Thermo-oxidation of laboratory-produced undoped and W-doped carbon films: A reaction product analysis

摘要

Highlights ? Films with and without tungsten doping were prepared by plasma deposition. ? Films underwent thermo-oxidation at 350?°C and 2Torr O2. ? Reaction products were found to be CO, CO 2 and D 2 O. ? No methane or other hydrocarbons were observed. Abstract Thermo-oxidation is a technique where O 2 gas is used to remove carbon co-deposits at elevated temperatures from plasma-facing materials of fusion devices. Following thermo-oxidation, the reaction products produced will need to be managed by a reactor's gas-handling system, including the tritium plant. Thus, it is important to know what molecular species are produced during oxidation. The reaction products of thermo-oxidation have previously been studied for undoped films indicating CO, CO 2 and D 2 O as the reaction products. The present study directly compares the reaction product evolution of undoped films to that of films doped with tungsten. A glow discharge was used to produce sets of undoped and W-doped films on stainless steel (SS) foil substrates. X-ray photoelectron spectroscopy (XPS) found the W-doped films to contain an average 0.1 at.% W/(W+C). Laser thermal desorption spectroscopy (LTDS) was used to measure the areal D-concentration. Reaction products during oxidation were measured using a quadrupole mass spectrometer (QMS). Both the undoped and W-doped specimens were oxidized in 2Torr O 2 , at 350 °C for 4h, total. LTDS was then used to determine how much D had been removed during oxidation (93% and 32% of the D was removed after oxidation for the undoped and W-doped cases respectively). The reduced D loss for the W-doped specimens is attributed to a change in film structure due to the incorporation of W in the film. Oxidation reaction products for both undoped and W-doped films include CO, CO 2 , and D 2 O, with no finding of D 2 or CD 4 within experimental uncertainty. Particle accounting was performed for oxygen, deuterium and carbon atoms.