TG and TGT investigations of the decomposition of nitrocellulose under quasi-isothermal conditions

A derivatographic study was made of the influence of the slow heat transport between the sample and its surroundings upon the courses of exothermic transformations. It was found that if the sample was placed in a thin film layer on the multiplate sample holder and the quasi-isothermal heating technique was applied, then the rate of the decomposition could already be regulated at will, up to a certain limit. Under the conventional thermoanalytical conditions the same sample decomposed in an explosion-like way. The examinations were supplemented with thermo-gas-titrimetric (TGT) measurements.

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Zusammenfassung Die Autoren untersuchten mit dem Derivatographen die Wirkung der langsamen Wärmeübertragung zwischen Probe und Umgebung auf den Verlauf exothermer Umwandlungen. Es wurde festgestellt, daß bei Auftragung der Probe in einer dünnen Filmschicht auf den Mehrplatten-Probenbehälter und bei Anwendung einer quasi-isothermen Aufheiztechnik die Zersetzungsgeschwindigkeit bis zu einer gewissen Grenze bereits nach Belieben gesteuert werden kann. Dieselbe Probe wird unter den üblichen thermoanalytischen Bedingungen explosionsartig zersetzt. Die Autoren ergänzten ihre Prüfungen auch mit thermogas-titrimetrischen (TGT) Messungen.

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Résumé Les auteurs ont étudié à l'aide d'unDerivatograph l'influence du transfert de chaleur lent entre l'échantillon et son environnement, sur l'allure des transformations exothermiques. Les résultats montrent que si l'échantillon est placé sous forme de films minces sur le support multiplaques et s'il est chauffé en régime quasi-isotherme, la vitesse de la décomposition peut-être contrôlée, jusqu'à une certaine limite, à volonté. Si l'on applique les conditions habituelles de l'analyse thermique, le même échantillon se décompose de manière explosive. Les auteurs ont complété leurs études en effectuant également l'analyse titrimétrique des gaz émis.

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, . , - - , . . -- ().

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The authors wish to thank Prof. E. Pungor for valuable discussions.     

Simultaneous thermogravimetric and thermo-gastitrimetric investigations under quasi-isothermal and quasi-isobaric conditions

The derivatograph has been modified to provide a new technique with the help of which the weight change of a sample and the amount of the evolving gases can be determined as a function of the temperature of the sample under quasi-isothermal and quasi-isobaric conditions. The thermal decompositions of potassium and sodium hydrogencarbonate were investigated; it was established that under special conditions the otherwise one-step thermal decomposition of the two materials becomes a two-step process. The phenomenon involves a change only from the point of view of kinetics, for the decomposition itself does not split into two consecutive processes.     

TG and EGA investigations of the decomposition of some metal ammonium phosphate monohydrates by means of the Derivatograph under conventional and quasi-isothermal — Quasi-isobaric conditions

The thermal decomposition of MgNH₄PO₄·H₂O, MnNH₄PO₄ · H₂O, CoNH₄PO₄ · · H₂O and CdNH₄PO₄·H₂O were investigated under conventional and under quasiisothermal-quasi-isobaric conditions. The experiments were carried out with a Derivatograph suitable for performing simultaneous TG and EGA examinations. It was found that the thermal decompositions of the four compounds each consist of two partial processes: the departure of the water of crystallization, and the subsequent inseparable escape of the ammonia and constitution water. Depending on the experimental conditions, the two processes more or less overlap. The relatively best separation of the two processes can be attained by using quasi-isothermal and quasi-isobaric conditions.     

Thermal decomposition of the magnesium sulphate hydrates under quasi-isothermal and quasi-isobaric conditions

In the course of thermal decomposition of the magnesium sulphate hydrates MgSO₄.nH₂O (n=7; 6; 5; 4; 3; 2; 5/4; 1) the intermediate steps MgSO₄.3H₂O, MgSO₄.2H₂O, MgSO₄.H₂O and — MgSO₄ are observed under quasi-isothermal and quasi-isobaric conditions atp 0.1 MPa dependent on the water contents. The structure of the obtained monohydrate phase is identical with that of kieserite. Thermal decomposition of the magnesium sulphate hydrates is essentially influenced by the water vapour partial pressure.

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Zusammenfassung Beim thermischen Abbau der Magnesiumsulfathydrate MgSO₄.nH₂O (n=7; 6; 5; 4; 3; 2; 5/4; 1) unter quasiisothermen- und quasiisobaren Bedingungen werden bei p–0.1 MPa, in AbhÄngigkeit von den Wassergehalten, die Zwischenstufen MgSO₄.3H₂O; MgSO₄.2H₂O; MgSO₄.H₂O sowie-MgSO₄ beobachtet. Die erhaltene Monohydratphase ist strukturell mit Kieserit identisch. Der thermische Abbau der Magnesiumsulfathydrate wird wesentlich vom Wasserdampfpartialdruck beeinflu\t.

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We gratefully acknowledge the assistance of Dr. K. Köhnke in providing X-ray diffraction investigations and the scanning electron micrographs provided by Dr. Ulrich, Bergakademie Freiberg.     

Thermogravimetric investigation of the decomposition of aquo-acido complexes under quasi-isothermal and quasi-isobaric conditions

Authors investigated with the help of quasi-isothermal and quasi-isobaric thermogravimetry the dehydration process of the EDTA-chelates: Mg₂L·9H₂O, Mn₂L·9H₂O, MgMnL·9H₂O and MgCdL·9H₂O (where L^4–=EDTA anion). It was established that under the applied special conditions transitionally numerous intermediary products were formed whose existence could not be identified earlier with conventional thermoanalytical methods. Results of the investigations contain a great amount of information material regarding the mechanism, kinetics and equilibrium conditions of the processes.

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Zusammenfassung Der Dehydratationsvorgang der ÄDTA-Chelate Mg₂L·9H₂O, Mn₂L·9H₂O, MgMnL·9H₂O und MgCdL·9H₂O (L^–4=ÄDTA-Anion) wurde mit Hilfe der quasi isothermen — quasi isobaren thermogravimetrischen Methode untersucht. Es wurde gefunden, dass unter den angewandten speziellen Versuchsbedingungen vorübergehend Intermediäre entstehen, deren Existenz mit den konventionellen thermoanalytischen Methoden nicht nachgewiesen werden konnte. Die Versuchsergebnisse bilden ein bedeutendes Informationsmaterial in bezug auf Mechanismus, Kinetik und Gleichgewichtsverhältnisse der untersuchten Vorgänge.

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Résumé On a étudié par thermogravimétrie quasi-isotherme/quasi-isobare le processus de la déshydratation des chélates suivants de l'EDTA: Mg₂L·9H₂O, Mn₂L·9H₂O, MgMnL·9H₂O et MgCdL· 9H₂O (L^–4=l'anion EDTA). Les conditions spéciales utilisées ici établissent que de nombreux produits intermédiaires se forment transitoirement. Leur existence n'avait pu être identifiée auparavant par les méthodes thermoanalytiques conventionnelles. Les résultats de la présente étude constituent une source importante de renseignements sur le mécanisme, la cinétique et les conditions d'équilibre des processus étudiés.

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- - , - : Mg₂L · 9H₂O, Mn₂L·9H₂O, MgMnL·9H₂O MgCoL·9H₂O ( L^–4= ). , , . , .

     

Thermogravimetric investigation of the decomposition of aquo-acido complexes under quasi-isothermal and quasi-isobaric conditions

The dehydration of some isostructural EDTA chelates MgNiL · 6H₂O, MgCoL · 6H2O, MgCuL · 6H₂O and MnCuL · 6H₂O, was studied by thermogravimetry under quasi-isobaric and quasi-isothermal conditions. In the TG curves four decomposition periods can be distinguished. The inflexion points of the curves probably refer to the transitional formation of the intermediates M_IM_IIL · 5H₂O, M_IM_IIL · 2H₂O and M_IM_IIL · H₂O.

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Zusammenfassung Die Dehydratisierung einiger isostruktureller EDTA-Chelate, wie MgNiL · 6 H₂O, MgCoL · 6 H₂O, MgCuL · 6 H₂O und MnCuL · 6 H₂O wurde thermogravimetrisch unter quasi isobaren und quasi isothermen Bedingungen untersucht. In den TG-Kurven können vier Zersetzungsabschnitte unterschieden werden. Die Inflexionspunkte der Kurven beziehen sich wahrscheinlich auf die übergangsbildung intermediÄrer Produkte der Zusammensetzungen M_IM_IIL · 5 H₂O, M_IM_IIL · 2 H₂O und M_IM_IIL · H₂O.

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Résumé On a étudié par thermogravimétrie, en conditions quasi-isobares et quasi-isothermes, la déshydratation de plusieurs chélates de l'EDTA isostructuraux: MgNiL · 6H₂O MgCoL · 6H₂O, MgCuL · 6 H₂O et MnCuL · 6 H₂O. On peut distinguer quatre étapes de décomposition sur les courbes TG. Les points d'inflexion des courbes se rapportent probablement à la formation transitoire de produits intermédiaires de composition M_IM_IIL · 5 H₂O, M_IM_IIL · 2 H₂O et M_IM_IIL · H₂O.

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- - : MgNiL. 6H₂O, MgCoL.6H₂O, MgCuL.6H₂O MnCuL.6H₂O. . , , M_IM_IIL. 5H₂O, M_IM_IIL. 2H₂O M_IM_IIL. H₂O.

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The authors wish to thank Prof. E. Pungor for valuable discussions, and Mrs. M. Wagner for her technical assistance.     

Kinetics and mechanism of the decomposition of pyrite under conventional and quasi-isothermal — quasi-isobaric thermoanalytical conditions

The kinetics and mechanism of the thermal decomposition of pyrite were examined by the method of quasi-isothermal and quasi-isobaric thermogravimetry (Q-TG). It emerged that by means of this technique the overlapping partial processes of the complicated oxidation and decomposition reactions of pyrite can be separated and studied independently from one another. It was found that the partial reactions FeS₂=FeS +S and Fe₂O_3–x(SO₄)_x=Fe₂O₃+SO₃ are endothermic processes taking place quasiisothermally and leading to equilibrium, while the oxidation FeS+O₂=Fe₂O_3–x(SO₄)_x is an exothermic process which takes place in an oscillating manner in a rather broad temperature interval.

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Zusammenfassung Autoren untersuchten die Kinetik und den Mechanismus der thermischen Zersetzung von Pyrit durch quasi-isotherme und quasi-isobare Thermogravimetrie (Q-TG). Es stellte sich heraus, daß sich überlagernde Teilprozesse der komplizierten Oxydations- und Zersetzungsprozesse von Pyrit mit Hilfe dieser Technik absondern und unabhängig voneinander untersuchen lassen. Es wurde festgestellt, daß die Teilreaktionen FeS₂=FeS+S und Fe₂O_3–x(SO₄)_x=Fe₂O₃+SO₃ endotherme Prozesse sind, die quasi-isotherm verlaufen und zu einem Gleichgewicht führen, während die Oxydation FeS+O₂=Fe₂O_3–x(SO₄)_x ein exothermer Prozeß ist, der oszillierend in einem ziemlich breiten Temperaturintervall verläuft.

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(Q-) . . , FeS₂=FeS+S Fe₂O_3–x(S₂O₄)_x=Fe₂O₃+SO₃ , . FeS+O₂ =Fe₂O_3–x(SO₄)_x , .

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The authors thank Prof. E. Pungor for valuable discussions, and Mrs. M. Kiss and Miss I. Fabian for their technical assistance.     

TG and EGA investigations of the decomposition of magnesium ammonium phosphate hexahydrate by means of the Derivatograph under conventional and quasiisothermal — Quasi-isobaric conditions

An investigation was made of the thermal decomposition of MgNH₄PO₄ · 6H₂O under conventional and under quasi-isothermal—quasi-isobaric conditions. The experiments were carried out with a Derivatograph-suitable for simultaneous TG and EGA examinations. It was found that the thermal decomposition of MgNH₄PO₄·6H₂O consists of three, more or less overlapping partial processes. First 5 moles, then 1 mole of water of crystallization depart, and finally, strictly simultaneously and in an inseparable way, the departure of the ammonia and water of constitution takes place. The three processes can be separated best under quasi-isothermal and quasi-isobaric conditions.

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Zusammenfassung Die Autoren untersuchten die thermische Zersetzung von MgNH₄PO₄·6H₂O unter konventionellen und quasi isothermischen — quasi isobaren Bedingungen. Die Versuche wurden mit einem zur TG- und EGA-Analyse geeigneten Derivatograph-Typ durchgeführt. Die Autoren fanden, daß die thermische Zersetzung von MgNH₄PO₄·6H₂O aus drei mehr oder weniger überlappenden Teilvorgängen besteht. Zuerst werden 5, dann 1 Mol Kristallwasser entfernt, das Konstitutionswasser und Ammoniak werden streng simultan und von einander untrennbar entfernt. Die drei Vorgänge können am besten unter quasi isothermischen und quasi isobaren Bedingungen von einander getrennt werden.

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Résumé Les auteurs ont étudié la décomposition thermique de MgNH₄PO₄·6H₂O dans les conditions conventionelles ainsi que dans des conditions presque isothermes et presque isobares. On a effectué les expériences à l'aide d'un Derivatograph qui se prête aux études simultanées par TG et AGE. Dans les conditions conventionnelles, la décomposition thermique de MgNH₄PO₄·6H₂O s'effectue en trois processus élémentaires qui se recouvrent plus ou moins. Le départ de 5 puis d'une molécule d'eau de cristallisation est suivi de celui d'ammoniac et d'eau de constitution, celui-ci étant strictement simultané et indissociable. Ces trois processus peuvent être mieux séparés si l'on opère dans des conditions voisines du régime isotherme et isobare.

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MgNH₄PO₄·6₂ - - . , TG GA . , MgNH₄PO₄·6₂ . , , . - - .

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The authors wish to thank Prof. E. Pungor for valuable discussions and Mr. M. Arnold for his assistance in performing the experiments.     

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

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.     

Tautomeric structure of 1-Oxy-2-phenylbenzimidazole

The synthesis of 3-methyl-2-phenylbenzimidazole-1-oxide (VIII) has been accomplished. Consequently, it has been possible to establish the tautomeric structure of I as 1-hydroxy-2-phenylbenzimidazole (Ia). Contrary to recent observations on the parent 1-oxybenzimidazole (IV), I shows no tendency to exist as an N-oxide (Ib) in aqueous solution.     

Thermogravimetric studies of non-stoichiometric cerium oxides under isothermal and quasi-isothermal conditions

Quasi-isothermal thermogravimetry is a new technique in which the programmed heating of a furnace automatically ceases when the rate of a reaction taking place in a sample, which is indicated by the DTG-signal, exceeds a preset limit. In this way reactions can be studied under nearly isothermal conditions. In this paper the data obtained using this method during oxidation and reduction experiments on nonstoichiometric cerium oxides are compared with the data obtained by conventional isothermal thermogravimetry. The kinetics of the composition changes during isothermal reduction and oxidation of CeO_2?x are also analyzed. It appears that, with some reservations, the experimental data are best described by the rate equation for a diffusion-controlled reaction. Finally, both the isothermal and the quasi-isothermal data suggest that the CeO_2?x phase region in the phase diagram consists of several subphases, each with a characteristic activation energy for the diffusion-controlled reactions.     

Simultaneous thermoanalytical investigations on the rapid decomposition of pentamminecobalt(III) complexes

The thermal decomposition of [Co(NH3)₅CO₃]NO₃, [Co(NH₃)₅NO₂](NO₃)₂ and [Co(NH₃)₅H₂O](NO₃)₃ complexes was studied by simultaneous TG, DTG, DTA (Derivatograph-C), termogastitrimetry, continuous selective water detection, TG-MS, and XRD methods.Due to the nearly explosive reaction of these complexes the samples were heated in a labyrinth-type crucible after a 10-fold dilution with alumina.Through the quantitative determination of NH₃ and H₂O it was possible to reveal the subtleness of decomposition of these complexes.Based on the qualitative and quantitative results obtained by the different thermoanalytical techniques used the equations of decomposition are given for both stages of the reactions.

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Zusammenfassung Mittels simultaner TG, DTG, DTA (Derivatograph-C), weiterhin mittels Thermogastitrimetrie, kontinuierlicher selektiver Wasserdetektierung, TG-MS und XRD-Verfahren wurde die thermische Zersetzung der Komplexe [Co(NH₃)₅CO₃]NO₃, [Co(NH₃)₅NO₃](NO₃)₂ und [Co(NH₃)_sH₂O](NO₃)₃ untersucht.Wegen dem beinahe explosiven Verlaufes der Reaktion dieser Komplexe wurden die Proben in einem Labyrinth-Tiegel in zehnfacher Verdünnung mit Aluminiumoxid erhitzt.Mittels der quantitativen Bestimmung von NH₃ und H₂O war es möglich, die komplizierte Zersetzungsreaktion dieser Komplexe aufzuklären.Ausgehend von den mit Hilfe der verschiedenen thermoanalytischen Verfahren erhaltenen qualitativen und quantitativen Ergebnissen wurden die Zersetzungsgleichungen für beide Reaktionsschritte gegeben.

     

Radiation-induced decomposition of PETN and TATB under extreme conditions

We conducted a series of experiments investigating decomposition of secondary explosives PETN and TATB at varying static pressures and temperatures using synchrotron radiation. As seen in our earlier work, the decomposition rate of TATB at ambient temperature slows systematically with increasing pressure up to at least 26 GPa but varies little with pressure in PETN at ambient temperature up to 15.7 GPa, yielding important information pertaining to the activation complex volume in both cases. We also investigated the radiation-induced decomposition rate as a function of temperature at ambient pressure and 26 GPa for TATB up to 403 K, observing that the decomposition rate increases with increasing temperature as expected. The activation energy for the TATB reaction at ambient temperature was experimentally determined to be 16 +/- 3 kJ/mol.     

Application of programmed thermodesorption of the liquid under quasi-isothermal conditions to investigate physicochemical properties of liquid layers and solid surfaces

This paper presents the results of measurements of the programmed thermodesorption of polar and nonpolar liquids from the surface of different types of solids. The course of thermodesoption was found to depend on the properties of the solid and the wetting liquid. Thermodesorption occurred not exponentially but in steps, which reflects the noncontinuous changes in the properties of the surface layer with the distance from the solid surface. This effect intensified with the increase in polarity of the wetting liquid and the heterogeneity of the solid surface. The earlier investigations showed that application of the method of differential thermal analysis allowed determination of the distribution of the adsorption potential of the liquid on the solid surface.The author is indebted to Prof. M. Jaroniec for very fruitful discussions and to Prof. J. Choma for the activated carbon samples.     

Application of programmable liquid thermodesorption under quasi-isothermal conditions to study physicochemical properties of liquid films and solid surfaces

The paper presents possible applications of differential thermal analysis for study of the physicochemical properties of liquid/solid systems, mainly through programmable liquid thermodesorption from the sample under quasi-isothermal conditions. The results prove its applicability in the determination of solid physicochemical properties, and particularly in calculations of adsorption potential distribution, the activation energy of molecules adsorbed on the surface and the surface heterogeneity by means of computer techniques.The authors are indebted to Dr. Ryszard Dobrowolski for very fruitful discussions, and to Prof. Jerzy Choma for the activated carbon samples.     

TBAF-catalyzed synthesis of 5-substituted 1H-tetrazoles under solventless conditions

Tetrabutylammonium fluoride (TBAF) is an efficient catalyst in the [3 + 2] cycloaddition reaction of organic nitriles 1 with trimethylsilyl azide (TMSN(3)) in solventless conditions. The corresponding 5-substituted 1H-tetrazoles 2 were obtained under mild conditions and in 80-97% yields.     

Computational study of the oxidation and decomposition of dibenzofuran under atmospheric conditions

The atmospheric degradation of dibenzofuran (DF) initiated by OH addition has been studied by using density functional theory (B3LYP method). Site C1 in DF is predicted to be the favored site for OH addition, with a branching ratio of 0.61 to produce a DF-OH(1) adduct. The calculated reaction rate constant for OH addition to DF has been used to predict the atmospheric lifetime of DF to be 0.45 day. Three different modes of attack of O2 ((3)Sigma(g)) on DF-OH(1) have been examined. Abstraction of hydrogen gem to OH in DF-OH(1) by O2 ((3)Sigma(g)) (producing 1-dibenzofuranol I) and dioxygen addition in the three radical sites in cis and trans orientation (relative to the ispo-added OH) of the pi-delocalized electron system of DF-OH(1) are feasible under atmospheric conditions. The free energy of activation (at 298.15 K) for the formation of 1-dibenzofuranol is 15.1 kcal/mol with a free energy change of -36.3 kcal/mol, while the formation of DF-OH(1)-O2 adducts are endergonic by 9.2-21.8 kcal/mol with a 16.3-23.6 kcal/mol free energy of activation. On the basis of the calculated reaction rate constants, the formation of 1-dibenzofuranol is more important than the formation of DF-OH-O2 adducts. The results presented here are a first attempt to gain a better understanding of the atmospheric oxidation of dioxin-like compounds on a precise molecular basis.     

TG and DSC kinetics of thermal decomposition and crystallization processes

The simplen ^th order model equation combined with the Arrhenius approach of the temperature dependency of the reaction rate constant is widely used in thermal analysis. The new Mettler software package for thermal analysis, GraphWare TA72 allows to access a full model comprising the power law and the crystallization kinetics (AvramiErofe'ev). The kinetics of the following reactions are studied to illustrate some applications:

thermal decomposition of dissolved dibenzoylperoxide, (dynamic and isothermal DSC measurement)

crystallization of polyethylene terephthalate (PET) (isothermal DSC measurements).

The kinetic model applied and the accuracy of the kinetic data obtained are discussed by means of a comparison of a predicted behaviour with the kinetic data measured isothermally.     

Dependence of the thermal decomposition of CuSO4·5H2O on the experimental conditions

The mechanism of thermal decomposition of CuSO₄·5H₂O is greatly influenced by the experimental conditions. Under conventional conditions, in an open crucible, the first partial reaction takes place in one step involving solid and gaseous phases. If a sample holder which creates a self-generated atmosphere is used, the reaction is separated into two consecutive processes. First the sample melts in an incongruent way, and thereafter the saturated solution formed beside solid CuSO₂·3H₂O evaporates under boiling. These two processes can be completely distinguished in the DTA curve. The selectivity of the examinations can be further increased through application of the quasi-isothermal heating technique.The two modes of decomposition can be correlated with the special phenomenon that, if the decomposition occurred according to the former mechanism, then the intermediate CuSO₄·3H₂O had stoichiometric composition, while in the latter case the compound consequently contained about 2.5% more water than that calculated.

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Zusammenfassung Der Mechanismus der thermischen Zersetzung von CuSO₄·5H₂O wird durch experimentelle Bedingungen in grossem Masse beeinflusst. Unter herkömmlichen Bedingungen, in einem offenen Tiegel, spielt sich die erste Teilreaktion in einem Schritt ab und hat sowohl feste als auch gasförmige Produktephasen zur Folge. Wird ein Probenhalter benutzt, der eine selbstgenerierte Atmosphäre erzeugt, wird die Reaktion in zwei konsekutive Vorgänge unterteilt. Zuerst schmilzt die Probe inkongruent, die dabei entstandene gesättigte Lösung (neben festem CuSO₄·3H₂O) dampft dann beim Verkochen ein. Diese beiden Vorgänge können mittels der DTA-Kurve vollkommen voneinander unterschieden werden. Die Selektivität der Untersuchung kann durch Anwendung der quasi-isothermen Heiztechnik weiter verbessert werden.Die zwei Zersetzungsarten stimmen mit der Beobachtung überein, dass bei der Zersetzung nach dem ersteren Mechanismus das Zwischenprodukt CuSO₄·3H₂O eine stöchiometrische Zusammensetzung besitzt, während es im letzteren Fall stets ungefähr 2,5% Wasser mehr enthält, als berechnet.

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. , . , . , , , . . . , , . , 2,5% .

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The authors thank Prof. E. Pungor for valuable discussions, and Miss I. Czene and Miss J. Forizs for their technical assistance.