TRAPPING AND DETRAPPING OF HYDROGEN IN CARBON-BASED MATERIALS EXPOSEDTO HYDROGEN GAS

Measurements of hydrogen solubility have been performed for several un irradiated and neutron-irradiated graphite (and CFC) samples at temper atures between 700 and 1050 degrees C under a similar or equal to 10 k Pa hydrogen atmosphere. The hydrogen dissolution process has been stud ied and it is discussed here. The values of hydrogen solubility vary s ubstantially among the samples by up to a factor of about 16. A strong correlation has been observed between the values of hydrogen solubili ty and the degrees of graphitization determined by the X-ray diffracti on technique. The relation can be extended even for the neutron-irradi ated samples. Hydrogen dissolution into graphite can be explained by t he trapping of hydrogen at defect sites (e.g. dangling carbon bonds) c onsidering an equilibrium reaction between hydrogen molecules and the trapping sites. The migration of hydrogen in graphite is speculated to result from a sequence of detrapping and retrapping events with high- energy activation processes.