Concretos refratários flexíveis baseados no sistema alumina-magnésia-titânia

Abstract

Refractory castables are essential components for industries, such as the steel and cement sectors, which are often subject to failure due to cyclic thermomechanical variations. To extend the service life of these linings, research has sought the development of flexible refractories, which make use of microstructural control to dissipate stress without affecting the overall integrity of the structure. In this context, the Al2O3–MgO–TiO2 (AMT) system emerges as a promising system for such a purpose, given that it presents phases such as spinels (MgAl2O4 and Mg2TiO4) and pseudobrookites (Al2TiO5 and MgTi2O5) with high potential for structural toughening. The central objective of this dissertation was to develop and optimize refractory castable compositions with superior flexibility based on this system. This study correlated computational thermodynamics and advanced experimental characterization results to identify oxide ratios that would maximize microcrack-induced toughening while preserving system stability. The results confirmed that the in-situ formation of complex pseudobrookite is the primary responsible for flexibility, generating a network of microcracks due to its high thermal expansion anisotropy, observing that the addition of titania up to a 50M-50T ratio resulted in a high level of microcracking, but above this threshold it caused a loss of structural cohesion. The 80M-20T ratio was the one that best balanced the effects of densification with controlled microcrack formation, resulting in high mechanical integrity and high resistance to thermal shock damage. This dissertation confirms that flexibility in alumina refractories can be engineered through controlled microcracking, using titania content as a strategy to extend the material’s service life. This work consolidates the AMT system as a versatile base for the high-temperature industry and highlighting the importance of integrating thermodynamic calculations with experimental characterization in the development of advanced materials.