A Reassessment of the Kinetics of the Thermal Decomposition of the High Explosive, HMX, in the Range 508 K to 524 K, as Studied by Isothermal Gravimetry
Abstract
In 1986, Bulusu et al. reported on the kinetics of the thermal decomposition of HMX at atmospheric pressure from 508 K to 555 K, using isothermal gravimetric analysis. Their work implied that the decomposition kinetics followed a simple Arrhenius temperature rate law dependency but their analysis did not describe the actual kinetic pathway in any detail. In the present study, some key experiments were repeated. As a result, the following points, most of which are pertinent to any mechanistic discussion but were not considered in Bulusu's paper, can be made: (1) Over the entire temperature range of the Bulusu study, HMX exists not in its beta polymorphic form but in its delta form. (2) The thermal decomposition of HMX follows a reaction rate law which fits a sigmoidal alpha-t relationship of the form d (alpha) / d t = k' alpha (1 - alpha), where k' is the kinetic rate constant, alpha is the fractional extent of the reaction and t is the time. (3) This reaction proceeds with the complete loss of mass in the form of volatile products. (4) Over the temperature range 508 K to 524 K, the kinetics follow an Arrhenius relationship, the Arrhenius pre-exponential, In A (min-1), over this temperature range having a value of 31.07 and the energy of activation, Ea, a value of 144 kJ mol-1. However, somewhere beyond 524 K, a decomposition reaction with a different Arrhenius dependency probably comes into play the rate of reaction observed at 539 K being much greater than that calculated using the lower temperature range Arrhenius parameters. The mechanistic implications of this study are placed in the context of information from other studies.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1998
- Accession Number
- ADA352601
Entities
People
- Daniel J. Whelan
- Mark R. Fitzgerald