RESUMO
The influence of temperature in the buoyancy driven Rayleigh-Taylor instability of reaction-diffusion fronts is investigated experimentally in Hele-Shaw cells. The acid autocatalysis of chlorite-tetrathionate reaction coupled to molecular diffusion yields exothermic planar reaction-diffusion fronts separating two miscible reactant and product solutions. The resulting chemical front moves downwards invading the fresh reactants, leaving the products of the reaction behind it. The density of the product solution is higher than the reactant solution; hence, the traveling front is buoyantly unstable and develops density fingers in time (Rayleigh-Taylor instability) when the products are above the reactants. The kinetic constant of a chemical reaction varies due to thermal effects. This may stabilize the exothermic descending front when temperature is increased, so that the mixing zone decreases, modifying the fingering patterns, until it almost disappears. The authors study the influence of the temperature variation on the instability pattern figure observed in the chlorite-tetrathionate reaction for long times, corresponding to the nonlinear regime.