JPS5915961B2 - Method for producing tungsten-rhenium powder mixture - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a powder mixture in which tungsten and rhenium metal powders are uniformly mixed and dispersed with each other.

Compared to pure tungsten, tungsten-rhenium alloys not only have higher electrical resistance, flexibility, and better workability, but also have a sufficiently high melting point (and do not deform even at high temperatures). In recent years, its uses have been expanding more and more, such as as filaments for light bulbs and electron tubes, and as structural materials for X-ray targets.

Traditionally, in order to manufacture such a tungsten-rhenium alloy, metal rhenium powder is first added to metal tungsten powder, which is further stirred and ground using a ball mill, etc., mixed, and then the resulting mixed powder is compression molded. A method is used in which the material is then sintered.

However, this method involves mixing fine metal powders, so it is extremely difficult to mix them uniformly.Therefore, even if sintered at high temperatures for a long time, it is difficult to obtain an alloy with a uniform composition. there were.

・Also, since a ball mill, etc. is used to ensure good mixing, the components of the balls and containers adhere to the powder surface during mixing, which tends to cause changes in the component composition and properties of the resulting metal powder. In order to prevent this, there is a problem in that an appropriate treatment must be performed to clean the powder surface after mixing.

The present invention was made to solve these problems, and provides a method for producing a homogeneous mixture of tungsten powder and rhenium powder.

The tungsten oxide used in the present invention includes tungsten trioxide obtained by sintering tungstic acid at a temperature of 700°C, and tungsten trioxide obtained by further reducing it at a temperature of 500°C. There are blue lower grade tungsten oxides, etc., and these are used in powder form.

The oxide of silicon, aluminum or potassium to be mixed with this tungsten oxide powder has the chemical formula 5i02, A
It is expressed as t203 or 20 and is added to improve the high temperature creep strength of the resulting alloy.

That is, in the tungsten-rhenium alloy obtained by sintering a powder mixture produced by the method of the present invention from tungsten oxide powder containing these oxides, the recrystallized structure is elongated in the axial direction. It is composed of long, elongated crystals, and the grain boundaries intersect with each other in a zigzag pattern, resulting in extremely high creep strength.

Therefore, especially when this alloy is drawn and used as a filament for incandescent light bulbs, electron tubes, discharge lamps, etc., there is an advantage that deformation and disconnection are extremely rare.

The amount of the oxide having such an effect added is preferably 0.005 to 0.1% by weight of the total.

The reason why the amount of 5i02 etc. added was limited to this range was because
If it is less than 0.005% by weight, there will be no recrystallized grain adjustment effect as described above, and if it exceeds 0.1% by weight,
This is because in the process of sintering the mixed powder, these additives volatilize in excess, causing blisters and cracks in the sintered body.

In the present invention, in addition to these oxides, dispersion strengthening agents such as thorium oxide (ThO2) and tantalum carbide (TaC) are added to the final alloy composition in an amount of 0.1 to 10
It can be added in an amount of % by weight together with the oxide or in a subsequent step.

These dispersion strengthening agents are added to strengthen the creep strength, and even after final processing, an added amount of 90 or more remains uniformly dispersed in the recrystallized structure of the alloy.

On the other hand, oxides such as 5i02 mentioned above are added to adjust the size and shape of recrystallized grains, but most of them volatilize during the sintering process, and the amount added after processing is small. Only less than 10% remains.

The water-soluble rhenium compounds used in the present invention include rhenic acid (HRcO), ammonium perrhenate, rhenium trichloride, and rhenium hexafluoride, and an aqueous solution of these compounds is added to the doped tungsten oxide. Add to and mix.

In this case, the ratio of addition is preferably such that the rhenium component accounts for 50 to 30,000 PPM to the tungsten component, but especially when the obtained alloy is used as a structural material such as an It is also possible to add amounts.

In the present invention, first, 2S is added to tungsten oxide powder.
After preparing a tungsten oxide powder to which silicon, aluminum, and potassium oxides are added by mixing an aqueous solution of i02, KCl, or AtC23 and heat-treating the mixture, an aqueous solution of the rhenium compound is mixed therein and stirred. while heating at about 80°C to evaporate to dryness.

Since tungsten oxide powder has countless pores, during mixing, the rhenium compound aqueous solution soaks into the tungsten oxide powder through these pores, and as a result, they are mixed uniformly. It becomes possible.

Therefore, in order to obtain a tungsten-rhenium powder mixture with a uniform composition, it is desirable to use a tungsten oxide powder that has as high a porosity as possible, that is, a large specific surface area.

In the present invention, the thus evaporated to dryness is subjected to primary reduction in a hydrogen atmosphere at a temperature of 300 to 400°C,
The metal tank is further reduced by secondary reduction in a hydrogen atmosphere at 700 to 100°C.

A tungsten-rhenium alloy can be produced by obtaining a powder mixture of sten and metallic rhenium, which is then compression molded and sintered by a conventional method.

As is clear from the above description, according to the method of the present invention, a powder mixture in which metallic tungsten powder and rhenium powder are mixed very efficiently and uniformly can be obtained, and the quality of the alloy obtained from the powder is therefore high. It becomes extremely homogeneous.

In addition, this alloy has a recrystallized structure composed of long crystals and has high creep strength particularly at high temperatures, so it is suitable for use in filaments for electron tubes, light bulbs, discharge lamps, and the like.

Next, examples of the present invention will be described.

Examples 1 to 5 Tungsten trioxide powder 10009, 1 K2S10210 aqueous solution 100CC and KCl
O,5ti aqueous solution 1oocc and htct3o,s
% aqueous solution was added and mixed, an aqueous solution of rhenic acid was added to the tungsten oxide powder obtained by heat treatment, and the mixture was evaporated to dryness at about 80° C. while stirring.

In this case, the amount of rhenic acid aqueous solution added to the tungsten oxide powder is 11000PP, 5000PP as a ratio of rhenium to the entire mixture finally obtained.
M, 10000PPM.

The amounts were set to correspond to 20,000 PPM and 30,000 PPM.

Next, the evaporated to dryness was placed in a stainless steel boat.
Charge a boat of about 3001, put it into a reduction furnace, and heat it to 300~ while flowing hydrogen at a rate of 500A/hour.
The primary reduction was carried out at a temperature of 400°C.

Thereafter, the hydrogen flow rate was changed to 2000 t/hour, and further secondary reduction was performed at a temperature of 700 to 1000°C.

After completion of the reduction, the powder was sufficiently cooled in the cooling section, and the sufficiently reduced powder was taken out from the furnace, and its particle size was measured by plain air permeation method.

The results are shown in the table below. At the same time, for comparison, the measurement results for tungsten powder obtained by reduction under the same conditions without mixing a rhenium compound are shown as rhenium content OPPM.

Next, 201 pieces of tungsten-rhenium mixed powder with a rhenium content of 30,000 PPM were taken, and this was
After compression molding at a pressure of 2t/ca,
Alloy pellets were obtained by sintering at a temperature of 200° C. for 5 hours.

The rhenium dispersion state of the pellet thus obtained was observed using an X-ray microanalyzer (EPMA).

The obtained tissue photograph at a magnification of 500 times is shown in FIG.

Note that the white part in the photo is the rhenium structure. Further, FIG. 2 shows a photograph of the structure of an alloy pellet obtained in the same manner from a mixed powder obtained by simply mechanically mixing tungsten metal powder and rhenium powder as in the past.

As is clear from the above examples, according to the method of the present invention, a tungsten-rhenium powder mixture having a sufficiently small particle size and a uniform mixture of both components is produced. By molding and sintering, rhenium is uniformly dispersed in the tungsten structure, resulting in an alloy with a homogeneous composition in all parts.

[Brief explanation of drawings]

Figures 1 and 2 show tungsten-rhenium powder mixtures produced by the method of the present invention and the conventional method.
A microstructure photograph taken using an X-ray microanalyzer of an alloy pellet obtained by sintering is shown.

Claims (1)

[Claims] 1. Tungsten oxide powder containing a small amount of one or more of silicon, aluminum, or potassium oxides is mixed with an aqueous solution of a water-soluble rhenium compound, and the mixture is evaporated to dryness. A method for producing a tungsten-rhenium powder mixture, which comprises heating and reducing the mixture in a hydrogen atmosphere. 2. A method for producing a tungsten-rhenium powder mixture according to claim 1, characterized by mixing an aqueous solution of a rhenium compound in an amount such that the rhenium content is 50 to 3 (LO-00 ppm). 3. Silicon, The amount of aluminum or potassium oxide added should be adjusted to O9.005 to 0 of the entire powder mixture.
．． Claim 1 characterized in that it is 1 weight pot.
A method for producing a tungsten-rhenium powder mixture according to item 1 or 2.