Synthesis of a Bulk Ti4SiC3 MAX Phase by Reduction of TiO2 with SiC

The bulk MAX phase Ti4SiC3 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 degrees C under vacuum conditions. It was found that the appearance of Ti4SiC3 was preceded by the formation of TiC and Ti4SiC2 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 Ti4SiC2. It was suggested that, apart from TiC and Ti4SiC2 solids, sublimed gaseous species such as Ti, Si, Si2C, SiC2, etc., could take part in the Ti4SiC3 formation that occurred in the next stage. The crystal structure of synthesized Ti4SiC3 was refined by X-ray diffraction Rietveld analysis and confirmed by high resolution scanning transmission electron microscopy. The measured structural characteristics of bulk Ti4SiC3 are in good agreement with those predicted by ab initio calculations reported in the literature.