JPS58107403A - Preparation of tungsten powder - Google Patents

Abstract

PURPOSE:To obtain an excellent wire for a tubular globe, by adding a K-compound to lower W-oxide containing a predetermined amount of O2 prior to reducing said W-oxide to eliminate a hydrofluoric acid washing process. CONSTITUTION:For example, yellow W-oxide is reduced in H2 to obtain lower W-oxide with O2-content of 6-14%. After a K-compound is added to this oxide alone, the resulting mixture is dried and subsequently subjected to secondary reduction in H2 to obtain a W-powder. This powder is washed by water to remove the excessive additive. By this method, the W-powder free from a vitreous substance and low in residual K-amount is obtained and a W-wire prepared from this W-powder is excellent in use of a tubular globe.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing tungsten powder mainly used for producing tube wire.

Tungsten wire is usually produced by hot rolling and drawing of an ingot made by powder metallurgy.

Since these tungsten wires are exposed to high temperatures during use, they are required to have high thermal properties. Small amounts of additives (doping agents) are usually added to the powder to improve the thermal properties of the wire.

Conventional tungsten powder was manufactured using the following steps.

That is, 1) the ore is refined to produce rose ammonium tungstate (APT), and 2) the obtained APT crystals are thermally decomposed in hydrogen or air to produce blue oxides (BO-0,
20.0-20.5%) or yellow oxide (WOs-O
x 20.6%), and ■ these oxides near μ minium, potassium, and silicon compounds to A# and O□, respectively! 0,5i01. (doping) to approximately 0.01 to 1.0%, and then
After reducing to metal in one or two stages at a temperature around 900 DEG C., the obtained tungsten powder is further washed with hydrochloric acid, then hydrofluoric acid, and finally washed with water and then dried.

The purpose of the final dilute acid cleaning step is to dissolve and remove most of the added dopant and make the powder uniform. Hydrofluoric acid is particularly used to remove Si, but the well-known method Hydrofluoric acid is a highly corrosive acid, and its use is subject to many restrictions due to equipment materials, and great care is required in its handling.

Most of the added dopant is removed in the acid cleaning process as described above, but it is removed in the subsequent sintering process.
However, some of the residual dopant evaporates and scatters. For example, regarding potassium, the powder after acid washing generally contains 70 to 70% potassium.
200 ppm, and 40-100 ppm in the wire
It is said that it is desirable that pm of potassium remain. It is known that potassium forms a row of fine pubs in the wire after drawing, prevents movement of grain boundaries, and improves the wire's thermal properties such as sag resistance at high temperatures.

On the other hand, it has become clear that there is no special relationship between the mechanical properties of silicon among the doping components. Furthermore, it is known that added silicon compounds often form glass-like lumps during reduction, and if washing with hydrofluoric acid is not sufficient, they remain in the powder, making the wire structure finer and deteriorating the wire properties. There is.

Figure 1 shows a mass of glassy material remaining in the powder (9
An example of the arrow in the figure is shown. Figure 1 (a) is an electron micrograph showing its morphology, and Figure 2 (b) is a characteristic X-ray photograph of silicon at the same position, showing that silicon compounds are densely segregated in a glassy substance. I understand very well.

The present invention aims to eliminate the drawbacks of the above conventional method,
This is a new method for manufacturing tungsten powder that was completed as a result of observing the behavior of dope components.The feature of the present invention is that the amount of oxygen is 6%.
It is possible to add a potassium compound alone to the 9-tungsten lower oxide within the range of 14% or less and then reduce it to the metal.

The method of the present invention has the following advantages over conventional methods.

(2) Since no Sin is added, cleaning with hydrofluoric acid is unnecessary and the process is shortened.

■There is no need to use highly corrosive hydrofluoric acid, so it is covered. There are no material restrictions in place.

■No glass-like lumps of silicon compounds remain in the powder, contributing to improved wire properties.

The method of the present invention will be explained in detail below.

Potassium hydroxide was added to various tungsten lower oxides obtained by reducing tungsten oxide in hydrogen at a temperature of 600 to 650'C for each time, and the mixture was heated at 700 to 900'C. It was reduced to tungsten powder in the temperature range of . Next, these tungsten powders are washed with dilute hydrochloric acid, then washed with water, and only those doped with tungsten lower oxides whose oxygen content is within the range of 6 to 14% are necessary for manufacturing tungsten wire for tubes. Sufficient potassium remains to achieve the objectives of the present invention.

On the other hand, after adding a potassium compound alone to tungsten yellow oxide, which is a conventional doped oxide,
The amount of potassium after acid treatment of the tungsten powder reduced under the same conditions in the temperature ranges of 0 to 650°C and 700 to 900°C was 10 pPm or less. Similarly, a powder obtained by adding a potassium compound alone to a blue oxide and then reducing the powder had a potassium content of 10 pP after acid treatment, and an ingot obtained by press-sintering this powder had a potassium content of 5 PFI. Furthermore, it was found that the amount of potassium in the ingot of the powder obtained by adding an aluminum compound to the blue oxide at the same time as a potassium compound remained at 4 PPm.

When processed into fine wires, these powders were significantly deformed at high temperatures and were unsuitable for manufacturing tungsten wires for tubes.

Figure 3 shows that potassium hydroxide is added to tungsten lower oxide which has been subjected to primary reduction for 1 hour at each temperature at a concentration of 0.2%.
This figure shows the relationship between the amount of potassium after acid treatment and the primary reduction temperature of tungsten powder, which was added to the tungsten powder and then subjected to secondary reduction at 700 to 900℃. It turns out that it doesn't have a big impact. Normally, reduction is often carried out at a temperature of 600 to 900°C.

Next, we looked at the relationship between the cleaning conditions for tungsten powder after reduction and the amount of residual potassium.

Table 1 shows powder Q100F which was subjected to secondary reduction after adding 0.2% potassium hydroxide (Km2O) to tungsten lower oxide with an oxygen content of 15.4%, 20% hydrofluoric acid, 20% hydrochloric acid, and water. This is a comparison of the amounts of residual potassium in powders that were washed with 50 ml of water, then washed with 21 ml of water, and dried. It can be seen that the purpose of cleaning to remove excess dopant mentioned above is fully achieved.

(Table 1) Next, the method of the present invention will be explained in more detail according to Examples.

Example 1 Yellow tungsten oxide was reduced to an oxygen content of 12.6% in a temperature range of 450 to 700°C in hydrogen, and an aqueous solution of furium hydroxide was added to the obtained lower oxide to reduce the amount of O to 0.2%. After addition, it was dried. Then 850-9 in hydrogen
Tungsten powder was obtained by secondary reduction at 00'C, washed with water to remove excess dopant, and then dried. The average particle diameter of the tungsten powder at this time was 2.1 μm, and the amount of residual potassium was 175 ppm.

No glassy material was found in the powder.

The obtained powder was pressed into a rod shape at a pressure of 1,300 kv #j, and was pre-sintered at 1,300"C in a hydrogen furnace to a theoretical density of 93
%. Thereafter, the wire was rolled and drawn according to a conventional method to obtain a wire with a 0.39 fi finish.

The amount of residual potassium in the obtained wire was 54 ppm, and 80% of the fusing current when the wire was bent into a hairpin shape.
The sag value in the sag test (the amount of drooping measured by the spread of the hairpin) was 9. It was an appropriate value for ON and tube wire. The tensile strength at 0.39fi was 27.6 to 9.

It shows excellent properties as a wire for cage tubes. Moreover, the workability with wire was also good.

As is clear from the above examples, the tungsten powder obtained by the method of the present invention is suitable for manufacturing wire for tubes, and the method of the present invention, in which a potassium compound is added alone to a lower tungsten oxide, is suitable for manufacturing process steps. It has many advantages such as being shortened.

[Brief explanation of drawings]

FIG. 1 shows gaseous substances in tungsten powder according to the conventional method. 2 shows the relationship between the amount of oxygen and the amount of residual potassium after the primary reduction, and FIG. 3 shows the relationship between the primary reduction temperature and the amount of residual potassium and the structure of the Gesten wire after recrystallization. (α) Sai 1 Mouth Sai 2 Thu 30

Claims (1)

[Claims] t. A method for producing tungsten powder, which comprises adding a potassium compound alone to a tungsten lower oxide having an oxygen content in a range of 696 to 14%, and then reducing the mixture to metal.