| Abstract | Time-resolved, direct Spectroscopic measurements of the PCO in an unperturbed high-temperature graphite furnace are reported, based on the attenuation of the CO(0,0) transition at 154.3 nm excited in a hollow cathode discharge. A model is presented to account for the kinetic and “diffusion” control regimes observed for oxidation of electrographite, pyrolytic graphite-coated and glassy carbon tubes. Heterogeneous equilibrium appears to be established only at T ⪢ 2200 K in coated tubes. Above 1500 K, glassy carbon tubes are as reactive toward 02 as coated tubes. The major source of O2 in the unloaded furnace tube is ingress of ambient atmosphere through the sample dosing hole, giving rise to a steady-state PCO of 1.2 × 10−3 atm at 2600 K. Release of oxidants from decomposition of sample matrices and their slow disappearance by diffusion/reaction processes contribute to an elevated PO2, in the tube at temperatures < 2000 K. |
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