Modeling the kinetic decomposition of Redox Frustrated Hybrid Energetic Materials

We model the thermal decomposition of 'Redox Frustrated Hybrid Energetic Materials' (RFH-EM) a concept proposed by Zdilla (O’Sullivan, Zdilla, Energetic Materials, Chem. Eur. J. 2017, 23, 14138 – 14142), where high valent oxidizers are linked with metal ions. Zdilla (Temple) and Goddard/Zybin (CalTech) recently studied the thermal decomposition of Mn6(mu3-NMe2Tz)6(ClO4)6 by reactive molecular dynamics simulation (RMD) and experiments (preprint). RMD shows robust thermal decomposition when the Mn-N cage breaks, with a cascade sequence of reactions. The continuum model uses six reduced components: 1, unreacted "Mn6-Cluster" molecular weight 1851.493 g/mol. Component 2, "Mn6-core" with light hydrocarbon groups stripped off the Mn6-Cluster, molecular weight 1418.597. Component 3 "LHC" represents groups stripped off the Cluster, with molecular weight of 72.148. Component 4 is the "Split-Core" with half molecular weight 709.298 of the Mn6-Core. Component 5, "Reactive Ligand, RLG", molecular weight 293.458 models a highly energetic reactive metal ligand. Component 6 is "Final Products, FP", molecular weight 43.774 represents equilibrium products, such as MnO, CO, CO2, etc and other lower weight species. The components are constrained by atomic mass conservation. A four step scheme is used for constant volume thermal explosions, (that mimic detonation conditions) and isobaric (high and low pressure) deflagration. Step 1) strips light molecular weight groups from Mn6-Cluster to get Mn6-Core. Step 2) splits open the Mn6-Core. Step 3) decomposition of the Split-Core to generate reactive ligand and fragments. Step 4) has reduced reactive ligands react with stripped molecules to generate final products. The RMD results are used to suggest representative reaction rates to compare the continuum model to the RMD simulations. How the equation of state of the reduced components and energies of formation of the reduced components are estimated is discussed.