Phase Transformations and Properties Evolution of Alumina-Based Refractory Castables Containing ZnO and SiO₂

Abstract

Although most of the studies presented in the literature are focused on MgAl₂O₄ formation and its role on alumina-based refractories performance, ZnO has been reported as a promising spinel inducer. Aiming to investigate the influence of ZnAl₂O₄ (ZA) and MgAl₂O₄ (MA) generation on the properties of alumina-based castables, three vibratable compositions containing calcium aluminate cement or hydratable alumina as binders and 1 wt% of silica fume, were evaluated in this work. Flexural strength, apparent porosity, hot elastic modulus, corrosion cup-tests, thermodynamic simulations, were carried out to analyze the performance of such ceramics. The results indicated that ZnAl₂O₄ was mainly formed above 800 °C, favoring an earlier sintering of the samples. Besides that, the softening of the castables was observed above 1200 °C, which resulted in the elastic modulus decay of the samples during their first heating cycle due to the formation of SiO₂-rich liquid phase in the resulting microstructure. Cement-free samples obtained after calcination (600 °C for 5h) presented enhanced corrosion resistance when placed in contact with molten slag at 1500°C. Although, silica fume addition to the castables negatively affected their corrosion performance, it helped to counterbalance the expansion associated with the spinel and calcium aluminates formation.

Keywords:
Alumina; ZnAl₂O_4, refractory castable; corrosion