Thermodynamic study of the sodium chromite NaCrO2

Abstract : A thermodynamic study was undertaken on two kinds of NaCrO2(s) powder, a commercial and an experimental one synthetized. Heat capacity measurements were carried out in the temperature range 25 °C to 610 °C using a differential scanning calorimeter. Gibbs energy of formation versus temperature was deduced using these experimental data, the enthalpy of formation from literature and the entropy at room temperature deduced from ab initio calculations. The equation obtained is given by: DeltafG°(T) (NaCrO2) (kJ/mol O2)=-876094+191.241xT. The temperature of phase transition measured by differential thermal analysis at (819±4) °C is slightly higher than the temperature in the literature attributed to the decomposition of NaCrO2 into Cr2O3 and Na2O. The X-ray diffraction patterns showed only NaCrO2 phase which did not confirm the decomposition reaction.