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Issue 46, 2017
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A theoretical prediction on the shear-induced phase transformation of TKX-50

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Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) is a new and attractive energetic material that outperforms numerous common explosives because of its excellent properties and performance, and is thus a promising candidate to replace some of them. Nevertheless, knowledge of its physico-chemical properties, in particular, the underlying mechanism for it undergoing external stimuli for complete decay still remains poor. In the present study, we ascertain a preferred slip system of (010)/[101] and a shear-induced phase transition of TKX-50 with the aid of theoretical calculations. In other words, a new phase of TKX-50, γ-TKX-50, is observed to be formed by shearing TKX-50 along a slip system of (010)/[101] or (010)/[10[1 with combining macron]] with a space group of P21/a, elevated energy of 9.4 kcal mol−1 and a unit cell expanded 4%, relative to the original TKX-50. Moreover, γ-TKX-50 can most readily be formed by shearing TKX-50 along (010)/[101] with a lowest energy barrier of 18.6 kcal mol−1, which is much below that for TKX-50 decay. The predicted elastic constants of γ-TKX-50 verify its mechanical stability with decreased mechanical anisotropy relative to the original TKX-50. In addition, we find that, after phase transition, the hydrogen bonding is weakened, while the electrostatic repulsion of Hδ+⋯Hδ+ increases, which disfavors the proton transfer from NH3OH+ to C2O2N82− to facilitate the thermal decay of TKX-50. This suggests that the shear-induced transition from TKX-50 to γ-TKX-50 can enhance thermal stability by elevating the energy barrier for proton transfer, potentially contributing to the low mechanical sensitivity of TKX-50. Hopefully, this study would enrich the insight into the underlying mechanism of TKX-50 against external thermal–mechanical stimuli. Moreover, in combination with the newly found heat-induced phase, the shear-induced phase observed in the present study and the original one, there are at least three phases for TKX-50.

Graphical abstract: A theoretical prediction on the shear-induced phase transformation of TKX-50

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Publication details

The article was received on 16 Sep 2017, accepted on 02 Nov 2017 and first published on 03 Nov 2017

Article type: Paper
DOI: 10.1039/C7CP06363F
Citation: Phys. Chem. Chem. Phys., 2017,19, 31054-31062
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    A theoretical prediction on the shear-induced phase transformation of TKX-50

    Z. Lu, X. Xue and C. Zhang, Phys. Chem. Chem. Phys., 2017, 19, 31054
    DOI: 10.1039/C7CP06363F

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