Electrochemical determination of gibbs energy of formation of NiTiO3 (ilmenite)

Gibbs energy of formation of NiTiO₃ (ilmenite) relative to its component oxides, NiO (rock salt) and TiO₂ (rutile), has been measured employing the solid-state electrochemical cell, . between 994 and 1371 K. The open-circuit electromotive force (emf) of the preceding solid-state galvanic cell was found to be reversible and to vary linearly as a function of temperature in the range of measurement. The results obtained in this study give for the reaction . Combining the Gibbs energy of formation of NiTiO₃ (ilm) from the component oxides with that for the formation of NiO (rs) from its elements gives for the reaction . Differential thermal analysis (DTA) of NiTiO₃ (ilm) between 373 and 1623 K indicated that NiTiO₃ (ilm) undergoes a reversible order-disorder phase transformation between 1540 and 1594 K. Based on the ideal mixing of cations on the cationic sublattice of NiTiO₃ (ilm) and a critical phase transformation of 1568 K obtained from the DTA, the Gibbs energy change for the order-disorder phase transformation in NiTiO₃ (ilm) is obtained as .