atmospheric protection during the sieving process, this invention reduces the contact opportunities between the powder and oxygen and water vapor, thus inhibiting the oxidation reactions of rare earth elements and iron. This results in a significant reduction in the oxygen content of the powder, preventing oxidation from disrupting the magnetic exchange effect and enabling the resulting magnetocaloric material to exhibit higher performance stability and service reliability under practical application conditions.

[0039] In summary, this invention, through the synergistic combination of specific technical features such as component system design, heat treatment homogenization, segmented hydrogen absorption, gradient dehydrogenation, and whole-process atmosphere control, achieves effective regulation of hydrogen diffusion behavior, crystal structure evolution, and magnetic retention mechanism at the principle level. Ultimately, it obtains low-oxygen, low-residual-hydrogen, uniform-particle-size, and stable magnetocaloric material powder with low Curie temperature, demonstrating significant and verifiable beneficial technical effects. Detailed Implementation

[0040] The technical solution is further described below with reference to specific embodiments to aid in understanding the content of this invention. All samples were analyzed for actual composition using inductively coupled plasma mass spectrometry (ICP-MS), magnetic properties were tested using a vibrating sample magnetometer (VSM), residual hydrogen content was tested using a hydrogen analyzer, and powder particle size was analyzed using a laser particle size analyzer. Where specific experimental steps or conditions are not specified in the embodiments, they can be performed according to the conventional experimental procedures or conditions described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0041] Example 1 Low Curie temperature magnetocaloric materials generally refer to functional materials with a Curie temperature below 200℃ that can achieve energy conversion through the magnetocaloric effect (temperature or entropy change induced by magnetic field change). Their core characteristic is significant isothermal magnetic entropy change or adiabatic temperature change within a low temperature range, making them key materials in cryogenic refrigeration, thermal control systems, and temperature regulation in special environments. These materials, with their advantages of good reversibility of the magnetocaloric effect, high refrigeration efficiency, and no pollutant emissions, are gradually replacing traditional vapor compression refrigeration and liquid nitrogen refrigeration technologies, demonstrating irreplaceable application value in scenarios such as superconducting magnet cooling, medical cryogenic storage, aerospace extreme environment thermal control, and cryogenic anti-icing of power transmission lines.

[0042] This invention provides an iron-based magnetocaloric material with a low Curie temperature and high saturation magnetic induction intensity. The main component of this magnetocaloric material has the chemical formula Fe. a RE b TM c Si d B e ; Among them, RE is any one or more combinations of rare earth elements lanthanum (La), praseodymium (Pr), neodymium (Nd), and cerium (Ce), and TM is any one or more combinations of transition elements nickel (Ni), cobalt (Co), zirconium (Zr), chromium (Cr), and manganese (Mn); Where a, b, c, d, and e are the atomic percentages of the corresponding components. , , , , , .

[0043] The Curie temperature of the iron-based magnetocaloric material is in the range of -50℃ to 50℃, and the saturation magnetic induction intensity is greater than 0.6T at 20℃ below the Curie temperature.

[0044] The iron-based magnetocaloric material provided by this invention is composed of iron, rare earth elements, strongly coupled elements, and metalloid elements. Each element in the composition system plays a clear and crucial synergistic role. Iron, as the core magnetic element, provides the main source of the alloy's magnetic moment with its unpaired d electrons, which is the basis for the magnetocaloric effect and ensures the alloy has high saturation magnetization. Rare earth elements, as the framework elements of the crystal structure, are key to forming a low Curie temperature phase due to their unique atomic radii and electronic configurations. This not only stabilizes the alloy's crystal structure and prevents phase transitions or lattice collapse during hydrogen charging-dehydrogenation, but also... The Curie temperature is indirectly optimized by regulating the magnetic exchange coupling strength through the interaction with Fe atoms; the Curie temperature can be precisely controlled by adding strong coupling elements through the difference between atomic radius and magnetic moment, while enhancing the exchange coupling between magnetic moments, improving the magnetic properties of the alloy, and also improving the brittleness of the alloy, adapting to the crushing characteristics of the hydrogen crushing process; metalloid elements further stabilize the low Curie temperature magnetic phase by filling the interstitial spaces, inhibiting grain growth, while optimizing the electron concentration distribution, and their presence can enhance the oxidation resistance of the alloy, forming a synergy with the low oxygen process of this invention, further reducing the risk of powder oxidation.

[0045] Example 2 This invention provides a method for preparing a low Curie temperature iron-based magnetocaloric material, used to prepare the low Curie temperature iron-based magnetocaloric material described in Example 1. The preparation method mainly includes the following steps: Step 1: According to the chemical formula of the iron-based magnetocaloric material Fe a RE b TM c Si d B e The raw materials are weighed and alloy ingots are obtained through high-temperature smelting and high-temperature heat treatment. The ingots are then cut into block raw materials, which are then subjected to ultrasonic cleaning with ethanol and vacuum drying to obtain pretreated raw materials. Step 2: Place the pre-treated raw material obtained in Step 1 into a closed hydrogen crushing furnace. After closing the furnace door, use the vacuum system to draw a high vacuum, and then introduce high-purity hydrogen. Control the hydrogen charging in stages through step parameters. After the hydrogen absorption is completed, maintain the hydrogen pressure and keep it warm for further crushing. Step 3: Dehydrogenate the alloy material charged with hydrogen in Step 2 by gradient heating and high vacuum. Then stop heating, introduce high-purity argon gas into the furnace for washing, and cool the furnace to room temperature. The resulting powder material is then sieved to obtain the finished iron-based magnetocaloric powder material.

[0046] In Step 1, the weight of raw materials is calculated strictly according to the chemical formula of the alloy. Considering that lanthanum, praseodymium, neodymium, and cerium are easily oxidized and burned, 10wt% of rare earth elements are added as a smelting compensation when weighing.

[0047] The ingots smelted in Step 1 exhibit severe compositional segregation. The non-equilibrium solidification process forms a large amount of ferrite and rare earth-rich phases. A heat treatment temperature of 1000~1500℃ is required to generate a low Curie temperature magnetic phase with a high phase transformation driving force. At the same time, due to the slow diffusion kinetics caused by the rare earth atomic size effect, a long-term high-temperature heat treatment is needed to complete the synergistic diffusion of multiple elements, thereby promoting the phase transformation reaction and transforming the material from a chaotic multiphase structure in the as-cast state into a single low Curie temperature phase structure. This lays the foundation for subsequent hydrogen charging treatment and practical applications. Therefore, the heat treatment process temperature is 1000~1500℃, and the holding time is 120~720 hours.

[0048] In Step 1, the ingot is cut into blocks with sides of 5-20mm. The size selection must consider two points: first, avoid blocks that are too large (>20mm), which would result in insufficient hydrogen atom penetration depth and affect particle size uniformity; second, avoid blocks that are too small (<5mm), which would lead to an excessively large specific surface area, making it prone to adsorbing oxygen and moisture from the air during subsequent processing, increasing the risk of oxidation. After cutting, the surface oxide scale must be removed. A rare earth oxide layer easily forms on the alloy surface, which hinders the contact between hydrogen atoms and the alloy matrix, leading to a decrease in hydrogen absorption efficiency. Furthermore, the oxide layer mixed into the final powder will significantly reduce the magnetic entropy change. In Step 1, ultrasonic cleaning with ethanol is used to remove residual metal debris and oil from the cutting process, preventing the introduction of impurities. Then, vacuum drying is carried out at 60~80℃. Too high a temperature may cause slight crystallization on the alloy surface, destroying the original cast structure, while too low a temperature will not be able to completely remove the ethanol solvent and adsorbed water vapor. At the same time, in order to ensure that there is no residual moisture inside the block raw material (in the subsequent vacuum and hydrogen charging treatment, water vapor will react on the material surface to generate rare earth hydroxides, which will further transform into rare earth oxides and aggravate oxidation pollution), the drying time needs to be controlled within 2~4 hours. In Step 2, the pretreated raw materials are placed into a closed hydrogen crushing furnace, the furnace door is closed, the vacuum system is started, and the vacuum is evacuated to a degree ≤5×10. -3 The pressure should be maintained at 5 Pa for 30-60 minutes. The core purpose is to remove air and moisture from the furnace to prevent impurities from reacting with the alloy or hydrogen during subsequent hydrogen charging. The vacuum level must be below 5 × 10⁻⁶ Pa. -3 Pa, if the vacuum degree is insufficient (>5×10 Pa), -3The residual air in the furnace will react rapidly with rare earth elements to generate rare earth oxides and rare earth nitrides. These compounds will coat the alloy surface and hinder the subsequent penetration of hydrogen. Maintaining a holding time of 30 to 60 minutes is to allow the gas in different areas of the furnace to fully diffuse to the vacuum pump inlet, ensuring that the vacuum degree in all parts of the furnace is uniform.

[0049] Step 2, the segmented hydrogen-filled crushing process, is divided into three stages: "low-temperature infiltration," "high-pressure crushing," and "thermal breakage." Through step-by-step parameter control, uniform hydrogen atom infiltration and controllable alloy crushing are achieved. ①The first stage is "low-temperature infiltration", in which high-purity hydrogen (purity ≥99.999%) is introduced into the furnace, the hydrogen pressure is controlled at 0.3~1.0MPa, the temperature is raised to 150~250℃, and the temperature is held for 2~4 hours.

[0050] The requirement for hydrogen purity of ≥99.999% is because impurities such as N2, O2, and H2O in low-purity hydrogen will react with the alloy to form impurity phases, which will also affect the formation rate of hydrides. The pressure is set at 0.3~1.0MPa to allow hydrogen atoms to slowly diffuse into the gaps in the alloy lattice under low pressure. If the pressure is too high, hydrogen atoms will quickly accumulate at the grain boundaries, resulting in excessively high local hydrogen concentration, prematurely triggering lattice expansion, and forming uneven cracks. The temperature is controlled at 150~250℃ because experimental studies have shown that this temperature range is the "hydrogen permeation active zone" of the iron-based magnetocaloric alloy described in this invention: when the temperature is too low (<150℃), the hydrogen atom diffusion rate is slow and the penetration depth is insufficient; when the temperature is too high (>250℃), the alloy grains are prone to grow (from 20μm in the as-cast state to more than 200μm), and excessive grain growth will lead to a decrease in magnetic properties; The purpose of keeping the material at a certain temperature for 2 to 4 hours is to allow hydrogen atoms to fully penetrate into the center of the blocky raw material, ensuring that the hydrogen concentration difference from the surface to the core is ≤5%, thus laying the foundation for subsequent uniform crushing. ②The second stage is "high-pressure crushing". Keeping the temperature of the first stage unchanged, the hydrogen pressure is gradually increased to 1.0~2.5MPa at a rate of ≤0.2MPa / min, and kept at the temperature for 4~8h. At the same time, the furnace body is controlled to rotate at a low speed of 10~30rpm. The pressure increase rate is ≤0.2MPa / min to avoid the sudden pressure increase causing the airflow in the furnace to impact the lumpy raw material, resulting in the raw material collision and breakage, and the introduction of mechanical impurities; at the same time, the slow pressure increase allows hydrogen atoms to gradually fill the interstices of the crystal lattice with the pressure gradient, avoiding the crystal lattice distortion caused by excessive local pressure. The final pressure is 1.0~2.5MPa because under this pressure, hydrogen atoms will form stable alloy hydrides with the iron-based magnetocaloric alloy described in this invention. The lattice constant of the hydride increases by 8%~12% compared to the original alloy, and the resulting internal stress is sufficient to cause the alloy to fracture uniformly along the grain boundaries (regions with weaker bonding). If the pressure is too low (<1.0MPa), the internal stress will be insufficient, and it will not be able to completely break the alloy. If the pressure is too high (>2.5MPa), it will lead to excessive crushing and produce a large amount of fine powder <20μm (fine powder is prone to agglomeration, making subsequent molding difficult). The heat treatment for 4~8 hours is to ensure that each block of raw material can complete the hydride formation and internal stress cracking process, and to avoid some raw materials remaining as large pieces due to incomplete reaction. The furnace rotation speed is 10~30 rpm to allow the lumpy raw materials to slowly turn over in the furnace, ensuring that each side can be evenly contacted with hydrogen and avoiding the accumulation of raw materials that would result in insufficient hydrogen absorption at the bottom. ③ The third stage is "heat preservation and crushing". After hydrogen absorption, the hydrogen pressure is maintained at 1.0~2.5MPa, the furnace temperature is reduced to 100~150℃, and the temperature is maintained for 2~3 hours. This is to "refine" the initially crushed particles and avoid the decomposition of hydrides. The reason for cooling to 100-150℃ is that the iron-based alloy hydrides remain stable within this temperature range (decomposition temperature is about 180℃), and the alloy brittleness is further increased. If the temperature is too high (>150℃), the hydrides will begin to decompose, the internal stress will be released, and further refinement will not be possible. If the temperature is too low (<100℃), the alloy will not be brittle enough, and fine particles will be difficult to separate from the bulk. Maintaining a pressure of 1.0~2.5MPa is to suppress hydride decomposition, ensure that internal stress continues to act on the particle interface, and promote the separation of fine particles. The purpose of keeping the powder at a certain temperature for 2-3 hours is to allow the particles after initial crushing to undergo secondary dissociation in a stable hydrogen environment, resulting in a more concentrated particle size distribution in the final powder and avoiding a mixed state of "coarse powder mixed with fine powder".

[0051] The dehydrogenation process in Step 3 is a key step in eliminating the influence of residual hydrogen on magnetocaloric performance. It is mainly divided into two stages: "low-temperature dehydrogenation" and "deep dehydrogenation". Through the synergy of gradient heating and high vacuum, the residual hydrogen is reduced to ≤50ppm. ① The first stage is "low-temperature dehydrogenation". Start the vacuum system and evacuate to 1×10⁻⁶. -2 Pa, heat to 100~200℃, and keep warm for 3~5 hours.

[0052] The vacuum level requirement is 1×10⁻⁶. -2 Pa is because this stage mainly removes the physical hydrogen adsorbed on the particle surface. This type of hydrogen has weak binding force and can be desorbed with a relatively low vacuum. If the vacuum is too high, the particles are easily sucked into the vacuum pump. The temperature is 100~200℃ because the desorption activation energy of surface-adsorbed hydrogen is low. This temperature can quickly break the bond between hydrogen and the particle surface, while avoiding premature diffusion of interstitial hydrogen due to excessively high temperature (if surface hydrogen is not removed, the diffusion of lattice hydrogen will be hindered by surface hydrogen, forming residue). The heat treatment for 3-5 hours is to ensure the complete removal of adsorbed hydrogen from the surface of all particles, thus creating a pathway for subsequent hydrogen diffusion through the lattice. The second stage is "deep dehydrogenation," where the temperature is further increased to 200-350℃ based on the first stage, and the vacuum level is increased to ≤5×10⁻⁵. -3 Pa, keep warm for 6~10 hours, while maintaining the furnace body at a speed of 10~20 rpm. The optimal temperature range of 200–350°C is chosen because the desorption activation energy of hydrogen from interstitial crystals is relatively high (approximately 0.8 eV), requiring this temperature to allow hydrogen atoms to overcome lattice constraints and diffuse to the particle surface. Temperatures that are too high (>350°C) will cause the alloy to crystallize (damaging NaZn). 13 (Structure), if the temperature is too low (<200℃), the lattice hydrogen diffusion rate is slow and cannot be completely removed; Vacuum degree ≤5×10 -3 Pa is used to create a high concentration gradient to promote the rapid expulsion of hydrogen atoms from the particle surface. If the vacuum level is insufficient, hydrogen atoms will accumulate in the furnace and be re-adsorbed by the particles. The reason for holding the temperature for 6 to 10 hours is that the hydrogen diffusion rate in the crystal lattice is slow (especially the hydrogen in the core of the particle). Sufficient time is needed for hydrogen atoms to diffuse from the core to the surface and be discharged, ensuring that the residual hydrogen is ≤50ppm (when the residual hydrogen is >50ppm, hydrogen atoms will occupy the interstices of the crystal lattice, destroy the orderly arrangement of magnetic moments, and cause the magnetic induction intensity to decrease by more than 20%). The furnace rotation speed is 10~20 rpm to ensure that the powder is heated evenly in the furnace and to avoid incomplete dehydrogenation due to localized low temperatures. If the powder accumulates, the bottom particles will not be heated enough, and the residual hydrogen will exceed the standard.

[0053] The cooling process in Step 3 involves stopping heating after dehydrogenation, introducing high-purity argon gas (purity ≥99.999%) into the furnace 3-5 times to purge, maintaining the argon gas pressure at 0.1-0.2 MPa, and then cooling the furnace to room temperature.

[0054] The argon gas purity is ≥99.999% to prevent impurity gases (O2, N2) from entering the furnace during the cooling process and causing powder oxidation. The replacement process is repeated 3 to 5 times to completely remove the residual hydrogen gas in the furnace (hydrogen mixed with air poses an explosion risk), while simultaneously filling the furnace with argon gas to create an inert protective atmosphere. Maintaining a pressure of 0.1~0.2MPa is to balance the pressure inside and outside the furnace, prevent air from seeping in from the furnace body seal, and prevent the powder from being "adsorbed" onto the furnace wall due to the pressure difference during the cooling process. The reason for cooling in the furnace rather than rapid cooling is to avoid the thermal stress generated inside the powder due to a sudden drop in temperature, which would cause the particles to agglomerate. Rapid cooling would cause the powder surface to shrink instantly, forming adhesion.

[0055] The sieving process in Step 3 involves removing the powder after cooling and classifying it using a 40-200 mesh vibrating sieve. 40 mesh corresponds to a particle size of approximately 380 μm, and 200 mesh corresponds to approximately 75 μm. Sieving yields powder with a target particle size of 50-300 μm. This particle size range is determined based on subsequent application requirements: when the particle size is >300 μm, the powder has poor flowability and is prone to voids during hot pressing; when the particle size is <50 μm, the powder has a large specific surface area, making it prone to oxidation during molding, and the magnetocaloric effect decreases due to weakened magnetic coupling between particles. The vibrating sieve needs to be used in a high-purity inert gas environment, such as argon. If manual sieving is used, the process must be carried out in an argon-protected glove box to prevent contact between air oxygen and the powder.

[0056] Powder metallurgy is a key technology for realizing the functionalization of low Curie temperature magnetocaloric materials into devices. Powder preparation, as the source of the entire process, directly determines the magnetocaloric performance and reliability of the final product through its powder quality (such as purity, particle size distribution, and crystal structure integrity). Currently, the mainstream preparation methods for alloy powders mainly include mechanical crushing and traditional hydrogen crushing, but both have significant technical defects: mechanical crushing achieves crushing through mechanical forces such as impact and shearing, which easily introduces metallic impurities, and the oxygen content of the powder is usually higher than 1.0 wt%. Oxidation products can destroy the ordered arrangement of magnetic moments, resulting in a magnetic entropy change decrease of more than 20%. At the same time, the particle size distribution is extremely uneven (high proportion of fine powder and severe agglomeration), affecting the uniformity of subsequent molding; although traditional hydrogen crushing can avoid the introduction of impurities, it has problems such as uneven hydrogen absorption and penetration, incomplete dehydrogenation (residual hydrogen content exceeding 100 ppm), and grain growth caused by high-temperature hydrogen absorption. This not only results in poor powder crushing effect and attenuation of magnetocaloric performance, but also poses safety hazards due to improper hydrogen pressure control, and has low production efficiency, making it difficult to meet the needs of industrial mass production.

[0057] Furthermore, the magnetocaloric properties of low Curie temperature magnetocaloric materials are closely related to their composition design. Existing processes have not achieved precise matching between compositional synergy and preparation techniques, further limiting the full realization of the alloy's magnetocaloric potential. Therefore, developing a low-oxygen, low-residual-hydrogen, uniform-particle-size, crystal-structure-complete, and safe-controllable powder preparation process for low Curie temperature magnetocaloric materials to overcome the core bottlenecks of existing technologies has become an urgent need to promote the industrial application of this type of magnetocaloric material.

[0058] This invention effectively solves the core problems of severe oxidation of alloy powder, excessive residual hydrogen, and uneven particle size distribution in traditional processes by precisely controlling segmented hydrogen absorption and multi-stage dehydrogenation. The oxygen content of the prepared iron-based magnetic alloy powder is controlled below 0.5 wt%, far lower than the above 1.0 wt% of traditional mechanical crushing methods, significantly reducing the damage of oxidation products to the ordered arrangement of magnetic moments; the residual hydrogen content is reduced to below 50 ppm, avoiding the attenuation of magnetic properties caused by hydrogen atoms occupying interstitial spaces in the crystal lattice. The Curie temperature can be adjusted within the range of -50℃ to 50℃, which is close to 100℃, and the saturation magnetic induction intensity is greater than 0.6T at 20℃ below the Curie temperature. This powder material, which combines low Curie temperature and high saturation magnetic induction intensity, can be fabricated into anti-icing magnetic material devices in the form of wires, rings, and cylinders through cold pressing, hot pressing, and isostatic pressing processes, adapting to the anti-icing requirements of AC transmission lines of various voltage levels.

[0059] This invention employs a "segmented pressurization + furnace rotation" hydrogen absorption design, with the pressurization rate controlled within 0.2 MPa / min. Combined with a low-speed furnace rotation of 10-30 rpm, this ensures uniform hydrogen penetration into the alloy, preventing uneven particle breakage due to localized stress concentration. It also effectively prevents equipment impact and leakage risks caused by sudden hydrogen pressure changes, significantly improving process safety. Simultaneously, the hydrogen absorption, crushing, and dehydrogenation processes are completed within the same sealed equipment, eliminating the need to transfer raw materials and reducing oxidation contamination from external air contact, thus simplifying the process flow. A single furnace can process 5-50 kg, with a production efficiency ≥5 kg / h, representing a 3-5 times improvement over traditional ball milling methods and a reduction in production costs of over 40%. This solves the bottlenecks of existing hydrogen crushing processes, which suffer from low output, high cost, and difficulty in large-scale application.

[0060] This invention strictly controls the hydrogen absorption temperature within the range of 150~250℃, avoiding the grain growth problem caused by existing high-temperature (>400℃) hydrogen absorption processes. After hydrogen charging and dehydrogenation, the alloy maintains a complete low Curie temperature magnetic phase structure with a grain size ≤30μm and no obvious phase transformation, crystallization, or lattice distortion. This advantage ensures that the magnetic moment coupling effect of the alloy is not affected by structural damage, and the Curie temperature remains stable in the near-room temperature range. This meets the performance requirements of core applications such as room temperature magnetic refrigeration and anti-icing of power transmission lines, solving the problem of irreversible magnetic property decay caused by structural damage in traditional processes.

[0061] Example 3: Parameter Minimum Dominant Type (Component + Process Lower Limit) 1.1 Composition Design (Atomic Percentage, Total 100, Components at Lower Limits) Chemical formula: Fe 78La3Ni2Si5B2 (a=78, b=3, c=2, d=5, e=2; RE is La as a single rare earth element, TM is Ni as a single transition metal element, both taken from the lower limit of the range). La was compensated at 10wt% during weighing, with an actual composition deviation ≤1.8wt.% and a burn-off rate of 8.2wt.%.

[0062] 1.2 Preparation process (using lower limit parameters to control costs) Step 1: After high-temperature melting, heat treatment is carried out at a temperature of 1000℃ (lower limit) and held for 120 hours (lower limit); the ingot is cut into blocks with a side length of 5mm (lower limit), ultrasonically cleaned with ethanol, and then vacuum dried at 60℃ (lower limit) for 2 hours (lower limit).

[0063] Step 2: Place in the hydrogen decomposition furnace and evacuate to a vacuum level of 5×10. -3 Pa (upper limit), hold for 30 min (lower limit); staged hydrogen charging: ① low temperature permeation: 0.3 MPa (lower limit), 150℃ (lower limit), hold for 2 h (lower limit); ② high pressure crushing: heat up to 1.0 MPa (lower limit), hold for 4 h (lower limit), rotate the furnace body at 10 rpm (lower limit); ③ heat preservation crushing: cool down to 100℃ (lower limit), hold for 2 h (lower limit).

[0064] Step 3: Dehydrogenation treatment: ① Low-temperature dehydrogenation: 1×10 -2 Pa, 100℃ (lower limit), hold for 3 hours (lower limit); ② Deep dehydrogenation: heat to 200℃ (lower limit), vacuum degree 5×10 -3 Pa, heat preservation for 6 hours (lower limit), furnace body rotation at 10 rpm (lower limit); argon gas purging 3 times (lower limit), pressure 0.1 MPa (lower limit), cooling with the furnace; 40 mesh (lower limit) vibrating screen grading.

[0065] 1.3 Performance Test Results Curie temperature -45℃ (close to the lower limit of -50℃), saturation magnetic induction intensity 0.62T (>0.6T) 20℃ below Curie temperature; residual hydrogen 42ppm (≤50ppm); powder particle size 80~200μm, with good particle uniformity.

[0066] Example 4: Parameter maximum value-dominated type (component + process upper limit) 2.1 Composition design (atomic percentage, total 100, composition biased towards the upper limit) Chemical formula: Fe 60 Ce 15 Co 10Si8B7 (a=60, b=15, c=10, d=8, e=7; RE is Ce, a single rare earth element, and TM is Co, a single transition metal element, both taken at the upper limit of the range). Ce is compensated at 10wt% during weighing, with an actual composition deviation ≤2.3wt.% and a burn-off rate of 9.5wt.%.

[0067] 2.2 Preparation process (using upper limit parameters) Step 1: Heat treatment temperature 1500℃ (upper limit), heat treatment for 720h (upper limit); cut the ingot into blocks with a side length of 20mm (upper limit), ultrasonically clean with ethanol, and vacuum dry at 80℃ (upper limit) for 4h (upper limit).

[0068] Step 2: Evacuate to 3×10 -3 Pa, maintain for 60 min (upper limit); staged hydrogen charging: ① low temperature permeation: 1.0 MPa (upper limit), 250℃ (upper limit), hold for 4 h (upper limit); ② high pressure crushing: raise the temperature to 2.5 MPa (upper limit), hold for 8 h (upper limit), and rotate the furnace body at 30 rpm (upper limit); ③ heat preservation crushing: lower the temperature to 150℃ (upper limit), hold for 3 h (upper limit).

[0069] Step 3: Dehydrogenation treatment: ① Low-temperature dehydrogenation: 1×10 -2 Pa, 200℃ (upper limit), hold for 5 hours (upper limit); ② Deep dehydrogenation: heat to 350℃ (upper limit), vacuum degree 2×10 -2 Pa, heat preservation for 10 hours (upper limit), furnace body rotation at 20 rpm (upper limit); argon gas purging 5 times (upper limit), pressure 0.2 MPa (upper limit), furnace cooling; 200 mesh (upper limit) vibrating screen grading.

[0070] 2.3 Performance Test Results The Curie temperature is 48℃ (close to the upper limit of 50℃), and the saturation magnetic induction intensity is 0.75T 20℃ below the Curie temperature; the residual hydrogen is 38ppm, the powder particle size is 10~40μm, and the dispersibility is excellent.

[0071] Example 5: Intermediate parameter value type (for general scenarios, with the best versatility) 3.1 Composition design (atomic percentage, total 100, all taken as median values) Chemical formula: Fe 72 Nd8Mn5Si6B9 (a=72, b=8, c=5, d=6, e=9; RE is Nd as a single rare earth element, TM is Mn as a single transition metal element, both are intermediate values). Nd is compensated at 10wt% during weighing, the actual composition deviation is ≤1.5wt.%, and the burn-off rate is 7.6wt.%.

[0072] 3.2 Preparation process (taking intermediate parameters to balance performance and cost) Step 1: Heat treatment temperature 1250℃ (intermediate value), hold for 420h (intermediate value); cut the ingot into blocks with a side length of 12mm (intermediate value), ultrasonically clean with ethanol, and vacuum dry at 70℃ (intermediate value) for 3h (intermediate value).

[0073] Step 2: Evacuate to 3×10 -3 Pa, maintain for 45 min (intermediate value); staged hydrogen charging: ① low temperature permeation: 0.6 MPa (intermediate value), 200℃ (intermediate value), hold for 3 h (intermediate value); ② high pressure crushing: raise the temperature and pressure to 1.8 MPa (intermediate value), hold for 6 h (intermediate value), and rotate the furnace body at 20 rpm (intermediate value); ③ heat preservation crushing: lower the temperature to 125℃ (intermediate value), hold for 2.5 h (intermediate value).

[0074] Step 3: Dehydrogenation treatment: ① Low-temperature dehydrogenation: 1×10 -2 Pa, 150℃ (intermediate value), hold for 4 hours (intermediate value); ② Deep dehydrogenation: heat up to 280℃ (intermediate value), vacuum degree 3×10 -3 Pa, heat preservation for 8 hours (intermediate value), furnace body rotation at 15 rpm (intermediate value); argon gas purging 4 times (intermediate value), pressure 0.15 MPa (intermediate value), furnace cooling; 120 mesh (intermediate value) vibrating screen grading.

[0075] 3.3 Performance Test Results With a Curie temperature of 5℃ (midpoint between -50℃ and 50℃), and a saturation magnetic induction intensity of 0.83T 20℃ below the Curie temperature; residual hydrogen of 30ppm; and powder particle size of 40~80μm, balancing uniformity and dispersibility. It is compatible with general-purpose magnetocaloric devices in most temperate regions of China, making it the most cost-effective solution.

[0076] Example 6: Optimal parameter type (optimal magnetic performance, adapted to core scenarios) 4.1 Composition design (optimized ratio, total 100, balancing magnetic properties and processability) Based on iterative optimization of Examples 3-5, chemical formula: Fe 75 Pr6Co3Si7B9 (a=75, b=6, c=3, d=7, e=9; RE is Pr, a single rare earth element, and TM is Co, a single transition metal element; the ratio is optimized to improve the saturation magnetic induction). Pr is compensated at 10wt% during weighing, with an actual composition deviation ≤1.2wt.% and a burn-off rate of 6.3wt.% (minimum burn-off).

[0077] 4.2 Preparation process (optimized parameters to maximize magnetic properties) Step 1: Heat treatment temperature 1300℃, hold for 360h (optimized time to promote magnetic phase generation); cut the ingot into 15mm side block raw materials and vacuum dry at 75℃ for 3h.

[0078] Step 2: Evacuate to 2×10 -3 Pa, hold for 50 min; segmented hydrogen charging: ① low temperature permeation: 0.8 MPa, 220℃, hold for 3.5 h (optimized permeation time); ② high pressure crushing: heat up to 2.0 MPa, hold for 7 h, furnace body rotates at 25 rpm; ③ heat preservation crushing: cool down to 130℃, hold for 2.5 h.

[0079] Step 3: Dehydrogenation treatment: ① Low-temperature dehydrogenation: 1×10 -2 ① Pa, 180℃, hold for 4.5h; ② Deep dehydrogenation: heat to 300℃, vacuum degree 2×10 -3 Pa, heat preservation for 9 hours (optimized dehydrogenation time), furnace body rotated at 18 rpm; argon gas purging 4 times, pressure 0.18 MPa, furnace cooled; 150 mesh vibrating screen for grading.

[0080] 4.3 Performance Test Results (Optimal Performance) Curie temperature -10℃ (suitable for core low-temperature magnetocaloric applications); saturation magnetic induction intensity 0.92T (maximum) 20℃ below Curie temperature; residual hydrogen 22ppm (minimum); powder particle size 30~60μm; optimal magnetic properties and dispersibility. Suitable for high-end precision magnetocaloric devices, core performance far exceeds basic requirements.

[0081] Example 7: Multi-component type (complex working conditions, strong anti-interference ability) 5.1 Composition design (multi-component, total 100, improving adaptability to operating conditions) Chemical formula: Fe 70 La4Nd4Cr4Si5B3 (a=70, b=8 (La and Nd ratio of 1:1 in composite rare earth), c=4 (Cr is a single transition metal), d=5, e=3). La and Nd were compensated at 10wt% during weighing, with an actual composition deviation ≤2.0wt.% and a burn-off rate of 8.4wt.%.

[0082] 5.2 Preparation process (adapting to multi-component components and optimizing process consistency) Step 1: Heat treatment temperature 1200℃, hold for 300h; cut the ingot into 10mm side length blocks and vacuum dry at 70℃ for 3h.

[0083] Step 2: Evacuate to 4×10 -3 Pa, hold for 40 min; segmented hydrogen charging: ① low temperature permeation: 0.7 MPa, 210℃, hold for 3 h; ② high pressure crushing: heat up to 1.6 MPa, hold for 5 h, rotate the furnace body at 22 rpm; ③ heat preservation crushing: cool down to 120℃, hold for 2.5 h.

[0084] Step 3: Dehydrogenation treatment: ① Low-temperature dehydrogenation: 1×10 -2 ① Deep dehydrogenation: Heat to 260℃, vacuum degree 3×10⁻⁶ -3 Pa, heat preservation for 7 hours, furnace body rotated at 16 rpm; argon gas purging 4 times, pressure 0.16 MPa, cooled with the furnace; 100 mesh vibrating screen for grading.

[0085] 5.3 Performance Test Results With a Curie temperature of 20℃ (suitable for scenarios with large day-night temperature differences), and a saturation magnetic induction intensity of 0.87T at 20℃ below the Curie temperature; residual hydrogen of 28ppm; powder particle size of 50~90μm; and a balance between mechanical toughness and magnetic properties. Suitable for magnetocaloric devices under complex working conditions, with strong anti-interference capabilities.

[0086] Comparative Example 1: Imbalance in component ratio (excessive RE) 1.1 Ingredient Design Chemical formula: Fe 55 Ce 20 Co5Si8B7 (a=55<60 lower limit, b=20>15 upper limit, sum 100). Ce was compensated at 10wt% during weighing, the actual composition deviation was 4.5wt.%, and the burn-off rate was 11.8wt.%.

[0087] 1.2 Preparation process (same as in Example 5, ensuring uniqueness of variables) 1.3 Performance Defects The Curie temperature is -58℃ (below the lower limit of -50℃, exceeding the range), and the saturation magnetic induction is 0.55T (<0.6T). Residual hydrogen is 45ppm, the powder is prone to agglomeration, and the magnetic phase distribution is uneven. This compositional imbalance leads to magnetic performance failure, making it unsuitable for magnetocaloric applications.

[0088] Comparative Example 2: Lack of hydrogen charging process (no three-stage hydrogen charging) 2.1 Component Design (Same as Example 5, ensuring uniqueness of variables) 2.2 Defects in the preparation process Step 2 omits the three-stage hydrogen charging process, directly introducing 2.0 MPa high-purity hydrogen gas and holding at 200°C for 10 hours. There are no step-by-step pressurization or cooling and holding steps, and the furnace body does not rotate. The remaining processes are the same as in Example 5.

[0089] 2.3 Performance Defects The hydrogen atom penetration is uneven, the powder particle size varies greatly (20~300μm), and the agglomeration is serious; the Curie temperature is 8℃ (the range meets the standard but the performance is unbalanced), the saturation magnetic induction intensity is 0.52T (<0.6T); the residual hydrogen is 92ppm (>50ppm), the dehydrogenation difficulty is significantly increased, and the magnetocaloric performance stability is extremely poor.

[0090] Comparative Example 3: Incomplete dehydrogenation (lacking deep dehydrogenation) 3.1 Component design (same as in Example 5, ensuring uniqueness of variables) 3.2 Defects in the preparation process Step 3 involves only low-temperature dehydrogenation (150°C, 4 hours), omitting the deep dehydrogenation stage. The remaining processes are the same as in Example 5.

[0091] 3.3 Performance Defects The residual hydrogen content is 120 ppm (far exceeding the upper limit of 50 ppm), and the residual hydride causes magnetic phase distortion; the Curie temperature fluctuates to 65℃ (> the upper limit of 50℃, exceeding the range), and the saturation magnetic induction intensity is 0.49T (<0.6T); the material is easily oxidized, and the magnetic properties decay rapidly.

[0092] Comparative Example 4: Rare Earth Without Compensation 4.1 Component Design (Same as Example 5, ensuring uniqueness of variables) 4.2 Defects in the preparation process In Step 1, when weighing the raw materials, Nd was not compensated at 10 wt% and was weighed directly according to the nominal composition. The remaining processes are the same as in Example 5.

[0093] 4.3 Performance Defects The Nd burn-off rate reached 12 wt.%, and the actual RE content was only 6 at.% (lower than the nominal value of 8 at.%); the Curie temperature was -30℃, the saturation magnetic induction intensity was 0.52T (<0.6T); the residual hydrogen was 38 ppm, the magnetic phase volume fraction was less than 60%, and the magnetocaloric efficiency was extremely low.

[0094] Comparative Example 5: The vacuum degree of hydrogen crushing does not meet the standard. 5.1 Component Design (Same as Example 5, ensuring uniqueness of variables) 5.2 Defects in the preparation process Step 2: Evacuate to 1×10⁻⁶ -2 Pa (>5×10) -3 (Pa upper limit), maintain for 45 minutes, with a relatively large amount of residual air in the furnace. The remaining process is the same as in Example 5.

[0095] 5.3 Performance Defects The raw material is severely oxidized, forming Fe3O4 impurity phase; Curie temperature is 12℃, saturation magnetic induction intensity is 0.56T (<0.6T); residual hydrogen is 78ppm (>50ppm); the powder has a dark color and poor mechanical properties, making it unsuitable for use in magnetocaloric devices.

[0096] In summary, Examples 1-7 cover the entire parameter range and fully meet the core indicators such as Curie temperature -50℃ to 50℃, saturation magnetic induction intensity >0.6T, and residual hydrogen ≤50ppm. Comparative Examples 1-5, however, do not meet the five innovative aspects of this invention: component ratio, three-stage hydrogen charging, deep dehydrogenation, rare earth compensation, and vacuum degree. All examples exhibit substandard magnetic properties or process failures. The comparative results clearly demonstrate that the component range and the staged hydrogen charging and gradient dehydrogenation processes defined in this application are necessary conditions for obtaining iron-based magnetocaloric materials with low Curie temperature and high saturation magnetic induction intensity, effectively ensuring the reliability of the material in various magnetocaloric applications.

[0097] Example 8 Based on the same inventive concept, the present invention also provides a de-icing device for power transmission lines, comprising: a ferromagnetic core and a conductive coating covering the outer surface of the ferromagnetic core; the device configuration is any one of an anti-icing self-heating ring, an anti-icing sleeve, pre-twisted wire, or ferromagnetic wire, used for fixed installation on the outside of the power transmission conductor; the ferromagnetic core is made of any of the low Curie temperature iron-based magnetocaloric materials described in Examples 1-7; when the ambient temperature is lower than the Curie temperature of the iron-based magnetocaloric material, the device can generate hysteresis loss and heat generation under the action of the alternating magnetic field of the power transmission conductor, thereby achieving anti-icing and de-icing.

[0098] Example 9 Based on the same inventive concept, the present invention also provides a magnetothermal anti-icing coating, the coating being composed of functional fillers, a film-forming matrix, and additives; the functional filler is any of the low Curie temperature iron-based magnetothermal materials described in Examples 1-7, which are dispersed in the film-forming matrix in powder form; the coating is applied to the surface of a power transmission line or power fitting and cured to form a magnetothermal anti-icing coating; when the ambient temperature is lower than the Curie temperature of the iron-based magnetothermal material, the coating utilizes the alternating magnetic field around the power transmission line to generate heat to achieve active anti-icing and de-icing.

[0099] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of the claims of the present invention.

Claims

1. A low Curie temperature iron-based magnetocaloric material, characterized in that, The chemical composition of the iron-based magnetocaloric material, expressed as an atomic percentage, is Fe. a RE b TM c Si d B e ;in, RE represents any one or more combinations of the rare earth elements lanthanum (La), praseodymium (Pr), neodymium (Nd), and cerium (Ce); TM represents any one or more combinations of transition elements nickel (Ni), cobalt (Co), zirconium (Zr), chromium (Cr), and manganese (Mn); a, b, c, d, e are the atomic percentages of the corresponding elements, and satisfy the following conditions: , , , , , .

2. The low Curie temperature iron-based magnetocaloric material according to claim 1, characterized in that, The material has a saturation magnetic induction intensity greater than 0.6T at 20°C below the Curie temperature.

3. The low Curie temperature iron-based magnetocaloric material according to claim 1, characterized in that, The material retains a single low Curie temperature magnetic phase structure after hydrogen absorption-dehydrogenation treatment, with a grain size of no more than 30 μm.

4. The low Curie temperature iron-based magnetocaloric material according to claim 1, characterized in that, The residual hydrogen content of the material is no more than 50 ppm.

5. The low Curie temperature iron-based magnetocaloric material according to claim 1, characterized in that, The material exists in powder form, with the powder particle size mainly distributed in the range of 50 to 300 μm.

6. A method for preparing a low Curie temperature iron-based magnetocaloric material, characterized in that, Includes the following steps: According to Fe a RE b TM c Si d B e The raw materials are prepared according to the specified component ratio, and then smelted at high temperature and subjected to high temperature homogenization heat treatment to obtain alloy ingots. The alloy ingot is cut into block raw materials, which are then cleaned and vacuum dried to obtain pretreated raw materials. The pretreated raw material is placed into a closed hydrogen crushing equipment and subjected to segmented hydrogen charging treatment with stepped parameter control under vacuum conditions to cause hydrogenation and crushing of the pretreated raw material to obtain hydrogen crushed alloy powder. The hydrogen-rich alloy powder is subjected to dehydrogenation treatment under gradient heating and high vacuum conditions, and after cooling and sieving, the low Curie temperature iron-based magnetocaloric material as described in any one of claims 1-5 is obtained.

7. The preparation method according to claim 6, characterized in that, When preparing raw materials, considering that lanthanum, praseodymium, neodymium, and cerium are easily oxidized and burned, the theoretically calculated amount of each rare earth element is increased by 10wt% as a smelting compensation.

8. The preparation method according to claim 6, characterized in that, The high-temperature homogenization heat treatment is performed at a temperature of 1000~1500℃ and a holding time of 120~720 hours to eliminate as-cast composition segregation and form a stable low Curie temperature phase.

9. The preparation method according to claim 6, characterized in that, The size range of the block raw material is 5~20mm.

10. The preparation method according to claim 6, characterized in that, The cleaning process uses ultrasonic cleaning with ethanol.

11. The preparation method according to claim 6, characterized in that, The vacuum drying temperature is 60~80℃, and the drying time is 2~4 hours.

12. The preparation method according to claim 6, characterized in that, The vacuum condition is a vacuum degree ≤ 5 × 10⁻⁶. -3 Pa, and maintain for 30-60 minutes.

13. The preparation method according to claim 6, characterized in that, The segmented hydrogen charging process includes a low-temperature infiltration stage, a high-pressure crushing stage, and a heat preservation and refining stage performed sequentially. By controlling the hydrogen pressure and temperature in a stepwise manner, uniform infiltration and controllable crushing of hydrogen atoms inside the alloy are achieved.

14. The preparation method according to claim 13, characterized in that, The hydrogen pressure during the low-temperature permeation stage is 0.3~1.0 MPa, the temperature is 150~250℃, and the holding time is 2~4 hours; wherein, the hydrogen purity is ≥99.999%.

15. The preparation method according to claim 13, characterized in that, During the high-pressure crushing stage, hydrogen gas is pressurized to 1.0~2.5MPa at a rate not exceeding 0.2MPa / min, and then kept at this pressure for 4~8 hours to cause the alloy to fracture along the grain boundaries.

16. The preparation method according to claim 13, characterized in that, The closed-loop hydrogen crushing equipment is a closed-loop hydrogen crushing furnace with a furnace rotation speed of 10~30 rpm.

17. The preparation method according to claim 13, characterized in that, The heat preservation and refinement stage includes: after hydrogen absorption, maintaining the hydrogen pressure at 1.0~2.5MPa, reducing the temperature to 100~150℃, and maintaining the temperature for 2~3 hours.

18. The preparation method according to claim 6, characterized in that, The dehydrogenation process includes a low-temperature dehydrogenation stage and a deep dehydrogenation stage; The cryogenic dehydrogenation stage is evacuated to 1×10⁻⁶. -2 Pa, heat to 100~200℃, and keep warm for 3~5 hours; The deep dehydrogenation stage continues to raise the temperature to 200~350℃ and increase the vacuum level to ≤5×10⁻⁶. -3 Pa, keep warm for 6~10 hours.

19. The preparation method according to claim 6, characterized in that, The cooling process includes: after dehydrogenation is completed, stopping heating, introducing argon gas with a purity of ≥99.999% into the furnace 3 to 5 times to purge, maintaining the argon gas pressure at 0.1 to 0.2 MPa, and then cooling the furnace to room temperature.

20. The preparation method according to claim 6, characterized in that, The sieving process includes classifying the alloy powder using a 40-200 mesh vibrating screen.

21. A de-icing agent for power transmission lines, characterized in that, The de-icing material includes a ferromagnetic core and a conductive coating covering the outer surface of the ferromagnetic core. The device is configured as any one of an anti-icing self-heating ring, an anti-icing sleeve, pre-twisted wire, or ferromagnetic wire, and is used for fixed installation on the outside of the transmission line. The ferromagnetic core is made of a low Curie temperature iron-based magnetocaloric material as described in any one of claims 1-5. When the ambient temperature is lower than the Curie temperature of the iron-based magnetocaloric material, the device can generate hysteresis loss and heat generation under the action of the alternating magnetic field of the transmission line, thereby achieving anti-icing and de-icing.

22. A magnetothermal anti-icing coating, characterized in that, The coating is composed of functional fillers, film-forming matrix and additives; the functional filler is any one of the low Curie temperature iron-based magnetocaloric materials according to claims 1-5, which is dispersed in the film-forming matrix in powder form; the coating is applied to the surface of the power transmission line or power fitting and cured to form a magnetocaloric anti-icing coating; when the ambient temperature is lower than the Curie temperature of the iron-based magnetocaloric material, the coating generates heat by utilizing the alternating magnetic field around the power transmission line to achieve active anti-icing and de-icing.