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Polymorphism, phase transformation and energetic properties of 3-nitro-1,2,4-triazole

Zhang, Pengcheng, Zhao, Xiuxiu, Du, Yao, Gozin, Michael, Li, Shenghua, Pang, Siping
RSC advances 2018 v.8 no.43 pp. 24627-24632
X-ray diffraction, crystallization, differential scanning calorimetry, heat, microscopy, nitro compounds, temperature, triazoles
We report the preparation, analysis, and phase transformation behavior of polymorphs of 3-nitro-1,2,4-triazole. The compound crystallizes in two different polymorphic forms, Form I (tetragonal, P4₁2₁2) and Form II (monoclinic, P2₁/c). Analysis of the polymorphs has been investigated using microscopy, differential scanning calorimetry, in situ variable-temperature powder X-ray diffraction, and single-crystal X-ray diffraction. On heating, Form II converts into Form I irreversibly, and on further heating, decomposition is observed. In situ powder X-ray diffraction studies revealed that Form II transforms to Form I above 98 °C, indicating that Form I is more stable than Form II at high temperature. Form II of 3-nitro-1,2,4-triazole has good detonation properties (Vdₑₜ = 8213 m s⁻¹, PC–J = 27.45 GPa), and low sensitivity (IS > 40 J, FS = 360 N, ESD = 29 J), which make it a competitive candidate for use as a new insensitive explosive.