Dynamics of Liesegang band formation in a multiple-precipitate toroidal reactor

Abstract

A small toroidal reactor is filled with CoCl2·6H2O and 1% agar gel solution. Two outer electrolytes, of suitably chosen concentrations, are employed to diffuse into the gelled solution: from one end NH4OH to precipitate Co(OH)2, and from the other end Na3PO4 to precipitate Co3(PO4)2. The resulting diffusion-precipitation (Liesegang) pattern exhibits unusual trends wherein gaps and formation of cobalt phosphate hydrates are observed. The different precipitates are characterized by IR, X-ray and SEM techniques. Using the well-known generic empirical laws, we compute the band locations, and represent them graphically within the torus, for two experiments with different sets of initial concentrations.