Experimental evidences of Nowotny phase incongruent melting

The Nowotny phase (NPh) Mo4.8Si3C0.6 was synthesized from preliminary obtained Mo5Si3 powder mixed with 1.7 wt% of carbon black with the help of reaction sintering in a solid state at 1750-1850 °C. Sintered and quenched samples were investigated with a help of the X-ray phase analysis, the scanning electron microscopy and X-ray microanalysis. Significant amount of Mo5Si3 in a mixture with NPh and some Mo2C was found after quenching of the samples melted in levitation conditions. Quenching of almost 100% NPh sintered sample melted in a narrow temperature interval above solidus temperature also results in a drastic increase of Mo5Si3 volume fraction. The analogous sample after being slowly cooled near the crystallization interval demonstrates rather high volume fraction of NPh. We suppose that here described results may be caused by the incongruent melting of NPh.