Thermodynamic study of the sodium chromite NaCrO2

• Published in: Journal of alloys and compounds 2021-11, Vol.882, p.160784, Article 160784
• Main Authors: Chatain, Sylvie, David, Nicolas, Bonina, David, Flèche, Jean-Louis, Bonnet, Christophe, Courouau, Jean-Louis, Rouhard, Marion
• Format: Article
• Language: English
• Subjects: Ab initio calculations; Chemical Sciences; Chromite; Decomposition reactions; Differential scanning calorimetry; Differential thermal analysis; Diffraction patterns; Enthalpy; Free energy; Heat of formation; Material chemistry; Phase transitions; Quasi-harmonic model; Room temperature; Sodium chromite; Sodium chromites; Statistical models
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.160784

•Heat capacity measurements of NaCrO2 up to 600 °C by DSC.•Thermodynamic data calculated by ab initio and quasi-harmonic statistical model.•New equation of the Gibbs energy of formation of NaCrO2 proposed. 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 of 25–600 °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 combining with a quasi-harmonic statistical model. The equation obtained is given by: ΔfG°(T) (NaCrO2) (kJ/mol O2)=−876.094+0.191xT (±2%). 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. However, the X-ray diffraction patterns showed only NaCrO2 phase which didn’t confirm the decomposition reaction.