EFFECT OF MULLITE-ZIRCONIA ADDITIONS ON THE CREEP-BEHAVIOR OF HIGH-ALUMINA REFRACTORIES

The creep behaviour of high-alumina refractories containing increasing amounts of a fused mullite-zirconia aggregate (MZA) of eutectic compo sition tvas studied experimentally. The MZA has been added with the in tention of improving the work of fracture and the thermal shock resist ance through microcrack toughening. The creep resistance was found to decrease with increasing MZA content. This was attributed to the forma tion of an increasing fraction of a substructure composed of small gra ins and an amorphous binder phase situated between the large agglomera te particles. Creep deformation mainly occurred within these fine-grai ned interagglomerate regions, but rate controlled by mullite formation kinetics as an accommodation process. This interpretation is substant iated by the measured values of the stress exponent (n = 1.2-2.7) and the activation energy for creep (Q approximate to 720 kJ/mol) and by t he finding that the creep rate was distinctly reduced by a preceding h eat treatment.