Thermal decomposition and crystallization of aqueous sol-gel derived zirconium acetate gels: Effects of the precursor solution pH

Crystalline zirconia has previously been formed by desiccation and pyrolysi s of a pH 3.4 zirconium acetate precursor solution. In this study, amorphou s gels were formed by desiccation of zirconium acetate precursor solutions at pH 0.9 to 3.4 obtained by adding hydrochloric acid and at pH 8.0 by addi ng ammonium hydroxide to the available pH 3.4 precursor solution. The conce ntrations of the uncomplexed zirconium ion and the 1 : 1 and 1 : 2 zirconiu m acetate complexes varied with pH. Decomposition of the amorphous gel and its structure evolution to form crystalline zirconia by pyrolysis were stud ied. Several decomposition and structure transition temperatures occurring in the pyrolysis and the polymorph distribution in the pyrolysis products w ere dependent on the pH of the precursor solution. These variations of stru cture evolution with pH were also related to the relative concentrations of specific zirconium complexes in the precursor solutions. Removal of carbon by pyrolysis was improved by adding hydrochloric acid or ammonium hydroxid e to the pH 3.4 precursor solution.