Preparation of Al2O3@CaCO3 aggregates and its effects on the thermal shock resistance of Al2O3‐MgO castables

Abstract

AbstractAl2O3@CaCO3 aggregates were prepared by impregnating corundum aggregates (particle sizes with 3‐1 and 5‐3 mm) in precursor solutions (Calcium hydrogen citrate, CaHC6H5O7) followed by heat treatment at 430°C. The phase composition and microstructure of the coatings were characterized via X‐ray diffraction and scanning electron microscope, respectively. The novel aggregates were used in Al2O3‐MgO castables. The effects of the Al2O3@CaCO3 aggregates on the physical properties and thermal shock resistance (TSR) of castables were investigated. The results show that uniform CaCO3 coating of aggregates (C15) with thickness about 10 µm can be attained when the concentration of Ca2+ in solution was 0.15 mol L−1. There was a strong bonding between the aggregates and coating that was constituted by particles with size about 0.2 µm. Both improving physical and TSR properties of the castables are related with the unique layer structure, calcium hexaluminate (CA6) layer in‐situ formed at the aggregate‐matrix interface, of added Al2O3@CaCO3 aggregates. There is a mass of multi‐deflection of cracks along with the CA6 layer which consumes more fracture surface energy. The castables with C15 exhibit optimal TSR and the residual strength ratio after the thermal shock test is 29.5%, which is 12.8% higher than the castables with corundum aggregates.