Solid state reaction between tungsten and amorphous carbon

The solid state reaction between tungsten and amorphous carbon was studied at 973, 1073 and 1173 K. An amorphous carbon film was deposited onto a tungsten sheet by vacuum evaporation. The specimens thus prepared were heated at given temperatures, and the time dependence of carbide growth was examined by means of X-ray diffraction. No carbide appeared at 973 K within 240 min. On the other hand, the peaks of W₂C appeared at 1073 and 1173 K after an induction period, although W₂C is not thermodynamically stable at these temperatures. The intensities of W₂C peaks increased with elapse of time and then decreased owing to the decomposition of W₂C. No diffraction peaks from WC were detected at both temperatures. It was concluded that the rates of nucleation and growth of W₂C are significantly higher than those of WC at these temperatures.