Effect of microporous magnesia aggregates on microstructure and properties of periclase-magnesium aluminate spinel castables

Abstract

The present study investigated three lightweight periclase-magnesium aluminate spinel castables containing microporous magnesia aggregates with a varying apparent porosity (12.8%, 30.8% and 39.3%). The effect of the apparent porosity of the aggregates on the phase composition, microstructure, fracture behavior and strength of the lightweight castables was investigated by XRD, SEM and three-point bending tests. Large cracks between the aggregates with an apparent porosity of 12.8% and the matrix reduced the strength of the castable. For the aggregates with an apparent porosity of 30.8%, an excellent interlocking interface with the matrix increased the strength considerably, but also reduced the fracture toughness. At the highest level of the apparent porosity of the aggregates of 39.3%, the formation of a small number of microcracks between the aggregates and matrix reduced the strength, while the fracture toughness was only slightly affected. The lightweight castables with the best combination of properties were achieved at an apparent porosity of the aggregates of 30.8% since they had a low bulk density of 2.63 g/cm3 as well as a high compressive and flexural strength of 70.2 MPa and 20.9 MPa, respectively.