Reactions and Interactions between Tank Refractory and Glass Melt

Abstract

This presentation gives an overview and summary of the present knowledge on refractory-glass melt interaction phenomena. Different mechanisms, governing the wear of the refractory materials applied in glass melting tanks are presented. The interaction between the glass melts and refractory materials, leading to glass faults such as bubbles and knots are shortly discussed and some examples are given. Mass transfer processes, mainly diffusion of refractory components in to the glassmelt, determine the kinetics of refractory dissolution in the glass melt. The formation of a protective high viscous reaction-product layer between the refractory and the melt acts as a diffusion barrier. However, some refractory types in contact with a molten glass hardly show the formation of such aboundary layer: As far as solubility concentrations of refractory components in molten glasses are low, the refractory dissolution rate will be low, but then a highly viscous boundary layer will hardly be present. The stability and thickness of the protective boundary layer is determined by local convection flows caused by density differences in the melt, by external forces or caused by surface tension gradients. The process parameters, which govern the mass transfer processes and boundary layer thickness levels will be presented and some measures to reduce refractory wear will be given. The boundary layer, containing the viscous reaction product of the interaction between the melt and refractory material, can lead to glass faults such as cords, ream, cat scratches or knots. Refractory materials with a very low solubility in the molten glass can be applied to avoid the formation of the viscous boundary layers, lowering the potential for glass faults. However, the absence of a high viscous boundary layer may lead to increased diffusion rates and may cause an increased dissolution of the refractory. Α boundary layer containing a high concentration of dissolved aluminium oxide will decrease the solubility of zirconium oxide. Therefore Al₂O₃-ZrO₂ based refractory materials show a high resistance against ZrO₂ dissolution in glass melts. During the casting procedure of the refractory, the zirconia phase will crystallize into a strong structure, subsequently the alumina crystals and glassy (silicate) phase will fill the pores and voids. The glass phase contains alkali oxides in order to avoid formation of mullite phases from this phase. Bubbles can be formed in the boundary layer or in the silicate phase of a refractory material, due to electrochemical processes. These bubbles detach frequently from the refractory material, often pushing a small part of the highly viscous Silicate phase or refractory grains from there fractory into the glass melt. This mechanism will also influence the glass fault potential (bubbles, highviscous knots and stones) of refractory materials.