Corrosion behavior of Al2O3 substrate by SiO2–MgO–FeO–CaO–Al2O3 slag

Abstract

Alumina–based refractory is widely used as lining material of rotary hearth furnace (RHF) in the direct reduction process. However, corrosion of refractory by the burden is a crucial problem which affects the RHF production. In this study, a sessile drop technique was used to investigate the wetting and corrosion behavior of Al2O3 substrate against SiO2–MgO–FeO–CaO–Al2O3 slag, whose composition was determined according to the slag obtained from smelting nickel laterite in the RHF process. The experimental results showed that the slags with basicity ((MgO+CaO)/SiO2) of 0.43 and 0.63 had a low apparent contact angle of approximately 25° and 30°, respectively. It indicated the slag samples could wet well on the Al2O3 substrate. The spreading of slag on the substrate was mainly ascribed to the decrease of surface tension at the initial stage. As the wetting process proceeded, Al2O3 dissolved into the slag forming an interfacial layer which gradually covered the substrate surface under the droplet and inhibited further dissolution of Al2O3. Good wettability and the dissolution of Al2O3 are two main factors that caused the corrosion of substrate. Separating the burden from the Al2O3 substrate was restrained after cooling, which would possibly bring severe sticking problems between the burden and alumina refractories.