Microstructure and mechanical properties of lightweight Al2O3-C refractories using different carbon sources

Two lightweight Al2O3-C refractories containing microporous corundum aggregates were fabricated by using flake graphite and microcrystalline graphite as the carbon source. The effect of these carbon sources on the microstructure and mechanical properties of lightweight Al2O3-C refractories with a silicon additive was then investigated. Using microcrystalline graphite resulted in more SiC whiskers in the microporous corundum aggregates compared to the specimens using flake graphite because microcrystalline graphite had a higher reactivity. The higher amount of SiC whiskers led to a more intertwined and compacter microporous aggregate/matrix interface structure. Due to the improved microporous aggregate/matrix interface together with the reinforcing effect of the well-developed SiC whiskers, the crack propagation along the aggregate/matrix interface was suppressed, whereas the percentage of cracks propagating within the aggregates was enhanced. Therefore, the lightweight Al2O3-C refractories using microcrystalline graphite had a similar apparent porosity of 24.5%, a similar bulk density of 2.71 g/cm3 but a 14.3% increased cold modulus of rupture (25.6 MPa), a higher fracture energy and a somewhat higher toughness than the ones using pricier flake graphite. Overall, the study provides a framework for the industrial application of lightweight Al2O3-C refractories with significantly improved mechanical properties.