TRAPPING AND DETRAPPING OF HYDROGEN IN GRAPHITE MATERIALS EXPOSED TO HYDROGEN GAS

Measurements of hydrogen solubility have been performed for several un irradiated and neutron-irradiated graphite (and CFC) samples at temper atures between 973 and 1323K under a similar to 10 kPa hydrogen atmosp here. The hydrogen dissolution process has been studied and it is disc ussed here. The values of hydrogen solubility vary substantially among the samples up to about a factor of 16. A strong correlation has been observed between the values of hydrogen solubility and the degrees of graphitization determined by X-ray diffraction technique. The relatio n can be extended even for the neutron irradiated samples. Hydrogen di ssolution into graphite can be explained with the trapping of hydrogen at defect sites (e.g. dangling carbon bonds) considering an equilibri um reaction between hydrogen molecules and the trapping sites. The mig ration of hydrogen in graphite is speculated to result from a sequence of detrapping and retrapping events with high energy activation proce sses.