Non-isothermal kinetics of dyeing

This paper aims to present an essay to use the non-isothermal kinetic method in order to obtain the kinetic parameters of dyeing in a certain dye-fibre system. Some limitations of the model are discussed.     

Non-isothermal kinetics in solids

The integral methods, which are obtained from the various approximations for the temperature integral, have been extensively used in the non-isothermal kinetic analysis. In order to obtain the precision of the integral methods for the determination of the activation energy, several authors have calculated the relative errors of the activation energy obtained from the integral methods. However, in their calculations, the temperature integral at the starting temperature was neglected. In this work, we have performed a systematic analysis of the precision of the activation energy calculated by the integral methods without doing any simplifications. The results have shown that the relative error involved in the activation energy determined from the integral methods depends on two dimensionless quantities: the normalized temperature θ=T/T ₀, and the dimensionless activation energy x ₀=E/RT ₀ (where E is the activation energy, T is the temperature, T ₀ is the starting temperature, R is the gas constant).     

Non-isothermal decomposition kinetics of diosgenin

The thermal stability and kinetics of isothermal decomposition of diosgenin were studied by thermogravimetry (TG) and Differential Scanning Calorimeter (DSC). The activation energy of the thermal decomposition process was determined from the analysis of TG curves by the methods of Flynn-Wall-Ozawa, Doyle, ?atava-?esták and Kissinger, respectively. The mechanism of thermal decomposition was determined to be Avrami-Erofeev equation (n = 1/3, n is the reaction order) with integral form G(α) = [?ln(1 ? α)]^1/3 (α = 0.10–0.80). E _a and logA [s^?1] were determined to be 44.10 kJ mol^?1 and 3.12, respectively. Moreover, the thermodynamics properties of ΔH ^≠, ΔS ^≠, and ΔG ^≠ of this reaction were 38.18 kJ mol^?1, ?199.76 J mol^?1 K^?1, and 164.36 kJ mol^?1 in the stage of thermal decomposition.     

Non-isothermal kinetics of CoOOH decomposition

The non-isothermal 'kinetics of the decomposition of CoOOH powder has been studied derivatographically in a temperature range of 20–450 °C in air. The reaction proceeds in two stages: up to about 280°C with an activation energy E₁ = 38–50 kcal mol^?1 and above that temperature with E₂ = 20–25 kcal mol^?1, depending on the kinetic equations which are employed. The results have been critically discussed on the basis of certain current concepts.     

竹材非等温热解动力学

利用热重分析技术对竹材在高纯N2条件下,从室温至1273K进行了非等温热解分析,研究了升温速率(5、10、20和40K/min)对热解过程的影响,探讨了其热解机理。研究表明,竹材非等温热解过程主要分为失水干燥、快速热解和缓慢分解三个阶段组成,其中第二阶段是整个过程的主要阶段,析出大量挥发分造成明显失重。升温速率对热解过程有显著影响,随着升温速率的增加,最大热解速度增大,对应的峰值温度升高,热滞后现象加重,热解各阶段向高温侧移动。热解机理满足一维扩散Parabolic法则,反应机理函数为g(α)=α2。不同升温速率下活化能为75.32-82.99kJ.mol-1,指前因子为1.17×105-1.12×106min-1。     

Non-isothermal kinetics of thermal degradation of chitin

Thermogravimetric studies of chitin in air atmosphere were carried out at six rates of linear increase of the temperature. The kinetics and mechanism of the thermal decomposition reaction were evaluated from the TG data by iso-conversional calculation procedure of Kissinger–Akahira–Sunose recommended from ICTAC kinetics committee, as well as 27 mechanism functions. The comparison of the results obtained showed that they strongly depend on the selection of proper mechanism function for the process. Therefore, it is very important to determine the most probable mechanism function. In this respect, the iso-conversion calculation procedure turned out to be the most appropriate one. In the present work, the values of the apparent activation energy E, pre-exponential factor A in Arrhenius equation, as well as the changes of entropy ΔS ^≠, enthalpy ΔH ^≠, and Gibbs free energy ΔG ^≠ for the formation of the activated complex from the reagent are calculated. All the calculations were performed using programs compiled by ourselves.     

Non-isothermal crystallization kinetics of some aventurine decorative glaze

Thermal and structural properties of three clays (sepiolite and two kaolinites) from Turkey were studied by thermal analysis (TG–DTA), X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FT-IR), and surface area measurement techniques The adsorption of sulfur dioxide (SO₂) gas by these clays was also investigated. SO₂ adsorption values of K1, K2, and S clay samples were measured at 20 °C and pressures up to 106 kPa. Sepiolite sample (S) primarily consists of pure sepiolite, only dolomite present as accompanying mineral. Both kaolinite samples, K1 and K2, mainly contain kaolinite as the major clay mineral and quartz as impurity. In K2 sample, muscovite phase is also present. Simultaneous TG–DTA curves of all clay samples were obtained at three different heating rates 10, 15, and 20 °C min⁻¹ over the temperature range 30–1200 °C. It was found that the retention value of SO₂ by S clay (2.744 mmol/g) was higher than those of K1 (0.144 mmol/g) and K2 (0.164 mmol/g) samples.     

Non-isothermal kinetics of dehydration of some selenite hexahydrates

The kinetics of dehydration of Al₂(SeO₃)₃·6H₂O, Ga₂(SeO₃)₃·6H₂O and In₂(SeO₃)₃·6H₂O were studied under non-isothermal heating on a derivatograph. The method of Coats-Redfern was used with different kinetics models. The values of the kinetics parameters characterizing the process were calculated. The dependencies observed were interpreted according to the generalized perturbation theory of chemical reactivity. Kinetic compensation effect was found.     

Non-isothermal crystallization kinetics of hot drawn polyester films

The non-isothermal crystallization kinetics of hot drawn poly(ethylene terephthalate) films were studied using the Kissinger and Ozawa equations. The influence of the initial drawing on the crystallization kinetics was investigated. The values of the apparent activation energy and of the Avrami exponent indicates that the nucleation and growth of crystallites depend greatly on the stress submitted to the samples.     

Non-isothermal degradation kinetics of MMA-St copolymer and EPS lost foams

Methylmethacrylate-styrene (MMA-St) random copolymer was synthesized by suspension copolymerization. The thermal degradation of MMA-St copolymer and EPS lost foams was studied by non-isothermal thermal gravimetric analysis under nitrogen purge. Thermal decomposition behavior of MMA-St copolymer lost foam was examined and compared with EPS. It was found that EPS foam starts to decompose at higher temperatures than MMA-St copolymer foam in all heating rates. The apparent activation energy was calculated by the Flynn-Wall-Ozawa method. It has been concluded that the model fitting methods unable to reveal the complexity of the pyrolysis process and the model-free methods can be suggested as a reliable way of determining the kinetic parameters.     

Non-isothermal kinetics of diffusion and its application to thermal analysis

Non-isothermal kinetics of diffusion are derived, extending the fundamental equation of diffusion to non-isothermal conditions, and the equation is solved for a few typical cases. From these theoretical considerations, two methods of analyzing thermoanalytical data of diffusion are proposed. One of the methods is applied to EGA curves of the volatilization of toluene from epoxy resin cured with ethylenediamine. The diffusion constants obtained as a function of temperature for two plate-specimens of different thicknesses at various heating rates are in good agreement with each other. The temperature dependence of the diffusion constant observed for a powdered sample is also in good agreement with those observed for the two plate-specimens.

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Zusammenfassung Die nicht-isotherme Kinetik der Diffusion wird abgeleitet, indem die Grundgleichung der Diffusion auf nicht-isotherme Fälle erweitert und für einige typische Fälle gelöst wird. Von diesen theoretischen Erwägungen ausgehend werden zwei Methoden zur Analyse thermoanalytischer Diffusionsangaben vorgeschlagen. Eine der Methoden wird für die EGA-Kurven der Verflüchtigung von Toluol aus mit Ethyländiamin behandeltem Epoxyharz angewandt. Die an zwei Platten-Arten verschiedener Dicke bei verschiedenen Aufheizgeschwindigkeiten als Funktion der Temperatur erhaltenen Diffusionskonstanten stimmen gut überein. Die an einer pulverförmigen Probe beobachtete Temperaturabhängigkeit der Diffusionskonstante ist ebenfalls in guter Übereinstimmung mit der an den zwei Plattenkörpern erhaltenen.

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Résumé On étudie la cinétique de diffusion en régime non isotherme, en étendant l'équation fondamentale de la diffusion aux cas non isothermes et l'on donne la solution de l'équation pour quelques cas typiques. A partir de ces considérations théoriques, on propose deux méthodes pour analyser les données thermoanalytiques de la diffusion. On applique l'une d'elles aux courbes AGE de stabilisation du toluène à partir des résines époxy traitées à l'éthylène diamine. Les constantes de diffusion obtenues en fonction de la température pour plusieurs vitesses d'échauffement sur deux échantillons en forme de plaquette sont en bon accord, de même que pour des échantillons pulvérulents.

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Non-isothermal kinetics of CrO3 decomposition pathways in air

The course of the non-isothermal decomposition of CrO₃ in air was explored kinetically, by using a number of widely accepted methods. The credibility of the values obtained from a given kinetic parameter (the reaction order, the activation energy and the frequency factor) was justified on the grounds of (i) a multiple correlation coefficient, and (ii) the merits and demerits of the method adopted. The results obtained may help towards a characterization of the non-isothermal conditions under which the encountered decomposition events and products could be resolved. The study was motivated by the results of previous physicochemical characterization studies [1, 2], in which catalytically important intermediates CrO_x(3<x<6) were structurally identified.