Fray International Symposium edition:1 location:Cancun, Mexico date:27 November-1 December 2011
Chemical degradation of a refractory lining is most commonly considered as a dissolution process whereby the refractory components dissolve into the liquid slag. Hence, the lining thickness is steadily reduced. The dissolution process is not merely limited to the slag-refractory contact surface, but due to capillary forces, also occurs inside the porous refractory brick. This paper describes how the interaction between slag and brick during infiltration, changes the slag composition as a function of infiltration depth. Knowledge about the selective filtering of certain slag components by a refractory brick is indispensible in predicting the chemical degradation, especially when significant changes in slag composition are present. In this case, often seen with non-ferrous slags, the situation in the interior of the brick cannot be adequately predicted based on the global slag and brick composition. To study this “filter effect”, a magnesia-chrome finger in contact with a PbO-SiO2-ZnO-Al2O3-CaO liquid slag at constant temperature is tested. Using SEM-EDS analyses the slag composition as a function of infiltration depth is measured. Based on the microstructure at different positions, the interactions leading to modified slag compositions are determined. They can be classified into two categories: (1) slag components that diffuse into the brick phases and (2) reaction between slag components and dissolved brick components forming new solid phases. Slow diffusion prevents the slag from reaching its equilibrium concentration before it infiltrates further in the brick. The slag composition, therefore, not merely depends on the occurring reactions but also on the relative diffusion rate in the refractory phases (compared to the slag infiltration rate).