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Pattern Selection in Three-Precipitate Liesegang Systems
Tamar Kanimian1, Pamela Nasr1,2, Rabih Sultan1
1Department of Chemistry, American University of Beirut, PO Box 11-0236 Riad El Solh, Beirut 1107 2020, Lebanon.
Abstract:
Liesegang patterns present a display of parallel stripes of precipitate that arise from the interdiffusion of coprecipitate ions in a gel medium. The bands observed in rocks are typical analogies of this phenomenon, and their composition is not restricted to the banded deposition of a single mineral. We here extend the study to a three-precipitate system, wherein Co2+, Ni2+, and Cd2+ cations are precipitated by the same anion (OH- from NH4OH) to form Co(OH)2, Ni(OH)2, and Cd(OH)2, respectively. The resulting pattern exhibits an alternation of compact mixed Co(OH)2 and Ni(OH)2 bands with granules of pure Cd(OH)2 between them. The obtained pattern confirms the generic type of (A + B)/C/(A + B)/C/(A + B)/C alternation conjectured analytically using the competitive particle growth (CPG) model and stability analysis.
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