On the emission spectra from the hypersonic wave flow field in a stoichiometric hydrogen-Oxygen mixture

Abstract

Following the authors' investigation on the slow oxidation of methane and using methods previously described, the effects of surfaces of various kinds on the course of the reactions have been studied at temperatures from 450° to 500° C and pressures from 100 to 400 mm Hg. The amounts of the intermediates, formaldehyde and hydrogen peroxide, have been determined. The reactions are more rapid when carried out in silica vessels or in Pyrex vessels treated with hydrofluoric acid and washed with water. In soda glass vessels or in vessels coated with potassium chloride or alkalis, the reaction proceeds much more slowly and with a long induction period; hydrogen peroxide is destroyed. In the treated vessels, the order of the reaction and the activation energy were found to be 2·3 and 39·3 kcal respectively. The effect on the reaction rate of size of vessel and of packing was determined. Almost a threefold increase in surface / volume ratio did not alter the order of the reaction rate or the formaldehyde maximum, though it slightly increased the hydrogen peroxide maximum. Packing inhibited the hydrogen peroxide formation. Experiments were also made in vessels coated with lead monoxide, boric oxide and silver and in a vessel of pure gold. Lead monoxide eliminated the peroxide and greatly diminished the reaction. Boric acid behaved rather similarly to a Pyrex surface treated with hydrogen fluoride. The gold surface prevented reaction, even at 500°C and 600 mm initial pressure. The effects of diluents such as nitrogen, argon and helium were investigated. The reaction rate and the percentage of formaldehyde increased slightly with increase in percentage of diluent. Water was found to have a slight promoting effect which was rather greater than that of carbon dioxide. The effect was relatively greater in a potassium chloride coated vessel, indicating that the diluent prevented access to the destructive surface. These and other results are discussed in relation to work on methane oxidation by Norrish, Hoare and Walsh, and others. It is concluded that other intermediates besides formaldehyde are controlling the rate and, as in the hydrogen-oxygen reaction, the radical HO2 plays an important part through the reaction HO2 + CH4→H2O2 + CH3. Alkaline and lead monoxide surfaces are particularly active in destroying HO2. As in the hydrogen-oxygen reaction, H2O2 can also lead to branching of a higher kinetic order than that introduced by OH radicals.