Pattern Selection in Three-Precipitate Liesegang Systems.

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 Co, Ni, and Cd cations are precipitated by the same anion (OH from NHOH) to form Co(OH), Ni(OH), and Cd(OH), respectively.

Rift Gaps in Chemical-Wave Network Systems.

We carry out experiments in diffusion-precipitation systems in a framework with multiple diffusion sources. The advancing precipitation fronts reach a point where they stop, leaving a rift or gap between the precipitate zones. In a similar setting, fractal metal deposits emerging from various reduction centers were synthesized.

Polygonal boundary gaps in multiple diffusion source precipitation systems in gel media.

We investigate multiple reaction-diffusion processes that engender the formation of distinct precipitation zones. In this paper, we carry out various original precipitation reactions in a gel medium, wherein the interdiffusion of the co-precipitates occurs from various sources arranged in a symmetric framework in 2D Petri dishes. The distinct precipitation zones are separated by clear polygonal boundaries, in congruence with the spatial distribution of the diffusion holes hosting the outer electrolyte.

Simulation of geochemical banding: Theoretical modeling and fractal structure in acidization-diffusion-precipitation dynamics.

In an earlier work, we presented an experimental study wherein reaction-transport processes were forged in a real rock medium. Zonation of CaSO_{4}-rich and CaSO_{4}-depleted domains were obtained and characterized. In the present study, we present a theoretical model to simulate the reaction-diffusion processes underlying the dynamics of the system.

Random Spacing between Metal Tree Electrodeposits in Linear DLA Arrays.

When we examine the random growth of trees along a linear alley in a rural area, we wonder what governs the location of those trees, and hence the distance between adjacent ones. The same question arises when we observe the growth of metal electro-deposition trees along a linear cathode in a rectangular film of solution. We carry out different sets of experiments wherein zinc trees are grown by electrolysis from a linear graphite cathode in a 2D film of zinc sulfate solution toward a thick zinc metal anode.

Revisited Chaos in a Diffusion-Precipitation-Redissolution Liesegang System.

Co(OH) Liesegang periodic precipitation systems exhibit oscillations in the number of bands due to band redissolution in high NHOH concentration. We revisit the problem previously considered (Nasreddine and Sultan, J. Phys.

Ag fractal structures in electroless metal deposition systems with and without magnetic field.

Metal electrodeposition systems display tree-like structures with extensive ramification and a fractal character. Electrolysis is not a necessary route for the growth of such dendritic metal deposits. We can grow beautiful ramification patterns via a simple redox reaction.

Routes to fractality and entropy in Liesegang systems.

Liesegang bands are formed when solutions of co-precipitate ions interdiffuse in a 1D gel matrix. In a recent study [R. F.

Fractal structures in two-metal electrodeposition systems II: Cu and Zn.

In this second part of our study on fractal co-electrochemical deposition, we investigate the Cu-Zn system. Macroscopic and microscopic inspection shows a sensitive dependence of the morphology of the final pattern on initial concentrations. The pattern is seen to undergo a transition from classical dendrites to randomly ramified deposits, with each slight increase in [Cu(2+)](0), while [Zn(2+)](0) is maintained constant.

Fractal structures in two-metal electrodeposition systems I: Pb and Zn.

Pattern formation in two-metal electrochemical deposition has been scarcely explored in the chemical literature. In this paper, we report new experiments on zinc-lead fractal co-deposition. Electrodeposits are grown in special cells at a fixed large value of the zinc ion concentration, while that of the lead ion is increased gradually.

Mechanism of revert spacing in a PbCrO4 Liesegang system.

Periodic precipitation of sparingly soluble salts yields parallel Liesegang bands in 1D whose spacings obey either one of two known trends. The overwhelming trend is an increase in spacing as we move away from the junction, while some systems display a decrease in spacing as the bands get further away from the interface. The latter trend is much less common and is known as the revert spacing law.

Band, target, and onion patterns in Co(OH)2 Liesegang systems.

The study of morphology and shape development has gained considerable interest in certain sciences, notably biology and geology. Liesegang experiments producing Co(OH)2 stratification are performed here, in one, two, and three dimensions for comparison of the pattern morphologies. We obtain well-resolved bands in one dimension, target patterns (rings) in two dimensions, and onion patterns (spherical shells) in three dimensions.

Ring morphology and pH effects in 2D and 1D Co(OH)2 Liesegang systems.

We study the factors that affect the morphology of Co(OH)(2) Liesegang rings, in a way to obtain concentric rings with large spacing, upon an appropriate variation in the experimental conditions. Such well-resolved patterns are obtained under optimum conditions: decrease in the concentration of the outer electrolyte, increase in the concentration of both the inner electrolyte and the gelatin in the hosting gel medium, and increase in the strength of a constant radial electric field applied across the pattern domain. The effect of pH on the bands in a 1D Co(OH)(2) Liesegang pattern is also investigated.

Propagating fronts in thin tubes: concentration, electric, and pH effects in a two-dimensional precipitation pulse system.

In this paper, we studied the dynamics of a CaCO3 precipitate deposition pulse in a thin, long tube connecting two reservoir sinks of coprecipitates. The pulse profile, as well as the time t(c) and distance x(c) of the first appearance of precipitate, is studied as a function of the initial concentration of CO(3)(2-) in the right reservoir, [CO(3)(2-)](0), and later as a function of an applied external electric field at different voltages. The time variations of the pulse location and the pH at the center of the tube are determined.

Front propagation in patterned precipitation. 3. Composition variations in two-precipitate stratum dynamics.

This paper is a study of the composition dynamics of Liesegang band strata of Co(OH)2 and Ni(OH)2 from NH4OH, with redissolution by complex formation with ammonia. At a fixed time, the cobalt hydroxide composition was found to exhibit a random variation with band number, yet within a general overall decrease. The decrease with band number becomes more pronounced as the initial concentrations of Co2+ and Ni2+ get closer to each other.

Patterns with high rhythmicity levels in multicomponent Liesegang systems.

Liesegang banding is the display of rhythmic strata of precipitate as co-precipitate ions interdiffuse in a gel medium. Complex periodic patterns as well as aperiodic structures could emerge, notably in systems where more than one salt is precipitated. The use of three cations (Co2+) Ni2+, and Mg2+) in the banded precipitation of their hydroxides resulted in an unusual pattern with a consistently increasing rhythmicity.

Effect of competitive complex formation on patterning and front propagation in periodic precipitation.

The Co(OH)2 Liesegang pattern (from Co2+ and NH4OH) propagates in space by periodic band formation at the head due to precipitation and band disappearance at the tail due to dissolution in excess NH4OH. Introduction of Ni2+, which competes with Co2+ for complex formation with ammonia, into the system led to several interesting observations: slower propagation, fewer bands, and increased spacing between them. Above a cutoff concentration of Ni2+ (0.