High meta-stability of tungsten sub-carbide W2C formed from tungsten/carbon powder mixture during eruptive heating in a solar furnace

At around 1600 °C, stable phase in W–C binary system being in equilibrium with excess carbon is acknowledged to be mono-carbide WC. Nevertheless, during carbide formation from mixed powders of tungsten and excess carbon (C/W atom ratio: 2) in inert Ar gas environment, sub-carbide W2C formed besides mono-carbide WC when the heating was done extremely rapidly (instant temperature rise to 1600 °C from ambient temperature within fractions of a second) in a solar furnace at PROMES-CNRS in Odeillo (France) and the formed W2C resisted to be converted fully to WC even after 30 min heating at a temperature exceeding 2500 °C in Ar gas. Under comparatively fast heating condition (heating from ambient temperature to 1600 °C in about 1 min) realised in a solar furnace at PSA (Plataforma Solar de Almeria) in Tabernas (Spain), equilibrium phase WC alone formed from the similar starting material (C/W atom ratio: 1.5). Consideration is given for the formation mechanism of W2C under the eruptive heating condition in the solar furnace at PROMES-CNRS and also for the meta-stability of the formed W2C phase.