Experimental studies of spatial patterns produced by diffusion-convection-reaction systems

The reactions between chlorite ions and a series of sulfur compounds are bistable and autocatalytic in hypochlorous acid. Unstirred solution mixtures of chlorite ions and thiourea, for example, can generate a travelling wave of chemical reactivity at the surface from a point of initial 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 unstirred solutions the travelling wave is followed by spatial patterns in the bulk of the solution. The spatial patterns, which show areas of varying acid concentrations, can be sustained for up to 15 min. Formation of the travelling wave is due to thermocapillary effects. The transition to patterns is fuelled by the coupling of buoyancy forces with thermocapillary convection.