Sonochemistry of Aqueous Solutions: H2-O2 Combustion in Cavitation Bubbles

Article abstract of DOI:10.1021/j100297a038

Water was insonated with 300-kHz ultrasound under H2-O2 mixtures of various compositions and the rates of gas consumption and of H2O2 formation were measured.These rates have pronounced maxima at H2:O2 ratios of 1:3 and 2:1 in the solution.The chain length of the combustion reaction is only about 10.This is explained by the high ratio of surface to volume of the tiny cavitation bubbles as intermediate radicals rapidly reach the interface where they no longer propagate the chains.The rate of Fe²⁺ oxidation in the absence and presence of Cu²⁺ ions was also investigated as well as the formation of carbon dioxide in dilute formate solution.The yields of OH, HO2, and H2O2 in the bulk solution were derived from these scavenger experiments.Fe³⁺ ions are not reduced when a solution is insonated under pure H2, and it is concluded that H atoms do not move to a substantial extent from the gas bubbles into the solution.The number of chemically active cavitation events is estimated as 1E9 L^-1 min^-1.