Evaluation of kinetic parameters and mechanisms of complex reactions from thermal analysis data

A method is for TA data-processing: the method of exponential multipliers (MEM). The application of this method permits determination of the steps of the process, the type of the kinetic function, the type of the reaction and the kinetic parameters of the reaction steps. The method is simple and is easily carried out with the use of a mini-computer. The efficiency of the method is illustrated on the example of the thermal decomposition of ammonia copper chromate. The mechanism of the process and the kinetic constants were determined. They agree with available literature data.

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Zusammenfassung Ein Verfahren zur Verarbeitung von TA-Daten wurde entwickelt: das Verfahren exponentieller Multiplizierglieder (MEM). Die Anwendung dieses Verfahrens erlaubt die Bestimmung der Schritte eines Vorganges, des Typs der kinetischen Function, des Reaktionstypes und der kinetischen Parameter der Reaktionsschritte. Es handelt sich um eine einfache Methode, die auf einem Mini-Computer leicht verwirklicht werden kann. Die Wirksamkeit dieses Verfahrens wird am Beispiel der thermischen Zersetzung von Ammoniumkupferchromat gezeigt. Der Mechanismus und die kinetischen Konstanten des Prozesses wurden bestimmt, sie stimmen mit erreichbaren Literaturdaten überinen.

     

Statistical analysis of thermoanalytical experimental data

A statistical technique based on the Wilcockson criterion is suggested for estimation of the reproducibility of thermoanalytical experiments. Reduction of the whole physicochemical process to a quasi-one-stage process is described.This work was carried out partially with the aid of International Science Foundation (Programme Students and Post-Graduate Students).     

Recommendations for reporting thermal analysis data

Recommendations for reporting of thermal analysis data relating to differential thermal analysis, differential scanning calorimetry, thermogravimetry and thermomechanical analysis were developed some two decades ago. Since that time there have been significant changes in the techniques, as well as a greater understanding of the effect of experimental variables on the results obtained from thermonalytical experiments. This paper reports on a preliminary review of the Recommendations by the Task Group established by the ICTAC Committee on Standardization to undertake their revision. Particular attention has been paid to the properties of the sample; control of the instrument variables; and the data acquisition and manipulation by computers.     

The use of data center recorders in thermal analysis

The application of a Data Center recorder to the thermal analysis techniques of TG, DTA and dilatometry is described. The recorder used is essentially an eight-channel data acquisition system that multiplexes and converts up to ± 10 V analog data into 12-bit digital data which are stored on a floppy disk. The stored data be recalled at the convenience of the operator and mathematically manipulated before they are replotted on the integral X–Y or Y—time plotter.     

Evaluation of four ABS resins by thermal analysis

Four new commercial grades of rubber toughened ABS (acrylonitrile-butadienestyrene) terpolymers were characterized by differential scanning calorimetry (DSC), mechanical analysis and gel permeation chromatography (GPC). These rubber toughened ABS molding compounds were manufactured by a new blended technology to yield resins which offer a broad range of flow properties and levels of toughness. Based upon DSC estimates of the level of rubber included, the four ABS compounds can be divided into two groups; the first has about 11 wt.% butadiene and the second near 18 wt.%. In addition, two styrene-acrylonitrile copolymers with different average molecular weights were found blended within each ABS group. By this blending process four resins are produced with impact strengths ranging from below three to near seven ft-lb in^–1. These analytical results show that a resin's impact strength is enhanced not only by increasing the level of rubber particles in a given ABS compound but also by raising the molecular weight of the SAN which is blended into the terpolymer.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThe authors acknowledge useful discussions with L. L. Blyler, Jr., X. Quan and L. Shepherd and A. Hale for his scanning electron microscopy results. GPC results were carried out by Jordi Associates.     

Correlation of thermal analysis data and hydrolysis resistance of polycarbonates

The initial activation energy at zero conversionE _o of thermooxidative decomposition has been taken as a measure of thermal stability of polycarbonates (PC) andE _o has been correlated with the relative hydrolysis rater _h as a measure of their hydrolyse resistance. It is suggested that both decomposition processes are initiated by the same mechanism, the attack of hydrolytic agent onto ester C?O bonds. The following values ofE _o have been found: 187 (PC-M)>87 (PC-A)>43 (PC-C) kJ/mol, and they are correlated with values ofr _h being 0.01 (PC-M)<1 (PC-A)<4.4 (PC-C). It has been found, using a computer modeling technique, that bothE _o andr _h depend on the minimized energy of conformations.     

New data on the thermal analysis of diphasic mullite gel

A diphasic mullite gel has been synthesized by using Ludox and Al(NO₃)₃-9H₂O in ammoniacal solution. Both DTA and DDTA studies have been performed with a sensitive differential thermal analyzer system. Besides usual exotherm due to mullite formation, a pronounced exotherm between 800–1300°C has been noted. Considering previous XRD data, it is explained as due to formation of Si-Al spinel phase, which is subsequently transformed exothermally at 1320°C to mullite.     

Evaluation of a glycerol derived biofuel by thermal analysis

This work describes thermal analysis evaluation of a glycerol derived compound (fatty acid esters of (2,2-dimethyl-1,3-dioxolan-4-yl) methanol) developed to work as a biofuel. Mixtures of these ketal–glyceryl esters with fatty acid methyl esters typical of soybean biodiesel were prepared and evaluated in relation to biodiesel critical thermal properties such as temperature of crystallization, thermal stability and volatilization measured by differential scanning calorimetry and thermogravimetric analysis. The volatility of the products containing fatty acid methyl esters and (2,2-dimethyl-1,3-dioxolan-4-yl) methyl esters could be predicted by thermogravimetric analyses conducted in nitrogen that avoided time consuming distillation and greatly reduced material expenditure.     

Evaluation of calcium carbonate in eggshells using thermal analysis

The eggshell of the hen is an important structure which provides protection for the developing chick, and also a container for the egg in the food industry. Egg breakage can reach up to 10% of total egg production, causing considerable economic losses. The eggshell consists of membranes, composed mainly of proteins, and the mineral shell composed mainly of the calcite polymorph of CaCO₃. The average CaCO₃ content of a chicken eggshell is between 93 and 97%, depending on animal genotype, age, housing system of laying hens and mineral nutrition. In the present study, eggs of the same breed and approximately same age were collected from four different production systems: organic farming, free-range production, deep litter system and battery cage system. The CaCO₃ content was determined by the standard titration method and by atomic absorption spectroscopy. Thermal properties of dried eggshell powder were measured by thermogravimetric measurements between 30 and 900 °C in air, showing a significant mass loss of?≈?43% between 600 and 850 °C corresponding to the decomposition of CaCO₃ to CaO and CO₂. The relations between the thermal mass loss and CaCO₃ content determined by the titration method/atomic absorption spectroscopy were studied using predictive models fitted by the linear regression method. A good prediction ability with an average prediction error of 0.01% was obtained between CaCO₃ determined by titration and the thermal mass loss, indicating that TG could provide a reliable method for evaluation of CaCO₃ content in eggshells.

     

Prediction of thermal explosion parameters for energetic materials on the basis of thermal analysis data

Results obtained in calculations of thermal ignition delay periods in a wide temperature range are in good agreement with published data for octogene samples in the form of a sphere 12.7 mm in diameter and cylindrical NEPE propellant samples with diameters of 20 to 80 mm. The kinetic parameters of the thermal decomposition of materials, used in the calculations, were obtained by the DSC method with the use of hermetically sealed crucibles and crucibles with perforated covers under a nitrogen pressure of 10 MPa at heating rates of 0.1 to 1.0 deg min^–1.     

Kinetic model of poly(3-hydroxybutyrate) thermal degradation from experimental non-isothermal data

The non-isothermal data given by TG curves for poly(3-hydroxybutyrate) (PHB) were studied in order to obtain a consistent kinetic model that better represents the PHB thermal decomposition. Thus, data obtained from the dynamic TG curves were suitably managed in order to obtain the Arrhenius kinetic parameter E according to the isoconversional F-W-O method. Once the E parameters is found, a suitable logA and kinetic model (f(α)) could be calculated. Hence, the kinetic triplet (E±SD, logA±SD and f(α)) obtained for the thermal decomposition of PHB under non-isothermal conditions was E=152±4 kJ mol⁻¹, logA=14.1±0.2 s⁻¹ for the kinetic model, and the autocatalytic model function was: f(α)=α^m(1−α)ⁿ=α^0.42(1−α)^0.56.     

Ignition characteristics of forest species in relation to thermal analysis data

The ignitability of various forest species was measured with a specifically designed apparatus, under precisely controlled temperature and airflow conditions. The ignitability tests were based on ignition delay time versus temperature measurements using five different forest species: Pinus halepensis, Pistacia lentiscus, Cupressus sempervirens, Olea europaea, Cistus incanus. These species are common in the Mediterranean region and frequently devastated by forest fires. The ignition characteristics of the forest fuels examined were related to thermogravimetric analysis data. The DTG curves showed that the mass changes related to cellulose decomposition in the temperature range of 320–370 °C are greatly responsible for the ignition behavior of the species tested. In addition, the mass of volatiles evolving between 120–160 °C has a significant effect on the ignitability. On the contrary, the inorganic ash content of forest fuels, measured by atomic absorption spectroscopy, seems to play an insignificant role on the ignitability characteristics of the forest fuels examined.     

Critical analysis of viscosity data of thermal argon plasmas at atmospheric pressure

Reliable values of the viscosity in thermal argon plasmas are most important for our understanding of the momentum transfer and for realistic modeling of various plasma applications. Despite numerous attempts to determine reliable viscosity values over the last three decades, discrepancies still exist among the data reported by different authors. In this paper, a critical analysis is undertaken of calculated and experimental data of the argon viscosity based on recent publications. Our recalculation of viscosities in thermal argon plasmas are performed by using Lennard-Jones, Morse, Aziz, and exponential repulsive potentials for Ar-Ar atom interactions in different temperature ranges from 300 to 20,000 K. The contributions of elastic collisions of e-Ar, e-Ar⁺, and Ar⁺-Ar, as well as charge exchange of Ar⁺-Ar, to the viscosity become important with increasing temperature and degree of ionization in argon plasmas. Based on a critical analysis and recalculations, improved values of the argon viscosity are recommended, covering temperatures from 300 to 20,000 K. Polynomial expressions have been developed for calculating argon viscosities, which will be useful for numerical work and other applications of thermal argon plasmas at atmospheric pressure.     

The use of complementary data in the application of thermal analysis techniques

The use of thermal analytical procedures to obtain both thermodynamic and kinetic parameters is outlined. The advantage of DTA techniques in establishing thermodynamic data is demonstrated. Kinetic data calculated from TG data is demonstrated. Kinetic data calculated from TG data leads to plots of the logarithm of the specific reaction rate constant against 1/T (whereT is the temperature in degrees Kelvin) and from this point onwards the calculation is the same to establish the kinetic parameters no matter whether the data was obtained from TG or isothermal studies. Information on changes in the density and surface area of solid residues in the decomposition process leads to the conclusion that the number of particles present changes significantly during the decomposition and it is pointed out that this factor is largely ignored in setting up kinetic models for the decomposition of solid materials.

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Zusammenfassung Der Einsatz thermoanalytischer Verfahren zur Bestimmung sowohl thermodynamischer als auch kinetischer Parameter wird beschrieben. Der Vorteil der DTA-Techniken bei der Ermittlung thermodynamischer Daten wird gezeigt. Die aus TG-Daten berechneten kinetischen Daten führen zu graphischen Darstellungen der Funktion des Logarithmus des spezifischen Reaktionsgeschwindigkeitskonstante gegen 1/T (wobeiT die Temperatur in Kelvin bedeutet). Hiervon ausgehend ist die Berechnung der kinetischen Parameter dieselbe, ungeachtet dessen, ob die Daten aus TG-Messungen oder aus isothermen Untersuchungen erhalten worden waren. Die Information bezüglich der Änderungen der Dichte und Oberfläche fester Rückstände von Zersetzungsprozessen führt zu der Folgerung, daß die Zahl der anwesenden Teilchen sich während der Zersetzung wesentlich ändert. Es wird betont, daß dieser Faktor bei der Entwicklung zur Zersetzung von Festkörpern in vielen Fällen ausser Acht gelassen wird.

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Résumé On donne un aperçu sur l'utilisation des procédés thermoanalytiques en vue d'obtenir les paramètres thermodynamiques et cinétiques. On montre les avantages des techniques d'ATD pour établir les données thermodynamiques. Les données cinétiques calculées à partir des courbes TG conduisent au tracé du logarithme de la constante spécifique de vitesse de réaction en fonction de 1/T, T étant la température en degrés Kelvin. A partir de là, le calcul pour établir les paramètres cinétiques est le même, que les données aient été obtenues par TG dynamique ou isotherme. Les données relatives aux changements de densité et de surface spécifique des résidus solides au cours des réactions de décomposition permettent de conclure que le nombre de particules présentes change d'une façon importante pendant la décomposition. On insiste sur ce fait qui reste souvent négligé lors de l'établissement des modèles cinétiques de décomposition des matériaux solides.

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Evaluation of low-temperature properties of gas oils via differential thermal analysis

Gas oils with different wax contents were tested via a developed differential thermal analysis (DTA) procedure and also according to standard test methods. From the DTA curves, the following parameters were measured: onset peak temperature, maximum peak temperature and peak area. The variations of these DTA parameters with the standard properties for the gas oils, e.g. cloud, pour and cold filter plugging points and wax contents, were examined and were found to give linear relationships. Correlation coefficients between these results were calculated according to the established equations, which were also used for prediction of the standard properties for other gas oil samples from their DTA curves.The precision limits for the developed DTA procedure were found to be satisfactory.

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Zusammenfassung Dieselöle mit unterschiedlichem Wachsgehalt wurden nach einem neu entwickelten DTA-Verfahren und auch nach Standardmethoden getestet. Folgende Parameter Wurden aus den DTA-Kurven bestimmt: die Temperaturen zu Beginn und beim Maximum des Peakes und die Peakfläche. Zwischen Veränderungen dieser DTA-Parameter und den Standardeigenschaften der Dieselöle, wie z. B. Trübungs-, Fließ- und Kaltfilterverstopfungspunkt sowie Wachsgehalt, wurden lineare Zusammenhänge festgestellt. Korrelationskoeffizienten wurden nach den bekannten Gleichungen berechnet, die auch zur Vorhersage der Standardeigenschaften anderer Dieselöle aus DTA-Kurven herangezogen wurden. Die Genauigkeitsgrenzen der ausgearbeiteten DTA-Methode sind ausreichend.

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