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.
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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DOI：
10.1039/c7cp04015f
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发表时间：
2017-08
期刊：
影响因子：
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通讯作者：
Zhipeng Lu;Q. Zeng;Xianggui Xue;Zengming Zhang;Fude Nie;Chaoyang Zhang
中科院分区：
文献类型：
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作者：
Zhipeng Lu;Q. Zeng;Xianggui Xue;Zengming Zhang;Fude Nie;Chaoyang Zhang
高温高压条件下的性能和行为是许多材料的基础。本文采用拉曼光谱测量和从头计算方法，研究了压力对一种新型含能离子盐TKX-50热分解的影响。结果表明，TKX-50的分解温度（Td）随压力（P）的增加呈二次曲线增加（Td = 6.28P ~ 2 + 12.94P + 493.33，Td和P分别以K和GPa计，R ~ 2 = 0.995），在不同压力下的分解反应是由分子间氢转移反应（双分子反应）引发的。令人惊讶的是，这一发现与关于压力对由中性分子组成的普通高能材料（EM）分解的影响的一般观察相反：如果它从双分子反应开始，则增加压力将阻碍分解。我们的研究结果还表明，增加压力阻碍H-转移通过增强的长程静电排斥H+δH+δ的相邻NH3 OH+，与分子间H-键的蓝移。并且氢转移中间体的后续分解也被抑制，因为分解从双分子反应进行到单分子反应，这通常通过压缩来防止。这两个因素是TKX-50的分解随压力增加而减缓的根本原因。因此，我们的发现突破了以往提出的对于凝聚态物质，压力的增加会加速由双分子反应引发的热分解的观点，揭示了压力影响热分解的独特机理。也就是说，增加压力并不总是促进通过双分子反应引发的凝聚物质衰变。此外，这种机制可能是可行的其他EIS由于类似的分子间相互作用。
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+δH+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.