Self-reinforced high-alumina refractory castables

Among the available routes to enhance the mechanical behavior and toughening degree of ceramics, in situ formation of acicular or platelet grains in the resulting microstructure has gained special attention. Various studies focused on investigating the self-reinforced role of these elongated phases (acting as bridging sites in the wake of a crack), as well as the use of very reactive raw materials to favor faster and more effective sintering/densification, have been carried out for compositions comprised mainly by fine raw materials. Nevertheless, there is a lack of studies considering more complex ceramics, such as refractory castables, which commonly present heterogeneous microstructures with coarse and fine components. Based on that, this work addresses the evaluation of self-reinforced high-alumina refractories containing reactive aluminas (AloxX spheres and/or submicron alumina) and calcium aluminate cement as binders. Boron carbide and microsilica were also added to some of the prepared compositions to favor the in situ formation of Al18B4O33 or CA(6) phases with needle-like morphology. Various experimental evaluations (cold and hot mechanical strength, hot elastic modulus, SEM, XRD, thermal shock resistance, refractoriness under load, etc.) were carried out to identify the influence of the new phases' formation in the overall performance of such materials. According to the attained results, both mineralizing agents (B4C and SiO2) induced the formation of Al18B4O33 or CA(6) grains in the designed compositions. However, a remaining liquid content was still present in these samples at a high temperature, resulting in some drawbacks concerning their hot properties. Additionally, submicron alumina proved to be an interesting binder as it induced improved sintering and led to a refractory with high stiffness (similar to 200 GPa), high thermal shock resistance and mechanical strength.