Destabilization of Zirconia by Cyclic Heating

Calcium-stabilized zirconia refractories used in a heatexchange furnace were found to lose their mechanical strength after a period of use. Mechanical deterioration was most severe in the positions in which the temperature cycled between 1600 and 2000 deg F. Since the zirconia used was only partly stabilized and because maximum destabilization occurred in the range in which monoclinic zirconia inverts to tetragonal zirconia, it appears that the cubic zirconia was destabilized by the inversion of nonoclinic and tetragonal zirconia. A sample of completely stabilized zirconia (100% cubic) was not affected by 100 cycles in laboratory tests. (P.C.H.)