Predicting the density of molten alloys using computational thermodynamics

The density of a molten alloy can be calculated from the quotient of its molar mass divided by its molar volume. The molar volume of a molten alloy, however, often deviates from the average of the molar volumes of its constituents. The deviation is caused mainly by the affinity (or lack of it) between dissimilar atoms, which can be quantified by the enthalpy of mixing. Up to now, the link between the enthalpy of mixing and the volume change has been determined empirically through the regression of experimental measurements of alloy densities. In the present study, the derivative of molar volume with respect to enthalpy was deduced and the molar volumes of molten alloys were computed entirely based on the properties of pure elements and the enthalpy of mixing of the alloys. The very slight increase in the packing density due to the size difference of different atoms was also considered. The effect of cluster formation due to short range ordering was also addressed. Over six hundred data points were used in validations. Excellent agreements were achieved between the calculated values and the experimental measurements.