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

Abstract

Refractory transition metal carbides were produced via carbothermal reduction of transition metal halides in a polymer precursor at low temperatures (<1200°C). This approach was used to generate TaC (Tm=3883°C), NbC (Tm=3610°C), and WC (Tm=2870°C) from TaBr5, NbBr5, and WCl4/WCl6, 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 TaBr5 and polyimide (or polystyrene) to 1200°C for 1 h. Even at temperatures as low as 1000°C, the major product remains TaC. The ability 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.

TaC Nanowire/Activated Carbon Microfiber Hybrid Structures from Bamboo Fibers

“…These properties make TMCs very useful as coating materials, tools, machine parts, and reinforcements in composites. Among TMCs, tantalum carbide (TaC) is especially interesting and promising owing to the unique combination of its properties, such as high hardness at room temperature (9–10, Mohshardness), very high melting‐point (approximately 3880 °C), high Young's modulus (283–550 GPa), excellent electrical conductivity (32.7–117.4 μΩ·cm at 25 °C), high temperature superconductivity at 10.5 K, good resistance to chemical attack and thermal shock, and outstanding catalytic activity for ammonia decomposition and hydrogen dissociation 5–15…”

“…One‐dimensional (1D) nanostructures such as nanowires (NWs), nanorods, and nanotubes have attracted tremendous attention because of their size‐dependent optical, electronic, mechanical, and sensing properties, opening up unprecedented opportunities to construct nanodevices with new functionalities which could be achieved at the micro/macro scales 16–19. Although TaC powders and whiskers have been prepared by carbothermal reduction, thermal plasma, solvothermal, sol‐gel, microwave heating, alkalide reduction, self propagating high temperature synthesis, and high frequency induction heated sintering,7–13 there are only few corresponding routes to synthesizing 1D TaC nanostructures. Fukunaga et al prepared TaC nanorods via carbon nanotubes confined vapor‐solid reaction 14.…”