Silver Halide Precipitation and Colloid Formation
Ingo H. Leubner, American Chemical Society Symposium Series, No.200; Colloids and Surfaces in Reprographic Technology. Michael Hair and Melvin D. Croucher, Editors, p.81-92 (1982)
Formation of colloidal silver halide dispersions (photographic emulsions) is one of the principal steps in the preparation of conventional photographic materials. At the same time, it presents scientific challenges, some of which are common to general colloid formation, such as control of crystal size, size distribution, and morphology. In the precipitation, two processes are of special interest, i.e., formation of stable crystal nuclei (nucleation) and subsequent growth. This sequential process I specifically involved in the double-jet precipitation of silver bromide.
For this case, a theoretical model of nucleation was derived, which is based on a dynamic mass balance and a growth mechanism, which includes bulk diffusion and the Gibbs-Thomson effect. In qualitative agreement with this theory, experiments showed that the number of stable nuclei increased with increasing reactant addition rate and decreased with increasing solubility and temperature. Subsequent growth of the crystals can be described by a simple mass-balance equation, as long as the growth rate is below a limiting maximum growth rate above which renucleation occurs. The growth rate was related to a growth model based on bulk diffusion and crystal number density. For AgBr, the morphology is dependent on the pAg of the crystal suspension.