Autopsy of refractory lining in anode kilns with open and closed design

Aluminosilicate refractory lining constitutes a major part of anode baking kilns, and during anode baking the lining is exposed to harsh conditions which limits the lifetime. Here, autopsies of refractory linings from both an open and closed top furnace are reported aiming to determine the microstructural and mineralogical changes in the lining during operation. Significant variations in density and porosity were observed, both across the brick cross sections, but also for the vertical position in the lining. The chemical and mineralogical composition of the bricks were investigated by electron microscopy and X-ray diffraction. Only minor changes in the mineralogical composition of the materials were observed, and sodium originating from green anodes was only observed to a minor degree. Evidence of silicon oxide transport from the lower to the upper part of the linings was observed, reflecting the changes in reducing-oxidizing conditions during an anode baking cycle. The main degradation mechanisms in these linings were due to densification of the material over time, particularly the uneven densification across a lining wall. The present findings are discussed and related to the main differences in the two furnace designs.