Polycarbosilane-derived Ti3SiC2 and its reaction mechanism

Abstract

Ti₃SiC₂ is a representative MAX phase that uniquely combines the merits of metals and ceramics. However, polymer-derived Ti₃SiC₂ has been less extensively studied, especially in terms of its reaction mechanism and structural evolution. In this study, Ti₃SiC₂ is synthesized by pressureless pyrolysis of PCS and TiH₂, the structural evolution and chemical reactions occurring during the organic-inorganic conversion and synthesis process are investigated. The results show that Ti₃SiC₂ with a mass fraction of 79.2 % can be achieved by pressureless pyrolysis of PCS and TiH₂ powders, with a Ti-to-Si atomic ratio of 3:1.7, at 1350 ℃. The presence of TiH₂ 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 TiH₂ 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 ℃, T₅Si₃ 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 Ti₃SiC₂. The formed Ti₃SiC₂ phase begins to decompose at 1450 ℃ and completely breaks down into TiC, SiC, and TiSi₂ at 1600 ℃.