Hydrogen and helium retention properties of B4C and SiC converted graphites

The hydrogen or helium retention properties of B4C converted graphite, SiC converted graphite and isotropic graphite were examined, by the irradiation of a hydrogen or helium ion, followed by a thermal desorption spectroscopy measurement. The energy of the hydrogen or helium ion was 1.7 or 5.0 keV, respectively. For both B4C and SiC, two peaks appeared in the H2 desorption spectra. The lower temperature peaks of B4C and SiC correspond to detrappings of B–H and Si–H bonds, respectively. It is considered that the higher peak is due to detrapping of the C–H bond. The amounts of retained hydrogen at room temperature (RT), obtained from the H2 desorption spectra, were 6.71×1017, 1.0×1018 and 5.8×1017 H cm−2 for isotropic graphite, B4C and SiC, respectively. For the He desorption spectrum in the case of B4C, two peaks appeared at 300 and 950°C. For SiC, a sharp desorption peak was observed at 850°C, in addition to the low temperature peak at ≈300°C. For graphite, the spectrum had a single peak at 300°C. When the helium fluence was increased, this peak temperature shifted to the higher temperature region. The amount of retained helium in B4C, SiC and isotropic graphite at RT were 2.7×1017, 4.2×1017 and 3.4×1017 He cm−2, respectively. It is seen that the trapped amount of helium is not negligibly small.