AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS3-TuA

Paper SS3-TuA3
The Effect of Boron on Water Dissociation and Surface Diffusion of Atomic Hydrogen on Single Crystal Ni@sub3@(Al, Ti) (110)

Tuesday, October 3, 2000, 2:40 pm, Room 210

Session: Water/Surface Interactions
Presenter: J. Wang, Northwestern University
Authors: J. Wang, Northwestern University
Y.-W. Chung, Northwestern University
Correspondent: Click to Email
Polycrystalline Ni@sub3@Al alloys are severely embrittled in a moist environment at room temperature. Ductility measurements showed that addition of boron suppresses this moisture-induced embrittlement. Previous results indicated that water dissociates on clean Ni@sub3@(Al, Ti) (100) and (110), resulting in hydrogen evolution at ~350 and 400 K respectively. To explore the effect of boron on water dissociation, we first dosed the surface of clean Ni@sub3@(Al, Ti) (110) with controlled amounts of boron, using a specially designed low-energy negative boron ion source, followed by low-temperature exposure to D@sub2@O. The interaction between water vapor and boron-modified Ni@sub3@(Al, Ti) (110) was investigated using temperature-programmed desorption, X-ray photoemission and Auger electron spectroscopy. Auger and X-ray photoemission studies on boron-modified Ni@sub3@(Al, Ti) (110) show that boron reacts with water to form hydroxyls at 130~190 K. Hydrogen desorption occurs at ~950 K from boron-modified Ni@sub3@(Al, Ti) (110), indicating strong B-H bonding. After water dosing at ~130 K, the surface diffusion coefficients of atomic hydrogen on clean and boron-modified Ni@sub3@(Al, Ti) (110) surfaces were measured at 270 K with electron stimulated desorption. The surface diffusion of atomic hydrogen on 0.05 monolayer boron-modified surface is about 10 times slower than that on clean boron-free surface. Therefore, the strong B-H bonding suppresses both hydrogen desorption and the surface diffusion of atomic hydrogen to the crack tip at room temperature. These results may explain the suppression of moisture-induced embrittlement of Ni@sub3@Al and related alloys by boron.