Some new aspects of the phase diagram of the NH 4 + /H+-W-O system

The phase composition of partially-reduced products of ammonium paratungstate (APT) was investigated. The samples were prepared by reducing the APT in a H₂ + N₂/129 volume ratio/atomosphere in the temperature range 610 to 860 K, and studied by means of chemical analysis, by X-ray diffraction analysis and by thermoanalytical methods. The reduction products can be described by the general formula of M_xWO_3–y+x/2 where M can be either H⁺ and/or NH₄⁺. Products considered as tungsten bronzes (TB) can be formed in a fairly narrow temperature range. Another product, the so-called decomposed APT (DAPT) is a mixture of bronzes and of some other compounds characterized by y/2 and considered as some intermediate phases between TB and tungstates.