Method for manufacturing magnetic refrigeration material

Abstract

The manufacturing method of the magnetic refrigeration material of the present application is characterized in that a magnetic refrigeration material powder containing a powder having a particle size of 150 μ m or more and 500 μ m or less is electroplated with Cu in a plating solution having a liquid temperature of 30°C or lower. According to the present application, a manufacturing method of a magnetic refrigeration material can be provided, which can manufacture a magnetic refrigeration material having less deterioration in characteristics and high corrosion resistance with good productivity.

Description

Technical Field

[0001] This invention relates to a method for manufacturing magnetic refrigeration materials that exhibit no property degradation and have high corrosion resistance. Background Technology

[0002] Because Freon-based refrigerants are ozone-depleting substances and contributors to global warming, new refrigeration and air conditioning systems that do not use Freon are attracting attention in order to protect the environment. Although the development of refrigerants to replace Freon is actively underway, new refrigerants that are satisfactory in terms of performance, cost, and safety have not yet been commercialized.

[0003] On the other hand, unlike traditional refrigeration and air conditioning systems, magnetic refrigeration systems that utilize the change in entropy with increasing magnetic field (magnetothermal effect, ΔS) have attracted attention. Among materials with large absolute values ​​of ΔS, Mn(As) can be cited as an example. 1-x Sb x (Patent Document 1) or La(Fe) 1-x Si x ) 13 H z (Patent Document 2), etc. In particular, the former has a very large ΔS of -30 J / kgK, making it an excellent magnetic refrigeration material. However, due to the... 1-x Sb x The As component of La(Fe) exhibits toxicity, making its application practically difficult. 1- x Si x ) 13 H z Second only to Mn(As) 1-x Sb x With a ΔS value as high as -25 J / kg K, and its constituent elements not exhibiting toxicity and not being rare metals, it is considered the most promising material. Furthermore, the variation in ΔS is limited to the magnetic transition temperature (T0) of the material exhibiting the magnetocaloric effect. c In the vicinity of a certain temperature, a material can only operate at a specific temperature point, thus preventing the development of refrigeration systems that require a substantially wide temperature difference. Therefore, to change the operating temperature, a method is used to replace some components with other elements.

[0004] These materials require operation near room temperature (approximately -70 to +70°C). However, unlike conventional magnetic refrigeration, which uses extremely low temperatures that are difficult to generate in gas refrigeration, magnetic refrigeration at the aforementioned operating temperature suffers from a reduction in the magnetocaloric effect due to the inability to ignore lattice vibrations. This problem can be solved by utilizing these lattice vibrations as a heat storage effect. Furthermore, an AMR (Active Magnetic Regenerative) cycle utilizing these lattice vibrations as a heat storage effect has been developed, making it possible to implement a refrigeration and air conditioning system near room temperature that utilizes the magnetocaloric effect.

[0005] In an AMR cycle, a magnetic refrigerant (referred to as a bed section) is filled with a gap through which a heat transfer medium, such as water, can pass. The heat transfer medium can move between the high-temperature and low-temperature ends through the gap. With the heat transfer medium present at the low-temperature end, a magnetic field is applied to the bed section using a permanent magnet or similar device to reduce the entropy of the magnetic refrigerant, thereby increasing its temperature. The heat transfer medium then moves from the low-temperature end to the high-temperature end. At this point, the heat transfer medium receives heat from the magnetic refrigerant, moves to the high-temperature end, and releases heat at the high-temperature end using a heat exchanger. Next, the magnetic field of the permanent magnet is removed, causing the entropy of the magnetic refrigerant to increase and its temperature to decrease. The heat transfer medium then moves from the high-temperature end to the low-temperature end. At this point, the heat transfer medium is cooled by the magnetic refrigerant. The cooled heat transfer medium absorbs heat in the heat exchanger. By repeating this cycle, a temperature difference is created between the high-temperature and low-temperature ends, thus establishing a refrigeration cycle.

[0006] The La(Fe 1-x Si x ) 13 H z By directing La(Fe) 1-x Si x ) 13 It is obtained by introducing hydrogen into the interlattice of the crystal. In the AMR cycle, the magnetic refrigeration material is in continuous contact with the medium, such as water. Therefore, when using La(Fe) 1-x Si x )13H z When used as a magnetic refrigeration material, directly filling the powder with the magnetic refrigeration material results in corrosion-induced degradation due to its large specific surface area, leading to micronization of the magnetic refrigeration material. Furthermore, the blockage caused by micronization or the reduction in the magnetocaloric effect due to corrosion pose significant practical problems. Additionally, since hydrogen intruding into the intercrystalline lattice is released in a vacuum above 500°C, it is difficult to produce materials favorable for La(Fe) 1-x Si x )13H z The heat exchanged bulk material was sintered and hydrogenated La(Fe) 1-x Si x) 13 H z The powder. In this regard, a method for manufacturing a blocky body with appropriate porosity while preventing hydrogen removal is described in Patent Document No. 3.

[0007] In addition, in Non-Patent Literature 1, in order to address the decrease in thermal conductivity when making porous bulk materials, an electroless Cu plating process was reported on La(Fe,Si)-based alloys.

[0008] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2003-28532, Patent Document 2: Japanese Patent Application Publication No. 2006-89839, Patent document 3: Japanese Patent Application Publication No. 2005-120391.

[0009] Non-patent literature Non-patent literature 1: Julia Lyubina, Ullrich Hannemann, Lesley F. Cohen, and Mary P. Ryan, “Novel La(Fe,Si)13 / Cu Composites for Magnetic Cooling”, Adv. Energy Mater. 2012, 2, 1323-1327. Summary of the Invention

[0010] The problem that the invention aims to solve In Patent Document 3, a Sn or Sn alloy-based metal film is coated around magnetic particles, and then heat-treated at 100°C to 300°C in an inert gas atmosphere to bond the magnetic particles together, forming a bulk body with a specified porosity. However, since the Sn-containing metal film is used for brazing to bond the individual magnetic particles, there are concerns that the bulk body may have poor thermal conductivity. Furthermore, there are concerns about the manufacturability of the bulk body when the metal film is made into a multilayer film.

[0011] In Non-Patent Literature 1, electroless Cu plating is performed on La(Fe,Si)-based alloy powder as a plating method for powders that are difficult to conduct electricity, which is a commonly practiced method. However, electroless plating has significant disadvantages in terms of cost and productivity, and therefore can hardly be considered an effective method.

[0012] The present invention was made in view of the above circumstances, and its object is to provide a method for producing magnetic refrigeration materials with good manufacturability, minimal degradation, and high corrosion resistance.

[0013] Methods for solving problems In order to achieve the above objectives, the inventors conducted in-depth research and found that by electroplating a magnetic refrigeration material of a specific size under specified temperature conditions, it is possible to manufacture a magnetic refrigeration material with minimal degradation of properties before and after plating and high corrosion resistance, thus completing the present invention.

[0014] Therefore, the present invention provides a method for manufacturing the following magnetic refrigeration material.

[0015] 1. A method for manufacturing a magnetic refrigeration material, characterized in that, in a plating bath with a liquid temperature below 30°C, a particle size of 150... m m or more and 500 m Electroplating Cu onto magnetic refrigeration material powder with a particle size of less than μm.

[0016] 2. The method for manufacturing the magnetic refrigeration material according to claim 1, wherein the magnetic refrigeration material is composed of the general formula: La(Fe 1-x Si x ) 13 H z The compound is represented by the general formula, in which 0.05 ≤ x ≤ 0.2 and 0.3 ≤ z ≤ 3.

[0017] 3. The method for manufacturing the magnetic cooling material according to 1 or 2, wherein the plating solution is an alkaline plating solution.

[0018] 4. The method for manufacturing the magnetic refrigeration material according to 3, wherein the plating solution is a copper pyrophosphate plating solution.

[0019] 5. The method for manufacturing the magnetic refrigeration material according to 1 or 2, wherein an inclined barrel is immersed in the plating solution, and the magnetic refrigeration material powder is electroplated with Cu in the inclined barrel.

[0020] 6. The method for manufacturing the magnetic cooling material according to 5, wherein the tilting barrel is a non-porous barrel without mesh.

[0021] 7. The method for manufacturing the magnetic refrigeration material according to 1 or 2, wherein the magnetic refrigeration material powder is electroplated with Cu together with a medium.

[0022] The effects of the invention According to the present invention, a magnetic refrigeration material with good manufacturability, minimal degradation of manufacturing characteristics, and high corrosion resistance can be produced. Attached Figure Description

[0023] [ Figure 1 Image of the magnetic refrigeration material powder that has been electroplated with Cu obtained in Example 1.

[0024] [ Figure 2Image of the magnetic refrigeration material powder that has been electroplated with Cu obtained in Comparative Example 3. Detailed Implementation

[0025] The method for manufacturing the magnetic refrigeration material of the present invention involves processing a 150-particle-size material at a solution temperature below 30°C. m m or more and 500 m A method for electroplating Cu onto magnetic refrigeration material powder with a particle size of less than μm.

[0026] For plating processes targeting powders such as magnetic refrigeration materials, electroless plating, which is based on chemical displacement and does not consider the electrical conduction of the powder, is commonly used. However, electroless plating solutions require disposal and replacement after a certain number of uses, resulting in high costs. Furthermore, since the plating tank, piping, and fixtures are also plated, there is significant wear and tear, and the stripping process is time-consuming, leading to substantial production drawbacks. Therefore, in this invention, electroplating is employed because the plating solution can be reused, liquid management is easy, and plating can be performed in a short time.

[0027] Regarding electroplating, suitable metallic elements can be used from the perspectives of thermal conductivity and cost, but Cu is used in this invention. Using Cu imparts corrosion resistance with minimal property degradation and is also cost-effective, thus becoming an important factor in achieving good manufacturability for this invention. It should be noted that the metallic element used for electroplating does not need to be just Cu; for example, metallic elements other than Cu, such as Ni or Ag, can be combined with Cu for electroplating. From a manufacturability point of view, single-layer plating is preferred over multi-layer plating. There are no particular limitations on the thickness of the plating film, and it can be set appropriately. However, if the plating layer is too thick, the volume ratio of the magnetic refrigeration material to the powder decreases relatively; therefore, the preferred plating thickness is 5 mm. m For m or less, 4 is more preferred. m Below m. On the other hand, if the coating is too thin, it will affect corrosion resistance, so a thickness of 3 is generally preferred. m m or more.

[0028] In the manufacturing method of the magnetic refrigeration material of the present invention, a particle size of 150 is used. m m or more and 500 m Magnetic refrigeration material powder with a particle size of less than μm. For a particle size of 150 μm... mWhen electroplating powders with a particle size of 500 μm or larger, the magnetic refrigeration material powder dissolves in the plating solution, which can suppress the deterioration of its properties. It should be noted that because the components of the magnetic refrigeration material dissolve in the plating solution, precipitates are easily formed in the plating tank. This not only adversely affects liquid circulation, such as filter clogging, but also makes it difficult to remove elements such as ionized Fe from the plating solution, requiring regular replacement of the plating solution, thus increasing costs. On the other hand, when the particle size is 500 μm... m In the case of powders with a particle size of less than μm, residual cracks caused by incomplete particle breakage can be suppressed, which could lead to a significant deterioration in corrosion resistance. The magnetic refrigeration material powder preferably contains 200 μm of fine particles. m m or more and 450 m Powder with a particle size of less than μm, more preferably containing 250 μm. m m or more and 400 m Powders with a particle size of less than μm. It should be noted that particle size can be determined by sieving, using values ​​obtained by sieving with sieves of various particle sizes.

[0029] Magnetic refrigeration material powder may contain particles smaller than 150. m m or more than 500 m magnetic refrigeration material powder with a particle size of m. However, for particles smaller than 150... m If powder with a particle size of m is electroplated, the magnetic refrigeration material powder may dissolve in the plating solution. Additionally, for particles larger than 500 μm... m In the case of powder with a particle size of 150 μm, incompletely broken powder particles are prone to residual cracks, which may significantly degrade corrosion resistance. Therefore, the particle size of magnetic refrigeration material powder is 150 μm. m m or more and 500 m The higher the proportion of magnetic refrigeration material powder with a particle size below 150 μm, the better. m m or more and 500 m The proportion of magnetic refrigeration material powder with a mass of less than m is preferably 80% or more and 100% or less by mass, more preferably 90% or more and 100% or less by mass, further preferably 95% or more and 100% or less by mass, even more preferably 99% or more and 100% or less by mass, and even more preferably 100% by mass.

[0030] In the manufacturing method of the magnetic refrigeration material of the present invention, it is necessary to keep the temperature of the plating solution during electroplating below 30°C. Generally, Cu is electroplated at a liquid temperature of 50-60°C, but in magnetic refrigeration materials, especially those using the general formula: La(Fe 1- x Si x ) 13 H z In the case of the hydride, it is known that even at such temperatures, hydrogen begins to gradually detach, Tc The temperature will deviate from the target temperature. Furthermore, at temperatures above 30°C, numerous plating defects such as surface roughness or bulges will occur, significantly worsening corrosion resistance. Additionally, since the magnetic refrigeration material powder easily dissolves in the plating solution, it may cause property degradation or precipitation, requiring replacement of the plating solution, making it undesirable. The preferred plating solution temperature is above 15°C and below 25°C. It should be noted that there are no particular restrictions on solution temperature management; appropriate management and adjustment using generally accepted methods are sufficient.

[0031] Other conditions for Cu electroplating can be adjusted appropriately to obtain the desired coating thickness. While there are no particular limitations, from the viewpoint of improving corrosion resistance, the plating voltage is preferably 3V or higher, more preferably 10V or higher. The plating time can be set considering the balance with the voltage of the application, for example, it can be set to 60 minutes or higher.

[0032] The magnetic cooling material used in electroplating in this invention is not particularly limited, but is preferably of the general formula: La(Fe 1-x Si x ) 13 H z The compound is composed of compounds represented by (0.05 ≤ x ≤ 0.2, 0.3 ≤ z ≤ 3, preferably 0.08 ≤ x ≤ 0.14, 1.2 ≤ z ≤ 1.6). La(Fe 1-x Si x ) 13 H z The compound shown possesses NaZn 13The crystal structure is of the type described above. This is because, in this invention, the removal of hydrogen from the magnetic refrigeration material can be reduced, thereby suppressing property degradation and improving corrosion resistance. A portion of La in the above general formula can be replaced by rare earth elements, specifically, preferably one or more rare earth elements selected from Ce, Pr, and Nd. As for the replacement ratio, there is no particular limitation, but it is preferably 0 atomic% or more and 50 atomic% or less of La, more preferably 20 atomic% or more and 40 atomic% or less. It is known that methods can be used to change ΔS or transition temperature by replacing a portion of La with other rare earth elements, and high properties can be obtained, especially by replacing a portion with Ce, Pr, and Nd. Therefore, it is preferable to make appropriate replacements according to the magnetic properties required. However, if the replacement ratio becomes too large, magnetic property degradation, including a decrease in ΔS, will occur. Therefore, it is preferable to set it within the above range. In addition, a portion of Fe in the above general formula can be replaced by transition metal elements, specifically, one or more elements selected from Co, Mn, Ni, Nb, W, Ta, Cr, Cu, and Ag, preferably including Co and Mn. The substitution ratio is not particularly limited, but preferably 0 atomic% or more and 0.03 atomic% or less of Fe, more preferably 0.005 atomic% or more and 0.025 atomic% or less. The magnetic transition temperature of the magnetic refrigeration material can be appropriately controlled by adding these elements.

[0033] The preferred liquid nature of the above plating solution is alkaline. This is especially true when the magnetic refrigeration material is composed of the general formula: La(Fe...) 1-x Si x ) 13 H z When the compound composition is as indicated, if the plating bath is acidic, the Fe component is easily dissolved; however, if it is alkaline, it has low corrosivity to the magnetic refrigeration material, which is suitable. The plating bath is not particularly limited, but a copper pyrophosphate plating bath is preferred. Copper pyrophosphate plating bath is a weakly alkaline complex salt bath, which has low corrosivity to the plated object. Furthermore, even with small-particle-size materials as used in this invention, it exhibits excellent uniform electrodeposition (coverage), low toxicity, and good operability. In addition, because the plated surface is smooth, it is easy to machine, and it has the advantages of being suitable for thickening coatings on Fe-containing materials and having good gloss.

[0034] The electroplating apparatus used in this invention is not particularly limited, and conventional electroplating apparatus can be used. As a general structure, examples include a plating tank, a filter, a heater for regulating the liquid temperature, a stirrer, a rectifier, a container, electrodes, etc. From the viewpoint of uniformly electroplating the powder, a tilted container is preferred. Furthermore, since this invention electroplats powder with a small average particle size, a non-porous container is used instead of a conventionally used container with mesh openings, thereby reducing powder loss and achieving good electroplating.

[0035] In the above electroplating process, it is preferable to contain the magnetic cooling material powder and the dielectric material together in a container for electroplating. When electroplating with a dielectric material is used, compared to electroplating without a dielectric material, the current is stable, preventing the powder from adhering to the electrodes, thus preventing unevenness or agglomeration and resulting in a coating of uniform thickness. There are no particular limitations on the material or size of the dielectric material used; commercially available dielectric materials can be used. Furthermore, electroplating can be effectively performed by using a dielectric material at a ratio of approximately 20% to 40% by volume relative to the container volume.

[0036] According to the above method, magnetic refrigeration materials with good industrial production properties and almost no property degradation and good corrosion resistance can be manufactured, and can be used as magnetic refrigeration materials suitable for magnetic refrigeration systems such as AMR cycles. Example

[0037] The following examples and comparative examples illustrate the invention in more detail, but the invention is not limited to the following examples.

[0038] [Example 1, Comparative Examples 1-3] La metal, Si metal, and electrolytic iron were weighed according to the specified composition, and melted in a high-frequency furnace at 1500°C in an Ar gas atmosphere. The mixture was then cooled by strip casting to produce a film with an average thickness of approximately 300 mm. m A thin alloy ribbon of m was subjected to homogenization heat treatment and hydrogenation heat treatment under specified conditions to obtain a La(Fe) alloy ribbon. 1-x Si x ) 13 H z The magnetic refrigeration material powder (x=0.11, z=1.5) was classified by sieving to obtain the particle sizes shown in Table 1. It should be noted that the composition of the magnetic refrigeration material was analyzed using a high-resolution ICP-ELISA spectrophotometer (manufactured by Hitachi High-Tech Corporation, trade name "SPS3500DD").

[0039] First, for magnetic refrigeration material powder, the temperature T caused by heat treatment is measured in advance. c The changes. It should be noted that T c The mT characteristic was measured using a VSM unit of a small, refrigerant-free physical property measurement device (manufactured by QuantumDesign Inc., trade name "VersaLab"). Based on the obtained mT characteristic, the dm / dT-T characteristic was obtained by performing temperature differentiation, and the temperature at which its peak value was obtained was taken as T. 峰 The results show that if the heat treatment temperature is above 50℃, then T 峰 The temperature gradually decreases, and the absorbed hydrogen is released when the temperature is above 50°C.

[0040] The obtained magnetic refrigeration material powder was electroplated with Cu under the conditions shown in Table 1. Cu electroplating was carried out using a small-scale production electroplating apparatus (tilted barrel precision filter kit, manufactured by Yamamoto Gold Plating Test Machine Co., Ltd.). It should be noted that a non-porous barrel without mesh was used for the tilting barrel. The plating bath contained copper pyrophosphate (concentration: 84.6 g / L), potassium pyrophosphate (concentration: 305.8 g / L), and potassium citrate (concentration: 52.3 g / L), with a P-to-P ratio (P₂O₇). 4- The Cu / Cu weight ratio was 6.9, the pH was 9.6, and the agitation was performed using air agitation.

[0041] [Table 1] Table 1 The magnetic refrigeration material powder after Cu electroplating was observed under a microscope. Additionally, 0.1g of each powder was sprinkled onto filter paper moistened with pure water and left for 24 hours; the rusting was then observed. The results are shown in Table 2. The weight changes before and after Cu electroplating are also presented.

[0042] [Table 2] Table 2 Example 1 yielded a well-coated magnetic refrigeration material powder. On the other hand, in Comparative Example 1, although the coating appeared good, the weight decreased before and after coating, indicating that the components of the magnetic refrigeration material dissolved more into the plating solution than were coated. In Comparative Example 2, extensive rust was observed from cracks on the particle surface, suggesting potential corrosion resistance issues if used as a magnetic refrigeration material. In Comparative Example 3, numerous coating defects were found, and it was also discovered that components of the magnetic refrigeration material dissolved into the plating solution.

[0043] The ΔS values ​​of Examples 1 and Comparative Examples 1 to 3 were measured. The results showed that, compared to the reduction in amount equivalent to the coating volume in Example 1, the reduction in Comparative Examples 1 to 3 was more than the amount equivalent to the coating volume, indicating significant degradation of characteristics.

[0044] In addition, Figure 1 and 2 Images of the electroplated Cu magnetic refrigeration material powders obtained in Example 1 and Comparative Example 3 are shown respectively. In Example 1, no unplated particles or bulges were found, indicating a glossy and well-plated state. On the other hand, the surface of Comparative Example 3 was dull and rough, confirming the presence of unplated particles or bulges.

Claims

1. A method for manufacturing magnetic refrigeration materials, characterized in that, In a plating bath with a liquid temperature below 30°C, for particles with a size of 150... μ m or more and 500 μ Electroplating Cu onto magnetic refrigeration material powder with a particle size of less than μm.

2. The method for manufacturing the magnetic refrigeration material according to claim 1, wherein, The magnetic refrigeration material is composed of the general formula: La(Fe 1-x Si x ) 13 H z The compound is represented by the general formula, in which 0.05 ≤ x ≤ 0.2 and 0.3 ≤ z ≤ 3.

3. The method for manufacturing the magnetic refrigeration material according to claim 1 or 2, wherein, The plating solution is an alkaline plating solution.

4. The method for manufacturing the magnetic refrigeration material according to claim 3, wherein, The plating solution is a copper pyrophosphate plating solution.

5. The method for manufacturing the magnetic refrigeration material according to claim 1 or 2, wherein, The tilting bucket is immersed in the plating solution, and the magnetic refrigeration material powder is electroplated with Cu in the tilting bucket.

6. The method for manufacturing the magnetic refrigeration material according to claim 5, wherein, The tilted bucket is a non-porous bucket without mesh.

7. The method for manufacturing the magnetic refrigeration material according to claim 1 or 2, wherein, The magnetic refrigeration material powder is electroplated with Cu together with the medium.

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