Effects of microsilica content on microstructure and strength of lightweight castable refractories containing porous corundum-spinel aggregate

High-strength, lightweight castable refractories based on spinel were prepared by introducing porous corundum-spinel aggregate and appropriate microsilica. The effects of microsilica content on microstructure and properties of lightweight castable refractories were investigated using SEM, XRD, mercury porosimetry measurements and FactSage thermochemical software. It's found that microsilica was almost dissolved into a liquid phase at high temperature, which promoted liquid sintering. With increasing microsilica content, the matrices became denser and average pore size of matrices increased, then apparent porosity decreased, crushing strength increased and content of liquid phase in castables at 1600°C increased. The appropriate microsilica content is 0.65 to 1.95 wt%, which reaches to a compromise among apparent porosity (33-38%), crushing strength (82-125MPa) and liquid content (1.80~4.97 wt%).