Theromodynamic investigation on some alloy systems of interest in metollothermic reductins by vapour pressure measurment and thermogravemetry

Abstract

The thermodynamic properties of pure liquid Mg and liquid Mg-Al and Mg-Cu alloys have been determined by vapour pressure measurement using the boiling point method, and those of the solid USi phase by measurement of equilibrium pressure of SiF (g) over a phase mixture containing UF + USi + Si, using the static vapour pressure measurement technique. In addition, the reactions of silicon with uranium fluorides (UF and UF ) have been investigated thermogravimetrically to identify the sequence of reactions involved and also to study the conditions under which various U-Si intermetallic compounds could be prepared. The temperature variation of the equilibrium pressure over pure liquid magnesium was measured in the temperature range 1004 to 1315 K. The liquid Mg-Al alloys studied, in the composition range 6 to 95 atom % Mg between 960 and 1230 K, were found to exhibit a small negative deviation of activities from ideal behaviour. The Mg-Cu alloys, investigated in the composition range 17 to 90 atom % Mg between 955 and 1250 K, exhibit large negative deviation of activities from ideal behaviour. The standard free energy of formation of the solid USi phase has been established in the temperature range 870 to 1040 K and is given by the relation: GUSi2 = 31.988 0.05×10 1 Tkcal/mol\Delta G^\circ_{\mathrm{USi_2}} = -31.988 - 0.05 \times 10^{-1} \, T \quad \text{kcal/mol} GUSi2 = 31.988 0.05×10 1Tkcal/mol The silicothermic reduction of uranium fluorides indicated that the reaction proceeds in a sequential manner and ultimately leads to the formation of the USi phase.