Thermodynamic Model for High Temperature Corrosion Applications: The (NaCl + Na2CO3 + Na2SO4 + Na2S2O7 + Na2CrO4 + Na2Cr2O7 + Na2MoO4 + Na2Mo2O7 + Na2O + KCl + K2CO3 + K2SO4 + K2S2O7 + K2CrO4 + K2Cr2O7 + K2MoO4 + K2Mo2O7 + K2O) System

A thermodynamic model has been developed for the condensed phases
of the salt system (NaCl + Na2CO3 + Na2SO4 + Na2S2O7 + Na2CrO4 + Na2Cr2O7 + Na2MoO4 + Na2Mo2O7 + Na2O + KCl + K2CO3 + K2SO4 + K2S2O7 + K2CrO4 + K2Cr2O7 + K2MoO4 + K2Mo2O7 + K2O) (diluted in free oxides), which is most often involved in combustion processes for energy production. This model is relevant in particular for the solid deposits formed in steel and stainless steel installations containing Ni, Cr, Mo, W, and V as alloying elements and permits the accurate prediction of thermodynamic properties and phase equilibria in the multicomponent system. The (NaCl + Na2CO3 + Na2SO4 + Na2S2O7 + Na2CrO4 + Na2Cr2O7 + Na2O + KCl + K2CO3 + K2SO4 + K2S2O7 + K2CrO4 + K2Cr2O7 + K2O) subsystem was critically evaluated in previous papers. In the present work, Na2MoO4, K2MoO4, Na2Mo2O7, and K2Mo2O7 have been added to the previously developed thermodynamic model. The available phase diagram and thermodynamic data have been critically evaluated, and model parameters have been obtained. The Modified Quasichemical Model in the Quadruplet Approximation was used for both the liquid solution and the high-temperature hexagonal solid solution (Na2CO3 + Na2SO4 + Na2CrO4 + Na2MoO4 + K2CO3 + K2SO4 + K2CrO4 + [K2MoO4]), whereas the Compound Energy Formalism (CEF) was used for all other solid solutions. Due to the lack of data, several common-ion binary subsystems have been investigated in this work at different compositions by differential scanning calorimetry-thermogravimetric analysis (DSC-TGA). In addition, the nonstoichiometric molybdenum-glaserite phase has been studied at the composition (35 mol% Na2MoO4 + 65 mol % K2MoO4) using scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS) and DSC-TGA, after annealing at 400 °C for 4 weeks.