WO3 powders were prepared by the thermal decomposition of tungstic acids (WO3.nH(2)O, n = 1/3, 1, 2). The tungstic acids were synthesized from WO42- aqueous solutions under a variety of conditions of pH, temperature and W(VI) concentrations. The thermal decomposition of the tungstic acids into WO3 was analysed by TG and DSC methods. Nano-sized WO3 powders with different morphological characteristics were obtained by thermal treatment of the tungstic acids at 500 degreesC in air atmosphere. The morphologies Of WO3 powders were characterised by scanning electron microscopy and infrared absorption spectroscopy. Patterns of infrared spectra were related with distinct powder morphologies. (C) 2003 Elsevier Ltd. All rights reserved.