JP2003034801A - Metal powder and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal powder consisting of platinum or a platinum-based alloy, which has a predetermined grain size and shape suitable for a material for forming a conductor film, to provide a conductive paste with the use of the metal powder, and to provide a method of manufacturing a metal powder consisting of a platinum group metal, or of an alloy mainly composed of a platinum group metal. SOLUTION: The objective metal powder mainly consists of platinum or the platinum-based alloy, has the average particle diameter of 0.1-1.0 μm, and has an approximately spherical shape. The objective conductive paste includes the metal powder. The method for manufacturing the metal powder consisting of the platinum group metal (typically platinum), or an alloy mainly composed of the metal, includes a process for forming mist of a raw material solution, and a process for heating and powderizing the mist. The raw material solution is characterized by containing hydroxide of the platinum group metal.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a metal powder (platinum group metal powder) made of a platinum group element or an alloy mainly containing a platinum group element and a method for producing the same. In particular, the present invention relates to a metal powder (platinum-based powder) made of platinum or an alloy containing platinum as a main component, having a property suitable as a material for preparing a conductor paste, a method for producing the same, and a conductor paste containing the powder. .

[0002]

2. Description of the Related Art A conductor paste is used as a material for forming a conductor film (wiring, electrode, etc.) of a predetermined pattern on a ceramic wiring board and other ceramic electronic components used for constructing hybrid ICs, multichip modules, etc. . This conductor paste contains metal powder as a main component forming a conductor and various additives (inorganic binder, glass frit, filler, etc.) added as necessary.
It is a conductor-forming material prepared by dispersing it in a predetermined vehicle (organic medium). Such a conductor paste is printed / applied to a ceramic firing base material or a ceramic base material before firing (for example, a dielectric green sheet for a laminated ceramic capacitor) by a general method such as screen printing. Then, by firing (baking) the coating material (coating film) at an appropriate temperature, or by firing the coating material and the ceramic base material before firing together.
A conductor film having a predetermined pattern is formed on the ceramic electronic component such as the ceramic base material.

Typical metal powders used in such conductor pastes are platinum group metals such as platinum (Pt) and palladium (Pd), as well as gold (Au) and silver (A).
Some are mainly composed of precious metals such as g). Also,
In some cases, alloy powder mainly composed of an alloy of these noble metals is used. A preferable example of the metal powder for the conductor paste is a metal powder made of platinum and an alloy mainly containing platinum (hereinafter, also referred to as “platinum-based powder”). As a conventional method for producing such a platinum-based powder, a method of heating a metal constituting the powder to a molten state and spraying and cooling the molten metal (melt spray method)
Alternatively, a liquid phase reduction method is known in which a solution containing a metal salt (raw material salt solution) that constitutes this powder is reduced.

[0004]

By the way, with the downsizing, high density, and high performance of ceramic electronic components, the metal powder for forming a conductor film has a relatively small particle size (for example, an average particle size of 0). 0.1 to 1.0 μm) is desired. However, it is difficult to obtain a metal powder having a relatively small particle size (for example, an average particle size of 1 μm or less) by the above-mentioned melt spraying method. Further, in the above liquid phase reduction method,
No spherical metal powder having a smooth surface can be obtained.

Here, for example, for Ag-Pd alloy powder, a so-called "spray pyrolysis method" is known as a method for producing a powder suitable for use in forming a conductor film and the like.
This is because a raw material solution containing an Ag source (for example, silver nitrate) and a Pd source (for example, palladium nitrate) is made into fine droplets (mist) by an ultrasonic oscillator and the solvent in this mist is evaporated at a high temperature and The obtained solid particles are thermally decomposed at a high temperature to obtain Ag-Pd alloy powder. According to this spray pyrolysis method, Ag-Pd alloy powder having a relatively small particle size and a shape close to a sphere can be obtained.
In such a spray pyrolysis method, usually, a metal powder (target product) obtained mainly from the concentration of metal components contained in the raw material solution and the size of mist (droplet diameter).
The particle size can be predicted and controlled. As the spray pyrolysis method and the related arts related thereto, JP-A-8-92613, JP-A-10-102108, JP-A-10-330802 and JP-265 are known.
0837 (JP-A-6-279816) and JP-2650838 (JP-A-6-23500).
7).

When the spray pyrolysis method is to be applied to the production of platinum-based powder, the Pt source contained in the raw material solution should be hexachloroplatinic acid (chloroplatinic acid), which is widely used in the production of various platinum compounds. Can be considered. However, a platinum-based powder obtained by a spray pyrolysis method from a raw material solution using hexachloroplatinic acid as a Pt source has a particle size predicted from the concentration of metal components contained in the raw material solution and the size of mist. Remarkably different, the particle size becomes too small (ultrafine particles). Moreover, these ultrafine particles are agglomerated with each other. A typical property of a platinum-based powder (platinum powder) produced by a spray pyrolysis method from a raw material solution using hexachloroplatinic acid as a Pt source is an aggregate mainly composed of ultrafine particles having a particle size of less than 0.1 μm. .

As described above, regarding the metal powder (platinum-based powder) made of platinum or an alloy containing platinum as a main component, the features of the general spray pyrolysis method (typically, the particle size of the obtained powder are It has not been found that a method of producing by this spray pyrolysis method by taking advantage of the fact that it is easy to predict and control and that powder having a shape close to a sphere is easily obtained. Therefore, it has been extremely difficult to obtain a platinum-based powder having properties suitable as a material for forming a conductor film. For example, a platinum-based powder having an average particle diameter in the range of 0.1 to 1.0 μm and formed into a substantially spherical shape and a method for producing the same have not been known so far.

Therefore, an object of the present invention is to provide a metal powder (platinum-based powder) made of platinum or an alloy containing platinum as a main component and having a predetermined particle size and shape, which is suitable as a material for forming a conductor film. To do. Another object of the present invention is to provide a conductor paste using such platinum-based powder. Still another object of the present invention is to use a metal powder (hereinafter, also referred to as “platinum group metal powder”) made of platinum or other platinum group element (typically platinum) or an alloy mainly containing them, and a conductor. It is an object to provide a metal powder having a predetermined particle size and shape suitable as a material for forming a film and a method for producing the metal powder. Another related object is to provide a conductor paste containing a platinum group metal powder (typically a platinum-based powder) produced by the method of the present invention. Furthermore, it is to provide a ceramic electronic component including a conductor film formed from such a conductor paste and a method for manufacturing the same.

[0009]

Means for Solving the Problems The present inventor uses platinum hydroxide (typically platinum hydroxo complex) as a Pt source to be contained in a raw material solution in the production of platinum-based powder by a spray pyrolysis method. By using it, the above-mentioned problems that occur when hexachloroplatinic acid is used as the Pt source (that is, excessive fine particle formation of the produced powder, aggregation, etc.)
It was found that Further, by subjecting such a raw material solution to spray pyrolysis, a platinum-based powder having properties suitable for conductor film forming applications and the like can be obtained, and the spray pyrolysis method using such a raw material solution is different from other platinum group metal powders. The present invention has been completed with the finding that it is also applicable to manufacturing.

That is, according to the present invention, a metal powder made of platinum or an alloy mainly composed of platinum, having an average particle diameter of 0.1 to 1.0 μm and formed in a substantially spherical shape (platinum System powder) is provided. Since the platinum-based powder of the present invention has the above-mentioned properties (particle size and shape), it can form a dense conductor film. Therefore, the platinum-based powder is suitable as a metal powder or the like used in a conductor paste for forming a conductor film. Among the preferred platinum-based powders of the present invention, the powders are substantially free of particles that have agglomerated with each other. In this way, the metal powder without agglomeration is easy to mix uniformly with other materials. For example, when used in a conductor paste, this metal powder is preferable because it can be uniformly dispersed in a vehicle. It is also advantageous for dispersibility that the shape of the metal powder is almost spherical.

In the present specification, the term "almost spherical" of the metal powder means that 70% by number or more of the metal powder is spherical. The term "spherical" means that the ratio of the minor axis to the major axis of particles (aspect ratio) is 0.8 or more, and more preferably 0.9 or more. "Platinum-based alloys" (hereinafter also referred to as "platinum-based alloys")
Is mainly platinum, and elements other than platinum (either precious metal elements other than platinum or non-precious metal elements may be used)
An alloy containing one or more of the above.

Preferred among the platinum-based powders of the present invention are those which consist essentially of platinum, or which consist essentially of platinum and platinum group elements other than platinum (Pd, Rh, Ru,
It is composed of a platinum alloy composed of one or more selected from Ir and Os). With such a platinum-based powder or a conductor paste containing this powder, it is possible to form a conductor film having excellent electrical characteristics (low resistivity, etc.), oxidation resistance, solder heat resistance, and the like. In another preferred platinum-based powder of the present invention, the particle size of 70% by number or more of this powder is in the range of 0.1 to 1 μm. Since the conductor paste containing the platinum-based powder having such a sharp particle size distribution has a good filling property of the powder, it is possible to form a more dense conductor film having excellent electric characteristics and the like.

The conductor paste provided by the present invention is
The present invention is characterized by containing the platinum-based powder of the present invention (typically, a metal powder substantially composed of platinum and a platinum group element other than platinum, and an alloy of these metal elements being alloyed). Since this conductor paste contains the platinum-based powder of the present invention (typically, this platinum-based powder is contained as the metal powder which is the main component forming the conductor), a dense conductor film can be formed. In addition, the conductor film formed from such a conductor paste exhibits excellent characteristics by mainly using a platinum alloy. For example, one or more of electrical characteristics, oxidation resistance, solder heat resistance, etc. are good.

According to the present invention, there is provided a method for producing a metal powder (platinum group metal powder) made of a platinum group element or an alloy mainly containing a platinum group element. This manufacturing method includes a step of generating a mist of a raw material solution and a step of heating the mist to powder. Here, as the raw material solution, a solution containing a hydroxide of a platinum group element is used. The term "hydroxide" as used herein means that a part or all of the hydroxide in the raw material solution is replaced by a salt (for example, a part of the hydroxyl groups is replaced by an alkali metal ion such as Na or K, a chlorine ion, a sulfate ion, or the like). (State) is meant to include those forming. Thus, by spray pyrolyzing a raw material solution containing a specific compound as a platinum group element source (that is, a hydroxide of the platinum group element, particularly preferably a hydroxo complex of the platinum group element), Platinum group metal powder having properties (particle size, shape, etc.) suitable for formation (for example, platinum-based powder and other platinum group metal powder having an average particle size of 0.1 to 1 μm and formed in a substantially spherical shape)
Can be manufactured. Further, according to this production method, there is little aggregation (preferably substantially no aggregation).
A platinum group metal powder can be obtained. In the present specification, the term "alloy containing platinum group element as a main component" means one or more of platinum group element (Pt, Pd, Rh, Ru, Ir and Os) as a main component, and platinum group element An alloy containing an element other than the above (either a noble metal element other than the platinum group or a non-noble metal element may be used).

Further, according to the present invention, there is provided a platinum-based powder manufacturing method in which the above-mentioned platinum-group metal powder manufacturing method is applied to the manufacture of powder (platinum-based powder) made of platinum or an alloy mainly containing platinum. That is, the method for producing a platinum-based powder of the present invention includes a step of generating a mist of a raw material solution and a step of heating the mist into a powder, wherein the raw material solution contains platinum hydroxide. Use one. According to this manufacturing method, a platinum-based powder (for example, having an average particle size of 0.1) having properties (particle size, shape, etc.) suitable for forming a conductor film.
.About.1 .mu.m, and a platinum-based powder having a substantially spherical shape can be produced. In addition, a platinum-based powder with little aggregation (preferably substantially no aggregation) can be obtained.

"Platinum hydroxide" contained in the raw material solution
A typical example is a platinum hydroxo complex. Of these, one or more selected from hexahydroxoplatinic acid and salts thereof are preferable, and hexahydroxoplatinic acid (platinum hydroxide) is most preferably used. As this hexahydroxoplatinic acid, it is preferable to use one obtained by the following method. That is, (1). A treatment of dissolving hexahydroxoplatinic acid in an acidic solvent, (2). A treatment of neutralizing the acidic solution to precipitate hexahydroxoplatinic acid, and (3). Precipitated hexahydroxoplatinic acid Hexahydroxoplatinic acid obtained by carrying out a purification step once or more including a treatment of separating from the solution.

The hexahydroxoplatinic acid thus obtained has a content ratio of an impurity element (typically, an alkali metal element) in comparison with, for example, hexahydroxoplatinic acid produced by omitting the purification step. Can be reduced. By spray pyrolysis of the raw material solution prepared using such hexahydroxoplatinic acid, a highly pure platinum-based powder can be produced. According to the conductor paste using such platinum-based powder, a conductor film having high purity can be formed. Such a conductor film is preferable because it has excellent electrical characteristics (low resistivity, etc.).

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail. The metal powder (platinum-based powder) of the present invention is made of platinum or an alloy mainly containing platinum. In this "alloy containing platinum as a main component", the metal element that can be alloyed with platinum includes platinum group elements such as rhodium (Rh) and palladium (Pd), and precious metals such as gold (Au) and silver (Ag). , Copper (Cu), nickel (Ni), cobalt (Co), iron (Fe), tin (Sn), zinc (Zn),
Examples include non-noble metals such as aluminum (Al), molybdenum (Mo), and tantalum (Ta). Among them, it is useful as a conductor forming material (for example, electrical characteristics,
A conductive film with excellent oxidation resistance and solder heat resistance can be formed)
Therefore, one kind or two or more kinds of noble metal elements other than platinum are preferable (as an example of a preferable platinum-based alloy, Pt-A).
u), more preferably one or more (typically one) of platinum group elements other than platinum. Specifically, Pt-Rh, Pt-Pd, P
Platinum-based alloys composed of combinations of t-Ru, Pt-Ir, and Pt-Os are all preferable, and combinations of Pt-Rh and Pt-Pd are particularly preferable. When the platinum-based powder of the present invention is composed of an alloy mainly composed of platinum, the alloying ratio of those metals is not particularly limited. Typically, platinum accounts for 50-99 wt% (preferably 7%).
The alloy may have a range of 0 to 95 wt%).
In addition, as the platinum-based powder of the present invention, a metal powder (platinum powder) substantially consisting of platinum is also preferable.

This platinum-based powder is formed in a "substantially spherical" shape. According to the platinum-based powder of the present invention having such a shape, it is possible to prepare a conductor paste or the like having a better dispersibility than the powder having a distorted shape. If the dispersibility of the powder is good, this conductor paste can be uniformly adhered to, for example, a predetermined position on the dielectric green sheet. Also,
The platinum-based powder of the present invention having such a shape has a better filling property than the powder having a distorted shape. When the powder filling property is good, for example, the metal powder of the present invention can be adhered densely (high density) to a predetermined position of the dielectric green sheet, for example, by applying and drying a conductor paste containing the metal powder. it can. Therefore, various ceramic electronic components (for example, multilayer ceramic capacitor: hereinafter, MLCC)
Also called. When the platinum-based powder of the present invention having the above-mentioned shape or a conductor paste containing the same is used for forming a conductor film (for example, an internal electrode of an MLCC) in the process (1), a ceramic electronic component with higher precision can be obtained. In order to improve the filling property, it is particularly preferable that the surface of the metal powder is smooth. Further, a metal powder having a high crystallinity (typically a single crystal) is preferable because the filling property can be further improved.

The platinum-based powder has an average particle size of 0.1 to 1 μm.
m, preferably 0.2 to 0.8 μm. The metal powder having a relatively small average particle diameter is
It is suitable for uses such as forming internal electrodes. Also, the specific surface area of this platinum-based powder (based on gas adsorption by the BET method)
Is preferably ¹ to 10 m ² / g. The platinum-based powder preferably has an average particle size within the above range and has a relatively sharp particle size distribution. For example, the particle size of 70% by number or more of the total metal powder is 0.1 to 1.
It is preferably in the range of 0 μm. Furthermore, it is preferable that the metal powder does not substantially contain particles having an excessively large particle size. Specifically, it is preferable that particles having a particle size of 10 μm or more (more preferably, a particle size of 5 μm or more) are not substantially contained.

Further, the platinum-based powder of the present invention preferably contains substantially no particles in which the powder is agglomerated with each other. Thus, the metal powder with less aggregation (typically, without aggregation) has good dispersibility in combination with the fact that the powder is formed into a substantially spherical shape. That is,
Compared with the case of using the agglomerated metal powder, such a metal powder makes it possible to prepare a conductor paste having a better dispersibility. This further enhances the above-mentioned effects based on this good dispersibility. The particle size, particle size distribution, and presence / absence of aggregation can be measured by, for example, analyzing a scanning electron microscope (SEM) photograph. The content of alkali metal in the platinum-based powder is preferably 1000 ppm or less, and 300 ppm
The following is more preferable. Thus, the platinum-based powder having a low alkali metal content (that is, high purity) is used, for example, in the preparation of a conductor paste, and can form a conductor film having excellent electrical characteristics and the like.

Next, the conductor paste according to the present invention will be described. This conductor paste usually contains the metal powder of the present invention and a vehicle as main components. Any vehicle can be used as long as it can disperse the metal powder of the present invention, and those used in conventional conductor pastes can be used without particular limitation. For example, organic polymers based on cellulosic polymers such as ethyl cellulose and hydroxyethyl cellulose, acrylic resins such as polybutyl methacrylate, polymethyl methacrylate and polyethyl methacrylate, epoxy resins, phenol resins, alkyd resins, polyvinyl alcohol, polyvinyl butyral and the like. Binder: Ester solvent such as butyl cellosolve acetate and butyl carbitol acetate, ether solvent such as butyl carbitol, ethylene glycol and diethylene glycol derivative, high boiling point organic solvent such as toluene, xylene, mineral spirit and terpineol can be used. .

The conductor paste of the present invention may contain various inorganic additives and / or organic additives as auxiliary components. Examples of this inorganic additive include vitreous and other ceramic powders and other various fillers. Examples of organic additives include various coupling agents such as silicon-based, titanate-based, and aluminum-based coupling agents for the purpose of improving the adhesion to the ceramic substrate. Furthermore, when it is desired to impart photocurability (photosensitivity) to the conductor paste of the present invention, various photopolymerizable compounds and photopolymerization initiators may be appropriately added. In addition to the above, the conductor paste of the present invention may appropriately contain a surfactant, a defoaming agent, a plasticizer, a thickener, an antioxidant, a dispersant, a polymerization inhibitor, etc., if necessary. . These additives may be used as long as they can be used to prepare a conventional conductor paste, and detailed description thereof will be omitted.

Next, the operation for preparing the conductor paste of the present invention will be described. Like the conventional conductor paste, the conductor paste of the present invention can typically be easily prepared by typically mixing the metal powder of the present invention with the vehicle. At this time, the above-mentioned additives may be added and mixed as needed. For example, the conductor paste of the present invention can be prepared by directly mixing the alloy powder and various additives with the vehicle at a predetermined mixing ratio using a three-roll mill or other kneading machine and kneading them together.

Although not particularly limited, it is preferable that the content of the metal powder of the present invention is 6 based on the whole conductor paste.
It is good to knead each material so that it becomes 0-95 wt%,
It is particularly preferable to knead so as to be 70 to 90 wt%. The amount of the vehicle used is appropriately about 1 to 40 wt% of the entire conductor paste, and the amount of about 1 to 20 wt% is particularly preferable. It should be noted that the above numerical ranges for the content of each component should not be strictly interpreted, and slight deviations from such ranges are allowed as long as the object of the present invention can be achieved. Further, the metal powder contained in the conductor paste of the present invention preferably substantially consists of the metal powder of the present invention, but powders of other metals or alloys may also be contained as an accessory component.

Since the conductor paste of the present invention produced in this manner contains the platinum-based powder having the above particle size and shape, various ceramic electronic components (for example, MLCC) are obtained.
And the like, it is possible to form a dense conductor film excellent in electrical characteristics and the like.

Next, a method for producing the metal powder (platinum-based powder or other platinum group metal powder) according to the present invention will be described. In this production method, a solution (typically an aqueous solution or a colloidal solution) containing a "hydroxide" of a platinum group element, which is a main component of the metal powder to be produced, is used as a raw material solution for spray pyrolysis. . As this hydroxide,
It is preferable to use a "hydroxo complex" of a platinum group element as a main component. Part or all of such a hydroxide may form a salt. Further, a metal element other than the main platinum group element contained in the platinum group metal powder to be produced (a platinum group element other than the main platinum group element, a noble metal element other than the platinum group element, or a non-precious metal element) The source may be contained as a hydroxide in the raw material solution or may be contained as another compound. The raw material solution that is preferably used contains, as a metal element source other than the main platinum group element, a hydroxide and / or a nitrate of those metal elements. As the hydroxide that can be contained in the raw material solution, depending on the composition of the platinum group metal powder to be produced, Rh (OH) ₃ , Pd (O
H) ₂ , Ru (OH) ₃ , H ₂ [Pt (OH) ₆ ], Na ₂
[Pt (OH) ₆ ], K ₂ [Pt (OH) ₆ ], Au (O
One or more selected from compounds such as H) ₃ , H [Au (OH) ₄ ] and K [Au (OH) ₄ ] can be used.

A typical example of the solvent that constitutes this raw material solution is
It is water or a mixed solvent containing water. As the solvent used in combination with water in the “mixed solvent containing water”, those that can be uniformly mixed with water (for example, alcohols, ketones, etc.) are used. The mixing ratio of water and other solvent is not particularly limited, but a mixed solvent having a composition in which 50 wt% or more (more preferably 80 wt% or more) of water is preferable. Examples of the solvent preferably used include water or a mixed solvent of water and a lower alcohol in a weight ratio of 80/20 to 99/1. In addition, it is preferable that the raw material solution is acidified. This can improve the solubility and dispersibility of the raw material solution such as hydroxide as the metal element source. That is, the stability of the raw material solution is improved. In order to adjust the acidity, the raw material solution may contain various organic acids and / or inorganic acids. Of these,
Compounds that can be decomposed and volatilized by spray pyrolysis (ie, leave no residue after spray pyrolysis) are preferred. Specifically, nitric acid, acetic acid, sulfuric acid, hydrochloric acid, etc. can be used,
It is particularly preferred to use nitric acid.

The specific operating method for preparing the raw material solution is not particularly limited. For example, a raw material solution can be prepared by dissolving or dispersing a hydroxide or the like as a metal element source in a mixture of a solvent and an acid (an acidic solvent) under heating, if necessary. Further, in the case of producing a metal powder made of an alloy, a source solution may be prepared by sequentially adding a metal element source corresponding to each metal element constituting the alloy to a solvent, or a different metal element may be prepared. After preparing two or more solutions containing the source, they may be mixed to prepare a raw material solution.

The method for producing the platinum group metal powder of the present invention is defined as platinum.
When applied to the production of system powder, it should be included in the raw material solution.
It is preferable to use a hydroxo complex of platinum as the Pt source.
Good Examples of such hydroxo complex include H₂[Pt
(OH)₆], Na₂[Pt (OH)₆], K₂[Pt (O
H)₆] Etc. are mentioned. Of these, H₂[Pt (OH)
₆] (Hexahydroxoplatinic acid) is most preferred
Good

The method for producing hexahydroxoplatinic acid used in the platinum-based powder production method of the present invention is not particularly limited.
As a typical production method, an alkaline compound (typically, an alkali metal hydroxide typified by NaOH and KOH) is added to a solution of hexachloroplatinic acid (typically an aqueous solution) to make it alkaline. A method in which the solution is heated and then neutralized to precipitate hexahydroxoplatinic acid can be mentioned. For the preparation of the raw material solution, for example, hexahydroxoplatinic acid precipitated by neutralization after heating may be filtered out from the solution and washed, and preferably dissolved in an acidic solvent in a wet state.

At this time, the hexahydroxoplatinic acid used in the raw material solution is (1). A treatment for dissolving hexahydroxoplatinic acid in an acidic solvent, (2). It is preferably obtained by performing a purification step including a treatment of precipitating, and a treatment of separating (recovering) the precipitated hexahydroxoplatinic acid from the solution. This purification step can improve the purity of hexahydroxoplatinic acid. This purification step can be repeated twice or more as necessary. For example, hexahydroxoplatinic acid as a raw material has a relatively high concentration of alkali metal elements (for example, 10,000 pp
m or more), the concentration of the alkali metal element is reduced by performing this purification step once or twice or more (for example, 1000 ppm or less, preferably 300 p
can be below pm). In particular, the hexahydroxoplatinic acid obtained by the above-mentioned typical production method generally contains a relatively high concentration of an alkali metal element in a state of being neutralized and precipitated after heating an alkaline solution. A highly pure platinum-based powder can be produced by performing the above-mentioned purification step on hexahydroxoplatinic acid in this state and spray pyrolyzing the purified raw material solution containing hexahydroxoplatinic acid.

In the purification step, various organic acids and / or inorganic acids (nitric acid, acetic acid, sulfuric acid, hydrochloric acid, etc.) can be used as the acidic solvent used in the treatment of the above (1). Of these, nitric acid or acetic acid is preferably used. Further, various basic compounds can be used for neutralization in the treatment of the above (2). However, it is preferable to use a compound containing no metal element (alkali metal element, alkaline earth metal element, etc.). It is particularly preferred to use water. In addition, when hexahydroxoplatinic acid precipitates in the treatment of (2) above, impurities (alkali metal element) contained in hexahydroxoplatinic acid before purification
Most of the remains in solution (supernatant). Therefore, hexahydroxoplatinic acid with high purity (with reduced content of alkali metal element) can be obtained by filtering and washing this precipitate by the treatment of (3) above. The number of times this purification step is performed is not particularly limited, but it is preferably 1 to 3 times from the viewpoint of production efficiency and the like.

In the method for producing the metal powder (platinum-based powder or other platinum group metal powder) of the present invention, the step of purifying the mist of the raw material solution and the step of heating the mist are the same as those in the conventionally known spray pyrolysis method and the like. Can be carried out.
For example, the mist of the raw material solution can be generated by ultrasonic vibration, spraying or other means. The generated mist is mixed with various carrier gases (typically N ₂ , Ar,
It is introduced into the heating furnace together with one or more gases selected from He and CO ₂ . Then, the mist is dried and pyrolyzed in the heating furnace under desired temperature conditions. As a result, the target metal powder is obtained. Unlike the case where hexachloroplatinic acid is used as the Pt source (which becomes an agglomerate of ultrafine particles), this metal powder has a particle size that is approximately the same as the particle size expected from the composition of the raw material solution and the mist size. Have a diameter. Therefore, according to the present invention, it is possible to stably produce a platinum group powder or other platinum group metal powder having an average particle size of 0.1 to 1 μm and formed in a substantially spherical shape. Further, the metal powder produced by spray pyrolysis in the production method of the present invention has less aggregation (preferably substantially no aggregation), unlike the case where hexachloroplatinic acid is used as the Pt source. This prevents or suppresses defects such as adhesion of aggregates to the spray pyrolysis device and other manufacturing devices.
In addition, dispersibility in vehicles and the like, particle uniformity (eg, particle size, shape uniformity, etc.), etc., without the need for a step of removing aggregates from the metal powder after spray pyrolysis by a complicated operation. An excellent metal powder can be obtained.

The metal powder of the present invention and the metal powder (platinum-based powder or other platinum group metal powder) obtained by the production method of the present invention are particularly suitable as a material for a conductor paste. The metal powder can also be used as a metal pigment (for example, a metal pigment used for decorating tableware and other ceramic products), a powder metallurgy material, and the like.

[0036]

EXAMPLES Hereinafter, some examples of the present invention will be described, but the present invention is not intended to be limited to those shown in the examples.

<Example 1: Production example (1) of platinum powder using hexahydroxoplatinic acid> H ₂ [PtCl ₆ ] (hexachloroplatinic acid) was dissolved in water, and NaO was added to this aqueous solution.
H or KOH (here NaOH was used) was added to make it alkaline. After heating this alkaline solution for a long time, it was neutralized with nitric acid or acetic acid (here nitric acid was used) to precipitate H ₂ [Pt (OH) ₆ ] (hexahydroxoplatinic acid). After the generated precipitate was filtered off and washed with water, the precipitate (hereinafter, also referred to as "unpurified hexahydroxoplatinic acid") was dissolved in nitric acid in a wet state, and a nitric acid solution of hexahydroxoplatinic acid was added. It was made. The Pt content of this nitric acid solution was measured, and the solution concentration at which the diameter of the powder obtained after thermal decomposition was 0.5 μm was calculated with the droplet size generated from the atomizer being 4.0 μm. The above nitric acid solution was diluted with concentrated nitric acid so as to match this solution concentration to prepare a raw material solution for spray pyrolysis.

A nitric acid solution (raw material solution) whose concentration had been adjusted was sprayed using an ultrasonic atomizer, and fine droplets (mist) were generated from this raw material solution. This mist was passed through a reaction tube kept at 1200 ° C. using N ₂ as a carrier gas. The powder remaining after drying and thermal decomposition was collected by an electrostatic collector. When the collected powder (platinum powder) was observed with a scanning electron microscope, the obtained platinum powder was substantially spherical and had a smooth surface, and the particle size was substantially uniform. No aggregation of particles was observed and the dispersibility was good. The platinum powder had an average particle size of about 0.5 μm, and a powder having a size substantially matching the design value was obtained. As a result of chemical analysis, this platinum powder (platinum powder obtained by using unpurified hexahydroxoplatinic acid)
Contained 11000 ppm Na.

<Example 2: Production example (2) of platinum powder using hexahydroxoplatinic acid> In the same manner as in Example 1,
A nitric acid solution of crude hexahydroxoplatinic acid was prepared.
Next, this nitric acid solution was neutralized with aqueous ammonia, and the generated precipitate was separated by filtration and washed with water. This precipitate (hereinafter, also referred to as “single-purified hexahydroxoplatinic acid”) was dissolved in nitric acid in a wet state to prepare a nitric acid solution of hexahydroxoplatinic acid. Then, the concentration of the raw material solution was adjusted and spray pyrolysis was performed in the same manner as in Example 1 to obtain a powder. When the obtained powder (platinum powder) was observed with a scanning electron microscope, the average particle size was about 0.5 μm.
Similar to the powder obtained in 1., it had good properties and dispersibility for preparing a conductor paste. As a result of chemical analysis, the Na concentration of this platinum powder (platinum powder obtained by using once-purified hexahydroxoplatinic acid) was 800 pp.
It was m. That is, by performing the purification step for hexahydroxoplatinic acid once, a higher purity platinum powder was obtained as compared with Example 1.

<Example 3: Production example (3) of platinum powder using hexahydroxoplatinic acid> In the same manner as in Example 1,
A nitric acid solution of crude hexahydroxoplatinic acid was prepared.
Next, this nitric acid solution was neutralized with aqueous ammonia, and the generated precipitate was separated by filtration and washed with water. The once-purified hexahydroxoplatinic acid was again dissolved in a nitric acid solution, neutralized with aqueous ammonia, and the formed precipitate was separated by filtration and washed with water. This precipitate (hereinafter, also referred to as “double-purified hexahydroxoplatinic acid”) was dissolved in nitric acid in a wet state to prepare a nitric acid solution of hexahydroxoplatinic acid. Then, the concentration of the raw material solution was adjusted and spray pyrolysis was performed in the same manner as in Example 1 to obtain a powder. Obtained powder (platinum powder)
When observed with a scanning electron microscope, the average particle diameter was about 0.5 μm, and it had good properties and dispersibility for preparing a conductor paste, similar to the powder obtained in Example 1. As a result of chemical analysis, the Na concentration of this platinum powder (platinum powder obtained by using twice-purified hexahydroxoplatinic acid) was 100 ppm or less. That is, by performing the purification step of hexahydroxoplatinic acid twice, a platinum powder having a higher purity than that of Example 2 was obtained.

<Example 4: Production example of Pt-Rh (95/5) alloy powder using hexahydroxoplatinic acid> The twice-purified hexahydroxoplatinic acid obtained in Example 3 was dissolved in nitric acid, A nitric acid solution of hexahydroxoplatinic acid was prepared. A nitric acid solution of Rh (OH) ₃ (rhodium hydroxide) was added thereto, and the weight ratio in terms of metal elements was Pt: Rh = 9.
The mixture was added and mixed to be 5: 5. Then, the concentration of the raw material solution was adjusted and spray pyrolysis was performed in the same manner as in Example 1 to obtain a powder. When the obtained powder (Pt-Rh alloy powder) was observed by a scanning electron microscope, the average particle size was about 0.5 μm, which was good for preparing a conductor paste like the powder obtained in Example 1. It had properties and dispersibility. As a result of the chemical analysis, the ratio of Pt and Rh contained in each powder particle was Pt: Rh = 95: 5 (weight ratio), which was almost constant. That is, alloy powder having a composition corresponding to the composition of the raw material solution used for spray pyrolysis was formed. The Na concentration of this Pt-Rh alloy powder (platinum-based powder obtained by using twice-purified hexahydroxoplatinic acid) was 100 ppm or less.

The X-ray diffraction pattern of the metal powder obtained in this example is shown in FIG. 1 (a), and its peak data is shown in FIG.
It shows in (b). For reference, peak data based on the X-ray diffraction pattern of Rh alone is shown in FIG. 1 (c), and peak data based on the X-ray diffraction pattern of rhodium oxide (Rh ₂ O ₃ ) is shown in FIG. 1 (d). The peak data based on the X-ray diffraction pattern of Pt alone is shown in FIG. Figure 1
As can be seen from the comparison of the peak data of (b), (c), and (e), the peaks of Pt simple substance and Rh simple substance disappeared in the powder obtained in this example, and one sharp peak was observed between them. A peak was observed. From this, Pt and R
It was confirmed that h and h were alloyed. Note that FIG.
From the comparison between (b) and FIG. 1 (d), the obtained metal powder contains almost no rhodium oxide and has high purity Pt-Rh.
It can be seen that it is composed of an alloy.

<Example 5: Production example of Pt-Rh (90/10) alloy powder using hexahydroxoplatinic acid> Rh
A nitric acid solution of (OH) ₃ (rhodium hydroxide) was added and mixed so that the weight ratio in terms of metal element was Pt: Rh = 90: 10. In all other respects, a powder was obtained in the same manner as in Example 4. When the obtained powder (Pt-Rh alloy powder) was observed by a scanning electron microscope, the average particle diameter was about 0.5 μm, which was similar to that of the powder obtained in Example 1 for preparing a conductor paste. It had properties and dispersibility. As a result of chemical analysis, the ratio of Pt and Rh contained in each powder particle was Pt: Rh = 90: 10.
The alloy powder was formed to have a substantially constant (weight ratio) and a composition corresponding to the composition of the raw material solution used for spray pyrolysis. In addition, N of this Pt-Rh alloy powder (platinum-based powder obtained by using twice-purified hexahydroxoplatinic acid)
The a concentration was 100 ppm or less. Further, when the X-ray diffraction pattern was analyzed in the same manner as in Example 4, it was confirmed that Pt and Rh were alloyed in this particle.

Comparative Example 1: Production Example of Platinum Powder Using Hexachloroplatinic Acid In this comparative example, hexachloroplatinic acid was used as the Pt source instead of hexahydroxoplatinic acid. That is, prepare an aqueous solution of hexachloroplatinic acid,
The Pt content of the aqueous solution was measured, and the solution concentration at which the diameter of the powder obtained after thermal decomposition was 0.5 μm was calculated with the droplet size generated from the sprayer being 4.0 μm. The above aqueous solution was diluted with hydrochloric acid so as to match this solution concentration to prepare a raw material solution for spray pyrolysis. Then, the raw material solution was subjected to spray pyrolysis in the same manner as in Example 1 to obtain a powder. When the obtained platinum powder was observed with a scanning electron microscope, the platinum powder obtained in Comparative Example 1 was an amorphous aggregate composed of ultrafine particles having a particle size of less than 0.1 μm. That is,
Unlike Examples 1 to 4, it was not possible to obtain substantially spherical and independent particles (having good dispersibility).

Comparative Example 2: Pt-Rh Powder Production Example Using Hexachloroplatinic Acid> The hexachloroplatinic acid aqueous solution prepared in Comparative Example 1 was mixed with an aqueous solution of RhCl ₃ (rhodium chloride) at a metal-equivalent weight ratio. Pt: Rh = 90: 10
And mixed so that Thereafter, the concentration of the raw material solution was adjusted and spray pyrolysis was performed in the same manner as in Comparative Example 1 to obtain a powder. When the obtained powder was observed with a scanning electron microscope, it was an amorphous aggregate composed of ultrafine particles having a particle size of less than 0.1 μm, as in Comparative Example 1.

Specific examples of the present invention have been described above in detail, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. Further, the technical elements described in the present specification or the drawings are
The technical usefulness is exhibited alone or in various combinations, and is not limited to the combinations described in the claims at the time of filing. In addition, the technique illustrated in the present specification or the drawings achieves a plurality of purposes at the same time, and achieving the one purpose among them has technical utility.

[0047]

As described above, since the platinum-based powder of the present invention has a relatively small average particle size (0.1 to 1 μm) and is formed into a substantially spherical shape, it has a good filling property and dispersibility. Is good. According to the conductor paste of the present invention containing this platinum-based powder, by containing the platinum-based powder having the above-mentioned particle size and shape, a conductor film that is dense and has excellent electrical characteristics (such as an internal electrode of an MLCC) The conductor film used) can be accurately formed.
Further, according to the method for producing a metal powder (platinum-based powder or other platinum group metal powder) of the present invention, a raw material solution containing a specific platinum group metal element source is sprayed and pyrolyzed to have a desired particle size. It is possible to obtain a metal powder having a substantially spherical shape. For example, the average particle size (0.1-1 μ
It is possible to stably produce platinum group powder and other platinum group metal powder having m) and formed into a substantially spherical shape.

When a conductor film made of an alloy mainly composed of a platinum group element (for example, a Pt-Rh alloy) is to be prepared using a conductor paste, such a composition (that is, a platinum group element is mainly composed) has hitherto been used. It has been difficult to obtain such an alloy powder having properties (particle size, shape, dispersibility, etc.) that are suitable for preparing a conductor paste, and it is difficult to prepare such a conductor film. On the other hand, mixed powder (for example, Pt powder and R
It is possible to produce a conductor film containing these metals (Pt and Rh) by applying and firing a conductor paste using a mixed powder of h powder). However, in the conductor film produced in this way, alloying of these metals is insufficient and the alloy composition is non-uniform,
The effect of alloying cannot be sufficiently exerted. According to the invention, an alloy based on a platinum group metal (typically platinum) (typically an alloy of platinum group elements, eg Pt).
-Rh alloy, Pt-Pd alloy, etc.), and an alloy powder having properties suitable for preparing a conductor paste can be provided. According to the conductor paste containing such alloy powder, a conductor film (electrode or the like) made of an alloy mainly containing a platinum group element (typically platinum) can be easily prepared.

[Brief description of drawings]

FIG. 1 is a characteristic diagram (chart) showing an X-ray diffraction pattern.
Where (a) is the X-ray diffraction pattern of the Pt-Rh alloy powder obtained in Example 4, (b) is its peak data, (c) is the peak data based on the X-ray diffraction pattern of Rh alone, ( (d) is peak data based on the X-ray diffraction pattern of Rh ₂ O ₃ , and (e) is peak data based on the X-ray diffraction pattern of Pt alone.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01B 1/22 C22B 11/04 13/00 501 3/00 Q (72) Inventor Hironobu Noritake Shincho, Nishi-ku, Nagoya City, Aichi Prefecture No. 3 1-36 Noritake Co., Ltd. Limited F-term (reference) 4K001 AA41 DB02 DB23 4K017 AA02 BA02 CA01 DA07 EJ02 4K018 BA01 BB03 BB04 BD04 5G301 DA12 DD01 DE03

Claims (5)

[Claims] 1. A metal powder composed of platinum or an alloy mainly composed of platinum, the metal powder having an average particle diameter of 0.1 to 1.0 μm and formed into a substantially spherical shape. 2. A conductor paste containing the metal powder according to claim 1. 3. A method for producing a metal powder composed of a platinum group element or an alloy mainly composed of a platinum group element, which comprises a step of producing a mist of a raw material solution, and a step of heating the mist to form a powder. And a method for producing a metal powder, wherein the raw material solution contains a platinum group element hydroxide. 4. A method for producing a metal powder composed of platinum or an alloy containing platinum as a main component, which comprises a step of producing a mist of a raw material solution and a step of heating the mist into a powder. Here, a method for producing a metal powder, wherein a solution containing platinum hydroxide is used as the raw material solution. 5. The hydroxide is hexahydroxoplatinic acid, and the hexahydroxoplatinic acid is (1). A process of dissolving hexahydroxoplatinic acid in an acidic solvent, (2). Neutralizing the acidic solution. 5. The purification step comprising: a treatment for precipitating hexahydroxoplatinic acid, and (3) a treatment for separating the precipitated hexahydroxoplatinic acid from the solution. Metal powder manufacturing method.