Thermally stimulated transformations in brookite-containing TiO$_2$ nanopowders produced by the hydrolysis of TiCl$_4$

TiO$_2$ nanopowder is produced by the low-temperature hydrolysis of TiCl$_4$. The phase composition of the sample is found to form at a hydrolysis temperature of 30–38$^\circ$C. Low-temperature annealing (up to 440$^\circ$C) increases the degree of crystallinity of the phases present in the sample (anatase, brookite) and only weakly affects their ratio. At 500$^\circ$C, the sample consists of three phases: rutile is detected apart from anatase and brookite. Brookite begins to fail at 600$^\circ$C; at 700$^\circ$C, crystalline brookite fails completely.