Thermodynamic Evaluation and Optimization of the (NaCl + Na ₂ CO ₃ + Na ₂ SO ₄ + Na ₂ S ₂ O ₇ + Na ₂ CrO ₄ + Na ₂ Cr ₂ O <sub>7</

A complete critical evaluation of all available phase diagram and thermodynamic data has been performed for all condensed phases of the salt system (NaCl + Na2CO3 + Na2SO4 + Na2S2O7 + Na2CrO4 + Na2Cr2O7 + Na2O + KCl + K2CO3 + K2SO4 + K2S2O7 + K2CrO4 + K2Cr2O7 + K2O) (diluted in free oxides), and optimized model parameters have been found. This system is important for the investigation of the chemistry of the different deposits formed in steel and stainless steel installations with Ni, Cr, Mo, W, and V as alloying elements during the combustion processes for energy production. The (NaCl + Na2CO3 + Na2SO4 + Na2S2O7 + KCl + K2CO3 + K2SO4 + K2S2O7) subsystem has been critically evaluated in previous articles. The Modified Quasichemical Model in the Quadruplet Approximation was used for both the molten salt phase and the high-temperature hexagonal solid solution (Na2CO3 + Na2SO4 + Na2CrO4 + K2CO3 + K2SO4 + K2CrO4) to take into account short-range-order between ions, while the Compound Energy Formalism was used for all other solid solutions. Owing to the lack of data, DSC-TGA experiments were conducted for several compositions in a few common-ion binary subsystems, with emphasis on solid–solid phase equilibria, and for one composition in a common-cation ternary subsystem. Also, the nonstoichiometric chrome-glaserite phase was investigated in particular at the composition (45 mol % Na2CrO4 + 55 mol % K2CrO4) using SEM-EDS and DSC-TGA, after annealing at 400 °C for 3 weeks. The model parameters obtained for the binary and ternary subsystems can be used to predict thermodynamic properties and phase equilibria for the multicomponent system.