JPS6057481B2 - Method for adjusting potassium content in tungsten powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adjusting the amount of potassium contained as a dopant in tungsten powder.

Tungsten powder, which is mainly used to manufacture filament materials for tubes, is produced by thermally decomposing ammonium paratungstate (A) obtained by scouring tungsten ore in air or hydrogen to produce tungsten oxide.
Next, aluminum (Al) is added to the oxide as a doping agent.
After adding 0.01 to 1.0% (weight percentage) of an aqueous solution of a compound of , potassium (ni), and silicon (Si) in the form of Al2O3, ni, O)SiO2, and drying,
It is obtained by reduction in a hydrogen atmosphere at a temperature range of about 400-900°C.

The obtained tungsten powder is treated with strong acid to remove excess dopant, dried, compacted into the desired shape, sintered at high temperature in a hydrogen atmosphere, and then rolled.
It is drawn into a tungsten wire. The method of adding aluminum, potassium, and silicon salts to tungsten oxide powder has been well known for a long time.

Most of these added dopants are removed in the acid treatment step, but there is a correlation between the amount of potassium remaining in the powder after acid treatment and the amount of potassium present in the ingot after sintering. It is also already known that the sagging resistance of tungsten wire depends on the amount of potassium contained in the ingot after sintering. Therefore, in the past, attempts have been made to adjust the amount of dopant added in order to adjust the sagging resistance or recrystallization temperature of tungsten materials for filaments, but such methods have not been able to sufficiently adjust the wire properties. I couldn't do it.

This is because, as described above, most of the added dopant is dissolved and removed in the acid treatment step, so that the amount of dopant added does not necessarily remain in the powder after the acid treatment. Recently, a method has been proposed to adjust the amount of residual potassium by controlling the amount of aluminum added at the same time as potassium. However, when the amount of aluminum, which is part of the dopant, is changed in this way, powder characteristics or sintering may be affected. There is a risk of seriously affecting the physical properties of the aggregate. The present invention eliminates the drawbacks of these conventional methods and provides an easier and more reliable method for adjusting the potassium content in tungsten powder.

As a result of investigating various forms of reduction of tungsten oxide with the addition of dopants, the present inventors found that the amount of potassium remaining in the powder after acid treatment was strongly influenced by the reduction rate at the initial stage of reduction. As a result of various studies on reduction conditions, the method of the present invention was completed.

A feature of the present invention is that in the reduction of tungsten oxide to which at least potassium is added as a doping agent, the tungsten powder after acid treatment is The purpose is to arbitrarily adjust the potassium content contained in the liquid.

According to the method of the present invention, the potassium content in tungsten powder can be easily and reliably adjusted.

Next, a method for adjusting the potassium content in tungsten powder according to the present invention will be specifically described with reference to examples.

Example 1 An aqueous solution of potassium silicate was added to a blue oxide obtained by thermally decomposing high-purity ammonium baratungstate in a hydrogen atmosphere.
0.4% as lO2 and 0.2% as K2O, and an aqueous solution of aluminum nitrate was added in the same weight percentage as Al2O3 to the blue oxide.
．． After adding it to a concentration of 0.3% and drying it,
'C for each time in a hydrogen atmosphere to form brown tungsten oxides with various oxygen contents, and one part was reduced in a hydrogen atmosphere with a temperature gradient of 650-85 (s), and another part was reduced in a hydrogen atmosphere with a temperature gradient of 650-85 ()
The parts were each reduced under certain conditions in a hydrogen atmosphere with a temperature gradient of 700-90°C, washed with hydrofluoric acid, washed with water, and dried.

FIG. 1 shows the relationship between the amount of potassium contained in the tungsten powder at this time and the oxygen content of the brown tungsten oxide at the time when the reduction temperature reaches 650° C. or higher. As is clear from Figure 1, the potassium content in the tungsten powder after acid treatment decreases as the oxygen content of the tungsten oxide increases at the time when the reduction temperature reaches 650°C or higher. It has been found that a desired amount of potassium can be easily incorporated into the tungsten powder by determining the amount. FIG. 1 also shows that the potassium content in the tungsten powder is almost unaffected by the reduction conditions after the reduction temperature reaches 6° C. or higher. As is well known, when reducing tungsten with hydrogen, a temperature of approximately 650°C or higher is required, and lower oxides are formed at lower temperatures. This indicates that there is a close relationship with the potassium content in the water.

By adjusting the amount of potassium contained in the tungsten powder in this way, it was possible to easily produce a tungsten wire having desired droop resistance and recrystallization temperature.

As is clear from the examples above, according to the method of the present invention, the amount of potassium in the tungsten powder could be easily adjusted.

In the above examples, tungsten blue oxide was used as the material to be doped, but in the practice of the present invention, other oxides may be used, and ammonium tungstate or other tungsten compounds containing oxygen may be added. It's okay.

[Brief explanation of drawings]

Figure 1 shows the relationship between the oxygen content of tungsten oxide and the potassium content of tungsten powder after acid treatment when the reduction temperature reaches 6500C or higher. Temperature gradient 650~
The black circles indicate the values when the reduction temperature is 850°C and the temperature gradient is 700 to 900°C.

Claims (1)

[Claims] 1. When producing a material containing tungsten as a main component, at least a potassium compound is added as a doping agent to tungsten oxide, and the oxide is reduced at least in a temperature range of 650° C. or higher to produce the dopant. In a method for producing tungsten powder, which includes a step of obtaining a tungsten powder containing a tungsten powder and then subjecting the tungsten powder to an acid treatment, the tungsten oxide at the time when the reduction temperature in the reduction step reaches 650° C. or higher. A method for adjusting the potassium content in tungsten powder, comprising arbitrarily adjusting the potassium content contained in the tungsten powder after the acid treatment by controlling the oxygen content of the tungsten powder.