JPS5937321B2 - 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 of tungsten and rhenium metal powders, which 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 a filament for electron tubes and as a structural material for X-ray targets.

Conventionally, 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 has the disadvantage that it is extremely difficult to mix fine metal powders uniformly, and therefore it is difficult to obtain an alloy with a uniform composition even if sintered at high temperatures for a long time. .

In addition, since a ball mill or the like is used to improve mixing, the components of the balls and containers may adhere to the powder surface during mixing, resulting in changes in the composition and properties of the resulting metal powder.
However, in order to prevent this, an appropriate treatment must be performed to clean the powder surface after mixing.

Furthermore, a method for producing tungsten-rhenium alloy powder has been developed in which a water-soluble tungsten compound and a water-soluble rhenium compound are mixed with water to form an aqueous solution, which is spray-dried and then thermally reduced. ,
There was a drawback that rhenium content was easily lost because perrhenic acid was easily sublimed during spray drying.

The present invention has been made to eliminate these drawbacks, and relates to a method for producing a powder mixture in which metallic tungsten and metallic rhenium powders are extremely uniformly mixed.

For the tungstenization (cx''1ts) in the present invention, any compound can be used as long as it is water-soluble, but ammonium tungstate or ammonium paratungstate is particularly preferred.

Further, as the powdered rhenium compound, it is preferable to use perrhenic acid, ammonium perrhenate, or rhenium oxide, and these compounds are added to the saturated aqueous solution of the tungsten compound and heated to dryness.

Although it is possible to produce any proportion by the method of the present invention, in the obtained mixed powder, the rhenium content is the whole (tungsten molecule rhenium content).
The weight factor should be 5 or less, more preferably 3 or less.

In the present invention, first, an aqueous solution of a tungsten compound is heated at a temperature of 80 to 100°C to evaporate water and concentrate, reaching a saturated state and crystals of a tungsten compound such as ammonium pertungstate precipitate. Once started, add and mix the powdered rhenium compound, and then heat and concentrate the aqueous solution.

Next, the mixed crystal of the tungsten compound and the rhenium compound obtained after the water has completely evaporated and dried is preliminarily reduced at a temperature of 300 to 500° C. in a hydrogen atmosphere.

As a result of such preliminary reduction, a mixture of blue lower tungsten oxide and rhenium oxide is produced, but in the present invention, these mixtures are treated with 5i02°At203 or
A secondary reduction can also be carried out after addition of oxides of silicon, aluminum or potassium, such as oxides of silicon, aluminum or potassium.

When these oxides are added, the crystal structure of the alloy obtained by molding and sintering the powder mixture will be composed of long crystals that are elongated in the axial direction, and the grain boundaries will be separated from each other. Since it has a zigzag intersecting structure, it has the advantage that the creep strength is significantly improved compared to the case where it is not added.

Therefore, there is little deformation or disconnection at high temperatures, making it particularly suitable for filaments in incandescent light bulbs, electron tubes, discharge lamps, and the like.

Therefore, the amount of these oxides added is such that silicon content is 1100 PP or more, aluminum content is 5 ppm or more, potassium content is 20 ppm or more, and the total amount is 1.5 Weight ratio or less preferably 0
．． It is desirable that the amount be less than 5% by weight.

The conditions for the secondary reduction in the present invention are 650 °C in a hydrogen atmosphere.
The temperature is ˜1000° C. and the reduction results in a mixture of metallic tungsten powder and metallic rhenium powder.

As is clear from the above description, according to the method of the present invention, an extremely uniform mixture of tungsten powder and rhenium powder is produced, and since some of the powder particles are alloyed, this mixture can be prepared using conventional methods. A homogeneous tungsten-rhenium alloy is obtained by compression molding and sintering.

Next, examples of the present invention will be described.

Examples 1-5 350 WO8? An ammonium tungstate aqueous solution containing / is concentrated while heating at a temperature of 80 to 100 ° C. When crystals of the tungsten compound begin to precipitate, ammonium perrhenate powder is added to this, mixed, and further heated. Concentrate and evaporate to dryness.

Here, the amount of ammonium perrhenate added is 1000 PPM, 500 PPM as a ratio of rhenium to the entire tungsten-rhenium powder mixture finally obtained.
0 PPM.

110000PP 20000PPM and 3000
The amount was set to account for 0 PPM.

Next, the evaporated to dryness was placed in a stainless steel boat.
Charge a boat of about 300f and make it with an inner diameter of 60rra.
After preliminary reduction at a temperature of 300 to 500° C., secondary reduction was further performed at a temperature of 650 to 1000° C. while flowing hydrogen at a rate of 25,007/hour.

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 the Blaine air permeation method.

The results are shown in the table below.

For comparison, the measurement results for tungsten powder obtained by reduction without mixing a rhenium compound under the same conditions other than that are shown as rhenium content OPPM.

Next, we took 202 pieces of phosphorous rhenium mixed powder with a rhenium content of 30,000 PPM, and welded it to a diameter of 10 m.
After compression molding at a pressure of 2000 kg/crtt, the mixture was sintered at a temperature of 2200° C. for 5 hours to obtain alloy pellets.

The dispersion state of rhenium in the alloy structure of the obtained pellets 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 a metal talegesten powder and a rhenium powder in the conventional manner.

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. A method for producing a tungsten-rhenium powder mixture, which comprises adding and mixing a powdered rhenium compound to a concentrated aqueous solution of a tungsten compound, evaporating the mixture to dryness, and then reducing the mixture by heating in a hydrogen atmosphere.