Estudo dos mecanismos de trincamento em agregado de magnésia-cromo eletrofundido e alternativas sem Cr

Abstract

There is a need in the metallurgical industry for refractory materials with good physical and chemical properties. In this context, magnesia-chrome ceramics, composed of magnesium oxide (MgO) and chromium oxide (Cr₂O₃), emerged as an efficient solution for various applications starting in the 1960s, due to their good resistance to corrosion and thermal shock damage. However, there is a growing concern regarding the use of these refractories due to the release of hexavalent chromium, a toxic and carcinogenic compound for humans. In this study, the microstructures of electrofused magnesia-chrome aggregate (EMCA) and two alternative compositions (Composition 1 and Composition 3) – containing iron oxide and magnesium oxide – were investigated, focusing on crack formation and their associated mechanisms. Experimental results indicate that the sequence of materials with the highest occurrence of cracks is: EMCA > Composition 3 > Composition 1. This behavior suggests that the variation in lattice parameters between the phases has a greater influence on crack nucleation than the difference in thermal expansion coefficients. A smaller critical radius for the interface to become incoherent generates higher stresses in the matrix, promoting a greater accumulation of dislocations and, consequently, the occurrence of the Zener Stroh mechanism. Thus, this study contributes to the understanding of the factors affecting thermal shock resistance in these materials, providing a foundation for the development of more efficient and sustainable refractory solutions.