Preparation and characterization of microporous mullite-corundum refractory aggregates with high strength and closed porosity

Abstract Four microporous mullite-corundum refractory aggregates were prepared from Al(OH)3 and kaolinite gangue through an in-situ decomposition synthesis technique. The effect of the compacting pressure (30–150 MPa) on the microstructure and strength were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The higher compacting pressure limited the rearrangement of Al(OH)3 pseudomorphs during the reaction sintering process and promoted the reaction between Al(OH)3 and kaolinite gangue, leading to the formation of closed mullite layers on the surface of Al(OH)3 pseudomorphs. The pore size distributions of all four microporous aggregates were bimodal with closed pores (0.1–1.0 μm) located inside of the Al(OH)3 pseudomorphs, whereas open pores (1.0–10.0 μm) were found between the pseudomorphs. When the compacting pressure was 150 MPa, the microporous mullite-corundum refractory aggregates had a high total porosity of 40.5%, a highly closed porosity of 16.2%, median pore size of only 0.74 μm as well as an excellent compressive strength of 103.2 MPa.