Preparation and properties of uniform mixed and coated colloidal particles

Colloidal dispersions of uniform spherical particles of zirconium basic sulphate and zirconium oxy-basic carbonate were prepared by ageing zirconium sulphate solutions at elevated temperatures in the presence of urea. Different chemical compositions of the above products resulted when the ageing temperature was altered. Depending on the nature of the original solids, calcination at 800° C resulted in the formation of tetragonal or monoclinic zirconia. Under certain conditions a mixed phase, including cubic zirconia, has also been identified. The particle morphology was retained during these transformations. Coprecipitation in mixed solutions of zirconium and yttrium salts aged at 80° C yielded composite spherical particles of basic carbonate with a zirconium to yttrium ratio of the solid similar to that used in the initial solution. Zirconium basic sulphate particles coated with yttrium basic carbonate were prepared by ageing, in the presence of urea, a Zr₂(OH)₆SO₄ dispersion containing yttrium nitrate.