Features of Hydrogen Ignition over Platinum-Group Metals at Low Pressure

— In experiments on the ignition of the stoichiometric mixture of hydrogen and oxygen over strips of palladium and platinum foil at a total pressure of up to 200 Torr and initial temperature up to 300°C, the temperature of the foils during ignition was measured using an infrared camera and data on temperature dependence of metal resistivity. The temperature of the ignition initiated at 40 Torr over a heated palladium foil was shown to be ~100°C lower than that over a platinum foil. Even the minimal measured foil temperature (623°C) is sufficient to ignite the explosive mixture, implying that the influence of a catalytic reaction of hydrogen oxidation over the noble metals is insignificant in the case of initiated ignition. The presence of water vapor was found to prevent ignition. In the case of thermal ignition, it was found out that at a pressure of up to 180 Torr and 288°C the catalytic activity of the palladium foil is significantly higher than that of the platinum foil. The palladium foil activity is manifested in the competition of two processes: the emergence of local ignition centers on the foil, from which a combustion wave propagates, and a dark catalytic reaction of transformation of the explosive mixture into water.