SOLID-STATE CHEMISTRY OF THERMALLY INDUCED YELLOW COLORING IN SYNTHETIC HYDROUS TITANIUM-OXIDE FROM TICL3

Calcination of hydrous titanium oxide (HTO) gel, synthesized by the hydrolysis of titanium(III) chloride (TiCl3) in the presence of urea, produces a brilliant yellow powder when the pale blue HTO gel is heated at 400-degrees-C in air. From the results of diffuse reflectance (DR) spectroscopy, thermogravimetry and/or differential thermal analysis (TG/DTA) and electron paramagnetic resonance (EPR) spectroscopy, this colouring is attributed to the formation of thermally induced Ti4+ peroxide. The colour is lost and the superoxide radical anion is generated when the temperature is increased to 800-degrees-C; this is accounted for by the thermal decomposition of the peroxide complex. The solid-state chemistry of the appearance and loss of the yellow colour is discussed along with results of X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA).