For the manufacture of chemical products, commercially available tungsten compounds such as sodium tungstate, ammonium tungstate, tungsten oxides or tungstic acid are commonly used as raw materials. The following list gives a few examples.
Inorganic pigments for ceramic glazes and enamels:
- Tungstic acid or tungsten oxide is used for bright yellow glazes.
- Tungsten bronzes, i.e. partly reduced alkali and alkaline earth tungstate, are available in many bright colors.
- Barium and zinc tungstate are examples for bright white pigments. Colored organic dyes and pigments based on phosphotungstic acid and phosphotungsto-molybdic acid are made for paints, printing inks, plastic, rubber and other materials.
- Tungsten disulphide is a lubricant for temperatures above the application range of molybdenum disulphide. It has also been used to form a self-lubricating surface on razor blades.
- Organic tungsten compounds have been patented as viscosity stabilizers in lubricant oils.
In chemical processes, catalysts are used to modify the mechanisms of chemical reactions. By providing an energetically favorable pathway, catalysts accelerate reactions which would normally be too slow or would not even take place. After the reaction, the catalyst remains essentially unchanged.
Main chemical applications of tungsten in the form of catalysts are:
- DeNOx catalysts for the removal of nitrogen oxides from stack gases of combustion power plants, chemical plants, cement plants or diesel engines by selective catalytic reduction with ammonia or urea, the products are harmless nitrogen and water vapor. Typical DeNOx catalysts are honeycomb-shaped TiO2-WO3-V2O5 ceramics.
- Catalysts for hydrocracking, hydrodesulphurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatisation (HAD) of mineral oil products, where tungsten and nickel oxides on ceramic carriers are used. These catalysts help to increase the yield of gasoline and other light hydrocarbons in crude oil processing and to make the products more environmentally friendly by reducing the contents of aromatic hydrocarbons, sulphur and nitrogen compounds.
- Other tungsten containing catalysts for various applications in the chemical industry, for example dehydrogenation, isomerization, polymerization, reforming, hydration and dehydration, hydroxylation, epoxidation, etc.
- Catalyst production usually starts with the highly water soluble ammonium metatungstate, tungstic acid or ammonium paratungstate. In the finished catalyst, tungsten is mostly present in the form of tungsten oxide or sulphide, or in the form of phosphor tungstic acid.
- Another example of a catalytically active tungsten compound is superfine tungsten carbide, mostly prepared by thermal decomposition of organic substances in the presence of a suitable tungsten compound. It is mainly used in oxidation/reduction reactions.
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In laboratories, tungsten is used in several applications, for example:
- High purity sodium tungstate as a reagent in biochemical analysis.
- Sodium Meta Tungstate for the preparation of heavy liquids to be used for the separation of minerals by density in mineralogy or for density gradient centrifugation in biochemical analysis.
- High purity tungsten granules as an accelerator in the determination of carbon and sulphur in metals by combustion in an induction furnace.