The influence of precipitation variables on zirconia powder synthesis

The scope of this work consisted of producing pure zirconia, yttria-stabilized zirconia and ceria-stabilized zirconia powders from zirconium oxychloride and yttrium and cerium chlorides using urea as precipitating agent and polyacrylic acid as dispersing agent. A factorial analysis was designed to study the effect of some precipitation variables (temperature, precipitation time, urea concentration, yttrium chloride concentration, cerium chloride concentration and polyacrylic acid concentration) on the characteristics of the dispersion (aggregate size and electrophoretic mobility of aggregates) and of the zirconia powders (crystalline structure). This study allowed the discussion of the precipitation mechanisms. raphs obtained from SEM revealed that, using urea as precipitating agent, spherical primary particles were produced with a size range between 300 and 500 nm. suggested that the structure of the dispersion species strongly influenced the crystalline structure of calcined zirconia powders. These species are zirconium polymers that can assume a three-dimensional structure similar to fluorite that favors the retention of tetragonal phase. The decomposition of urea supplied the solution with OH− ions at a slow rate enabling the formation of the three-dimensional structured zirconium polymers. On the other hand, polyacrylic acid prevented the formation of these three-dimensional structures possibly because polyacrylate ions adsorb on sites of the polymeric structure previously available for polymerization reactions. le of polyacrylic acid as a dispersing agent was evaluated. In the zirconia–yttria system, electrosteric repulsion mechanisms would be responsible for a better dispersion, whilst in the zirconia–ceria system, the same effect would be associated with steric repulsion mechanisms.