Abstract

The oxidation-induced microstructure evolution of nuclear graphite (IG-110 and NBG-17) is studied. Graphite samples were oxidized in air at 500 °C. Complicated oxidation paths were observed on the ion-milled surface of oxidized graphite samples. The weight loss of graphite samples during oxidation is mainly attributed to the oxidation paths which are extended and broadened constantly. In contrast, the original gas-escape pores do not show obvious change in sizes during oxidation. The oxidation paths are characterized to be much thinner and more tortuous than the gas-escape pores, which should be taken into account in estimating the oxygen diffusivity in oxidized graphite. The edges of graphite sheets exposed in the oxidation paths could scatter the phonon and electrons strongly. Therefore, the thermal conductivity declines dramatically with oxidation time. At weight loss around 30 %, the thermal conductivity of the oxidized graphite decreased to ∼16.8 % of the corresponding original value.