Retention and desorption behavior of tritium in Si related ceramics

Hydrogen isotope retention and desorption behaviors for Silicon carbide (SiC), Silicon nitride (Si₃N₄) and Silicon dioxide (SiO₂) were studied to elucidate the fundamental process of hydrogen isotope in Si related ceramics by means of T-IP (tritium imaging plate), thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS). The tritium gas exposure at 673 K showed that tritium was precipitated on the surface for SiO₂, although that for SiC was uniformly retained inside the bulk. The 0.2 keV D2+ implantation revealed that the deuterium desorption stages for Si related ceramics were consisted of four desorption stages at around 450 K, 650 K, 800 K, and 950 K, attributing to the desorptions of deuterium trapped on the surface, retained in interstitial sites, trapped as Si-D bond and trapped as C/N/O-D bond, respectively. The retention enhancement of deuterium trapped by Si as Si-D bond and the reduction of deuterium trapped on the surface would be associated with the enhancement of covalent bond characteristics for Si related ceramics. These results indicate that the dangling bonds in the covalent ceramics have higher hydrogen isotope trapping efficiency to form chemical bond like Si-D bond. On the other hand, the surface adsorption of hydrogen isotope was enhanced for the higher ionicity ceramics by charge localization.