Method for manufacturing magnetic refrigeration material

Abstract

A method for manufacturing a magnetic refrigeration material according to the present invention is characterized in that powder of a magnetic refrigeration material including powder having a particle size of 150-500 μm is electroplated with Cu in a plating solution having a liquid temperature of 30°C or less. According to the present invention, it is possible to provide a method for manufacturing a magnetic refrigeration material with which it is possible to manufacture, with good productivity, a magnetic refrigeration material having little deterioration in characteristics and high corrosion resistance.

Description

Manufacturing method of magnetic refrigeration material

[0001] The present invention relates to a method for producing a magnetic refrigeration material that is free from deterioration of characteristics and has high corrosion resistance.

[0002] Because fluorocarbons are ozone-depleting substances and greenhouse gases, new refrigeration and air-conditioning systems that do not use fluorocarbons are attracting attention for environmental conservation. Although active development of alternative refrigerants to fluorocarbons has been underway, no new refrigerants that are satisfactory in terms of performance, cost, and safety have yet been put into practical use.

[0003] On the other hand, unlike conventional refrigeration and air conditioning systems, magnetic refrigeration systems that utilize the change in entropy (magneto-caloric effect, ΔS) that accompanies an increase in magnetic field have attracted attention. Materials with a large absolute value of ΔS include Mn(As １－ｘ Sb ｘ ) (Patent Document 1) and La(Fe １－ｘ Si ｘ ) １３ H ｚ (Patent Document 2) and the like. In particular, the former has a very large ΔS of -30 J / kgK, making it an excellent magnetic refrigeration material. However, Mn(As １－ｘ Sb ｘ ) is difficult to apply because of its toxicity. １－ｘ Si ｘ ) １３ H ｚ ΔS is -25 J / kgK and Mn(As １－ｘ Sb ｘ ), and its constituent elements are non-toxic and not rare metals, making it the most promising material. The change in ΔS is also related to the magnetic transition temperature (T ｃ ) and a single material can only operate at a certain temperature, so refrigeration systems that require a wide temperature difference cannot be realized. Therefore, methods such as replacing some of the components with other elements are used to change the operating temperature.

[0004] These substances must operate near room temperature (approximately -70 to +70°C). However, unlike conventional magnetic refrigeration, which has been used as a means of generating extremely low temperatures that are difficult to achieve using gas refrigeration, magnetic refrigeration at the above operating temperatures has the problem of a reduced magnetocaloric effect due to non-negligible lattice vibrations. This problem can be solved by utilizing these lattice vibrations as a heat storage effect. The AMR (Active Magnetic Regenerative) cycle, which utilizes these lattice vibrations as a heat storage effect, has been developed, and refrigeration and air conditioning systems that operate near room temperature using the magnetocaloric effect have become a reality.

[0005] In the AMR cycle, the magnetic refrigeration material is filled with a gap (called the bed section) 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 at the low-temperature end, a magnetic field is applied to the bed section using a permanent magnet or other device to reduce the entropy of the magnetic refrigeration material and raise its temperature. The heat transfer medium is then moved from the low-temperature end to the high-temperature end. The heat transfer medium receives heat from the magnetic refrigeration material and moves to the high-temperature end, where it is released using a heat exchanger. The magnetic field from the permanent magnet is then removed, increasing the entropy of the magnetic refrigeration material and lowering its temperature. The heat transfer medium is then moved from the high-temperature end to the low-temperature end. The heat transfer medium is then cooled by the magnetic refrigeration material. The cooled heat transfer medium absorbs heat in the heat exchanger. Repeating this cycle creates a temperature difference between the high-temperature and low-temperature ends, creating a refrigeration cycle.

[0006] The above-mentioned La(Fe １－ｘ Si ｘ ) １３ H ｚ is La(Fe １－ｘ Si ｘ ) １３ In the AMR cycle, the magnetic refrigeration material is in contact with the flowing medium such as water. １－ｘ Si ｘ ) １３ H ｚWhen used as a magnetic refrigeration material, if the powder of the magnetic refrigeration material is filled as it is, its large specific surface area causes deterioration due to corrosion, and the magnetic refrigeration material is pulverized. Then, clogging caused by the pulverization of the magnetic refrigeration material and a decrease in the magnetocaloric effect of the magnetic refrigeration material due to corrosion are serious practical problems. In addition, hydrogen that has penetrated between the lattices is released in a vacuum at 500°C or higher, so La(Fe １－ｘ Si ｘ ) １３ H ｚ In order to prepare a bulk body advantageous for heat exchange, hydrogenated La(Fe １－ｘ Si ｘ ) １３ H ｚ It is difficult to sinter powders of this kind. In this regard, Patent Document 3 describes a method for producing a bulk body having a suitable amount of voids while preventing hydrogen desorption.

[0007] Furthermore, Non-Patent Document 1 reports that electroless Cu plating is performed on a La(Fe, Si)-based alloy to address the decrease in thermal conductivity that occurs when a porous bulk body is fabricated.

[0008] Japanese Patent Application Laid-Open No. 2003-28532 Japanese Patent Application Laid-Open No. 2006-89839 Japanese Patent Application Laid-Open No. 2005-120391

[0009] 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.

[0010] In Patent Document 3, magnetic particles are coated with a metal film of Sn or an Sn alloy, and then heat treated in an inert gas atmosphere at 100°C to 300°C to bond the magnetic particles together to form a bulk body with a predetermined porosity. However, because the magnetic particles are soldered together using a metal film containing Sn to bond them together, there are concerns that the bulk body may have poor thermal conductivity, and if the metal film is a multilayer film, there are also concerns about the productivity of the bulk body.

[0011] In Non-Patent Document 1, electroless Cu plating is performed on La(Fe,Si)-based alloy powder, which is a common plating method for powders that are difficult to conduct electricity through. However, electroless plating has significant disadvantages in terms of cost and productivity, so it cannot be said to be an effective method.

[0012] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a magnetic refrigeration material with high productivity and high corrosion resistance, which exhibits little deterioration in characteristics.

[0013] As a result of extensive research to achieve the above object, the present inventors discovered that by electroplating a magnetic refrigeration material of a specific size under predetermined temperature conditions, it is possible to produce a highly corrosion-resistant magnetic refrigeration material with little deterioration in properties before and after plating with good productivity, and thus completed the present invention. Therefore, the present invention provides the following method for producing a magnetic refrigeration material. 1. A method for producing a magnetic refrigeration material, comprising electroplating a magnetic refrigeration material powder containing powder having a particle size of 150 μm or more and 500 μm or less with Cu in a plating solution having a liquid temperature of 30° C. or less. 2. The magnetic refrigeration material is a magnetic refrigeration material having a general formula: La(Fe １－ｘ Si ｘ ) １３ H ｚ (0.05≦x≦0.2, 0.3≦z≦3). 3. A method for producing a magnetic refrigeration material according to 1 or 2, wherein the plating liquid is a basic plating liquid. 4. A method for producing a magnetic refrigeration material according to 3, wherein the plating liquid is a copper pyrophosphate plating liquid. 5. A method for producing a magnetic refrigeration material according to 1 or 2, wherein an inclined barrel is immersed in the plating liquid and the powder of the magnetic refrigeration material is electroplated with Cu in the inclined barrel. 6. A method for producing a magnetic refrigeration material according to 5, wherein the inclined barrel is a non-perforated barrel with no openings. 7. A method for producing a magnetic refrigeration material according to 1 or 2, wherein the powder of the magnetic refrigeration material is electroplated with Cu together with a medium.

[0014] According to the present invention, a magnetic refrigeration material with little deterioration in characteristics and high corrosion resistance can be produced with good productivity.

[0015] 1A and 1B are images of powder of a magnetic refrigeration material electroplated with Cu obtained in Example 1. 1C and 1D are images of powder of a magnetic refrigeration material electroplated with Cu obtained in Comparative Example 3.

[0016] The method for producing a magnetic refrigeration material of the present invention involves electroplating a powder of magnetic refrigeration material having a particle size of 150 μm to 500 μm with Cu under conditions where the temperature of the plating solution is 30° C. or lower.

[0017] Electroless plating, a chemical substitution plating method that eliminates the need to consider the problem of passing electricity through powder, is often used for plating powders such as magnetic refrigeration materials. However, electroless plating solutions require disposal and replacement after a certain number of uses, resulting in relatively high costs. Furthermore, plating tanks, piping, jigs, and other components are also plated, resulting in significant waste. The process of removing these components takes time, resulting in significant disadvantages in terms of productivity. Therefore, in the present invention, electroplating is used because it allows for continuous use of the plating solution, is easy to manage, and allows plating to be performed in a short time.

[0018] For electroplating, any suitable metal element can be used from the viewpoints of high thermal conductivity and cost. In the present invention, Cu is used. The use of Cu provides corrosion resistance while minimizing property degradation and is cost-effective, making it an important factor for achieving good productivity in the present invention. The metal element used for electroplating does not necessarily have to be Cu alone; for example, a combination of Cu and a metal element other than Cu, such as Ni or Ag, can also be used for electroplating. From the viewpoint of productivity, single-layer plating is preferable to multi-layer plating. The thickness of the plating film is not particularly limited and can be set as appropriate. However, if the plating is too thick, the volume ratio of the magnetic refrigeration material to the powder decreases relatively. Therefore, the plating thickness is preferably 5 μm or less, and more preferably 4 μm or less. On the other hand, if the plating is too thin, corrosion resistance is affected, so a thickness of 3 μm or more is generally preferred.

[0019] The method for manufacturing a magnetic refrigeration material of the present invention uses a magnetic refrigeration material powder containing powder with a particle size of 150 μm or more and 500 μm or less. When powder with a particle size of 150 μm or more is electroplated, the magnetic refrigeration material powder dissolves in the plating solution, preventing deterioration of the properties. Furthermore, dissolution of magnetic refrigeration material components in the plating solution can easily form precipitates in the plating tank, adversely affecting liquid circulation such as filter clogging. Furthermore, ionized Fe, for example, is difficult to remove from the plating solution, necessitating periodic replacement of the plating solution, which increases costs. On the other hand, powder with a particle size of 500 μm or less is prone to cracks remaining, which significantly deteriorates corrosion resistance. The magnetic refrigeration material powder preferably contains powder with a particle size of 200 μm or more and 450 μm or less, and more preferably contains powder with a particle size of 250 μm or more and 400 μm or less. The particle size can be measured by a sieving method, and the value selected by sieving through sieves of each particle size can be used.

[0020] The magnetic refrigeration material powder may contain magnetic refrigeration material powder with a particle size of less than 150 μm or more than 500 μm. However, when powder with a particle size smaller than 150 μm is electroplated, the magnetic refrigeration material powder may dissolve in the plating solution. Furthermore, powder with a particle size larger than 500 μm may not completely split, leaving cracks, which may significantly deteriorate corrosion resistance. Therefore, the higher the proportion of magnetic refrigeration material powder with a particle size of 150 μm to 500 μm in the magnetic refrigeration material powder, the better. The proportion of magnetic refrigeration material powder with a particle size of 150 μm to 500 μm in the magnetic refrigeration material powder is preferably 80% by mass to 100% by mass, more preferably 90% by mass to 100% by mass, even more preferably 95% by mass to 100% by mass, even more preferably 99% by mass to 100% by mass, and even more preferably 100% by mass.

[0021] In the method for producing a magnetic refrigeration material of the present invention, the temperature of the plating solution during electroplating must be 30°C or less. Generally, Cu electroplating is carried out at a solution temperature of 50 to 60°C. However, the temperature of the plating solution for magnetic refrigeration materials, particularly those containing Cu as a base metal, is 50 to 60°C. １－ｘ Si ｘ ) １３ H ｚ In the case of a hydride represented by the formula ｃ It was found that the plating temperature deviates from the target temperature. Furthermore, temperatures higher than 30°C result in numerous plating defects such as surface roughness and smearing, significantly deteriorating corrosion resistance. Furthermore, the magnetic refrigeration material powder is more likely to dissolve in the plating solution, which is undesirable because it can lead to deterioration of characteristics, the formation of precipitates, and the need to replace the plating solution. The plating solution temperature is preferably between 15°C and 25°C. There are no particular restrictions on how the solution temperature should be controlled, and it can be controlled and adjusted as appropriate using commonly used methods.

[0022] Other conditions for the electric Cu plating can be adjusted as appropriate to obtain the desired plating thickness. Although not particularly limited, the voltage during plating is preferably 3 V or higher, more preferably 10 V or higher, from the viewpoint of improving corrosion resistance. The plating time can be set in consideration of the balance with the applied voltage, and can be, for example, 60 minutes or longer.

[0023] The magnetic refrigeration material to be electroplated in the present invention is not particularly limited, but may be a material having the general formula: La(Fe １－ｘ Si ｘ ) １３ H ｚ (0.05≦x≦0.2, 0.3≦z≦3, preferably 0.08≦x≦0.14, 1.2≦z≦1.6). １－ｘ Si ｘ ) １３ H ｚ The compound represented by the formula: １３The magnetic refrigeration material has a crystalline structure of the type described above. This is because the present invention can reduce hydrogen desorption from the magnetic refrigeration material, suppress deterioration of properties, and improve corrosion resistance. La in the above general formula can be partially substituted with a rare earth element, and specifically, preferably one or more rare earth elements selected from Ce, Pr, and Nd. The substitution ratio is not particularly limited, but is preferably 0 atomic % to 50 atomic % of La, and more preferably 20 atomic % to 40 atomic %. A method for changing ΔS and transition temperature by partially substituting La with other rare earth elements is known, and high properties can be obtained by partial substitution with Ce, Pr, or Nd, in particular. Therefore, it is desirable to substitute an appropriate amount depending on the required magnetic properties. However, as the substitution ratio increases, deterioration of magnetic properties, including a decrease in ΔS, occurs, so it is preferable to keep it within the above range. Furthermore, the Fe in the general formula above can be partially substituted with a transition metal element, 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 is preferably 0 atomic % or more and 0.03 atomic % or less of Fe, and more preferably 0.005 atomic % or more and 0.025 atomic % or less. These additional elements can suitably control the magnetic transition temperature of the magnetic refrigeration material.

[0024] The plating solution is preferably basic. In particular, the magnetic refrigeration material is preferably a material having a general formula: La(Fe １－ｘ Si ｘ ) １３ H ｚWhen the plating solution is composed of a compound represented by the formula (I), if the plating solution is acidic, the elution of the Fe component is likely to occur, but if the plating solution is basic, it is suitable as it has low corrosion resistance to magnetic refrigeration materials. While there are no particular limitations on this plating solution, a copper pyrophosphate plating solution is preferred. Copper pyrophosphate plating solutions are weakly basic complex salt baths that are low in corrosion resistance to the substrate, and at the same time, they have excellent uniform electrodeposition (throwing power) even for materials with small particle sizes, such as those used in the present invention, low toxicity, and good workability. Furthermore, the smooth surface after plating makes them easy to machine, and they are suitable for thick plating on materials containing Fe, and they also have the advantages of good gloss.

[0025] The electroplating equipment used in the present invention is not particularly limited, and a conventional electroplating equipment can be used. A typical configuration includes a plating tank, a filter, a heater for adjusting the liquid temperature, a stirrer, a rectifier, a barrel, electrodes, and the like. It is preferable to use an inclined barrel in order to achieve uniform electroplating of the powder. Furthermore, since the present invention electroplates powder with a small average particle size, a barrel without holes can be used instead of a commonly used barrel with openings such as a mesh, thereby achieving good electroplating with reduced powder loss.

[0026] In the above-mentioned electroplating, it is preferable to place both the magnetic refrigeration material powder and media in the barrel and perform electroplating. When electroplating with media is performed, the current is stabilized compared to electroplating without media, preventing the powder from adhering to the electrode, preventing variations and aggregation, and achieving a uniform plating thickness. There are no particular restrictions on the material or size of the media used, and commercially available media can be used. Furthermore, effective electroplating can be achieved by using media in a ratio of approximately 20% to 40% by volume relative to the volume of the barrel.

[0027] According to the above-described method, it is possible to produce a magnetic refrigeration material with good corrosion resistance and with good productivity, which is hardly subject to deterioration in characteristics, and which can be suitably used in magnetic refrigeration systems such as AMR cycles.

[0028] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0029] [Example 1, Comparative Examples 1 to 3] La metal, Si metal, and electrolytic iron were weighed to obtain a predetermined composition, and the materials were melted in an Ar gas atmosphere in a high-frequency melting furnace by heating to 1500°C, and then cooled by a strip casting method to produce an alloy ribbon having an average thickness of about 300 μm. The alloy ribbon was subjected to a homogenization heat treatment and a hydrogenation heat treatment under predetermined conditions to obtain La(Fe １－ｘ Si ｘ ) １３ H ｚ A powder of a magnetic refrigeration material represented by the formula (x = 0.11, z = 1.5) was obtained. The obtained powder was classified by sieving to obtain the particle sizes shown in Table 1. The composition of the magnetic refrigeration material was analyzed using a high-resolution ICP optical emission spectrometer (manufactured by Hitachi High-Tech Corporation, product name "SPS3500DD").

[0030] First, the magnetic refrigeration material powder was subjected to heat treatment. ｃ The change in T ｃ The change in mT characteristic was measured using the VSM unit of a small refrigerant-free physical property measuring device (manufactured by Quantum Design Co., Ltd., product name "VersaLab"), and the dm / dTT characteristic was calculated by temperature differentiation from the obtained mT characteristic, and the temperature at which the peak was obtained was defined as T. ｐｅａｋ As a result, when the heat treatment temperature was 50°C or higher, T ｐｅａｋ It became clear that the temperature gradually decreased and the absorbed hydrogen was released at 50°C or higher.

[0031] The obtained powder of magnetic refrigeration material was subjected to Cu electroplating under the conditions shown in Table 1. The Cu electroplating was carried out using an electroplating device for small-scale production (inclined barrel precision filtration set, manufactured by Yamamoto Plating Test Instruments Co., Ltd.). The inclined barrel used was a barrel without holes. 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), and the P ratio (P ２ O ７ ４－ / Cu weight ratio) was 6.9, pH was 9.6, and stirring was by air stirring.

[0032]

[0033] The powder of the Cu electroplated magnetic refrigeration material was observed under a microscope. Also, 0.1 g of each was scattered on filter paper moistened with pure water, and after 24 hours, the rusting state was observed. The results are shown in Table 2. The weight change before and after Cu electroplating is also shown.

[0034]

[0035] In Example 1, a well-plated magnetic refrigeration material powder was obtained. On the other hand, in Comparative Example 1, although the appearance of the plating film appeared good, the weight decreased before and after plating, and it was found that more components of the magnetic refrigeration material than plated had eluted into the plating solution. In Comparative Example 2, numerous rusting was observed from cracks on the particle surface, and if this were used as a magnetic refrigeration material, there would be problems with corrosion resistance. In Comparative Example 3, numerous plating defects were observed, and components of the magnetic refrigeration material were also observed eluting into the plating solution.

[0036] When ΔS was measured for Example 1 and Comparative Examples 1 to 3, it was found that in Example 1, the decrease was equivalent to the plating volume, whereas in Comparative Examples 1 to 3, the decrease was greater than the equivalent to the plating volume, resulting in significant deterioration of characteristics.

[0037] 1 and 2 show images of the Cu-electroplated magnetic refrigeration material powder obtained in Example 1 and Comparative Example 3, respectively. In Example 1, no unplated particles or deposits were found, indicating a glossy, well-plated state. In Comparative Example 3, on the other hand, the surface was dull and rough, and unplated particles and deposits were observed.

Claims

1. A method for manufacturing a magnetic refrigeration material, comprising electroplating a powder of a magnetic refrigeration material containing a powder having a particle size of 150 μm or more and 500 μm or less in a plating solution having a liquid temperature of 30°C or less with electrical Cu plating.

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

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

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

6. The method for manufacturing a magnetic refrigeration material according to claim 5, wherein the inclined barrel is a barrel without holes and without openings.

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

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