Shock tube techniques

Because of its high thermal stability compared to that of other hydrides, water does not decompose extensively below 2000 °K. Thus, at one atmosphere and 2500 °K it is only dissociated to the extent of 9 %. Accordingly, it is impossible to study the homogeneous decomposition by classical methods. It is only with the shock tube technique that the rates of pyrolysis of water and heavy water have been measured. 

The vivid interest in hydrazine as a powerful propellant has stimulated many investigations both of its thermal decomposition and of its oxidation. Although hydrazine decomposes much more readily than ammonia, the study of its homogeneous decomposition by classical means using a static system is complicated considerably by wall catalysis. Thus, other experimental techniques have had to be applied, e.g. decomposition flames, flash photolysis, studies of explosion characteristics and the shock-tube technique. 

The thermal decomposition of N02 has been studied222-224 in the temperature range 1400-2300 °K by the shock-tube technique. Changes in the concentration of N02 in shock-heated argon-diluted N02 were monitored by visible absorption222 or visible emission224 spectrophotometry. The data fitted a complex rate law of the form... 

As noted above, it should be realized that understanding the activity on a surface is not the only issue needed to fully characterize the catalytic system. There must be an understanding of how the surface reactions produce intermediates that can desorb and initiate gas phase reactions close to the surface. To that extent, the author is developing a catalytic shock tube technique to probe the interface of the catalyst surface and the immediate gas phase layer, bridging the gap between surface mechanisms and gas phase mechanisms. 

A detailed description of shock tube techniques is given in Ref 7, pp 74-97 the experimental results are listed on pp 98-111 and discussion is given on pp 112- 18. A brief description of shock tube techniques is given in Section 8, p D522... 

Detonation, shock tube technique studies in 4D522... 

The shock tube technique employed in the pyrolytic decomposition of polyfluorohydro-carbons22,27,28 showed that the elimination of molecular hydrogen fluoride is the predominant reaction. Yet, a side process of C—C bond breaking becomes important as the temperature is increased beyond 1300 K. Several fluoroethanes have been found to react by molecular dehydrofluorination in chemical activation process29 and Table 2 summarizes the kinetic parameters for the gas-phase pyrolysis of this type of compound. In the case of 1,1,2-trifluoroethane, three olefin products were obtained (equations 3-5). 

A comparison of two single-pulse shock-tube-technique experiments applied to the HC1 elimination of ethyl chloride and -propyl chloride in the temperature range of 960-1100 K was made by Evans and coworkers48. The observed rate coefficients were compared with those of previous works. In this investigation it was believed that the activation energy Ea of 242.6 kJ mol-1 for CH3CH2C1 - CH2=CH2 + HC1 is more appropriate than the most commonly reported E values of 234.2-236.8 kJ mol-1. 

Daiber and Freedman , using shock-tube techniques, investigated the homogeneous decomposition in argon between 3000 and 4300 °K. They were able to show that two alternative decomposition paths were initially occurring, viz. 

Fishburne and Edse obtained above 1500 °K using shock-tube techniques. Their result... 

There has been considerable interest in the elimination of hydrogen halides from halogenated hydrocarbon molecules and radicals which have been vibration-ally excited by chemical activation, by photochemical methods or by shock-tube techniques. Studies on fluorinated species have been reported by Trotman-Dickenson et a/.7 3.839-84i,846.908,909 by Pritchard et fl/.747,748.905.919.920 ... 

The complementary techniques for determining rate constants for thermal electron attachment, detachment, and dissociation are the flowing afterglow, the microwave technique, the ion cyclotron resonance procedures, the swarm and beam procedures, the shock tube techniques, the detailed balancing procedures, the measurement of ion formation and decay, and the high-pressure mass spectrometer procedures. In all cases the measurement of an ion or electron concentration is made as a function of time so that kinetic information is obtained. In the determination of lifetimes for ions, a limiting value of the ion decay rate or k is obtained. 

SPST single-pulse shock tube technique... 

J. V. Michael and J. R. Fisher, Rate constants for the reaction D + H2 - HD + H over the temperature range 655-1979 K, by the flash photolysis-shock tube technique, J. Phys. Chem. 94 3318 (1990) and references therein. 

For details of the shock tube technique we refer the reader to the extensive literature. New aspects of instrumentation are included in the article of Getzinger and Schott in this book. A recent discussion of real shock wave behaviour and its consequences for dissociation rate studies is particularly important. ... 

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