Mechanisms Limiting Ti3SiC2 Formation During Carbothermal Reduction of Liquid Ti-Si-C-O Precursors.

The traditional precursor-derived ceramic (PDC) route uses micron-sized titanium sources and silicon carbide precursors to prepare Ti3SiC2, which limits its application in fine-scale fields. We propose a fully liquid Ti-Si-C-O precursor, consisting of tetrabutyl titanate (TBT) and liquid polycarbosilane (LPCS), inspired by the carbothermal reduction of solid oxides to prepare Ti3SiC2. The fully liquid precursor can offer processing advantages that are not achievable through previous PDC processes. The pyrolysis of the TSO-1 (TBT:LPCS = 3:2) undergoes four stages: dehydration condensation (RT~200 °C), alkoxy removal (200~400 °C), inorganic conversion (400~800 °C), and carbothermal reduction (>800 °C). The products of TSO-1 pyrolyzed to 1400 °C and 1600 °C are Ti3O5, SiO2 and TiC, and Ti3O5, Ti2O3, SiO2 and TiC, respectively. Increasing the LPCS content in the system can promote the formation of TiC, but will not produce Ti3SiC2. This phenomenon stems from the dual constraints: thermodynamically, titanium oxides outcompete SiO2 for carbon; kinetically, the gaseous escape of effective carbon and its microscale non-uniform distribution further impair the carbothermal reduction of SiO2. These combined factors prevent the gas-solid reaction from establishing, rendering Ti3SiC2 unattainable.