Gasification of Silicone Fluids Under External Thermal Radiation.
Gasification of Silicone Fluids Under External Thermal
Radiation.
(5581 K)
Austin, P. J.; Buch, R. R.; Kashiwagi, T.
NISTIR 6041; 83 p. July 1997.
Available from:
National Technical Information Service
Order number: PB97-196844
Keywords:
silicones; gasification; thermal radiation; degradation
products; heat of vaporization; thermal degradation
Abstract:
Transient gasification rate and fluid temperatures were
measured for polydimethylsiloxanes having fluid
viscosity from 0.65 cS to 60,000 cS in a nitrogen
atmosphere at external radiant fluxes from 20 kW/m2 to
70 kW/m2. Trapped volatile products and fluid residues
collected at different gasification stages were analyzed
to determine their chemical structure using various
analytical methods. Detailed energy balance of fluid
samples was conducted to determine global heat of
vaporization including absorption of incident radiation
by the volatile products, reradiation loss from heated
fluids and heat loss to the substrate. The measured
average gasification rate of all siloxanes studies in
this work increases linearly with an increase in
external radiant flux. The global heat of vaporization
per unit mass of siloxane increases with an increase in
the molecular weight of the siloxanes up to a 50 cS
fluid and its value remains constant at about 1,200 J/g
for all higher molecular weight dimethylsiloxanes. The
gasification of siloxanes occurs via two modes or
regimes or combinations thereof: 1) volatilization of
molecular species native to the polymer, and 2)
volatilization of cyclic molecules which result from the
thermally induced degradation of the polymer via
siloxane bond rearrangement. The former process
dominates for low molecular weight siloxanes (<10 cs)
and the latter process dominates for high molecular
weight siloxanes (>1,000 cS). For the intermediate
molecular weight siloxanes, both volatilization and
degradation processes occur.
