Hydrogen pumping and release by graphite under high flux plasma bombardment

Technical Report · Fri Jan 01 04:00:00 EST 1988

DOI:https://doi.org/10.2172/5497289· OSTI ID:5497289

Hirooka, Y; Leung, W K; Conn, R W; Goebel, D M; LaBombard, B; Nygren, R; Wilson, K L

Inert gas (helium or argon) plasma bombardment has been found to increase the surface gas adsorptivity of isotropic graphite (POCO-graphite), which can then getter residual gases in a high vacuum system. The inert gas plasma bombardment was carried out at a flux approx. = 1 x 10/sup 18/ ions s/sup -1/ cm/sup -2/ to a fluence of the order of 10/sup 21/ ions/cm/sup 2/ and at temperatures around 800/sup 0/C. The gettering capability of graphite can be easily recovered by repeating inert gas plasma bombardment. The activated graphite surface exhibits a smooth, sponge-like morphology with significantly increased pore openings, which correlates with the observed increase in the surface gas adsorptivity. The activated graphite surface has been observed to pump hydrogen plasma particles as well. From calibrated H-alpha measurements, the dynamic hydrogen retention capacity is evaluated to be as large as 2 x 10/sup 18/ H/cm/sup 2/ at temperatures below 100/sup 0/C and at a plasma bombarding energy of 300 eV. The graphite temperature was varied between 15 and 480/sup 0/C. Due to the plasma particle pumping capability, hydrogen recycling from the activated graphite surface is significantly reduced, relative to that from a pre-saturated surface. A pre-saturated surface was also observed to reproducibly pump a hydrogen plasma to a concentration of 9.5 x 10/sup 17/ H/cm/sup 2/. The hydrogen retention capacity of graphite is found to decrease with increasing temperature. A transient pumping mechanism associated with the sponge-like surface morphology is conjectured to explain the large hydrogen retention capacity. Hydrogen release behavior under helium and argon plasma bombardment was also investigated, and the result indicated the possibility of some in-pore retrapping effect. 43 refs., 11 figs.

• Research Organization: California Univ., Los Angeles (USA). Dept. of Mechanical, Aerospace and Nuclear Engineering; Sandia National Labs., Livermore, CA (USA)
• DOE Contract Number: AS03-84ER52104
• OSTI ID: 5497289
• Report Number(s): UCLA/PPG-1123; ON: DE88005880
• Country of Publication: United States
• Language: English

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ACTIVATED CARBON
ADSORBENTS
ALPHA SPECTROSCOPY
CARBON
CROSS SECTIONS
DESORPTION
ELEMENTAL MINERALS
ELEMENTS
EROSION
FLUIDS
GASES
GRAPHITE
HELIUM
HYDROGEN
MATERIALS
MINERALS
MODIFICATIONS
NONMETALS
RARE GASES
SPECTROSCOPY
SURFACE PROPERTIES
THERMONUCLEAR REACTOR MATERIALS