JPH06299211A - Production of oxidation resistant palladium powder - Google Patents

Abstract

PURPOSE:To provide the production of an oxidation resistant palladium powder. CONSTITUTION:This production features that the oxidation-resistant palladium powder is produced by reducing palladium ion in its solution to recover a metallic palladium precipitate and by heat-treating the recovered metallic palladium under pressure. Thus the palladium powder having excellent oxidation resistance can be produced easily and a uniform, spherical palladium powder which has excellent oxidation resistance and is also appropriately used as an electrode material can be produced in a high yield.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a conductive palladium powder having excellent oxidation resistance, which is used for a film conductor of an electronic circuit, an electrode of an electronic component and the like.

[0002]

2. Description of the Related Art In multilayer capacitors and the like, internal electrodes are formed by using a conductive paste of palladium powder. For example, in a barium titanate multilayer capacitor or the like, a laminated body in which a conductive paste containing palladium powder is interposed between barium titanate insulating layers is formed, and the laminated body is integrally fired to form an internal electrode. Manufactures capacitors. Conventionally, as a method for producing such a palladium powder, sodium hydroxide is added to an aqueous solution containing palladium ions to adjust the pH, and a reducing agent such as hydrazine, formic acid or sodium borohydride is added to reduce the palladium ions. A method of recovering as metallic palladium is conventionally known, but the palladium powder obtained by this method has a non-uniform particle size and an irregular particle shape, in order to eliminate this drawback,
There is also known a production method in which a tetraamminepalladium (II) salt is used as a raw material palladium ion source and a hydrazine compound is used as a reducing agent (JP-A-3-277706).

[0003]

However, any of the palladium powders produced by the above method is apt to be oxidized, and there is a problem that the electrodes of the capacitor are broken or the layers are separated. For example, a barium titanate capacitor has a laminated body in which a conductive palladium paste is sandwiched between insulating layers of barium titanate.
It is formed by firing at 200 to 1400 ° C. During this firing, the palladium powder is oxidized at around 600 ° C to become palladium oxide, and the volume of the particles expands by about 60%. When the firing temperature rises to 850 ° C. or higher, this palladium oxide is thermally decomposed and reduced to metallic palladium, and the volume of the particles shrinks to return to the original size. Such volume expansion and contraction during firing cause electrode breakage and delamination. As a method for preventing the above electrode breakage and delamination, it is known to coat the surface of palladium powder with an oxide or hydroxide of silicon, Al or the like (Japanese Patent Laid-Open No. 63-216204).
However, the current situation is that even in this method, electrode breakage and the like cannot be sufficiently prevented. The present invention provides a manufacturing method that solves the above problems in the conventional manufacturing method, and according to the present invention, a palladium powder having excellent oxidation resistance can be obtained.

[0004]

According to the method for producing a palladium powder of the present invention, a palladium ion in a solution is reduced to recover a metal palladium precipitate, and the metal palladium is heated and pressed to obtain an oxidation resistant palladium powder. It is characterized by In a preferred embodiment of the present invention, before adding the reducing agent, the pH of the solution containing palladium ions is adjusted to 5.5 to 9 and a polymer dispersant or a surfactant is added to further reduce the pH. The pH of the solution of the agent is 5.5 to 7
And is added to the solution containing the palladium ion. INDUSTRIAL APPLICABILITY The present invention is a highly practical manufacturing method, which makes it possible to easily obtain a palladium powder having oxidation resistance to the extent that the above electrode breakage does not occur simply by adding an autoclave treatment.

[0005]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the flow sheet of the manufacturing method shown in the drawings. In the method of the present invention, as the palladium raw material, dichlorodiaminepalladium, palladium ammine (I
I) Salt compounds and the like are used. The present invention will be described by taking the case of using dichlorodiamine palladium Pd (NH ₃ ) ₂ Cl ₂ as an example. To the aqueous solution containing dichlorodiamine palladium and ammonium chloride, ammonia water is added to adjust the pH of the solution to 5.5 to 9, preferably. Is 5.9 to 6.2
And the palladium compound is dissolved. If the pH of the solution is less than 5.5, palladium will precipitate and p
When H exceeds 9, the particle size of the obtained palladium powder is 1μ
Since it becomes larger than m, contact failure tends to occur when used as an electrode material, which is not preferable. Note that ammonium nitrate may be used instead of ammonium chloride.

A polymer dispersant and a surfactant are added to the palladium solution, and a reducing agent is further added to reduce palladium ions to metallic palladium. As the polymer dispersant, gelatin, gum arabic, polyethylene glycol and the like are used. The polymer dispersant acts to control the particle shape, and by adding the polymer dispersant, uniform spherical palladium particles can be obtained. The addition amount of the polymer dispersant is preferably 1 to 6 g / l. When the amount added is less than 1 g / l, the palladium particles aggregate to form particles of 1 μm or more, and when the amount added exceeds 6 g / l, the filterability of the precipitate deteriorates. When the amount added is in the range of 1 to 6 g / l, the pH is stable, spherical palladium powder of 1 μm or less is obtained, and the dispersibility in a solution is good. Further, as the surfactant, a nonionic surfactant is preferable. Specifically, polyoxyethylene alkyl ether is preferably used.

As a reducing agent, hydrazine compounds such as hydrazine and hydrazine sulfate are commonly used. The hydrazine solution is adjusted to pH 5.5 to 7, preferably 6.5 to 6.8 and added to the palladium solution. When the pH of the hydrazine solution is less than 5.5, the particle size of the palladium powder is 0.
If it is finer than 1 μm, and if it is higher than pH 7, the particle size of the palladium powder becomes larger than 1 μm. The addition of hydrazine precipitates metallic palladium, which is recovered. If the particle size is less than 0.1 μm, sufficient oxidation resistance cannot be obtained, and if it exceeds 1 μm, electrode breakage tends to occur when the electrode is formed, which is not preferable.

The recovered metallic palladium is put into an autoclave and heated and pressurized at 100 to 300 ° C., 1 atm or more for 24 to 72 hours. During autoclave treatment, if the heating temperature is lower than 100 ° C, the particles will not grow sufficiently,
Above 0 ° C, the palladium powder oxidizes.

[0009]

Example 1 Dichlorodiamine palladium solution (Pd: 20
ammonium chloride (40 g / l) and gelatin (3 g / l) to make a 1 liter aqueous solution, and then add aqueous ammonia to pH 6
Adjusted to. On the other hand, hydrochloric acid was added to 50 ml of hydrazine hydrate to adjust the pH to 7. These are heated to a temperature of 55 ° C., an aqueous hydrazine solution is added while stirring the palladium solution,
After solid-liquid separation, it was washed and dried to obtain metallic palladium powder.
100 g of this palladium powder was autoclaved (capacity 300
ml) and heated at 200 ° C. for 72 hours. When this palladium powder was heated to 1250 ° C at a heating rate of 10 ° C / min,
The weight increase due to oxidation at 800 ° C was 13.1%. on the other hand,
When commercially available palladium powder was heated under the same conditions,
The weight increase due to oxidation was 14.9%, and the weight increase due to oxidation of the palladium powder of this example was about 12% compared to the conventional powder.
There were few.

[0010]

Example 2 Dichlorodiamine palladium solution (Pd: 20
(g / l) Ammonium chloride (40 g / l) was added to make a 1 liter aqueous solution, and then ammonia water was added to adjust the pH to 6 and 3 g of nonionic surfactant (polyoxyethylene alkyl ether) was added. While stirring, an aqueous hydrazine solution was added, and after solid-liquid separation, washing and drying were performed to obtain a metal palladium powder. This palladium powder 1
Charge 00g into an autoclave (capacity 300ml) and add 200g.
The mixture was heated at ℃ for 72 hours. When this palladium powder was heated to 1250 ° C at a heating rate of 10 ° C / min, the weight increase due to oxidation at 800 ° C was 12.8%, which was about 14% less than the conventional powder. .

[0011]

According to the manufacturing method of the present invention, palladium powder having excellent oxidation resistance can be easily manufactured.
Further, according to the specific method shown in the examples, it is possible to obtain a uniform spherical palladium powder which is excellent in oxidation resistance and suitable as an electrode material in a high yield.

[Brief description of drawings]

FIG. 1 is a flowchart of a manufacturing method of the present invention.

Claims (3)

[Claims] 1. A method for producing a palladium powder, characterized in that an oxidation resistant palladium powder is obtained by reducing a palladium ion in a solution to recover a metal palladium precipitate, and subjecting the metal palladium to heat and pressure treatment. 2. Metallic palladium at 100 to 300 ° C., 1
The method according to claim 1, wherein the heating and pressurizing treatment is performed at atmospheric pressure or higher. 3. Before adding the reducing agent, the pH of the solution containing palladium ions is adjusted to 5.5 to 9, a polymer dispersant or a surfactant is added, and the pH of the solution of the reducing agent is further adjusted. The method according to claim 1, wherein the solution is adjusted to 5.5 to 7 and added to the solution containing the palladium ion.