Kinetic analysis of thermal decomposition reactions

The effect of⁶⁰C0-gamma radiation on the kinetic parameters of the thermal decomposition of potassium bromate crystals has been investigated. Radiation did not modify the mechanism of thermal decomposition reaction, but resulted in a decrease in activation energy and frequency factor with a rate which is large at small doses and decreases at higher doses. The results showed that the increase in the concentration of decomposition nuclei tends to be more important than the increase in the porous character of the solid.     

Kinetic analysis of derivative curves in thermal analysis

Two methods of obtaining kinetic parameters from derivative thermoanalytical curves are proposed. The methods are based on the general form of kinetic formulae and are applicable to general types of reactions governed by a single activation energy. One method utilizes the linear relation between peak temperature and heating rate in order to estimate the activation energy, and only the information of the rate of conversion versus the temperature is necessary. The other method needs the information of both the conversion and the rate of conversion versus the temperature, and the Arrhenius plot is made for an assumed kinetic mechanism.

     

Kinetic analysis of thermal decomposition of magnesite

The excess enthalpy of magnesite accumulated by vibration grinding at low specific grinding energy consumption is due predominantly to an increase in specific surface area; at higher energy supply, it is caused by changes in the X-ray amorphous phase content, and when the supplied energy exceeds ca 2000 kJ kg^–1 it is a result of the generation of other kinds of defects. The generated defects are relatively stable below 800 K and are the reason for a broad range of distribution of local molar Gibbs energies. Thus, at low temperatures only the active portion of samples is able to decompose. Defects relax above ca 800 K, with rates comparable with the rate of decomposition itself. Accordingly, the efficiency of mechanical activation is impressive only below this temperature.Dedicated to Dr. Robert Mackenzie on the occasion of his 75th birthday     

Environmental applications for thermal analysis

A review is presented of the applications of thermoanalytical techniques to problems encountered in the measurement and control of air pollution. A number of suggestions are offered regarding new or extended applications of these techniques.     

Kinetic analysis of cis-trans thermal isomerization of polyacetylene

A single broad exothermic peak due to cis-trans isomerization appears near 140°C in the differential scanning calorimetry (DSC) curve of polyacetylene (PA) films, polymerized by a nonsolvent method using a high-temperature-aged catalyst. This exothermic peakis described by a two-state model, in which population probabilities for cis and trans states are assumed to change through the forward and backward reactions. The enthalpy difference between the two states is 1.69 kcal/mol, which was derived from the slope of the plot of heat of isomerization versus cis content. The activation energy was determined experimentally from the heating-rate dependence of the peak temperature. A single activated process with an activation energy of 28 kcal/mol was observed for the PA film. Other parameters such as the preexponential factor were estimated by comparing theoretical and experimental DSC curves.     

Kinetic analysis of reversible thermal decomposition of solids

The isoconversional method was used to elucidate the kinetics of reversible solid-state reactions occurring under nonisothermal linear heating. The characteristic dependencies of the effective activation energy (E) on the extent of conversion (W) were established for two model processes: a reversible first-order reaction and a reversible reaction followed by an irreversible one. For the first process, E is almost independent of W and varies between the activation energy of the direct and inverse reaction. For the second, process with an endothermic reversible step, the dependence of E on W is of decreasing shape. The effective activation energy is limited by the sum of the activation energy of the irreversible reaction and the enthalpy of the reversible reaction, at low conversions, and by the activation energy of the irreversible reaction at high conversions. Analyses of the kinetic data for the dehydration of crystalhydrates, as well as other processes proceeding through a reversible step, show the dependencies of E on W characteristic of a reversible reaction followed by an irreversible one. © 1995 John Wiley & Sons, Inc.     

Some applications of thermal analysis to fullerenes

Thermal analysis is a convenient means of characterizing the soot used as a source of the carbon clusters, the extracted mixture of fullerenes, and the individual clusters themselves. TG in an inert atmosphere will rapidly assay the volatile fractions, presumably the lower molecular weight clusters. TG in oxygen indicates — a slight weight gain for the soots and clusters prior to their combustion.DSC in oxygen is used to determine the heat of combustion for the separated C₆₀ and C₇₀ materials. The combustion occurs around 300°C for the clusters. There is a small exothermic peak before this which is attributed to the oxidation associated with the slight weight gain. The heats of combustion measured are –18.7 and –21.0 kJ·mol^–1 for the C₆₀ and C₇₀ respectively.MS-EGA indicates the loss of small amounts of water and argon at temperatures around 250°C in vacuum and of solvent at about 350°C prior to sublimation.

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Zusammenfassung Thermoanalyse ist ein praktisches Hilfsmittel zur Charakterisierung von Ruß als Quelle für Kohlenstoffcluster, extrahierte Gemische von Fullerenen und die individuellen Cluster an sich. TG in einer inerten Atmosphäre ergibt schnell die flüchtigen Fraktionen, wahrscheinlich die niedermolekularen Cluster. TG in Sauerstoff zeigt einen leichten Gewichtszuwachs für Ruß und Cluster vor ihrer Zersetzung.DSC in Sauerstoff wurde angewendet, um die Verbrennungswärme der getrennten C₆₀ und C₇₀ Materialien zu ermitteln. Die Verbrennung erfolgt für die Cluster bei etwa 300°C. Davor kann ein kleiner exothermer Peak beobachtet werden, welcher der Oxidation in Verbindung mit dem geringen Gewichtszuwachs zugeschrieben wird. Die gemessenen Verbrennungswärmen betragen –18.7 und –21.0 kJ·mol^–1 für C₆₀ bzw. C₇₀.MS-EGA zeigt den Verlust von geringen Mengen an Wasser und Argon bei Temperaturen von etwa 250°C in Vakuum und von Lösungsmittel bei etwa 350°C, bevor die Sublimation eintritt.

     

Kinetic parameters of different asphalt binders by thermal analysis

Each year, 100 millions tons of asphalt are manufactured worldwide and 88% of them are designated to act as binder in mineral aggregate producing asphalt mixtures in the paving industry. The present study investigates the kinetics parameters of thermal degradation through thermal analysis behavior of three different asphalt binders’ samples: an asphalt cement C and two asphalt binders modified by polymers: copolymer styrene–butadiene–styrene S and polyphosphoric acid L. By Thermokinetics software a model-free kinetic analysis could be made using two models: Friedman and Ozawa–Flynn–Wall. Kinetic parameters following both models, through Thermogravimetric curves, showed that for the first step, the binder L presented the highest activation energy followed by binder S. Between all simulations, the FnF1 model was the one which best correspond to the experimental data for all samples.     

Kinetic study of heavy crude oils by thermal analysis

The present work investigates the thermal behavior and kinetic of four types of petroleum samples: a medium crude oil—P1, one heavy oil—P2, and two extra heavy oils—P3 and P4 by TG, DTG, and DSC methods. Thus, this study may contribute to the characterization of petroleum with different °API values.     

Kinetic phenomena in non-crystalline materials studied by thermal analysis

The structural relaxation and viscosity behavior of Ge₃₈S₆₂ glass has been studied by thermomechanical analysis. The relaxation response to any thermal history is well described by the Tool-Naraynaswamy-Moynihan model. The apparent activation energy of structural relaxation is very close to the activation energy of viscous flow (Eη=478±12 kJ mol^-1). However, the activation energy of crystal growth obtained by optical microscopy is about one half of this value. Similar result has been obtained from isothermal DSC measurement (Ea=220±20 kJ mol^-1). The kinetic analysis of these data reveals interface controlled crystal growth with zero nucleation rate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetic analysis of the thermal oxidative degradation of upper peat

Differential thermogravimetric analysis was used to study the thermal oxidative degradation of peat samples from different districts of the Ivanovo Region. The study was performed in nonisothermic conditions. It was found that the thermal oxidative processes involve a few steps. Kinetic characteristics [activation energy (E_a), preexponential factor (ln A), and reaction order (n)] were estimated for each step. It was found that the limiting stage of the entire process is a chemical reaction. The resulting data can be used to develop prognostic models for peatbog combustion.     

Photothermal applications to the thermal analysis of solids

Major application of optically-induced thermal waves to the thermal and thermodynamic analysis of solids are reviewed. The spectrum of available techniques,from the conventional photoacoustic detection to novel photothermal laser probing and frequency multiplexing is discussed, and their utilization for the measurement of thermophysical thermal transport-related parameters of solids is presented. These include the thermal diffusivity, effusivity, conductivity and specific heat. The ability of photothermal methods to perform thermal analysis on large classes of solids, including conducting and insulating bulk materials, crystals, layered porous and coated structures, thin films and inhomogeneous thermal profiles is highlighted. Finally, special capabilities of photothermal analysis, such as the monitoring of surface thermodynamic phenomena and phase transition studies, including high-T _c superconductors, are described in order to give a complete overview of the rich potential of photothermal-based methodologies.     

Kinetic investigation on alcoholysis of triethylaluminium by differential thermal analysis

The alcoholysis of triethylaluminium can be investigated by DTA in the liquid phase. The reaction enthalpy of the alcoholysis with primary alcohols is from –150 to –170 kJ mole^–1 in tetrahydrofuran/toluene as solvent. The reaction rate in pure hydrocarbons is higher than in the presence of Lewis bases. The reaction mechanism is probably ofS _E2 type and the reactivity decreases in the sequence primary, secondary, tertiary alcohol. In the second step of substitution the diethylaluminium alkoxides are less reactive than triethylaluminium because of the stronger association of the alkoxides. For the turnover of two moles of alcohol with one mole of triehylaluminium two DTA peaks appear in accordance with consecutive reactions.

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Zusammenfassung Die Reaktion zwischen einer Lösung von Alumimumtriethyl und einer Reihe von aliphatischen oder aromatischen Alkoholen kann mittels DTA quantitativ verfolgt werden. Die negative Reaktionsenthalpie der Alkoholyse mit primären Alkoholen beträgt 150 bis 170 kJ mol^–1, sofern ein Lösungsmittelgemisch aus Tetrahydrofuran/Toluen eingesetzt wird. Die Reaktionsgeschwindigkeit in unpolaren Kohlenwasserstoffen ist grösser als in Gegenwart von Lewis-Basen. Wahrscheinlich ist der Reaktionsmechanismus vom TypS _E2, wobei die Reaktivität in der Folge primäre, sekundäre, tertiäre Alkohole fällt. Der zweite Schritt der Alkoholyse, ausgehend vom Diethylaluminiumalkoxid, ist wegen der starken Selbstassoziation weniger reaktiv. Bei Umsatz von 2 Mol Alkohol treten entsprechend der Folgereaktion zwei DTA-Peaks auf.

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. –150 –170 ^–1 - . , . , S _E2 , , . , , . -, .

     

Some applications of thermal methods of analysis to polymers

Some examples are given of the application of thermogravimetry, differential scanning calorimetry, thermomechanical analysis, torsional braid analysis, stress relaxometry and dynamic viscoelastometry to the study of cross-linked polymer systems. The information derived by the use of each technique is outlined and the advantages and disadvantages of the different methods are compared.

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Zusammenfassung Einige Beispiele der Anwendung der Thermogravimetrie, Differential Scanning Kalorimetrie, thermomechanischen Analyse, Torsionsfadenanalyse, Streßrelaxometrie und dynamischen Viscoelastometrie zur Untersuchung quervernetzter Polymersysteme werden gegeben. Die an Hand des Einsatzes der einzelnen Techniken erhaltenen Informationen werden beschrieben und die Vor- und Nachteile der verschiedenen Methoden miteinander verglichen.

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Résumé On donne quelques exemples de l'application de la thermogravimétrie, de l'analyse calorimétrique différentielle (DSC), de l'analyse thermomécanique, de l'analyse au fil de torsion, de la mesure de la relaxation des tensions, de la viscoélastométrie dynamiques, à l'étude des polymères à réseau tri-dimensionnel. On souligne les renseignements obtenus en utilisant chacune de ces techniques et on compare les avantages et les inconvénients de ces différentes méthodes.

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, , , - , - . , , .

     

Kinetic analysis of a thermal dechlorination and oxidation of gadolinium oxychloride

Kinetics of a thermal dechlorination and oxidation of gadolinium oxychloride (GdOCl) originating from a molten salt process was investigated under various oxygen partial pressures by using a non-isothermal thermogravimetric (TG) analysis. The results of isoconversional analysis of the TG data suggests that the dechlorination and oxidation of GdOCl follows a single step reaction and the observed activation energy was determined as 137.7±4.1 kJ mol⁻¹. The kinetic rate equation was derived for a conversion of the GdOCl with a linear-contacting boundary reaction model. The power dependency for oxygen and the pre-exponential factor was determined as 0.306 and 1.012 s⁻¹ Pa^−0.306, respectively.     

Kinetic analysis of the thermal degradation of an epoxy-based intumescent coating

The aim of this work is to analyse and to simulate the kinetics of pyrolysis of an intumescent formulation designed to protect steel in the case of hydrocarbon and jet fires. The coating is based on a thermoset epoxy-amine resin system into which two fire retardant agents, boric acid and ammonium polyphosphate derivative have been incorporated. Industrial tests (jet fire tests) are usually used to evaluate the degradation mode of an intumescent coating. But these tests are quite expensive, and as the heating rates are extremely high (between 500 and 800 °C/min), it is not possible to evaluate the thermal degradation behaviour of the intumescent coating directly by thermogravimetric analyses. That is why it is necessary to develop predictive models of kinetics of degradation of these intumescent coatings. In this work, the coating has been pyrolyzed at different heating rates and a predictive model of its kinetics of degradation has been developed.     

Some applications of thermal analysis to the coordination chemistry

The behaviour of complexes of the type MeD2I2 (Me=Co,D = acetylacetone or benzoylacetone,I = imidazole and derivatives in the course of the stepwise thermal degradation is different. In the case ofD = acetylacetone in the first step acetylacetone is split off. At D = benzoylacetone the decomposition starts with the partial elimination of the heterocyclic ligands.In-position unsubstituted nickelacyclic complexes from type (bipy)Ni(CH₂CH₂CH₂COO) decompose by a reductive elimination and separating of CO₂ forming a (bipy)Ni-intermediate. A single reductive decoupling is hindered by blocking up the-position.Opposite to the high thermal stability of the trimesityl aluminium the intermediates Almes₂Cl and AlmesCl₂ show with decreasing amounts of mesityl groups and increasing content of halogene, respectively, a significant decreasing thermal stability.The thermal degradation of nickelchelates of alkylsubstituted chinolin-8-ol starts with the dehydration followed by a different separation of the ligands as a function of the chain-length and the position of the substituents of the ligands.

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Zusammenfassung Das Zersetzung Verhalten der Komplexverbindungen vom Typ C0D2I2 (P = acetylaceton, Benzoylaceton;I = Imidazol oder Derivate) erfolgt stufenweise. Im Falle vonD = Acetylaceton erfolgt zuerst eine Eliminierung von Acetylaceton wärend beiD = Benzoylaceton zuerst ein Heteroligand eine Abspaltung erfährt.Bei einer unsubstituierten-Position von Nickelacyclen des Typs (bipy)Ni(CH₂CH₂CH₂COO) erfolgt eine thermisch induzierte-Hydrideliminierung unter Ringspaltung und Freisetzung von CO₂.Im Gegensatz zur hohen thermischen Stabilität des Trimesityl Aluminium erfahren die Zwischenverbindungen Almes₂Cl und AlmesCl₂ mit abnehmenden Mesityl- bzw. zunehmenden Chlorgehalt einen wessentlich früheren thermischen Zerfall. Bei zunehmenden Kovalenzgrad ist hier ein Einfluss der veränderten Polarisation anzunehmen.Der thermische Abbau der prinzipiell wasserhaltig kristallisierenden Nickelchelate von alkylsubstituierten Chinolin-8-ol beginnt jeweils mit der Dehydratisierung. In Abhängigkeit von der Kettenlänge und der Position der Substitution am Chinolin schliesst sich der thermische Abbau der Chelatliganden ein- bzw. mehrstufig an.

     

Kinetic analysis of thermal decomposition of praseodymium(III) nitrate hexahydrate

The kinetics of thermal decomposition of praseodymium(III) nitrate hexahydrate was studied by using isothermal and dynamic thermogravimetric techniques. Kinetic analysis of the isothermal data with respect to various solid-state reaction models showed that the reaction is best described by phase boundary-controlled and random nucleation models. Kinetic analysis of the dynamic TG curves was discussed and a critical comparison was made of two integral methods, that of Coats and Redfern and that of Ozawa. The results showed that the Ozawa method gives a better correlation, and the results are in good agreement with those obtained under isothermal thermogravimetric conditions.

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Zusammenfassung Mittels isothermer und dynamischer thermogravimetrischer Methoden wurde die Kinetik der thermischen Zersetzung des Hexahydrates von Praseodymnitrat untersucht. Eine kinetische Auswertung der isothermen Meßdaten unter Anwendung verschiedener Feststoffreaktionsmodelle ergab, daß die Reaktion am besten durch ein phasengrenzenkontrolliertes Randomkeimbildungsmodell beschrieben werden kann. Die kinetische Auswertung der dynamischen TG-Kurven wurde diskutiert und ein kritischer Vergleich zwischen zwei Integriermethoden, der von Coats und Redfern und der von Ozawa, angestellt. Die Betrachtungen ergaben, daß die Methode von Ozawa eine bessere Korrelation liefert und daß die Resultate gut mit denen der isothermen thermogravimetrischen Messungen übereinstimmen.

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Kinetic analysis of the process of thermal degradation of poly-N-vinylcarbazole and its derivatives

Thermal studies of poly-N-vinylcarbazole and its derivatives containing ?Cl, ?Br, ?I and ?CH₃ as functional groups were carried out by means of thermogravimetry. The kinetics of the processes of thermal degradation of these polymers was examined. Kinetic parameters, i.e. apparent activation energy, reaction order and pre-exponential factor, were evaluated by using an integral method.     

Kinetic analysis of thermogravimetric data. XI thermal decomposition of some metal dithionates

A thermal analytical study of Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba and Zn dithionates is reported. The decomposition of the dithionate ion is endothermic in the case of the Na, K, Rb, Cs and NH₄ salts, but exothermic with Li, Mg, Sr, Ba and Zn. Kinetic parameters have been derived from the TG curves by means of the Coats-Redfern method. The validity of a linear kinetic compensation law is reported for the loss of crystal water and separately for the decomposition of the dithionate ion.

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Zusammenfassung Es wird über eine thermoanalytische Untersuchung der Dithionate von Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba und Zn berichtet. Die Zersetzung des DithionatIons ist im Falle von Na, K, Rb, Cs und NH₄-Salzen endotherm, im Falle von Li, Mg, Sr, Ba und Zn hingegen exotherm. Die kinetischen Parameter wurden aus den TG-Kurven mittels der Coats-Redfern-Methode abgeleitet. Es wird über die Gültigkeit eines linearen kinetischen Kompensationsgesetzes für den Verlust von Kristallwasser berichtet und gesondert für die Zersetzung des Dithionat-Ions.

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Résumé On présente les résultats d'une étude par analyse thermique des dithionates de Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba et Zn. La décomposition est endothermique dans le cas des sels de Na, K, Rb, Cs et ammonium tandis qu'elle est exothermique dans le cas des sels de Li, Mg, Sr, Ba et Zn. Les paramètres cinétiques sont déduits des courbes TG par la méthode de Coats-Redfern. La validité d'une loi de compensation cinétique linéaire est étudiée pour la perte de l'eau d'hydratation ainsi que pour la décomposition de l'ion dithionate.

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Li, Na, K, Rb, Cs,. NH₄, Mg, Ca, Sr, Ba Zn. [ Na, K, Rb, Cs NH₄ , Li, Mg, Sr, Ba Zn . - . .