Propagating Fronts and Morphological Instabilities in a Precipitation Reaction

Abstract

Precipitation processes are essential in many natural systems, especially in biomineralization and in geological pattern formation. We observe temporal oscillations in the total mass of the precipitate, the formation of propagating and annihilating waves, and morphological instabilities in a thin precipitation layer in a two-side-fed gel reactor containing the AlCl3/NaOH reaction-diffusion system. Contrary to the standard Liesegang patterns, these structures form in the lateral direction at the meeting of the counterpropagating diffusion fronts of the electrolytes. The two main ingredients of the system are the amphoteric precipitate and the cross gradient of the chemicals due to the fixed boundary conditions. Simulations with a four-variable precipitation/redissolution model qualitatively reproduce the oscillations in the total mass of the precipitate and point out the stratified three-dimensional structure of the precipitate.

Self-organization in precipitation reactions far from the equilibrium

“…( H ) Pattern selection in the aluminum hydroxide system as a function of reactant ion concentration [adapted with permission from Dúzs et al . ( 171 )]. ( I ) Cusp-like front in HgI 2 system [adapted with permission from Ayass and Al-Ghoul ( 173 )].…”

“…Moreover, collisions between these waves cause mutual annihilation. Further experiments were conducted in a flow reactor that continuously supplies the reactant ions and thus maintains nonequilibrium chemical conditions ( 171 ). In this system, a pattern-free precipitate layer forms after a short induction period but then swiftly develops patterns similar to those shown in Fig.…”

Synthesis and composition modification of precipitate tubes in a confined flow reactor

“…[2][3][4][5] Besides the simple injection process, there are various methods which can influence the quality of the forming tubes such as bubble guidance, 6,7 and growth in the cation-exchange membrane 8,9 or in gel medium. 10,11 Haudin et al have presented the chemical garden pattern formation in a quasi two dimensional horizontal confined flow reactor (so-called Hele-Shaw cell) by applying the reactions of different metal ions with silicate solution. 12 By comparing the macroscopic precipitate tube structures, it was observed that the chemical nature of the reactants does not play a key role in the tube growth at extremely high concentrations and flow rates.…”

Magnetic‐Field‐Manipulated Growth of Flow‐Driven Precipitate Membrane Tubes

“…Complex precipitation patterns and instabilities can be obtained by coupling precipitation reactions and diffusion . However, a higher level of hierarchy and a better control on the system may be achieved by introducing other transport processes, such as osmosis, migration, or convection.…”

“…Complex precipitation patterns andi nstabilities can be obtained by coupling precipitationr eactions andd iffusion. [1][2][3] However,ahigher level of hierarchya nd ab etter control on the system may be achieved by introducing other transport processes, such as osmosis, migration, or convection. In this context,the growth of three-dimensionali norganic silicate precipitate tubes, so calledc hemical gardens is focusedf rom many different aspects.…”