Effects of impurities on shock wave stability and structure in ionizing monatomic gases

The effects of impurities - hydrogen, water vapor, and sodium chloride - on shock wave stability and structure in ionizing-argon and krypton flows were investigated. The addition of small amounts of hydrogen to test gas stabilizes the entire flow and at the same time drastically shortens the relaxation length to about 1/3 of the original value in argon and 2/3 in krypton. The addition of about 1% of water vapor to the argon test gas also stabilizes the flow and shortens the relaxation region. A thin coating of dissolved sodium chloride in water on the shock tube wall does not seem to have any effect on the flow. The experimental results provide the data for a theoretical study which took into account atom-atom collisions, electron-atom collisions and radiation-energy losses to deduce a precise value for the atom-atom collision excitation cross-section constants for argon and krypton having values of S* sub Ar-Ar = 1.0 times 10 to the -19th power sq cm/eV and S* sub Kr-Kr = 1.2 times 10 to the -19th power sq cm/eV, respectively.