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A study was undertaken to examine the crystallite size effect on the low-temperature transformation of tetragonal zirconia. Zirconia was prepared by precipitation from a solution of zirconium tetrachloride by adding ammonium hydroxide to produce a pH of 2.95. Portions of the sample, after drying, were calcined at 500°C for various time intervals. Phase transformation was followed by X-ray diffraction; the data show that the tetragonal phase was initially formed and it was transformed to the monoclinic phase at longer periods of calcination. It was observed by TEM particle size and XRD crystallite size that the transformation does not appear to be due to a critical particle size effect. [Key words: particle size, zirconia, X-ray diffraction, transmission electron microscopy, phase transformations.]

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A batch of zirconia was prepared at a pH of 2.95 using a sol-gel technique. The crystal structures formed during 500 ~ calcination was followed by X-ray diffraction. The tetragonal phase was the major component after the initial calcination period of 15.5 h; however, it gradually transformed to the monoclinic crystal form during 200 h of calcination at 500 ~ Electron microdiffraction was employed in the present investigation to determine the crystal structure of individual particles, and to identify whether these particles contained twin variants. A technique has been developed to get a dispersion of agglomerated particles by condensing and spreading the beam on the agglomerates at 200 kV. The data revealed that some of the individual zirconia particles are featureless and some of them appear to contain single or multiple twin variants.