两种量热模式下物质热分解的动力学补偿效应

热分析量热仪主要包括动态、等温、恒温及绝热四种操作模式。很多学者基于动态及等温模式的测试结果,采用Arrhenius速率常数进行动力学计算,进而发现了所谓的“动力学补偿效应”。为了解绝热模式下是否也存在动力学补偿效应,分别采用绝热加速量热法(ARC)及动态差示扫描量热法(DSC)研究了过氧化二异丙苯(DCP)、40%(质量分数,下同)DCP溶液、葡萄糖、45%葡萄糖溶液的热分解特性,在此基础上基于Arrhenius公式计算了对应的表观活化能E和指前因子A,并对计算结果进行了分析。结果表明:绝热模式下,不同质量的同种样品及其溶液的最佳动力学参数,或者同一组数据采用不同的反应级数获得的lnA和E之间均存在明显的线性关系。此外,尽管由动态DSC数据计算获得的E和lnA普遍小于绝热模式的结果,但两种模式下获得的lnA和E之间仍然存在动力学补偿效应。由此可以推断,具有相同或类似反应机理的反应,虽然实验模式不同,但其E和lnA之间存在明显的动力学补偿效应。     

Obtaining more,and better,information from simple ramped temperature screening tests

Thermal screening of materials is a vital part of hazard assessment in the chemical industry. There is the need to identify the worst potential hazards and to further investigate these scenarios. Several screening methods are presented, and the subject of ramped temperature screening tests is studied in detail. Methods for the detection of exothermic reaction 'onset' temperatures are given. It is shown that, under some circumstances, the temperature data obtained during a simple controlled ramp heating experiment can be used to estimate the expected temperature rise that would occur under adiabatic conditions and the heat of reaction. The use of the data to obtain n^th order kinetic parameters is also demonstrated. Data obtained using the Thermal Screening Unit (TS^U) are compared to those obtained using other forms of apparatus. Heats of reaction and kinetic data have also been calculated and compare very well with data obtained using much more sophisticated adiabatic calorimeters. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparative kinetic study of decomposition of some diazepine derivatives under isothermal and non-isothermal conditions

Thermal analysis is one of the most widely used methods for studying the solid state of pharmaceutical substances. TG/DTG and DSC curves provide important information regarding the physical properties of the pharmaceutical compounds (stability, compatibility, polymorphism, kinetic analysis, phase transitions etc.). The purpose of a kinetic investigation is to calculate the kinetic parameters and the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances. A kinetic study regarding the diazepam, nitrazepam and oxazepam thermal decomposition was performed, under non-isothermal and isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 483, 498, 523, 538 and 553 K. The TG/DTG data were processed by three methods: isothermal model-fitting, Friedman’s isothermal-isoconversional and Nomen-Sempere non-parametric kinetics. In the model-fitting methods the kinetic triplets (f(α), A and E _a) that defines a single reaction step resulted in being at variance with the multi-step nature of diazepines decomposition. The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation energies on the extent of conversion. It is very difficult to obtain an accord with the similar data which resulted under non-isothermal conditions from a previous work. The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as well as a different strategy of experimental data processing.     

Determination of Michaelis-Menten parameters obtained from isothermal flow calorimetric data

Recent papers have reported [Thermochim. Acta 399 (2003) 63; Thermochim. Acta, in press] the results of a preliminary inter/intra laboratory study into the suitability of the base-catalysed hydrolysis of methyl paraben as a test and reference reaction for isothermal flow-through calorimeters. It was shown that this reaction can be used to investigate the flow characteristics of the instrument being used. It has also allowed, for the first time, the calculation of accurate values for the rate constant and for the enthalpy change, ΔH (hereafter H (enthalpy) for simplicity) of reaction directly from the calorimetric data, free from assumption. These findings have been extended to permit the direct determination of Michaelis-Menten based kinetic parameters from calorimetric data again free from assumption (except that the system conforms to Michaelis-Menten kinetic theory). This paper describes the method used for such an analysis and reports the results of a preliminary study on the urea/urease enzymatic system.     

Time-parameter Method for Studying Kinetics of Consecutive First-order Reactions in Calorimeter

Thermogravimetric analysis (TG) was used in this work to study the degradation kinetics of industrial PVC plastisols. In order to model the pyrolitic degradation of plastisols in nitrogen, a kinetic model based on phenomenological considerations was developed. Two different processes were observed during the first degradation stage. The model parameters, such as activation energies and pseudo orders of reaction, were calculated using a non-linear regression analysis. The model developed was able to describe the degradation behaviour both in isothermal and in dynamic modes. The results of such analysis were applied to obtain long-term data from short-term experiments as an engineering approach to evaluate the thermal resistance of plastisols. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetic study of an epoxy system badge (n=0)/1, 2 dch modified with an epoxy reactive diluent

The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (n=0) and 1, 2 diaminecyclohexane (DCH) with an epoxy reactive diluent vinylcyclohexane dioxide was studied by temperature modulated differential scanning calorimetry (TMDSC). The models proposed by Kamal and by Horie et al. were employed in the kinetic study. From these studies reaction orders, rate constants, and activation energies were determined. The technique of TMDSC allows to include in the kinetic study the effect of diffusion by means of the mobility factor, calculated from the curves of the complex heat capacity registered during the curing isothermal experiments. The results were compared to those obtained for the same system employing the reaction rate data. This revised version was published online in July 2006 with corrections to the Cover Date.     

Curing reaction of glycidylthioether resins: Kinetic model study by near infrared spectroscopy and multivariate curve resolution

The reactivity of sulfur‐based epoxy monomers was studied by monitoring of a model system involving phenylglycidylthioether and aniline. The reaction was carried out under isothermal conditions and monitored in situ by near infrared spectroscopy. Using multivariate curve resolution‐alternating least squares made it possible to obtain the concentration and spectral profiles of each species throughout the reaction. To obtain the kinetic rate constants, the values of the recovered concentration profiles were fitted to a kinetic model proposed for the reaction. Reactivity was evaluated by comparing the concentration profiles and kinetic rate constants obtained with the same parameters obtained for phenylglycidylether/aniline as a reference system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4846–4856, 2006     

FTIR法研究乙酸酚醛酯固化邻甲酚环氧树脂的反应动力学

用ＦＴＩＲ原位测量技术研究了乙酸酚醛酯与邻甲酚环氧树脂在２－甲基咪唑存在下进行恒温固化反应的动力学，测定了固化反应的动力学参数，研究结果表明，固化反应是按照一级固化反应动力学进行的，根据羰基峰在固化反应前后的变化对固化反尖机理进行了初步探讨。     

煤焦水蒸气气化动力学模型及参数敏感性研究

在热重分析仪上对小龙潭煤焦、府谷煤焦和晋城煤焦水蒸气气化过程进行了研究。使用收缩核模型、混合模型和随机孔模型模拟了三种煤焦水蒸气气化反应过程。结果表明,混合模型总体上模拟效果最好,收缩核模型和随机孔模型对低变质程度的小龙潭煤焦气化过程模拟效果不佳,但是适用于模拟另外两种煤阶较高的煤焦气化过程。求解了三种模型的动力学参数,并分析了不同模型参数出现差异的原因。同时,采用敏感性分析法定量研究了模型中的参数发生偏差时引起模型误差的大小,并通过比较发现反应速率常数k为敏感性因素,而混合模型中反应级数n和随机孔模型中孔结构参数ψ为非敏感性因素。     

A unified theory for the kinetic analysis of solid state reactions under any thermal pathway

The Ozawa concept of generalized time has been used for developing master plots for the different kinetic models describing solid state reactions. These plots can be indistinctly used for analysing isothermal or non-isothermal experimental data. It is demonstrated that it is not possible to discriminate the kinetic model from a single non-isothermal curve without a previous knowledge of the activation energy. However, it has been shown that the ln [(da/dt)/f(a)] data taken from a set of DTG curves obtained at different heating rates lie on a single straight line when represented as a function of 1/T only if the kinetic model really obeyed by the reaction is considered. Moreover, the true values of E and A are obtained from the slope and the intercept of this straight line. This revised version was published online in July 2006 with corrections to the Cover Date.     

Isothermal and non-isothermal pyrolysis kinetics of Kapton polyimide

The kinetics involved in the thermal decomposition of Kapton^® polyimide 100HN under nitrogen atmosphere were studied by applying various fitting techniques to the isothermal and non-isothermal gravimetric data. The correlation of the reaction mechanism fitting, the analytical model fitting and the isoconversional method to these data was examined in relation to the kinetic parameters and the kinetic predictions. The mechanisms for solid-state reactions fit the isothermal data very well but result in highly uncertain values for the kinetic parameters when applied to the non-isothermal data. Isoconversional methods show that the apparent activation energy depends on the extent of conversion but do not provide information for the reaction order and the pre-exponential factor. Three single heating-rate analytical models by Coats-Redfern, MacCallum-Tanner and van Krevelen were analysed using the non-isothermal data. A multi-heating rate model is proposed and its validity is compared to the single-heating rate models on the basis of kinetic predictions.     

Thermal stability of ketoprofen

The purpose of this investigation is to calculate the kinetic parameters and the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances. A kinetic study regarding the ketoprofen—involving active substance’s thermal decomposition—was performed under isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 260; 265; 270; 275; and 280 °C. The thermogravimetry/derivative thermogravimetry data were processed by three differential methods: isothermal–isoconversional, Friedman’s isothermal–isoconversional, and isothermal model-fittings. The obtained results are in good accordance with those obtained under non-isothermal conditions of a previous study, and confirm the necessity for the kinetic parameters to be determined, under different thermal conditions, by the adequate calculation methods.     

Solid-state reactions from isothermal heat conduction microcalorimetry theoretical approach and evaluation via simulated data

Several recent publications from this laboratory have reported developments in the capacity to calculate thermodynamic and kinetic parameters, such as rate constant, enthalpy, order of reaction, from isothermal micro-calorimetric data. To date these developments have all been associated with the calculation of the desired parameters from solution phase reactions. This paper furthers these developments to a theoretical consideration of solid-state reactions and the calculation of the values for the rate coefficient, k, the fitting parameters m and n, the total number of joules released over the lifetime of reaction, Q, and hence either the specific enthalpy or the molar enthalpy of reaction, H. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermokinetic parameters and thermal hazard evaluation for three organic peroxides by DSC and TAM III

The thermokinetic parameters were investigated for cumene hydroperoxide (CHP), di-tert-butyl peroxide (DTBP), and tert-butyl peroxybenzoate (TBPB) by non-isothermal kinetic model and isothermal kinetic model by differential scanning calorimetry (DSC) and thermal activity monitor III (TAM III), respectively. The objective was to investigate the activation energy (E _a) of CHP, DTBP, and TBPB applied non-isothermal well-known kinetic equation to evaluate the thermokinetic parameters by DSC. We employed TAM III to assess the thermokinetic parameters of three liquid organic peroxides, obtained thermal runaway data, and then used the Arrhenius plot to obtain the E _a of liquid organic peroxides at various isothermal temperatures. In contrast, the results of non-isothermal kinetic algorithm and isothermal kinetic algorithm were acquired from a highly accurate procedure for receiving information on thermal decomposition characteristics and reaction hazard.     

Kinetic study of dipivaloylmethane by ozawa method

The lanthanidic complexes of general formula Ln(C₁₁H₁₉O₂)₃ were synthesized and characterized by elementary analysis, infrared absorption espectroscopy, thermogravimetry (TG) and differential scanning calorimetry (DSC). The reaction of thermal decomposition of complexes has been studied by non-isothermal and isothermal TG. The thermal decomposition reaction of complexes began in the solid phase for Tb(thd)₃, Tm(thd)₃ and Yb(thd)₃ and in the liquid phase for Er(thd)₃ and Lu(thd)₃, as it was observed by TG/DTG/DSC superimposed curves. The kinetic model that best adjusted the experimental isothermal thermogravimetric data was the R1 model. Through the Ozawa method it was possible to find coherent results in the kinetic parameters and according to the activation energy the following stability order was obtained: Tb(thd)₃>Lu(thd)₃>Yb(thd)₃>Tm(thd)₃>Er(thd)₃ This revised version was published online in August 2006 with corrections to the Cover Date.     

Curing kinetics of the epoxy system diglycidyl ether of bisphenol A/isophoronediamine by Fourier transform infrared spectroscopy

The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE, n = 0) and isophoronediamine (IPD), was studied by Fourier transform infrared spectroscopy (FTIR). The degree of conversions and the reaction rates at different isothermal curing temperatures were calculated from the infrared spectra using a method derived from Beer's law. This method is based on the ratio of the height of the characteristic absorbance peak to reference absorbance peak. A kinetic model proposed by Sourour and Kamal has been used to fit experimental data. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermal stability of piroxicam

The application of thermal method is of great importance regarding the pharmaceutical problems such as the control of raw materials, the determination of purity, the qualitative and quantitative analysis of drug formulation, tests of thermal stability and compatibility and the determination of kinetic parameters etc. The purpose of a kinetic investigation is to calculate the kinetic parameters and the determination of the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances. A kinetic study regarding the piroxicam—active substance’s thermal decomposition was performed under isothermal conditions and nitrogen atmosphere, for the temperature steps: 200, 205, 210, 215 and 220 °C. The TG/DTG data were processed by three differential methods: isothermal—isoconversional, Friedman’s isothermal isoconversional and isothermal model-fitting. The obtained results are in good accord between them, as well as with those obtained under non-isothermal conditions from a previous work and confirm the necessity of the kinetic parameters determining in different thermal conditions, by the adequate calculation methods.     

黏胶废液对福建无烟煤水蒸气催化气化的动力学和补偿效应

采用黏胶废液为催化剂,对福建尤溪无烟粉煤在常压热分析仪中的水蒸气催化气化动力学进行了研究。在850℃～950℃测定了黏胶废液催化剂添加量（NaOH浓度为计算基准）从0～12%时的碳转化率随气化时间的变化,表明黏胶废液具有提高碳转化率和气化速率的作用,同时确定了该黏胶废液催化剂的加载饱和浓度。基此得出的尤溪无烟粉煤水蒸气催化气化反应动力学符合缩芯模型,并给出相应的动力学参数。进而分析表明,该催化气化过程存在明显的补偿效应,最后给出黏胶废液对尤溪无烟粉煤水蒸气催化气化包括补偿效应的动力学方程。     

Effects of experimental sample mass on the calorimetric study of thermoset resins

It is known that experimental parameters may affect peak characteristics in DSC studies. Kinetic parameters calculated from isothermal and dynamic runs, can also be affected by the choice of experimental conditions.The sample mass can affect the determination of reaction parameters because of the heat transport and the self-insulating properties of large masses.In the curing process of thermoset resins like unsaturated polyester crosslinked by styrene, the exothermal heat results from the reaction advance but it also produces an autocatalytic process that induces an increase in the reaction rate. The sample mass, in this kind of experiments, can influence the determination of reaction parameters not only through the effect of heat transport or thermal lag on the calorimetric results but also through the action that the sample mass exerts on the exothermal heat, and consequently, on the autocatalytic process.In this paper we intend to present the results obtained in the study of the curing kinetics of thermoset resins by DSC technique using different sample masses. We will point out that the reaction heat determined by dynamic measurement was found to be independent of the sample mass. We have obtained differences in the kinetic parameters like the reaction order, activation energy and preexponential factor when the sample mass was changed.The research reported was supported by CICYT under Grant no. MAT89-377-C02-02.     

Thermal properties,induction period,interfacial energy and nucleation parameters of solution grown benzophenone

The kinetic parameters (reaction order, n, activation energy, E, pre-exponential factor, A, constant rate, k) for the dehydration step due to elimination of osmotic water and hydrogen-bounded water with the carboxylic groups, and for the anhydrifying step owing to the dehydration of two neighboring (-COOH) groups, were determined under non-isothermal conditions for some carboxylic resins with acrylic-divinylbenzene (DVB) matrix. The kinetic parameters were evaluated by means of isoconversional methods from (TG/DTG) thermal analysis data. The results show a dependence of the apparent kinetic parameters on the cross-linking degree, granulation, gel/macroporous matrix nature, exchange capacity and heating rate.