Knudsen effusion mass spectrometric studies of the B2 phase in the Al – Co system

Abstract

The vaporisation of Al – Co alloys has been investigated in the temperature range of 1 201 to 1 552 K using Knudsen effusion mass spectrometry. Nine different compositions have been examined in the composition range x(Co) = 0.62 to 0.47. Al(g) and Co(g) were the vapour species observed over all the alloy samples excepting x(Co) = 0.47 over which only Al(g) could be identified. Partial pressure – temperature relations and thermodynamic activities of Co and Al were derived. The enthalpies and Gibbs free energies of formation of Al _0.5Co _0.5(s) at 298.15 K were obtained as Δ _f H ^o _m=− 54.9 ± 4.8 kJ mol ⁻¹ and Δ _f G ^o _m=− 51.4 ± 1.4 kJ mol ⁻¹. This is the first time activities of Co have been determined experimentally across the B2-AlCo(s) single phase region.