EXPERIMENTAL STUDIES OF SPATIAL PATTERNS PRODUCED BY DIFFUSION-CONVECTION-REACTION SYSTEMS

The reactions between chlorite ions and a series of sulfur compounds a re bistable and autocatalytic in hypochlorous acid. Unstirred solution mixtures of chlorite ions and thiourea, for example, can generate a t ravelling wave of chemical reactivity at the surface from a point of i nitial perturbation These reactions are highly exothermic and exhibit a sharp temperature jump at the wave front (Delta T approximate to 3-5 degrees C). In stoichiometric excess of chlorite ions and in unstirre d solutions the travelling wave is followed by spatial patterns in the bulk of the solution. The spatial patterns, which show areas of varyi ng acid concentrations, can be sustained for up to 15 min. Formation o f the travelling wave is due to thermocapillary effects. The transitio n to patterns is fuelled by the coupling of buoyancy forces with therm ocapillary convection.