Influence of calcium hexaluminate gradation on interfacial microstructure and fracture behavior of cement-bonded alumina castables

To reduce the brittleness of cement-bonded alumina castables for purging plug, different gradations (5-3, 3-1 and 1-0 mm) of calcium hexaluminate aggregates are introduced to replace the tabular alumina aggregates. The interfacial microstructure and fracture behavior with or without calcium hexaluminate aggregates are system-atically analyzed. The results show that the large (5-3/3-1 mm) and small (1-0 mm) particle sizes of calcium hexaluminate contributed to the interfacial bonding and prolonged crack propagation path of cement-bonded alumina castables, respectively. Accordingly, the strength is promoted and the fracture mode is significantly affected under tensile stress. Specifically, the proportion of cracks propagating along the interface can be reduced by introducing 5-3-or 3-1 mm calcium hexaluminate particles. Besides, the introduction of 1-0 mm particles reduces the proportion of cracks propagating within the aggregate. Cement-bonded alumina castables containing three particle sizes (5-3/3-1/1-0 mm) of calcium hexaluminate have simultaneously better strength and toughness than castables containing a single particle size.