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1 Central European Journal of Energetic Materials

1 2006

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Activation Energy of Propellants at Low Temperature Range

100%

Ticmanis U. , Wilker S. , Pantel G.

tom Vol. 3, nr 4

51-72

This paper describes a new approach to determine the activation energy of propellant decomposition reactions which quantifies the temperature dependence of a reaction rate at temperatures below 50 C by using an indirect microcalorimetric method. Whereas the determination of life time and stability of propellants is usually performed by artificial ageing at elevated temperatures with a temperature range usually between 70 and 130 C only few and scattered data are available for temperatures below 50 C.Normally these activation energies for propellant decomposition reactions are not known below temperatures of about 50 C because (i) the reaction rates are very small and thus ageing times have to be very long and (ii) because of slow reactions the chemical change of the propellant becomes very small which - in combination with too short ageing times - may lead to wrong estimations and calculations. The main reason for this is that the experimental error is relatively big in comparison with the real change of the propellant.To be on the 'safe side' people usually assume a low value of activation energy. This has the effect that measuring times at high temperatures are much longer than they should be and that maybe good material is thrown away too early in fear of a thermal instability.To overcome this problem we have established a new approach by an indirect microcalorimetric method. This method evaluates the shift of typical points in the heat flow curve to earlier times after artificial ageing at relatively low (30-70 C) temperatures. From the time shift of a specific point in the heat flow curve (compared to the unaged material) and the temperature difference between ageing temperature and measuring temperature activation energies of the whole temperature range between 89 C and 30 C are available. We have verified the usability of this approach with six different nitrocellulose based propellants.