Homogeneous and heterogeneous reaction rates for the reactions of carbon with carbon dioxide and water

High-temperature high-pressure shock tube experiments were performed on the water-gas shift reaction and two heterogeneous reactions believed to play a key role in the chemical attack of carbon composite rocket nozzles. The homogeneous water-gas shift reaction has been studied at elevated pressures 194--490 atm temperatures ranging from 1200--2100 K in the high-pressure shock tube facility at the University of Illinois at Chicago. The water-gas shift reaction becomes important when the heterogeneous surface reactions produce H2 and CO in the presence of the main exhaust flow components CO2 and H2O. The heterogeneous reactions of solid carbon reacting with gaseous carbon dioxide and steam were also studied under high pressure and high temperature conditions with post-shock pressures ranging from 40--412 atm, temperatures ranging between 1404--2534 K, and nominal reaction times of 1 ms. Both amorphous carbon particles and graphite particles were injected into the shock tube just prior to the bursting of the diaphragm by means of a particle injector specifically designed for these experiments. The carbon particles were injected into the shock tube containing mixtures of varying concentrations of H2O or CO2 in Ar as balance. The overall reaction rate constants for all three reactions have been calculated and compared to rate constants of previous theoretical and experimental values to determine if pressure influences the rate of the reactions. The wide temperature range of the experimental conditions allowed the observation of equilibrium for the water-gas shift reaction as well as both reaction and transport limiting regimes for the heterogeneous reactions. Theoretical techniques were used to analyze the homogeneous and heterogeneous reactions in order to fully understand the observed experimental phenomena.