Kinetics of precipitation in gel

The formation of a precipitate in a gel by reaction between two components entering the reaction zone by diffusion is explained as a result of the interplay between global diffusion through the gel and particle growth kinetics. The theory accounts quantitatively for the length of the induction period, the position of the precipitate in the gel, the equivalence rule, and the apparent critical concentration. The kinetics of particle growth are shown to be more influenced by diffusion at nonequivalent concentrations than at equivalent concentration, the deficient component being more important for the rate-control than the excessive component. Diagrams showing the dependence of the particle growth rates on the concentrations of the two components are constructed and are shown to have a ridge at equivalent concentrations. The theory is thoroughly tested by means of experimental data for BaSO4. Also data for AgCl, AgBr, Ag2CrO4, MgF2, BaMoO4 and PbCrO4 are found to agree with the theory