Influence of TiO2 addition on the growing behavior of dense reaction layer in Al2O3 ceramics during CMAS corrosion at 1250 °C

This work investigates the growing behavior of reaction layers on TiO 2 -doped Al 2 O 3 ceramics in molten CMAS at 1250 °C. Initial reactions rapidly form Ca 2 MgSi 2 O 7 and CaAl 2 Si 2 O 8 phases. A thin-dense CaAl 2 Si 2 O 8 reaction layer (DRL) forms within 15 min, evolving into a double-layered structure (outer CaAl 2 Si 2 O 8 / inner MgAl 2 O 4 ) after 4 h. The reaction layer thickening follows the parabolic law, with a rate that decreases significantly after 4 h as the DRL plays a positive role in inhibiting the diffusion of Si 4+ , Al 3+ , and less effect on the, Mg 2+ and Ca 2+ . Crucially, the study elucidates the mechanism by which TiO 2 modulates the growing kinetics: TiO 2 enhances the chemical driving force for Ca 2+ infiltration through the DRL. This accelerated diffusion leads to the precipitation of a CaTiO 3 zone beneath the DRL, which alters the local compositional gradients and sustains the reaction layer growth. Kinetic models describing the layer thickness over time were established, and the underlying corrosion mechanisms were analyzed.