Thermal shock behavior of andalusite-based refractories: Microstructural investigation of crack bridging and grain-matrix interactions

Andalusite-based refractories are characterized by superior thermal shock resistance. Although the demand for alternative raw materials is increasing, it is proving difficult to replicate the thermal shock behavior of andalusite with alternative materials. The physico-mechanical properties of andalusite refractories are well-studied. However, comprehensive chemical and microstructural analysis is still needed to fully understand factors influencing the thermal shock resistance. This investigation highlights the use of complementary microstructural techniques (3D digital microscopy, scanning electron microscopy–energy-dispersive X-ray spectroscopy, and micro-X-ray fluorescence) to analyze crack propagation as well as glass bridge formation and composition in aluminosilicate-based refractory castables. Andalusite-based refractories are compared with chamotte 45 and chamotte 60, before and after a thermal shock, as well as after an additional firing. Factors influencing the thermal shock resistance of aluminosilicate refractory castables include (1) crack shape, size, occurrence, and propagation (2) glass bridge formation, size, occurrence, and composition, and (3) aggregate-matrix interactions.