Reactions of Modulated Molecular Beams with Pyrolytic Graphite. I. Oxidation of the Basal Plane

Olander, D.R.; Siekhaus, Wigbert J.; Jones, R. H.; Schwarz, John H.

doi:10.1063/1.1677980

Cited by 134 publications

(61 citation statements)

References 19 publications

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“…The CO hysteresis behaviour observed by Olander et al [50] was again seen in more recent molecular beam experiments by Murray et al [51], as shown by the top right plot in Figure 2.5. They also observed that CO 2 production quickly slows with increasing surface temperature, which was attributed to the "Boudouard reaction" (CO 2 + (s) + C(b) − −− → (s) + 2 CO).…”

Section: Oxidationsupporting

confidence: 58%

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Hypervelocity shock layer emission spectroscopy with high temperature ablating models

Lewis¹

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During reentry into the atmosphere, a vehicle can encounter extreme convective and possibly radiative heating loads. Such spacecraft must rely on a carefully designed thermal protection system to maintain the integrity of the underlying structure, thus ensuring the survival of any cargo or crew it may contain. Despite many past developments and research efforts, to this day there remain large uncertainties associated with the prediction of heat shield performance. In particular, accurate modelling of ablation phenomena is critical to minimising uncertainties, reducing excess weight, and increasing safety. This includes thermochemical ablation by oxidation, nitridation, and sublimation, as well as the mechanical removal of material via spallation. Due to the high costs associated with in-flight testing, and the difficulty of mounting precision instruments and advanced diagnostics on flight vehicles, ground-based experiments stand as a cost-effective method for reducing modelling uncertainties.Ablation testing is generally conducted in long-duration facilities such as arc jets, which are well suited to investigating in-depth material response due to their ability to provide representative heating rates for extended periods. They are, however, unable to reproduce a realistic in-flight shock layer due to low Reynolds numbers and, depending on the facility type, a high degree of thermal and chemical nonequilibrium in the free-stream. In contrast, impulse facilities such as shock tubes and their variants are well suited to reproducing realistic flight conditions with free-streams that are a closer match for flows dominated by binary processes in terms of Reynolds number, temperature, and chemical composition. Due to their extremely short test times, however, ranging from the order of 10 µs to several milliseconds, they are unable to aerothermally heat test models up to representative in-flight temperatures, or recreate the quasi-steady heat and mass flux balance of flight. This key limitation of impulse facilities was recently overcome in experiments using the University of Queensland's X2 expansion tunnel by electrically pre-heating samples to temperatures approaching 2500 K immediately prior to a test.In this work, the pre-heating methodology was enhanced to generate maximum surface temperatures approaching 3300 K in order to study sublimation phenomena. It was found that although sublimation-regime temperatures could be achieved, the relevant surface processes themselves were suppressed due to the high pitot pressures of the conditions used. Instead, the nitridation process was studied by observing air shock layer CN emissions with pure graphite models heated to surface temperatures ranging from 1770-3300 K. These results were compared with numerical simulations which predicted a monotonic increase of emissions with surface temperature for all models considered, whereas the experiments showed an initial increase from 1770-2500 K and then remained relatively constant from 2500-3300 K. The simulations also su...

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Section: Oxidationsupporting

confidence: 58%

“…The concept of there being two types of reaction zones was further investigated in molecular beam experiments by Olander et al [50]. Here, hysteresis behaviour was observed for CO production, whereby the apparent reaction probability was higher while heating up than when cooling down for the same surface temperature (shown in Figure 2.4).…”

Section: Oxidationmentioning

confidence: 90%

Hypervelocity shock layer emission spectroscopy with high temperature ablating models

Lewis¹

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“…If we use a risky assumption that the oxidation of FeS(c) by 0 2 is similar to that Of Cgraphite, we can use a pre-exponential factor of -1012 and an activation energy for desorption of -85 kJ/mol (because 0 2 is likely not strongly bonded to FeS(c)); this leads to a desorption rate of -107 molecules/s. However this is conjectural, particularly since there is likely to be more than one temperature regime for reaction, as in the case of graphite oxidation (Olander et al, 1972). A further complication is the rate of difision of FeS(c) to the surface of the meteoroid; this is likely to be the rate-limiting step, but it is also likely to be the source of the persistent emissions.…”

Section: Heterogeneous Atmospheric Reactionsmentioning

confidence: 99%

“…For example, reactions (3) and (4) which are very exothermic, may be likened to the oxidation reaction ofgraphite (-99% vis 0 2 + Cgraphite + Cog, + 0 and -1% via 0 2 + Cgraphite + C02 gas) which has been studied by many authors (Olander et al, 1972;Rosner and Allendorf, 1968). In these studies it has been found that the catalytic reaction on graphite proceeds via a complex sequence of steps: ( I ) the surface has two different active sites; 0 2 chemisorbs preferentially on one site (labeled A) where it forms adsorbed CO and 0, where 0 is a labile adsorbed species.…”

Section: Heterogeneous Atmospheric Reactionsmentioning

confidence: 99%

Heterogeneous chemical processes as a source of persistent meteor trains

Murad

2001

Meteorit & Planetary Scien

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Abstract-Observations of long-lasting persistent trains following the entry of some meteoroids into the Earth's atmosphere are suggested to arise in part from the interaction between meteoroid components and the atmosphere and in the heterogeneous recombination reaction of atmospheric 0 atoms with NO. The latter occurs on the surfaces of dust left by the explosive fragmentation of larger meteoroids. A strong role is attributed to reactions of troilite (FeS), a meteorite component, with the atmosphere at elevated temperatures. The suggestions made in this paper complement previous work that suggested that long-lived emissions results from a variety of species made in the shock of larger meteoroids.

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“…For lesser energy ratios only Equations (64a) and (65a) need be considered and the resulting P 11 ~ P 11 ( 2).…”

mentioning

confidence: 99%

Reaction Probabilities Implied by Multiple Gas-Surface Interactions.

Williams¹,

Baron²

1976

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Reactions of Modulated Molecular Beams with Pyrolytic Graphite. I. Oxidation of the Basal Plane

Cited by 134 publications

References 19 publications

Hypervelocity shock layer emission spectroscopy with high temperature ablating models

Hypervelocity shock layer emission spectroscopy with high temperature ablating models

Heterogeneous chemical processes as a source of persistent meteor trains

Reaction Probabilities Implied by Multiple Gas-Surface Interactions.

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