Low-Temperature Formation of Ultra-High-Temperature Transition Metal Carbides from Salt-Polymer Precursors

摘要

Refractory transition metal carbides were produced via carbo-thermal reduction of transition metal halides in a polymer precursor at low temperatures (< 1200℃). This approach was used to generate TaC (T_m = 3883℃), NbC (J_m = 3610℃), and WC (T_m = 2870℃) from TaBr_5, NbBr_5, and WCl_4/WCl_6, respectively. Solubility of transition metal halides and polymers in the same organic solvents allows for intimate mixing on the molecular level, which reduces the synthesis temperature. Greater than 90% TaC conversion was achieved by exposing a 50:50 weight ratio mixture of TaBr_5 and polyimide (or polystyrene) to 1200℃ for 1 h. Even at temperatures as low as 1000℃, the major product remains TaC. The abih'ty to process these high-temperature materials so simply, and at relatively low temperatures, makes them accessible for different applications requiring thermal protection such as coatings for metallic components of hypersonic aircraft, rocket engine components, fibers, or refractory containers.