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Decomposition of Phenolic Impregnated Carbon Ablator (PICA) as a Function of Temperature and Heating Rate
Version 2 2017-06-19, 13:48
Version 1 2017-06-16, 15:19
journal contribution
posted on 2017-05-25, 00:00 authored by Brody
K. Bessire, Timothy K. MintonMaterial response
models for phenolic-based thermal protection
systems (TPSs) for atmospheric entry are limited by the lack of knowledge
of the nonequilibrium processes that may govern the decomposition
pathways of phenolic resin at heating rates up to tens of degrees
Celsius per second. We have investigated the pyrolysis of phenolic
impregnated carbon ablator (PICA) by measuring the molar yields of
the volatile decomposition products as a function of temperature at
four nominal heating rates of 3.1, 6.1, 12.7, and 25 °C s–1, over the temperature range of 100–1200 °C.
A mass spectrometer was used to probe the 14 significant gaseous products
directly as PICA samples were heated resistively in vacuum. Four products,
H2, CH4, H2O, and CO, overwhelmingly
dominated the molar yields. However, in terms of mass yield, phenol
and its methylated derivatives, cresol and dimethyl phenol, were significant.
The temperature-dependent molar yields of the observed products exhibited
a marked dependence on heating rate. The heating-rate-dependent behavior
of the molar yields has been attributed to two main competing decomposition
processes that occur as the temperature passes from roughly 300 to
500 °C: (1) cross-linking reactions that produce ether functional
groups and carbon–carbon bonds and eliminate H2O
and (2) breakdown of the polymer backbone through scission of methylene
bridges and liberation of phenol and its methylated derivatives. The
latter process competes more effectively with the former as the heating
rate increases. The relative rates of these processes appear to have
a significant effect on the molar yields of volatile products from
subsequent decomposition processes as the temperature is increased
further. Thus, the heating rate strongly affects the pathways taken
during the pyrolysis of the phenolic resin in PICA. The new data may
be used to test nonequilibrium models that are designed to simulate
the response of TPS materials during atmospheric entry of spacecraft.
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PICAdecomposition processesTPSmethylated derivativestemperature-dependent molar yieldsHeating Rate Material response modelstest nonequilibrium modelsphenolic impregnated carbon ablatorPhenolic Impregnated Carbon Ablatormolar yieldsCHCOheating ratesH 2 Oheating ratephenolic resinheating rate increases
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