Noble metal alloy powder, noble metal alloy paste, noble metal alloy film, and production methods of those

Abstract

The present invention provides a noble metal alloy powder which has both high crystallinity and composition uniformity. This noble metal alloy powder is formed of an alloy of five or more noble metal elements, and has an average particle diameter of 10 µm or less and a crystallite size of 80 nm to 140 nm. With respect to the X-ray diffraction spectrum of this noble metal alloy powder, one peak is found within the diffraction angle 2θ range of 38° to 44°.

Description

Precious metal alloy powder, precious metal alloy paste, precious metal alloy film, and methods for producing the same

[0001] The present invention relates to a precious metal alloy powder, a precious metal alloy paste, a precious metal alloy film, and methods for producing the same.

[0002] Precious metal powders are chemically stable and have catalytic activity for various chemical reactions, and are therefore used in a variety of applications. For example, in the manufacture of electronic components, electrodes and wiring are formed by printing and firing pastes containing precious metal powders. They are also widely used as various catalysts, including electrode catalysts for fuel cells.

[0003] 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 a single 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 vary significantly depending on their composition. Therefore, to improve the functions and properties of noble metal powders, powders made from noble metal alloys with various compositions are in demand.

[0004] Furthermore, in recent years, research has also been conducted on high-entropy alloys made of precious metals. Although the definition varies, in the narrow sense, high-entropy alloys refer to alloys that contain five or more elements in roughly equiatomic amounts and form a single-phase solid solution. These alloys have attracted attention because they exhibit properties significantly different from those of ordinary alloys. High-entropy alloys are generally made using base metal elements such as Cr, Mn, Fe, Co, and Ni, but high-entropy alloys made only of precious metal elements have also been synthesized.

[0005] For example, in Non-Patent Document 1, a powder of a high-entropy alloy consisting of eight precious metal elements is produced by a wet reduction method (also called a liquid-phase reduction method or a chemical reduction method), and Non-Patent Document 1 also reveals that the powder exhibits extremely excellent catalytic activity for the hydrogen generation reaction.

[0006] Thus, multi-component precious metal alloy powders made of a variety of precious metal elements are attracting attention.

[0007] JP 10-102107 A JP 2011-162868 A JP 2022-150862 A JP 2022-139228 A

[0008] Journal of the American Chemical Society, February 2022, Vol. 144, No. 8, p.3365-3369

[0009] It is known that the physical properties of precious metal powders depend not only on their composition but also on their crystallinity. Therefore, it is necessary to control the crystallinity of the above-mentioned precious metal alloy powders. In particular, in various anticipated applications, high crystallinity is desirable from the viewpoints of ease of sintering, high activity, etc.

[0010] However, the inventors have found through their investigation that the noble metal alloy powder obtained by the wet reduction method employed in Non-Patent Document 1 has a relatively low crystallinity.

[0011] On the other hand, in addition to the wet method, a method of calcining a powder of a noble metal or a noble metal compound (hereinafter referred to as the calcination method) is also known as a method for producing noble metal powder.

[0012] For example, Patent Document 1 proposes a method for producing a Pt—Rh alloy powder by mixing Pt powder and Rh powder and firing the mixture in the presence of calcium carbonate. Patent Document 1 discloses that this method makes it possible to control the particle size and crystallite size of the resulting powder.

[0013] Furthermore, Patent Document 2 proposes producing a precious metal powder by subjecting a precious metal chloride to a reduction heat treatment to obtain agglomerates, crushing the agglomerates, and then calcining the agglomerates in the presence of calcium carbonate. Patent Document 2 discloses that this method can produce a precious metal powder with high crystallinity and purity.

[0014] Thus, the firing method makes it possible to produce a noble metal powder with excellent crystallinity.

[0015] However, as a result of further investigations by the present inventors, it was found that when precious metal alloy powder is produced by the conventional firing methods proposed in Patent Documents 1 and 2, uneven distribution of the constituent elements occurs, i.e., variations in the alloy composition occur. Variations in the alloy composition also cause variations in the properties of the powder, and therefore, in order to make the most of the inherent properties of precious metal alloys, a precious metal alloy powder with excellent uniformity in composition is required.

[0016] 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.

[0017] As described above, conventional techniques have had the problem that it is difficult to obtain a noble metal alloy powder that has both high crystallinity and excellent uniformity of composition.

[0018] Furthermore, if a noble metal alloy powder with excellent composition uniformity can be obtained, it would be beneficial in forming a noble metal alloy film. This point will be explained below.

[0019] There are various methods for forming metal films, such as electroplating, electroless plating, and physical vapor deposition (PVD), but in recent years, methods using metal pastes have become widely used, particularly in the electronics field.

[0020] Metal pastes are made by dispersing metal powder in a solvent, and can be easily patterned using techniques such as screen printing, making them suitable for forming wiring, electrodes, and resistors for small electronic components. Metal pastes can also be used as conductive bonding materials for joining various semiconductor elements to substrates.

[0021] Various metals can be used as the metal powder contained in such metal pastes, but noble metals are the most commonly used because noble metal elements are chemically stable and have various excellent properties such as low electrical resistance, high thermal conductivity, and catalytic activity in various chemical reactions.

[0022] As mentioned above, Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os belong to the same group of precious metal elements, but their actual physical and chemical properties differ. It is also known that the properties of precious metal alloys made of these precious metal elements vary significantly depending on their composition. Therefore, in the field of metal pastes, it has been proposed to form films made of multiple precious metal elements.

[0023] For example, Patent Document 3 proposes forming a thick-film resistor using a paste containing Ag powder and Pd powder. The temperature coefficient of resistance of the thick-film resistor can be controlled by adjusting the mixing ratio of the Ag powder and the Pd powder contained in the paste.

[0024] Furthermore, Patent Document 4 proposes forming a detection electrode of an ammonia sensor using a paste containing a powder of a precious metal alloy such as a Pt-Au alloy.

[0025] A film containing two kinds of precious metal elements can be formed using conventional pastes such as those disclosed in Patent Documents 3 and 4. However, if it were possible to form a multi-component precious metal alloy film made of more kinds of precious metals, it is expected that even more diverse properties could be obtained.

[0026] However, as a result of the inventors' investigations, it was found that simply using a paste containing a mixture of multiple precious metal powders results in uneven distribution of the constituent elements within the obtained precious metal alloy film, i.e., variation in the alloy composition. Although the reason for this is not completely clear, one possible reason is that there are large differences in properties such as melting point and specific gravity between precious metal elements.

[0027] Such variations in alloy composition result in variations in film properties, and therefore, in order to maximize the inherent properties of precious metal alloys, a paste capable of forming precious metal alloy films with excellent composition uniformity is required.

[0028] In particular, to produce a film made of the high-entropy alloy described above, it is necessary to minimize the imbalance in the composition. This is because if there is an imbalance in the composition, the condition of containing each element in equiatomic amounts will not be met, and the inherent properties of the high-entropy alloy will not be obtained. Furthermore, if the imbalance in the composition is too great, it may not be possible to form a single-phase solid solution.

[0029] As described above, conventional techniques have had the problem that it is difficult to obtain a multi-component noble metal alloy film with excellent composition uniformity.

[0030] The present invention aims to solve the above problems and provide a precious metal alloy powder that combines high crystallinity and uniformity of composition. It is also an object of the present invention to provide a precious metal alloy paste containing the precious metal alloy powder. It is also an object of the present invention to provide a multi-component precious metal alloy film that has excellent uniformity of composition.

[0031] As a result of investigations conducted to achieve the above object, the inventors of the present invention have found that a precious metal alloy powder having both high crystallinity and uniform composition can be obtained by adjusting the pH of a slurry containing raw material powder to 8.0 or higher and then firing the slurry. The present invention has been completed based on this finding, and its gist is as follows.

[0032] 1. A precious metal alloy powder comprising an alloy of five or more kinds of precious metal elements, the powder having an average particle size of 100 μm or less, a crystallite size of 60 nm or more, and an X-ray diffraction spectrum in which the number of peaks observed in the diffraction angle 2θ range of 38 to 44° is one.

[0033] 2. The precious metal alloy powder according to item 1, wherein the coefficient of variation CV of the content of all of the precious metal elements measured by energy dispersive X-ray spectroscopy is 0.2 or less.

[0034] 3. The precious metal alloy powder according to 1 or 2 above, having an average particle size of 10 μm or less.

[0035] 4. The precious metal alloy powder according to item 1 or 2 above, having an average particle size of more than 10 μm and not more than 100 μm.

[0036] 5. A precious metal alloy paste comprising the precious metal alloy powder according to any one of 1 to 4 above, a resin, and a solvent.

[0037] 6. A precious metal alloy film obtained by applying the precious metal alloy paste described in 5 above and firing it.

[0038] 7. A method for producing a precious metal alloy powder consisting of an alloy of five or more kinds of precious metal elements, comprising: a raw material preparation step of preparing the five or more kinds of precious metal elements as raw material powders, each separately in the form of a metal powder or a metal oxide powder; a slurry preparation step of mixing the raw material powder, calcium carbonate, and water to form a slurry and adjusting the pH of the slurry to 8.0 or higher; a mixing step of mixing the slurry; a first firing step of firing the slurry in a non-oxidizing atmosphere to form an alloy powder; a first acetic acid treatment step of treating the alloy powder with acetic acid; and a first washing step of washing and drying the alloy powder after the first acetic acid treatment step.

[0039] 8. The method for producing a precious metal alloy powder according to the above item 7, further comprising a second firing step of firing the alloy powder after the first washing step in a non-oxidizing atmosphere.

[0040] 9. The method for producing a precious metal alloy powder according to claim 8, further comprising a third firing step of mixing the alloy powder after the second firing step with calcium carbonate and firing the resulting mixture in a non-oxidizing atmosphere, a second acetic acid treatment step of treating the alloy powder after the third firing step with acetic acid, and a second washing step of washing and drying the alloy powder after the second acetic acid treatment step.

[0041] 10. The method for producing a precious metal alloy powder according to 3 or 4 above, further comprising, prior to the second firing step, a particle size adjusting step of adjusting the particle size of the alloy powder after the first washing step.

[0042] 11. A method for producing a precious metal alloy paste, comprising mixing the precious metal alloy powder according to any one of 1 to 4 above, a resin, and a solvent to form a paste.

[0043] 12. A method for producing a precious metal alloy film, comprising applying the precious metal alloy paste according to 5 above onto a substrate, and firing the applied precious metal alloy paste to form a precious metal alloy film.

[0044] According to the present invention, a noble metal alloy powder having both high crystallinity and uniformity of composition can be provided, and by using a noble metal alloy paste containing the noble metal alloy powder, a noble metal alloy film having excellent uniformity of composition can be obtained.

[0045] Fig. 1 is a flow chart showing a method for producing a precious metal alloy powder according to a first embodiment of the present invention; Fig. 2 is a flow chart showing a method for producing a precious metal alloy powder according to a second embodiment of the present invention; Fig. 3 is a flow chart showing a method for producing a precious metal alloy powder according to a third embodiment of the present invention; Fig. 4 is an EDX map showing the distribution of each element in Inventive Example No. 2, Comparative Example No. 10, and Comparative Example No. 11.

[0046] Hereinafter, embodiments of the present invention will be specifically described, but the present invention is not limited to the embodiments described below.

[0047] [Noble Metal Alloy Powder] The noble metal alloy powder according to one embodiment of the present invention is a noble metal alloy powder made of an alloy of five or more noble metal elements, and satisfies the following conditions (1) to (3): (1) an average particle size of 100 μm or less, (2) a crystallite size of 60 nm or more, and (3) the number of peaks observed in the diffraction angle 2θ range of 38 to 44° in the X-ray diffraction spectrum is 1 or less.

[0048] Noble Metal Element The noble metal constituting the noble metal alloy powder of the present invention is not particularly limited and any noble metal element can be used. That is, the noble metal alloy powder of the present invention is a powder of an alloy containing at least five elements selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os.

[0049] Among the above-mentioned noble metal elements, Os has a tendency to volatilize during the firing process, and therefore, from the viewpoint of ease of production, the noble metal alloy powder is a powder of an alloy containing at least five elements selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ir, and Ru.

[0050] The number of precious metal elements constituting the alloy is not particularly limited as long as it is 5 or more. That is, the alloy may contain all eight precious metal elements. The number of precious metal elements may be 6 or 7.

[0051] The proportion (content) of each precious metal element contained in the precious metal alloy powder of the present invention 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 approximately equal. 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 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 %.

[0052] Average particle size: 100 μm or less According to the manufacturing method described below, it is possible to obtain a precious metal alloy powder having a wide range of average particle sizes of 100 μm or less. Therefore, the average particle size of the precious metal alloy powder is set to 100 μm or less. On the other hand, there is no particular restriction on the lower limit of the average particle size. However, from the viewpoint of ease of manufacturing and ease of handling, the average particle size is preferably 0.1 μm or more, and more preferably 0.2 μm or more.

[0053] The noble metal alloy powder of the present invention can be used for various purposes including metal paste, and therefore can have an average particle size suited to the purpose.

[0054] For example, in certain applications, powders having a relatively small average particle size are preferably used. In such cases, the average particle size is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. Such fine noble metal alloy powders are more preferably used as raw materials for metal pastes, for example.

[0055] However, when the average particle size of a precious metal alloy powder is 10 μm or less, the particles tend to aggregate, reducing the powder's fluidity, making it unsuitable for use in 3D printers. For example, when using a powder in a powder-bed additive manufacturing device, poor powder fluidity makes it difficult to perform proper squeegeeing. Therefore, for applications requiring fluidity, such as 3D printers, it is preferable to set the average particle size to greater than 10 μm. On the other hand, if the average particle size exceeds 100 μm, the density of the molded object decreases when modeled using a 3D printer, and the surface roughness also increases. Therefore, the average particle size is preferably 80 μm or less, more preferably 50 μm or less, and even more preferably 20 μm or less.

[0056] 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.

[0057] Crystallite size: 60 nm or more The noble metal alloy powder 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.

[0058] The crystallite size can be determined from the half-width of a diffraction peak obtained by X-ray diffraction (XRD) measurement.

[0059] Number of peaks in the XRD spectrum: 1 If the precious metal elements contained in the powder are not sufficiently alloyed, multiple peaks attributable to each element are observed in the X-ray diffraction spectrum at a diffraction angle 2θ of 38 to 44°. Therefore, in the present invention, the number of peaks observed in this range is defined as 1. If there is one peak in the XRD spectrum, it can be said that uniform alloying has been achieved. Note that the range of the 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.

[0060] Coefficient of variation CV of content measured by EDX In the present invention, for all metal elements constituting the precious metal alloy powder, the coefficient of variation CV of 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 content of each precious metal element constituting the precious metal alloy powder is 0.2 or less. According to the present invention, an extremely uniform precious metal alloy powder having a coefficient of variation CV of 0.2 or less can be obtained. On the other hand, 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.

[0061] 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.

[0062] Average circularity coefficient: The shape of the noble metal alloy powder is not particularly limited, but from the viewpoint of further improving suitability for applications such as 3D printers, it is desirable that the particles constituting the powder have high sphericity. Specifically, the average circularity coefficient of the particles constituting the noble metal alloy powder is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, and most preferably 0.92 or more.

[0063] Here, the average circularity coefficient is defined as a value obtained by the following method. First, the target precious metal alloy powder is observed under a microscope, and 100 particles are randomly selected from the particles contained within the field of view. Next, the area A and perimeter P are determined for each of the selected 100 particles. The circularity coefficient φ of each particle can be calculated from the area A and perimeter P of the particle using the following equation (1). Here, the circularity coefficient φ is a dimensionless number: φ=4πA / P ２ ...(1) The circularity coefficient is calculated for each of the selected 100 particles, and the average value is taken as the average circularity coefficient.

[0064] The upper limit of the average circularity coefficient is not particularly limited, but the upper limit by definition is 1. When the circularity coefficient is 1, it means that the particle is a perfect circle.

[0065] As described above, the noble metal alloy powder of the present invention has excellent properties, including high crystallinity and uniform composition. The applications of the noble metal alloy powder of the present invention are not particularly limited, and it can be used for any application.

[0066] For example, the precious metal alloy powder of the present invention can be suitably used as a component of the precious metal alloy paste described below. Furthermore, the precious metal alloy powder of the present invention can be suitably used for manufacturing metal components using a 3D printer. The 3D printer is not particularly limited, and any type of 3D printer can be used. Examples of 3D printers include powder bed printers, directed energy deposition (DED), fused deposition modeling (FDM), arc welding printers, binder jet printers, supersonic deposition printers, and liquid metal jet printing printers. In particular, the precious metal alloy powder of the present invention can be suitably used as a material for additive manufacturing using the powder bed printer.

[0067] [Method for producing precious metal alloy powder] Next, a method for producing a precious metal alloy powder of the present invention will be described. The production methods in the present disclosure can be broadly divided into two methods: a method in which firing is performed only once, and a method in which firing 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 method for producing the powder will be described below.

[0068] - Production of powder with a relatively small average particle size Figure 1 is a flow diagram showing a method for producing a precious metal alloy powder in one embodiment of the present invention. As shown in Figure 1, the method for producing a precious metal alloy powder in one embodiment of the present invention includes the following steps (1) to (6), and one firing is performed in this production process: (1) Raw material preparation step (2) Slurry preparation step (3) Mixing step (4) First firing step (5) First acetic acid treatment step (6) First washing step

[0069] 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.

[0070] (1) Raw Material Preparation Step 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. The number of precious metal elements may be five or more, and there is no particular upper limit. In other words, all eight types of precious metal elements may be included. The number of precious metal elements may be six or seven. For example, when producing a five-element alloy, five raw material powders may be prepared.

[0071] 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 also not particularly limited, but may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more.

[0072] 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, the density ρ (g / cm) of the particles constituting the raw material powder. ３ ) and BET specific surface area s (m ２ / g) according to the following formula (2): d=6 / ρs (2)

[0073] The raw material powder may be either a metal powder or a metal oxide powder. For example, for Pt, Pt powder may be used, but platinum oxide (PtO ２ ) powder can also be used. ２ , RhO ３ Alternatively, oxide powders such as palladium oxide (PdO) can be used. These oxide powders are thermally decomposed during firing and function as a source of precious metals. Basically, there is no difference in the function of the raw material whether a metal powder or a metal oxide powder is used, so the powder can be selected depending on the availability of the powder.

[0074] However, for Ru, ruthenium oxide (RuO ２ It is preferable to use metallic ruthenium powder as the raw material, rather than ruthenium carbide powder.

[0075] 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.

[0076] (2) Slurry Preparation Step: 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 step 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, and thus contribute to the refinement of the final precious metal alloy powder.

[0077] 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.

[0078] The calcium carbonate can be added in any form. Typically, calcium carbonate powder may be used. When calcium carbonate powder is used, the average particle size of the calcium carbonate powder is not particularly limited, but 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, is determined by the density ρ (g / cm) of the particles constituting the calcium carbonate. ３ ) and BET specific surface area s (m ２ / g) according to the following formula (2): d=6 / ρs (2)

[0079] pH: 8.0 or higher In the above-mentioned slurry preparation step, it is important to maintain the pH of the slurry at 8.0 or higher. If the pH of the slurry is less than 8.0, the compositional uniformity of the final 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.

[0080] 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.

[0081] 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 is saturated. Furthermore, if the pH is increased above 10, a large amount of alkali must be added. As a result, large amounts of sodium, potassium, and other elements added as alkali may remain 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.

[0082] (3) Mixing Step 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 of these, it is preferable to use a bead mill.

[0083] (4) First Firing Step: 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 step can be performed in any device without particular limitations. Typically, an electric furnace can be used.

[0084] 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.

[0085] 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 equal to or lower 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 T １ is defined 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. １ is defined by the following formula: Ｈ It is preferable to set it as follows: T Ｌ (°C) = T Ｍ (K)×0.55-273.15T Ｈ (°C) = T Ｍ (K) × 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.

[0086] The firing time in the first firing step is not particularly limited, but is preferably 1 hour or more from the viewpoint of grain growth of the alloy, and is preferably 5 hours or less from the viewpoint of production efficiency.

[0087] (5) First Acetic Acid Treatment Step Next, the fired product (alloy powder) obtained in the first firing step is treated with acetic acid. By performing the acetic acid treatment, calcium contained in the alloy powder can be removed. Note that 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 alloy homogeneity. 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.

[0088] The method of the acetic acid treatment is not particularly limited, but typically, the alloy powder is stirred in an acetic acid aqueous solution to dissolve the calcium contained in the alloy powder. The acetic acid treatment can be performed 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 performed two or more times, and more preferably three or more times. On the other hand, the upper limit of the number of times the acetic acid treatment is performed is not particularly limited, but from the viewpoint of production efficiency, it is preferably 10 times or less, and more preferably 5 times or less. When the acetic acid treatment is performed multiple times, it is preferable to use a new acetic acid aqueous solution for each time.

[0089] During the acetic acid treatment, the alloy powder may be placed in a pre-prepared aqueous acetic acid solution, or the alloy powder may be placed in pure water first, and then acetic acid may be added to the pure water.

[0090] A specific example of a suitable acetic acid treatment method will be described below.

[0091] First, the alloy powder is placed in pure water and stirred. This converts the calcium oxide contained in the alloy powder 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. The above treatment can be repeated two or more times.

[0092] (6) First Washing Step Next, the alloy powder after the first acetic acid treatment is washed with water and dried (first washing step). By washing with water, the acid and calcium dissolved in the acid are removed.

[0093] It is preferable to use pure water for the water washing. The method for water washing is not particularly limited, but for example, after removing the supernatant liquid in the first 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. The water washing is preferably repeated two or more times, more preferably three or more times. On the other hand, there is no particular upper limit to the number of times the water washing is performed, but from the viewpoint of production efficiency, it is preferably 10 times or less, more preferably 5 times or less. After the water washing, it is preferable to filter the powder to separate the water from the powder, and then subject the obtained powder to the subsequent drying step.

[0094] The drying can be carried out by any method that can remove moisture. Natural drying may be used, but heated drying is preferable to efficiently remove moisture. When heated drying is performed, 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 higher, more preferably 5 hours or higher. It may be 10 hours or higher. On the other hand, the upper limit of the heating time is not particularly limited, but is typically preferably 100 hours or lower, more preferably 50 hours or lower.

[0095] After the drying, the obtained noble metal alloy powder is preferably sieved to loosen particles that have aggregated during the washing process.

[0096] By the above procedure, a noble metal alloy powder that satisfies the conditions of the present invention can be obtained.

[0097] Production of 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 with an average particle size of up to 100 μm. Specifically, this production method is suitable for producing powder with an average particle size of more than 5 μm, and more suitable for producing powder with an average particle size of more than 10 μm.

[0098] 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.

[0099] (When firing is performed twice) Fig. 2 is a flow diagram showing a manufacturing method when firing is performed twice. As shown in Fig. 2, 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. 1.

[0100] For the sake of explanation, the process from the raw material preparation process to the first washing process will be referred to as the "pre-process," and the process after the first washing process will be referred to as the "post-process." Furthermore, after the first washing process and before the second firing process, a particle size adjustment process may be optionally performed. When a particle size adjustment process is performed, the particle size adjustment process is included in the post-process, as shown in FIG. 2 .

[0101] In this embodiment, a powder with high crystallinity and excellent compositional uniformity is first produced in a pre-process. However, the powder obtained at this stage is composed of relatively small particles (primary particles). These primary particles then aggregate to form roughly spherical aggregates (secondary particles), and these secondary particles have particle sizes on the order of several tens to several hundred microns. Therefore, by further processing the powder in a post-process, it is possible to further increase the average particle size while maintaining high crystallinity and compositional uniformity.

[0102] Particle Size Adjustment Step In a post-process, the particle size of the alloy powder after the first washing step may be adjusted (particle size adjustment step) prior to the subsequent second firing step. By performing particle size adjustment, it is possible to more easily obtain a precious metal alloy powder with the 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 subsequent second firing step). Therefore, in the particle size adjustment step, the particle size may be adjusted to match the particle size of the precious metal alloy powder that is finally desired to be obtained.

[0103] 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 recovered. This removes coarse particles from the alloy powder. The recovered powder is then sieved through a sieve with even finer openings, and the powder remaining on the sieve is recovered. This removes excessively fine powder. By passing the powder through two sieves with different openings in this way, a powder of the desired particle size can be obtained.

[0104] 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 step and use the powder that did not pass through the sieve (over-sieved powder).

[0105] Second Firing Step: 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.

[0106] 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, so if they are mixed with calcium carbonate before the second firing, the secondary particle agglomerates will break up, 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 more appropriately control the particle size.

[0107] 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 a temperature at which the melting point T Ｍ Therefore, the second baking temperature T ２ is defined by the following formula: Ｌ That’s all, T Ｈ It is preferable to set it as follows: T Ｌ (°C) = T Ｍ (K)×0.45-273.15T Ｈ (°C) = T Ｍ (K) × 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.

[0108] The time for which the second baking is performed (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.

[0109] 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.

[0110] (When firing is performed three times) Figure 3 is a flow diagram showing a manufacturing method when firing is performed three times. As shown in Figure 3, 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 Figure 2. Each of steps (8) to (10) will be described below. In this embodiment, as in the case of Figure 2, a particle size adjustment step can be optionally performed after the first washing step and before the second firing step.

[0111] Third Firing Step: 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 stages, the primary particles constituting the secondary particles can be more firmly bonded together and the sphericality of the particles can be further increased. The third firing step can be performed in any device without any particular limitations. Typically, an electric furnace can be used.

[0112] 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.

[0113] 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.

[0114] 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 a temperature that is higher than the melting point T Ｍ The third baking temperature T ３ 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. ３ is defined by the following formula: Ｈ It is preferable to set it as follows: T Ｌ (°C) = T Ｍ (K)×0.55-273.15T Ｈ (°C) = T Ｍ (K) × 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.

[0115] The firing time in the third 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.

[0116] Second Acetic Acid Treatment Step: 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. Note that 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.

[0117] 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.

[0118] Second Washing Step: The alloy powder after the second 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.

[0119] By the above-mentioned treatment, a noble metal alloy powder that satisfies the conditions of the present invention can be obtained.

[0120] [Paste] Next, a description will be given of a precious metal alloy paste according to one embodiment of the present invention. The precious metal alloy paste (hereinafter, sometimes simply referred to as "paste") according to one embodiment of the present invention is a paste containing a precious metal alloy powder, a resin, and a solvent.

[0121] [Noble Metal Alloy Powder] The noble metal alloy powder used is the noble metal alloy powder described above. The disclosures in the above description of the noble metal alloy powder are all incorporated by reference in this embodiment.

[0122] Average particle size: If the precious metal alloy powder contained in the paste is coarse, the film obtained using the paste will also be rough, making it unsuitable for forming fine patterns or thin films. Furthermore, because the surface roughness of the film increases, when multiple films are stacked, part of the lower layer film will penetrate through the upper layer film, causing a short circuit. Therefore, the average particle size of the precious metal alloy powder contained in the paste is set to 100 μm or less, preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less.

[0123] On the other hand, although there is no particular lower limit for the average particle size, if the particles are too small, they will re-aggregate even after being dispersed in a solvent, and coarse aggregates will likely form in the paste. The formation of coarse aggregates not only reduces the stability of the paste, but also makes the film obtained using the paste coarse. Furthermore, coarse aggregates can cause problems such as clogging of the screen in screen printing and clogging of the dispenser nozzle in dispenser application. Furthermore, if the particles are too small, there is a risk of fire when mixed with an organic solvent due to the catalytic activity of the precious metal. Therefore, the average particle size of the precious metal alloy powder is preferably 0.1 μm or more, and more preferably 0.2 μm or more.

[0124] The precious metal alloy powder used in the paste can be produced by the above-mentioned production method. That is, it can be produced by firing raw material powder. While wet reduction is also known as a method for producing precious metal alloy powder, the powder obtained by wet reduction has low crystallinity and does not satisfy the crystallite size requirement of the present invention. Furthermore, when using powder obtained by wet reduction, significant shrinkage occurs when the applied paste is fired, which can result in the film being broken.

[0125] [Resin] Next, the resin, which is one component of the precious metal alloy paste of the present invention, will be described. The resin is a component that functions as a binder, and after application, it is decomposed and removed by firing, so it usually does not remain in the precious metal alloy film.

[0126] 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 because it does not affect other components during paste production or film firing.

[0127] The resin content in the paste is not particularly limited and may be adjusted depending on the form of use of the paste. Typically, the resin content in the paste is preferably 0.5% by mass or more, more preferably 1.0% by mass or more. On the other hand, the upper limit of the content is not particularly limited, but is preferably 10.0% by mass or less, more preferably 7.0% by mass or less. Here, the resin content in the paste is the ratio of the mass of the resin to the total mass of the paste, expressed as a percentage.

[0128] [Solvent] The noble metal alloy paste of the present invention contains a solvent as another component. The solvent volatilizes after the paste is applied, and therefore does not usually remain in the noble metal alloy film.

[0129] The solvent is not particularly limited and any solvent can be used, but it is preferable that the boiling point be 300°C or less. Typically, an organic solvent can be used as the solvent. 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, Texanol, ethylene glycol, propylene glycol, ethylene glycol monophenyl ether, benzyl alcohol, kerosene, paraffin, γ-butyrolactone, N-methylpyrrolidone, butyl carbitol, turpentine oil, α-terpineol, turpineol, and terpineol acetate, and it is more preferable to use Texanol.

[0130] In one embodiment of the present invention, the precious metal alloy paste may be a precious metal alloy paste comprising the above-described precious metal alloy powder, a resin, and a solvent. In another embodiment, the precious metal alloy paste may further include optional additional components. The additional components may include, for example, at least one selected from the group consisting of a surfactant, a thickener, a plasticizer, and an inorganic filler.

[0131] Surfactants Surfactants function as dispersants and improve the stability of the solid content in the paste. Surfactants also have the effect of improving the wettability of the paste when it is applied. The surfactant is not particularly limited, and any surfactant can be used. The surfactant may be any of cationic surfactants, anionic surfactants, amphoteric surfactants, and nonionic surfactants. Among these, anionic surfactants are preferred, and diamine-based anionic surfactants are more preferred.

[0132] Thickener: An organic thickener can be added to adjust the viscosity of the paste. Any thickener can be used without any particular limitation. The thickener may be either an organic thickener or an inorganic thickener, or both.

[0133] As the organic thickener, any organic thickener can be used, such as dibenzylidene-D-sorbitol (1,3:2,4-bis-O-benzylidene-D-glucitol), hydrogenated castor oil, amide wax, polyethylene oxide, vegetable oil polymer, surfactant, etc. For example, organic thickeners that are vegetable oil derivatives and are used as thickeners for paints, inks, etc. include Devizol, Lilanit HT, and Lilanit Special (all manufactured by Henkel Hakusui Chemical Co., Ltd.). Furthermore, examples of the inorganic thickener include ultrafine powders of alumina and silica (average particle size of 0.1 μm or less), bentonite, calcium carbonate, etc.

[0134] Plasticizer: The plasticizer may be either a phthalate-based plasticizer or a non-phthalate-based plasticizer. The phthalate-based plasticizer is not particularly limited, and any phthalate ester may be used. Examples of the phthalate ester include bis(2-ethylhexyl) phthalate (DEHP) and diisononyl phthalate (DINP). Examples of the non-phthalate plasticizer include adipic acid-based plasticizers (adipic acid esters), phosphate-based plasticizers (phosphate esters), and trimellitic acid-based plasticizers (trimellitic acid esters).

[0135] The inorganic filler is not particularly limited, and powder of any inorganic material can be used. It is preferable to use at least one selected from the group consisting of glass powder, ceramic powder, and metal oxide powder as the inorganic filler. From the viewpoint of improving adhesion, it is preferable that the inorganic filler contains a powder made of the same material as the material contained in the substrate to which the paste is applied. Furthermore, when an inorganic filler having a higher melting point than the precious metal alloy powder is used, the inorganic filler functions as a sintering inhibitor.

[0136] The glass powder is not particularly limited, and powder made of any glass can be used. The glass may be, for example, borosilicate glass. The particle size of the glass powder is preferably 0.1 to 5.0 μm. Furthermore, from the viewpoint of improving adhesion when the paste is applied to a substrate to form a film, the softening point (Ts) of the glass powder is preferably 400 to 700°C, and more preferably 450 to 650°C.

[0137] The ceramic powder is not particularly limited, and powder made of any ceramic can be used. Examples of the ceramic include ZrO ２ The ZrO containing ceramic can be used. ２ The ceramic containing ZrO is preferably stabilized zirconia. ２ The ceramic-containing material may further contain an oxide having ion conductivity, such as at least one oxide selected from the group consisting of La, Ce, Pr, Nd, Sm, and Hf.

[0138] As the metal oxide powder, for example, at least one powder selected from the group consisting of nickel oxide, tantalum oxide, niobium oxide, aluminum oxide, zirconium oxide, yttrium oxide, magnesium oxide, silicon oxide, titanium oxide, manganese oxide, calcium oxide, bismuth oxide, copper oxide, yttrium oxide, zirconium oxide, and zinc oxide can be used.

[0139] The average particle size of the inorganic filler is not particularly limited, but from the viewpoint of dispersibility, it is preferably 0.1 to 10 μm, more preferably 5 μm or less, and even more preferably 3 μm or less.

[0140] The average particle size of the inorganic filler is defined as the 50% particle size D50 in the cumulative particle size distribution based on volume, i.e., the median diameter. The average particle size can be measured using a laser diffraction particle size distribution analyzer. The average particle size of the inorganic filler can be measured in the same manner as the average particle size of the precious metal alloy powder.

[0141] (Solid Content) The content of each component in the paste of the present invention is not particularly limited. However, if the solid content is too low, the resulting film will be too thin. Therefore, the solid content of the paste is preferably 50% by mass or more. On the other hand, if the solid content is too high, it may be difficult to form the paste. Therefore, the solid content of the paste is preferably 90% by mass or less.

[0142] [Method for Producing Paste] Next, a preferred method for producing the noble metal alloy paste will be described. The noble metal alloy paste can be produced by mixing a noble metal alloy powder that satisfies the above-mentioned conditions with a resin and a solvent.

[0143] The mixing is not particularly limited and can be carried out by any method. From the viewpoint of uniformly dispersing the precious metal alloy powder in the paste, it is preferable to mix the components and then knead them. The kneading can be carried out 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, and 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.

[0144] After kneading, filtration can be optionally performed. By performing filtration, aggregates and foreign matter contained in the paste can be removed. Any paste filtration device can be used for the filtration.

[0145] After filtration, the viscosity can be further adjusted as desired. To adjust the viscosity, for example, the viscosity of the paste can be measured using a viscometer, and a solvent, resin, or the like can be added to achieve the desired viscosity. Adding a solvent decreases the viscosity, while adding a resin increases the viscosity.

[0146] The viscosity of the paste is not particularly limited and may be adjusted appropriately depending on the intended use. However, if the viscosity is excessively high, it becomes difficult to apply to the base. Therefore, the viscosity of the paste is preferably 500 Pa·s or less, more preferably 400 Pa·s or less. On the other hand, if the viscosity is excessively low, the resulting film will be too thin. Therefore, the viscosity of the paste is preferably 1 mPa·s or more, more preferably 5 mPa·s or more.

[0147] The optimum viscosity of the paste differs depending on the application method, so it is preferable to adjust the viscosity in advance to suit the expected application method. Examples of viscosities suitable for application methods are listed below. Screen printing: 100 to 400 Pa·s Spray coating: 1 mPa·s to 100 mPa·s Inkjet: 1 mPa·s to 50 mPa·s Dispense: 1 Pa·s to 200 Pa·s

[0148] [Noble Metal Alloy Film] Next, a metal alloy film according to one embodiment of the present invention will be described. The noble metal alloy film is obtained by applying the noble metal alloy paste and firing it. The noble metal alloy film thus obtained is a film made of an alloy of five or more noble metal elements contained in the noble metal alloy powder used. The noble metal alloy film has excellent compositional uniformity. Typically, the number of peaks observed in the X-ray diffraction spectrum within the diffraction angle 2θ range of 38 to 44° is one.

[0149] [Method for producing a precious metal alloy film] The precious metal alloy paste can be applied to a substrate and then fired to produce a precious metal alloy film. The method for applying the paste to the substrate is not particularly limited, and any method can be used, but it is preferable to use a method that allows patterned application, such as screen printing. Furthermore, the substrate to be used is not particularly limited, and the paste can be applied to any substrate.

[0150] After applying the paste, it is preferable to dry it before firing it to volatilize the solvent contained in the applied paste. The drying temperature is not particularly limited and may be determined depending on the type of solvent used. A preferred drying temperature is 50 to 200°C. The drying can be performed in any atmosphere, but is typically performed in air.

[0151] Next, the paste is fired. By firing, the particles of the precious metal alloy powder contained in the paste are sintered together to form a precious metal alloy film. During this process, the resin contained in the paste is decomposed and removed.

[0152] The firing is preferably carried out in two stages. In the first firing stage, the resin contained in the paste is removed (binder removal). The first firing stage can be carried out in the atmosphere.

[0153] The baking temperature in the first baking step may be adjusted depending on the type and composition of the resin used, but is preferably 200° C. or higher. On the other hand, from the viewpoint of preventing oxidation of the precious metal elements, it is preferably 500° C. or lower, and more preferably 400° C. or lower.

[0154] Thereafter, firing is carried out in the second firing step. The second firing step can be carried out in a non-oxidizing atmosphere. 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.

[0155] The firing temperature in the second firing step is preferably 1000° C. or higher to promote firing, and more preferably 1300° C. or higher. On the other hand, if the firing temperature is too high, the effect will saturate, so the firing temperature is preferably 1500° C. or lower.

[0156] The effects of the present invention will be specifically described below with reference to examples and comparative examples of the present invention, but the present invention is not limited thereto.

[0157] Example 1 First, a quinary precious metal alloy powder consisting of Ru, Rh, Pd, Ir, and Pt was produced by the following procedure.

[0158] [Pre-process] As raw material powder, Pt, Pd, IrO ２ Among the powders, Pt black, Pd black, and Rh black were used as the Pt, Pd, and Ph powders, respectively. The Ru powder was RuO ２ It was prepared by reducing the powder.

[0159] The raw material powder was mixed with calcium carbonate powder and water (pure water) to prepare a slurry. An alkali was added for pH adjustment as necessary, and the pH of the slurry was adjusted to the values ​​shown in Table 1. In Inventive Examples 1 and 2 and Comparative Examples 10 and 11, powders with different particle sizes and crystallite sizes were obtained by changing the conditions in the slurry preparation step (the pH of the slurry and the amounts of calcium carbonate and water added). For example, in Inventive Example 2, the amount of calcium carbonate added was 0.8 times the weight of the total amount of raw material powder, and the amount of water added was 2 times the weight of the total amount of raw material powder and calcium carbonate powder.

[0160] 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.

[0161] The mixed slurry was ２ -H ２ The mixture was fired in a 3% H atmosphere to obtain an alloy powder. Specifically, the slurry was first dried in a dryer at 130°C to remove moisture, and a mixed powder was obtained. 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 3% H. ２ / 97%N ２ The firing was performed in a gas atmosphere at a firing temperature of 1300° C. for 5 hours.

[0162] Next, the alloy powder obtained in the firing step was treated with acetic acid, washed with pure water, and dried.

[0163] (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 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 liquid was repeated twice more.

[0164] Next, the powder was washed with pure water three times according to 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.

[0165] (Drying) After the washing, the powder was separated from the water by filtration, and the obtained powder was dried at 130° C. for 12 hours.

[0166] The dried powder was sieved to break down any agglomerated powder. A stainless steel test sieve with a mesh size of 125 μm was used as the sieve. All particles passed through the sieve, with no particles remaining on the sieve.

[0167] [Post-Processing] In Examples 4 to 9, in order to obtain a noble metal alloy powder having a larger average particle size, the following post-processing was further carried out.

[0168] (Particle Size Adjustment Step) The alloy powder obtained in the previous step was subjected to particle size adjustment. The particle size adjustment was performed using a stainless steel test sieve under the following conditions. However, for Inventive Example No. 6, particle size adjustment was not performed for comparison. - Inventive Examples Nos. 5, 7, 8, and 9: The alloy powder was sieved through a 53 μm mesh sieve, and the powder remaining on the sieve was subjected to the subsequent second firing step. - Inventive Example No. 4: 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. The powder that passed through the 38 μm mesh sieve was further sieved through a 20 μm mesh sieve, and the powder remaining on the sieve was subjected to the subsequent second firing step.

[0169] (Second Firing Step) Next, the alloy powder after the particle size adjusting step was subjected to a second firing in a non-oxidizing atmosphere. The second firing was performed by placing the alloy powder in a crucible and using an atmospheric heating electric furnace. The firing atmosphere was 100% N ２ The second firing was performed in a gas atmosphere at a temperature of 1000°C for one hour. For comparison, however, the second firing temperature was set to 800°C in Inventive Example No. 5 and 1100°C in Inventive Example No. 9.

[0170] (Third Firing Step) Next, the powder after the second firing step was further mixed with calcium carbonate and subjected to the third firing. Specifically, first, the powder after the second firing step was mixed with calcium carbonate powder to prepare 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 100% N ２ The third firing was performed in a gas atmosphere at a temperature of 1300° C. for a period of 5 hours.

[0171] However, for comparison, inventive example No. 7, the third firing step and subsequent steps were not performed.

[0172] (Second Acetic Acid Treatment Step) Next, the alloy powder obtained in the calcination 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, following the procedure below. First, the calcined product (alloy powder) was placed in pure water and stirred. This caused the calcium oxide contained in the calcined product to convert to calcium hydroxide. Next, acetic acid was further 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 further added, and the process of stirring, standing, and removing the supernatant liquid was repeated twice.

[0173] (Second Washing Step) 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 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.

[0174] Next, the average particle size, crystallite size, number of peaks in the XRD spectrum, and coefficient of variation CV in the EDX spectrum were measured for each of the obtained noble metal alloy powders by the following procedures. The measurement results are shown in Table 1.

[0175] (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.

[0176] (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 formula.

[0177] (Number of Peaks in XRD Spectrum) In the XRD spectrum obtained by the above crystallite size measurement, the number of peaks observed in the diffraction angle 2θ range of 38 to 44° was determined. 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.

[0178] (Coefficient of Variation CV in EDX) The coefficient of variation CV of the content of each precious metal element contained in the obtained precious metal alloy powder was calculated from the measurement results of energy dispersive X-ray spectroscopy. For the measurement, a scanning electron microscope (SEM)-energy dispersive X-ray analyzer (EDX) JSM-6010LA manufactured by JEOL Ltd. was used, and the alloy powder was fixed on carbon tape to prepare a measurement sample. 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. For reference, the distribution of each element obtained by the EDX measurement for the powders of Invention Example No. 2, Comparative Example No. 10, and Comparative Example No. 11 is shown in FIG. 4.

[0179]

[0180] As can be seen from the results shown in Table 1 and Figure 4, the present invention can provide a precious metal alloy powder that combines high crystallinity and uniformity of composition. On the other hand, the powders of the comparative examples, in which the pH of the slurry did not satisfy the conditions of the present invention, were inferior in crystallinity and uniformity of composition.

[0181] For comparison, a precious metal alloy powder was prepared using a mixed powder instead of the alloy powder obtained in the previous step (Comparative Example No. 12). The mixed powder was prepared by mixing Ru powder, Rh powder, Pd powder, Ir powder, and Pt powder so that the precious metal elements were equiatomic. Other conditions were the same as those for Invention Example No. 8. The number of peaks in the XRD spectrum and the coefficient of variation CV in EDX were measured for the obtained alloy powder, and the results are shown in Table 1.

[0182] As can be seen from these results, simply mixing and sintering multiple precious metal alloy powders does not produce a precious metal alloy powder with high crystallinity and uniform composition, as in the present invention. In Comparative Example No. 12, multiple peaks were observed in the XRD spectrum used to calculate crystallite size. Therefore, the crystallite size could not be determined unambiguously, and therefore the crystallite size is not shown in Table 1. Furthermore, since the powder of Comparative Example No. 12 clearly did not satisfy the requirements of the present invention, measurement of the average particle size was omitted. However, based on the appearance of the powder, it is believed that the average particle size of the powder of Comparative Example No. 12 is roughly the same as that of Invention Example No. 2.

[0183] Example 2 A precious metal alloy paste was produced using the precious metal alloy powder obtained in Example 1, and a precious metal alloy film was produced using the paste. The specific procedure was as follows.

[0184] <Preparation of Paste> As a representative example, pastes were prepared using the precious metal alloy powders of Invention Examples Nos. 1 to 3 according to the following procedure.

[0185] First, the precious metal alloy powder, resin, and solvent were weighed and mixed to prepare a paste having a final paste content of 80% by mass of precious metal alloy powder, 1.8% by mass of resin, and 18.2% by mass of solvent. Ethyl cellulose was used as the resin, and Texanol was used as the solvent.

[0186] The resulting paste was then further kneaded using a three-roll mill to thoroughly disperse each component, completing the paste (samples a to c).

[0187] For comparison, a paste (sample d) was prepared using a mixed powder instead of the above-mentioned precious metal alloy powder. 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 for samples a to c.

[0188] <Production of Noble Metal Alloy Film> Next, using the obtained pastes (samples a to d), noble metal alloy films were produced in the following procedure.

[0189] First, 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. Next, the paste was fired in an air atmosphere at 400°C using an electric furnace to decompose and remove the resin in the paste (first firing step). After that, the paste was further fired in a nitrogen atmosphere at 1500°C using an atmospheric heating electric furnace to obtain a precious metal alloy film (second firing step).

[0190] <Evaluation of Noble Metal Alloy Film> The obtained noble metal alloy film was 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.

[0191] (Number of Peaks in XRD Spectrum) The XRD spectrum of the obtained noble metal alloy film was measured using an Ultima IV X-ray diffractometer manufactured by Rigaku. 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 scan speed: 30° / min. In the obtained XRD spectrum, the number of peaks observed in the diffraction angle 2θ range of 38 to 44° was determined. 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.

[0192] (Coefficient of variation CV in EDX) The coefficient of variation CV of the content of each precious metal element contained in the obtained precious metal alloy film was calculated from the measurement results of energy dispersive X-ray spectroscopy. For the measurement, a scanning electron microscope (SEM)-energy dispersive X-ray analyzer (EDX) JSM-6010LA manufactured by JEOL Ltd. was used. The measurement was performed by fixing the alumina substrate and the film formed thereon to a sample stage with carbon tape. The measurement conditions were a magnification of 3000x and an acceleration voltage of 20 kV. Under the above 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 value and standard deviation of the obtained content.

[0193]

[0194] As can be seen from the results shown in Table 2, the precious metal alloy film obtained using the paste 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 shows that the precious metal alloy elements are completely alloyed in the precious metal alloy film, and the composition is extremely uniform. In contrast, the precious metal alloy film of sample d, which used the mixed powder, was not sufficiently alloyed, and the composition was non-uniform.

Claims

1. A precious metal alloy powder comprising an alloy of five or more precious metal elements, The average particle size is more than 10 μm and 100 μm or less, The crystallite size is 60 nm or more, A precious metal alloy powder having one peak observed in an X-ray diffraction spectrum at a diffraction angle 2θ in the range of 38 to 44°.

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

3. A precious metal alloy paste comprising a precious metal alloy powder, a resin, and a solvent, The precious metal alloy powder is A precious metal alloy powder made of an alloy of five or more precious metal elements, The average particle size is 100 μm or less, The crystallite size is 60 nm or more, and The number of peaks observed in the X-ray diffraction spectrum at a diffraction angle 2θ of 38 to 44° is 1; Precious metal alloy paste.

4. The precious metal alloy paste as described in claim 3, 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.

5. A precious metal alloy film obtained by applying the precious metal alloy paste according to claim 3 or 4 and firing the paste.

6. A method for producing a precious metal alloy powder comprising an alloy of five or more precious metal elements, comprising: a raw material preparation step of preparing the five or more kinds of precious metal elements separately in the form of metal powder or metal oxide powder as raw material powders; a slurry preparation step of mixing the raw material powder, calcium carbonate, and water to prepare a slurry, and adjusting the pH of the slurry to 8.0 or more; A mixing step of mixing the slurry; a first firing step of firing the slurry in a non-oxidizing atmosphere to obtain an alloy powder; a first acetic acid treatment step of treating the alloy powder with acetic acid; a first washing step of washing the alloy powder after the first acetic acid treatment step with water and drying it; and a second firing step of firing the alloy powder after the first cleaning step in a non-oxidizing atmosphere.

7. a third firing step in which the alloy powder obtained by the second firing step is mixed with calcium carbonate and fired in a non-oxidizing atmosphere; a second acetic acid treatment step of treating the alloy powder after the third firing step with acetic acid; 7. The method for producing a precious metal alloy powder according to claim 6, further comprising a second washing step of washing the alloy powder after the second acetic acid treatment step with water and drying it.

8. The method for producing a precious metal alloy powder according to claim 6 or 7, further comprising a particle size adjusting step of adjusting a particle size of the alloy powder obtained after the first washing step, prior to the second firing step.

9. A method for producing a precious metal alloy paste, comprising mixing a precious metal alloy powder, a resin, and a solvent to form a paste, the method comprising the steps of: The precious metal alloy powder is A precious metal alloy powder made of an alloy of five or more precious metal elements, The average particle size is 100 μm or less, The crystallite size is 60 nm or more, and The number of peaks observed in the X-ray diffraction spectrum at a diffraction angle 2θ of 38 to 44° is 1; A method for producing a precious metal alloy paste.

10. A method for producing a precious metal alloy paste as described in claim 9, wherein the precious metal alloy powder has a content coefficient of variation CV measured by energy dispersive X-ray spectroscopy of 0.2 or less for all of the precious metal elements.

11. Applying the precious metal alloy paste according to claim 3 or 4 onto a substrate, The applied precious metal alloy paste is fired to form a precious metal alloy film.