The interaction of carbon with Mo5Si3 and W5Si3 silicides. Nowotny phase synthesis

High-temperatures reactions of Mo5Si3 and W5Si3 silicides powders with the carbon soot were studied experimentally on sintered and melt-quenched samples. It was shown that Nowotny phase Mo4.8Si3C0.6 may be synthesized after annealing at 1600–2000 °C of initial mixture of Mo5Si3 with the carbon soot compacted at room temperature, simultaneously the small quantity of Mo2C phase was synthesized also. We have not found the Nowotny phase for W (like W4.8Si3C0.6) after reactions of W5Si3 or W5Si3 + WSi2 eutectic powders mixtures with carbon neither for the solid state reactions, nor for the melt-quenched samples. Only in some experiments with quenching of melted on the graphite substrate W5Si3 and WSi2 silicides eutectic there were found some evidences of the phase like W4.8Si3C0.6 possible presence along with W5Si3 and WSi2 silicides and WC carbide. In the melt-quenched Mo5Si3 + C sample Nowotny phase for Mo was distinguished from the Mo5Si3 phase in the back-scattered electron image, Mo2C carbides were revealed also.