ACTIVITY OF ALUMINUM IN MOLTEN TI-AL ALLOYS

The activity of aluminum in molten Ti-Al alloy was measured by 'free e vaporation method'. The specimen was melted and held at constant tempe rature in an electron beam vacuum furnace. The weight change was measu red and converted to the rate of evaporation of constant composition. The Hertz-Knudsen equation was then applied to calculate the vapor pre ssure of the element, and the activity was obtained by comparing that with the pressure of the pure substance. The activity coefficient al m ole fractions of aluminum less than 0.1 is about 0.03 and that for ove r 0.2 was about 0.1. The activity of titanium was also calculated by i ntegration of the Gibbs-Duhem equation for a binary mixture based on t he activity of aluminum. (C) 1997 Elsevier Science S.A.