Syntheses and crystal structures of titanium oxide sulfates

Abstract

When titanium dioxide, metatitanic acid or iron titanate (ilmenite) is heated with 65-95 wt% H2SO4, TiOSO4 or TiOSO4·H2O is formed depending on the water content of the sulfuric acid. The contours of reaction mechanisms are discussed. TiOSO4 and TiOSO4-H2O dissolve slightly in cold or hot water during short-term treatment. On longer contact with water the solubility becomes more appreciable. The undissolved remainder, as well as the dissolved fraction after removal of the water posse, proves to have been converted into X-ray amorphous products with composition TiOSO4-.xH2O, x≈1. The crystal structure of TiOSO4 [orthorhombic, a=1095.3(3), b=515.2(1) and c=642.6(1) pm] has been determined on the basis of powder X-ray diffraction data. The structure of TiOSO4·H2O has been redetermined. Both structures contain ...-O-Ti-... zigzag chains with short Ti-O distances. The chains are connected via sulfate groups, and the structures probably suffer from some disorder. For both structures the possibility of deviations from the centrosymmetric space group Pnma is discussed. The close structural relationship between TiOSO4 and TiOSO4·H2O is discussed. On heating, TiOSO4 undergoes a reversible phase transition at around 330°C and decomposes into TiO2-a (anatas) at ca. 525°C. TiOSO4·H2O looses its crystal water at ca. 310°C. However, liberation of SO3, starts at about 40°C lower temperature than for TiOSO4, and the decomposition shows a two-step character in TG, DTG and DTA. Attempts to isolate intermediate decomposition product(s) have so far not been successful. © Acta Chemica Scandinavica 1996.