热动力学特征对比参量法及其应用研究

基于简单级数反应的积分和微分热动力学方程，建立了热动力学特征对比参量 法的数学模型，提出了一种由特征时间参量计算特征对比参量的方法，通过几种不 同级数模型反应的热动力学研究证明了方法的正确性，并利用该法研究了过氧化氢 在磷酸盐缓冲液中氧化对苯醌反应的动力学特征，实验结果表明该反应动力学方程 可以表示为：dC(醌)/dt=kC(醌)C(H_2O_2)~0.5C(H~+)~(-0.5)     

绝热式热动力学的研究4: 可逆反应的热谱解析

本文建立了可逆反应在绝热系统中的热动力学研究法, 并用自制的绝热式自动热量计, 研究了三个可逆反应体系的热动力学, 验证了本文方法的正确性。     

Application of isoconversional and multivariate non-linear regression methods for evaluation of the degradation mechanism and kinetic parameters of an epoxy resin

The thermo-oxidative degradation of an epoxy resin obtained by curing of an industrially produced DGEBA mixture with 4,4′-methylene-dianiline (MDA) and used as electric insulator has been investigated by TG + DTG + DSC simultaneous analyses performed in static air atmosphere, at five heating rates. TG, DTG and DSC curves showed that, in the temperature range 25-900 °C, a glass transition followed by three thermo-oxidative processes occur. The processing of the non-isothermal data corresponding to the first process of thermo-oxidation was performed by using Netzsch Thermokinetics - A Software Module for Kinetic Analysis. The dependence of the activation energy, evaluated by isoconversional methods, on the conversion degree and the relative high standard deviations of this quantity show that the investigated process is a complex one. The mechanism and the corresponding kinetic parameters were determined by multivariate non-linear regression program and checked for quasi-isothermal data. It was pointed out that the first process of thermo-oxidation of the investigated resin consists in four steps, each step having a specific kinetic triplet. The obtained results were used for prediction of the thermal lifetime of the material corresponding to some temperatures of use and the end point criterion 5% and 10% mass loss.     

Effect of NQ content on the thermal decomposition of nitroguanidine propellant using isoconversional methods

Journal of Thermal Analysis and Calorimetry - The effect of nitroguanidine (NQ) content on thermal decomposition of nitroguanidine propellants was studied using three nitroguanidine propellants...     

Investigation of the radical polymerization kinetics using DSC and mechanistic or isoconversional methods

In this research, an effort was undertaken to investigate radical polymerization kinetics using experimental data from DSC measurements and mechanistic or isoconversional models. Polymerization of a polar monomer, namely 2-hydroxyethyl methacrylate in the presence of benzoyl peroxide initiator was studied. The variation of the effective activation energy with conversion was directly interpreted in terms of the physical phenomena taking place during the reaction in a microscale. Both isothermal and non-isothermal DSC data were employed and the effect of diffusion-controlled phenomena on the reaction kinetics at different conversion regimes was assessed. Finally, the effect of the presence of nanofiller on polymerization kinetics and the activation energy values were estimated and correlated to physical phenomena taking place during polymerization.     

镨配合物的热化学及其对酵母菌作用的热动力学研究

用六水合氯化镨、硫代脯氨酸(C4H7NO2S)和水杨酸(C7H6O3)合成了三元固体配合物[Pr(C7H5O3)2(C4H6NO2S)]-2H2O.根据盖斯定律设计一个热化学循环,用溶解-反应量热法研究得到合成反应的标准摩尔焓变为(133.70±1.02)kJ/mol,配合物298.15K时的标准摩尔生成焓为-(2909.3±3.2)kJ/mol.用TAMair微量热仪测定其在28.00℃时对粟酒裂殖酵母作用的产热曲线,进而算出在配合物作用下,酵母菌生长代谢的最大发热功率Pmax、速率常数κ、传代时间tG、抑制率I和半抑制浓度cI,50等热动力学参数.结果表明:稀土水杨酸硫代脯氨酸配合物在低浓度下对酵母菌有刺激作用,高浓度下为抑制作用,即稀土配合物对微生物的生长具有双向生物效应,也称为Hormesis效应.     

Studies on reactive blending of LDPE and cenosphere

The present work aims to modify conventional low density polyethylene (LDPE) by preparing its particulate composite with cenosphere. Cenosphere is a potential waste produced in bulk from the coal fired thermal power plant. In this context, surface modification of cenosphere was done by γ- aminopropyl triethoxy silane (ATS) coupling agent. Furthermore, LDPE was grafted by glycidyl methacrylate (GMA) to be used as compatibilizer. The resulting surface modified and unmodified cenosphere as well as glycidyl methacrylate grafted LDPE (LDPE-g-GMA) were functionally characterized by Fourier Transform Infrared (FT-IR) spectroscopy. LDPE-cenosphere particulate composites were processed in their different formulations and evaluated with various properties such as thermal stability, mechanical properties, chemical resistance and flow behaviour. Dispersibility of cenosphere in LDPE matrix was studied by Scanning Electron Microscopy (SEM). Series of analysis was performed in order to understand the effect of cenosphere content and its modification on the final properties of particulate composites. Mechanical properties were found to be statistically significant as per ANOVA and Post hoc Tukey HSD test. Particulate composites prepared with modified interphase were observed to possess good combination of properties.     

Studies on the interaction mechanism between CXS and papain by spectroscopic and molecular modeling methods

We have studied the interaction between cefuroxime sodium (CXS) and papain at different temperatures by a fluorescence method, and confirmed that the mechanism of fluorescence quenching of CXS to papain is mainly static quenching. We also determined the binding constant K. Based on the thermodynamic functions at different temperatures, the results show that the major forces between CXS and papain are van der Waals’ forces and H bond. According to the Forster non-radiation energy transfer mechanism, we determined the binding distance between CXS and papain, and studied the confirmation effect of CXS to papain by synchronous fluorescence and UV–Vis spectroscopy. Molecular simulations show that the binding types of CXS and papain are van der Waals’ forces, hydrophobic interaction, and H-bond.     

The mathematical incorrectness of the integral isoconversional methods in case of variable activation energy and the consequences

Kinetic parameters resulting from the application of isoconversional methods mostly depend on the degree of conversion. This paper shows that the integral isoconversional methods are mathematically incorrect if the activation energy depends on conversion. In this case, the incorrectness resides in improper separation of variables in the general rate equation. As a consequence, non-sensical snake-like shape of the conversion versus time curves is observed when the kinetic results are extrapolated to lower temperatures.     

Thermodynamic and thermokinetic study on pyrolysis process of heavy oils

Enthalpy of pyrolysis and its variation in the pyrolysis process of four heavy oils: Daqing vacuum residue (DQVR), Karamay vacuum residue (KRVR), Liaohe vacuum residue (LHVR), and Venezuela vacuum residue (VNVR), have been quantitatively studied by differential scanning calorimetry associated with thermogravimetry. The results indicate that overall enthalpies at different heating rates show a linear trend with respect to the final coke yields in the thermal analysis. Classical kinetic method (Friedman method) is used to further analyze pyrolysis enthalpy variation in the pyrolysis process and determine the thermokinetic parameters. The main stage of thermal reaction (conversion ranges from 0.1 to 0.9) could be described by 1.5 order reaction model for four heavy oils. The mean activation energies determined by Friedman method are 216.3, 194.9, 173.9, and 168.7 kJ mol^?1 for DQVR, KRVR, LHVR, and VNVR, respectively. It means that endothermic enthalpy of pyrolysis in the thermal process of VNVR is easier to change compared with other oil sample cases. For the sake of simplification of kinetic treatment, Sharp method is tentatively used to perform kinetic analysis. The comparison between results from two methods indicates that activation energies from Sharp method are valid to a certain degree under the condition that the mechanism of thermal process is properly chosen although isoconversional method (Friedman method) is recommended and thought to be the better way.     

木质素模化物紫丁香酚热解机理的量子化学研究

采用密度泛函理论方法B3LYP/6-31G++(d,p),对木质素模化物紫丁香酚的热解反应机理进行了量子化学理论研究。提出了三种可能的热解反应途径,对各种反应的反应物、产物、中间体和过渡态的结构进行了能量梯度全优化。计算了各热解反应途径的标准动力学参数,分析了各种主要热解产物的形成演化机理。键离解能计算结果表明,紫丁香酚中CH₃-O键的键离解能最小,各种键离解能的大小顺序为CH₃-O < O-H < CH₃O-C_aromatic < CH₂-H < HO-C_aromatic < C_aromatic-H。在反应路径(1)中,主要热解产物是3-甲氧基邻苯二酚,其形成反应的总能垒为366.6 kJ/mol;在反应路径(2)中主要热解产物是2-甲氧基-6-甲基苯酚,其形成反应的总能垒为474.8 kJ/mol;在反应路径(3)中形成邻甲氧基苯酚的总能垒很低,为21.4 kJ/mol,这表明,在连接甲氧基的碳原子上加氢后能够有效地降低木质素芳环模化物紫丁香酚去甲氧基反应的反应能垒。     

NC3O分子体系的异构化及其结构和性能的理论研究

采用 DFT, QCISD 及 CCSD(T)方法, 对 NC3O 分子体系的异构化进行了系统的研究, 得到了5个稳定的异构体, 其中包括4个链状异构体和1个带有支链的平面结构异构体. 这5个稳定异构体都具有较高的动力学和热力学稳定性.     

AXAFS技术在Ni/ZnO吸附剂上模型油反应吸附脱硫机理研究中的应用

原子X射线吸收精细结构（AXAFS）由吸收原子的外围束缚电子对出射光电子波的背散射引起,AXAFS信号与嵌入原子势能、原子间隙势能和吸收原子电子密度的分布密切相关,可以作为精确的探针来探测原子的电子化学结构。研究利用AXAFS技术,以Ni/ZnO脱硫吸附剂为研究对象,探讨了模型油在不同气体气氛下的脱硫反应机理。结果表明,在氢气气氛下、350 ℃和3.0 MPa的条件下,从Zn元素的原位AXAFS谱图中可观察到脱硫过程中Zn元素的化学态变化。根据这些结果,揭示了氢气在脱硫过程中的重要作用,阐述了原位反应条件下吸附剂中Zn元素的化学态变化。     

Studies of dithiiranes and thiosulfines as reactive intermediates

Indirect, but compelling evidence for the intermediacy of dithiiranes 1 and thiosulfines 2 has been found by us and is also provided by literature data. The intriguing dithiirane → dithioester rearrangement as well as most of the interrelations and conversions postulated in Scheme 1 have been demonstrated experimentally. In a number of cases acetyl α-chloroalkyl disulfides 16 (X = Cl, Y = COCH₃) are useful starting materials for the synthesis of thioamides such as 40.     

Studies on the mechanism of coagulation

Summary ζ-potential measurements have been carried out on positive silver iodide sols in the presence of anionic surface active agents at various concentrations. The conditions employed were the same as those used for the stability measurements described in Part I. The curves of ζ against log concentration of surface active agent were compared with those expected theoretically on the basis of a single adsorbed layer of surface active agent, and from the gradient of the curves at the point of zero ζ-potential the free energy of adsorption of the first adsorbed layer was calculated. It was found that to explain the form of the curves at higher surface active agent concentrations, i. e. negative ζ-potentials, postulation of a second adsorbed layer was required. The free energy of adsorption of the second layer was found to be lower than the first and to be consistent with the idea of adsorption occurring due to van der Waals attractions between the hydrocarbon chains. Combination of the potential data with the stability (W) data from Part I gave curves of log W against ζ which were compared with those expected theoretically.

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Zusammenfassung ζ-Potentialmessungen wurden an positiv geladenen Silberjodidsolen in Gegenwart von anionischen oberfl?chenaktiven Mitteln mit verschiedener Konzentration ausgeführt. Die Bedingungen waren dieselben wie für die Stabilit?tsmessungen, mitgeteilt im vorangehenden Teil I. Die Kurven der ζ-Werte gegen den log (Konzentration des oberfl?chenaktiven Mittels) wurden mit den theoretisch zu erwartenden verglichen, berechnet auf Annahme einer einzelnen adsorbierten Schicht. Aus der Steigung der Kurven im Punkt für das ζ-Potential Null wurde die freie Energie für die Adsorption dieser ersten Schicht berechnet. Um auch den Verlauf der Kurven bei h?heren Konzentrationen an oberfl?chenaktivem Agens zu erkl?ren, z. B. negative ζ-Potentiale, wurde die Annahme einer zweiten adsorbierten Schicht erforderlich. Die freie Energie der Adsorption dieser zweiten Schicht erwies sich als niedriger als die für die erste, und ihr Wert war konsistent mit der Annahme einer Adsorption auf Grund von van der Waals-Anziehung zwischen den Kohlenwasserstoffketten. Die Kombination der Potentialmessungen mit den Stabilit?tswerten W aus Teil I ergab Kurven von log W als Funktion von ζ, die mit theoretisch zu erwartenden verglichen wurden.

     

Studies on the mechanism of coagulation

Summary In previous work it was found that at certain concentrations of anionic surface agents the particles of positive silver iodide sols became coated with a double adsorbed layer of the surface active agent; under these conditions stable sols were formed the properties of which were found to be dependent on the nature of the head group of the surface active agent. Utilising this fact stable sols have been prepared of silver iodide particles coated with sodium tetradecyl sulphate and their stability and electrophoretic behaviour examined in the presence of a number of cations of different valency. The cations used were, Th⁺⁺⁺⁺, La⁺⁺⁺, Ba⁺⁺, Ca⁺⁺, Mg⁺⁺, Zn⁺⁺, UO₂ ⁺⁺, Mn⁺⁺, Cd⁺⁺, Na⁺, K⁺ and Li⁺. The curves of stability as a function of ionic strength and particle radius revealed marked specificity of the cations; this was attributed to cation binding with the sulphate groups of the second layer of adsorbed surface active agent. The results obtained appear to be in general agreement with those predicted in the theoretical treatment given in part 4.

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Zusammenfassung In einer der vorausgehenden Arbeiten wurde gefunden, da? bei gewissen Konzentrationen von anionischen oberfl?chenaktiven Agenzien die Teilchen von positiven Silberjodidsolen mit einer doppelten adsorbierten Schicht des Agens überzogen werden; unter diesen Bedingungen werden stabile Sole gebildet, deren Eigenschaften abh?ngig von der Kopfgruppe des Agens sind. Indem man diese Tatsache anwendet, kann man Partikel aus Silberjodid, überzogen mit Natriumtetradecylsulfat, herstellen und ihre Stabilit?t und ihr elektrophoretisches Verhalten in Gegenwart einer Reihe von Kationen von verschiedener Valenz prüfen. Verwendet wurden die Kationen Th⁺⁺⁺⁺, La⁺⁺⁺, Ba⁺⁺, Ca⁺⁺, Mg⁺⁺, Zn⁺⁺, UO₂ ⁺⁺, Mn⁺⁺, Cd⁺⁺, Na⁺, K⁺ und Li⁺. Die Stabilit?tskurven als Funktion der Ionenst?rke und des Partikelradius zeigen deutliche Spezifit?t in Abh?ngigkeit von den Kationen. Dies wird der Bindung der Kationen mit den Sulfatgruppen der zweiten Schicht des adsorbierten Agens zugeschrieben. Die Ergebnisse scheinen in allgemeiner übereinstimmung mit den Voraussagen der theoretischen überlegung, dargestellt in Teil IV, zu stehen.

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One of us (A. W.) wishes to thank the British Council for a Scholarship and the University of Cambridge for the award of theOliver Gatty Studentship.     

核黄素电化学还原研究

本文采用循环伏安、本体电解、荧光光谱、电子自旋共振波谱等技术对核黄素电化学还原机理进行了研究。结果表明,在DMSO溶液中,核黄素以质子化和非质子化两种形式存在,它们的还原电位分别是-0.78和-1.05(vs.SEC)。两种形式的核黄素都可在汞电极上得到一个电子,生成相应的自由基。自由基的g值分别为2.005和2.002。对质子化式的自由基的ESR超精细谱进行了理论分析,提出了核黄素可能的电化学还原机理。