Study on the fabricated non-stoichiometric titanium dioxide by in-situ reduction with carbon powder via spark plasma sintering

A novel technology was proposed to fabricate non-stoichiometric titanium dioxide (TiO_2−x) compacts in one-step thermal process by in-situ reduction of rutile TiO₂ with carbon powder via spark plasma sintering (SPS). The rutile TiO₂ powder was reduced with three different carbon powders for comparison, and the effect of the sintering conditions on the fabricated compacts was investigated. It is found that the in-situ reduction of rutile TiO₂ with charcoal powder was easily achieved at a low pressure and high temperature (above 1473 K). Besides, the design of dynamic sintering pressure during SPS was proposed, and the results suggest that the dynamic sintering pressure contributes to the reduction of TiO₂ and the fabrication of the compacts with high-density. In addition, density methods, X-ray diffraction, scanning electronic microscopy and laser micro-Raman spectrometer were performed to analyze the sintering sates, microstructures, crystal structures and phase distributions. The results show that a stable sintering environment without an increase in the pressure caused by reaction gas is a crucial role for the reduction of TiO₂ and the TiO_2−x fabrication, even the formation of Magnéli phases Ti_nO_2n−1. Finer charcoal powder is more conducive to fabricating the compact with a single Magnéli phase Ti₆O₁₁. It is expected to achieve a new breakthrough in fabrication method of the non-stoichiometric TiO₂ by a safe and economically viable method.