Synthesis in molten salts and formation reaction kinetics of tantalum carbide coatings on various carbon fibers

Abstract

Tantalum carbide (TaC) coatings were prepared on polyacrylonitrile (PAN)-based, graphitized PAN-based and pitch-based carbon fibers by synthesis in molten salts. The characteristics of the TaC coating were studied in relation to the structure of the carbon fiber, the molten salt composition, reaction temperature and reaction time. Thicker TaC coatings with larger grain sizes tended to form on carbon fibers with a lower degree of crystallinity. Molten salt mixtures with a relatively low melting point are appropriate for use as the reaction medium for synthesis of TaC coatings on carbon fibers. However, with increasing reaction temperature and reaction time, the thickness and grain size of the TaC coating increase obviously. Internal diffusion control and external diffusion control models of TaC coating growth were established on the basis of mass transfer and reaction dynamics theory. The result indicates that the TaC coating growth is controlled by the internal diffusion of tantalum in the TaC coating.