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The core material of cemented carbide - tungsten powder

2018-07-31
What is the property of tungsten powder?
It is a gray-black metal with a metallic luster (body-centered cubic crystal). The temperature of 3400 ° C. Boiling point 5555°C. The hardness of tungsten is the hardest among metals.
The hardness of the sintered tungsten strip is 200-250, and the tungsten rod passing through the hammer is 350-400. A mixed acid dissolved in nitric acid and hydrofluoric acid.
Melted with a mixture of sodium hydroxide and sodium carbonate. Slightly soluble in nitric acid, sulfuric acid, aqua regia; insoluble in water, hydrofluoric acid, potassium hydroxide.
There are two variants of tungsten, a and B. Type a is a stable body-centered cubic structure at standard temperature and pressure. Type B tungsten can only be present in the presence of oxygen.
It is stable below 630 ° C, converted to a tungsten above 630 ° C, and the process is irreversible.
What is the production method of tungsten powder?

It is prepared by hydrogen reduction of tungsten trioxide or ammonium paratungstate. The process of preparing tungsten powder by hydrogen reduction method is generally divided into two stages: the first stage is at a temperature of 500 to 700 ° C, and the tungsten trioxide is reduced to tungsten dioxide; the second stage is at a temperature of 700 to 900 ° C, and the second stage is oxidized. The tungsten is reduced to tungsten powder. The reduction reaction is often carried out in a tubular electric furnace or a rotary furnace.
The properties (such as purity, particle size, particle size composition, etc.) of the reduced tungsten powder depend mainly on the reduction process. When reducing tungsten powder in a tube furnace, the main process parameters affecting the reduction rate are the reduction temperature, the loading of tungsten oxide in the boat, the moving speed of the boat, the hydrogen flow rate, and the moisture content in the hydrogen. As the reduction temperature increases, the particle size of the tungsten powder becomes coarse.
In addition to the hydrogen reduction method, the preparation of tungsten powder has an early reduction method of tungsten oxide carbon, and the reduction temperature is higher than 1050 °C. The tungsten powder obtained by this method is low in purity. In addition, research work on the reduction of tungsten oxide by metal aluminum, calcium, zinc, etc. is also underway. For special applications requiring high purity, ultrafine particle size tungsten powder, a tungsten chloride hydrogen reduction method has been developed, and the obtained tungsten powder has a particle size of less than 0.05 μm.
Industrial production can be obtained by reducing tungsten trioxide with hydrogen; or treating ammonium paratungstate with acid, and then decomposing to obtain tungsten trioxide, which is obtained by reduction with hydrogen.
Hydrogen reduction of tungsten trioxide: reduction with hydrogen can be carried out in two stages. In the first stage, tungsten trioxide is heated to 550-800 ° C, reduced with hydrogen, and the second stage is reduced at 650-850 ° C to obtain tungsten. Powder finished product.
Alternatively, ammonium paratungstate can be reduced to blue tungsten oxide (blue tungsten) by hydrogen or no hydrogen, and then reduced to tungsten powder by hydrogen. The particle size and particle size composition of tungsten powder are important quality indicators of tungsten powder. The reduction is carried out in a tubular electric furnace or a rotary electric furnace.
What is the application of tungsten powder?

Most of tungsten is used to produce cemented carbide and tungsten iron. Tungsten and chromium, molybdenum and cobalt are used to form heat-resistant and wear-resistant alloys for the production of tools, metal surface hardening materials, gas turbine blades and combustion tubes. Tungsten and bismuth, antimony, molybdenum and other refractory alloys. Tungsten copper and tungsten silver alloys are used as electrical contact materials. A high-density tungsten-nickel-copper alloy is used as a radiation protection shield. Wires, rods, sheets, etc. of metal tungsten are used to make electric bulbs, components of the tubes, and electrodes for arc welding. Tungsten powder can be sintered into filters of various porosity. FW-1 is used for large slab and tungsten-rhenium galvanic materials. FW-2 is used for contact alloys and high specific gravity shielding materials. FWP-1 is used for plasma spray materials.
Tungsten powder is the main raw material for processing powder metallurgy tungsten products and tungsten alloys. Pure tungsten powder can be made into processed materials such as silk, rods, tubes and plates, and certain shaped products. Tungsten powder is mixed with other metal powders to form various tungsten alloys such as tungsten-molybdenum alloy, tungsten-rhenium alloy, tungsten-copper alloy and high-density tungsten alloy. Another important application of tungsten powder is the production of tungsten carbide powder to produce cemented carbide tools such as turning tools, milling cutters, drill bits and molds.

Tungsten powder