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Thermochemistry of MgCr2O4, MgAl2O4, MgFe2O4 spinels in SO2−O2−SO3 atmosphere

Gerle Anna (Institute of Ceramics and Building Materials, Refractory Materials Division in Gliwice, Gliwice, Poland)
Piotrowski Jerzy (Silesian University of Technology, Faculty of Chemistry, Department of Inorganic, Analytical Chemistry and Electrochemistry, Gliwice, Poland)
Podwórny Jacek (Institute of Ceramics and Building Materials, Refractory Materials Division in Gliwice, Gliwice, Poland)

The present paper investigates high-temperature sulphate corrosion of basic refractory ceramics containing magnesium spinels (MgAl2O4, MgFe2O4, MgCr2O4 and their solid solutions) widely used in metallurgy, chemical, ceramic and glass industry. This group of refractories are exposed to a number of destructive factors during a working campaign. One of such factors is gas corrosion caused by sulphur oxides. However, gas sulphate corrosion of basic refractory materials containing magnesium spinels, which has a great practical meaning for the corrosion resistance of the material main components, is not sufficiently examined. This work presents a thermodynamic analysis of (MgCr2O4, MgAl2O4, MgFe2O4)−SO2−O2−SO3 system aimed to calculate: i) the standard free enthalpy of chemical reactions, ii) the equilibrium composition of the gas mixture initially containing SO2 and O2 and iii) sulphates equilibrium dissociation pressure and equilibrium partial pressure for the reaction of SO3 with the spinels to predict the temperature range of corrosion products’ stability. A thermochemical calculation provides information about equilibrium state in the analysed system. In real conditions the state of equilibrium does not have to be achieved. For this reason, the results of calculations were compared with experimental data. The experiment results were consistent with the theoretical predictions.

Keywords: spinels, corrosion, refractories, sulphur oxides