Contributions on Thermal Behaviour and Crystal Chemistry of Anhydrous Phosphates. XXXIV [1] Oxygen Equilibrium Pressures in Ternary Systems M / P / O (M = Co,Ni) and Heats of Formation of Anhydrous Cobalt(II) and Nickel(II) Phosphates |
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Authors: | Matthias Blum Klaus Teske Robert Glaum |
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Abstract: | Oxygen equilibrium pressures have been measured in the temperature range 800 °C to 1000 °C by coulometric/potentiometric techniques for several equilibrium regions in the ternary systems M / P / O (M = Co, Ni). In both systems oxygen coexistence pressures of three‐phase equilibrium solids phosphide/phosphate are about 3 to 5 orders of magnitude smaller than p(O2) above the corresponding Ms / MOs system. Heats of formation ΔfH°298 and standard entropies S°298 for the phosphates have been obtained from 2nd and 3rd law evaluation of the temperature dependence of the oxygen coexistence pressures. Thermodynamic data from literature for the phosphides of cobalt and nickel and estimated heat capacities for the anhydrous phosphates Co3(PO4)2, Co2P2O7, Ni3(PO4)2, Ni2P2O7 and Ni2P4O12 were used for these calculations. Thus obtained enthalpies and entropies are compared to results from thermodynamic modelling of observed solid phase equilibria in the ternary systems M / P / O (M = Co, Ni). |
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Keywords: | Phosphates Thermodynamic data Thermochemistry Gibbs phase triangles |
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