Heat-induced solid-state polymorphic transition of 4,4′,5,5′- tetranitro-1H,1′H-[2,2′-biimidazole]-1,1′-diamine (DATNBI)

Abstract

Polymorphs of energetic materials generally exhibit distinct features, such as density, thermal stability, sensitivity, and detonation performance. These features are important in determining the appropriate applications of a given polymorph. To understand the thermal stability of new high explosive 4,4′,5,5′-tetranitro-1H,1′H- [2,2′-biimidazole]-1,1′-diamine (DATNBI), we systematically investigated its polymorphic transition (PT) under thermal stimulation and discovered a novel stable γ form of DATNBI. The results showed that the solid-solid PT path was β→α→γ. In this study, the three polymorphs of DATNBI were prepared through solvent recrystallization, and their PT processes in solution were explored. Crystal structure analysis of γ-DATNBI suggested that its special cross-cross grid crystal packing may be the main reason for its stable existence at room temperature and its lack of PT process before chemical decomposition, which starts at 240 ​°C. To further explore the PT process of DATNBI, the solid phase transition mechanism of DATNBI was analyzed using non-isothermal kinetics. The results demonstrated that the two high-temperature PT processes—β→α and α→γ—were not single-step reactions but complex multi-step reactions. The PT activation energy of the β→α process was slightly higher than that of the α→γ process. In addition, the influences of different polymorphs on the performance of DATNBI were explored. The results revealed that safety and detonation performance should decrease as a result of the incorporation of γ-DATNBI. This study contributes to understanding the PT behavior and the crystal structure evolutionary mechanism of DATNBI. This study provides practical support for formula design, process condition selection, and thermal stability evaluation of DATNBI explosives.