Convection-Induced Fingering Fronts in the Chlorite–Trithionate Reaction

Based upon a former study, the chlorite–trithionate reaction can avoid the side reactions arising from the well-known alkaline decomposition of polythionates, making it a suitable candidate for investigating spatial front instabilities in a reaction–diffusion–convection system. In this work, the chlorite–trithionate reaction was investigated in a Hele-Shaw cell, in which fingering patterns were observed over a wide range of reactant concentrations. A significant density increment crossing the propagating front indicates that the fingering pattern is generated as a consequence of the buoyancy-driven instability due to the density changes of solute when the gap thickness is less than 4 mm. The velocity of the steepest descent in the propagating front depends almost linearly on the gap thickness but displays a saturation-like profile on the trithionate concentration as well as a maximum on the chlorite concentration. Numerical simulation using the Stokes–Brinkman Equation coupled to the reaction–diffusion processes, including hydrogen ion autocatalysis and consumption, reproduces the observed fingering fronts.