Showing papers in "Journal of Thermal Analysis and Calorimetry in 1973"

Investigations under quasi-isothermal and quasi-isobaric conditions by means of the Derivatograph

Abstract: It is proved that under the conditions of dynamic thermoanalytical examinations the course of a decomposition reaction is determined primarily by the gas- and heattransfer partial processes, i.e. indirectly by the experimental conditions. This raises the question of whether it is justified to make kinetic calculations based on the shapes of similar curves. A new measuring technique is reported which uses a slightly modified Derivatograph. With this new method decomposition reactions can be examined under “quasi-isothermal” and “quasi-isobaric” conditions. The pernicious effects of the gas- and heat-transfer processes are thus eliminated, and the shapes of the curves obtained provide the possibility of studying the decomposition reactions in a new and more thorough way.

Kinetic analysis of thermogravimetric data, VI: Some problems of deriving kinetic parameters from TG curves

Abstract: Thermal decompositions of solids are very complicated processes, involving the decomposition of one chemical compound and the formation of others, the destruction of the initial crystal lattice, the formation of crystallization centres and their growth, the adsorption and desorption of gaseous products, the diffusion of the gases, heat transfer, and many other elementary processes. The overall process in influenced by many procedural variables, such as the heating rate, the heat conductivities of the furnace atmosphere, the sample and the sampler holder, the static or dynamic character of the atmosphere, the physical state of the sample, particle size, compactness, sample weight, etc. Such a complicated kinetic process cannot be described of course by means of a general equation. This is why in the theoretical treatment of thermal decomposition two main lines have been chosen. The first, used especially for deriving kinetic equations for isothermal conditions, starts from a theoretical model of the process, while the second uses the formal kinetics of homogeneous reactions. In deriving kinetic parameters from TG curves recorded under dynamic temperature conditions, all the methods are based upon !relations taken from the formal kinetics of homogeneous reactions.

Critical examination of several problems typically found in the kinetic study of thermal decomposition under vacuum

Abstract: After considering several problems peculiar to the kinetics of thermal decompol sition under vacuum (formalism, separation of successive steps, influence of residuapressure and of heat or mass transfers) the author suggests, as a possible answer, the use of constant decomposition rate thermal analysis, in association or not with thermogravimetry or calorimetry. The interest of the method is shown for the following measurements: apparent orders of reaction, energies of activation, differential enthalpies of dissociation. It appears to be specially suited to the study of thermal decomposition under high vacuum.

Characterization of petroleum products by DSC analysis

Abstract: Some petroleum products, as paraffin waxes, microcrystalline waxes, lube oils, fuel oils, bitumens, were studied using DSC. DSC makes it possible to determine the wax content of various petroleum fractions, to study the effects of additives, to determine the glass transitions of bitumens; it is a useful technique both for research and for product analysis.

Kinetic studies on the thermal decomposition of glucose and fructose

Abstract: The thermal decompositions of glucose and fructose were studied by means of the Derivatograph. From the melting temperature up to 300‡ these monosaccharides decompose and give brown caramel matter. The TG curves as functions of time were taken at various heating rates (0.5–10‡/min) by the Derivatograph and the activation energies of the decompositions were determined by Ozawa's method.

Rational approach to thermodynamic rrocesses and constitutive equations in isothermal and non-isothermal kinetics

Abstract: Isothermal and non-isothermal kinetics are classified according to the viewpoint of rational approach. The appropriate selection of basic quantities and constitutive equations is stressed. The extensive discussion recently focused to the meaning of the partial derivatives is reinvestigated and clarified considering the origin of following equation $$\alpha = f(T,t)$$ whereα is the extent of reaction,T andt are the temperature and time respectively, andf represents a function. The meaning of partial derivatives is demonstrated in details. The disagreement sometimes claimed between the data evaluated by means of isothermal and non-isothermal kinetics is also reviewed, but no fundamental differences are established.

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

Abstract: 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.

Some considerations regarding the kinetics of solid-state reactions

Abstract: The present state of non-isothermal kinetics for solid-state reactions is discussed on the basis of the literature. Experimental data are given on the effects of sample size, heating rate, particle size and atmosphere on the thermogravimetric (TG) curve, as well as the values of the kinetic parameters calculated from them. One solution of the formal kinetics is introduced.

Kinetic analysis of thermogravimetric data, V: Compensation effect in the thermal decomposition of bisdioximatocobalt(III) complexes

Abstract: The statistical analysis of activation energy and of logZ values derived from thermogravimetric data for 134 decomposition reactions of bisdioximatocobalt(III) complexes shows the validity of a linear compensation law, i.e. both the effects of heating rate and of the nature of the ligand manifest themselves in the kinetic compensation effect. The parametera of the compensation law is sensitive to ligand effects and its value is influenced both by the nature of the coordinated dione-dioxime and by the nature of the outer sphere anion X, which replaces an ammonia molecule in the thermal decomposition reaction.RésuméL'analyse statistique des valeurs des énergies d'activation et de celles de logZ obtenues à partir des résultats thermogravimétriques de 134 réactions de décomposition des complexes différent de bisdioximato-cobalt(III) montre la validité d'une loi de compensation linéaire du type (1); ceci signifie que l'effet de la vitesse de chauffage et celui de la nature du ligand sont responsables en première approximation de l'effet de compensation cinétique. Le paramètrea de la loi de compensation est sensible aux effets du ligand et la nature de la bis-dioxime coordonnée ainsi que la nature de l'anion X dans la sphère externe remplaÇant une molécule d'aminé durant la réaction de décomposition thermique influencent sa valeur.ZusammenfassungDie statistische Analyse der aus den thermogravimetrischen Resultaten erhaltenen Aktivierungsenergiewerte und log Z-Werte von 134 Zersetzungsreaktionen der verschiedenen bisdioxamato Kobalt(III) Komplexen zeigte die Gültigkeit eines Gesetzes der linearen Kompensation, d.h. der Effekt der Heizungsgeschwindigkeit und der Natur des Liganden verursachten in erster Näherung den kinetischen Kompensationseffekt. Parametera des Kompensationsgesetzes (1) repräsentiert den Ligandeffekt. Sein Wert wird durch die Natur des koordinierten Dion-dioxims und des Anions X in der äußeren Sphäre beeinflußt, das ein Aminmolekül während der thermischen Zersetzungsreaktion ersetzt.РЕжУМЕстАтИстИЧЕскИИ АНАл Иж ВЕлИЧИН ЁНЕРгИИ АктИВАцИИ И logZ, ВыВЕДЕН Ных Иж РЕРМОгРАВИМЕтРИЧЕс кИх ДАННых Дль 134 РЕАкц ИИ РАспАДА кОМплЕксОВ БИс-ДИОкс ИМАтОкОБАльтА(III), пОкАжыВАЕт спРАВЕДл ИВОсть жАкОНА лИНЕИН ОИ кОМпЕНсАцМИ. пАРАМЕт Рa жАкОНА кОМпЕНсАцИИ Ч УВстВИтЕлЕН к лИгАНД У И НА ЕгО жНАЧЕНИЕ ВлИьЕт пРИР ОДА кООРДИНИРОВАННО гО ДИОН-ДИОксИМА И ВНЕшН ЕсФЕРНОгО АНИОНА X, кОт ОРыИ жАМЕЩАЕт МОлЕкУлУ АММИАкА В хОДЕ РЕАкцИ И тЕРМИЧЕскОгО РАспА ДА.

Fundamental principles of kinetic data evaluation from thermal analysis curves

Abstract: A method for the evaluation of kinetic data of heterogeneous processes, including the most probable mechanism, from TG traces is described. Results are illustrated for the decarbonization of calcite and magnesite in vacuo, and the dehydration ofα-calcium sulphate hemihydrate. The advantages of the approach to the study of the kinetics, resulting in descriptions based on the known process mechanisms are demonstrated.

Some experimental aspects of DSC determination of kinetic parameters in thermal decompositions of solids

Abstract: Some particular methods of collecting and treating DSC data for the determination of kinetic parameters in thermal decompositions of solids are suggested. These are mainly concerned with an extrapolation method to avoid the effect of the sample mass; with an approximate method to obtain the activation energy and the exponent of the decay-law for runs at constant temperature in which the total area under the thermal curve is not known with accuracy; and with a method to ascertain whether a particular decomposition takes place by a single mechanism or by a sequence of different mechanisms.

Thermal reactions of inorganic hydroxy-compounds under applied electric fields, II

Abstract: The effect of electric fields on the thermal dehydration of amorphous hydrated iron(III) oxide under oxidizing, inert and reducing atmospheres was studied by X-ray diffractometry. In oxidizing and inert atmospheres, the transformation toα-Fe2O3 was enhanced by electric fields, especially at the negative electrode. The crystallite size of the product was also greatest at the negative electrode. Both results are explained in terms of the migration of protons to the negative electrode, where they subsequently form water which acts as a nucleating agent for the crystalline phase. In reducing atmospheres the formation of Fe3O4 and FeO at the expense of Fe2O3 is facilitated by electric fields, particularly at the negative electrode. Possible reaction mechanisms are considered, and the role of protons in stabilizing defect-spinel intermediates and products is discussed.

Thermal analysis of polymers

Abstract: Results of research on the quantitative thermal analysis of polymers by calorimetry are reviewed. Adiabatic and scanning calorimeters are briefly described and data obtained are discussed in terms of current theories. Heat capacities, glass transition phenomena and melting of macromolecules are treated.

Thermal decomposition of strontium hydroxide

Abstract: The thermal behaviour of strontium hydroxide octahydrate was studied by thermal analysis, an X-ray diffraction technique and optical microscopy. Up to 210° this compound transforms to the hexahydrate and then to the monohydrate. Anhydrous strontium hydroxide crystallizes in the tetragonal system and a polymorphous transformation may occur at 480°. From 530° on it decomposes in three stages. Amorphous strontium oxide is obtained at 700°.

The vapour pressures of several metal-2,2,6,6-tetramethyl-3,5-heptanedione complexes measured by a Knudsen effusion method

Abstract: The melting points, vapour pressures and heats of sublimation of the complexes of Ga, In, Y, La, Gd, Fe, Zn, Pb and Li with 2,2,6,6-tetramethyl-3,5-heptanedione are reported for the temperature range below the melting point of 40‡ to 250‡C and pressures from 10 to 10−2 torr. The measurements were made with an easily constructed Knudsen effusion cell in conjunction with a Mettler thermobalance.

Studies on the thermal decomposition of calcium carbonate in the presence of alkali salts (Na2Co3, K2CO3 and NaCl)

Abstract: Mixtures of CaCO3 and varying amounts of Na2CO3, K2CO3 and NaCl were subjected separately to thermal analysis. DTG, DTA, TG analyses indicate that the presence of alkali salts in CaCO3 influences its decomposition behaviour. A minimum DTA peak temperature of CaCO3 decomposition is noticed at low concentrations of alkali salts (K2CO3 and Na2CO3); an increase in concentration increases the DTA peak temperature. However, in the case of NaCl no appreciable lowering of the DTA peak temperature of CaCO3 decomposition is observed. Similarly, the minimum temperature at which decomposition completes is found to correspond to the concentration of 1 per cent salt (K2CO3 and Na2CO3) in CaCO3.

Quantitative determination of specific heat by differential scanning calorimetry

Abstract: The influence of some experimental parameters on the quantitative determination of specific heats by DSC is discussed. Conditions allowing measurement of the specific heat with a maximum relative error of 1.5 % are proposed. The specific heats of NaA zeolite,Cp=0.227±0.003 cal.°C−1.g−1, and AgA zeoliteCp=0.205±0.003 cal.°C−1.g−1 have been determined.

Heterogeneous reactions of solid nickel(II) complexes, V: Thermal decomposition of compounds of the type Ni(NCS)2L2. Part C: Kinetic study of pseudooctahedral complexes

Abstract: The kinetics of the thermal decomposition of solid complexes of the type Ni(NCS)2L2 (L=pyridine,β-picoline and quinoline), of pseudooctahedral configuration, were studied by using isothermal methods, on the basis of losses of weight, in the temperature range 90–191‡. The most suitable reaction order for all the complexes under investigation was found to ben=2/3, i.e. the total decomposition rate is determined by the chemical process proper. The calculated values ofEa(in kcal · mole−1) decrease in the following order: Ni(NCS)2py2 (29.4)>Ni(NCS)2(β-pic)2 (27.6)>Ni(NCS)2Q2 (24.3). With increasing volume of the ligand L the reaction rate also increases, and this suggests that the reaction proceeds by dissociative activation. For all the investigated complexes it was found that δH>EA; this may be explained by a several-step mechanism and the complex Ni(NCS)2L is then considered an intermediate.RésuméOn a étudié la cinétique de la décomposition thermique des complexes solides du type Ni(NCS)2L2 (L=pyridine,β-picoline et quinoléine) de configuration pseudo-octaédrique, d'après la perte de poids en régime isotherme entre 90 – 191‡C. L'ordre de la réaction obtenu pour les complexes examinés s'élève àn=2/3, c'est-à-dire que la vitesse de la décomposition totale est déterminée par la réaction chimique elle-mÊme. Les valeurs calculées pourEa (en kcal · mol−1) diminuent suivant l'ordre Ni(NCS)2py2 (29.4)>Ni(NCS)2 (β-pic)2 (27.6)>Ni(NCS)2Q2 (24.3). La vitesse de réaction croÎt lorsque le volume des ligands L augmente ce qui permet de suggérer un mécanisme réactionnel avec activation de la dissociation. On a trouvé δH>Ea pour tous les complexes examinés ce qui peut s'expliquer par un mécanisme avec plusieurs étapes, le complexe Ni(NCS)2L étant alors considéré comme produit intermédiaire.ZusammenfassungDie Kinetik der thermischen Zersetzung der festen Komplexe vom Typ Ni(NCS)2L2 (L=Pyridin,β-Picolin oder Chinolin) und pseudooktaedrischer Konfiguration wurde durch isotherme Methoden auf Grund der Gewichtsverluste zwischen 90–191‡ untersucht. Die geeignetste Reaktionsordnung wurde fürn=2/3 gefunden, d.h. die totale Zersetzungsgeschwindigkeit wird durch den eigentlichen chemischen Vorgang bestimmt. Die errechnetenEa Werte (in kcal · mol−1) nehmen in folgender Reihenfolge ab: Ni(NCS)2py2 (29.4)>Ni(NCS)2(β-pic)2 (27.6)>Ni(NCS)2Q2 (24.3). Mit zunehmendem Volumen der Liganden nimmt also die Reaktionsgeschwindigkeit zu, der Reaktionsverlauf richtet sich folglich nach der dissoziativen Aktivierung. Für alle untersuchten Komplexe ergab sich δH>Ea. Dies läßt sich durch einen Mehrstufenmechanismus erklären, wobei der Komplex Ni(NCS)2L als Intermediär gilt.РЕжУМЕИжУЧЕНА кИНЕтИкА тЕР МОРАспАДА тВЕРДых кОМплЕксОВ тИпА Ni(NCS)2L2 (L== п ИРИДИН,β-пИкОлИН И хИНОлИН) п сЕВДООктАЁДРИЧЕскО И кОНФИгУРАцИИ пРИ ИжО тЕРМИЧЕскИх УслОВИьх НА ОсНОВАНИ И пОтЕРИ ВЕсА В ОБлАст И тЕМпЕРАтУРы 90–191‡C. УстА НОВлЕНО, ЧтО НАИБОлЕЕ сООтВЕт стВУУЩИИ пОРьДОк РЕА кцИИ Дль ВсЕх ИжУЧЕННых кОМпл ЕксОВn=2/3, т. Е. ОБЩАь скОРОсть РАс пАДА ОпРЕДЕльЕтсь спЕцИФИЧЕскИМ хИМИЧ ЕскИМ пРОцЕссОМ. РАсс ЧИтАННыЕ ВЕлИЧИНыEa(ь ккАл · МОл−1) УМЕНьшАУтсь В слЕДУУЩЕМ пОРьДкЕ: Ni(NCS)2py2 (29.4) > Ni(NCS)2(β-pic)2 (27.6) > Ni(NCS)2Q2 (24.3). с УВЕлИЧИ ВАУЩИМсь ОБЩЕМОМ лИгАНДА L скОРОсть РЕА кцИИ тАкжЕ УВЕлИЧИВА Етсь. ЁтО пОжВОльЕт пРЕДпОлОж Ить, ЧтО хОД РЕАкцИИ сООтВЕтстВУ Ет ДИссОцИАтИВНОИ Ак тИВАцИИ. НАИДЕНО, ЧтО Дль ВсЕх И жУЧЕННых кОМплЕксОВδН>Ea. ЁтО ОБЩьсНьЕтсь МНОгОстУпЕНЧАтыМ МЕхАНИжМОМ, пРИ кОтОР ОМ кОМплЕкс Ni(NCS)2L пРОМЕжУтОЧНыИ пРОД Укт.

The determination of kinetic parameters for some solid state reactions

Abstract: The kinetics of many solid state reactions can best be explained in terms of an order of reaction; this is particularly true in the case of polymer degradation. The methods currently available for the determination ofn andk, from isothermal data, are either limited in the range ofα which can be used or are difference-difference techniques where the data must of necessity be highly accurate. This paper presents a review of these methods and introduces a new approach by whichn andk can be obtained directly, giving results which are unique and objective in that they provide a best fit to the experimental data.

Reaction of alkali and ammonium bifluorides with aluminium and silicon

Abstract: The reactions of alkali and ammonium bifluorides with aluminium and silicon were studied by DTA. Reaction temperatures were determined and reaction products identified. The reaction mechanism of the fluorinating reaction was established. Hydrofluorides appear very promising fluorinating agents.

Determination thermogravimetrique des energies d'activation I

Abstract: Apres une revue critique de divers procedes d'obtention thermogravimetrique des energies d'activation, on selectionne certains d'entre eux en vue de les appliquer d'une part a la deshydratation thermique de divers borates et acides boriques, d'autre part a l'oxydation du nickel a temperature elevee. On compare les resultats qu'ils fournissent respectivement.

The determination and use of the second derivative thermogravimetric function (DDTG) and the calculation of the kinetic constants of some decomposition reaction types

Abstract: As previously pointed out by the authors, the determination and use of the second derivative thermogravimetric curve (DDTG) permits the accurate calculation of kinetic parameters of simple reactions, using the methods of numerical analysis. Furthermore, the method outlined makes possible the kinetic analysis of some composite reactions which frequently occur in thermoanalytical practice. The cases of independent and competitive reactions are discussed. In the latter the proposed method of evaluation is suitable for the on-line work of a combined thermobalance—mass spectrometer system.

Kinetics of the thermal dehydration of variscite and specific surface area of the solid decomposition products

Abstract: The surface properties of active solids resulting from decomposition of AlPO4 · 2 H2O by thermal treatment in vacuum and in air are studied in connection with the parameter governing the kinetics of the dehydration process. The values obtained for the activation energies of decomposition under isothermal conditions agree acceptably well with those computed from TG curves by the Freeman and Carroll method. Kinetic results, which are analysed in terms of the Mampel theory, strongly suggest that the activation energy of the nucleation process determines the rate of surface formation, and justify the observed fact that the specific surface areas of samples treated in vacuum are higher than those of samples treated in air.

The possibility of a simple transformation of thermogravimetric curves

Abstract: A simple method is suggested for the Arrhenius-like representation of the thermal decomposition of a wide variety of materials. It consists in the transformation of the TG and the corresponding DTG curves, obtained as a single measurement by a derivative thermobalance. The method consists mainly in the division of the momentary DTG ordinates by the corresponding momentary TG values, the transformation of this value into logarithmic form, and the plotting of the logarithmic expression as a 1/T function. In many cases a straight line results testifying to a first-order reaction or a tolerable approximation of it.

Thermal Decomposition of azo-bis-isobutyronitrile in the solid phase

Abstract: The thermal decomposition of solid azo-bis-isobutyronitrile (AIBN) has been studied below its melting point by means of differential scanning calorimetry. The two-step nature of the decomposition is explained by different mechanisms of formation of active growth nuclei. The apparent activation energy of the formation of the active growth nuclei for the decomposition initiation is nearly three times higher than the activation energy of the decomposition of AIBN in solution. The initiation process of the decomposition depends on the history of the AIBN and on the nature of the mixture.

Thermal analysis of pyrotechnical mixtures, I: Studies on the mechanism of the reaction MnO2+FeSi90

Abstract: The author investigated a two-component pyrotechnical mixture used in the manufacture of delay detonators. Comparing the thermogravimetric, derivative thermogravimetric and differential thermal analysis curves of components with that of mixtures containing the components in different ratios, a relation has been found between the reaction rate and ratio. Initial temperature of reaction can be defined as well. Release of oxygen and oxidation takes place separately at certain temperatures and ratios. Mixture of highest rate of reaction generates the lowest heat of reaction.RésuméL'auteur a étudié un mélange pyrotechnique à 2 constituants utilisé dans la production des détonateurs à retardement. En comparant les courbes d'analyse thermogravimétrique, de thermogravimétrie dérivée et d'analyse thermique différentielle de chacun des constituants à celles de leurs mélanges en proportions différentes, on a trouvé une corrélation entre la vitesse de réaction et la composition. La température initiale de la réaction peut également Être étudiée. Le dégagement de l'oxygène et l'oxydation s'effectuent séparément à températures données dépendant du rapport des constituants. Les chaleurs de réaction les plus faibles correspondent aux mélanges possédant les vitesses de réaction les plus élevées.ZusammenfassungVerfasser untersuchte ein bei der Herstellung von Verzögerungszündern verwendetes pyrotechnisches Zweikomponentengemisch. Der Vergleich der thermogravimetrischen, derivativ-thermogravimetrischen und differentialthermoanalytischen Kurven der Komponenten mit jenen von Gemischen, welche die Komponenten in verschiedenen Verhältnissen enthielten, führte zu der Auffindung eines Zusammenhanges zwischen Reaktionsgeschwindigkeit und Verhältnis. Die Anfangstemperatur der Reaktion kann ebenfalls ermittelt werden. Sauerstoffabgabe und Oxydation erfolgen gesondert bei bestimmten Temperaturen und unter bestimmten Verhältnissen. Gemische von höchster Reaktionsgeschwindigkeit entwickeln die geringste Reaktionswärme.РЕжУМЕИсслЕДОВАНА пИРОтЕх НИЧЕскАь сМЕсь сОстО ьЩАь Иж 2 кОМпОНЕНтОВ, ИспОл ьжУЕМАь В пРОИжВОДстВЕ жАМЕД льУЩИх ДЕтОНАтОРОВ. ДЕРИВАтОгРАММы кОМп ОНЕНтОВ сРАВНЕНы с ДЕРИВАтОгРАММАМИ сМ ЕсЕИ, сОДЕРжАЩИх кОМп ОНЕНты В РАжлИЧНых пРОпОРцИь х И НАИДЕНО сООтНОшЕНИЕ МЕжДУ ск ОРОстьУ РЕАкцИИ И ДОл ЕИ кОМпОНЕНтОВ. ОтМЕЧЕН О ЧЕткОЕ ОпРЕДЕлЕНИЕ НАЧАльНОИ тЕМпЕРАтУ Ры РЕАкцИИ. пРИ РАжлИЧ Ных тЕМпЕРАтУРАх И сОДЕР жАНИИ кОМпОНЕНтОВ ИсслЕДОВАН ЁФФЕкт УД АлЕНИь. сМЕсь, ОБлАДАУ ЩАь НАИБОльшЕИ скОРОсть У, РЕАкцИИ, ДАЕт НАИМЕНьшУУ тЕпл ОтУ РЕАкцИИ.