Fused cast refractories are the most important glass melt contact materials. They contain a varying amount of glassy phase which is necessary to lower the fusion temperatures of the batch and to stabilize the material's microstructure as in the case of fused cast AZS and of high zirconia. A glassy phase between the crystals of the refractory compounds remains the weakest constituent of the material, vunerable to corrosion attack. However, glassy phase exuding from fused cast refractories during service often causes several glass defects such as blisters, knots, stones and cords. In this paper the exudation behaviour of fused cast AZS, high zirconia and alumina and their influence on the formation of glass defects is discussed. Some examples of experimental results concerning the influence of various factors are presented.
