Oxidation of ATJ graphite by low concentrations of water vapor and carbon dioxide in helium

Abstract

The rates of reaction of a spherical specimen (1 in. diameter) of ATJ graphite with low partial pressures of carbon dioxide and water vapor were determined in flowing helium at a total pressure of 1 atm. The rates were obtained from continuously recorded weight changes and from intermittent analyses of the effluent gases. The effects of temperature, flow rate, partial pressure of oxidant, and burnoff were examined. Activation energies of ~50 kcal/mole were observed for the H 2O-graphite system in the temperature range of 775–925°C at 110 and 460 vpm (parts per million by volume). Values of ~60 kcal/mole were found for the CO 2-graphite system in the same temperature range using CO 2 concentrations of 550 and 1000 vpm. The apparent order of the two systems was found to be between 0.6 and 0.7 at 875°C in the concentration ranges of 50–1000 vpm of CO 2 and 30–760 vpm of H 2O. Strong and about equal retardation of the H 2O-graphite reaction was noted upon the addition of either H 2 or CO. The CO 2-graphite reaction also was found to be strongly retarded by either CO or H 2. Differences in the results obtained for ATJ graphite from those found previously for Speer Moderator-2 graphite are noted.