Nano-meter size WC whiskers grown over a compacted pellet of graphite/tungsten powder mixture heated with an ultra-fast heating rate by a concentrated solar beam

Abstract

In equilibrium binary W-C system, mono-carbide WC is acknowledged as the stable phase under presence of excess free carbon up to temperature 2700°C whereas sub-carbide W2C would form between 1250°C and 2700°C under the carbon-deficiency condition. In unique setup of solar furnace at PROMES-CNRS in Odeillo (France), temperature of specimen is raised from the ambient temperature to target temperature up to 2000°C within fractions of a second. In the recent experimental attempts of W2C phase synthesis using this unique experimental facility starting from compacted pellet consisted of graphite and tungsten powders at ratios smaller than 0.50, we detected growth of nano-meter size WC whisker at the top surface directly exposed to the concentrated solar beam. The presence of WC was confirmed also by X-ray diffraction (XRD) of the top surface but, when the specimen as a whole was subjected to powder XRD analysis, WC became indiscernible being masked by principal W:C phase. Mechanism of formation of the detected WC nano-whisker over sub-stoichiometric C/W pellet during ultra-fast heatingby concentrated solar beam is discussed. © 2007 The Japan Institute of Metals.