The nature and preparation method of tungsten

In 1781 by the Swedish chemist discovered in scheelite, and extract the new elements acid – tungsten acid, in 1783 the Spanish discovered wolframite and extracted tungstate, the same year, with carbon reduce tungsten trioxide to first gottungsten powder, and named the element, tungsten content in the crust is 0.001%. Tungsten-containing minerals have been found 20 species. Tungsten deposits are generally accompanied by granitic magma activity to form. Through smelting tungsten is a silvery white lustrous metal, high melting point, great hardness.

Tungsten is silvery white, is a rare refractory metal, belonging to the sixth cycle of the periodic table (the second longest cycle) of the Group VIB. Tungsten is a silvery-white metal that looks like steel, high melting point, low vapor pressure, the evaporation rate is also smaller. Chemical properties of tungsten is very stable, at room temperature is not react with air and water, without heating, any concentration of hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid and aqua regia can not work to tungsten, when the temperature rose to 80-100, the above-mentioned acids, in addition to hydrofluoric acid, the other acids are occurring weak effect with tungsten. At room temperature, the tungsten can be quickly dissolved in a mixture of hydrofluoric acid and nitric acid, but it does not work in an alkaline solution. With the presence of air, the molten base may be oxidized tungsten to tungstate, in the case of oxidizing agent (NaNO3, NaNO2, KClO3, PbO2) exist, the reaction generated tungstate is more violent. Under high temperature can be combined with chlorine, bromine, iodine, carbon, nitrogen, sulfur and so on, but not combined with a hydride.

Tungsten is a metal with the highest melting point, melting point is up to 3400, ranking first in all metals, boiling point is 5555, specific gravity (monocrystalline tungsten) is 19.3, and has a high hardness, good high temperature strength and conductivity, heat transfer properties, chemical properties is stable at room temperature, corrosion resistance, do not work with hydrochloric acid or sulfuric acid. Concentrates are used for producing tungsten, tungsten carbide, tungsten alloys and compounds.

With a reduce agent reducing pure tungsten compound to metal tungsten powder is pyrometallurgical process, a part of tungsten metallurgy process. According to metal powder supplier, the pure tungsten compounds for producing tungsten powder has tungsten trioxide, ammonium paratungstate and blue tungsten, etc., generally use hydrogen, carbon powder and so on as reducing agent. Since the application department has stringent requirements on the chemical tungsten powder purity, particle size and particle size distribution, so it often to be based on the different requirements of tungsten powder to select production methods.

The more widely used tungsten powder prepared method in modern industrial production is mainly the tungsten trioxide hydrogen reduction, ammonium paratungstate hydrogen reduction and blue tungsten hydrogen reduction. Tungsten powder for preparing tungsten carbide has also been used tungsten trioxide hydrogen reduction. Modern times is more commonly used hydrogen reduce paratungstate to prepare blue tungsten, then the blue tungsten by hydrogen reduction to prepare tungsten powder. In the 1960s developed fluorine (chlorine) tungsten hydrogen reduction method, using hydrogen reduce gaseous fluorine (chlorine) can be obtained ultrafine particles grade tungsten powder or can be directly made from tungsten tubes and other metal products. In order to obtain with specific properties tungsten materials and tungsten alloys, it often adding trace additives in blue tungsten raw materials. For example, when preparing with non-sag performance thermostability tungsten wire, added silicon, aluminum, potassium compounds and other trace additives in blue tungsten.

Source:http://www.mhcmp.com