HIGH-PURITY ZIRCONIA POWDERS VIA WET CHEMICAL-PROCESSING - A COMPARATIVE-STUDY

Comparison has been made of the achievable purity levels and agglomeration characteristics of zirconia powders obtained via six different wet chemical routes where the starting material was an impure Zr-oxychloride solution obtained from Indian zircon sand. For the highest purity (2-15 ppm of other oxides except Hf), two routes were found to be effective: crystallization of the oxychloride via the basic sulphate, or double crystallization of the oxychloride, followed by dissolution and hydroxide precipitation. The average agglomerate size was the largest (10-15 mum) for the powders obtained by direct decomposition of the basic sulphate at 1000-degrees-C, though the size distribution was narrow and distinctly monomodal. For smaller agglomerates (1.5-2.5 mum), on the other hand, the size distribution was very wide. Calcination at 800-degrees-C of powders obtained via hydroxide precipitation from a solution always yielded only tetragonal zirconia as the crystalline phase.