Abstract
The crystal structure of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaiso-wurtzitane (CL-20) p-xylene solvate, and the solvent effects on the crystal faces of CL-20 were studied through a combined experimental and theoretical method. The properties were analyzed by thermogravimetry-differential scanning calorimetry (TG-DSC), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD).The growth morphology of CL-20p-xylene solvate crystal was predicted with a modified attachment energy model. The crystal structure of CL-20p-xylene solvate belonged to the Pbca space group with the unit cell parameters, a = 8.0704(12) Å, b=13.4095(20) Å, c = 33.0817(49) Å, and Z = 4, which indicated that the p-xylene solvent molecules could enter the crystal lattice of CL-20 and thus the CL-20 p-xylene solvate is formed. According to the solvent-effected attachment energy calculations, (002) and (11−1) faces should not be visible at all, while the percentage area of the (011) face could be increased from 7.81% in vacuum to 12.51% in p-xylene solution. The predicted results from the modified attachment energy model agreed very well with the observed morphology of crystals grown from p-xylene solution.
Highlights
Crystal morphology is very important because it can determine many properties of a material, such as shelf life, vapor pressure, solubility, bioavailability, and density, which further influence the related downstream products [1]
The growth morphology algorithm is based on the attachment energy (AE) method, which is proposed by Hartman and Bennema based upon period bond chain (PBC) theory [26]
Single crystal X-ray diffraction showed that CL-20 p-xylene solvate crystal belonged to the orthorhombic system, space groupPbca, with the unit cell parameters, a = 8.0704(12) Å, b = 13.4095(20) Å, c = 33.0817(49) Å, V = 3580.10(92) Å3, and Dcrystal = 1.8228 g/cm3.The measured molecular weight of CL-20p-xylene solvated crystal was 3930.16 g/mol, which was equal to the total molecular weight summation of CL-20 andp-xylene, indicating that the molecular number ratio of CL-20 top-xylene was 1:1
Summary
Crystal morphology is very important because it can determine many properties of a material, such as shelf life, vapor pressure, solubility, bioavailability, and density, which further influence the related downstream products [1]. The growth rate, a center-to-plane distance is assigned to each face This information is used to deduce the morphology. Since the explosiveCL-20 crystallizes in the solvent [25], it is very important to study the solvent effects on CL-20 crystal faces and morphology In this present work, a combination of experimental and simulated morphology had been done to allow us to understand roles of solvents on crystal morphology. The growth model of explosive CL-20 crystals in p-xylene solution at a given temperature. These results provided the fundamental information to predict the potential morphology changes during the formation of solvated CL-20 or other explosives
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