Intermediates, such as tungsten trioxide, tungsten blue oxide, tungstic acid, and ammonium metatungstate can be derived from APT as shown below, either by partial or complete thermal decomposition or by chemical attack.
Tungsten trioxide is almost exclusively manufactured by calcination of APT under oxidising conditions (in air). WO3 is one of the most important, highly pure intermediates for the production of other tungsten compounds including tungsten metal powder. In the latter application, it was substituted to a large extent by tungsten blue oxide. Because of its bright yellow colour it is used as a pigment in oil and water colours. It is employed in a wide variety of catalysts, most recently for the control of air pollution and industrial hygiene (DeNOx).
Tungsten trioxide particles are pseudomorphous to APT; which means the particles have the same shape and size as the former APT crystals, but consist of very small WO3 grains. The yellow powder is packaged in sealed polyethylene-lined steel drums and individual packaging (20 to 50kg).
TBO is manufactured by calcination of APT under more or less reducing conditions which vary from producer to producer. TBO is not a chemically defined compound, but consists of various different constituents, like trioxide, tungsten bronzes and different lower tungsten oxides. The relative amount of these compounds in TBO depends on the calcination parameters, (the parameter x typically varies between 0.01 and 0.10).
TBO is the most important precursor in the line from oxide to W and WC powder. The colour varies between deep dark blue to blue, faint blue and green blue. Also the TBO particles are pseudomorphous to the original APT crystals, as described for tungsten trioxide.
Tungstic acid, formally the most important intermediate in tungsten chemistry, is now exclusively manufactured from APT, in order to make use of the high purity APT level. For that purpose an aqueous APT slurry is treated with hydrochloric acid and tungstic acid is precipitated, which is then filtered, washed and dried. Tungstic acid has a very high active surface and is only used in small quantities for special purposes such as the production of ultrafine W and WC powders and tungsten chemicals.
Tungstic acid is a fine yellow powder and is packaged in sealed polyethylene-lined steel drums.
Ammonium Metatungstate (NH4)6[H6W12O40].3H2O has gained increasing usage for a variety of applications, especially chemicals and catalysts, because of its excellent solubility in water. The usual commercial product contains 3 to 4 molecules of water. On an industrial scale, it is obtained by partial thermal decomposition or partial replacement of ammonium ions by hydrogen ions using selective ion exchange and subsequent evaporation.
AMT is a white crystallised powder. Between 200 and 300°C, it converts to the anhydrous form. Further decomposition leads to WO3. At 80°C, 2,200 g WO3/l are dissolved in water.
AMT is used for the preparation of heteropoly acids, which consist of inorganic oxyacids of phosphorous or silicon and that of tungsten. Such compounds are attractive catalysts for many kinds of organic reactions.