Fracture Process Zone in Refractory Castables after High-Temperature Thermal Shock
Most ceramic materials exhibit a critical temperature difference (ΔTc) as a minimum temperature required for fracture initiation. Refractories exhibit within their heterogeneous structure already pores, aggregates of different size and cracks. To understand the influence of the temperature difference (ΔT) and the temperature level, a new high temperature thermal shock furnace was designed and constructed. Unlike standard thermal shock tests with compressed air or water, the new furnace’s two separately heatable and interconnected chambers enable the transfer of samples between two high temperatures without exposing them to the surrounding atmosphere at room temperature. To understand the effect of rapid temperature changes, the natural aggregate andalusite and the synthetic aggregates Al2O3–ZrO2–SiO2 and Al2O3–ZrO2 are incorporated in a model low cement castable formulation based on tabular alumina. The influence of these aggregates on the elastic and thermomechanical properties is examined and correlated to the microstructure.