ZnO AS AN INDUCER OF SPINEL-LIKE PHASE FORMATION ON ALUMINA-BASED CASTABLES

Environmental and occupational issues regarding Cr⁶⁺ formation urge the replacement of chrome-containing refractories by greener alternatives. For the latest decades, magnesium-containing refractories have been investigated for this purpose, however, few studies evaluated the likelihood of using other chemical elements as inducers of spinel-like phase formation in refractory castables. In this work, the addition of zincite (ZnO) in alumina-based vibrated castables bonded with calcium aluminate cement (CAC) or hydratable alumina (HA) was evaluated and compared with its MgO counterpart. The formation of the Zn-based spinel (ZnAl₂O₄, gahnite) took place at a lower temperature (1100 ºC) than MgAl₂O₄ (1300 ºC), resulting in the anticipated strengthening of these compositions. Despite the challenges regarding using ZnO – as its volatilization under reduced atmosphere and fast reaction kinetics –, lower linear dimensional changes, comparable cold modulus of rupture and enhanced thermal shock damage resistance was detected.