Polycarbosilane-derived Ti3SiC2 and its reaction mechanism

Ti 3 SiC 2 is a representative MAX phase that uniquely combines the merits of metals and ceramics. However, polymer-derived Ti 3 SiC 2 has been less extensively studied, especially in terms of its reaction mechanism and structural evolution. In this study, Ti 3 SiC 2 is synthesized by pressureless pyrolysis of PCS and TiH 2 , the structural evolution and chemical reactions occurring during the organic-inorganic conversion and synthesis process are investigated. The results show that Ti 3 SiC 2 with a mass fraction of 79.2 % can be achieved by pressureless pyrolysis of PCS and TiH 2 powders, with a Ti-to-Si atomic ratio of 3:1.7, at 1350 ℃. The presence of TiH 2 enhances the ceramic yield of PCS at 1000 ℃ compared to pure PCS, as some branched and crosslinking structures form between 100 ℃ and 300 ℃. By 800 ℃, the organic-inorganic conversion of PCS and the decomposition of TiH 2 are complete, resulting in the formation of amorphous SiC, free C and porous Ti. Concurrently, some SiC may transform into amorphous Si and C in the presence of porous Ti. At 1000 ℃, T 5 Si 3 forms within the porous Ti matrix, while TiC is generated on the periphery. Between 1200℃ and 1350 ℃, a reaction between these two phases and free C leads to the synthesis of Ti 3 SiC 2 . The formed Ti 3 SiC 2 phase begins to decompose at 1450 ℃ and completely breaks down into TiC, SiC, and TiSi 2 at 1600 ℃.