Mullite–zirconia composite for the bonding phase of refractory bricks in hazardous waste incineration rotary kiln

Abstract Although mullite–zirconia composites made from zircon, alumina, and andalusite meet the requirements for many refractory applications, little effort has been made to transfer these composites to the bonding phase (the ‘matrix’) of refractory bricks. In this paper, we investigate how this could be achieved through better control of secondary oxides. The high temperature phases were simulated with thermodynamic software and linked to the microstructures, mineralogy, and properties of the composites. The results revealed that the system is very sensitive to Na2O, which harmed the microstructure considerably. By contrast, TiO2 and P2O5 additions proved beneficial, allowing complete zircon decomposition at 1550 °C while providing the required green strength. Decohesion between the matrix and aggregates due to high matrix shrinkage can be prevented by partially substituting andalusite with the volume-increasing mineral kyanite. Based on these findings, a novel refractory brick was developed and tested with success at an industrial scale.