Thermochemical decomposition of cobalt doped ammonium paratungstate precursor

The calcination is one of the important steps in the preparation of nanostructured WC and WC-Co powders from chemically co-precipitated W-Co precursors. In the present paper, the processing of the precursor prepared by co-precipitation from cobalt(II) hydroxide and ammonium paratungstate is reported. The precursor was calcined at different temperatures under various atmospheres. The resulting powders were investigated using scanning electron microscopy, X-ray diffraction, thermogravimetric analysis (TGA), differential TGA, BET, and mass spectrographic analysis techniques. The results showed that the precursor decomposes differently by calcination under different atmospheres, i.e. nitrogen, air, and helium-5% oxygen. Different decomposition behaviour was observed when the calcination was carried out at medium temperature in flowing and non-flowing air. Nanostructured powders with particle size of around 90 nm can be obtained after calcination. The precursor decomposes into CoWO4 and WO3 oxides at 520degreesC in air after a weight loss of 10.3%. (C) 2002 Elsevier Science B.V. All rights reserved.