Investigations into the kinetics and mechanism of gas–solid state processes in MgO–MgR2O4 (R: Al, Cr, Fe) spinels–SO2–O2 system

In refractory ceramics magnesia-spinel materials continue to play an important role for both economic and research reasons. Although their basic properties are considered to be well-known, problems connected with production technology and improvement of application remain to be solved. The aim of this work is to describe and explain the behaviour of spinels in gaseous environment having high concentration of sulfur oxides. Thermodynamic analysis of chemical reactions in MgO–MgR2O4 (R: Al, Cr, Fe) spinels–SO2–O2 system as well as kinetic investigations and phase analysis of reaction products were carried out. Kinetic investigation results enabled to compare the chemical reactivity of spinels: MgAl2O4, MgCr2O4, MgFe2O4 and MgO at temperature 773, 1073 and 1273 K. On the basis of shrinking core model activation energy of the reaction MgO + SO3 → MgSO4 was calculated. Kinetic measurements confirmed the influence of early suggested phase changes on chemical reactivity of spinels within characteristic temperature range and revealed unexpectedly high reactivity of MgFe2O4 in comparison with the other spinels and MgO. It points out the criteria of selecting raw materials in basic refractory ceramics.