EFFECT OF CHEMICAL AND HEAT-TREATMENT ON THE TETRAGONAL-TO-MONOCLINIC TRANSFORMATION OF ZIRCONIA

A rapid in situ diffraction technique, synchrotron radiation-energy dispersive diffraction, has been used to obtain direct information on the kinetics of the tetragonal-to-monoclinic transformation temperatures for zirconia synthesized by heating the hydroxide up to temperatures between 900 and 1300-degrees-C. In all cases the monoclinic phase appears only during the cooling stage. The effects of chemical (hydroxide preparation-pH) and heat treatments (top dwell temperature and dwell time) have been investigated. The transformation temperature increases with both top temperature and dwell time. For the lesser heat treatments (generally temperatures <1000-degrees-C) the high-pH material displays the higher transformation temperatures, whereas with greater heat treatments (generally temperatures >1000) the low-pH material displays the higher transformation temperatures. These data do now give reliable indications on how to design a required metastability into the final room temperature product.