COMMENTS ON THE ACTIVITY OF CARBON IN LIQUID-IRON

Existing data on the activity of carbon in liquid iron have been critically assessed and interpreted by using new equations derived by the author. These equations are the standard Gibbs energy of melting of graphite, the graphite-liquid iron saturation equation, and the interrelationship in the Margules equation. The resulting equation is g2 = 130,330 - 32.19 T- (108,330 - 15.47 T) x1(2) - (344,000 - 220.4 T) x1(2)x2 + (512,500 - 380.3 T) x1(2)x2(2) where g2 is the partial excess Gibbs energy of dissolved carbon in J/mol, T is the temperature in K, and x1 and x2 are the mole fractions of iron and carbon in the melt, respectively. g2 refers to graphite as the standard state so that g2 = R T In gamma2 = - R T In x2 (at graphite saturation), where R is the gas constant, and gamma2 is the activity coefficient. From the preceding equation, g1 for