CHEMISTRY OF TUNGSTEN-OXIDE BRONZES

Ammonium paratungstate (APT) is the generally accepted starting material in tungsten manufacturing. The dopants, which are responsible for the non-sag properties, are given to some tungsten oxide bronze (TOB)-type compounds which are formed by thermal reductive decomposition of APT. The doped TOE is reduced in a H-2 atmosphere to tungsten metal grains. The powder metallurgical processing and the following thermomechanical treatment of the metal powder result in the formation of the non-sag wire. The bronze forming compounds (M(x)(z)) in this case are NH4+ or H+ ions, or 4 both of them, but the degree of reduction, i.e, the oxygen deficiency, may vary in the WO3, therefore, the description of the possible compounds seems to be necessary. We have the general formula of M(x)((z))WO3-y+z.x/2, where y less than or greater than zx/2 conditions are possible. We also give a phase diagram in which we have located the possible types of compounds. The preparation methods of oxide bronzes (OBs) and the general structural characterization of OBs are described with special attention to ATOB and HTOB compounds. Because many experiences prove the advantages of ion-exchange doping, such properties of TOBs have also been discussed.