Isoconversional Approach to Evaluating the Hoffman–Lauritzen Parameters (U* and Kg) from the Overall Rates of Nonisothermal Crystallization

Summary: An equation has been derived that correlates the temperature coefficient of the growth rate with the temperature dependence of the effective activation energy of the overall crystallization rate, which can be measured by differential scanning calorimetry. The dependence is evaluated by using an advanced isoconversional method and is parameterized in terms of the Hoffman–Lauritzen equation. The parameters obtained for the nonisothermal crystallization of the poly(ethylene terephthalate) melt are consistent with the parameters reported for isothermal crystallization.

The fit of the equation derived here is shown for data corresponding to the dependence of the effective activation energy on average temperature (fit = solid line).     

The temperature dependence of mercury saturated vapor pressure over the whole range of its liquid state

The Boltzmann distribution with normalization with respect to the boiling point was used to calculate the temperature dependence of vapor pressure, which included the temperature and heat of boiling only. A refined equation of mercury vaporizability with mutually consistent characteristics such as vapor pressure and the temperature and heat of boiling was obtained. The equation correctly described this dependence over the whole liquid state range, including the critical point.     

On the relaxation theory of glass transition in liquids

A method for calculating the constant in the main equation of glass transition (which relates the relxation time and the cooling rate near the glass transition temperature) with consideration given to the temperature dependence of the activation energy in this region is proposed. A modification of the main glass transition equation is considered. Application of this equation to the relaxation spectrometry of amorphous polymers and inorganic glasses is discussed.     

Temperature dependence of the dynamic viscosity of liquid mercury

The dependence of the dynamic viscosity of mercury on temperature is calculated and expressed in terms of the cluster associate model, based on the Boltzmann distribution and with normalization at the melting point. The resulting refined equation for mercury viscosity adequately reflects this dependence over the range of the liquid state, including the critical point.     

Study of the thermal oxidation of polyolefins—III: Pressure and temperature dependence of the rate of oxygen absorption

The kinetics of oxygen absorption by high pressure polyethylene (PE) have been studied between 8 and 650 torr oxygen pressure and in the temperature range 140 to 180°. The mechanism of thermal oxidation has been described and the equation for the rate of oxygen absorption has been derived. The rate equation has been studied in the initial stage and at points of the maximum rate of oxygen absorption. Some rate constant combinations (characteristic of the process) and their temperature dependence have been determined from experimental data. The pressure dependence of the initial and maximum rates of oxygen absorption, in the pressure range investigated, is well described by the proposed mechanism.     

The Adam-Gibbs equation and the out-of-equilibrium alpha relaxation of glass forming systems

The temperature dependence of the alpha-relaxation time out of equilibrium has been investigated by means of dielectric relaxation in a series of fragile glass formers including several polymers. The influence of physical aging on this behavior has also been studied. The experimental results have been quantitatively compared with the predictions of the Adam-Gibbs equation. It has been found that, whereas for small molecule glass formers the experimental values of the apparent activation energy agree quite well with the prediction of the Adam-Gibbs equation, for polymers the experimental activation energy values are systematically higher. Moreover, whereas for small molecule glass formers the experimental values of the apparent activation energy remains essentially unaffected by physical aging, for polymers a pronounced reduction of the experimental apparent activation energy is observed. These results are found to be consistent with the Adam-Gibbs equation if a significant temperature variation of the configurational entropy in the investigated temperature range would occur for nonannealed polymers, being the possible variation hardly noticeable for the small molecules. With this assumption, all the obtained results would support the validity of the Adam-Gibbs equation for describing the temperature dependence of the time scale of the alpha-relaxation also out of equilibrium, at least for fragile glass formers.     

碳氧化反应速率常数与温度特殊关系的理论解释

对于碳氧化反应,在不同温度范围内,温度对反应速率常数的影响呈现不同规律的现象进行了讨论。指出第一阶段主要由氧气在碳表面化学吸附平衡受温度的影响决定。第二阶段则由碳在二氧化碳中发生气化反应,特别是其中的酮基脱附步骤决定。对已有的反应机理进行了比较,提出了新的简化机理,并采用速率控制步骤近似和平衡近似对机理进行了近似处理,得出的第二阶段动力学方程可以较好地解释相关实验规律。     

对聚合物玻璃化转变的几点新认识

基于聚合物玻璃化转变的定义,探讨了聚合物宏观单晶体和聚合物单链单晶的玻璃化转变问题,指出玻璃化转变的温度依赖性不服从普适的Arrhenius方程,可以把WLF方程看作是聚合物玻璃化转变的特有温度依赖关系。介绍了二维状态下聚合物可能的玻璃化转变。     

A new modification of the UNIQUAC equation including temperature dependent parameters

The UNIQUAC equation was modified by introduction of a linear temperature dependence of the volume and surface area parameters, r_i and q_i. The slope of r_i and q_i functions were found to be the same for hydrocarbons and pyridine. The modified equation was used for prediction of vapor–liquid equilibria (VLE) in binary mixtures of hydrocarbons and pyridine with hydrocarbons as well as for the prediction of the excess enthalpy (H^E) in binary mixtures formed by pyridine with aliphatic alkanes. The results obtained were compared with predictions by UNIFAC and further with UNIQUAC equation and its modification involving temperature dependant coordination number z. The proposed temperature dependence of the r_i and q_i parameters enables prediction of the VLE at various temperatures and leads to reasonable values of H^E. The necessary input reduces to one set of isothermal VLE data. One set of UNIQUAC interaction parameters u_ij is sufficient for representation of VLE in a wide range of temperature and to obtain a reasonable prediction of H^E.     

DSC Analysis of the Induction Period in the Vulcanisation of Rubber Compounds

Vulcanisation of rubber compounds was studied by DSC under isothermal and non-isothermal conditions. The parameters of an Arrhenius-like equation describing the temperature dependence of induction period have been obtained both from isothermal and non-isothermal measurements. A new method for obtaining the kinetic parameters from non-isothermal measurements, based on the dependence of onset temperature of vulcanisation peak on heating rate, is presented. Also, a procedure for the evaluation of temperature difference between the furnace and sample is proposed. It has been shown that the treatment of non-isothermal DSC measurements gives the kinetic parameters free of systematic errors. The new method can also be used for studying other reactions exhibiting the induction period. This revised version was published online in August 2006 with corrections to the Cover Date.     

A modification of the martin equation of state for calculating vapour-liquid equilibria

A modification of the Martin (1979) equation of state suitable for vapour-liquid equilibrium calculations is presented. The temperature dependence of this modification is determined from the second virial coefficient correlation of Tsonopoulos (1974) and the pure-component vapour pressures. Excellent predictions of phase equilibria have been obtained for a number of binary systems, including a system containing hydrogen. For the systems tested, the equation of this study is more accurate than the Peng-Robinson (1976) equation of state.     

Breakthrough characteristics of volatile organic compounds in the -10 to + 170 degrees C temperature range on Tenax TA determined by microtrap technology

In this work the breakthrough volumes (BTVs) of volatile organic compounds (VOCs) on Tenax TA were determined in the -10 to 170 degrees C temperature range by using microtrap (MT) technology. The MT technology allowed experimental investigation of the temperature dependence of BTVs. Along with the BTV data, we also discuss the thermodynamics of the temperature dependence of the BTV through a two-parameter equation In (BTV) = A1/T + C1 where T is temperature (K), A1 = -deltaH/R where deltaH is enthalpy of sorption and C1 is constant. This equation fitted well the experimental results with R2 values between 0.9737 (acetone) and 0.9995 (dimethyl disulfide), with n between 6 and 11. However, for n-pentane, n-hexane and 1-hexene it proved that a three parameter equation In (BTV) = A2/ T + BTB + C2 fitted better to the experimental results, with A2 = -deltaHT0/R, B = deltaCp/R, TB = 1n(T/T0) + (T0 - T)/T, C2 a constant, deltaHT0 the adsorption enthalpy at reference temperature T0 and deltaCp the difference in the molar heat capacity of compound under investigation between the sorbed and the free gas phase state. The statistical analysis showed for example for n-pentane now R2 = 0.9969 instead of R2 = 0.9746, and Fisher statistics F = 487 instead of F = 153, with a significance level P = 0.018 for the third parameter. The results show that microtrap technology well serves as a technology to get information on temperature dependence of BTVs in an extended range. Simultaneously, it turns out that MT technology, extending the operational temperature range, is well served by a careful investigation of the temperature dependence models of BTVs.     

A note on the temperature dependence of the coordination number

An empirical equation describing the temperature dependence of the coordination number of a molecule in a liquid is examined in terms of Bernal's model for the liquid state. To effect this comparison the non-associated compound n-C₁₁H₂₄ is chosen to represent the temperature span of the empirical equation. Predictions from Bernal's model based on volume expansion and latent heat data are in good agreement with the empirical correlation.     

氧化锆基固体电解质材料与温度无关的离子电导活化能

氧化锆(ZrO2)基固体电解质材料的离子电导率随温度的变化关系呈现非线性Arrhenius特征;相应地,由经典的Arrhenius公式计算得到的电导活化能是一个与温度有关的参数.本文通过对实验获得的几种Y2O3稳定立方ZrO2(YSZ) 材料的电导率－温度关系的分析,对经典的Arrhenius公式进行了修正.由修正后的Arrhenius公式计算得到的电导活化能是一个与温度无关的常数.此外,还进一步借助于物理化学中的过渡状态理论,从材料离子导电机制出发对这一与温度无关的电导活化能的合理性进行了讨论,发现这一活化能在数值上与理论计算结果吻合得很好.     

凝胶型聚合物电解质的电导率与温度的关系

凝胶型聚合物电解质的电导率与温度的关系孙晓光，林云青，齐力，景遐斌，王佛松（中国科学院长春应用化学研究所长春１３００２２）关键词凝胶电解质，离子电导率，活化能无定形聚合物电解质电导与温度的依赖关系一般可用Ｖｏｇｅｌ－Ｔａｍｍａｎ－Ｆｕｌｃｈｅｒｃ（Ｖ...     

Relationship between the dynamic viscosity of hydrocarbons and the Wiener topological index

Dependences of the dynamic viscosity on the product of the molecular weight into the Wiener topological index to the 2/3 power are obtained for some hydrocarbons. Relationships between the latter quantity and the parameters of the Frenkel-Andrade equation for the temperature dependence of the dynamic viscosity are established.     

On some features of glass transition in amorphous substances

In Bartenev’s well-known approach to determining the dependence of glass-transition temperature on melt cooling rate, it was proposed to take into account the temperature dependence of the activation energy of the liquid-to-glass transition. The physical meaning of parameters of the obtained equation is discussed.     

A comparison between the bond-strength-coordination number fluctuation model and the random walk model of viscosity

We have studied the temperature dependence of the viscosity of some polymeric materials by using both, the bond-strength-coordination number fluctuation model and the random walk model. The results reveal that both models show an excellent agreement with the experimental data. For the random walk model, two equations corresponding to two temperature regimes (low-T and high-T) separated by the critical temperature T _c, which is difficult to determine, are needed to describe the temperature dependence of the viscosity of a fragile system, whereas for the bond-strength-coordination number fluctuation model, a single equation with clear physical meaning describes the temperature dependence of the viscosity of both, the fragile and strong systems. We have also studied the relationship between the normalized temperature range of cooperativity and the fragility index. A theoretical expression for the relationship has been derived based on the bond-strength-coordination number fluctuation model. The comparison with the experimental data shows a good agreement, leading to the conclusion that the kinetic properties of glass forming liquids and the cooperativity of molecular relaxations are correlated.     

Temperature Dependence of the Detergency of Sodium Alkylbenzenesulfonate and Compositions Thereof

Temperature dependence of the detergency of one of the basic components of synthetic detergents, sodium alkylbenzenesulfonate, and compositions thereof was studied. The influence of the temperature on the detergency equation parameters was elucidated.     

Fictive temperature, cooling rate, and viscosity of glasses

The physical correlation between the fictive temperature dependence of the cooling rate of the melts and the temperature dependence of the equilibrium viscosity has been found by doing differential scanning calorimetric and viscometric measurements on a silicate melt, and by performing finite element simulations of the fiber drawing from that melt. This correlation is governed by a correlation factor Kc (in Pa K) which is constant and universal for silicate glasses. The factor Kc is obtained in the cooling rate range from 10(-2) to 10(6) K/s and is in good agreement with that theoretically predicted. The physical feature of the correlation is discussed in the paper. When the fictive temperature equals the actual temperature, a linear relation exists between the cooling rate and the Maxwell relaxation rate, the slope of which depends on the fragility of the glass melts. The Avramov equation is extended to describe the cooling rate dependence of the fictive temperature. The cooling rate equation contains only one adjusting parameter, i.e., the fragility parameter alpha.