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Does Pressure Increasing Always Accelerate the Condensed Material Decay Initiated through Bimolecular Reactions? A Case of the Thermal Decomposition of TKX-50 at High Pressures

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, Raman spectroscopy measurements and ab initio simulations. As results, we find a quadratic increase in decomposition temperature (Td) of TKX-50 with pressure (P) increasing (Td = 493.325 + 12.944 P + 6.282 P2, Td and P in K and GPa, respectively, and R2=0.995), and the decompositions under various pressures are 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 that the decomposition retarded with pressure increasing 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 mechanism may be feasible to other EISs due to the similar intermolecular interactions.

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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, Accepted Manuscript
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    Does Pressure Increasing 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, Accepted Manuscript , DOI: 10.1039/C7CP04015F

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