Small-angle x-ray scattering studies of early-stage colloid formation by thermohydrolytic polymerization of aqueous zirconyl salt solutions

Early-stage processes involving the polymerization of zirconium species in aqueous solutions at elevated temperatures (∼100 °C) as well as colloid formation were studied. Small-angle x-ray scattering (SAXS) data were analyzed via Guinier, “longrods,” and Porod plots to determine particle growth kinetics and morphology. Our SAXS data suggest that zirconium tetramers and octamers polymerize into larger clusters and elongated-rod-(or needle)-shaped primary particles, which have a length of a few nanometers and a radius of gyration of cross section between 4 and 5 Å. Cube-shaped particles are aggregates of the needlelike primary particles. The transition from zirconium tetramer to a colloidal sol particle follows a mass-fractal growth (1 < fractal dimension, D