JPH06299212A - Production of oxidation resistant palladium powder - Google Patents

Abstract

PURPOSE:To produce an oxidation resistant palladium powder by adding a nonionic surfactant at the time of adding the reducing agent in the production of the metallic palladium powder which is performed by reducing palladium ion in its solution. CONSTITUTION:The palladium powder is produced by adding a nonionic surfactant to a solution contg. palladium ion, thereafter adding a reducing agent to precipitate metallic palladium, separating the solid material from the liquid phase, washing the recovered solid material with water and then drying the material to produce the objective palladium powder. The palladium powder thus produced is hardly oxidized and shows only a little volume change even at the time of sintering it at a high temp. Further the palladium powder, the particle size and shape of which are controllable by adding the nonionic surfactant and which has such an extent of oxidation resistance as not to cause breakage of the electrode, etc., at the time of using the palladium powder as the electrode material, can be produced easily and 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]

A method for producing a palladium powder according to the present invention is a method for reducing a palladium ion in a solution to obtain a metal palladium powder, and by adding a nonionic surfactant when adding a reducing agent, acid resistance is improved. It is characterized by obtaining a oxidizable palladium powder. Further, the production method of the present invention, as a preferred embodiment thereof, after adding a nonionic surfactant to a solution containing palladium ions, a reducing agent is added to precipitate metallic palladium, and after solid-liquid separation, the recovered product is washed with water and dried. It is characterized by doing. It is a conventional means to control the reaction by adding a surfactant to the solution, but the palladium powder produced by adding this surfactant is hard to be oxidized even if it is fired at high temperature, and its volume change is small. This has never been known so far, and no such study has been made. The present invention is intended to easily obtain a palladium powder having such oxidation resistance that does not cause electrode breakage by controlling the particle size and particle shape by adding a nonionic surfactant. It is a highly practical manufacturing method.

[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.

After adding a nonionic surfactant to the palladium solution, a reducing agent is added to reduce palladium ions to metallic palladium. There is no effect even if the surfactant is added after adding the reducing agent. By adding the surfactant, aggregation of the metallic palladium precipitate is prevented and a precipitate having a particle size of 0.1 to 1 μm is obtained. With surfactants other than the nonionic surfactant, the precipitate particles aggregate, and the effect of the present invention cannot be obtained. As the nonionic surfactant, polyoxyethylene nonylphenyl ether or the like can be used. The amount of the surfactant added is preferably 1 g / l to 6 g / l. When the amount added is less than 1 g / l, the palladium particles aggregate, and when the amount added exceeds 6 g / l, the particles become 1 μm or more.

As a reducing agent, hydrazine compounds such as hydrazine and hydrazine sulfate are commonly used. The pH of the hydrazine aqueous solution is preferably 6.5 to 7.0. If the pH is less than 1, the particle size of the palladium powder will be smaller than 0.1 μm, and if it is higher than pH 7, the particle size of the palladium powder will be 1 μm.
Greater than m. The addition of hydrazine precipitates metallic palladium, which is recovered. By the above production method, spherical palladium powder having an average particle diameter of 0.1 to 1 μm and a uniform shape can be obtained.

[0008]

Example 1 Dichlorodiamine palladium solution (Pd: 20
g / l) ammonium chloride 20 g / l and nonionic surfactant (polyoxyethylene nonylphenyl ether) 3 g
After adding / l to make a 1 liter aqueous solution, ammonia water was added to adjust the pH to 6. While stirring the palladium solution, p
A hydrazine aqueous solution adjusted to H7 was added to generate a metal palladium precipitate, which was solid-liquid separated, washed and dried to obtain a metal palladium powder having an average particle diameter of 0.8 μm. 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 12.9%. On the other hand, when a commercially available palladium powder was heated under the same conditions, the weight increase due to oxidation was 14.9%, and the palladium powder of this example shows a weight increase due to oxidation of about 14.9% compared to the conventional powder.
13% less.

[0009]

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 (2)

[Claims] 1. A method for obtaining a metal palladium powder by reducing palladium ions in a solution, wherein a nonionic surfactant is added at the time of adding a reducing agent to control the particle size to obtain an oxidation resistant palladium powder. A method for producing a palladium powder, which comprises: 2. The method according to claim 1, wherein a nonionic surfactant is added to a solution containing palladium ions, and then a reducing agent is added to precipitate metallic palladium. After solid-liquid separation, the recovered material is washed with water and dried.