Mechanism and kinetics of decomposition from isothermal DSC data: Development and application



A method for deriving kinetic equations of decomposition of thermally unstable chemicals from isothermal DSC experiments was developed. The following steps are included in the method:

  • collecting experimental data in the form of heat flow versus time from isothermal DSC experiments at three or four different temperatures, and in the form of temperature versus time from one adiabatic ARC experiment,

  • converting the experimental DSC data into concentration versus time data using DSC Isothermal Kinetics Data Analysis Program, Part 1 (TA Instruments),

  • fitting a specific kinetic equation to the concentration versus time data using Rate Program (Batch CAD),

  • calculating rate constants at the experimental temperatures using Rate Program (Batch CAD),

  • determining activation energy and frequency factor from temperature dependence of k,

  • verifying the kinetic equation by simulating adiabatic decomposition of the chemical in an ARC bomb using the derived kinetic equation and Reaction Program (Batch CAD) and comparing the simulation results with experimental.

The decomposition kinetics and mechanism for the following six groups of chemicals were analyzed: nitrobenzene, nitrosobenzene, hydrazine, and tetrazoles derivatives, alkynes ([BOND] C [TRIPLE BOND] C [BOND]), and monomers (H2C [DOUBLE BOND] C [BOND]). The first four groups were determined to decompose by an autocatalytic mechanism. Full kinetic equations were developed and analyzed for six tetrazoles. The mechanism of decomposition for all six chemicals appeared to be autocatalytic, showing various reaction orders (0.7–2.2) with respect to the chemical and the autocatalyst. Reaction orders, activation energies, and frequency factors were determined and compared for all six chemicals.