Synchrotron SAXS Study of the Mechanisms of Aggregation of Sulfate Zirconia Sols

Abstract

This is a systematic investigation, using in situ synchrotron small-angle X-ray scattering, of the mechanisms of aggregation of sulfate zirconia sols under different preparation conditions. We have studied the effects of the variations of acid, water, and sulfate contents on the process of aggregate growth. These effects were investigated using open and sealed sample cells. It was observed that two clearly different mechanisms govern the aggregation at the beginning and at advanced stages of the process. In the early stages, small needle-shaped clusters are formed. They have a time independent cross-section and progressively grow by increasing their length. At advanced stages, the initially isolated needle-shaped clusters start to build up a 3D structure, their aggregation being governed by the classical mechanism of diffusion-limited cluster aggregation (DLCA). The experimental results also suggested an effect of sulfate concentration on the structure of the aggregates. Even though the structures of the final sols vary markedly due to differences in the chemical and physical preparation conditions, our experimental results suggest that a single and remarkably simple model explains the aggregation process for all the studied solutions.

Understanding microstructural properties of Perovskite ceramics through their wet-chemical synthesis

“…Both groups found that cylinder shaped particles of constant cross-sectional radius formed in early stages of sol development. An analogous polydisperse cylinder model was used to analyze data [60], yielding comparable results as I obtained here. The measured radius of the cylinder crosssection equaled 0.46 nm.…”

“…Thus, only the central Zr-based framework contributes to scattering contrast. This may explain why the cross-sectional radius observed by me is lower than in studies where zirconia chloride, nitrate, and sulphate salts were synthesized [59,60]. In the zirconia sol L w increased only slightly from 1.79 to 1.85 nm.…”

“…They observed discrete [Zr 4 (OH) 8 24 Cl 12 species at a given pH-dependent equilibrium [58], with radii of gyration of 0.37 and 0.50 nm, respectively. Growth and aggregation of zirconium hydrous polymers were extensively studied under various experimental conditions with SAXS by Singhal et al [59] and by Riello et al [60]. Both groups found that cylinder shaped particles of constant cross-sectional radius formed in early stages of sol development.…”

“…Riello et al reported an analytical solution for the number distribution in ref. [60]. They modeled the scattering intensity by averaging the scattering contribution over the square of volume, which simplifies to integrating over L 2 for L-polydisperse cylinders.…”

Oxo‐Anion Modified Oxides

“…Zirconium salt solutions have a number of industrial uses [59,60] and their chemistry has been studied extensively [61][62][63][64][65][66][67][68][69][70][71][72][73]. In general, zirconium(IV) cations have a strong tendency to hydrolyze in aqueous medium, i.e.…”