Hydrogen pumping and release by graphite under high flux plasma bombardment
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 Lab. (SNL-CA), Livermore, CA (United States)
- DOE Contract Number:
- AS03-84ER52104
- OSTI ID:
- 5497289
- Report Number(s):
- UCLA/PPG-1123; ON: DE88005880; TRN: 88-010994
- Resource Relation:
- Other Information: Paper copy only, copy does not permit microfiche production. Original copy available until stock is exhausted
- Country of Publication:
- United States
- Language:
- English
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GRAPHITE
ACTIVATED CARBON
THERMONUCLEAR REACTOR MATERIALS
ALPHA SPECTROSCOPY
CROSS SECTIONS
DESORPTION
EROSION
HELIUM
HYDROGEN
MODIFICATIONS
SURFACE PROPERTIES
ADSORBENTS
CARBON
ELEMENTAL MINERALS
ELEMENTS
FLUIDS
GASES
MATERIALS
MINERALS
NONMETALS
RARE GASES
SPECTROSCOPY
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