1984-07-01

Materials Development for Multiple Performance Requirements 840920

In order to analyze the effects of material performance on the flight characteristics of a reentering vehicle, models describing the materials must be developed for use in computer studies. This report discusses the thermal/ablation models developed for silicone-based materials. These materials consist of mixtures of Sylgard 182 (silicone), silica, silica fibers, and a catalyst. They are designated as Silicone A and Silicone B each with and without the catalyst. Silicone A contains silica fibers where Silicone B does not.Included in this report are 1) the elemental composition of the virgin material, pyrolysis gases, and the residual (char) material, 2) the virgin and residual (char) material heats of formation derived from previous models and from residual elemental analysis, 3) the decomposition kinetics developed from Thermal Gravimetric Analysis (TGA) tests, 4) the enthalpy of the pyrolysis gases using both frozen and equilibrium chemistry, 5) the development of the thermochemical surface energy balance tables, and 6) thermal conductivity and specific heat models developed by correlating arc test thermocouple response data.One major result from the development of these thermal models is that, although the TGA curves demonstrate significant differences between the residual densities of the silicones with and without the catalyst, the chemical analyses and the thermocouple response curves resulted in models which do not differentiate between catalyst loaded and unloaded material.

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