Kinetics and Mechanism of Oxidation of the Reinforced Carbon/Carbon on the Space Shuttle Orbiter

Jacobson, Nathan; Hull, David R.; Cawley, James D.; Curry, D. M.

doi:10.1002/9780470943960.ch1

Cited by 2 publications

(12 citation statements)

References 21 publications

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“…The analyses of both the top surface and of the cross-section were compatible with the descriptions of this type of reinforced carbon/carbon found in the literature [9].…”

Section: Pristine Materialssupporting

confidence: 87%

“…The 30x30x4.8 mm samples studied were cut from a 4.8 mm thick plate of C/C coated with a conversion coating of SiC and vacuum infiltrated with TEOS (tetra-ethyl orthosilicate) [9].…”

Section: Samplesmentioning

confidence: 99%

“…The individual fibre diameter was about 8 m. The manufacturing method is propriety but the C/C and coating are similar to the reinforced C/C with its SiC conversion coating that protected the wing leading edge of the Space Shuttle Orbiter [9]. The processing temperature of the SiC coating was 1650°C, the TEOS is reportedly transformed to SiO 2 after a mild heat treatment, and an additional sodium silicate glass coating is applied to the top of the SiC coating [9].…”

Section: Samplesmentioning

confidence: 99%

“…These maps were complemented with an analysis of the microstructures using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The type of C/C and coating system studied was employed successfully on the on the leading edges of the Space Shuttle Orbiter [2,9], thus this system, and the strain distributions measured here, provide a baseline against which alternative coatings [3] or improvements can be compared. In the discussion we analyse the origin of the observed residual strains and, based on this analysis, propose methods for reducing the level of strain and the number of through-thickness cracks with the intention of further improving the oxidation resistance.…”

Section: Introductionmentioning

confidence: 99%

“…It may be noticed that the measured peak temperature (1500+100) °C was less than the melting point of pure SiO 2 (1723°C) [14] but the melting point of the extra oxide may have been lowered [15] because of the migration of some Na from the sodium silicate [9]. 10wt% of sodium silicate would have been sufficient for the oxide to melt at 1500 °C [15].…”

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confidence: 99%

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Phase and strain mapping of a protective coating on carbon–carbon

Thornton

Dale

Ruff

et al. 2016

Surface and Coatings Technology

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Carbon-carbon (C/C) is used in high temperature structures. To prevent rapid oxidation of the carbon, protective coatings are applied. This paper examines such a protective coating with high energy X-ray diffraction. The coating consisted of a 0.01 mm outer layer of sodium silicate glass on a 0.2 mm layer of silicon carbide (SiC) with a 0.1 mm transition layer into the C/C of carbon fibres surrounded by a SiC matrix. It was examined in its pristine state and after heating with an oxy-acetylene torch. An area X-ray detector was used to obtain phase and strain information as a function of depth through the coating. In-plane tensile strains were observed in both a crystalline SiO 2 phase and within the SiC of the transition layer. Oxidation protection was compromised by through-thickness cracks in the SiC layer caused by the large tensile cooling strains in the layer. The strains and the density of the cracking increased after heating. However, several mechanisms were identified that moderated the strains. Based on two of these mechanisms a buffer layer of graphite between the C/C and the SiC was proposed to improve oxidation resistance. The low elastic modulus of the graphite reduces the strains in the SiC coating, which reduces the crack density, which in turn improves oxidation resistance. Adding SiC fibres to the graphite and SiC was also proposed to further reduce cracking.

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“…The analyses of both the top surface and of the cross-section were compatible with the descriptions of this type of reinforced carbon/carbon found in the literature [9].…”

Section: Pristine Materialssupporting

confidence: 87%

“…The 30x30x4.8 mm samples studied were cut from a 4.8 mm thick plate of C/C coated with a conversion coating of SiC and vacuum infiltrated with TEOS (tetra-ethyl orthosilicate) [9].…”

Section: Samplesmentioning

confidence: 99%

Section: Samplesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Phase and strain mapping of a protective coating on carbon–carbon

Thornton

Dale

Ruff

et al. 2016

Surface and Coatings Technology

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High-Temperature Oxidation of SiC-Based Composite: Rate Constant Calculation from ReaxFF MD Simulations, Part II

2013

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Space vehicles often encounter very high temperature and harsh oxidative environments. To ensure proper thermal protection, layers composed of SiC and EPDM polymer are placed on the outer surface of the space vehicle. The O 2 and H 2 O molecules are able to oxidize the SiC network, creating SiO 2 -type structures that may form a protective layer, while also pyrolyzing and burning the EPDM polymer, causing ablation. Reactive molecular dynamics simulations nicely complement experiment, as they provide direct observation and information to calculate physical parameters such as transport diffusivities and reaction constants. In this study, rate models were developed and molecular dynamics simulated trajectories were used to extract Arrhenius parameters that describe the initial stages of transport and kinetics of SiC oxidation by O 2 and H 2 O and the combustion and pyrolysis of EPDM. The simulations showed that O 2 was able to oxidize SiC more efficiently than H 2 O, with the transport activation barrier of O 2 in the range of 40−70 kJ/mol, and for H 2 O at 125−150 kJ/mol. The oxidizer molecules created a continuous surface of SiO 2 that grew on top of the SiC layer. The O atoms insert themselves in between the Si−C bonds, causing the C atoms to migrate into a carbonaceous phase in the center of the simulation box. A model of the EPDM polymer was used for the combustion and pyrolysis simulations. An Arrhenius analysis gave activation barriers of 183 kJ/mol for combustion and 213 kJ/mol for pyrolysis. By comparison, experimental observations of EPDM and similar polymers conclude a range of ∼100−250 kJ/mol for both combustion and pyrolysis, indicating that ReaxFF can give reasonable quantitative predictions for these thermal studies, demonstrating the possibility of direct calculation of Arrhenius parameters from reactive molecular dynamics simulations.

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Kinetics and Mechanism of Oxidation of the Reinforced Carbon/Carbon on the Space Shuttle Orbiter

Cited by 2 publications

References 21 publications

Phase and strain mapping of a protective coating on carbon–carbon

Phase and strain mapping of a protective coating on carbon–carbon

High-Temperature Oxidation of SiC-Based Composite: Rate Constant Calculation from ReaxFF MD Simulations, Part II

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