Oxidative erosion of graphite in air between 600 and 1000K

Balden, M.; Klages, K.U.; Jacob, W.; Roth, J.

doi:10.1016/j.jnucmat.2005.01.006

Cited by 40 publications

(22 citation statements)

References 46 publications

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“…There is, however, some indication that some relatively small dust particles are being oxidized. The low reactivity to O 2 at this temperature is consistent with the results on the oxidation of a variety of solid graphites [15][16][17].…”

Section: Discussionsupporting

confidence: 88%

“…This is consistent with the suggestion that dust collected from beneath the tiles originated primarily from the Grafoil sheets used as a thermally conducting compliant layer behind the tiles [14]. Previous experiments have shown that the oxidation of various forms of solid graphite results in very little mass loss at 350 ºC [15,16]. Recent oxidation results for pieces of Grafoil also did not show measurable mass loss [17].…”

Section: Diii-d Dustsupporting

confidence: 85%

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Thermo-oxidation of tokamak carbon dust

Davis

Fitzpatrick

Sharpe³

et al. 2009

Journal of Nuclear Materials

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The oxidation of dust and flakes collected from the DIII-D tokamak, and various commercial dust specimens, has been measured at 350 ºC and 2.0 kPa O 2 pressure. Following an initial small mass loss, most of the commercial dust specimens showed very little effect due to O 2 exposure. Similarly, dust collected from underneath DIII-D tiles, which is thought to comprise largely Grafoil™ particulates, also showed little susceptibility to oxidation at this temperature. However, oxidation of the dust collected from tile surfaces has led to ~ 18% mass loss after 8 hours; thereafter, little change in mass was observed. This suggests that the surface dust includes some components of different composition and/or structure -possibly fragments of codeposited layers. The oxidation of codeposit flakes scraped form DIII-D upper divertor tiles showed an initial 25% loss in mass due to heating in vacuum, and the gradual loss of 30-38% mass during the subsequent 24 hours exposure to O 2 . This behavior is significantly different from that observed for the oxidation of thinner DIII-D codeposit specimens which were still adhered to tile surfaces, and this is thought to be related to the low deuterium content (D/C ~ 0.03 -0.04) of the flakes.

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Section: Discussionsupporting

confidence: 88%

Section: Diii-d Dustsupporting

confidence: 85%

Thermo-oxidation of tokamak carbon dust

Davis

Fitzpatrick

Sharpe³

et al. 2009

Journal of Nuclear Materials

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“…These values of the apparent activation energies are remarkably low. Firstly, the activation energy for a-C film is much lower than that for oxidative removal of graphitic materials in an oxygen atmosphere, which is about 1.7 eV [28]. This is not too surprising since an oxygen plasma is a source for species with a much higher reactivity than stable ground state oxygen molecules.…”

Section: Resultsmentioning

confidence: 99%

“…To independently determine the density the mass change of a complete silicon wafer (4 inch in diameter) due to deposition of the a-C film was measured by a microbalance and the film thickness was determined by profilometry. This yields a carbon number density of 8.48×10 28 atoms/m 3 , corresponding to a mass density of 1.67 g/cm 3 . This value is in excellent agreement with the value determined from RBS and the layer thickness.…”

Section: Methodsmentioning

confidence: 99%

Erosion of tungsten-doped amorphous carbon films in oxygen plasma

Wang

Jacob

Balden

et al. 2012

Journal of Nuclear Materials

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Abstract:Tungsten-doped amorphous carbon films with 0-9 at.% W concentration were produced by magnetron sputtering and eroded in oxygen plasmas applying different bias voltages and substrate temperatures. The partial C and W erosion rates were determined from the C and W areal density changes measured by Rutherford backscattering spectrometry (RBS). The initial C removal rate increases with increasing ion energy and temperature and decreases with increasing W concentration. For W-doped films the erosion rate decreases with increasing plasma exposure duration. At low bias voltages the erosion process stops after W accumulation at the surface, which protects the carbon underneath from further erosion. RBS and X-ray photoelectron spectroscopy suggest that the Wrich layer at the surface is carbon free and consists of porous WO 3 . Biasing to 200 V leads to removal of W by physical sputtering and, therefore, inhibits the formation of the protecting W oxide layer and the C erosion proceeds.

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“…The erosion rate increases by two orders of magnitude to 4 × 10 −2 nm/s when the temperature is increased from 290 to 580 K. From the Arrhenius plot an effective activation energy of 0.25 eV is determined. This effective activation energy has to be compared with 1.3 eV and 1.7 eV found for thermal oxidation of a-C:H [26] and graphite [34], respectively. Obviously, the reactive species produced in the plasma are much more reactive than molecular oxygen.…”

Section: A Temperature Dependencementioning

confidence: 99%

Fuel removal from tile gaps with oxygen discharges: reactivity of neutrals

et al. 2009

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Carbon removal in so-called remote areas, where no energetic species can reach the surface, is investigated with low-temperature glow discharges in pure oxygen. Plasma-deposited amorphous hydrogenated carbon thin films are used as a model system for redeposited films. Erosion measurements are performed on flat substrates as well as on two different 3D test structures. One design consists of 19 mm deep gaps with widths ranging from 0.5 to 4 mm to simulate ITER tile gaps. A second design consists of a flat box-like structure where particles can enter only through a narrow slit. Measurements are performed for substrate temperatures ranging from 290 to 580 K. Erosion rates follow an Arrhenius-type dependence on substrate temperature with an effective activation energy of 0.25 eV. While at room temperature the surface loss probability of the dominant eroding species is 50 % it becomes smaller at elevated temperatures. At elevated temperatures the films are not only removed faster but simultaneously erosion penetrates deeper into the gaps.

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Oxidative erosion of graphite in air between 600 and 1000K

Cited by 40 publications

References 46 publications

Thermo-oxidation of tokamak carbon dust

Thermo-oxidation of tokamak carbon dust

Erosion of tungsten-doped amorphous carbon films in oxygen plasma

Fuel removal from tile gaps with oxygen discharges: reactivity of neutrals

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