High-alumina refractory castables bonded with metakaolin-based geopolymers prepared with different alkaline liquid reagents

This study explored the feasibility of utilizing varying proportions of metakaolin - MK (4, 6, or 8 wt%) and two types of alkaline liquid reagents - LR (incorporating nanosilica and NaOH or KOH) to induce in situ geopolymer formation in high-alumina refractory castables. The impact of geopolymeric binders on processing behavior, as well as on the physico-mechanical and structural properties of the designed refractories, was investigated within a temperature range of 40-1250 degrees C. Optimal physico-mechanical performance and thermal shock resistance were achieved with compositions 8 MK-Na (prepared with 8 wt% MK and NaOH-based LR) and 6 MK-K (containing 6 wt% MK and KOH-based LR). The liquid generation during viscous sintering enhanced castable densification at 1100-1250 degrees C and promoted the formation of nepheline, kalsilite or leucite phases. This resulted in microstructures featuring a suitable interfacial bond strength between the glassy phase and alumina grains, leading to an interlocking structure and improved castable properties. These achievements underscore the potential of geopolymer-bonded high-alumina castables for applications involving intermediate temperatures (800-1200 degrees C), such as those found in the petrochemical and non-ferrous metal industries.