https://geosci.uchicago.edu/~grossman/COG77E.pdf

Distribution of the pre-solar component in allende and other carbonaceous chondrites

The Effect of Higher Alkanes on the Ignition of Methane-Oxygen-Argon Mixtures in Shock Waves

A single pulse shock tube has been designed and constructed in order to achieve extremely high pressures and temperatures to facilitate gas-phase chemical kinetic experiments. Postshock pressures of greater than 1000 atmospheres have been obtained. Temperatures greater than 1400 K have been achieved and, in principle, temperatures greater than 2000 K are easily attainable. These high temperatures and pressures permit the investigation of hydrocarbon species pyrolysis and oxidation reactions. Since these reactions occur on the time scale of 0.5–2 ms the shock tube has been constructed with an adjustable length driven section that permits variation of reaction viewing times. For any given reaction viewing time, samples can be withdrawn through a specially constructed automated sampling apparatus for subsequent species analysis with gas chromatography and mass spectrometry. The details of the design and construction that have permitted the successful generation of very high-pressure shocks in this unique app...

Design of a high-pressure single pulse shock tube for chemical kinetic investigations

The shock tube as wave reactor for kinetic studies and material systems

Two chemical thermometers, 1,1,1-trifluoroethane and cyclohexene, have been used to calibrate the temperatures behind reflected shock waves, T5real, in a unique high-pressure, single-pulse shock tube. Experiments with 1,1,1-trifluoroethane were performed at nominal postshock pressures of 5000 psi and 9000 psi, and T5real was calculated from the extent of the reaction and literature values for k∞. Both parent molecule decomposition and product formation were used to calculate the extent of reaction. At each pressure the two methods of calculating T5real are in excellent agreement. The values for T5real obtained from the cyclohexene experiments are in good agreement with those from 1,1,1-trifluoroethane. The range of the temprature calibration is 1050–1350 K. No discernable pressure dependence between the two sets of experiments was observed for the calculated values of T5real. The effect of a 10% rise in pressure during the residence time on the calculated temperatures was also examined and is found to give rise to only small errors in T5real. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 722–731, 2001

Calibration of reaction temperatures in a very high pressure shock tube using chemical thermometers

The kinetics of the homogeneous exchange reaction in molecular nitrogen highly diluted in argon was studied in a single‐pulse shock tube over a wide range of temperatures, initial pressures, and compositions. The reaction order with respect to the total nitrogen, argon, and the over‐all reaction order were determined. A rate law: Rate=kb[Ar][N214]+kb[Ar ][N215], which is a sum of two parallel reactions, was found to be compatible with the experimental results kb=1013.82±0.31 exp[−(116±5)×103/RT) cc mole−1·sec−1. It was shown that the exchange reaction does not proceed via a radical chain. A mechanism based on vibrational excitation of the nitrogen molecule to a critical vibrational level as a rate determining step is proposed. A rate constant, computed from available vibrational relaxation data in nitrogen agrees very well with the observed rate constant.It was found that slight amounts of oxygen, up to O2/N2∼0.01, had very little effect on the reaction rate. In the presence of higher oxygen concentration...

Kinetics of the Homogeneous Exchange Reaction: 14–14N2+15–15N2⇋214— 15N2. Single‐Pulse Shock‐Tube Studies

The effect of the cold boundary layer on kinetic parameters was studied behind reflected shocks in a single pulse shock tube. By inserting hollow cylinders into the test section, parallel to the tube walls, the surface relative to the volume was increased, and the lowering of the chemical conversion was determined as a function of the surface per unit volume. The test reaction studied was the unimolecular decomposition of perfluorocyclobutane (C4F8→2C2F4). It was shown that the lowering of the chemical conversion was proportional to the surface‐to‐volume ratio in the test section. A hypothetical cold layer δc in which no conversion occurred was found to be around 0.2 mm. It was concluded that in a shock tube of ∼ 2‐in. i.d., at an initial pressure of p1 ≥ 100 torr the cold boundary layer has very little effect on kinetic parameters obtained in a single‐pulse shock tube. At lower pressures and in smaller diameters shock tubes these effects should be considered when interpreting kinetics results.

Boundary Layer Effects on Chemical Kinetics Studies in a Shock Tube

The isotopic exchange reaction between two CO molecules was studied under homogeneous conditions in a single‐pulse shock tube at high dilution in argon within the 2000–2675°K temperature range. From a total of 100 shocks, run at varying initial pressures and compositions, the following rate law was derived: rate of exchange= kb[CO]1.45[Ar]0.55, where kb = 1014.36±0.42exp{− (76 ± 5) × 103 / RT} cc mole−1·sec−1. The possibility of a chain mechanism was ruled out. A two‐step mechanism composed of a vibrational excitation step and an atom‐switching step is proposed. It was found that exchange occurs at high probability when one of the CO molecules is elevated to the 7th–10th vibrational level before colliding with another CO molecule. A dipole interaction stabilizing the transition state is proposed in explanation of the relatively low activation energy of this exchange reaction. Two alternative reaction systems are described, and the corresponding rate constants are computed and compared with the experimenta...

Akiva Bar‐Nun

Papers

Kinetics of the Homogeneous Exchange Reaction: 14–14N2+15–15N2⇋214— 15N2. Single‐Pulse Shock‐Tube Studies

Boundary Layer Effects on Chemical Kinetics Studies in a Shock Tube

Kinetics of the Homogeneous Exchange Reaction 12C18O+13C16O⇆13C18O+12C16O. Single‐Pulse Shock‐Tube Studies