CORROSION MECHANISMS OF ZIRCONIA/CARBON BASED REFRACTORY MATERIALS BY SLAG IN PRESENCE OF STEEL

Abstract

Zirconia is usually utilised in Submerged Entry Nozzle (SEN) in the slag contact zone, because of its high resistance to corrosion. However inconsistency of component performance and apparently erratic behaviours, in terms of corrosion rate, are frequently experienced. An important cause of the unexplained variability of component performance is the typical trial-and-error approach used to develop materials for the specific applications, and the “Darwinian selection” for the choice of the most suitable material despite the fact that a number of studies are available in literature. As a matter of fact, although almost all the mechanisms that have been proposed are based on some form of cyclic mechanism where the oxide is attacked by the slag and the exposed graphite is then attacked by the metal, contradictory conclusions can be often found about specific features. It is not to be excluded that contradictory results could be dependant on the experimental conditions used. In this paper laboratory experiments have been carried out, using together slag and steel, in order to clarify their role on the global corrosion mechanism. The results showed that, besides the dissolution of carbon in steel and oxide in slag, other phenomena contribute to the corrosion. In particular the experiments put in evidence the critical role of steel in dissolving the products of reactions between slag components and carbon, pushing the attack of slag to carbon. The consequence is that the corrosion phenomenon is complex, and parameters such as activity of slag components, porosity of refractory matrix, characteristics of carbon material are involved in the tendency of the carbon to react with slag, hence on the global corrosion rate.