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Gasification of Silicone Fluids Under External Thermal Radiation.


pdf icon 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.