Structure Property Correlations in Primary Explosives

Abstract

Abstract : The objective of this study was to identify the characteristics of primary explosives that account for their action as primaries by correlating their physical and chemical properties with their molecular structures. It was found that molecular structure could be correlated with properties within classes in a qualitative sense; however, quantitative data such as heats of formation and bond energies must still be developed before a firm scientific base can be established for designing molecular structure and predicting properties, as is possible for secondary explosives. Essential primary explosive properties are the ability to remain ignited and quickly undergo deflagration to detonation transition (DDT). Several practical primaries such as lead styphnate and lead azide have detectable burn times before detonation. Thus the study of DDT in cast explosives was initiated to establish whether DDT measurements were useful as a method to screen explosives for primary properties. DDT studies of two potential castable primaries, the isomers 1-methyl-5-nitrotetrazole (1MNT) and 2-methyl-5-nitrotetrazole (2-MNT) were undertaken as a first step to achieving this objective. Experiments showed that DDT occurs more readily in cast 2-MNT than in cast 1-MNT. Macek's model for DDT in cast explosives was modified in a theoretical study to provide a more realistic treatment of the accelerating flame. Times and distances for DDT in cast pentolite and crystalline lead azide were predicted and agreed well with the meager experimental data available.