Theoretical simulation study on crystal property and hygroscopicity of ADN doping with nitramine explosives (RDX, HMX, and CL-20)

Abstract

To effectively modify the strong hygroscopicity of ammonium dinitramide (ADN) crystal, the modification of ADN crystal in the 298 K under vacuum environment was studied through theoretical calculation. Three kinds of energetic nitramine molecules (X = RDX, HMX, and CL-20) were inserted into ADN crystal in different proportions (the molecular ratios of ADN to X are 6/1, 12/1, 18/1, and 24/1), to form a total of 12 kinds of designed ADN crystals. The results show that with the modification of ADN crystal with RDX, HMX, and CL-20, the crystal space group, cell parameters, crystal density, and growth morphology will be changed under vacuum conditions. According to the analyses of adsorption heat data, four proportional modification systems all reduced the hygroscopicity of ADN crystal to varying degrees. It is worth noting that the hygroscopicity of modified ADN crystal tends to decrease with the increase of the proportion of doping molecules, but the stability gradually deteriorates, especially 18ADN/1CL-20 and 24ADN/1CL-20. Although they have an excellent anti-moisture effect, from the perspective of crystal energy stability, the actual syntheses of these two kinds of crystal cells are the most difficult. Combined with the energy stability and hygroscopicity analysis, 1HMX/24ADN crystal is a more suitable anti-hygroscopicity modification scheme among the doped ADN crystals. In this case, the isothermal adsorption heat of ADN crystal decreases from 0.692 kcal/mol to 0.573 kcal/mol. The theoretical simulation study of ADN doping modification in a vacuum will provide significant references for ADN modification in the actual situation.

Keywords: Crystal modification; Energetic materials; Moisture absorption; Molecular simulation; Theoretical calculation.