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

• 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 960–1085 K and 850–960 K, 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 298.15 K: ΔfHm° = −1543 ± 46 kJ mol−1; ΔfGm° = −1294 ± 46 kJ mol−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.