Prediction of the Thermal Behaviour of Energetic Materials by Advanced Kinetic Modelling of HFC and DSC Signals

Abstract

High energetic materials can slowly decompose during storage or transport particularly at elevated temperatures which may result in reduced performance and correct functionality. Even very low decomposition progress of the exothermic reaction resulting in minor heat release can significantly change the properties of the propellants leading to shortening of the service life-time. The reaction progress influencing already the behaviour of the samples can be in the range of ca. 1-2% of the total decomposition degree. There are the literature reports showing that the amount of the evolved heat during decomposition as low as ca. 40 J/g can alter the material properties. Monitoring such a minor heat release requires very sensitive techniques as Heat Flow Calorimetry (HFC).

Proposed method for simulation of the amount of heat evolved during aging of the energetic materials which allows predicting the thermal behaviour of the samples is based on the elaboration of the difference between the HFC signals recorded for the unaged and differently altered samples. The samples aged in furnaces at 50, 60 and 70°C were investigated by HFC technique at 80°C and obtained signals were compared with the traces of the unaged sample recorded during 10 days also at 80°C. Observed changes of the recorded heat flows as a function of time at 80°C for the differently aged samples related to the heat flow of the unaged sample allowed the determination of the kinetic parameters of the decomposition process. They were determined by the differential isoconversional method applying the principle of the compensation effects widely used in the kinetics of the solid heterogeneous reactions. The knowledge of the kinetics of the early stage of the process allowed the precise prediction of the reaction rate at any temperature mode. It allowed also the simulation of arbitrarily chosen cumulative heat release (e.g. 40 J/g) at any temperature profile such as storage conditions depicted in STANAG 2895 or A1 cycles “extreme hot climate” with daily temperature fluctuations between 32 and 71°C.

The application of the proposed advanced kinetic method of the elaboration of the HFC signals significantly shortens the time of the experiments: note that the required information is gained from the HFC experiments carried out at relatively high temperature of 80°C.