Nitrogen Surface Catalyzed Recombination Efficiency From Two-Photon Laser Induced Fluorescence Measurements

Measurements of temperature and species gradients in the thermal boundary layer adjacent to different surfaces exposed to nitrogen plasma are made to characterize surface-catalyzed recombination. Laser-induced nitrogen atom fluorescence signals are obtained with submillimeter spatial resolution to provide a direct indication of surface-catalyzed reactivity. Further analysis of the measured quantities balancing the diffusive reactant flux with the consumption of atoms by surface reaction yields direct quantitative values for surface-catalyzed reaction rates and catalytic efficiencies. Materials tested in the present work include metals and quartz, and the surface-catalyzed recombination efficiencies are (8.05 +/- 2.01) x 10(-3), (5.74 +/- 1.44) x 10(-3), (2.10 +/- 0.53) x 10(-3), and (1.03 +/- 0.26) x 10(-4) for polished copper, cooled virgin nickel, unpolished copper, and cooled quartz, respectively. Comparisons between these values and previously published results suggest that this technique provides a useful means to characterize the catalytic behavior of high-temperature materials in plasma test facilities.