Synthesis of a Bulk Ti 4 SiC 3 MAX Phase by Reduction of TiO 2 with SiC.

The bulk MAX phase Ti4 SiC3 was first synthesized with a yield of 86% by a long-time thermal treatment of TiO2 and SiC powder mixture with a molar ratio of 2:3 at 1600 °C under vacuum conditions. It was found that the appearance of Ti4 SiC3 was preceded by the formation of TiC and Ti3 SiC2 as a result of the following reactions: (1) combined carbothermic and silicothermic reduction of TiO2 to TiC accompanied by evolution of SiO and CO gases; (2) silicidation of TiC with gaseous SiO, leading to the growth of Ti3 SiC2 . It was suggested that, apart from TiC and Ti3 SiC2 solids, sublimed gaseous species such as Ti, Si, Si2 C, SiC2 , etc., could take part in the Ti4 SiC3 formation that occurred in the next stage. The crystal structure of synthesized Ti4 SiC3 was refined by X-ray diffraction Rietveld analysis and confirmed by high-resolution scanning transmission electron microscopy. The measured structural characteristics of bulk Ti4 SiC3 are in good agreement with those predicted by ab initio calculations reported in the literature.