活用dF=δW'推导热力学公式

应用dF=δW'推导了拉普拉斯方程、开尔文方程、毛细管液柱高度计算公式、杨方程、贝林方程和大气分布定律等热力学公式,给出了这类推导的一般思路。     

论化学平衡中的独立等量关系

物料平衡等式(MBE)、电荷平衡等式(CBE)和质子平衡等式(PBE)是化学平衡定量解析中的常用等量关系。本文从理论上证明了CBE可以由MBE导出,因此在计算中不是一个必不可少的独立条件。由于H~+来源的多样性,在涉及酸碱的化学平衡中,CBE比MBE的计算效率更高。这些结论与计算实践相一致,即在配位平衡、氧化还原平衡和沉淀平衡的计算中,MBE为主,CBE起辅助作用;在酸碱平衡计算中,CBE为主,MBE为辅。PBE也不是一个独立等量关系,而且仅适用于酸碱平衡,可以完全被效率更高的CBE代替。本研究明确了化学平衡中的独立等量关系,不仅有助于提高化学平衡定量解析的效率,而且使其理论结构更加简洁明晰。     

超临界氢在活性炭上的吸附等温线研究

通过７７－２９８Ｋ范围内氢在ＡＸ－２１活性炭上的吸附数据，探讨如何用普通Ｉ－型等温线模型处理超临界条件下的吸附等温线，以获取关于超临界吸附系统的正确信息，结果表明，Ｌａｎｇｍｕｉｒ方程虽然可用来表达实验数据，但不能提供关于该吸附系统的任何可靠信息，Ｖｉｒｉａｌ方程虽不是整组数据的最好模型，但却能够可靠地确定Ｈｅｎｒｙ定律常数，然后可从ｖａｎｔＨｏｆｆ标绘决定等量吸附热，通过将实验数据拟合到Ｄｕｂｉ     

Particles dispersed in a dilute gas: Limits of validity of the Langevin equation

The problem of the limits of validity of the Langevin equation is considered in detail in the case of (microscopic) test-particles in very dilute gases. It is shown that, in this case, the current Langevin equation follows from the Newton’s law in an exact way only in the Maxwell test-particle–gas-particle interaction model, and in an approximate way only in the Rayleigh-gas limit and in the low-velocity limit, while in any other interaction model, or limit, only a Langevin-like equation with speed-dependent friction coefficient and speed-dependent fluctuating force can be written. Such a circumstance, although probably limited to the particular physical situation considered in this paper, suggests that, in general, some preliminary, specific check of the validity of the Langevin equation should be performed before using the said equation to interpret laboratory experiments.     

A proposal for the estimation of binary mixture activity coefficients from surface tension measurements throughout the entire concentration range

A method to estimate the concentration dependence of the bulk activity coefficients of both binary mixture components from experimental surface tension data covering the whole concentration range is presented. To this end, high-quality experimental surface tension data as a function of the concentration, paying special attention to the diluted regions, are needed. The method is based on the application of equilibrium conditions to the surface chemical potential arisen from the Volmer equation (the simplest non-ideal surface EOS) and to the bulk chemical potential coming from the three-suffix Margules equation for activity coefficients. It can be applied provided that positive aneotropy is not present and the second derivative of the surface pressure as a function of the mole fraction is not positive in any composition region, which means rather unrestrictive conditions. In order to test the method, a compilation of 25 systems for which surface tension and activity coefficient data are simultaneously available in the literature was performed, turning out that most of them involved water. It was found that surface tension data with enough concentration coverage and good quality are really scarce, which makes the development of this kind of methods difficult.     

A Thermal Analysis Study of Hydroxy Benzoic Acid Derivatives Using Rising Temperature Thermogravimetry

Hydroxy benzoic acids were subjected to rising temperature thermogravimetric analysis. After optimizing the procedural variables, the kinetics of decomposition was determined and methyl paraben was taken as the calibration compound to characterize the evaporation patterns for the ortho and meta derivatives. The E _act values for ortho, meta and para derivatives were 64.8, 78.2, and 119.1 kJ mol^–1, respectively. The Antoine and Langmuir equations were utilized to determine the coefficient of evaporation k, which was 124525±0.8, units being in the SI system. The vapor pressure plots were generated for the ortho and meta derivatives; ΔH _vap for these two compounds were obtained as 66.7 and 80.4 kJ mol^–1, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

外推法求高分子特性粘数中的误差分析

从数学与解析几何角度,分析了在外推Huggins与Kraemer方程求高分子特性粘数时,出现误差的原因,并半定量得出了误差范围,同时确证了最佳测试的浓度范围为10^-3g／cm^3数量级。     

An equation of state for melts of linear homopolymers

We analyze the capability of the continuous Gaussian chain model to describe melts of linear homopolymer chains. We derive the equation of state of a system of n interacting chains by including long chain correlations by means of the one loop diagrams. These correlations which give rise to two combinations of the molecular parameters are found to be necessary for the proper quantification of pressure-volume-temperature (PVT) behaviour of the melts. The adjustment of the value of the prefactor of the small density term which is in accord with the liquid character of polymeric melts lead to a complete agreement between the experimental results and the outcomes of the theory. The proper dependence on the molecular weight is also predicted and isotherms of narrow distribution polystyrenes of three different molecular weights are used for the evaluation of the molecular parameters.     

Equation for the direct determination of the density matrix: Time-dependent density equation and perturbation theory

The density equation proposed previously for the direct determination of the density matrix, i.e. for the wave mechanics without wave, is extended to a time-dependent case. The time-dependent density equation has been shown to be equivalent to the time-dependent Schr?dinger equation so long as the density matrix, included as a self-contained variable, is N-representable. Formally, it is obtainable from the previous time-independent equation by replacing the energy E with . The perturbation theory formulas for the density equation have also been given for both the time-dependent and time-independent cases. Received: 16 June 1998 / Accepted: 2 September 1998 / Published online: 8 February 1999     

热力学方程在计算热力学函数中的应用

热力学方程是包含热力学基本方程、热力学状态方程以及吉布斯-亥姆霍兹方程在内的广泛的一组方程。文中对目前物理化学教材中很少提及的其他热力学状态方程进行了系统的总结和推导,同时强调理论的系统性和完整性在教学中的重要性,并在此基础上导出了物理化学教材中很少见到的吉布斯-亥姆霍兹第一方程及其在表面化学中的应用。在物理化学教学中需要特别强调特征变量的重要性,以及特征变量和化学反应条件之间的内在关系,并注意与交叉学科物理专业的热力学和统计物理学的衔接。     

Development of thermogravimetric method for quantitative determination of metronidazole

The objective of this work was to develop and validate a fast and reproducible method to determine the concentration of metronidazole in drug substance and tablets. The samples were analyzed by dynamic thermogravimetry, using 10, 20, 40, 60 and 80°C min^–1 heating rates in nitrogen and in nitrogen with synthetic air. Obtained data were used in the Antoine and Langmuir equations in order to have the pressure curves. Vapor pressure curves of drug and tablet of metronidazole were evaluated using the mathematical indexes of difference factor, f ₁, and similarity factor, f ₂, to compare their profiles. The data showed that there is no significant difference between the vapor pressure profiles of drug and tablet of metronidazole in both environmental conditions, which confirms that the process is really vaporization. The concentration of metronidazole was determined in the raw material and tablets of the drug.     

Thermal analysis study on vaporization of some analgesics. Acetanilide and derivatives

The thermal behaviour of acetanilide (Ac) and two of its analogues, namely the para-ethoxyacetanilide (p-Eto Ac) and the para-bromoacetanilide (p-Br Ac), which are used as analgesics in the pharmaceutical industry was studied with a simultaneous TG/DSC unit. The examined analgesics showed two endothermic DSC peaks due to melting and vaporization. By combining the experimental TG data with the corresponding reference vapour pressure data obtained with the Antoine equation the plot of P versus v was derived. From the slope of this equation the constant k-value was determined for Ac. Then, using the same k-value the vapour pressures of p-Eto Ac and p-Br Ac were determined in the same temperature range. The vaporization enthalpies for all the studied compounds were obtained from different methods and a very good agreement was found. Vaporization follows a zero-order kinetics. The activation energy of vaporization (E_vap) was calculated from the dynamic TG experiments, using the Arrhenius equation.     

Errors in evaluation of the kinetic parameters in temperature programmed reduction

The objective of this work was to develop and validate a fast and reproducible method which is able to determine the concentration of ketoconazole in raw materials and tablets. The samples were analyzed by dynamic thermogravimetry at heating rates of 10, 20, 40, 60 and 80°C min⁻¹ in nitrogen and nitrogen-synthetic air mixture. The concentrations of ketoconazole in the raw material and in the tablets were obtained from the vapor pressure curves. The data showed that there is no significant difference between the vapor pressure profiles of ketoconazole itself and in its tablet in both studied environmental conditions confirming that the process is really vaporization. The concentration of ketoconazole was determined in the raw material and tablets of the drug.     

Aqueous solutions of amphiphilic polysaccharides: Concentration and temperature effect on viscosity

Amphiphilic polymers have been prepared by chemical modification of a neutral bacterial polysaccharide, dextran, consisting of α-1,6 linked glucose units. Various amounts of aliphatic hydrocarbon groups with six carbon atoms are attached along the dextran chains by ether links. The viscosities of their aqueous solutions in the dilute domain and in the beginning of the semi-dilute domain are considered with particular interest for the variation with temperature and polymer concentration.The equations of Fedors and Martin are shown to conveniently depict the effect of polymer concentration over the whole investigated range. A semi-empirical equation is established between the critical concentration deduced from Fedors equation and both the Huggins coefficient and the intrinsic viscosity (parameters deduced from the results in the dilute domain).The variation of solution viscosity with temperature is also examined. Andrade equation, combined with Martin or Fedors equation, is shown to account for the temperature effect. Particularly, the variation of the activation energy with polymer concentration is conveniently depicted. The validity of the derived semi-empirical equations is extended to other polymer solutions using literature data.     

On the Correct Use of the Dubinin-Astakhov Equation to Study the Mixed-Gas Adsorption Equilibria

This paper presents the possibilities of Integral Equation (IE) approach to study the mixed-gas adsorption equilibria. As a result, the generalizations of Dubinin-Astakhov equation for the case of mixed-gas adsorption are presented. These new equations are examined using a few adsorption systems recently published in literature.     

Viscometric Analysis of Miscibility and Interactions for Binary,Ternary Polycarbonate/Brominated Polystyrene + Chloroform Systems at Different Temperatures

Viscosities of ternary systems consist of polycarbonate (PC)/brominated polystyrene (PBrS) in chloroform and their corresponding binary systems were measured at different temperatures (20, 25, and 30°C). All the measurements were carried out at the concentration ranges of 0.1–0.6 g·dL^?1. The mass ratio of PC to PBrS was selected as 75:25, 50:50, and 25:75 in the ternary solutions. Two empirical expressions of Huggins and Kraemer equations with three-parameters were used for reproducing of the experimental viscosity data. The fitting parameters were obtained for the corresponding temperatures. The miscibility criteria on the basis of the sign of Δ[η]_m based on the difference between experimental and ideal values of [η]_m, was calculated by applying the Garcia et al., theoretical equation. The effect of temperature on the viscosity data was also studied. The results from this method were correlated with the miscibility data obtained for the same system by differential scanning calorimeter (DSC) findings.     

Development of thermogravimetric method to quantitative determination of mebendazole

The objective of this work was to develop and validate a fast and reproducible method able to determine the concentration of mebendazole in raw materials and tablets. The samples were analyzed by dynamic thermogravimetry, in the heating rates of 10, 20, 40, 60 and 80°C min^–1, in the atmospheres of nitrogen and nitrogen with synthetic air. Obtained data were used in the equations of Antoine and Langmuir, with the purpose to get the pressure curves of those. Vapor pressure curves of drug and tablet of mebendazole were evaluated using the mathematical indexes of difference factor, f ₁, and similarity factor, f ₂, to compare its profiles. The data showed that there is no significant difference between the vapor pressure profiles of drug and tablet of mebendazole in both environmental conditions studied, what confirms that the process is really vaporization. The concentration of mebendazole was determined in the raw material and tablets with the drug.     

The Drude-Smith Equation and Related Equations for the Frequency-Dependent Electrical Conductivity of Materials: Insight from a Memory Function Formalism

The Drude-Smith equation is widely used for treating the frequency-dependent electrical conductivity of materials in the terahertz region. An attractive feature is its sparsity of adjustable parameters. A significant improvement over Drude theory for these materials, the theory includes backscattering of the charge carriers. It has nevertheless been criticized, including by Smith himself, because of the arbitrariness of a step in the derivation. We recall a somewhat similar behavior of back scattering in fluids observed in molecular dynamics computations and discussed in terms of memory functions. We show how theories such as Drude-Smith and Cocker et al. are examples of a broader class of theories by showing how they also arise as particular cases of a memory function formalism that divides the interactions into short and long range.     

从高分子运动的温度依赖关系看高分子运动特点

高分子的运动是高分子科学中最为基本、最为重要的问题之一,也是教学的重点之一,它是联系高分子微观结构与高聚物宏观性能之间的桥梁,本文就高分子运动的特点尤其是高分子运动的温度依赖关系进行了讨论,进而从本质上理解高聚物结构与性能之间的关系.     

Another Approach to the Modified Zhuravlev Equation on the Basis of the Oxidation of V2O4 and V6O13

It has been found that the modified Zhuravlev equation, [(1−α)^−1/3−1]²=ktⁿ, which describes the kinetics of oxidation of V₂O₄ and V₆O₁₃ in the temperature range 820–900 K and in the oxygen pressure range 1.0–20 kPa, can be derived via the assumption that the changes in the observed activation energy result from the changing contributions of the two diffusion processes controlling the reaction rate. The values of the observed activation energy are in the range 160–175 kJ mol⁻¹ for V₂O₄ and 188–201 kJ mol⁻¹ for V₆O₁₃ in the scope of the experimental oxygen pressures and temperatures and conversion degrees of 0.1–0.9. This revised version was published online in August 2006 with corrections to the Cover Date.