The influence of zircon in a model aluminosilicate glass tank forehearth refractory

Abstract

Standard aluminosilicate forehearth refractories are normally fabricated with a small proportion of zircon to improve their performance. To identify possible bases for the action of the zircon, fine-grain aluminosilicate materials of similar compositions were prepared and tested, to model the behaviour of the finer grain bond phase in the standard refractory. The reference materials contained a range of proportions of zircon, and further sets of materials were prepared in which the zircon was replaced by varying amounts of very fine alumina, silica or zirconia powders. The alumina and zirconia powders increased the strength at room temperature of the base aluminosilicate, with zirconia having the largest effect; silica had only a slight effect. It appears that the zircon increases strength through three mechanisms: the reduction in porosity brought about by improved efficiency of the particle packing, a faster rate of sintering of the fine grained bond phase, and a transformation toughening of the bond phase, caused by tetragonal zirconia formed in situ by high temperature dissociation of the zircon