Microstructural evolution of magnesia-based castables containing microsilica

The higher performance of refractory materials applied in steelmaking vessels is mainly associated with the development of high-magnesia bricks. However, the same success has not yet been attained for the production of high-quality magnesia-based castables, due to the well-known magnesia hydration trend. In order to overcome this drawback, microsilica addition was tested as an anti-hydration additive in the present work. As it also leads to liquid formation at high temperatures in high-alumina CAC-containing castable compositions, the microstructural development of microsilica-containing magnesia-based castables was also analyzed by scanning electron microscopy, thermodynamics simulations and sintering assisted tests. According to the results, microsilica hindered the magnesia hydration and provided an additional bonding mechanism due to the reaction with MgO and water. Moreover, it helped to control the material's volumetric change by reducing the expansion associated with the spinel formation and also the shrinkage level afterwards.