Synthesis, pyrolysis mechanism, and ceramic ablation performance of a TaC precursor with unsaturated bonds

Tantalum carbide (TaC) is widely used in aerospace thermal protection due to its high melting point and excellent high-temperature mechanical properties. Conventional solid-phase carbothermal reduction for TaC powders preparation suffers from high reaction temperature, large particle size, and low purity. While tantalum alkoxide complex precursors offer improvements, challenges such as limited crosslinking sites and lack of molecular-level mixing of Ta and C sources remain. To solve these issues, this study synthesized an unsaturated tantalum alkoxide monomer PTC-Pentene using TaCl₅ and 1-penten-3-ol as the Ta source and allyl-modified linear phenolic resin as the C source. C=C bonds served as crosslinking active centers during copolymerization to form a dense crosslinked network and resolve insufficient crosslinking sites, while also enabling covalent bonding between Ta source and C source to achieve uniform molecular-level mixing. Analysis of the precursor's carbothermal reduction kinetics revealed that the process occurs in two stages: the 930~1255℃ range controlled by 1.5-order chemical reactions, and the 1255~1400℃ range jointly controlled by 3D diffusion and phase-boundary reactions. By optimizing the C source addition ratio (m(AN):m(TaCl₅) =0.6) and pyrolysis conditions (1400℃ for 2 h), TaC powders with an average particle size of 140 nm and an oxygen content of 0.40 wt% were obtained. Using these powders, TaC ceramics were fabricated via SPS process, and their oxyacetylene ablation mechanism was analyzed. The results showed that the Ta₂O₅ melt resisted O diffusion but was eroded by gas flow. High temperatures caused thermal cracking, while molten Ta₂O₅ filled the cracks.