JP3343283B2 - Silver-palladium coprecipitated powder and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precious metal powder and a method for producing the same. In particular, it relates to a silver-palladium coprecipitated powder and a method for producing the same.

[0002]

2. Description of the Related Art In the field of the electronics industry, conductive pastes in which a noble metal powder is dispersed in an inert liquid vehicle are used for producing a thick film circuit. This noble metal powder
In recent years, a method of manufacturing by a wet reduction precipitation method has become mainstream. In the case of a silver-palladium alloy powder or a silver-palladium composite powder, a coprecipitation reduction method represented by Japanese Patent Publication No. 44-21968 is well known.

[0003] In this coprecipitation reduction method, in order to obtain preferable particles, the precipitation is restricted by limiting the reducing agent or adjusting the pH of the reaction solution with aqueous ammonia or the like, and further stabilizing the pH by adding a buffer. Various control of particles is performed.

For example, in the above publication, a basic substance is added to a metal salt-containing solution to perform a reduction reaction at a pH of 4.5 to 6.5. In Japanese Patent Publication No. 58-55204, hydrazine hydrochloride is used as a reducing agent, and the reduction reaction is carried out at pH
It is carried out under three or more conditions.
In the publication, an acidic salt of hydrazine is used as a reducing agent, and a buffering agent is added to perform a reduction reaction in a pH range of 1 to 11. Further, JP-A-2-294416 uses a hydrazine compound as a reducing agent and an ammonia compound as a buffer for pH.

[0005] Both ammonium hydroxide and ammonia compounds added to the reaction solution in the above prior art are pH
Acts only as a buffer for adjusting or stabilizing the pH, the effect is limited only to the appearance that particles of a preferred size and shape are obtained, and affects the properties of the reduced and precipitated metal powder itself Did not occur at all.

[0006]

However, it is still impossible to avoid the generation and mixing of fine particles of less than 0.1 μm in the metal powder produced by the above method. In addition, the composite coprecipitated powder produced from two kinds of metal salts such as the silver-palladium coprecipitated powder had an uneven mixing degree, and as a result, alloying at a low temperature was hard to occur. Therefore, the metal powder obtained by the above-mentioned conventional technique has a large amount of oxidation increase, and the electrode characteristics remain unsatisfactory.

Accordingly, the present invention is to provide a silver-palladium coprecipitated powder suitable for practical use, which can be alloyed at a low temperature because the degree of mixing is uniform, and which does not contain fine particles of less than 0.1 μm. With the goal. It is another object of the present invention to provide a method for producing the silver-palladium coprecipitated powder in an industrially stable manner.

[0008]

Means for Solving the Problems As a result of intensive research pursuing the above object, the present invention shown below has been completed.

That is, the present invention provides a method for producing a metal powder in which a solution containing a metal salt and a solution containing a reducing agent are mixed and reduced to precipitate and powder the metal. A step of adjusting the pH of a solution containing a palladium salt (hereinafter referred to as a metal salt-containing solution) to an alkaline region, and separately (b) the pH of a reducing agent-containing solution using ammonium formate and a hydrazine hydrate compound as a reducing agent. (C) the step (a)
Adding at least one or more selected from ammonium acetate or ammonium carbonate to at least one of the metal-containing solution prepared in the above and the reducing agent-containing solution prepared in the step (b), (d) Mixing the metal-containing solution and the reducing agent-containing solution, and simultaneously reducing and precipitating silver and palladium, wherein the particle shape is substantially spherical and the particle diameter is 0.1 to 2 The present invention relates to a method for producing a silver-palladium coprecipitated powder within a range of 0.0 μm and a silver-palladium coprecipitated powder obtained by the production method.

[0010]

Preferred Embodiment and Operation The silver-palladium coprecipitated powder obtained by the production method of the present invention has a substantially spherical particle shape, a particle size of 0.1 to 2.0 μm, and a narrow particle size distribution range. Things. Such silver-palladium coprecipitated powder has good printability when made into a paste. Further, they are uniformly mixed, and have the property that the amount of oxidation increase (TGA) is small since alloying occurs at a low temperature, and they are suitable for capacitor electrodes.

It is not yet fully understood how the constituent elements of the present invention contribute to the effect. However, even if one of them is missing, the above-mentioned silver-palladium coprecipitated powder cannot be obtained.

First, a hydrazine compound having a strong reducing power is applied as a reducing agent, but hydrazine hydrate and ammonium formate must be used in combination. With other reducing agents, a metal powder having the above characteristics cannot be obtained stably. Generally, a reducing agent has a difference in reducing power due to a difference in pH of a reaction solution, and greatly varies. For example, in the case of hydrazine hydrate, on the acidic side, there is almost no reducing power for silver salts, but on the alkaline side, the reducing power for silver salts acts strongly, causing a difference in reduction rate between palladium salts and silver and palladium. Are separately deposited.

Therefore, in the production method of the present invention, hydrazine hydrate is used in the acidic region as a reducing agent for palladium salt, and in order to supplement the reduction of silver salt, hydrazine hydrate has the same reducing power as palladium salt. Is used in combination with ammonium formate which has in the acidic region with respect to the silver salt. By using this reducing agent, the silver salt and the palladium salt are reduced and precipitated to the same extent, and it is considered that a coprecipitated powder with a good mixing degree can be obtained.

The mixing ratio of hydrazine hydrate and ammonium formate depends on the mixing ratio of silver and palladium in the desired silver-palladium coprecipitated powder. The total amount of the reducing agent is preferably used in excess of the theoretical amount for allowing the reduction reaction to proceed completely, but it is sufficient if there is 1.5 equivalents required to reduce the silver salt or palladium salt.

The pH value of the reaction solution is a critical factor that affects the nucleation rate and particle growth rate of the metal powder particles. If the pH is too low, the particle growth rate is slow, and only fine powder is obtained. Even if the pH is too high, the nucleation rate of the metal particles exceeds the particle growth rate, so that most of the generated particles are smaller than 0.1 μm.

In the present invention, for the above-mentioned reason, the pH of the solution containing the reducing agent needs to be in the acidic range, and is preferably from pH 4 to pH 7. However, when the metal salt-containing solution was also set in the acidic region, the nucleation reaction rapidly proceeded when both solutions were mixed, and the powder was not balanced with the particle growth rate, and only fine particles of less than 0.1 μm were produced. Therefore, the pH of the metal salt-containing solution needs to be in an alkaline range, and is preferably in the range of pH 7 to pH 11. That is, in the present invention, the reduction reaction of the metal salt performed by mixing both solutions is preferably performed in a pH range of 7 to 10.5.

Furthermore, another feature of the present invention is that at least one of ammonium acetate and ammonium carbonate is added to at least one of the metal-containing solution and the reducing agent-containing solution. Thus, in the reductive precipitation reaction when the two solutions are mixed, the reduction reaction between the silver salt and the palladium salt is performed while being harmonized and controlled slowly, so that the degree of mixing of the silver component and the palladium component is good and 0.1. Particles having an extremely narrow particle size distribution of 1 to 2.0 μm (SEM observation) are generated and alloyed at a low temperature, so that the amount of increase in oxidation during firing is small. This effect cannot be obtained in the presence of an ammonia compound other than ammonium acetate or ammonium carbonate, and the resulting coprecipitated powder has a high alloying temperature and a large amount of oxidation during firing.

As a preferred mode of adding the ammonium compound, at least one selected from ammonium nitrate or ammonium acetate or ammonium carbonate is added to the metal salt-containing solution, and / or ammonium nitrate or acetic acid is added to the reducing agent-containing solution. Is to add ammonium.

However, when adding ammonium nitrate to the metal salt-containing solution, it is necessary to further add at least one of ammonium acetate and ammonium carbonate to the metal salt-containing solution or to add ammonium acetate to the reducing agent-containing solution. On the other hand, when adding ammonium nitrate to the reducing agent-containing solution, ammonium acetate must be further added to the reducing agent-containing solution, or at least one of ammonium acetate and ammonium carbonate must be added to the metal salt-containing solution. No.

The reduction reaction may be performed at a temperature of 25 ° C. or higher at which reduction precipitation occurs. From the viewpoint of ease of alloying silver and palladium, the higher the reduction precipitation temperature, the better. However, the higher the reaction temperature is, the smaller the size of the precipitated particles is. Therefore, the temperature is preferably in the range of 40 ° C to 60 ° C.

[0021]

The silver-palladium coprecipitated powder obtained according to the present invention has a substantially spherical particle shape, a particle size in the range of 0.1 to 2.0 μm, and a narrow particle size distribution. is there. Such a silver-palladium coprecipitated powder has the characteristics of good printability when formed into a paste, and having a small amount of oxidized weight gain (TGA) because silver and palladium are uniformly mixed and dispersed and alloyed at a low temperature. It is suitable for a capacitor electrode. Further, the silver-palladium coprecipitated powder can be supplied industrially stably by the production method of the present invention.

[0022]

【Example】

[Evaluation Test] A metal salt-containing solution and a reducing agent-containing solution having the formulations shown in Tables 1 to 3 below were prepared and mixed to produce a silver-palladium coprecipitated powder. The particle diameter of each of the produced coprecipitated powders was measured,
The calcining was performed at 50 ° C., and the amount of increase in oxidation before and after firing was measured. Further, Comparative Example 1 was obtained for Reference Example 1-2, Example 2-2, Comparative Example 2, Example 2-1 and Example 3.
For each of Example-1, Example 4, and Comparative Example 3, the coprecipitated powder was fired at 250 ° C. and then subjected to X-ray analysis to examine the degree of alloying.

The measurement conditions of the X-ray analysis are as follows. X-ray source: Cu output: 50 kV, 50 mA Slit system: 1 ° -0.15 mm-1 ° Scanning speed: 4 ° / min Counting step: 0.02 ° (2θ)

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

Comparative Examples 1-1 and 1-2 and Reference Example 1
-1 and Reference Example 1-2 differ in the type of reducing agent used (see Table 1). The reference example in which ammonium formate and hydrazine hydrate were used as the reducing agent as in the present invention was able to obtain a coprecipitated powder in which fine particles were not generated and the particle diameters were uniform as compared with the comparative example ( See Table 4).

FIGS. 3 to 7 show Example 1, Reference Example 1-1, Reference Example 1-2, Comparative Example 1-1 and Comparative Example 1-2, respectively.
An electron micrograph of the produced particles is shown (magnification: upper stage × 10
00, lower row × 5000). In the comparative examples, it is confirmed that both contain a large amount of fine particles. On the other hand, in Reference Examples and Examples, it can be confirmed that the particle shapes are spherical and almost uniform. That is, a silver-palladium coprecipitated powder having a particle size suitable for printing can be obtained by the combination of the reducing agents shown in the present invention.

Further, when comparing the oxidation weight increase, Reference Example 1-
Comparative Example 1-1 and Comparative Example 1
Example 1 showed a lower oxidation gain, relative to less than 2. This indicates that, in the present invention, addition of ammonium carbonate or ammonium acetate is important in addition to limiting the type of reducing agent.

Next, the types of ammonia compounds as additives were compared (see Table 2). The coprecipitated powders produced in Comparative Example 2, Example 2-1 and Example 2-2 were fired and X
As a result of the line analysis, the maximum peaks of Example 2-1 and Example 2-2 in which at least one or more of ammonium acetate or ammonium carbonate was added were higher than those of Comparative Example 2 in which other ammonia compounds were added. To indicate that alloying is progressing (see FIG. 1).

Further, when the X-ray spectra of Reference Example 1-2, Example 2-1 and Example 2-2 are compared (see FIG. 1), the maximum peak of Example 2-1 and Example 2-2 is This shows that the angle is shifted to the higher angle side than in Reference Example 1-2, and the effect of adding ammonium carbonate or ammonium acetate is not limited to the effect on appearance such as particle shape and size, but also to the silver-palladium coprecipitated powder itself. It is also recognized that it is affecting.

Further, in both Example 2-1 and Example 2-2, the amount of increase in oxidation was smaller than that of Comparative Example 2 (see Table 4). That is, the silver-palladium coprecipitated powder according to the present invention is excellent in the characteristics of the capacitor electrode.

A similar test was conducted by changing the mixing ratio of silver and palladium (see Table 3). The coprecipitated powders produced in Comparative Example 3 and Example 4 were calcined and analyzed by X-ray analysis (FIG. 2).
In Example 4, the maximum peak was shifted to the higher angle side as compared with Comparative Example 3, indicating that alloying was in progress. The oxidation gains of both were almost equal (see Table 4).
However, the alloying of Example 3 shown in FIG. 1 is further advanced than that of Example 4, and the amount of increase in oxidation is small. Similarly, in Examples 5 and 6, alloying was further advanced than in Example 4 (data not shown), and the amount of increase in oxidation was small (see Table 4).

As described above, the silver-palladium coprecipitated powder according to the present invention is a powder having a substantially spherical particle shape and a particle size within a narrow range of the particle size distribution.
It has excellent printing characteristics, furthermore, silver and palladium are uniformly mixed, alloying progresses at a low temperature, and the amount of increase in oxidation is small, and the capacitor electrode characteristics are excellent.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention, Examples 2-1 and 2-2, Example 3 and Reference Example 1-2 which is a comparative product thereof.
The silver-palladium coprecipitated powder obtained in Comparative Example 2 was heated at 250 ° C.
FIG. 4 is a spectrum diagram showing the result of X-ray analysis of the product fired in FIG.

FIG. 2 is an X-ray analysis of calcined silver-palladium coprecipitated powders obtained in Example 4 showing the embodiment of the present invention and Comparative Examples 1-1 and 3, which are comparative products, at 250 ° C. FIG. 9 is a spectrum diagram showing the result of the measurement.

FIG. 3 is an electron micrograph of the silver-palladium coprecipitated powder of the product of the present invention manufactured according to Example 1, showing the particle structure of the coprecipitated powder. The upper part has a magnification of × 1000, and the lower part shows the white frame portion of the upper part enlarged to × 5000.

FIG. 4 is an electron micrograph of a silver-palladium coprecipitated powder of a reference product of the present invention produced according to Reference Example 1-1, showing the particle structure of the coprecipitated powder. The upper row has a magnification of × 1000
In the lower part, the white frame part of the upper part is enlarged to × 5000.

FIG. 5 is an electron micrograph of a silver-palladium coprecipitated powder of a reference product of the present invention produced according to Reference Example 1-2, showing the particle structure of the coprecipitated powder. The upper row has a magnification of × 1000
In the lower part, the white frame part of the upper part is enlarged to × 5000.

FIG. 6 is an electron micrograph of a silver-palladium coprecipitated powder of a comparative product manufactured according to Comparative Example 1-1, showing the particle structure of the coprecipitated powder. The upper row has a magnification of ×
1000, and the lower part represents the white frame part of the upper part as x500.
It is enlarged to zero.

FIG. 7 is an electron micrograph of a silver-palladium coprecipitated powder of a comparative product of the present invention manufactured according to Comparative Example 1-2, showing the particle structure of the coprecipitated powder. The upper row has a magnification of ×
1000, and the lower part represents the white frame part of the upper part as x500.
It is enlarged to zero.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomoki Saruki 3-36, Noritake Shinmachi, Nishi-ku, Nagoya City, Aichi Prefecture Inside Noritake Company Limited (72) Inventor Akio Takimoto 3-chome Noritake Shinmachi, Nishi-ku, Nagoya City, Aichi Prefecture No. 1 No. 36 Noritake Co., Limited (56) References JP-A-62-280308 (JP, A) JP-B-44-21968 (JP, B1) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) B22F 9/24

Claims (6)

(57) [Claims] A metal is precipitated by mixing and reducing a solution containing a metal salt and a solution containing a reducing agent.
In the method for producing a metal powder to be powdered, (a) a step of adjusting the pH of a solution containing a silver salt and a palladium salt (hereinafter, referred to as a metal salt-containing solution) to an alkaline region, and (b) ammonium formate And adjusting the pH of the reducing agent-containing solution using a hydrazine hydrate compound as a reducing agent to an acidic region, (c) the metal-containing solution prepared in the step (a) and the reduction prepared in the step (b). Adding at least one or more selected from ammonium acetate or ammonium carbonate to at least one of the solution containing the agent, (d) mixing the metal-containing solution and the reducing agent-containing solution, and adding silver and palladium. Simultaneously reducing and precipitating the particles, wherein the particle shape is substantially spherical and the particle diameter is in the range of 0.1 to 2.0 μm. Silver - palladium co-precipitated powder manufacturing method. 2. The method according to claim 1, wherein in the step (c), at least one selected from ammonium acetate and ammonium carbonate is added to the metal salt-containing solution prepared in the step (a). A method for producing a silver-palladium coprecipitated powder of the above. 3. The process for producing a silver-palladium coprecipitated powder according to claim 1, wherein in the step (c), ammonium acetate is added to the reducing agent-containing solution prepared in the step (b). Method. 4. The method for producing a silver-palladium coprecipitated powder according to claim 2, wherein in the step (c), an ammonium nitrate salt is added to the metal salt-containing solution prepared in the step (a). 5. The method for producing a silver-palladium coprecipitated powder according to claim 2, wherein in the step (c), an ammonium nitrate salt is added to the metal salt-containing solution prepared in the step (b). 6. A step of (a) adjusting the pH of a solution containing a silver salt and a palladium salt (hereinafter referred to as a metal salt-containing solution) to an alkaline region; and (b) separately forming an ammonium formate and a hydrazine hydrate compound. Adjusting the pH of the reducing agent-containing solution using the reducing agent to an acidic region, (c) at least the metal-containing solution prepared in the step (a) and the reducing agent-containing solution prepared in the step (b). Adding at least one or more selected from ammonium acetate or ammonium carbonate to one of the solutions, (d) mixing the metal-containing solution and the reducing agent-containing solution, and simultaneously reducing and depositing silver and palladium. A silver-parameter having a substantially spherical particle shape and a particle size in the range of 0.1 to 2.0 μm. Codium precipitated powder.