The Precipitation of Barium Chromate with Slow Development of Supersaturation. Kinetics of the Crystal Growth

Abstract

AbstractSlow barium chromate precipitation was studied in well‐stirred solutions — final concentration 0.002 mole 1−1 — at 20°C at mixing rates varying from 0.2 to 2 · 106 mole 1−1 sec−1; the kinetics of the crystal growth process were studied by chemical analysis and by optical microscopy. The crystal growth started after induction periods; regular growth then took place on the nuclei formed during these periods. For the main growth, up to about seventy percent precipitation time, growth rates at any time depended on the (residual excess solute concentrations in solution)2. Immediately after the induction periods, crystal lengths varied with growth time according to the relation, equation image for the main growth, crystal lengths varied with growth time according to a more complex relation, equation image where kl is the rate constant for surface growth, Rc is the rate of development of metal salt concentration and K is a constant that depends on the number of precipitate crystals.After some growth time τ = τ*, when lτ = lτ*, all fresh solute added to the solution was utilised immediately and was deposited onto the growing crystals; then, for the final thirty percent precipitation, crystal lengths varied with growth time according to the relation, equation image .