Adsorption of hydrogen chloride on microcrystalline silica

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Virginia Polytechnic Institute and State University

The National Aeronautics and Space Administration's Space Shuttle employs a solid rocket propellant. Combustion of the solid propellant produces hydrogen chloride as one of the major products. In this thesis, the hydrogen chloride/silica system was investigated. Silica was chosen as a model compound to represent ground debris transported into the exhaust cloud as a result of convection. The silica adsorbent was characterized by x-ray diffraction, infrared spectroscopy, and surface area.

Interaction of hydrogen chloride with silica (𝔞-quartz) was studied by various techniques including adsorption/readsorption isotherms, ESCA, and calorimetry. Adsorption of hydrogen chloride at 30°C was found to be dependent on the outgas temperatures and reversibility was dependent on the reoutgas temperatures. ESCA analysis on silica after exposure to HCl. indicated the presence of chloride ion. Angular probe studies showed that the chloride ion resides on the surface of silica rather than in the bulk of the sampling region. Calorimetric work was performed to measure heats of immersion of silica outgassed at various temperatures in different concentration of hydrochloric acid. Heats of immersion were found to increase with increasing outgas temperature and concentration of acid. Similar investigation of the hydrogen chloride/silica system was then extended to ground debris samples from the Kennedy Space Center. These samples were characterized by SEM/EDAX. The amount of HCl adsorption per unit area was more than three times greater than on pure silica. Apparently, HCl has a greater affinity towards some component of the ground debris other than silica.