Thermodynamic investigation on Al 1 − xMn x melts by Knudsen cell mass spectrometry

Abstract

The thermodynamic activities of the components in Al 1 − x Mn x alloys have been measured from 1250 to 1550 K by Knudsen cell mass spectrometry, using the “ion-current ratio method”. Owing to the high pressure of Mn, the measurements are limited to the range 0 <x Mn s ̌ 0.5 and a reference based on the measurements of pure metals is introduced. The excess Gibbs free energies are deduced and the minimum value of the excess molar Gibbs free energy is −(8500 ± 350) J mol −1 at x = 0.45. Combined with calorimetric quantities, these data allow calculation of the entropies of formation which are found to be very small. The thermodynamic behaviour corresponds to rather large negative interactions between the aluminium and manganese atoms and a moderate chemical short-range order in agreement with the conclusions of the structural study of the literature.