Prediction of thermodynamic activities in binary iron-based alloys using two-point Pade approximants

A method for predicting activities as a function of the concentration in liquid solutions for binary FeCo, FeCu, FeNi, FeMn and FePd systems using Pade approximants is presented. Pade approximants of orders 4/0 and 1/3 are proposed for the model using as input variables only the conditions from Henry's law at a given temperature. Results derived from the approximant 4/0 show good agreement with the experimental data in systems with moderate positive and negative deviations from the Raoultian behaviour. On the other hand, the approximant 1/3 shows a satisfactory agreement in the FeCu system which exhibits a high positive deviation from the Raoultian behaviour. A comparison with the results from a Redlich-Kister expansion using the same input conditions is discussed.