Surface modification of ET-10 graphite by helium irradiation and preoxidation: Morphology, microstructure and chemical states

Abstract

The synergistic effect of neutron irradiation and oxidising impurities inside reactors has a considerable influence on the modification and performance of nuclear graphite. We investigated the modification of the surface morphology, structure and functional groups of preoxidised ET-10 graphite by He+ beam irradiation. A distinct lamellar structure after high-temperature preoxidation indicates the depletion of the binders. Raman parameters |q−1| and ID1/(ID1+ID2) were calculated to reflect the variation in defect and crystallite size, and the crystallite size (La) of ET-10 graphite was reduced from 12.66 nm to 1.4 nm after irradiation. The high-temperature oxidation, on the one hand, increased La by the annealing recovery of defects; on the other hand, led to faster surface oxidation, destroying crystals and reducing La. Furthermore, changes in the electronic structure and elemental composition were qualitatively and quantitatively measured by X-ray photoelectron spectroscopy. The irradiation reduction occurred mainly at 5 × 1014 He+/cm2, where the ratio of O-containing groups was restored from the unirradiated 47% to 27%, which was close to the level of the graphite matrix. Lastly, while previous researches suggest that nuclear stopping power has a similar effect. The irradiation reduction is found to be related the energy transferred by the electron interaction combined with SRIM simulations.