Convective Chemical Fronts in the 1,4-Cyclohexanedione-Bromate-Sulfuric Acid-Ferroin System

Traveling waves were investigated in the Belousov−Zhabotinsky reaction in which 1,4-cyclohexanedione was the substrate. Isothermal density change (Δρc) and reaction enthalpy were determined. Δρc is positive, while the reaction enthalpy is negative; therefore, double-diffusive convection was expected according to the Pojman−Epstein model. Experiments were carried out in tubes and in spectrophotometric cells. In tubes the effect of the diameter and the orientation of the tube on the wave velocity and on the wave shape was studied; gravitational anisotropy and the expected double-diffusive convection were found. Experiments in cells were compared to the calculations of Wu et al. (Wu, Y.; Vasquez, D. A.; Edwards, B. F.; Wilder, J. W. Phys. Rev. E 1995, 51, 1119−1127). They predicted a critical cell width under which no simple convection should occur. However, because double-diffusive convection was observed, their calculations are not directly applicable.