Concretos refratários aluminosos espinelizados
Braulio, Mariana de Albuquerque Lima
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The increasing steelmaking production level in association with the steel quality requirements led to the use of high performance materials. In this context, the use of refractory castables increased, due to their production and application versatilities. Magnesia is one of the most important refractory raw material, as it presents a high refractoriness and corrosion resistance to basic slags. Due to their ability to accommodate slags elements without loosing structural integrity, in-situ spinel castables (MgAl2O4) are commonly used for steel ladle lining. Nevertheless, there are many simultaneous challenges for this system optimization: (i) the MgO hydration can spoil the castable structure and result in processing problems, on shaping and drying; (ii) the intermediate temperatures mechanical strength level should be kept at suitable values and (iii) the expansion, as a consequence of spinel and CA6 formation, must be under control. Due to the lack of a systemic and conclusive analysis related to these aspects, the evaluation of these castables raw materials and their association was carried out in this work, based on the requirements pointed out above. Concerning magnesia hydration, advances were attained by the correct dispersion and particles packing. The compositions designed also resulted in suitable mechanical properties at intermediate temperatures, inhibiting cracking problems during the material s pre-heating stage. Regarding the expansive phases formation at high temperatures, all evaluated variables (cement content, binder system, magnesia source, microsilica content and aggregates nature) affected in a significant way the alumina-magnesia castables stability, providing several routes for the expansion control by the microstructural engineering of these materials. The results attained helped the scientific and technological advances in this subject.