Corrosion of high alumina and near stoichiometric spinels in iron-containing silicate slags

Dissolution of alumina-rich spinel aggregates in iron-containing silicate slag was studied using grain corrosion tests. High alumina spinels (AR90, 90% Al2O3) dissolve indirectly while dissolution of near stoichiometric (AR78, 78% Al2O3) spinel is entirely direct. This behaviour arises because higher alumina spinels can accommodate more cations from the slag due to the greater number of Mg2+ vacancies in their crystal structures. Removal of these cations increases the viscosity of the remaining silica-rich local slag so that alumina-rich spinels exhibit better penetration resistance. However, thermodynamic calculations predict that near stoichiometric spinel (AR78) is more corrosion resistant since more slag is needed to dissolve it completely.