正庚烷热裂解的反应分子动力学模拟

研究表明正庚烷热裂解的主产物是C₂H₄, H₂, CH₄以及C₃H₆,模拟结果和实验吻合很好. 温度对产物分布具有明显的影响,当温度上升,目标产物乙烯的量会迅速增加. 正庚烷转化率以及主产物的摩尔分数分别通过反应分子动力学和化学动力学模拟计算得到,两种方法模拟结果相吻合. 我们还通过动力学分析研究了正庚烷热裂解反应的动力学参数,反应活化能为47.32 kcal/mol,指前因子为1.78×10¹⁴ s^-1.     

反应物振动激发对O(3P)+D2→OD+D立体动力学的影响

运用准经典轨线方法,基于Roger的³A"势能面,在碰撞能为104.5 kJ/mol时对O(³P)+D₂反应的立体动力学性质进行了理论研究. 详细讨论与产物矢量相关的的极化分布函数以及四个极化微分反应截面进行了. 结果表明,产物OD的立体动力学性质对反应物分子H_{2相似文献}   

超高碰撞能23.84 kJ/mol下反应F+D2→DF+D的交叉分子束研究

本文搭建了一套新的实验设备,首次将氢原子里德堡态标记的飞行时间谱技术与激光爆破束源技术相结合,进行超高碰撞能下化学反应的动力学研究. 初步进行了F+D₂→DF+D在超高碰撞能23.84 kJ/mol下的实验研究. 在研究中应用了两种类型束源：一类是通过激光爆破过程产生的高能F原子束源,另一类是通过液氮冷却脉冲阀而产生的D₂束源. 实验中探测了反应产物振动态分辨的微分散射截面. 结果显示,大部分反应产物DF主要呈现侧向和后向散射分布,而产物DF(v''=4)则主要分布在前向. 对前向散射产物DF(v''=4)的动力学来源进行了讨论.     

反应N(2D)+H2→NH+H和N(2D)+D2→ND+D的立体动力学理论研究.

基于Ho等人的精确势能面(J. Chem. Phys. 119, 3063(2003))研究,运用准经典轨线方法计算了21.3 kJ/mol碰撞能下反应N(²D)+H₂→NH+H和N(²D)+D₂→ND+D的产物与反应物之间的矢量相关．发现两个反应的产物角分布都是前向和后向呈现峰值分布,产物的转动角动量矢量j′不仅是取向的,而且是在y轴负方向上定向的．两个反应显示出的同位素效应主要归因于同位素质量的差别．     

CL20/BTF共晶高温热分解ReaxFF/lg分子动力学模拟

用ReaxFF/lg反应力场模拟CL20/BTF共晶在2000~3000 K高温条件下的热分解过程,获得了势能和物种数的演化、初始反应路径及热分解产物等详细信息。通过指数函数对势能的演化曲线进行拟合得到反映特征时间等参数,采用经典的Arrhenius反应速率方程描述总包反应,获得CL20/BTF共晶的活化能E_a=60.8 kcal/mol。研究得到CL20/BTF共晶热分解的初始路径,CL20分子中N-NO₂首先断裂,在热分解起始阶段占主导作用。在不同温度条件下,CL20分子均在BTF分子前完全分解。CL20/BTF共晶的主要产物为NO₂、NO、NO₃、HNO、N₂、H₂O、CO₂、O₂、N₂O、HONO 等。温度对产物均产生一定程度的影响.     

金属离子诱导下DNA折叠的不同机理

利用等温滴定量热仪、圆二色谱和荧光光谱,研究和分析了人工合成的DNA单链序列d(T₆C₆T₆C₆T₆C₆T₆)与Hg²⁺和Ag⁺相互作用的折叠过程. 在改变离子添加顺序的情况下,尽管热力学数据显示两种情况下都能通过两种不同反应路径得到一种相对稳定的发夹结构,但等温滴定量热仪数据却显示最终产物形成的机理截然不同.当先加入Hg²⁺时,发夹结构首先通过T-Hg-T碱基对形成然后C-Ag-C碱基对得到进一步稳定. 然而当先加入Ag⁺时,通过圆二色谱和荧光分析确认了一种不常见的金属碱基对T-Ag-C取代了经典的C-Ag-C碱基对.     

硫酸(氢)根吸附层对Pd(111)电极上甲酸氧化反应的影响研究

本文使用循环伏安法和电势阶跃法分别研究了添加和不添加Na₂SO₄的0.1 mol/LH₂SO₄+0.1 mol/LHCOOH溶液中Pd(111)电极上甲酸氧化反应(FAO)的动力学行为,并与同样条件下0.1 mol/LHClO₄中的动力学行为进行比较. 加入0.05 mol/L或者0.1 mol/LNa₂O₄后,在相同的电位下负向扫描的FAO电流比正向扫描的显著减小. 本文推测在(SO₄^*_ad)_m+[(H₂O)_n-H₃O⁺]或(SO₄^*_ad)_m+[Na⁺(H₂O)_n-H₃O⁺]吸附层相转变电势以正的电位, 这个吸附层的结构可能随着电位的增加或Na₂SO₄的加入变得更加致密和稳定. 因此,破坏或者脱附致密的硫酸(氢)根吸附层变得更加困难,使得FAO 动力学在较高电位和随后的负扫电位受到明显的抑制.     

瞬态磷光发射光谱研究阿替洛尔与单线态氧反应的动力学

药物活性化合物阿替洛尔是一种β受体阻滞剂,若将其排放到地表水资源中会对人类健康和生态系统产生不利的影响. 受光驱动的直接光降解以及间接光降解法可以有效去除环境中的阿替洛尔. 在间接光降解方法中,¹O₂是降解阿替洛尔这类污染物的重要活性物种. 然而,关于阿替洛尔与¹O₂反应动力学的信息还比较缺乏,二者间的反应速率常数仍存在争议. 本文通过直接观察¹O₂在1270 nm处衰减动力学来研究阿替洛尔与¹O₂在不同溶剂中的反应速率常数：在重水中为7.0×10⁵ (mol/L)^-1·s^-1,在乙腈中为8.0×10⁶ (mol/L)^-1·s^-1,在乙醇中为8.4×10⁵ (mol/L)^-1·s^-1. 在极性强、给氢能力弱的溶剂中阿替洛尔与¹O₂的反应速率常数更大. 这些结果对光降解阿替洛尔等β受体阻滞剂提供相关动力学信息.     

从银电极上氢析出的温度效应得到的反应动力学启示

利用循环伏安法研究了多晶银电极在0.1 mol/L HClO₄溶液中氢析出反应的温度效应. 发现当从析氢起始电位负向扫描至零电荷电位(-0.4 V)时,氢析出反应的表观活化能(E_a,app)和指前因子(A)均随着电势的负移而增大(对应的E_a,app从24 kJ/mol增大至32 kJ/mol).继续负向扫描至零电荷电位以后,E_a,app随电势的负移而减小但A不随电势变化. 推测E_a,app和A在零     

4-硝基联苯酚三重态质子化和去质子化过程中瞬态物种的指认

近年利用超快光谱技术对于4-硝基联苯酚(HO-Bp-NO₂)的研究发现，其在单重态和三重态时均会发生光致质子耦合电子转移(PCET)反应. 其瞬态吸收光谱450 nm处有一个独特的尖锐吸收带，但无羟基取代的对硝基联苯(Bp-NO₂)未观察到此现象. 本文利用酸性溶液作为外加可控质子供体，通过在强酸(∽10^-1 mol/L)和弱酸(∽10^-4 mol/L)溶液中的光谱和动力学结果，指认这个新吸收带为开壳层单重态O-Bp-NO₂H. 它是HO-Bp-NO₂的互变异构体，由三重态HO-Bp-NO₂中硝基氧得质子后羟基快速去质子产生. 动力学分析表明，非质子极性溶剂中三重态HO-Bp-NO₂与基态母体间还会发生PCET或先质子后电子转移生成自由基·O-Bp-NO₂. 这一反应与O-Bp-NO₂H竞争，导致其产率较低. 这些结果阐明了三重态HO-Bp-NO₂在非质子极性溶剂中的失活机制.     

Application of the model-free approach to the study of non-isothermal decomposition of un-irradiated and γ-irradiated hydrated gadolinium acetylacetonate

The non-isothermal decomposition of unirradiated and γ-irradiated hydrated gadolinium acetylacetone with 10² kGy γ-ray absorbed dose was carried out in air and in nitrogen atmospheres and in the temperature range of 25–1000°C. The results indicate that gadolinium acetylacetonate decomposes through four main decomposition steps leading to the formation of intermediate products whose chemical structure is independent of the gas atmosphere applied and on the investigated absorbed dose. The final product at 820°C was found to be Gd₂O₃ irrespective of the gas atmosphere and the irradiation conditions. The non-isothermal data were analyzed using linear Flynn–Wall–Ozawa and non-linear Vyazovkin (VYZ) iso-conversional methods. The results of the application of these free models on the present kinetic data showed that the activation energy, E_a is independent of α in a very wide conversion range (0.1–0.9) indicating that the decomposition process is controlled by a unique kinetic model. The results of the model-fitting analysis showed that the decomposition course of the four decomposition steps of hydrated gadolinium acetylacetone was controlled by the D₃ Jander diffusion model. Pure phase of Gd₂O₃ nanoparticles was obtained by thermal oxidation of γ-irradiated GdAcAc.3 H₂O at 800°C for 6 h. X-ray diffraction, transmission electron microscopy (TEM) and atomic force microscopy (AFM) techniques were employed for characterization of the as-synthesized nanoparticles. This is the first attempt to prepare Gd₂O₃ nanoparticles by solid-state thermal decomposition of γ-irradiated hydrated gadolinium acetylacetone.     

Kinetics of the apparent isothermal and non-isothermal crystallization of the α-Fe phase within the amorphous Fe81B13Si4C2 alloy

Kinetics of the apparent isothermal and the non-isothermal crystallization of α-Fe phase within the amorphous Fe₈₁B₁₃Si₄C₂ alloy were investigated by an X-ray diffraction (XRD) and by a differential scanning calorimetry (DSC). It was established that the apparent isothermal crystallization of α-Fe phase within amorphous Fe₈₁B₁₃Si₄C₂ alloy could be described by the Johnson-Mehl-Avrami (JMA) kinetic model (with parameter n_iso=4.0). The apparent isothermal crystallization process includes a constant rate of nucleation and three-dimensional growth of nuclei. The results of X-ray diffraction (XRD) data of the isothermally crystallized samples confirmed the above established kinetic model. From the kinetic analysis of the non-isothermal crystallization of the α-Fe phase within this amorphous alloy, it was concluded that the autocatalytic two-parameter Šesták-Berggren (SB) reaction model (with kinetic exponents M=0.72 and N=1.02) describes well the studied process under the given conditions. The non-isothermal crystallization process involves the constant nucleation rate of stable nuclei with additional secondary two-dimensional (surface) nucleation and overlapping of the growing nuclei on account of the non-isothermal activation.     

A new method to study the crystallization or chemical reaction kinetics using thermal analysis technique

In this work, a new method to study the transformation kinetics is introduced. With this method, the activation energy, E_c, for crystallization (phase transition or chemical reaction), the pre-exponential coefficient of effective overall reaction rate, k_o, and the reaction order, n, can be determined. No approximation has been used in this method. This method can be used for isothermal and non-isothermal study. It is deduced from Avrami's equation without any approximation. This new method has been tested to study the amorphous-crystalline transformation kinetics under isothermal and non-isothermal conditions in the context of glassy selenium. The source of error is discussed. The calculated values of E_c, under isothermal and non-isothermal conditions are 75.3±2.5 and 79.4±2.3 kJ/mol, respectively. The predominant crystallization mechanism of the amorphous phase of glassy selenium in isothermal or non-isothermal conditions is one-dimensional growth. The deduced values of k_o were found to be 19.4±0.9 and 20.8±0.7 s⁻¹ for isothermal and non-isothermal conditions, respectively. Resulting values of the parameter, n, are compared with values obtained from other known methods used to study the reaction kinetics in thermal analyses. The difference in the results obtained with this method and the results obtained with other known methods is acceptable or lie within the experimental error range.     

Influence of the lithium salt nature over the surface film formation on a graphite electrode in Li-ion batteries: An XPS study

The formation of a passivation film (solid electrolyte interphase, SEI) at the surface of the negative electrode of full LiCoO₂/graphite lithium-ion cells using different salts (LiBF₄, LiPF₆, LiTFSI, LiBETI) in carbonate solvents as electrolyte was investigated by X-ray photoelectron spectroscopy (XPS). The analyzes were carried out at different potential stages of the first cycle, showing the potential-dependent character of the surface film species formation and the specificity of each salt. At 3.8 V, for all salts, we have mainly identified carbonated species. Beyond this potential, the specific behavior of LiPF₆ was identified with a high LiF deposit, whereas for other salts, the formation process of the SEI appears controlled by the solvent decomposition of the electrolyte.     

Three-dimensional non-grey gas radiative transfer analyses using the statistical narrow-band model

Three-dimensional non-grey gas radiation analyses were conducted using the statistical narrow-band model with updated band parameters and three implementation methods: the exact or the correlated formulation, the non-correlated expression, and the grey-band approximation with the absorption coefficient estimated using the local properties. The accuracy of the two approximate narrow-band implementation methods was evaluated for both low-resolution spectral intensity and spectrally integrated radiative source term and wall heat flux in a rectangular enclosure containing (1) isothermal pure water and (2) a CO₂/H₂O/N₂ mixture with a furnace type gas temperature distribution. For spectrally integrated quantities, results of the grey-band approximation are very close to those of the non-correlated formulation and are in qualitative agreement with the results of the correlated formulation. The two approximate methods are capable of predicting qualitatively correct and fairly accurate distributions of low-resolution spectral radiation intensities for the isothermal case. However, they predict less accurate low-resolution spectral intensities for the non-isothermal case.     

Kinetic studies for the non-isothermal decomposition of un-irradiated and γ-irradiated ruthenium(III) acetylacetonate

Kinetic studies for the non-isothermal decomposition of un-irradiated and γ-irradiated ruthenium(III) acetylacetonate in air were carried out. The results show that the decomposition proceeds in one major step in the temperature range of 150–250 °C with the formation of RuO₂ as a final solid residue for un-irradiated Ru(acac)₃. For γ -irradiated Ru(acac)₃ with 10² KGy total γ-ray dose, the decomposition goes eventually to completion with almost 100% decomposition and proceeds in one major step, which contains four overlapping decomposition stages in the temperature range of 200–320 °C. The kinetics is shown to be non-isothermal, using both model-fitting and model-free approaches. Infrared (IR) spectroscopy and X-ray powder diffraction techniques were employed to follow the chemical composition of the solid residue obtained at different temperatures.     

Transcrystallization of polypropylene on different modified jute fibers

This article deals with the transcrystallization of polypropylene on untreated, MAH-polypropylene grafted, and alkali treated jute fibers due to isothermal as well as non-isothermal crystallization conditions. In both cases, TCL-thickness as well as TCL growth initiation temperature were dependent on fiber treatment. The chosen T_C in isothermal conditions was of great significance on TCL growth rate. The experimental data were successfully fitted by using an Arrhenius-type relationship.     

Adsorption behaviour of SO2 and SOF2 gas on Rh-doped BNNT: a DFT study

Abstract

As the insulating medium, SF₆ is widely used in gas insulation equipment. Partial discharge and local overheating can cause the decomposition of SF₆, resulting in a decrease in insulation strength of the equipment. The detection of SF₆ decomposition gas can be used for on-line insulation detection of gas insulation equipment in electric power industry. In order to develop a new sensor gas sensing material for gas detecting. In this work, based on the first-principles density functional calculation (DFT) method of DMol³, the adsorption of SF₆ decomposition gas on (5,0) Z-type Rh-BNNT in different ways was explored. The adsorption energy, adsorption distance, charge transfer as well as density of states were discussed. The results show that the adsorption strength between SO₂ molecule with Rh-BNNT is larger than with SOF₂ molecule, combined with desorption time, theoretically predicts Rh -BNNT have the potential to be a material for SO₂ gas sensors.     

Study on the kinetics properties of lithium hexafluorophosphate thermal decomposition reaction

The thermal decomposition of lithium hexafluorophosphate was studied by using C80 calorimeter, and the samples were heated at a 0.2 K·min^− 1 heating rate from ambient temperature to 573 K in pressure-sensitive transducer fitted and sealed vessel with argon atmosphere. It is found that LiPF₆ decomposes near 433 K, and the gas product PF₅ causes the pressure increasing. The LiPF₆ decomposition reaction order is calculated based on the pressure data by two methods, its average value is n = 1.5, then, the reaction is assumed to be dependent on the Arrhenius law and mass action law, and thus the activation energy and pre-exponential factor were calculated to be E = 104.2 kJ·mol^− 1, A = 1.12 × 10⁷ s^− 1, respectively.     

羟基碳纳米管吸附SF6放电分解组分的DFT计算

本文根据密度泛函理论(density functional theory , DFT), 采用MS分子动力学仿真软件对羟基修饰的单壁碳纳米管(SWNT-OH) 吸附SF₆局部放电分解的四种主要组分SOF₂, SO₂F₂, SO₂和CF₄进行了详细的理论计算, 通过分析气体分子和SWNT-OH的前线轨道, 吸附过程中吸附能、电荷转移量和电子态密度的情况, 以及吸附前后SWNT-OH能隙的变化, 评判了SWNT-OH对气体分子的敏感性和选择性, 给出了SWNT-OH是否可以制备气体传感器检测SF₆局部放电分解组分的理论依据.