Abstract

The main features of magnesium aluminate spinel (MgAl2O4) are related to its chemical stability and the volumetric expansion that takes place during its in situ formation. Although the volume increase can close joints and generate compressive stresses, it can also spoil the refractory’s performance if not properly designed. In order to master the expansion and improve the corrosion resistance to basic slag, a unique binder (CMA72) obtained by co-sintering calcium oxide, magnesia and alumina has been recently developed, aiming to homogeneously attain ultra-fine spinel throughout the refractory matrix. Regarding the studies associated with the expansive behavior of spinel-forming castables, they are usually conducted in free-expansion environments, which is not in tune with the working structural conditions that involve limited room for volumetric change. Considering that the restrained expansion can act as a strengthening mechanism by reducing the castables’ porosity levels, the results attained in lab-scale conditions (expansion-free situation) may not represent the practical ones, when the compositions are applied in steel ladles. In this context, this work addressed the evaluation of thermo-mechanical properties after firing the castables under constraint, for compositions containing different amounts of pre-formed spinel and CMA72 binder. After drying bar-shaped samples (25 mm x 25 mm x 150 mm) at 600°C for 5h, they were embedded by an alumina-calcium aluminate cement castable and, after that, the whole system was fired at 1500°C for 5h. The samples were then cut for thermal shock and hot modulus of rupture evaluation and their results were compared with those of samples fired with no constraint (expansion-free). The results of these two conditions were remarkably different, pointing out that the constrained expansion procedure should be adopted for the development and evaluation of advanced spinel-forming castables’ compositions aiming to improve the working life of steel ladle linings.