About tungsten powder
Tungsten powder is a metallic luster of gray-black metal (body-centered cubic crystal). The melting point is 3400 ℃. The boiling point of 5555 ℃. The hardness of tungsten is the hardest among metals, the hardness of sintered tungsten bar is 200 ~ 250, and the hardness of rotary hammer tungsten bar is 350~400. A mixture of nitric acid and hydrofluoric acid. Fused with a mixture of sodium hydroxide and sodium carbonate. Tungsten powder slightly soluble in nitric acid, sulfuric acid, aqua regia; Insoluble in water, hydrofluoric acid, potassium hydroxide. There are two types of tungsten, A and B. Type A is a stable body-centered cubic structure at standard temperatures and pressures. Type B tungsten can only be present in the presence of oxygen. It is stable below 630 ° C and converted to A-tungsten above 630 ° C, and this process is irreversible.
Preparation method of tungsten powder
Tungsten powder is prepared by hydrogen reduction of tungsten trioxide or ammonium para tungstate. The process of preparing tungsten powder by hydrogen reduction method is generally divided into two stages: the first stage is at the temperature of 500 ~ 700℃, tungsten trioxide is reduced to tungsten dioxide; In the second stage, tungsten dioxide is reduced to tungsten powder at the temperature of 700 ~ 900℃. Reduction reactions are usually carried out in tubular or rotary furnaces.
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