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

Tantalum carbide (TaC) is widely used for aerospace thermal protection because of its high melting point and excellent high-temperature mechanical properties. Conventional solid-phase carbothermal reduction for TaC powder preparation suffers from high reaction temperatures, large particle sizes, and low purities. While tantalum alkoxide complex precursors offer improvements, challenges such as limited crosslinking sites and a lack of molecular-level mixing of Ta and C sources remain. To solve these issues, this study synthesized a TaC precursor named PTC-pentene (polytantalcarbane synthesized from 1-penten-3-ol) using TaCl₅ as the Ta source and allyl novolac (AN) resin as the C source. C=C bonds served as crosslinking active centers during copolymerization, leading to a dense crosslinked network that resolved the issue of insufficient crosslinking sites. Furthermore, they enabled bonding between the Ta and C sources, achieving uniform molecular-level mixing. Analysis of the precursor carbothermal reduction kinetics revealed that the process occured in two stages: the 930–1255 °C range controlled by 1.5-order chemical reactions, and the 1255–1400 °C range jointly controlled by three-dimensional diffusion and phase-boundary reactions. By optimizing the C source addition ratio (m(AN) : m(TaCl₅) = 0.6) and pyrolysis conditions (1400 °C 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 spark plasma sintering (SPS) process, and their oxyacetylene ablation mechanism was analyzed. The results revealed that the Ta₂O₅ melt resisted O diffusion but was eroded by gas flow. High temperatures caused thermal cracking, whereas molten Ta₂O₅ filled the cracks.