JPS6148585B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing base metal coated powders.
More particularly, the present invention relates to a method of producing a base metal coated powder consisting of particles of a substrate material that are substantially completely coated with a coating layer of base metal.

The composite sintered body obtained by molding and sintering metal powders such as copper, nickel, zinc, and iron and ceramic powders has the characteristics of both metals and ceramics, so it can be used as a bearing material, wear-resistant material, and high-temperature resistant material. Used for various purposes such as materials. However, in the case of manufacturing composite sintered bodies of metals, in many combinations, the difference in specific gravity between the metals is not very large, so a homogeneous mixed powder is produced by normal mixing of one metal powder and the other metal powder. However, since there is generally a large difference in specific gravity between metal and ceramic powders, special mixing equipment, molding equipment, etc. are required to prepare a homogeneous mixed powder and obtain a homogeneous fired product, and the operation is also complicated. Become. The degree of homogeneity of the obtained baked product is also not high.

The present invention provides a method for producing a base metal-coated powder particularly suitable for producing a composite sintered body made of metal and ceramics as described above.

The present invention includes a base metal compound, a nonmetallic ammonium salt, and aqueous ammonia or caustic alkali.
This is a method for producing a base metal-coated powder, which is characterized in that a reducing agent is added to a dispersion in which a ceramic substrate powder is uniformly dispersed in a gel-like aqueous solution having a pH of 5-10, under stirring.

The powder produced according to the present invention is a coated powder consisting of composite particles having a ceramic base particle as a core and a coating layer made of a base metal provided around the core. According to the production method of the present invention, a homogeneous and strong base metal coating layer can be provided on the ceramic base particles, and unlike the coating layer produced by the conventional chemical plating method, this coating layer is made of base metal components. Since it is virtually free from contamination, it can be formed as a highly pure base metal coating. Furthermore, in the present invention, a thicker, more homogeneous, and stronger coating layer can be obtained compared to conventional chemical plating methods. Furthermore, with the conventional chemical plating method, it was difficult to obtain a uniform metal-coated powder for powders with an average particle size of 1 micron or less, but the method of the present invention makes it possible to obtain uniform metal-coated powders from such fine-particle powders. Coating is easily achieved. Therefore, the base metal coated powder obtained by the present invention can be used for various purposes other than manufacturing sintered bodies.

Next, the present invention will be explained in detail.

Examples of base metals used in the present invention include titanium,
Examples include transition metals belonging to the fourth period of the periodic table, such as vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc. Additionally, air-stable base metals such as lead, molybdenum, tin, etc. are also suitable for forming the coating layer of the present invention. These base metals are not limited to the use of only one type, but may be used in combination of two or more types.
It is also possible to mix and use noble metals in a relatively small amount (weight ratio) with respect to base metals. Base metal compounds can be used in their aqueous solutions (aqueous solutions, mineral acid solutions,
There is no particular restriction as long as an alkaline aqueous solution (alkaline aqueous solution, etc.) can be prepared. Examples include base metal sulfates, nitrates, halides, and cyanides. Furthermore, complex compounds of base metals can also be used, and solutions of simple base metals dissolved in mineral acids can also be used.

Examples of non-metallic ammonium salts include ammonium chloride, ammonium acetate, ammonium sulfate, ammonium nitrate, and ammonium phosphate, with ammonium chloride being particularly preferred.

PH5-10 containing base metal compounds, nonmetallic ammonium salts, and aqueous ammonia or caustic alkalis
A gel-like aqueous solution of is prepared, for example, as follows. A base metal or base metal compound is once dissolved in any aqueous solvent such as water, dilute acid, concentrated acid, mixed acid, alkaline aqueous solution (a solvent that dissolves the target base metal or base metal compound), and this solution and ammonium chloride ( By mixing ammonium salts such as NH ₄ Cl) and adding aqueous ammonia or aqueous caustic alkaline solution (aqueous solution of caustic soda, caustic potash, etc.) to this mixture, the pH of the mixture can be adjusted to 5-10.
(preferably 6-8). The mixture is made into a gel by adding an ammonium salt to the base metal solution, or by further adding aqueous ammonia or an aqueous caustic alkali solution to adjust the pH of the mixture to 5-10. The amount of ammonium salt such as ammonium chloride added is preferably an amount equal to or more than the equivalent amount to the base metal of the base metal compound and not more than three times the equivalent amount. If the amount of ammonium salt added is less than this range, it will be difficult to disperse the ceramic substrate powder stably and uniformly, while if the amount of ammonium salt is more than the above range, the viscosity of the gel will be high. If it becomes too much, the reaction tends to become non-uniform, and the ammonium salt tends to be mixed into the coating layer of the base metal coated powder after it is produced.

The ceramic substrate used in the present invention is not particularly limited as long as it does not exhibit substantial solubility in the above-mentioned gel-like aqueous solution, and examples thereof include silicon oxide, zirconium oxide, titanium dioxide, alumina, and barium titanate. Examples include oxide ceramics such as oxide ceramics such as titanium carbide, titanium nitride, tungsten carbide, silicon carbide, and other non-oxide ceramics.

Ceramic-based powders typically have an average particle size of 30
Powders with an average particle size of 10 microns or less are used, but powders with an average particle size of 10 microns or less are used.
The particle size does not need to be particularly uniform. Furthermore, as mentioned above, uniform coating of powder with an average particle size of 1 micron or less is also possible.

There is no particular restriction on the ratio of the ceramic base powder and the base metal compound contained in the dispersion liquid, but when the base metal coated powder to be produced is assumed to be used as a composite sintered body, the ratio between the ceramic base powder and the base metal in the metal compound is The ratio is preferably in the range of 2:98 to 98:2 (weight ratio). A more desirable range is ceramic substrate:base metal=5:95-
The ratio is 95:5 (weight ratio).

The dispersion of the present invention is prepared by adding ceramic substrate powder to a gel-like aqueous solution of pH 5-10 containing a base metal compound, a nonmetallic ammonium salt, and ammonia water or caustic alkali, prepared as described above, with stirring. A uniform dispersion can be obtained by this method. Stirring can be performed by any method and at any time, and any type of stirring tool or device can be used.

The reducing agent is added to the dispersion while stirring. There are no particular restrictions on the stirring method, but since the dispersion of the gel-like aqueous solution and the ceramic base powder is to be stirred, a method that allows strong stirring is desirable.

The reducing agent is not particularly limited as long as it can reduce the base metal compound in the gel-like aqueous solution and convert it into a base metal element. Examples of reducing agents include lithium aluminum hydride, sodium borohydride, etc., but are not limited to these reducing agents. The reducing agent is added in an amount sufficient to reduce the base metal compound in the gel-like aqueous solution to a base metal element.

By adding a reducing agent to the stirred dispersion of the gelled aqueous solution and the ceramic substrate powder, the gel state of the dispersion disappears and at the same time a base metal coated powder is formed.

The produced base metal coated powder is then removed by decantation, removal, etc., washed, dried, and used for various purposes.

Next, examples of the present invention will be shown.

Example 1 6 g of cupric chloride (CuCl ₂ ) was dissolved in 450 ml of water, and 5 g of ammonium chloride (based on copper) was dissolved in 450 ml of water.
1.05 equivalent times) then ammonia water (28% aqueous solution)
A blue gel-like solution (PH
Approximately 7) was obtained. Add 40 g of barium titanate (BaTiO ₃ ) powder (average particle size 0.13 microns) to this solution.
was added and thoroughly stirred to obtain a uniform dispersion. When 100 ml of an aqueous sodium borohydride solution (NaBH ₄ 2 g/100 ml H ₂ O) was added to this dispersion while thoroughly stirring the dispersion, the gel state disappeared and a gray powder was produced. Next, the powder was taken, washed with water and hot water, and dried at 65°C to obtain 41.12 g of copper-coated barium titanate powder. Yield 96%. Barium titanate/copper weight ratio in coating powder: 93.4/
6.6.

The copper-coated barium titanate powder obtained above was placed in a container, an electrode was inserted into the container, and the resistance value was measured. The resistance value was approximately 0, which matched the resistance value of pure copper powder.

In addition, when the copper-coated barium titanate powder obtained above was pressed into a mid-plate shape at a pressure of 1 ton/cm ² and fired at 1150°C for 1 hour under an argon gas atmosphere, it was found to be solid with a homogeneous surface condition. A fired product was obtained.

Example 2 42.3 g of cupric chloride was dissolved in 3 parts of water, and 35.3 g of ammonium chloride (1.05 times the equivalent of copper) was added to this.
Next, caustic soda aqueous solution (NaOH100g/500ml)
A blue gel-like solution (PH
About 7) was obtained. 20 g of titanium dioxide (TiO ₂ ) powder was added to this solution and thoroughly stirred to obtain a uniform dispersion. While stirring this dispersion liquid, a sodium borohydride aqueous solution (NaBH ₄ 14g/700
When 700 ml of mlH ₂ O) was added, the gel state disappeared and a gray powder was produced. Next, the powder was taken, washed with water and hot water, and dried at 65°C to obtain 39.2 g of copper-coated titanium dioxide powder. Yield 98%. Titanium dioxide/copper weight ratio in coating powder: 50/50.

The copper-coated titanium dioxide powder obtained above was placed in a container, an electrode was inserted into the container, and the resistance value was measured. The resistance value was approximately 0, which matched the resistance value of pure copper powder.

Furthermore, when the copper-coated titanium dioxide powder obtained above was pressed into a disc shape under a pressure of 1 ton/cm ² and fired at 1000°C for 1 hour under an argon atmosphere, a strong fired product with a homogeneous surface condition was obtained. I got something.

Example 3 22g of nickel chloride (NiCl ₂ 6H ₂ O) in 200ml of water
A blue gel-like solution (PH about 7) was obtained by adding 16 g of ammonium chloride (1.6 equivalents to nickel) and then 140 ml of a caustic soda aqueous solution (NaOH 50 g/250 ml H ₂ O). 40 g of titanium dioxide powder (average particle size: 2 microns) was added to this solution and thoroughly stirred to obtain a uniform dispersion. While thoroughly stirring this dispersion, add 250 g of sodium borohydride aqueous solution (NaBH ₄ 5g/250mlH ₂ O).
When ml was added, the gel state disappeared and a gray powder was produced. Next, the powder was taken, washed with water and hot water, and dried at 65°C to obtain 44.54 g of nickel-coated titanium dioxide powder. Yield 98
%. Titanium dioxide/nickel weight ratio in coating powder: 88/12.

The nickel-coated titanium dioxide powder obtained above was pressed into a disk shape at a pressure of 1 ton/cm ² ,
When fired at 1200°C for 1 hour under an argon atmosphere, a strong fired product with a homogeneous surface condition was obtained.

Claims (1)

[Claims] 1. Base metal compound, nonmetallic ammonium salt,
and PH5- containing ammonia water or caustic alkali
1. A method for producing a base metal-coated powder, which comprises adding a reducing agent to a dispersion in which a ceramic base powder is uniformly dispersed in a gel-like aqueous solution under stirring. 2. The manufacturing method according to claim 1, wherein the nonmetallic ammonium salt is ammonium chloride. 3. The manufacturing method according to claim 1, characterized in that the content of the nonmetallic ammonium salt is at least an equivalent amount to the base metal of the base metal compound and at most three times the equivalent amount. 4. The manufacturing method according to claim 1, wherein the base metal is a transition metal in the fourth period of the periodic table. 5. The manufacturing method according to claim 1, wherein the average particle size of the base material powder is 1 micron or less.