INFLUENCE OF ATMOSPHERE ON CRYSTALLIZATION OF ZIRCONIA FROM A ZIRCONIUM ALKOXIDE

Dibutoxybis (acetylacetonata) zirconium, a difunctional zirconium alko xide, was polymerized at 130 degrees C for 5 h in vacuo to produce oli gomers that could be pyrolyzed to form a tetragonal zirconia (t-ZrO2), metastable at room temperature. This metastable phase was retained co nsiderably below the equilibrium transformation temperature (similar t o 1200 degrees C) without the use of dopants. Comparative pyrolysis of the oligomers between 600 and 900 degrees C in either flowing O-2 or N-2 for processing times under 12 h indicated t-ZrO2 nucleated first. Pyrolysis in oxygen facilitated transformation to the monoclinic symme try, whereas pyrolysis in nitrogen demonstrated retention of the tetra gonal phase. The formation of oxygen vacancies during pyrolysis, their role in stabilizing the metastable tetragonal phase, and contribution s of O-2 and crystallite size in the polymorphic transformation are di scussed.