Orientation-dependent density fingering in an acidity front

Dependence of dispersion relation on the orientation of front propagation for an acid-catalyzed reaction was determined by carrying out density fingering of the chlorite-tetrathionate reaction in a Hele-Shaw cell. Planar fronts were initiated electrochemically by applying 3 V potential difference between a pair of thin Pt-wire electrodes. Results indicated that in the chlorite-tetrathionate reaction the downward propagating planar fronts were hydrodynamically unstable. This gave rise to a fluid flow which represented a small wave number instability, with the higher modes remaining stable as a result of the diffusive flux of the reaction.