Electron Microscope Observations of the Initial Stages in the Hydrolytic Polymerization of Zirconyl Chloride

Abstract

ELECTRON microscopic studies of colloidal inorganic materials have so far been limited to observing the final products of the process that produces the colloid. But because colloidal zirconia is produced by a multi-stage process we preferred not to use this method in the work that is reported here. Earlier workers^1,2 had shown that extensive polymerization of Zr(IV) ions took place as hydrogen ions were liberated from the aqueous complex, and a degree of polymerization between three and four in 1 M HCl was deduced from ultracentrifuge studies³. In concentrated solutions of zirconyl chloride⁴ and crystalline zirconyl chloride octahydrate⁵, the fundamental structural unit has been postulated to be a cyclic tetrameric ion [Zr(OH)₂4H₂O]⁸₄⁺; further polymerization of these ions could be brought about by continued boiling of an aqueous solution⁶. What we have done is to boil 0.055 molar zirconyl chloride solutions under reflux and to remove 10 ml. samples at specific time intervals. The rate of polymer and colloid formation was much reduced as the samples cooled to room temperature. To avoid spurious effects during the transfer of the samples to electron microscope specimen mounts, the samples were sprayed on to the mount from a glass atomizer. This method of preparation minimized evaporation effects, which would be greater in transferring a drop of sample and leaving it to dry on an electron microscope mount.