Development and validation of a model for the chemical kinetics of graphite oxidation

A model of the chemical kinetics and primary reactions of graphite oxidation is developed and successfully validated for pyrolytic carbon thin films. The model uses Gaussian distributions of the activation energies for adsorption and desorption and the measured active surface area (ASA) as a function of burn-off. The activation energies distributions and the pre-exponential rate coefficients for the four elementary oxidation kinetics reactions in the model are obtained from the reported measurements of the gases yields and adsorbed oxygen using a multi-parameter optimization algorithm. The model calculates the production rates of CO and CO2 and the gasification rate as functions of temperature and oxygen partial pressure, and its predictions are in excellent agreement with reported experimental measurements. Results for pyrolytic carbon thin films show that when the oxygen pressure is kept constant, the gasification rate depends on both temperature and ASA until a full burn-off is reached. By contrast, in a depleting oxygen environment, only partial burn-off is possible; gasification ceases following the consumption of the free oxygen in the enclosure. This model represents the first phase in an ongoing effort to develop a model for predicting the oxidation kinetics of nuclear graphite following a massive air ingress in high temperature reactors.