Gasification of Silicone Fluids Under External Thermal Radiation. Part 2. Gasification Products: Characterization and Quantitation.
Gasification of Silicone Fluids Under External Thermal
Radiation. Part 2. Gasification Products:
Characterization and Quantitation.
(1145 K)
Buch, R. R.; Austin, P. J.; Kashiwagi, T.
Fire and Materials, Vol. 22, 239-252, 1998.
Keywords:
silicones; gasification; thermal radiation; degradation
products; heat of vaporization; thermal degradation
Abstract:
The gasification behavior for a wide range of
polydimethylsiloxane fluids in a nitrogen atmosphere was
investigated. Part 1 of this study addressed the
measurement of the energy (global heat of gasification)
required for the gasification of a wide range of
dimenthylsiloxanes. Several significant corrections were
required to reconcile measured gasification energy(s)
with calculated heat(s) of gasification based on
fundamental thermochemical data. The identification of
the dominant mode(s) of gasification via the
characterization of pyrolysis products provided a firm
basis and rationale for understanding and directing
efforts at quantifying these correction factors. In Part
2, the gasification products were identified and
quantified at various stages of the gasification process
corresponding to ignition, fire growth, and steady-state
burning. Pyrolysis of methylated siloxanes occurs via
two modes: (1) the volatilization of short chain and
intermediate chain length species native to the polymer,
and (2) the volatilization of short chain and
intermediate chain length species resulting from thermal
degradation via siloxane rearrangement. The former
process is the dominant gasification mechanism for short
chain oligomers and low viscosity fluids and the latter
process is dominant in all higher molecular weight
polymers. Both gasification mechanisms are evident in
all polymers; the dominant mechanism is dependent upon
polymer size and distribution thereof, the gasification
stage, and the presence of trace catalysts in the
polymer. Because of their structural similarity, the
combustion of all gasification products emanating from
PDMS regardless of the stage of the pyrolysis process or
the dominant mode of gasification will result in
virtually identical combustion products, i.e. SiO2, CO2,
and H2O.
