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Introduction: 1,3,5-Trinitroperhydro-1,3,5-triazine (RDX), an important secondary explosive, has attracted the attention of scientists for many years since it was synthesized by Henning in 1899 for medicinal use and used as an explosive in 1920 by Herz (Akhavan, 2004: 41-42). The most stable crystalline structure of RDX was found to be α-RDX. RDX is one of the most effective energetic materials with applications ranging from explosives to propellants (Zhu, Xiao, Zhu, Xiao, 2009: 1082-1088). The impact sensitivity (h50) of RDX is 24 cm in which RDX is classified as a sensitive explosive (Storm, Stine, Kramer, 1990: 605-639). Triazoles can be used in preparation of high performance primary and secondary explosives, since these nitrogen rich aromatic rings provide good kinetic and thermal stabilities to these explosives in addition to the production of nitrogen gas after explosion (Dippold, Izsák, Klapötke, 2013: 12042-12051). Coburn synthesized highly thermally stable explosives of 3-(picrylamino)-1,2,4-triazole (PATO) and 3-amino-5-(picrylamino)-1,2,4-triazole (APATO) containing of both trinitrobenzene and triazole rings (Chioato, Klapötke, Mieskes, Stierstorfer, Weyrauther, 2016: 956-962). Nitro group bonded triazole ring and hydroxyl group bonded tetrazole ring containing triazole-tetrazole derivative, 5-(3-nitro-1H-1,2,4-triazol-5-yl)tetrazol-1-ol (NTTO), was synthesized in which the friction and impact sensitivities were much higher than that of RDX. Another advantage of this compound was its ballistic performances which did not decrease so much (Dippold, Izsák, Klapötke, 2013: 12042-12051). Dihydroxylammonium salt of 3,5-bis(dinitromethyl)-1,2,4-triazole (BDT) was synthesized with low sensitivity relative to RDX in which the ballistic performances were high enough to compete with it (Dharavath and Shreeve, 2018: 48-53). Purpose: The purpose of this research is to investigate how the material and explosive properties of α-RDX change in case of triazole ring attachment, computationally. Scope: The calculations were performed on first α-RDX structure and then triazole ring attached α-RDX structure in order to compare the differences between the two in terms of insensitivity, ballistic and chemical properties. Limitations: Relative comparisons were done in the limitations of the method, functional and basis set used in this computational study. Method: The DFT method with UB3LYP functional and 6-31G(d,p) basis set was used throughout the study (DFT UB3LYP/6-31G(d,p)) (Kohn and Sham, 1965: A1133-A1138). Gaussian 09 software was used for all the computations (Frisch et al., 2013). Findings: The triazole ring attachment increased the sensitivity of RDX contrary to the expectations. The weakest N−NO2 bond dissociation energy of 131,7 kJ/mol in RDX decreased to 110,4 kJ/mol in RDX-triazole. The results showed that the electrostatic potential around RDX N−NO2 bonds shifted to more positive region in RDX-triazole compound which indicated that the electron density around RDX N−NO2 bonds decreased in a significant amount in new compound. As a result, this deficiency caused to more sensitive bonds. The reduced amount of ballistic performances (detonation velocity (D) and detonation pressure (P)) were obtained with respect to RDX (D(RDX) = 9,02 km/s, D(RDX-triazole) = 8,52 km/s, P(RDX) = 35,85 GPa, P(RDX-triazole) = 32,02 GPa). The chemical hardness (η) of RDX was found to be higher than RDX-triazole (η(RDX) = 0,27 eV, η(RDX-triazole) = 0,22 eV). The electrophilicity index of RDX was greater than RDX-triazole (ω(RDX) = 0,072 eV, ω(RDX-triazole) = 0,049 eV) which indicated that RDX had more electrophilic character than RDX-triazole. However, the frontier molecular orbital energy ratios (EHOMO/ELUMO: fH/L) showed that RDX-triazole was more resistant to oxidation compared to RDX (fH/L(RDX-triazole) = -5,10; fH/L(RDX) = -6,46). Conclusion: Ballistically less powerful, thermally more sensitive and chemically more oxidizable energetic material was obtained via attachment of triazole ring to RDX.
Anahtar Kelimeler: RDX, Triazole, Ballistics, Insensitivity, Density Functional Theory
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