Laboratory Determination of Thermal Protection System Materials Surface Catalytic Properties

Different experimental approaches to measuring catalytic reaction efficiencies on thermal protection system materials are reviewed. Special emphasis is given to the theory and application of the diffusion tube side-arm reactor technique. In this technique, reactants diffuse into a dead-end tube and are progressively removed from the gas phase by surface reactions on the walls, establishing unique steady-state concentration profiles along the length of the tube. Reactant loss probabilities are determined by matching experimentally measured species profiles to calculated solutions of a reaction-diffusion model. The advantages of laser-based methods for species concentration measurements are summarized and different approaches to reactor modeling and the extraction of reaction efficiencies from measured data are presented. The advantages and limitations of the diffusion-tube side-arm technique, the associated uncertainties in derived loss probabilities, and the prospects for further laboratory development, are presented.