Synthesis of tungsten trioxide hydrates and their structural properties

Tungsten trioxide hydrates were synthesized by (a) cation exchange reaction from sodium tungstate solution and (b) precipitation from sodium tungstate solution by the addition of HCl solution. The samples were analyzed by XRD , DTA/TGA, Raman and FT-IR spectroscopy. XRD showed formation of WO3. H2O b y cation exchange reaction, whereas WO3. 0.33H(2)O was identified by XRD as a product of the acidification of sodium tungstate solution with HCl solut ion. After heating at 320 degrees C, WO3. H2O transformed into WO3, whereas the WO3. 0.33H(2)O crystal structure remained and these results were in ag reement with DTA/TGA measurements. The WO3. H2O sample synthesized by catio n exchange reaction showed a weight loss corresponding to one molecule of w ater in the crystal structure. However, samples WO3. 0.33H(2)O showed a muc h greater weight loss upon heating than could be expected on the basis of t he WO3 0.33H(2)O formula. The phase transition WO3. H2O --> WO3 was also mo nitored by Raman and FT-IR spectroscopy. In the case of WO3. 0.33H(2)O samp les, the basic features of Raman and FT-IR spectra did not change on heatin g to 320 degrees C, thus indicating that the heating of WO3. 0.33H(2)O up t o this temperature did not destroy the original crystal structure. Contrary to this, after heating the WO3. H2O sample to 320 degrees C, the Raman and FT-IR spectra showed a series of new bands caused by the phase transition WO3. H2O --> WO3. (C) 2000 Elsevier Science S.A. All rights reserved.