Vaporisation thermodynamics of the nickel-rich phases in the Ni-Te binary system-a high temperature mass spectrometric study

Abstract

The vaporisation of the metal-rich nickel tellurides (βh₂, gb₁, and β₁) was studied by Knudsen effusion mass spectrometry. The vapour phase was found to consist of Te₂(g) and Te(g). Partial pressure-temperature relationships over the Ni + β₂ phase field were determined to be log(^PTe₂/Pa) = (-12563 ± 223)/ T(K) + 10.945 ± 0.236 and log(^PTe/Pa) = (-13350 ± 425)/ T(K) + 11.109 ± 0.450, in the temperature range 893-993 K. Enthalpy and Gibbs energy of formation of the β₂ phase, at the nickel-rich boundary (NiTe_0.634), at 298 K were derived as -33.3 ± 5.1 and -35.0 kJ mol^-1, respectively. The temperature of phase transition from Ni+β₂ to Ni+gb₁ was confirmed to be 1009 ± 10 K. P-T equations over Ni + gb₁ the phase field (1020-1055 K) were deduced as log(^PTe₂/Pa) = (-10883 ± 461)/ T(K) + 9.305 ± 0.444 and log(^PTe₂/Pa) = (-11189 ± 510)/ T(K) + 8.949 ± 0.492. Those over the Ni + β₁ phase field (1090-1190 K) were log(^PTe₂/Pa) = (-11187 ± 344)/ T(K) + 9.649 ± 0.301 and log(^PTe₂/Pa) = (-11930 ± 400)/ T(K) + 9.671 ± 0.349. At the nickel-rich boundary (NiTe_0.587), Δ_fH° and Δ_fG° for the g b₁ phase were determined to be-27.7 − 4.1 and -30.1 kJ mol^-1 at 1038 K and those for the β₁ phase as -30.5 − 3.2 and -30.7 kJ mol^-1 at 1140 K.