AVS 47th International Symposium
    Surface Science Thursday Sessions
       Session SS2+VT-ThM

Paper SS2+VT-ThM9
The Behavior of Zirconium Surfaces in the Presence of Oxygen, Nitrogen, and Hydrogen Containing Adsorbates

Thursday, October 5, 2000, 11:00 am, Room 209

Session: Adsorption and Desorption Phenomena II
Presenter: Y.C. Kang, University of Akron
Authors: Y.C. Kang, University of Akron
D.A. Clauss, University of Akron
R.D. Ramsier, University of Akron
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Zirconium and its alloys exhibit a unique combination of physical properties that have led to their widespread use as structural materials in fission reactors as well as in a variety of chemical engineering applications involving harsh environments. Common to these applications is the presence of oxygen, nitrogen, and hydrogen containing moieties. Mechanistic studies of the chemistry of such species on zirconium surfaces are necessary to answer fundamental questions which cannot be addressed by phenomenological models of environmentally assisted degradation in these systems. As part of an effort to address these questions, low energy electron diffraction (LEED) and temperature programmed desorption (TPD) techniques have been applied to the adsorption of water, nitric oxide, and ammonia on Zr(0001) surfaces. Water adsorption at 180 K at exposures above 0.75 L results in water desorption in a broad TPD feature near 550 K. Data from LEED indicate that this adsorption does not result in ordered layers until 700 K annealing, and that the formation of ordered structures depends on exposure and annealing conditions. Low exposures of nitric oxide and ammonia at 160 K results in essentially no thermal desorption features, but high (greater than 20 L) ammonia exposures results in the production of water during TPD experiments and the formation of complex residual LEED patterns. These TPD and LEED data indicate a competition between the kinetics of recombination and desorption with those of diffusion involving the near-surface regions.