Characterizing thermal-oxidation behaviors of nuclear graphite by combining O2 supply and micro surface area of graphite.

ABSTRACT

The effects of different parameters on oxidation rate are non-linear, interactive and diversified in which the change of adequacy of O2 supply is an important indicator. The influence of microstructure on oxidation rate became stronger worsening the fitting linearity to calculate the activation energy based on present method with the decreased adequacy of O2 supply due to the increase of temperature, the decrease of gas flow rate, etc. Here, we proposed a method to characterize thermal-oxidation behaviors of nuclear graphite by combining O2 supply and micro surface area of graphite. The proposed method improved the linearity and reduced the standard error of Arrhenius plots of oxidized graphite IG-110 (10 L/min reactant gas) and ET-10 (0.2 L/min reactant gas). The value of activation energy of graphite IG-110 oxidized under ASTM D7542 condition is calculated as 220 kJ/mol by this method echoing the results of previous studies with sufficient O2 supply. For the conditions with less O2 supply at low gas flow rate and/or high temperature, the change of microstructure of oxidized graphite should be obtained as an important factor influencing oxidation rate of graphite.