Front Propagation in Patterned Precipitation. 3. Composition Variations in Two-Precipitate Stratum Dynamics

Abstract

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. At equal concentrations, periodic oscillations in Co(OH)2 composition appear over consecutive bands. The time evolution of the total Co(OH)2 mass percent (over the entire pattern of strata) passes through a maximum. The dynamics of this complex system has been simulated by theoretical calculations using the model of Müller and Polezhaev, modified by Al-Ghoul and Sultan in a series of two papers in J. Phys. Chem. A; the present paper is the third in the series. The simulations capture the essential features of the experimentally observed dynamics.

Self-organization in precipitation reactions far from the equilibrium

“…Additional observations in these systems include the occurrence of dynamic Liesegang patterns, temporal chaos in the number of precipitation bands, and a nontrivial spatial distribution of these bands ( Fig. 4D ) ( 162 – 164 ).…”

Rhythmic precipitate patterns and fractal structure

“…Of particular interest and richness in the pattern display, are systems where multiple co-precipitate ions of one kind (cations or anions) are involved in the dynamics. Two-precipitate Liesegang systems have been studied [32,33], and sometimes classified [34]. The onset of real complex rhythmicity starts with three-component systems.…”

Design of equidistant and revert type precipitation patterns in reaction–diffusion systems

“…It has been supposed in all models ever developed to describe pattern formation phenomena that the given threshold values are constant in space and time in order that the produced bands (zones, rings) may satisfy the existing regularities. [38][39][40][41][42][43][44][45][46][47][48][49][50] Constant threshold values also require that the spatial distribution of the pattern be quasiperiodic. Therefore, an appropriate temporal and/or spatial control of the coagulation threshold can result in different types of patterns compared to classical and regular ones.…”