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Issue 34, 2017
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Does increasing pressure always accelerate the condensed material decay initiated through bimolecular reactions? A case of the thermal decomposition of TKX-50 at high pressures

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Abstract

Performances and behaviors under high temperature–high pressure conditions are fundamentals for many materials. We study in the present work the pressure effect on the thermal decomposition of a new energetic ionic salt (EIS), TKX-50, by confining samples in a diamond anvil cell, using Raman spectroscopy measurements and ab initio simulations. As a result, we find a quadratic increase in decomposition temperature (Td) of TKX-50 with increasing pressure (P) (Td = 6.28P2 + 12.94P + 493.33, Td and P in K and GPa, respectively, and R2 = 0.995) and the decomposition under various pressures initiated by an intermolecular H-transfer reaction (a bimolecular reaction). Surprisingly, this finding is contrary to a general observation about the pressure effect on the decomposition of common energetic materials (EMs) composed of neutral molecules: increasing pressure will impede the decomposition if it starts from a bimolecular reaction. Our results also demonstrate that increasing pressure impedes the H-transfer via the enhanced long-range electrostatic repulsion of H+δ⋯H+δ of neighboring NH3OH+, with blue shifts of the intermolecular H-bonds. And the subsequent decomposition of the H-transferred intermediates is also suppressed, because the decomposition proceeds from a bimolecular reaction to a unimolecular one, which is generally prevented by compression. These two factors are the basic root for which the decomposition retarded with increasing pressure of TKX-50. Therefore, our finding breaks through the previously proposed concept that, for the condensed materials, increasing pressure will accelerate the thermal decomposition initiated by bimolecular reactions, and reveals a distinct mechanism of the pressure effect on thermal decomposition. That is to say, increasing pressure does not always promote the condensed material decay initiated through bimolecular reactions. Moreover, such a mechanism may be feasible to other EISs due to the similar intermolecular interactions.

Graphical abstract: Does increasing pressure always accelerate the condensed material decay initiated through bimolecular reactions? A case of the thermal decomposition of TKX-50 at high pressures

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Publication details

The article was received on 15 Jun 2017, accepted on 04 Aug 2017 and first published on 04 Aug 2017


Article type: Paper
DOI: 10.1039/C7CP04015F
Citation: Phys. Chem. Chem. Phys., 2017,19, 23309-23317
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    Does increasing pressure always accelerate the condensed material decay initiated through bimolecular reactions? A case of the thermal decomposition of TKX-50 at high pressures

    Z. Lu, Q. Zeng, X. Xue, Z. Zhang, F. Nie and C. Zhang, Phys. Chem. Chem. Phys., 2017, 19, 23309
    DOI: 10.1039/C7CP04015F

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