Influence of the thermal treatment in the crystallization of NiWO4 and ZnWO4

NiWO 4 and ZnWO 4 were synthesized by the polymeric precursor method at low temperatures with zinc or nickel carbonate as secondary phase. The materials were characterized by thermal analysis (TG/DTA), infrared spectroscopy, UV–Vis spectroscopy and X-ray diffraction. NiWO 4 was crystalline after calcination at 350 °C/12 h while ZnWO 4 only crystallized after calcination at 400 °C for 2 h. Thermal decomposition of the powder precursor of NiWO 4 heat treated for 12 h had one exothermic transition, while the precursor heat treated for 24 h had one more step between 600 and 800 °C with a small mass gain. Powder precursor of ZnWO 4 presented three exothermic transitions, with peak temperatures and mass losses higher than NiWO 4 has indicating that nickel made carbon elimination easier.