Tungsten Silver Composite Powder by Sol Spray Reduction Method Preparation

Silver has the best thermal conductivity, excellent processability and high oxidation resistance among all metals, so silver is the most important and economical precious metal contact material, and plays an important role in the field of low voltage electrical contacts. But silver is too soft, poor resistance to fusion and corrosion, and polarity transfer will occur.

On the contrary, tungsten has high hardness, high melting point, good wear resistance and low electrical conductivity. Therefore, the combination of tungsten and silver has become a kind of tungsten-silver composite with good thermal and electrical conductivity, electrical wear resistance, welding resistance, oxidation resistance and other advantages.

Because of the great difference in melting point and density between tungsten and silver, they can not be melted and manufactured, so powder alloy technology is needed to obtain them. The technological process of preparing W-Ag alloy by powder metallurgy is as follows: batching, mixing, pressing, sintering, infiltration and cold working. The performance of the products produced by conventional powder mixing, molding and sintering processes has been difficult to meet the increasing requirements of modern science and technology.

To overcome the shortcomings of traditional technology, a sol spray reduction method for preparing ultrafine tungsten silver composite powder was proposed, which included the following steps:

(1)Using ammonium partrunate (APT) and silver nitrate, citric acid and polyethylene glycol as raw materials.

(2)The above raw materials, ammonium paratungstate, silver nitrate, distilled water, citric acid and polyethylene glycol, were mixed rapidly at the mass ratio of 90:100:600:240:20 and heated in water bath until the citric acid sol system was formed.

(3)The sol system was sprayed on a spray dryer for pyrolysis to obtain a mixed powder precursor.

(4)Ultrafine tungsten-silver oxide composite powders were prepared by calcining the precursors at 550 ℃ for 120 min.

(5)W-50Ag ultrafine tungsten-silver composite powders were prepared by reducing the composite powders prepared by the above steps (4) in hydrogen atmosphere at 750 ℃ for 150 min.

The ultrafine tungsten-silver composite powder prepared by this method has fine particle size, uniform composition distribution, high purity and good sintering activity. It can be used to prepare high-quality electrical contact materials, electrode materials, electronic packaging materials. The method has high yield and is suitable for large-scale industrial production.

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