Facile Electrochemical Preparation of Nano-sized Ultra-high-temperature Ta1−xHfxC Ceramic Powders

Abstract

Nano-sized powders of the Ta1−xHfxC class of ceramics, with compositions of Ta0.2Hf0.8C, Ta0.5Hf0.5C and Ta0.8Hf0.2C, were successfully synthesized from mixtures of the corresponding metal oxides and graphite by electro-deoxidation in molten CaCl2 at 1173 K. X-ray diffraction revealed that the as-prepared Ta0.8Hf0.2C mixed carbide had a single-phase cubic structure whereas Ta0.5Hf0.5C and Ta0.2Hf0.8C had dual-phase cubic structures, indicating that the large proportion of Ta promoted the formation of a homogeneous solid solution of TaC and HfC during synthesis. Electron microscopy proved that the particle size of the mixed carbides was in the nano range, while energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy confirmed that the intended compositions had been attained. Notably, the electrochemical method of synthesizing Ta1−xHfxC mixed carbides proceeds at a significantly lower temperature than the conventional preparation methods. This offers a number of key advantages in that it saves energy, gives better control over composition and allows for higher purity, and it suppresses in situ sintering and thus enables the formation of nanoparticles.