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 ( β h2 , g ́ b 1 , and β 1) was studied by Knudsen effusion mass spectrometry. The vapour phase was found to consist of Te 2(g) and Te(g). Partial pressure-temperature relationships over the Ni + β 2 phase field were determined to be log( P Te 2 Pa ) = (−12563 ± 223)/T(K) + 10.945 ± 0.236 and log( P Te Pa ) = (−13350 ± 425)/T(K) + 11.109 ± 0.450 , in the temperature range 893–993 K. Enthalpy and Gibbs energy of formation of the β 2 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+ β 2 to Ni+ǵb 1 was confirmed to be 1009 ± 10 K. P− T equations over the Ni+ g ́ b 1 phase field (1020−1055 K) were deduced as log( P Te 2 Pa ) = (−10883 ± 461)/T(K) + 9.305 ± 0.444 and log( P Te Pa ) = (−11189 ± 510)/T(K) + 8.949 ± 0.492 . Those over the Ni + β 1 phase field (1090–1190 K) were log( P Te 2 Pa ) = (−11187 ± 344)/T(K) + 9.649 ± 0.301 and log( P Te 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 ́ b 1 phase were determined to be −27.7 ± 4.1 and −30.1 kJ mol −1 at 1038 K and those for the β 1 phase as −30.5±3.2 and −30.7 kJ mol −1 at 1140 K.