JPS6169907A - Production of pulverous tungsten powder - Google Patents

Abstract

PURPOSE:To produce easily and efficiently fine tungsten powder by heating tungsten and the composite oxide powder of the other elements to decompose and reduce the same in a hydrogen atmosphere then subjecting the powder to an acid treatment. CONSTITUTION:The composite oxide powder obtd. by adding an aq. soln. of the other element compds. to an aq. tungstate soln. is heated in the hydrogen atmosphere to obtain the composite tungsten power which is subjected to the acid treatment to liberate the tungsten. The pulverous tungsten powder is thus obtd. Copper or aluminum is preferably used for the element for forming the composite oxide with tungsten. The pulverous tungsten powder of about <=0.5mu is thus obtd. with good productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing fine tungsten powder having a particle size of 0.5 μm or less. These fine powders are used as raw materials for manufacturing tungsten sintered bodies or tungsten alloy sintered bodies.

[Conventional technology]

Tungsten powder is usually made from tungsten oxide obtained by thermal decomposition of ammonium paratungstate.
It is made by reduction in a hydrogen atmosphere.

It is known that when producing tungsten or tungsten alloy sintered bodies, a high-density sintered body can be obtained at a relatively low temperature by using fine tungsten powder as a raw material. There was a limit to the degree of tungsten powder, and it was difficult to produce fine tungsten powder.

It has long been known that fine tungsten powder can be obtained by thinning the powder layer on the reduction boat and increasing the hydrogen flow rate during hydrogen reduction. The layer thickness is limited to 1 to 71QO1, and the hydrogen flow rate per unit weight of raw material WO3 powder is 0.0.
5R/a+in.

A method for producing fine tungsten powder having a particle diameter of d or more is described.

[The gap that the invention attempts to solve]

However, when using this method, the amount of powder in the reduction boat and the amount of powder per unit amount of hydrogen are limited,
There were drawbacks such as a significant drop in productivity.

For example, in the above-mentioned Japanese Patent Application Laid-Open No. 15361/1983.

In order to obtain fine tungsten powder with a particle size of about 0.1 μ5 (BET average particle size), when the thickness of the oxide layer is 5 ns,
．． 02 A/win, ailg hydrogen and 0,3 fl/min when the oxide layer thickness is 10 m11
, cnf, g of hydrogen are required. (
In normal tungsten reduction, the thickness of the oxide layer is 10~
At 20mTn, hydrogen flow rate is 0.003 u/ll
l1n-cxl, g or less. ) The present invention eliminates the drawbacks of the above-mentioned conventional methods and provides a method for producing fine tungsten powder with high productivity.

[Means for solving the problems] The present invention was completed as a result of various studies on the reduction behavior of various tungsten composite oxides. The method involves heating the powder in a hydrogen atmosphere to decompose and reduce it, and then treating the resulting tungsten composite powder with acid to liberate tungsten.By using copper or aluminum as an element to form a composite oxide with tungsten, be.

[Effect]

Methods for producing various tungsten composite oxide powders are conventionally known. Many composite oxides can be produced by adding aqueous solutions of other elemental compounds that form composite oxides to an aqueous tungstate solution. The present inventors have conducted various studies on the reduction behavior of these tungsten composite oxides. As a result, when reducing tungsten composite oxide, depending on the type of constituent elements forming the composite oxide with tungsten,
i) When both tungsten and the constituent elements are reduced to a metal to form an alloy, and (i) When both are reduced to a metal but do not form an alloy and form a composite powder in which they are mutually dispersed (e.g. copper-tungsten). Complex oxides are a typical example. ), =) When only tungsten is reduced to metal, other constituent elements are not reduced or form lower oxides and become composite powders (aluminum-tungsten composite oxides). is an example of this.) Furthermore, it has been found that fine tungsten powder can be obtained when the composite oxide powder corresponding to ii) and ii) above is reduced and then treated with an acid to remove constituent elements and liberate tungsten. The tungsten particles produced by reduction in the composite oxide powder are fine with little grain growth even under normal reduction conditions, but this is because the constituent elements present in the composite powder prevent adjacent tungsten particles from coming into contact with each other in the composite powder. This is thought to be to prevent the growth of tungsten particles. The particle size of the tungsten powder obtained by the method of the present invention is usually about 0.1 μm.

In carrying out the present invention, it is necessary for the element that forms a composite oxide with tungsten that: (1) the composite oxide exhibits the reduction behavior described in 5) or (2) above; and (2) it must be easily removed by acid treatment after reduction. , here we have selected copper and aluminum as representative examples.

The content of the present invention will be explained in more detail below with reference to Examples.

〔Example〕

Example 1゜WO:Cu was added to a nitric acid aqueous solution at a weight ratio of 1 to an ammonium tungstate aqueous solution having a concentration of about 151/V%.
0:2.7, and the product was washed with water, filtered, and dried to obtain a blue copper-tungsten composite oxide powder. ll by X-ray diffraction! I! However, the powder obtained was amorphous.

When the powder was roasted at 600°C in air, a peak of Cu WO 4 was observed.6 The dried composite oxide powder was placed in a heat-resistant steel boat and reduced for 150 minutes at 650°C to 700°C in a hydrogen atmosphere. did.

The hydrogen flow rate per 100g of Wo during reduction is 2゜0m3
/hr. (When converted to the flow rate of hydrogen flowing through the unit cross-sectional area of the pipe per unit weight of WOS, it is approximately 0, OO4
6n/min, a#, g. ) This is the normal tungsten reduction and no-flame condition.

FIG. 3 shows the X-ray diffraction pattern of the reduction product.

Both copper and tungsten in the composite oxide powder have been reduced to metal.

Next, the obtained reduced product was boiled in concentrated hydrochloric acid for 1 hour to dissolve the copper in the composite powder.Then, the powder was washed with dilute ammonia water, further washed with water and alcohol, and finally at 80℃ or less. Fine tungsten powder was obtained by drying at a low temperature.

FIG. 1 shows an electron micrograph of the obtained tungsten powder, which consists of fine particles with a particle size of about 0.1 μm.

In addition, the residual steel in the tungsten fine powder is 2.8 as Cu.
%Met.

[Example 2] wo, once an aluminum nitrate aqueous solution is added to an ammonium tungstate aqueous solution of about 15 W/V%, m) L/ratio W
o, : A Q20. The mixture was added at a ratio of 5:2 and then boiled, and the product was washed with water, filtered, and dried to obtain a white aluminum-tungsten composite oxide powder. The powder obtained as a result of observation by X-ray diffraction was amorphous, but when the powder was roasted in air at 600'C, it became Al120.・
A peak of 3WO, or 2Au, O, .5WO, was shown.

The dried composite oxide powder was placed in a heat-resistant ml boat and reduced in a hydrogen atmosphere at 800'C for 2 hours. Wo at the time of reduction
, the hydrogen flow rate per 100 g was 1.3 m3/hr.

(WO, when converted to the hydrogen flow rate flowing through a unit cross-sectional area in the pipe per unit weight, it is approximately 0, OO312/min
, ai, g. ).

Figure 4 shows the X-ray diffraction pattern of the reduction product, where only the tungsten peak was observed and the aluminum compound peak was 1! ! ! The aluminum is probably amorphous aluminum oxide.

Next, the obtained reduction product was boiled in concentrated hydrochloric acid for 1 hour, and further fertilized in hydrofluoric acid with a concentration of about 20% at room temperature for about 2 hours to remove aluminum.Then, it was washed with water and alcohol, and finally A fine tungsten powder was obtained by drying at a low temperature of 80° C. or less.6 Figure 2 shows an electron micrograph of the obtained tungsten powder, and the powder consists of fine particles with a particle size of about 0.1 μm.

In addition, the residual aluminum in the tungsten fine powder is Al,
It was 0.0.095%.

〔Effect of the invention〕

As described above, according to the method of the present invention, 0.5μ
Fine tungsten powder of less than m can be easily and efficiently produced. The method of the present invention enables the production of fine tungsten powder on an industrial scale, and has great utility value.

[Brief explanation of the drawing]

Figures 1 and 2 are electron micrographs of fine tungsten powder produced by the method of the present invention, and Figures 3 and 4 are
The figure shows the X-ray diffraction pattern of the reduction product produced by the method of the present invention. Cited document: Japanese Patent Application Laid-Open No. 47-15361

Claims (1)

[Claims] 1. A composite oxide powder of tungsten and other elements is heated in a hydrogen atmosphere to decompose and reduce it, and the resulting tungsten composite powder is treated with an acid to liberate tungsten. A method for producing fine tungsten powder. 2. The method for producing fine tungsten powder according to claim 1, wherein the element forming a composite oxide with tungsten is copper. 3. The method for producing fine tungsten powder according to claim 1, wherein the element forming the composite oxide with tungsten is aluminum.