Multicomponent Convection Induced by Fronts in the Chlorate-Sulfite Reaction

An application of a new method is presented for the measurement of the temperature profiles of chemical waves propagating through a solution. Using solutions of thermocolor materials, the temperature distribution caused by the heat released in the propagating chlorate oxidation of sulfite was visualized and recorded using digital image processing methods. After calibration, the temperature gradient was calculated from the gray scale value in a digitized image. Extensive multicomponent convection ('fingering') was induced by descending fronts. Only ascending fingers were observed because of the large thermal gradient that suppressed descending ones. The characteristics of the temperature profile were determined as a function of initial sulfite and chlorate concentration, and tube diameter. Unusual behavior was observed when the fronts propagated under conditions of continuously changing diameter in a conical vessel. Fingering occurred periodically in a front descending in a flask with an increasing diameter. However, when a front propagated down in flask whose diameter decreased, no multicomponent convection was observed.