Electrochemical determination of the stability of mono‐ and dicalcium stannates

Abstract

The thermodynamic properties of mono- and dicalcium stannates have been determined in the temperature range 973–‐1423°K from the electromotive force measurements on solid oxide galvanic cells Pt, Ni + NiO//CaO-ZrO₂/Y₂0₃-ThO₂//SnO₂ + Sn, W, Pt Pt, Ni + NiO//CaO-ZrO₂/Y₂0-ThO//CaSn0₃ + SnO₂ + Sn, W, Pt Pt, Ni + NiO//CaO-ZrO₂/Y₂0₃-ThO₂//Ca₂SnO₄+CaSn0₃ + Sn, W, Pt and Pt, Ni + NiO//CaO-ZrO₂/Y₂0₃-ThO//Ca₂Sn0₄ + CaO, W, Pt The Gibbs free energy changes accompanying the formation of the stannates from component oxides may be represented by the equations 2CaO + Sn02→Ca₂Sn04 ΔG=-17,040+0.85T (±300) cal CaO + SnOs→CaSnO₃ ΔG=-17,390 + 2.0T (±300)cal The partial pressures of the tin bearing oxide species resulting from the decomposition of the stannates have been calculated as a function of the oxygen partial pressure by combining the results of this study with published information on the partial pressures and composition of oxide species over stannic oxide.