Direct and Reverse Chemical Garden Patterns Grown upon Injection in Confined Geometries

Spatial precipitate patterns resulting from the growth of chemical gardens in a confined quasi-two-dimensional horizontal geometry are studied experimentally upon radial injection of a solution of one reactant into the other at a fixed flow rate. We show that, at large enough concentrations, the patterns are different when injecting a solution of cobalt chloride into a solution of silicate (the direct case) than in the reverse case of silicate displacing the metal-ion solution. We discuss the possible influences of the viscosity ratio, density difference, pH, and concentrations of the reactants on the dynamics observed and characterize quantitatively the growth of some typical structures.