Molded body, fired body, and manufacturing method thereof

Abstract

The present invention provides: a noble metal alloy molded body which has both high crystallinity and excellent composition uniformity; and a sintered body. The molded body is formed of an alloy powder and a resin. The alloy powder is a noble metal alloy powder which is formed of an alloy of five or more noble metal elements, and has an average particle diameter of 0.1 µm to 100 µm and a crystallite size of 60 nm or more. With respect to the X-ray diffraction spectrum of the alloy powder, one peak is found within the diffraction angle 2θ range of 38° to 44°.

Description

[Technical Field]

[0001] The present invention relates to a molded body, a fired body, and methods for producing the same. [Background technology]

[0002] Powder metallurgy is a technology in which raw metal powder is mixed with a binder, if necessary, and then molded and sintered to obtain a metal product (sintered body). This powder metallurgy technology allows for the production of products of various shapes by using molds shaped to suit the product. Powder metallurgy also allows for the production of products made from alloys of multiple metal powders by mixing them together. In this case, by adjusting the blending ratio of each metal powder, it is possible to change the alloy composition of the resulting product and the various physical properties that are determined by the alloy composition. Due to these advantages, powder metallurgy is used to manufacture a variety of products.

[0003] Powder metallurgy is primarily used to produce products made from Fe, Cu, Ni, Cr, W, Mo, Ti, etc., but it has also been proposed to be used to produce precious metal alloy products.

[0004] For example, Patent Document 1 proposes producing a sintered precious metal alloy consisting of elements such as Au, Ag, and Cu by mixing multiple raw material powders consisting of different components, and then molding and sintering the mixture.

[0005] Here, examples of noble metal elements include gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and osmium (Os). Although these elements belong to the same group known as noble metal elements, their actual physical and chemical properties differ. It is also known that the properties of noble metal alloys made from these noble metal elements change significantly depending on their composition. Therefore, it is expected that powder metallurgy technology can be used to manufacture sintered bodies made from various noble metal alloys.

[0006] In recent years, research has also been conducted on high-entropy alloys made from precious metals. While definitions vary, in the narrow sense, high-entropy alloys refer to alloys containing five or more elements in roughly equiatomic amounts, forming a single-phase solid solution. These alloys have attracted attention because they exhibit properties significantly different from those of conventional alloys. While high-entropy alloys typically contain base metal elements such as Cr, Mn, Fe, Co, and Ni, high-entropy alloys made solely from precious metal elements have also been synthesized.

[0007] For example, in Non-Patent Document 1, a powder of a high-entropy alloy consisting of eight kinds of precious metal elements is produced by a wet reduction method (also called a liquid-phase reduction method or a chemical reduction method).Non-Patent Document 1 also reveals that the powder exhibits extremely excellent catalytic activity for the hydrogen generation reaction.

[0008] Thus, multi-component precious metal alloys containing a variety of precious metal elements are attracting attention. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 06-057303 [Non-patent literature]

[0010] [Non-Patent Document 1] Journal of the American Chemical Society, February 2022, Vol. 144, No. 8, p.3365-3369 Summary of the Invention [Problem to be solved by the invention]

[0011] However, the inventors have found through their investigations that conventional powder metallurgy techniques are not suitable for producing products made of multi-component precious metal alloys such as those described above.

[0012] For example, when multiple powders made of different components are mixed and used, the resin is removed by firing, causing the mixture to become brittle and crumble, and the fired body may not be able to maintain its shape. The reason for this is not entirely clear, but one possible reason is that there are large differences in properties such as melting points between precious metal elements.

[0013] Furthermore, it has been found that even when the strength of the sintered body is not a problem, microscopic deviations in the distribution of the constituent elements in the sintered body, i.e., variations in the alloy composition, occur. Since variations in the alloy composition result in variations in the properties, a sintered precious metal alloy with excellent uniformity in composition is required to demonstrate the inherent properties of the precious metal alloy.

[0014] In particular, when producing the high-entropy alloy described above, it is considered desirable to minimize the imbalance in the composition. In other words, if there is an imbalance in the composition, the condition of containing each element in equiatomic amounts will not be satisfied in that portion, and the inherent properties of the high-entropy alloy may not be obtained. Furthermore, if the imbalance in the composition is large, it may not be possible to form a single-phase solid solution.

[0015] Furthermore, it is known that the physical properties of precious metals are also greatly dependent on their crystallinity, and therefore, the above-mentioned sintered precious metal alloys are also required to have high crystallinity.

[0016] An object of the present invention is to solve the above problems and to provide a formed body and a sintered body of a precious metal alloy that have high crystallinity and excellent uniformity of composition. [Means for solving the problem]

[0017] As a result of investigations conducted by the inventors of the present invention to achieve the above-mentioned object, it was found that the above-mentioned problems can be solved by using a precious metal alloy powder having a specific average particle size, crystallite size, and number of peaks in an X-ray diffraction spectrum as a raw material, instead of using multiple powders consisting of different components. The present invention was completed based on this finding, and its gist is as follows.

[0018] 1. A compact made of alloy powder and resin, The alloy powder is a precious metal alloy powder consisting of an alloy of five or more kinds of precious metal elements, and Average particle size is 0.1 to 100 μm, Crystallite size is 60 nm or more, A molded product in which the number of peaks observed in the diffraction angle 2θ range of 38 to 44° in an X-ray diffraction spectrum is 1.

[0019] 2. The molded body according to 1 above, wherein the precious metal alloy powder has a content coefficient of variation CV of 0.2 or less for all of the precious metal elements as measured by energy dispersive X-ray spectroscopy.

[0020] 3. A sintered body of a precious metal alloy, The noble metal alloy is a noble metal alloy consisting of five or more noble metal elements, The fired body is The crystallite size is 60 nm or more, and A fired body in which the number of peaks observed in the diffraction angle 2θ range of 38 to 44° in an X-ray diffraction spectrum is 1.

[0021] 4. The sintered body according to 3 above, wherein the coefficient of variation CV of the content of all the noble metal elements measured by energy dispersive X-ray spectroscopy is 0.2 or less.

[0022] 5. A method for producing a molded body made of alloy powder and resin, comprising: an alloy powder preparation step of preparing the alloy powder as a raw material; a mixing step of mixing the resin with the alloy powder; a molding step of applying pressure to the alloy powder and the resin mixed in the mixing step to form the compact, The alloy powder is a precious metal alloy powder consisting of an alloy of five or more kinds of precious metal elements, and Average particle size is 0.1 to 100 μm, Crystallite size is 60 nm or more, A method for producing a molded body, in which the number of peaks observed in an X-ray diffraction spectrum at a diffraction angle 2θ in the range of 38 to 44° is 1.

[0023] 6. In the mixing step, a solvent is mixed with the alloy powder in addition to the resin; 6. The method for producing a molded body according to 5 above, further comprising a drying step of evaporating the solvent after the mixing step and before the molding step.

[0024] 7. A method for producing a sintered body of a precious metal alloy, comprising: an alloy powder preparation step of preparing alloy powder as a raw material; a mixing step of mixing the alloy powder with a resin; a molding step of applying pressure to the alloy powder and the resin mixed in the mixing step to form a compact; and a firing step of firing the compact to form a fired body, The alloy powder is a precious metal alloy powder consisting of an alloy of five or more kinds of precious metal elements, and Average particle size is 0.1 to 100 μm, Crystallite size is 60 nm or more, A method for producing a sintered body, in which the number of peaks observed in the X-ray diffraction spectrum at a diffraction angle 2θ in the range of 38 to 44° is 1.

[0025] 8. In the mixing step, a solvent is mixed with the alloy powder in addition to the resin; 8. The method for producing a fired body according to 7 above, further comprising a drying step of evaporating the solvent after the mixing step and before the molding step. [Effects of the Invention]

[0026] According to the present invention, it is possible to provide a molded body and a sintered body of a precious metal alloy that have high crystallinity and excellent uniformity of composition. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a flow diagram showing a method for producing a precious metal alloy formed body in one embodiment of the present invention. [Figure 2] 1 is a flow diagram showing a method for producing a sintered precious metal alloy body according to an embodiment of the present invention. [Figure 3] FIG. 1 is a flow diagram showing an example of a method for producing a precious metal alloy powder as a raw material. [Figure 4] FIG. 10 is a flow chart showing another example of a method for producing a precious metal alloy powder as a raw material. [Figure 5] FIG. 10 is a flow chart showing another example of a method for producing a precious metal alloy powder as a raw material. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, embodiments of the present invention will be specifically described, but the present invention is not limited to the embodiments described below.

[0029] [Molded body] The molded article according to one embodiment of the present invention is a molded article made of an alloy powder and a resin. The alloy powder is a precious metal alloy powder made of an alloy of five or more precious metal elements, and satisfies the following conditions: Average particle size: 0.1 to 100 μm ·Crystallite size is 60nm or more The number of peaks observed in the X-ray diffraction spectrum at a diffraction angle 2θ of 38 to 44° is 1.

[0030] ·Precious metal elements The noble metal constituting the noble metal alloy is not particularly limited and any noble metal element can be used, i.e., the noble metal alloy is an alloy containing at least five elements selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os.

[0031] Of the above noble metal elements, Os has the property of easily volatilizing when heated during the manufacturing process, and therefore, from the viewpoint of ease of manufacturing, the noble metal alloy is preferably an alloy containing at least five elements selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, and Ru.

[0032] The number of precious metal elements constituting the alloy is not particularly limited as long as it is 5 or more. In other words, the alloy may contain all eight precious metal elements. The number of precious metal elements may be 6 or 7.

[0033] The proportion (content) of each precious metal element contained in the precious metal alloy powder is not particularly limited and can be any value. For example, when producing a precious metal alloy powder made of the high-entropy alloy described above, the proportions of each precious metal element contained in the precious metal alloy powder may be set to approximately equal values. Specifically, ΔC, defined as the difference (Cmax-Cmin) between the maximum content (Cmax) and the minimum content (Cmin) of all the precious metal elements contained in the precious metal alloy powder (atomic %), is preferably 10.0 atomic % or less, more preferably 5.0 atomic % or less, even more preferably 3.0 atomic % or less, and most preferably 2.0 atomic % or less. Meanwhile, the lower the ΔC, the better, and the lower limit may be 0 atomic %.

[0034] ·Average particle size: 0.1~100μm If the average particle size of the alloy powder is less than 0.1 μm, the apparent density will be significantly low. If the apparent density of the powder is low, the shrinkage (volume reduction) during compaction will be extremely large. Therefore, the average particle size is set to 0.1 μm or more. On the other hand, if the average particle size is greater than 100 μm, the compact will be brittle. Therefore, the average particle size is set to 100 μm or less, preferably 80 μm or less, more preferably 50 μm or less, even more preferably 20 μm or less, and most preferably 10 μm or less.

[0035] The average particle size of the noble metal alloy powder is defined as the 50% particle size D50 in the cumulative particle size distribution on a volume basis, i.e., the median diameter. The average particle size can be measured using a laser diffraction particle size distribution analyzer.

[0036] ·Crystallite size is 60nm or more The noble metal alloy powder contained in the compact has high crystallinity, specifically, a crystallite size of 60 nm or more, preferably 80 nm or more, while the upper limit of the crystallite size is not particularly limited, and may typically be 140 nm or less, or may be 120 nm or less.

[0037] The crystallite size can be determined from the half-width of the diffraction peak obtained by X-ray diffraction (XRD) measurement.

[0038] Number of peaks in XRD spectrum: 1 When the precious metal elements contained in the precious metal alloy powder are not sufficiently alloyed, multiple peaks attributable to each element are observed in the diffraction angle 2θ range of 38 to 44° in the X-ray diffraction spectrum. Therefore, in the present invention, the number of peaks observed in this range is defined as 1. If there is only one peak in the XRD spectrum, it can be said that uniform alloying has been achieved. Note that the range of diffraction angle 2θ for counting the number of peaks is set to 38 to 44° because peaks of precious metal elements (Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os) are observed in this range.

[0039] Coefficient of variation of content measured by EDX (CV) For all precious metal elements constituting the precious metal alloy powder, the coefficient of variation CV of the content measured by energy dispersive X-ray spectroscopy (EDX) is preferably 0.2 or less, more preferably 0.15 or less. Here, a coefficient of variation CV of 0.2 or less means that the coefficient of variation CV of the content of each precious metal element constituting the precious metal alloy powder is 0.2 or less. According to the manufacturing method described below, an extremely uniform precious metal alloy powder having a coefficient of variation CV of 0.2 or less can be obtained. Meanwhile, the lower the coefficient of variation CV, the better, so there is no particular restriction on the lower limit. Typically, the coefficient of variation CV may be 0.05 or more, or 0.08 or more.

[0040] If the coefficient of variation CV of the content measured by EDX satisfies the above condition, it can be said that the alloying is more uniform.

[0041] The use of the above-mentioned molded body is not particularly limited, and it can be used for any purpose. For example, in applications where high strength is not required, the molded body can be used as it is as a final product. In addition, the molded body may be used to produce a fired body described later.

[0042] [Fired body] The sintered body in one embodiment of the present invention is a sintered body of a precious metal alloy, and the precious metal alloy satisfies the following conditions. ·Crystallite size is 60nm or more The number of peaks observed in the X-ray diffraction spectrum at a diffraction angle 2θ of 38 to 44° is 1.

[0043] ·Precious metal elements The noble metal constituting the noble metal alloy is not particularly limited and any noble metal element can be used, i.e., the noble metal alloy is an alloy containing at least five elements selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os.

[0044] Of the above noble metal elements, Os has the property of easily volatilizing when heated during the manufacturing process, and therefore, from the viewpoint of ease of manufacturing, the noble metal alloy is preferably an alloy containing at least five elements selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, and Ru.

[0045] The number of precious metal elements constituting the alloy is not particularly limited as long as it is 5 or more. In other words, the alloy may contain all eight precious metal elements. The number of precious metal elements may be 6 or 7.

[0046] The proportion (content) of each precious metal element contained in the sintered precious metal alloy of the present invention is not particularly limited and can be any value. For example, when producing a sintered precious metal alloy made of the aforementioned high-entropy alloy, the proportions of each precious metal element contained in the sintered precious metal alloy may be set to approximately equal values. Specifically, ΔC, defined as the difference (Cmax - Cmin) between the maximum content (Cmax) and the minimum content (Cmin) of all precious metal elements contained in the sintered precious metal alloy (atomic %), is preferably 10.0 atomic % or less, more preferably 5.0 atomic % or less, even more preferably 3.0 atomic % or less, and most preferably 2.0 atomic % or less. Meanwhile, the lower the ΔC, the better, and the lower limit may be 0 atomic %.

[0047] Crystallite size: 60nm or more The sintered body of the present invention has high crystallinity, specifically, a crystallite size of 60 nm or more, preferably 80 nm or more. On the other hand, the upper limit of the crystallite size is not particularly limited, but may typically be 140 nm or less, or may be 120 nm or less.

[0048] The crystallite size can be determined from the half-width of the diffraction peak obtained by X-ray diffraction (XRD) measurement.

[0049] Number of peaks in XRD spectrum: 1 If the precious metal elements contained in the sintered body are not sufficiently alloyed, multiple peaks attributable to each element will be observed in the diffraction angle 2θ range of 38 to 44° in the X-ray diffraction spectrum. Therefore, in the present invention, the number of peaks observed in this range is defined as 1. If there is only one peak in the XRD spectrum, it can be said that uniform alloying has been achieved. Note that the range of diffraction angle 2θ for counting the number of peaks is set to 38 to 44° because peaks of precious metal elements (Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os) are observed in this range.

[0050] Coefficient of variation of content measured by EDX (CV) In the present invention, the coefficient of variation CV of the content of all metal elements constituting the precious metal alloy, as measured by energy dispersive X-ray spectroscopy (EDX), is preferably 0.2 or less, more preferably 0.15 or less. Here, a coefficient of variation CV of 0.2 or less means that the coefficient of variation CV of the content of each precious metal element constituting the precious metal alloy is 0.2 or less. According to the present invention, a highly uniform sintered precious metal alloy having a coefficient of variation CV of 0.2 or less can be obtained. Meanwhile, the lower the coefficient of variation CV, the better, so there is no particular restriction on the lower limit. Typically, the coefficient of variation CV may be 0.05 or more, and may be 0.08 or more.

[0051] If the coefficient of variation CV of the content measured by EDX satisfies the above condition, it can be said that the alloying is more uniform.

[0052] The application of the sintered body is not particularly limited, and it can be used for any application. For example, by utilizing the properties of the precious metal alloy, it can be used for applications such as hydrogen storage materials, molecular sieves, catalysts, electrodes, and contacts. The sintered body of the present invention is uniformly alloyed as described above, providing a uniform reaction field. Therefore, the reaction can proceed uniformly throughout the sintered body, and the reaction efficiency per unit amount of precious metal used can be increased. Furthermore, high crystallinity means that the precious metal element exists in a stable state. Therefore, deterioration during use is suppressed, and excellent durability can be obtained.

[0053] [Manufacturing method] Next, a method for producing a molded body and a fired body according to one embodiment of the present invention will be described.

[0054] The green body and sintered body of the present invention can be manufactured by powder metallurgy. FIG. 1 is a flow diagram showing a method for manufacturing a green body in one embodiment of the present invention. FIG. 2 is a flow diagram showing a method for manufacturing a sintered body in one embodiment of the present invention. The method for manufacturing a green body in one embodiment of the present invention includes an alloy powder preparation step, a mixing step, and a molding step. The method for manufacturing a sintered body in one embodiment of the present invention further includes a sintering step in addition to the steps of the green body manufacturing method.

[0055] In addition, the method for producing a compact and a sintered body according to another embodiment of the present invention may further include a drying step for evaporating the solvent after the mixing step and before the compacting step. Each step will be described in detail below. Note that, unless otherwise specified, the process can be carried out in accordance with general powder metallurgy techniques.

[0056] [Alloy powder preparation process] First, an alloy powder is prepared as a raw material. The alloy powder is a precious metal alloy powder made of an alloy of five or more precious metal elements, and must satisfy the following conditions: Average particle size is 0.1 to 10 μm, -Crystallite size is 60nm or more, The number of peaks observed in the X-ray diffraction spectrum at a diffraction angle 2θ of 38 to 44° is 1.

[0057] ·Average particle size: 0.1~100μm If the average particle size of the alloy powder is less than 0.1 μm, the apparent density will be significantly low. A powder with a low apparent density will experience significant shrinkage (volume reduction) during compaction and sintering, making it unsuitable for producing compacts and sintered bodies. Therefore, the average particle size is set to 0.1 μm or more. On the other hand, if the average particle size is greater than 100 μm, the final sintered body will be brittle. Therefore, the average particle size is set to 100 μm or less, preferably 80 μm or less, more preferably 50 μm or less, even more preferably 20 μm or less, and most preferably 10 μm or less.

[0058] Crystallite size: 60nm or more In order to obtain a sintered body having a crystallite size of 60 nm or more, the crystallite size of the alloy powder must be 60 nm or more. Therefore, the crystallite size of the alloy powder is set to 60 nm or more, preferably 80 nm or more. On the other hand, the upper limit of the crystallite size is not particularly limited, but may typically be 140 nm or less, or 120 nm or less.

[0059] The crystallite size can be determined from the half-width of the diffraction peak obtained by X-ray diffraction (XRD) measurement.

[0060] Number of peaks in XRD spectrum: 1 In order to ensure that the number of peaks observed in the X-ray diffraction spectrum at a diffraction angle 2θ of 38 to 44° in the final sintered body is 1, the number of peaks observed in the X-ray diffraction spectrum at a diffraction angle 2θ of 38 to 44° in the alloy powder must also be 1.

[0061] Coefficient of variation of content measured by EDX (CV) For all metal elements constituting the above-mentioned precious metal alloy powder, the coefficient of variation CV of the content measured by energy dispersive X-ray spectroscopy (EDX) is preferably 0.2 or less, more preferably 0.15 or less. Here, a coefficient of variation CV of 0.2 or less means that the coefficient of variation CV of the content of each precious metal element constituting the precious metal alloy powder is 0.2 or less. By using a powder having a coefficient of variation CV of 0.2 or less as the alloy powder, the coefficient of variation CV of the finally obtained precious metal alloy sintered body can also be made 0.2 or less. The lower the coefficient of variation CV, the better, so there is no particular restriction on the lower limit. Typically, the coefficient of variation CV may be 0.05 or more, and may be 0.08 or more.

[0062] The method for preparing the alloy powder is not particularly limited. In one embodiment of the present invention, a precious metal alloy powder produced by the method described below can be used as the alloy powder. The production methods disclosed herein can be broadly divided into two types: a method in which sintering is performed only once, and a method in which sintering is performed multiple times. The former is a method suitable for producing powder with a relatively small average particle size, and the latter is a method suitable for producing powder with a relatively large average particle size. Each production method will be described below.

[0063] -Production of powder with a relatively small average particle size Fig. 3 is a flow diagram showing a method for producing a precious metal alloy powder in one embodiment of the present invention. As shown in Fig. 3, the method for producing a precious metal alloy powder in one embodiment of the present invention includes the following steps (1) to (6). (1) Raw material preparation process (2) Slurry preparation process (3) Mixing process (4) First firing process (5) First acetic acid treatment step (6) First cleaning process

[0064] This manufacturing method is suitable for producing powders with a relatively small average particle size. Specifically, this manufacturing method is suitable for producing powders with an average particle size of approximately 10 μm or less, more suitable for producing powders with an average particle size of 5 μm or less, and even more suitable for producing powders with an average particle size of 3 μm or less. Each step will be described in detail below.

[0065] (1) Raw material preparation process First, in the raw material preparation step, powders (raw material powders) to be used as raw materials for producing a precious metal alloy powder are prepared. The raw material powders are prepared separately for each of the precious metal elements that constitute the precious metal alloy to be finally produced. For example, when producing a quinary alloy, five raw material powders are prepared.

[0066] The particle size of the raw material powder is not particularly limited, but from the viewpoint of making the final precious metal alloy powder more uniform, it is preferable to use a fine raw material powder. Specifically, the average particle size of each raw material powder used is preferably 1000 nm or less, more preferably 500 nm or less, and even more preferably 100 nm or less. On the other hand, the lower limit of the average particle size is not particularly limited, but may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more.

[0067] Here, the average particle diameter of the raw material powder is defined as the average particle diameter d calculated from the specific surface area of ​​the raw material powder using a spherical model. The average particle diameter d (μm) is generally called the BET diameter, and specifically, it is calculated based on the density ρ (g / cm) of the particles constituting the raw material powder. 3 ) and BET specific surface area s(m 2 / g) can be calculated using the following formula (1). d=6 / ρs …(1)

[0068] The raw material powder may be either a metal powder or a metal oxide powder. For example, for Pt, Pt powder can be used, but platinum oxide (PtO2) powder can also be used. Similarly, oxide powders such as rhodium oxide (RhO2, RhO3) and palladium oxide (PdO) can also be used. These oxide powders are thermally decomposed during firing to function as a precious metal source. Basically, whether a metal powder or a metal oxide powder is used, the function as a raw material is the same, so the choice can be made depending on factors such as the availability of the powder.

[0069] However, for Ru, it is preferable to use metallic ruthenium powder as the raw material, rather than ruthenium oxide (RuO2) powder.

[0070] For example, in one embodiment of the present invention, it is preferable to use, as the raw material powder, at least five types of powder selected from the group consisting of gold, silver, silver oxide, platinum, platinum oxide, palladium, palladium oxide, rhodium, ruthenium, rhodium oxide, iridium, iridium oxide, and osmium.

[0071] (2) Slurry preparation process Next, the raw material powder, calcium carbonate, and water are mixed to form a slurry, and the pH of the slurry is adjusted to 8.0 or higher. The calcium carbonate is thermally decomposed in the firing process to at least partially become calcium oxide. Calcium carbonate and calcium oxide have the effect of inhibiting the grain growth of the precious metal alloy, which contributes to the refinement of the final precious metal alloy powder.

[0072] The amount of calcium carbonate added is not particularly limited, but from the viewpoint of enhancing the above-mentioned effect, it is preferably 0.1 times or more, more preferably 0.2 times or more, and even more preferably 0.5 times or more, in terms of weight ratio relative to the total raw material powder. On the other hand, the upper limit is also not particularly limited, but even if an excessive amount is added, the effect will saturate. Therefore, it is preferably 10 times or less, more preferably 5 times or less, and even more preferably 2 times or less, in terms of weight ratio relative to the total raw material powder.

[0073] The calcium carbonate can be added in any form. Typically, calcium carbonate powder can be used. When calcium carbonate powder is used, the average particle size of the calcium carbonate powder is not particularly limited, but it is preferably 0.2 to 1.0 μm. Here, the average particle size of the calcium carbonate is defined as the average particle size d calculated from the specific surface area of ​​the calcium carbonate using a spherical model. The average particle size d (μm) is generally called the BET diameter, and specifically, it is calculated based on the density ρ (g / cm) of the particles constituting the calcium carbonate. 3 ) and BET specific surface area s(m 2 / g) can be calculated using the following formula (1). d=6 / ρs …(1)

[0074] pH: 8.0 or higher In the above-mentioned slurry preparation step, it is important to set the pH of the slurry to 8.0 or more. If the pH of the slurry is less than 8.0, the composition uniformity of the finally obtained precious metal alloy powder decreases, and the coefficient of variation CV in EDX measurement increases. Furthermore, if the pH of the slurry is less than 8.0, the number of peaks observed in the diffraction angle 2θ range of 38 to 44° in the XRD spectrum cannot be set to 1.

[0075] The method for adjusting the pH of the slurry is not particularly limited. For example, if the pH is less than 8.0, an alkali may be added to the slurry. For example, the pH can be adjusted by adding at least one selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, and ammonia to the slurry. Examples of the alkali metal hydroxide include sodium hydroxide and potassium hydroxide. Examples of the alkaline earth metal hydroxide include calcium hydroxide. The pH of the slurry can be measured using a general pH meter.

[0076] The upper limit of the pH of the slurry is not particularly limited. However, even if the pH is increased above 10, the effect of homogenizing the alloy becomes saturated. Furthermore, if the pH is increased above 10, a large amount of alkali must be added. As a result, the sodium and potassium added as the alkali may remain in large amounts as impurities. Furthermore, if ammonia is used as the alkali, it is dangerous because a large amount of harmful ammonia gas is generated during the manufacturing process. Therefore, it is preferable that the pH of the slurry be 10 or less.

[0077] (3) Mixing process In the mixing step, the slurry is mixed. Any mixer can be used for the mixing without any particular limitation. Examples of the mixer include a ball mill, a planetary mill (planetary type ball mill), a bead mill, and an attritor. From the viewpoint of more uniform mixing, it is preferable to use a bead mill or a planetary mill, and among these, it is preferable to use a bead mill.

[0078] (4) First firing process Next, the slurry mixed in the mixing step is fired in a non-oxidizing atmosphere to obtain alloy powder. In the present invention, since the alloy powder is obtained by firing, the purity can be higher than when a wet reduction method is used. The firing can be performed in any device without any particular limitation. Typically, an electric furnace can be used.

[0079] The first firing step is carried out in a non-oxidizing atmosphere to prevent oxidation of the components. The non-oxidizing atmosphere is not particularly limited, and any non-oxidizing atmosphere can be used. Typically, a nitrogen gas atmosphere, an argon gas atmosphere, an atmosphere consisting of hydrogen gas and nitrogen gas, or an atmosphere consisting of hydrogen gas and argon gas can be used. From the viewpoint of reliably preventing oxidation of the raw materials, it is preferable to use an atmosphere consisting of hydrogen gas and nitrogen gas or hydrogen gas and argon gas.

[0080] The firing temperature in the first firing step (first firing temperature) is not particularly limited, and can be any temperature as long as it can fire the powder. A preferred first firing temperature is a temperature that is higher than the melting point T M From the viewpoint of promoting the diffusion of the raw material powder and further increasing the crystallinity, the first firing temperature T1 is determined by the following formula: L On the other hand, the upper limit of the first firing temperature is not particularly limited, but if the first firing temperature is excessively high, necking between alloy particles may occur, resulting in the generation of coarse powder. Therefore, the first firing temperature T1 should be set to T defined by the following formula: H It is preferable to do the following: T L (℃)=T M (K) x 0.55-273.15 T H (℃)=T M (K) x 0.77-273.15 where T M is the weighted average of the melting points of all the precious metal elements that make up the precious metal alloy. The weighted average is calculated using the content (mass%) of each precious metal element.

[0081] The firing time in the first firing step is not particularly limited, but is preferably 1 hour or more from the viewpoint of alloy grain growth, and is preferably 5 hours or less from the viewpoint of production efficiency.

[0082] (5) First acetic acid treatment step Next, the fired product obtained in the first firing step is treated with acetic acid. By carrying out the acetic acid treatment, calcium contained in the fired product can be removed. If an acid other than acetic acid (e.g., hydrochloric acid or nitric acid) is used, not only calcium but also precious metal elements will dissolve, resulting in a decrease in the homogeneity of the alloy. In contrast, acetic acid does not dissolve precious metal elements regardless of their concentration. Therefore, it is important to use acetic acid to remove calcium in the present invention.

[0083] The method of the acetic acid treatment is not particularly limited, but typically, the calcined product is stirred in an aqueous acetic acid solution to dissolve the calcium contained in the calcined product. The acetic acid treatment can be carried out any number of times, one or more times. From the viewpoint of reducing the amount of calcium remaining as an impurity as much as possible, the acetic acid treatment is preferably carried out two or more times, and more preferably three or more times. When the acetic acid treatment is carried out multiple times, a new aqueous acetic acid solution is used for each time.

[0084] During the acetic acid treatment, the fired product may be placed in a pre-prepared aqueous acetic acid solution, or the fired product may be placed in pure water first, and then acetic acid may be added to the pure water.

[0085] A specific example of a suitable acetic acid treatment method will be described below.

[0086] First, the fired product is placed in pure water and stirred. This converts the calcium oxide contained in the fired product into calcium hydroxide. Next, acetic acid is added and stirred to dissolve the calcium hydroxide. After that, stirring is stopped and the mixture is left to stand, allowing the powder to settle, and the supernatant liquid is removed. This completes one acetic acid treatment. After that, pure water and acetic acid are added, and the process of stirring, standing, and removing the supernatant is repeated twice.

[0087] (6) First cleaning process Next, the fired product (alloy powder) after the acetic acid treatment is washed with water and dried (washing step). By washing with water, the acid and calcium dissolved in the acid are removed.

[0088] It is preferable to use pure water for the water washing. The method of water washing is not particularly limited, but for example, after removing the supernatant liquid in the above acetic acid treatment, pure water can be added and the mixture can be stirred to wash. After stopping the stirring, the mixture is left to stand to allow the powder to settle, and the supernatant liquid is removed. It is preferable to repeat the water washing process two or more times, and more preferably three or more times. After the water washing, the water is separated from the powder by filtration, and the obtained powder is preferably subjected to the subsequent drying process.

[0089] The drying can be carried out by any method that can remove moisture. Natural drying is also acceptable, but heated drying is preferable to efficiently remove moisture. When heated drying is carried out, the heating temperature is not particularly limited, but is preferably 50°C or higher, more preferably 80°C or higher. It may be 100°C or higher. On the other hand, the upper limit of the heating temperature is not particularly limited, but is typically preferably 200°C or lower, more preferably 150°C or lower. The drying time is also not particularly limited, and can be any time depending on the amount of powder to be dried. From the viewpoint of sufficient drying, it is preferably 1 hour or longer, more preferably 5 hours or longer, or may be 10 hours or longer. On the other hand, the upper limit of the heating time is not particularly limited, but is typically preferably 100 hours or shorter, more preferably 50 hours or shorter.

[0090] After the drying, the obtained noble metal alloy powder is preferably sieved to loosen particles that have aggregated during the washing process.

[0091] By the above procedure, a noble metal alloy powder having a relatively small particle size (for example, an average particle size of 10 μm or less) can be obtained.

[0092] - Manufacturing powder with a relatively large average particle size Next, a method for producing a precious metal alloy powder according to another embodiment of the present invention will be described. The production method according to this embodiment is suitable for producing a relatively large powder having an average particle size of up to 100 μm. Specifically, this production method is suitable for producing a powder having an average particle size of more than 5 μm, and more suitable for producing a powder having an average particle size of more than 10 μm.

[0093] In the manufacturing method of this embodiment, firing is performed multiple times. The manufacturing method of this embodiment can be broadly divided into two methods: a method in which firing is performed twice, and a method in which firing is performed three times. Each method will be described below.

[0094] (When firing is performed twice) Fig. 4 is a flow diagram showing a manufacturing method when firing is performed twice. As shown in Fig. 4, the manufacturing method of a precious metal alloy powder in one embodiment of the present invention further includes a second firing step (7) in addition to steps (1) to (6) in the embodiment shown in Fig. 3.

[0095] For the sake of convenience, the process from the raw material preparation process to the first washing process will be referred to as the "pre-process," and the process from the first firing process onward will be referred to as the "post-process." Furthermore, a particle size adjustment process may be included after the first washing process and before the first firing process. When a particle size adjustment process is performed, the particle size adjustment process is included in the post-process, as shown in FIGS. 4 and 5.

[0096] In this embodiment, a powder with high crystallinity and excellent composition uniformity is first produced in a pre-process. However, the powder obtained at this stage is composed of relatively small particles (primary particles) with an average particle size of approximately 10 μm or less. The primary particles then aggregate to form approximately spherical aggregates (secondary particles), and the secondary particles have particle sizes on the order of several tens to several hundred μm. Therefore, by further processing the powder in a post-process, the average particle size can be further increased while maintaining high crystallinity and composition uniformity.

[0097] ·Particle size adjustment process In a post-process, the particle size of the alloy powder after the first washing process may be adjusted (particle size adjustment process) prior to the next first firing process. By performing particle size adjustment, it is possible to more easily obtain a precious metal alloy powder with a desired particle size. The particle size of the finally obtained precious metal alloy powder will be approximately equal to the particle size of the powder after particle size adjustment (i.e., the powder to be subjected to the next first firing process). Therefore, in the particle size adjustment process, the particle size may be adjusted to match the particle size of the precious metal alloy powder that is finally desired to be obtained.

[0098] The method for adjusting the particle size is not particularly limited, but typically, the alloy powder is sieved. The sieve is not particularly limited, and any suitable sieve can be used. It is possible to use either powder that passed through the sieve (undersieve) or powder that did not pass through the sieve (oversieve). The particle size of the alloy powder may also be adjusted by sieving it two or more times. For example, the alloy powder is first sieved, and the powder that passed through the sieve is collected. This removes coarse particles from the alloy powder. The collected powder is then sieved through a sieve with even finer openings, and the powder remaining on the sieve is collected. This removes excessively fine powder. By passing the powder through two sieves with different openings in this way, powder of the desired particle size can be obtained.

[0099] Sieving alloy powder not only adjusts the particle size, but also spheroidizes the powder particles. This is thought to be because the alloy powder, which is an agglomerate, is subjected to mechanical forces such as vibration, rolling, and friction on the sieve, reducing the surface roughness of the particles. The spheroidization effect is achieved in both under-sieved and over-sieved particles, but is more pronounced in over-sieved particles. Therefore, from the perspective of enhancing the spheroidization effect, it is preferable to sieve the alloy powder at least once in the particle size adjustment process and use the powder that did not pass through the sieve (over-sieved powder).

[0100] Second firing process Next, the alloy powder is subjected to a second firing (second firing step). If particle size adjustment is not performed, the alloy powder after the first washing step is simply fired. If particle size adjustment is performed, the alloy powder after particle size adjustment is simply fired. The secondary particles before the second firing are brittle and easily disintegrate upon physical contact or impact. Therefore, by performing the second firing, the primary particles that form the secondary particles are necked together, thereby fixing the particle state.

[0101] As will be described later, calcium carbonate is used in the third firing step to prevent necking between secondary particles. However, as mentioned above, the secondary particles before the second firing are brittle, and if they are mixed with calcium carbonate before the second firing, the agglomerates of the secondary particles will break down, making it difficult to control the particle size. Therefore, by performing the second firing to stabilize the structure of the secondary particles and then mixing them with calcium carbonate, it becomes possible to appropriately control the particle size.

[0102] The temperature at which the second firing is carried out (second firing temperature) is not particularly limited, and can be any temperature as long as sintering between primary particles occurs. A preferred second firing temperature is the melting point T M Therefore, the second firing temperature T2 is determined by the following formula: L That's all, T H It is preferable to do the following: T L (℃)=T M (K) x 0.45-273.15 T H (℃)=T M (K) x 0.60-273.15 where T M is the weighted average of the melting points of all the precious metal elements that make up the precious metal alloy. The weighted average is calculated using the content (mass%) of each precious metal element.

[0103] The time for the second baking (second baking time) is not particularly limited, but is preferably 5 hours or less, more preferably 2 hours or less, and is preferably 30 minutes or more, more preferably 40 minutes or more, and even more preferably 50 minutes or more.

[0104] The second firing step is carried out in a non-oxidizing atmosphere to prevent oxidation of the components. The non-oxidizing atmosphere is not particularly limited, and any non-oxidizing atmosphere can be used. Typically, a nitrogen gas atmosphere, an argon gas atmosphere, an atmosphere consisting of hydrogen gas and nitrogen gas, or an atmosphere consisting of hydrogen gas and argon gas can be used. From the viewpoint of reliably preventing oxidation of the raw materials, it is preferable to use an atmosphere consisting of hydrogen gas and nitrogen gas or hydrogen gas and argon gas.

[0105] (When firing three times) Fig. 5 is a flow diagram showing a manufacturing method in which firing is performed three times. As shown in Fig. 5, the manufacturing method of a precious metal alloy powder in one embodiment of the present invention further includes (8) a third firing step, (9) a second acetic acid treatment step, and (10) a second washing step in addition to steps (1) to (7) in the embodiment shown in Fig. 4. Each of steps (8) to (10) will be described below. In this embodiment, as in the case of Fig. 4, a particle size adjustment step can be optionally performed after the first washing step and before the second firing step.

[0106] Third firing process The alloy powder after the second firing is further fired in a non-oxidizing atmosphere (third firing step). By firing the alloy powder obtained in the previous step in two steps in this way, the primary particles constituting the secondary particles can be more firmly bonded together and the sphericity of the particles can be further increased. The third firing can be carried out in any apparatus without any particular limitations. Typically, an electric furnace can be used.

[0107] In the third firing step, in order to prevent the secondary particles from bonding together to form coarse particles, the mixture is fired in a state where it is mixed with calcium carbonate as a sintering inhibitor. The amount and form of the calcium carbonate to be added are not particularly limited, but can be the same as those in the first firing step.

[0108] The third firing step is carried out in a non-oxidizing atmosphere to prevent oxidation of the components. The non-oxidizing atmosphere is not particularly limited, and any non-oxidizing atmosphere can be used. Typically, a nitrogen gas atmosphere, an argon gas atmosphere, an atmosphere consisting of hydrogen gas and nitrogen gas, or an atmosphere consisting of hydrogen gas and argon gas can be used. From the viewpoint of reliably preventing oxidation of the raw materials, it is preferable to use an atmosphere consisting of hydrogen gas and nitrogen gas or hydrogen gas and argon gas.

[0109] The firing temperature in the third firing step (third firing temperature) is not particularly limited, and can be any temperature as long as it can fire the powder. A preferred third firing temperature is the melting point T M The third firing temperature T3 is defined by the following formula: L On the other hand, the upper limit of the third firing temperature is not particularly limited, but if the third firing temperature is too high, necking between alloy particles may occur, resulting in the generation of coarse powder. Therefore, the third firing temperature T3 should be set to T defined by the following formula: H It is preferable to do the following: T L (℃)=T M (K) x 0.55-273.15 T H (℃)=T M (K) x 0.77-273.15 where T M is the weighted average of the melting points of all the precious metal elements that make up the precious metal alloy. The weighted average is calculated using the content (mass%) of each precious metal element.

[0110] The firing time in the second firing step is not particularly limited, but is preferably 1 hour or more, while from the viewpoint of production efficiency, it is preferably 5 hours or less.

[0111] Second acetic acid treatment process Next, the alloy powder (calcined product) after the third calcination step is treated with acetic acid (second acetic acid treatment step). By performing the acetic acid treatment, calcium contained in the calcined product can be removed. If an acid other than acetic acid (e.g., hydrochloric acid or nitric acid) is used, not only calcium but also precious metal elements will dissolve, resulting in a decrease in the homogeneity of the alloy. In contrast, acetic acid does not dissolve precious metal elements regardless of their concentration. Therefore, it is important to use acetic acid to remove calcium in the present invention.

[0112] The conditions for the second acetic acid treatment step are not particularly limited, but can be the same as those for the first acetic acid treatment step described above.

[0113] Second cleaning process The alloy powder after the first acetic acid treatment is washed with water and dried (second washing step). By washing with water, acetic acid and calcium dissolved in the acetic acid can be removed. The conditions for the second washing step are not particularly limited, but can be the same as those for the first washing step described above.

[0114] By the above-mentioned treatment, a noble metal alloy powder that satisfies the above-mentioned conditions can be obtained.

[0115] [Mixing process] Next, the alloy powder prepared as a raw material in the alloy powder preparation step is mixed with a resin (mixing step).

[0116] The resin is not particularly limited and any resin can be used. For example, the resin may be at least one selected from the group consisting of known polyamides such as nylon 11, nylon 12, and nylon 6, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, acrylonitrile-ethylene-styrene (AES) resin, vinyl acetate resin, polystyrene, polyethylene, polypropylene, polyvinyl chloride, acrylic resin, methacrylic resin, polyvinyl alcohol resin, polyvinyl ether, polyacetal, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyvinyl butyral, polysulfone, polyetherimide, ethyl cellulose, cellulose acetate, fluorine-based resin, polyolefin elastomer, and saturated polyester resin. Multiple resins can also be used in combination. Among these, ethyl cellulose is preferably used as the resin.

[0117] In one embodiment of the present invention, in the mixing step, a solvent can be mixed with the alloy powder in addition to the resin. The solvent is not particularly limited and any solvent can be used, but it is preferable that the solvent has a boiling point of 300°C or less. Generally, an organic solvent can be used. For example, acetate, ether, hydrocarbon, etc. can be used as the solvent. More specifically, it is preferable to use at least one selected from dibutyl carbitol, butyl carbitol acetate, and Texanol, and it is more preferable to use Texanol.

[0118] The mixing is not particularly limited and can be carried out by any method. When a solvent is not used, the precious metal alloy powder and the resin can be mixed using any mixing means. When a solvent is used, the precious metal alloy powder, the resin, and the solvent can be mixed using any mixing means. Examples of the mixing means include a ball mill, a planetary mill (planetary type ball mill), a bead mill, an attritor, and a mortar. From the viewpoint of more uniform mixing, it is preferable to use a bead mill or a planetary mill, and of these, it is preferable to use a bead mill.

[0119] When using a solvent, it is preferable to mix and then knead the components in order to uniformly disperse the precious metal alloy powder in the solvent. The kneading can be performed using various devices, such as a sand mill, a roll mill, a ball mill, a colloid mill, a jet mill, a bead mill, a kneader, a homogenizer, or a propellerless mixer. Of these, it is preferable to use a roll mill. As the roll mill, for example, a two-roll mill or a three-roll mill can be used, and it is preferable to use a three-roll mill.

[0120] [Drying process] If a solvent is used in the mixing step, it is preferable to evaporate the solvent after the mixing step and before the subsequent molding step (drying step). The drying method is not particularly limited, but typically, the solvent can be evaporated by heating the solvent-containing paste obtained in the mixing step. To promote evaporation, it is preferable to spread the paste on the surface of a substrate such as a resin and heat it in this state. For example, a PET (polyethylene terephthalate) film can be used as the substrate. The heating temperature can be adjusted depending on the solvent used, but can be, for example, about 120 to 200°C. The heating method is also not particularly limited, and any method can be used. For example, the substrate coated with the paste can be heated on a hot plate or in a dryer.

[0121] When the solvent is removed by drying, the precious metal alloy powder and the resin may solidify. In such cases, the mixture may be pulverized into a powder form prior to the subsequent molding step. The pulverization method is not particularly limited, and any method may be used. For example, pulverization may be performed using a ball mill, a planetary mill (planetary ball mill), a bead mill, an attritor, a mortar, or the like. When pulverizing, it is not necessary to pulverize the mixture into excessively fine particles; it is sufficient to pulverize the mixture to a size that can fit into a mold used in the subsequent molding step.

[0122] [Molding process] Next, the mixed alloy powder and resin are subjected to pressure to form a compact (also called a green compact) (the compacting process). There are no particular limitations on the method of compacting, but as with ordinary powder metallurgy, the powder may be filled into a mold and compacting pressure may be applied.

[0123] The method for applying the molding pressure is not particularly limited, but typically, a press can be used. The press is not particularly limited and any press can be used. For example, the press may be a twist press.

[0124] The molding pressure is not particularly limited, but from the viewpoint of ensuring the strength of the molded body, it is preferably 1000 N or more, more preferably 1500 N or more, and even more preferably 2000 N or more. The upper limit of the molding pressure is not particularly limited, but it may be 1000 N or less, or may be 5000 N or less. In addition, it is preferable to maintain the molding pressure applied for 30 seconds or more, and more preferably 60 seconds or more.

[0125] By the above procedure, a molded article according to one embodiment of the present invention can be produced.

[0126] [Firing process] When producing a sintered body, the compact obtained in the above molding step is further sintered to form a sintered body (sintering step), as shown in Figure 2. By performing the sintering, the resin added as a binder is decomposed and removed, and the precious metal alloy particles are bonded together to form a sintered body. The conditions for the sintering are not particularly limited and may be adjusted depending on the precious metal alloy powder and resin used.

[0127] For example, if the firing temperature is too low, the decomposition of the resin and the bonding of the powder particles will not proceed sufficiently. Therefore, the firing temperature is preferably 500°C or higher, more preferably 800°C or higher, and even more preferably 1000°C or higher. When high strength is required, firing at an even higher temperature is desirable to thoroughly sinter the powder particles. In this case, the firing temperature is preferably 1000°C or higher, more preferably 1200°C or higher, and even more preferably 1400°C or higher. A fired body obtained by firing at such a high temperature is sometimes called a sintered body. On the other hand, since the effect saturates even if the firing temperature is excessively high, the firing temperature is preferably 1800°C or lower, more preferably 1700°C or lower, and even more preferably 1600°C or lower. When sintering does not need to proceed, firing at a lower temperature is sufficient. In this case, the firing temperature is preferably 1500°C or lower, more preferably 1400°C or lower, and even more preferably 1300°C or lower.

[0128] The temperature can be raised to the firing temperature at any rate. For example, the time from the start of temperature rise until the temperature reaches the firing temperature (temperature rise time) may be 30 to 240 minutes, or 60 to 180 minutes.

[0129] After the firing temperature is reached, it is preferable to maintain the temperature at that temperature. The time for maintaining the firing temperature is not particularly limited, but may be, for example, 1 to 5 hours, or 2 to 4 hours.

[0130] The firing step is preferably carried out in a non-oxidizing atmosphere to prevent oxidation of the components. The non-oxidizing atmosphere is not particularly limited, and any non-oxidizing atmosphere can be used. Typically, a nitrogen gas atmosphere, an argon gas atmosphere, an atmosphere consisting of hydrogen gas and nitrogen gas, or an atmosphere consisting of hydrogen gas and argon gas can be used. From the viewpoint of reliably preventing oxidation of the raw materials, it is preferable to use an atmosphere consisting of hydrogen gas and nitrogen gas or hydrogen gas and argon gas.

[0131] The firing can be carried out using any heating device, for example, an electric furnace. As the electric furnace, it is preferable to use an electric furnace equipped with a means for controlling the atmosphere inside the furnace. [Example]

[0132] The effects of the present invention will be specifically described below with reference to examples and comparative examples of the present invention.

[0133] <Production of precious metal alloy powder> First, for use in the examples, a quinary precious metal alloy powder consisting of Ru, Rh, Pd, Ir, and Pt was prepared by the following procedure.

[0134] (Powder No.1) First, powder No. 1 having a relatively small average particle size was prepared according to the procedure shown in Figure 3. The specific conditions are explained below.

[0135] [Pre-process] The raw material powders were prepared as Pt, Pd, IrO2, Ru, and Rh. Of these powders, Pt black, Pd black, and Rh black were used for the Pt, Pd, and Ph powders, respectively. The Ru powder was prepared by reducing RuO2 powder.

[0136] The raw material powder was mixed with calcium carbonate powder and water (pure water) to form a slurry, whereupon an alkali was added to adjust the pH of the slurry to 9.0, as needed.

[0137] The slurry was then mixed in a planetary ball mill at a rotation speed of 200 rpm for 6 hours. A polyamide pot was used as the mixing container, and polyamide balls with a diameter of 10 mm were used as the media.

[0138] The mixed slurry was fired in an N2-H2 atmosphere to obtain an alloy powder. Specifically, the slurry was first dried in a dryer at 130°C to remove moisture, obtaining a mixed powder. The mixed powder was then placed in a crucible and fired. The firing was carried out using an atmospheric heating electric furnace. The firing atmosphere was a 3% H2 / 97% N2 gas atmosphere, with a firing temperature of 1300°C and a firing time of 5 hours.

[0139] Next, the alloy powder obtained in the firing step was treated with acetic acid, washed with pure water, and dried.

[0140] (Acetic acid treatment) The acetic acid treatment was carried out three times using the following procedure. First, the fired product (alloy powder) was placed in pure water and stirred. This converted the calcium oxide contained in the fired product into calcium hydroxide. Next, acetic acid was added and stirred to dissolve the calcium hydroxide. After that, stirring was stopped and the mixture was left to stand, allowing the powder to settle, and the supernatant liquid was removed. This completed one acetic acid treatment. Then, pure water and acetic acid were added, and the process of stirring, standing, and removing the supernatant liquid was repeated twice more.

[0141] Next, the powder was washed with pure water three times using the following procedure. First, after removing the supernatant liquid from the third acetic acid treatment, pure water was added and stirred. After stopping the stirring, the powder was left to settle and the supernatant liquid was removed. The above washing procedure was repeated three times.

[0142] (Dry) After the washing, the water and powder were separated by filtration, and the resulting powder was dried at 130° C. for 12 hours.

[0143] The dried powder was sieved to break down any agglomerated powder. A stainless steel test sieve with 125 μm openings was used as the sieve. No particles remained on the sieve; all particles passed through the sieve.

[0144] (Powder No.2) Next, powder No. 2 having a relatively small average particle size was produced according to the procedure shown in Figure 5. Specifically, powder No. 1 was further subjected to post-processing under the following conditions.

[0145] (Particle size adjustment process) The alloy powder obtained in the previous step was subjected to particle size adjustment. Specifically, the alloy powder was sieved through a 53 μm mesh sieve, and the powder that passed through the sieve was further sieved through a 38 μm mesh sieve. A stainless steel test sieve was used as the sieve.

[0146] (Second firing process) Next, the alloy powder after the particle size adjustment step was subjected to a second firing in a non-oxidizing atmosphere. The second firing was carried out by placing the alloy powder in a crucible and using an atmospheric heating electric furnace. The firing atmosphere was a 100% N2 gas atmosphere, with the second firing temperature set to 1000°C and the second firing time set to 1 hour.

[0147] (Second firing process) Next, the powder after the second firing step was further mixed with calcium carbonate and subjected to a third firing. Specifically, first, the powder after the second firing step was mixed with calcium carbonate powder to form a mixed powder. At this time, the amount of calcium carbonate added was 5 times the volume ratio of the powder. The mixing was carried out in a powder mixer for 1 minute. Next, the mixed powder was placed in a crucible and fired in a non-oxidizing atmosphere. The firing was carried out using an atmospheric heating electric furnace. The firing atmosphere was a 100% N2 gas atmosphere, with a third firing temperature of 1300°C and a third firing time of 5 hours.

[0148] (Second acetic acid treatment step) Next, the alloy powder obtained in the firing step was subjected to a second acetic acid treatment. The second acetic acid treatment was carried out three times in the same manner as the first acetic acid treatment step, using the following procedure. First, the fired product (alloy powder) was placed in pure water and stirred. This caused the calcium oxide contained in the fired product to change to calcium hydroxide. Next, acetic acid was added and stirred to dissolve the calcium hydroxide. After that, stirring was stopped and the mixture was left to stand, allowing the powder to settle, and the supernatant liquid was removed. This completed one acetic acid treatment. Then, pure water and acetic acid were added, and the process of stirring, standing, and removing the supernatant was repeated twice more.

[0149] (Second cleaning process) Next, similar to the first washing step, washing with pure water was performed three times according to the following procedure. First, after removing the supernatant liquid in the third acetic acid treatment, pure water was added and stirred. After stopping the stirring, the mixture was left to stand to allow the powder to settle, and the supernatant liquid was removed. The above washing process was repeated three times. After the above washing, the water and powder were separated by filtration, and the obtained powder was dried. The drying was performed at 130°C for 12 hours.

[0150] Next, the average particle size, crystallite size, and number of peaks in the XRD spectrum of each of the obtained precious metal alloy powders were measured by the following procedure. The measurement results are shown in Table 1.

[0151] (Average particle size) The average particle size of the obtained precious metal alloy powder was measured using a laser diffraction particle size distribution analyzer MT-3000 manufactured by Microtrackbell. Specifically, the alloy powder was placed in an aqueous solution of sodium hexametaphosphate circulating inside the particle size distribution analyzer, and after 1 minute of ultrasonic dispersion, the particle size distribution was measured. The obtained 50% particle size (D50) on a volume basis was taken as the average particle size of the precious metal alloy powder.

[0152] (crystallite size) The crystallite size of the obtained precious metal alloy powder was measured using an Ultima IV X-ray diffractometer manufactured by Rigaku. For the measurement, the powder to be measured was filled into a glass cell for powder measurement to prepare a sample. The measurement conditions were as follows: target: Cu, tube voltage: 40 kV, tube current: 40 mA, scanning range: 10 to 100°, sampling interval: 0.02°, and scanning speed: 30° / min. The crystallite size was calculated from the half-width of the diffraction peak obtained by the measurement using the Scherrer equation.

[0153] (Number of peaks in the XRD spectrum) In the XRD spectrum obtained by measuring the crystallite size, the number of peaks observed in the diffraction angle 2θ range of 38 to 44° was counted. In counting the number of peaks, the XRD peaks were separated by Gaussian fitting, and peaks with a peak width of 0.1° or more and a peak intensity of 1 / 100 or more of the maximum peak were considered to be peaks.

[0154] [Table 1]

[0155] <Production of Molded Product> Next, a compact was produced using the obtained precious metal alloy powder according to the procedure shown in FIG.

[0156] Specifically, the precious metal alloy powder, resin, and solvent were weighed and mixed to form a paste with the final paste contents of 80% by mass of the precious metal alloy powder, 1.8% by mass of the resin, and 18.2% by mass of the solvent. Ethyl cellulose was used as the resin, and Texanol was used as the solvent.

[0157] Next, the obtained paste was further kneaded using a three-roll mill to thoroughly disperse each component (mixing step).

[0158] Next, the paste was applied to an alumina substrate in the form of a film by screen printing. The applied paste was then dried at 120°C to volatilize the solvent contained in the paste, forming a thin film (drying step). The resulting thin film was peeled off from the substrate and pulverized in a crucible to obtain an alloy powder-resin mixed powder in which the precious metal alloy powder and resin were thoroughly and uniformly mixed.

[0159] Next, the alloy powder-resin mixed powder was subjected to pressure to produce a compact (green compact) (compacting step). Specifically, the alloy powder-resin mixed powder was placed in a mold and pressure was applied using a press. The compacting pressure was 500 MPa, and the pressing time was 1 minute.

[0160] <Production of fired body> The compact obtained in the molding step was then fired to obtain a fired body at the firing temperature shown in Table 2. The firing atmosphere was a 3% H2-97% N2 gas atmosphere, and the firing time was 5 hours.

[0161] For comparison, a mixed powder was used instead of the alloy powder to produce a compact and a sintered body. The mixed powder was a mixture of Ru powder, Rh powder, Pd powder, Ir powder, and Pt powder, with equiatomic amounts of each precious metal element. Other conditions were the same as those in the above-mentioned examples.

[0162] The obtained compacts and fired bodies (hereinafter referred to as samples) were each measured for crystallite size, the number of peaks in the XRD spectrum, and the coefficient of variation CV in the EDX spectrum by the following procedure. The measurement results are shown in Table 2.

[0163] (Average particle size) The average particle size of the alloy powder contained in the compacts of the obtained samples was measured using a Microtrackbell laser diffraction particle size distribution analyzer MT-3000. Specifically, the alloy powder was placed in an aqueous solution of sodium hexametaphosphate circulating within the particle size distribution analyzer, dispersed by ultrasound for 1 minute, and then the particle size distribution was measured. The obtained 50% particle size (D50) on a volume basis was taken as the average particle size of the precious metal alloy powder. Note that the average particle size of the compacts was the same as that of the precious metal alloy powder used as the raw material. The average particle size of the sintered bodies was not measured. This is because the particles in the sintered bodies are sintered together and do not maintain their particle shape.

[0164] (Number of peaks in the XRD spectrum) The XRD spectrum of the obtained sample was measured using a Rigaku Ultima IV X-ray diffractometer. The measurement conditions were: target: Cu, tube voltage: 40 kV, tube current: 40 mA, scan range: 10-100°, sampling interval: 0.02°, scan speed: 30° / min. In the obtained XRD spectrum, the number of peaks observed in the diffraction angle 2θ range of 38-44° was calculated. In counting the number of peaks, the XRD peaks were separated using Gaussian fitting, and peaks with a peak width of 0.1° or more and a peak intensity of 1 / 100 or more of the maximum peak were considered to be peaks.

[0165] (crystallite size) The crystallite size of the obtained precious metal alloy powder was measured using an Ultima IV X-ray diffractometer manufactured by Rigaku. For the measurement, the powder to be measured was filled into a glass cell for powder measurement to prepare a sample. The measurement conditions were as follows: target: Cu, tube voltage: 40 kV, tube current: 40 mA, scanning range: 10 to 100°, sampling interval: 0.02°, and scanning speed: 30° / min. The crystallite size was calculated from the half-width of the diffraction peak obtained by the measurement using the Scherrer equation.

[0166] However, in the comparative sample prepared using the mixed powder, multiple peaks were observed in the XRD spectrum used to calculate the crystallite size, and therefore the crystallite size could not be determined unambiguously, and therefore it is not shown in Table 2.

[0167] (Coefficient of variation in EDX) The coefficient of variation (CV) of the content of each precious metal element contained in the obtained sample was calculated from the measurement results of energy dispersive X-ray spectroscopy. For the measurement, a JEOL JSM-6010LA scanning electron microscope (SEM)-energy dispersive X-ray analyzer (EDX) was used. The measurement was performed on an alumina substrate and the film formed thereon, fixed to a sample stage with carbon tape. The measurement conditions were a magnification of 3000x and an acceleration voltage of 20 kV. Under these conditions, EDX quantitative measurement was performed at 30 randomly selected points to determine the content of each precious metal element. The coefficient of variation (CV) was calculated from the average and standard deviation of the obtained content.

[0168] [Table 2]

[0169] As can be seen from the results shown in Table 2, the compacts and sintered bodies of the present invention had one peak in the XRD spectrum, and the coefficient of variation (CV) in EDX was 0.2 or less for all five precious metal elements. This indicates that the precious metal alloy elements were completely alloyed and that the composition was extremely uniform. In contrast, in the comparative example using the mixed powder, the alloying was not sufficiently advanced and the composition was non-uniform.

Claims

1. A molded body made of alloy powder and resin, the alloy powder is a precious metal alloy powder made of an alloy of five or more kinds of precious metal elements, Among the contents of all precious metal elements contained in the precious metal alloy powder, ΔC, defined as the difference Cmax-Cmin between the maximum content Cmax and the minimum content Cmin, is 10.0 atomic % or less; and an average particle size, defined as the 50% particle size D50 in the volume-based cumulative particle size distribution, of 0.1 to 100 μm; The crystallite size is 60 nm or more, A molded body, wherein when peaks in an X-ray diffraction spectrum are separated by Gaussian fitting, and a peak having a peak width of 0.1° or more and a peak intensity of 1 / 100 or more of the maximum peak is regarded as a peak, the number of peaks observed in the X-ray diffraction spectrum within a diffraction angle 2θ range of 38 to 44° is 1.

2. 2. The molded body according to claim 1, wherein the precious metal alloy powder has a coefficient of variation CV of content of all the precious metal elements measured by energy dispersive X-ray spectroscopy of 0.2 or less.

3. A sintered body of a precious metal alloy, the noble metal alloy is a noble metal alloy consisting of five or more noble metal elements, Among the contents of all precious metal elements contained in the precious metal alloy, ΔC, which is defined as the difference Cmax-Cmin between the maximum content Cmax and the minimum content Cmin, is 10.0 atomic % or less; The fired body is The crystallite size is 60 nm or more, and A fired body, wherein when peaks in an X-ray diffraction spectrum are separated by Gaussian fitting, and a peak having a peak width of 0.1° or more and a peak intensity of 1 / 100 or more of the maximum peak is regarded as a peak, the number of peaks observed in the X-ray diffraction spectrum at a diffraction angle 2θ in the range of 38 to 44° is 1.

4. 4. The sintered body according to claim 3, wherein the coefficient of variation CV of the content of all the noble metal elements measured by energy dispersive X-ray spectroscopy is 0.2 or less.

5. A method for producing a molded body made of alloy powder and resin, comprising: an alloy powder preparation step of preparing the alloy powder as a raw material; a mixing step of mixing the resin with the alloy powder; a molding step of applying pressure to the alloy powder and the resin mixed in the mixing step to form the compact, the alloy powder is a precious metal alloy powder made of an alloy of five or more kinds of precious metal elements, Among the contents of all precious metal elements contained in the precious metal alloy powder, ΔC, defined as the difference Cmax-Cmin between the maximum content Cmax and the minimum content Cmin, is 10.0 atomic % or less; and an average particle size, defined as the 50% particle size D50 in the volume-based cumulative particle size distribution, of 0.1 to 100 μm; The crystallite size is 60 nm or more, A method for producing a molded body, wherein, when peaks in an X-ray diffraction spectrum are separated by Gaussian fitting, and a peak having a peak width of 0.1° or more and a peak intensity of 1 / 100 or more of the maximum peak is regarded as a peak, the number of peaks observed in the X-ray diffraction spectrum within a diffraction angle 2θ range of 38 to 44° is 1.

6. In the mixing step, a solvent is mixed with the alloy powder in addition to the resin, The method for producing a molded body according to claim 5 , further comprising a drying step of evaporating the solvent after the mixing step and before the molding step.

7. A method for producing a sintered body of a precious metal alloy, comprising: an alloy powder preparation step of preparing alloy powder as a raw material; a mixing step of mixing the alloy powder with a resin; a molding step of applying pressure to the alloy powder and the resin mixed in the mixing step to form a compact; and a firing step of firing the compact to form a fired body, the alloy powder is a precious metal alloy powder made of an alloy of five or more kinds of precious metal elements, Among the contents of all precious metal elements contained in the precious metal alloy powder, ΔC, defined as the difference Cmax-Cmin between the maximum content Cmax and the minimum content Cmin, is 10.0 atomic % or less; and an average particle size, defined as the 50% particle size D50 in the volume-based cumulative particle size distribution, of 0.1 to 100 μm; The crystallite size is 60 nm or more, A method for producing a sintered body, wherein when peaks in an X-ray diffraction spectrum are separated by Gaussian fitting, and a peak having a peak width of 0.1° or more and a peak intensity of 1 / 100 or more of the maximum peak is regarded as a peak, the number of peaks observed in the X-ray diffraction spectrum at a diffraction angle 2θ in the range of 38 to 44° is 1.

8. In the mixing step, a solvent is mixed with the alloy powder in addition to the resin, The method for producing a fired body according to claim 7 , further comprising a drying step of evaporating the solvent after the mixing step and before the molding step.

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