Nucleation behavior in the precipitation of a sparingly soluble salt - AgBr

Abstract

Nucleation behavior during the early stages of the precipitation of a sparingly soluble salt (AgBr) was studied experimentally. Direct electron microscopy and light-scattering photometry were used to determine the average diameter and the number of the AgBr nuclei. For a given reactant addition rate R, the number of AgBr nuclei increased at first, reached a maximum, and then started to decrease. The slope of the ln-ln plot of the maximum number versus R was ∾ 1.5, indicating a bulk-diffusion growth mechanism for the AgBr nuclei. The average diameter of the nuclei was 0.008–0.015 μm, and changed with precipitation time. The supersaturation ratio S, calculated from the average nuclei diameter and the Gibbs-Thomson equation, showed the same behavior as that from a theoretical prediction. However, the calculated S values were significantly smaller than a critical value reported for the homogeneous nucleation of AgBr nuclei. These smaller S values can be explained qualitatively by a nuclei survival concept.