Influence of structure on the thermal oxidation of reactor graphites

Graphite is used as a bearing and seal material at gas outlet temperatures in CAGRs under which condition it is subject to thermal corrosion. During thermal oxidation in CO2-based gas mixtures most graphites exhibit an increase in reactivity. However the relation between structure and changes in thermal reactivity has received little attention, particularly in the nuclear context where the major oxidation reactions are radiolytic. The reactivity of a sample of graphite is a function of the amount and nature of the surface accessible to the gas. The variation in reactivity with weight loss therefore reflects changes in surface area and/or surface nature. The development of surface area is governed by changes in pore structure. It could be expected that the surface nature may be a function of material source and preparation. The purpose of this paper is to describe briefly an investigation of the relationship between reactivity, weight loss and structural changes for two Gilso-carbon based graphites. (author)