Vaporization studies over (NiO+Ni2Te3O8) in the Ni–Te–O system by transpiration thermogravimetry and Knudsen effusion mass spectrometry

• Published in: Thermochimica acta Vol. 600; pp. 67 - 76
• Main Authors: Lakshmi Narasimhan, T.S., Nalini, S., Sai Baba, M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.01.2015
• Subjects: Knudsen effusion mass spectrometry; Ni–Te–O system; Thermodynamic data; Threshold tellurium potential; Transpiration thermogravimetry; Vapor pressure; Threshold tellurium potential; Transpiration thermogravimetry; Vapor pressure; Thermodynamic data; Knudsen effusion mass spectrometry; Ni–Te–O system
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2014.11.024

•Total pressure over (NiO+Ni2Te3O8) phase region in the Ni–Te–O system determined by TTG method for the first time.•From p(Te2), p(TeO) and p(TeO2) measured by KEMS, p(O2) was derived by evaluating the gas phase reactions.•Total pressure by TTG and KEMS showed good agreement enabling to resolve discrepancy existing in literature data.•Enthalpies of solid–gas and gas-phase equilibria and thermodynamic data pertinent to Ni2Te3O8(s) phase were deduced.•Tellurium potential required for formation of Ni2Te3O8 phase on SS clad of mixed oxide fuelled fast reactor was calculated. Vaporization studies over (NiO+Ni2Te3O8) in the Ni–Te–O system were carried out by transpiration thermogravimetry (TTG) and Knudsen effusion mass spectrometry (KEMS) in the temperature ranges of 960–1085K and 850–960K, respectively. Comparison of total pressures obtained by TTG with that deduced using partial pressures of vaporizing species from KEMS showed a good agreement providing reliable vapor pressures over this phase region. From vapor pressures, enthalpies of solid–gas and gas-phase equilibria were evaluated. Subsequently, enthalpy and Gibbs free energies of formation of Ni2Te3O8(s) were deduced at 298.15K: ΔfHm°=−1543±46kJmol−1; ΔfGm°=−1294±46kJmol−1. A thermochemical assessment was made to examine the possibility of formation of the ternary Ni2Te3O8(s) phase on stainless steel clad of mixed-oxide fuelled fast breeder nuclear reactors.