Experimental Support for Ablation Model Parameter Development and Solid State Thermal Decomposition
Start Date
1-3-2011 8:00 AM
End Date
3-3-2011 12:30 PM
Description
To predict the high temperature behavior of a carbon/phenolic charring ablator, a model of the thermal decomposition of resin is required. This model should represent the intrinsic behavior of the resin independent of the experimental conditions. The current method of representation is to use an Arrhenius expression, the apparent kinetic parameters having been obtained from a thermogravimetric analysis (TGA) test. This can simply be described as a curve fitting exercise, without any chemical significance attributable to the calculated apparent kinetic parameters. The scientific community has not, to our knowledge, provided any other method of representation of the kinetics of a reaction in the solid state. Therefore the ablation community continues to make use of this empirical expression. The result is that there is currently no connection between the kinetic parameters used to represent the solid-state thermal decomposition of the resin and the pyrolysis gas chemistry. As well as this, there is limited understanding of the fundamental thermal decomposition reaction mechanism. Succinctly put, the current research goal is to predict a thermogravimetric analysis test (mass loss versus temperature curve, at a given heating rate) under a prescribed set of experimental conditions. This requires understanding of the intrinsic chemical rate of reaction independent of the effects of heat and mass transfer.
The presentation will briefly cover 3 areas:
- Standard TGA testing of phenolic resin and the interpretation of the decomposition events as a function of heating rate. Current work including high rate tga (up to 500ºC/min) will be compared with previous high rate TGA in the literature.
- Results of preliminary analytical pyrolysis of phenolic resin to identify the condensable and gaseous, decomposition products.
- Preliminary molecular dynamics modeling of the thermal decomposition process of phenolic resin using ReaxFF.
It would be useful to discuss the current aspirations of the ablation community as well as the relevance of the approach outlined above.
Experimental Support for Ablation Model Parameter Development and Solid State Thermal Decomposition
To predict the high temperature behavior of a carbon/phenolic charring ablator, a model of the thermal decomposition of resin is required. This model should represent the intrinsic behavior of the resin independent of the experimental conditions. The current method of representation is to use an Arrhenius expression, the apparent kinetic parameters having been obtained from a thermogravimetric analysis (TGA) test. This can simply be described as a curve fitting exercise, without any chemical significance attributable to the calculated apparent kinetic parameters. The scientific community has not, to our knowledge, provided any other method of representation of the kinetics of a reaction in the solid state. Therefore the ablation community continues to make use of this empirical expression. The result is that there is currently no connection between the kinetic parameters used to represent the solid-state thermal decomposition of the resin and the pyrolysis gas chemistry. As well as this, there is limited understanding of the fundamental thermal decomposition reaction mechanism. Succinctly put, the current research goal is to predict a thermogravimetric analysis test (mass loss versus temperature curve, at a given heating rate) under a prescribed set of experimental conditions. This requires understanding of the intrinsic chemical rate of reaction independent of the effects of heat and mass transfer.
The presentation will briefly cover 3 areas:
- Standard TGA testing of phenolic resin and the interpretation of the decomposition events as a function of heating rate. Current work including high rate tga (up to 500ºC/min) will be compared with previous high rate TGA in the literature.
- Results of preliminary analytical pyrolysis of phenolic resin to identify the condensable and gaseous, decomposition products.
- Preliminary molecular dynamics modeling of the thermal decomposition process of phenolic resin using ReaxFF.
It would be useful to discuss the current aspirations of the ablation community as well as the relevance of the approach outlined above.