Finite-rate oxidation model for carbon surfaces from molecular beam experiments

Poovathingal, Savio J.; Schwartzentruber, Thomas E.; Murray, Vanessa J.; Minton, Timothy K.; Candler, Graham V.

doi:10.2514/6.2016-3842

“…5a and 7a for FiberForm and vitreous carbon respectively, for both the increasing and the decreasing temperature surveys. The TD-prompt flux increases markedly beyond 1200 K for vitreous carbon which may be ascribed to surface-adsorbed O desorbing promptly as the surface temperature is increased [5,27,28]. A similar trend is observed for FiberForm, where the TD-prompt flux dominates beyond 1300 K. However, the rate of TD-prompt flux increase for vitreous carbon is approximately 2.8 times faster than for FiberForm.…”

Section: Inelastic and Reactive Scattering Of O And O2 From Fiberformsupporting

confidence: 55%

“…Ablative heat shields are currently overdesigned as a result of large uncertainties [1,4] in the understanding of the oxidation mechanisms. A better understanding of the oxidation process would enable improved carbon-oxygen kinetic rate models for computational fluid dynamics (CFD) [5][6][7] and direct simulation Monte Carlo (DSMC) simulations of heat shield behavior during hypersonic flight [8,9]. The oxidation of a porous carbon network (FiberForm) has been studied in flow-tube experiments where the reactive gas was O2 [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Reactive and Inelastic Scattering Dynamics of Hyperthermal O and O2 from a Carbon Fiber Network

Poovathingal¹,

Qian²,

Murray³

et al. 2021

Preprint

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The reactive and inelastic scattering dynamics of ground-state atomic and molecular oxygen from a carbon fiber network at 1023-1823 K was investigated with a molecular beam-surface scattering technique. A molecular beam containing hyperthermal O and O2 with a mole ratio of 0.92:0.08 and nominal velocity of 8 km s-1 was directed at the network, and time-of-flight distributions of the scattered products were collected at various angles with the use of a rotatable mass spectrometer detector. O atoms exhibited both impulsive scattering (IS) and thermal desorption (TD) dynamics, where the TD O-atom flux increased with surface temperature and the IS O-atom flux remained relatively constant. While the majority of the TD O atoms desorbed promptly after the beam pulse struck the network, signatures of thermal processes occurring over long residence times were also observed. Evidence of O2 reactions was not observed, and the behavior of the inelastically scattered O2 was invariant to the temperature of the network and showed both IS and TD dynamics. The dominant reactive product was CO, whereas CO2 was a minor product. Both these products showed only TD dynamics. The observed flux of CO initially increased with temperature and then reached a plateau above which the flux no longer increased with temperature, over the temperature range studied. Thermally desorbed CO products exited the network promptly or after relatively long residence times, and two populations of CO with long residence times were distinguished. Hysteresis was observed in the temperature-dependent flux of thermally desorbed O and CO, with opposing trends for the two products. This work follows similar studies in our laboratory where the target materials were vitreous carbon and highly oriented pyrolytic graphite. The data suggest that the chemical reactivity of the three forms of sp2 carbon surfaces is similar and that the differences arise from the variations of the morphology.

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“…The TD-slow signal decreases as the surface temperature increases, with the TD-slow flux accounting for ~8% of the total flux at 1123 K and ~5% at 1823 K. The flux components of O are shown in Figures 5a and 7a for FiberForm and vitreous carbon respectively, for both the increasing and the decreasing temperature sweeps. The TD-prompt flux increases markedly beyond 1200 K for vitreous carbon, which may be ascribed to surface-adsorbed O desorbing promptly as the surface temperature is increased [5,27,28]. A similar trend is observed for FiberForm, where the TD-prompt flux dominates beyond 1300 K. However, the rate of TDprompt flux increase for vitreous carbon is approximately 2.8 times faster than for FiberForm.…”

Section: Inelastic Andsupporting

confidence: 52%

“…Ablative heat shields are currently overdesigned as a result of large uncertainties in the understanding of the oxidation mechanisms [1,4]. A better understanding of the oxidation process would enable improved carbon-oxygen kinetic rate models for computational fluid dynamics (CFD) [5][6][7] and direct simulation Monte Carlo (DSMC) simulations of heat shield behavior during hypersonic flight [8,9]. The oxidation of a porous carbon network (FiberForm) has been studied in flow-tube experiments where the reactive gas was O2 [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Reactive and Inelastic Scattering Dynamics of Hyperthermal O and O2 from a Carbon Fiber Network

Poovathingal¹,

Qian²,

Murray³

et al. 2021

Preprint

Self Cite

0

View full text Add to dashboard Cite

The reactive and inelastic scattering dynamics of ground-state atomic and molecular oxygen from a carbon fiber network at 1023-1823 K was investigated with a molecular beam-surface scattering technique. A molecular beam containing hyperthermal O and O2 with a mole ratio of 0.92:0.08 and nominal velocity of 8 km s-1 was directed at the network, and time-of-flight distributions of the scattered products were collected at various angles with the use of a rotatable mass spectrometer detector. O atoms exhibited both impulsive scattering (IS) and thermal desorption (TD) dynamics, where the TD O-atom flux increased with surface temperature and the IS O-atom flux remained relatively constant. While the majority of the TD O atoms desorbed promptly after the beam pulse struck the network, signatures of thermal processes occurring over long residence times were also observed. Evidence of O2 reactions was not observed, and the behavior of the inelastically scattered O2 was invariant to the temperature of the network and showed both IS and TD dynamics. The dominant reactive product was CO, whereas CO2 was a minor product. Both these products showed only TD dynamics. The observed flux of CO initially increased with temperature and then reached a plateau above which the flux no longer increased with temperature, over the temperature range studied. Thermally desorbed CO products exited the network promptly or after relatively long residence times, and two populations of CO with long residence times were distinguished. Hysteresis was observed in the temperature-dependent flux of thermally desorbed O and CO, with opposing trends for the two products. This work follows similar studies in our laboratory where the target materials were vitreous carbon and highly oriented pyrolytic graphite. The data suggest that the chemical reactivity of the three forms of sp2 carbon surfaces is similar and that the differences arise from the variations of the morphology.

show abstract

“…Ablative heat shields are currently overdesigned as a result of large uncertainties in the understanding of the oxidation mechanisms [1,4]. A better understanding of the oxidation process would enable improved carbon-oxygen kinetic rate models for computational fluid dynamics (CFD) [5][6][7] and direct simulation Monte Carlo (DSMC) simulations of heat shield behavior during hypersonic flight [8,9]. The oxidation of a porous carbon network (FiberForm) has been studied in flow-tube experiments where the reactive gas was O2 [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Reactive and Inelastic Scattering Dynamics of Hyperthermal O and O2 from a Carbon Fiber Network

Poovathingal¹,

Qian²,

Murray³

et al. 2021

Preprint

Self Cite

0

View full text Add to dashboard Cite

The reactive and inelastic scattering dynamics of ground-state atomic and molecular oxygen from a carbon fiber network at 1023-1823 K was investigated with a molecular beam-surface scattering technique. A molecular beam containing hyperthermal O and O2 with a mole ratio of 0.92:0.08 and nominal velocity of 8 km s-1 was directed at the network, and time-of-flight distributions of the scattered products were collected at various angles with the use of a rotatable mass spectrometer detector. O atoms exhibited both impulsive scattering (IS) and thermal desorption (TD) dynamics, where the TD O-atom flux increased with surface temperature and the IS O-atom flux remained relatively constant. While the majority of the TD O atoms desorbed promptly after the beam pulse struck the network, signatures of thermal processes occurring over long residence times were also observed. Evidence of O2 reactions was not observed, and the behavior of the inelastically scattered O2 was invariant to the temperature of the network and showed both IS and TD dynamics. The dominant reactive product was CO, whereas CO2 was a minor product. Both these products showed only TD dynamics. The observed flux of CO initially increased with temperature and then reached a plateau above which the flux no longer increased with temperature, over the temperature range studied. Thermally desorbed CO products exited the network promptly or after relatively long residence times, and two populations of CO with long residence times were distinguished. Hysteresis was observed in the temperature-dependent flux of thermally desorbed O and CO, with opposing trends for the two products. This work follows similar studies in our laboratory where the target materials were vitreous carbon and highly oriented pyrolytic graphite. The data suggest that the chemical reactivity of the three forms of sp2 carbon surfaces is similar and that the differences arise from the variations of the morphology.

show abstract

Finite-rate oxidation model for carbon surfaces from molecular beam experiments

Cited by 6 publications

References 43 publications

Reactive and Inelastic Scattering Dynamics of Hyperthermal O and O2 from a Carbon Fiber Network

Reactive and Inelastic Scattering Dynamics of Hyperthermal O and O2 from a Carbon Fiber Network

Reactive and Inelastic Scattering Dynamics of Hyperthermal O and O2 from a Carbon Fiber Network

Reactive and Inelastic Scattering Dynamics of Hyperthermal O and O2 from a Carbon Fiber Network

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