Abstract
Time-resolved, direct Spectroscopic measurements of the P CO 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 0 2 as coated tubes. The major source of O 2 in the unloaded furnace tube is ingress of ambient atmosphere through the sample dosing hole, giving rise to a steady-state P CO 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 P O 2 , in the tube at temperatures < 2000 K.
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