液态硝基甲烷热分解行为及压力效应的第一性原理研究

采用基于密度泛函理论的第一性原理分子动力学方法对液态硝基甲烷的热分解行为进行了模拟,结合各产物布居数随时间的演化,讨论了热分解初期可能发生的3种反应,即分子内/分子间的质子迁移反应和C—N键的断裂.在长时间（30 ps）的模拟过程中,H₂O是主要产物.研究了液态硝基甲烷在不同密度（压力）条件下热分解的动力学行为.发现不同密度（压力）条件下液态硝基甲烷热分解呈现明显不同的变化趋势,并给出了解释. 关键词： 硝基甲烷 分子动力学 热分解 压力效应     

Multiactivation of organic reactions high pressure cycloaddition reactions catalyzed by lanthanides

Abstract

Combination of lanthanide catalysis and high pressure is highly beneficial in the Diels-Alder addition of ethyl vinyl ether to unsaturated keto compounds. The method is particularly appropriate for the synthesis of sterically congested dihydropyrans. The activation volumes of catalyzed and thermal hetero-Diels-Alder reactions do not differ significantly. This means conservation of the pericyclic character of the process.     

High pressure effect on the chemoselectivity of catalyzed [2+2] and [2+2+2] addition reactions involving acetylenic esters

Abstract

The chemoselectivity is changed by pressure in the catalyzed addition of propynoates to norbornadiene, but is not altered in the corresponding addition to norbornene.     

高压下固相硝基甲烷分解的分子动力学计算

基于ReaxFF, 采用NVT系综和Berendsen方法对0–7 GPa时和2500 K时固相硝基甲烷的 分解过程进行分子动力学计算, 通过分析硝基甲烷发生分解反应生成的碎片数量随时间的变化, 对不同压强下硝基甲烷的分解机理进行研究. 计算结果表明在0–3 GPa时, 初始分解路径为C–N键断裂和硝基甲烷的异构化; 在4–7 GPa 时, 初始分解路径为分子间质子转移和C–N, N–O键的断裂; 在硝基甲烷的第二阶段反应中存在H₂O, NO, NO₂, HONO, 硝基甲烷分子自身的催化反应. 硝基甲烷在高温高压下发生热分解反应生成碳团簇, 且团簇中碳原子的数量和碳团簇的空间构型随着压强的变化而变化. 关键词： ReaxFF 分子动力学 热分解 压强效应 碳团簇     

The effect of ambient pressure on laser-induced plasmas in air

A detailed investigation of the effect of ambient pressure in the range of 0.1 to 1.0 atm on the size, temperature, electron number density, and fraction of laser energy absorbed in a laser-induced plasma in air has been conducted. As pressure is reduced the size of the plasma, its electron number density, its peak emission intensity, and the fraction of incident laser energy that is absorbed are all found to decrease significantly. The temporal temperature profile in the plasma and the fraction of the absorbed laser energy that is converted to thermal energy in the plasma remain constant, at least down to 0.2 atm.     

不同催化剂热解法制备硼碳氮纳米管过程中的影响

对以钴、镍、钴/镍、钴/二茂铁、镍/二茂铁和二茂铁为催化剂高温热解法制备的硼碳氮（BCN）纳米管的结构、产率等的影响进行了分析.实验中发现催化剂在BCN纳米管的生长过程中有重要作用.高分辨率透射电子显微镜图像显示在860℃时，以镍/二茂铁、钴/二茂铁为催化剂生成的BCN纳米管具有“竹节状”结构，且管壁较薄，镍、钴或镍/钴作催化剂生成的BCN纳米管不具有明显的“竹节状”结构，管壁较厚，且粗细不均匀，而以二茂铁作催化剂没有BCN纳米管生成.在所有生成的BCN纳米管中含有催化剂颗粒.通过对生成的BCN纳米管的结 关键词： BCN纳米管 热解 催化剂 拉曼光谱     

影响压力传感器温度特性的因素分析

压力传感器性能易受温度变化的影响,从而增加了测量结果的误差。文中通过对压力传感器工作原理及结构的介绍,理论分析了影响压力传感器温度特性的因素,并建立一套压力传感器变温校验系统,进而通过实验说明了温度变化对压力传感器信号输出的影响。同时,也对目前国内在低温环境下压力传感器的应用及研究情况进行了介绍。     

Structural and kinetic aspects of hydrostatic pressure effect on polymer network formation

Abstract

Effect of hydrostatic pressure up to 250 MPa on structurization kinetics and morphology of network polymers based on epoxy oligomers has been studied using the methods of measurements of resistivity and optical microscopy.     

A model for the pressure dependence of diffusion in condensed matter

In the present paper, a model has been used to develop a simple relation to study the pressure dependence of self-diffusion in solids and liquids that has two adjustable parameters. The computation done in each substance is found to be in very good agreement with the experimental data. It is interesting to note that the present relation is also capable of giving the activation volume in solids and liquids. The activation volume computed in the solids is found to be in very good agreement with the data available.     

Effect of thermal treatment under high pressure on the quality of a meat sauce

Abstract

It is known that pressure alone is not able to make shelf-stable any food stored in room conditions. Acid products are normally spoiled by enzymes, and low acid products are spoiled even by spore-forming micro-organisms. To overcome the problem the role of heat in the process has been re-evaluated and the possibility of destroying at the same time spores and enzymes has been found. This work compares the effect of sterilisation by High Pressure Processing (HPP) with one of the conventional retort processing techniques. Two batches of meat sauce were kept in room conditions over a year and their quality was evaluated periodically during the shelf life simulation. The physico-chemical characteristics of the retorted ones showed a progressive appearance of the typical thermal damage. The High Pressure Sterilised samples on the contrary showed limited damage, related to the unavoidable pre-heating. Their quality markers were constant over the shelf life evaluated period.     

Effects of pressure on the structure and the thermal decomposition kinetics of RDX

Abstract

High pressure and temperature structural changes for RDX were investigated to 7.0 GPa and 570 K in a diamond anvil cell apparatus using FTIR absorption, optical microscopy, and energy-dispersive powder x-ray diffraction techniques. Three distinct solid phases were observed. The effects of pressure on the thermal decomposition kinetics as a function of RDX pressure were investigated using an infrared absorption technique. Solid phase I was found to have a pressure enhanced reaction rate with an energy and volume of activation of 51 Kcal/mole and -5.6 cc/mole respectively. Solid II was not observed to react and the observed reaction rate of Solid III decreased with increasing pressure.     

Irradiation effect on the activation energy of thermal decomposition of polymers

The present work looks into the aspect of thermal modifications induced in polymers by proton irradiation. The kinetics of thermal decomposition of polymers is investigated by using the thermogravimetric (TG) technique. It has been observed that the degradation of polymers is a multi-step process that involves sequential and competing processes, and obeys the Arrhenius kinetics which allows us to connect the rate constant with the absolute temperature and the activation energy. The activation energy of thermal decomposition has been calculated from the TG curves, and its variation with different irradiation doses has been derived.     

In-situ EXAFS study on the thermal decomposition of TiH_2

Thermal decomposition behaviors of TiH_2 powder under a flowing helium atmosphere and in a low vacuum condition have been studied using an in situ EXAFS technique.By an EXAFS analysis containing the multiple scattering paths including H atoms,the changes of the hydrogen stoichiometric ratio and the phase transformation sequence are obtained.The results demonstrate that the initial decomposition temperature is dependent on experimental conditions,which occurs,respectively,at about 300 and 400℃ in a low vacuum condition and under a flowing helium atmosphere.During the decomposition process of TiH_2 in a low vacuum condition,the sample experiences a phase change process:δ(TiH_2)→δ(TiH_x)→δ(TiH_1)+β(TiH_x)→δ(TiH_x)+β(TiH_x)+α(Ti)→β(TiH_x)+α(Ti)→α(Ti)+β(Ti).This study offers a way to detect the structural information of hydrogen.A detailed discussion about the decomposition process of TiH_2 is given in this paper.     

The effect of pressure on the thermal conductivity of ordered and disordered alloys

A comparison is made between the results from experimental studies into the effect of hydrostatic pressures of up to 400 MPa in the temperature range 273–523 K on the phonon thermal conductivity of CdSnAs₂ alloy and the effective thermal conductivity of granite. Pressure was demonstrated to lead to a change in the degree of structural ordering of the studied specimens.     

Solvent,salt and high pressure effects on the rate and equilibrium constants for the formation of tri‐n‐butylphosphoniumdithiocarboxylate

Solvent, salt and high pressure effects on the rate and equilibrium constants for the formation of tri‐n‐butylphosphoniumdithiocarboxylate at 298.2 K are reported. This equilibrium is shifted to the phosphobetaine in polar solvents, salt solutions and under high external pressure. The reaction volume changes dramatically on going from less polar diethyl ether (?69 cm³ mol^?1) and tetrahydrofurane (THF) (?66 cm³ mol^?1), to more polar acetonitrile (?39 cm³ mol^?1) and acetone (?38 cm³ mol^?1). Copyright © 2010 John Wiley & Sons, Ltd.     

二茂铁在高温热解乙二胺制备CN_x纳米管过程中的催化性能研究

采用高温热解法 ,以二茂铁 乙二胺有机溶剂为前驱液制备CNx 纳米管过程中 ,改变前驱液配比 ,对 86 0℃ ,不同二茂铁含量条件下制备出的CNx 纳米管进行了产量统计、形貌结构观察和拉曼光谱研究。结果显示 :随着前躯液中二茂铁含量的相对增大 ,不但CNx 纳米管产量随之增加 ,而且产物中“竹节状”结构纳米管相对“中空”结构纳米管的比重也增大 ;拉曼光谱结果进一步证实了由于“竹节状”结构CNx 纳米管的含量或比重增加所带来的纳米管样品整体或平均含氮量的升高而导致的样品结晶有序程度的降低。对单独钴粉和二茂铁催化条件下生成CNx 纳米管的形貌观察进一步证实 :二茂铁在热解法制备“竹节状”结构CNx 纳米管过程中的浮动催化作用显著 ,有利于实现含氮量较高、结构均匀的CNx 纳米管的可控制生长。     

二茂铁在高温热解乙二胺制备CNx纳米管过程中的催化性能研究

关键词：     

Effect of pressure on the thermal expansion of MgO up to 200~GPa

Constant temperature and pressure molecular dynamics (MD) simulations are performed to investigate the thermal expansivity of MgO at high pressure, by using effective pair-wise potentials which consist of Coulomb, dispersion, and repulsion interactions that include polarization effects through the shell model (SM). In order to take into account non-central forces in crystals, the breathing shell model (BSM) is also introduced into the MD simulation. We present a comparison between the volume thermal expansion coefficient α dependences of pressure P at 300 and 2000~K that are obtained from the SM and BSM potentials and those derived from other experimental and theoretical methods in the case of MgO. Compared with the results obtained by using the SM potentials, the MD results obtained by using BSM potentials are more compressible. In an extended pressure and temperature range, the α value is also predicted. The properties of MgO in a pressure range of 0--200~GPa at temperatures up to 3500~K are summarized.     

Computational studies on the thermal decomposition of the CH2FOCHFO radical

Theoretical studies have been carried out on the kinetics and thermochemistry of the thermal decomposition of the CH₂FOCHFO radical formed during the photo-oxidation of CH₂FOCH₂F (HFE-152E) using the dual-level method of obtaining the optimised structure at DFT(M06-2X)/6-311++G(d,p) followed by a single-point energy calculation at the G3 level of theory. The rate constant for different reaction channels involved during the decomposition processes of CH₂FOCHFO is evaluated at 298 K and 1 atm using canonical transition-state theory. The results point out that the C–H bond scission is the dominant path involving an energy barrier of 9.5 kcal mol^?1 determined at the G3 level of theory. A potential energy diagram is constructed and the results are compared with the data available from the literature for a structurally similar molecule.     

The influence of pressure on freezing in molecular liquids

We present the results of experimental investigation of some liquid alkanes PVT behaviour. Their molecular structure was investigated by MoK X-ray scattering method. The obtained data allow suggesting the equation of state and determination of the relation of these equation parameters to molecular characteristics such as molecular mass and exponents of the potential of molecular interaction.