Thermodynamic study on refractory metal silicides Original Research Article

Thermodynamic calculations and discussions for refractory metal silicides were performed by using the results of the EMF measurements and the literature data. Phase relations for M(Nb, Ta, Mo and W)–Si–O ternary system at 1373 K were considered by means of the potential diagrams and the isothermal sections of the phase diagram. Silicon concentration cells used in EMF measurements were composed of SiO2-saturated lithium silicate molten electrolyte and the electrodes of three phases mixture of the compounds in M–Si–O ternary system. Within the experimental temperature range (from 1280 to 1500 K), the activity of silicon at the three phases equilibria of the systems, i.e. Nb5Si3+NbO+SiO2, NbSi2+Nb5Si3+SiO2, TaSi2+Ta5Si3+SiO2, W5Si3+W+SiO2 and WSi2+W5Si3+SiO2, was obtained as a function of temperature. Applying the results, the standard free energy of formation for NbSi2 Nb5Si3, WSi2 and W5Si3 was determined.