Synthesis and Stability Kinetics of Nanoporous TaC Derived from Ta Precursors
Ultra-high temperature ceramics (UHTCs) are promising materials for use in next-generation aerospace structures but have primarily been used as monolithic materials or coatings due to processing limitations. Here, new functionality (e.g., ablation resistance) is introduced to these materials by developing a porous form factor that can be later infiltrated with a secondary phase. This UHTC scaffold is synthesized via gas-phase carburization of nanoporous tantalum to the ultra-high-temperature ceramic, TaC. The kinetics of Ta conversion in a carburizing environment was examined over a range of temperatures to determine rate-limiting behavior and activation energy for the process. A 1-D moving interface model was constructed to predict carburization depth and compare data from the present work to that in the literature. It was found that the activation energy for carburization increases as conversion proceeds, suggesting a transition from grain boundary to bulk diffusion. Additionally, to simulate potential use cases of this nanoporous ceramic, the compositional and morphological stability was evaluated in a high temperature environment. Finally, the utility of this thermally stable porous UHTC was demonstrated through synthesis of a nanostructured composite of TaC and oxidation-resistant material, SiO2.