Particle Growth Kinetics in Zirconium Sulfate Aqueous Solutions Followed by Dynamic Light Scattering and Analytical Ultracentrifugation:  Implications for Thin Film Deposition

Abstract

Acidic aqueous solutions of Zr(SO4)2·4H2O can be used to deposit nanocrystalline zirconium oxide films on functionalized surfaces. Because zirconium hydrolyzes easily, such solutions are potentially unstable toward colloid formation and precipitation. Particle growth (conditions: 2 or 4 mM Zr(SO4)2, 0.4 or 0.6 N HCl, T = 323, 328, 333, or 343 K) was investigated using dynamic light scattering (DLS, in situ) and analytical ultracentrifugation (AUC, ex situ after quenching to 77 K and rethawing to 298 K). The AUC measurements revealed three stages of growth (all dimensions given are hydrodynamic radii): (1) coexistence of several discrete polynuclear complexes with r h = 0.43−2.29 nm; (2) particle size distribution with a single sharp maximum; (3) above r h ≈ 260 nm rapid transition to polydisperse medium with particles up to 100 μm. The DLS measurements revealed a linear increase of the hydrodynamic radii (z-average of particle population) from 5 nm to 1000−2500 nm with rates of 0.01−0.6 nm·s-1. The rates were proportional to the Zr(SO4)2 concentration, while the increase of the HCl concentration slowed or even inhibited growth. The apparent activation energy for this step was 136 kJ·mol-1. From the induction period before detection of first particles, initial growth rates (r h < 5 nm) were calculated to be ≈1 × 10-4 to 5 × 10-3 nm·s-1. Independent of the conditions, the two reaction rates were always proportional to each other, indicating linked rate laws. A 4 mM Zr(SO4)2 in 0.4 N HCl solution exhibited no particle growth at 323 K, but complexes of a constant radius (after 6, 12, and 24 h) of 1.16 nm were detected (AUC). Under these conditions, films were deposited and their thickness increased linearly with time, specifically by 2.1 × 10-4 nm·s-1. This rate corresponds to the initial growth rate in solution. In contrast to films grown from media with significant particle growth, these films showed surfaces free of attached particles, cracks, and holes.

Adsorption–desorption equilibrium investigations of n-butane on nanocrystalline sulfated zirconia thin films

“…[18,19] Further development by Fischer and co-workers [20,21] to prevent homogenous deposition, by lowering of the film deposition temperature, resulted in smooth, non-porous, continuous sulfated zirconia thin films. To optimise the deposition conditions the stability of the sulfated zirconia precursor solution was investigated, [22] as well as on the forces between the SAMs and zirconia particles in solution. [23] Pyrolysis of the deposited material in argon produces a polycrystalline layer of tetragonal sulfated zirconia, as shown by transmission electron microscopy (TEM).…”

Simultaneous Identification of Spectral Properties and Sizes of Multiple Particles in Solution with Subnanometer Resolution

“…[4–5] During an AUC experiment particles are separated hydrodynamically in a centrifugal field based on their different size, mass, density and frictional properties, whereby the process of sedimentation is captured by different detectors such as absorbance, interference or fluorescence optics. The resulting sedimentation data are then evaluated to give access to the particle size distribution (PSD).…”

Oxo‐Anion Modified Oxides

“…Heating promotes hydrolysis [87]. The kinetics of formation of larger particles in zirconium sulfate solutions have been investigated, the growth was accelerated at higher temperature, higher zirconium concentration and lower acid concentration [88]. From the available data it becomes clear that not only concentration, temperature and pH but also aging will play a role in formation of the primary solid.…”