Retarded solid state reactions

Reconstructive phase transitions and formation or decomposition reactions in the solid state exhibit in DTA-measurements a more or less great hysteresis between the temperatures from heating and cooling curves; at worst the reaction can be suppressed completely. By e.m.f.vs. T-measurements in appropriate galvanic cells for solid electrolytes equilibrium temperatures in the case of such kinetic hindrance can be determined and additionally the existence of metastable states can be proved.

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Zusammenfassung Rekonstruktive Phasenumwandlungen sowie Bildungs- und Zersetzungsreaktionen im festen Zustand zeigen bei DTA-Messungen eine mehr oder minder große Hysteresis zwischen den aus Aufheiz- bzw. Abkühlkurven ermittelten Temperaturen; schlimmstenfalls kann die Festkörperreaktion völlig unterdrückt sein. Mißt man in geeigneten galvanischen Zellen für Festelektrolyte EMK-gegen-T-Kurven, so erhält man auch im Falle kinetischer Hemmungen Gleichgewichtstemperaturen und kann darüber hinaus das Vorliegen metastabiler Zustände nachweisen.

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We have to thank the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industry for supporting our work from the outset.     

Solvent free reactions in the solid state: solid state metathesis

Transition Metal Chemistry -     

Kinetics of solid state thermal decomposition reactions

The author wishes to thank Prof. C. G. R. Nair, Dr. V. R. Gowarikar, Mr. M. R. Kurup and Dr. K. V. C. Rao for their encouragements. Thanks are due to Prof. P. M. Madhusudanan and Dr. K. Krishnan for helpful discussions and to Director, VSSC for the kind permission to publish this work.     

Kinetic studies in solid state reactions by sample-controlled methods and advanced analysis procedures

A comparative study of both conventional rising temperature and sample-controlled methods, like constant rate thermal analysis (CRTA), is carried out after analyzing a set of solid state reactions using both methods. It is shown that CRTA avoids the influence of heat and mass transfer phenomena for a wide range of sample sizes leading to reliable kinetic parameters. On the other hand, conventional rising temperature methods yield α–T plots dependent on experimental conditions, even when using samples sizes smaller than 2 mg. Moreover, it is shown that the discrimination of overlapping processes is dramatically improved using sample-controlled methods instead of conventional heating procedures. An advanced method for performing the kinetic analysis of complex processes from a single CRTA experiment is proposed.     

Application of SCTA methods for kinetic analysis of solid state reactions and synthesis of materials

Journal of Thermal Analysis and Calorimetry -     

Thermal polymerization of acrylamide in the solid state

The role of imperfections in thermal polymerization of acrylamide in the solid state was studied. The polymer yield and the degree of polymerization are highly dependent on the particle size and on the pressure to which the monomer is subjected prior to polymerization reaction. There is an enhancement in the rate of polymerization in air unlike in the case of radiation-induced polymerization. Thermal polymerization of acrylamide in pelletized form results in the formation of water-soluble linear polymer and water-insoluble cross-linked product with the evolution of ammonia. The activation energy (E) values obtained in the present investigation reveal that basically there are two processes taking place, one with E = 34–36 kcal/mole, corresponding to the initiation process, and the other with E = 19 ± 3 kcal/more for the propagation process.     

固态有机反应新进展

总结了一些典型的固态有机反应。由于固态反应的特性，多数固态有机反应表现出较溶液中更高的反应效率和更好的选择性，在某些情况下，利用光活性主体与反应物形成包结物，可实现对映选择性的不对称固态合成。     

Retarded solid state reactions III [1]

Solid state reactions and reconstructive phase transitions exhibit more or less a large hysteresis between reaction temperatures taken from DTA-heating and -cooling curves. For ternary lanthanide chlorides the equilibrium temperatures could be obtained bye.m.f.-measurements in galvanic chlorine cells for solid electrolytes usingA ⁺-ion (A=alkaline metal) conducting diaphragms. By quenching, high-temperature phases can often be transformed to metastable room-temperature phases. In this case the equilibrium state must be established by annealing at sufficiently high temperature, or it must be tried to synthesize the compound in its stability range from suitable precursor systems.I want to thank the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie for supporting our research work for more than thirty years.     

Thermal reactions involving solids: a personal view of selected features of decompositions,thermal analysis and heterogeneous catalysis

Journal of Thermal Analysis and Calorimetry - Nylon 11/CaCu3Ti4O12 (CCTO) nanocomposites were prepared via solution casting method followed by vacuum drying and characterized using X-ray...     

Thermal reactions of selected solids including reactants that melt during chemical change

Selected kinetic and mechanistic studies of thermal reactions of initially solid substances are reviewed with emphasis on the evidence that some of these chemical changes proceed with the essential participation of melting. The reactions considered are classified on the extent and the role of such melting and the various types of behaviour observed are discussed with reference to solid state rate processes in crystals. It is stressed that melting is an important feature in theoretical considerations of crystal reactivity because chemical changes often proceed more rapidly in a melt than in the solid state. However, literature reports concerned with reactions of solids do not always explicitly mention the possibility of melting during discussions of reactions mechanisms. The present paper comments on methods capable of detecting liquefaction during reaction, a feature of behaviour that is not always easily identified experimentally. Also considered here is the recognition of reaction intermediates, which provide important evidence concerning the course of the chemical changes through which the reactant is transformed into product. This short review draws attention to the considerable value of chemical evidence in elucidating mechanisms of reactions of solids including the necessity for identifying intermediates and the role of any melt or liquid participating.     

Thermal Decomposition of hydrazinium monoperchlorate in the solid state

Hydrazinium monoperchlorate (HP-1) has been shown to decompose thermally in the solid state according to the chemical equation:

The activation energy for the evolution of HCl as determined mass spectrometrically is 8.05 kcal mol^?1 in the temperature range of 80 to 120°C. The rate of decomposition is seen to be altered by doping HP-1 with small concentrations of SO^2?₄, Ca²⁺ and Al³⁺.     

A unified theory for the kinetic analysis of solid state reactions under any thermal pathway

The Ozawa concept of generalized time has been used for developing master plots for the different kinetic models describing solid state reactions. These plots can be indistinctly used for analysing isothermal or non-isothermal experimental data. It is demonstrated that it is not possible to discriminate the kinetic model from a single non-isothermal curve without a previous knowledge of the activation energy. However, it has been shown that the ln [(da/dt)/f(a)] data taken from a set of DTG curves obtained at different heating rates lie on a single straight line when represented as a function of 1/T only if the kinetic model really obeyed by the reaction is considered. Moreover, the true values of E and A are obtained from the slope and the intercept of this straight line. This revised version was published online in July 2006 with corrections to the Cover Date.     

Linear free energy relations in solid state reactions II

Kinetics of the reaction between solid cobalt(II) acetate and solid substituted aniline hydrochlorides have been studied by thermal analysis. All the reactions go to completion. The crystalline products were characterized by physico-chemical methods. The energy of activation is 83.4,44.2,64.2,100.9,79.8,99.9, 135.9 and 168.7 kJ mol^–1for the reactions of aniline, 3- and 4-chloro-, 4-iodo-, 4-bromo-, 4-fluoro-, 4-methyl- and 4-methoxy aniline hydrochlorides with cobalt acetate. A plot of energy of activation against Hammett's constant is linear with a slope of –169.9 kJ mol^–1. A comparison between the reactivity of these reactions by the capillary and the thermal methods has been done.

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Zusammenfassung Mittels Thermoanalyse wurde die Kinetik der Festkörperreaktion zwischen Kobalt(II)azetat und substituierten Anilinhydrochloriden untersucht. Alle Reaktionen laufen vollständig ab. Die kristallinen Produkte wurden mittels physikalisch-chemischer Methoden charakterisiert. Die Aktivierungsenergie der Reaktion von Kobalt(II)azetat mit Anilin, 3- und 4-Chlor-, 4-Jod-,4-Brom-, 4-Fluor-, 4-Methoxy- und 4-Methylanilin beträgt 83.4,44.2,64.2,100.9,79.8,99.9,168.7 bzw. 135.9 kJ/mol. Bei der Darstellung der Aktivierungsenergie in Abhängigkeit von der Hammettkonstante konnte Linearität mit einem Anstieg von – 169.9 kJ/mol festgestellt werden. Die Reaktivität dieser Reaktionen wurde mittels Kapillar- und thermischen Verfahrens verglichen.

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. . - . , 3- 4--, 4--, 4--, 4--, 4- - 4- , , 83,4; 44,2; 64,2; 100,9; 79,8; 99,9; 135,9 168,7 ·^–1. - –169,9 ·^–1. , .

     

Isoconversional analysis of solid state transformations

There are many mathematical methods to determine the activation energy from non-isothermal experiments. However, controversies arise over the different values obtained by these methods. We will show that the origin of these discrepancies is either inaccurate approximations of the so-called temperature integral or the occurrence of complex transformations. We will review and compare the most commonly used methods. For those methods that lack accuracy, we will introduce simple numerical modifications to make them exact. In addition, we will introduce a new method that allows easy and accurate determination of the activation energy.     

Isoconversional analysis of solid state transformations

We will analyze the discrepancies between isoconversional methods when applied to complex transformations. The practical analysis of particular transformations leads us to conclude that (a) conventional integral methods based on integrated equations are essentially incorrect when dealing with variable activation energy; and (b) experimental inaccuracies and noise tend to give an apparent evolution of the energy variation, so that, non-constancy of the activation energy does not necessarily mean deviations from single-step transformations with constant activation energy.     

The determination of kinetic parameters for some solid state reactions

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 of 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.

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Zusammenfassung Die Kinetik vieler Reaktionen in fester Phase kann am besten an Hand einer Reaktions-Ordnung erklärt werden; dies besteht besonders bei dem Abbau von Polymeren. Die für die Bestimmung vonn undk aus isothermen Daten zur Verfügung stehenden Methoden sind entweder auf den verwendbaren Bereich von beschränkt oder sind Differenz-Differenz-Methoden, bei welchen es äußerst genauer Angaben bedarf. Die vorliegende Veröffentlichung gibt eine übersicht dieser Methoden und führt eine neue Annäherung ein, durch welchen undk unmittelbar erhalten werden können. Diese Methode ergibt einzigartige und zielgerechte Ergebnisse, indem diese sich den Versuchsdaten am besten anpassen.

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Résumé Pour de nombreuses réactions dans l'état solide l'ordre de réaction constitue un très bon moyen pour exprimer leur cinétique; c'est le cas, en particulier, de la dégradation des polymères. Les différentes méthodes dont on dispose pour déterminern et k à partir des données isothermes sont limitées à l'intervalle d'utilisation de ou opèrent par différences successives ce qui nécessite des données très précises. L'article présente une revue de ces méthodes et introduit une nouvelle approche oùn etk peuvent Être obtenus directement, en donnant des résultats uniques et objectifs qui assurent un meilleur accord avec les données expérimentales.

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; . , n ,k . , « — », . , n k. .

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The calculations presented in this paper were performed on an ICL 4130 computer using the program SOLITER. This program was written in ALGOL 60.     

High-temperature thermogravimetric analysis. Influence of gas pressure on kinetics of reactions in the solid state

A magnetic balance apparatus has been set up to follow reactions in the solid state under controlled conditions of pressure and temperature (25–1000°). Magnetic properties are characteristic of solid structures, and thermomagnetic analysis (T. M. A.) can give the variations of the sample susceptibility during the course of a reaction (susceptibilities of the new phases and of initial compounds not yet transformed). By continuous measurement of this susceptibility with the Faraday method, the conversion degree of the synthesis can be obtained.T. M. A. has been used to study the influence of a gas on a solid-solid reaction in which no gas can be evolved or consumed. An example is given for iron tungstate synthesis: Fe₂O₃(s)+WO₃(s) Fe₂WO₆(s). At 800° the reaction kinetics depends on the nature and the pressure of the gas.

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Zusammenfassung Festkörperreaktionen unter kontrollierten Druck- und Temperaturbedingungen (25–1000°) wurden mit einer magnetischen Waage verfolgt. Magnetische Eigenschaften sind charakteristisch für feste Strukturen, und die thermomagnetische Analyse (TMA) kann Veränderungen der Susceptibilität der Probe im Verlaufe der Reaktion (Susceptibilitäten neuer Phasen und noch nicht umgeformter Ausgangsverbindungen) aufzeigen. Durch kontinuierliche Messung dieser Susceptibilität nach der Faraday-Methode kann der Konversionsgrad der Synthese erhalten werden. TMA wurde zur Untersuchung des Einflusses eines Gases auf eine Fest-Fest-Reaktion, bei der kein Gas freiesetzt oder verbraucht werden lann, herangezogen. Als Beispiel wird die Synthese von Eisenwolframat angeführt: Fe₂O₃(s)+WO₃(s) Fe₂WO₆(s). Bei 800° hängt die Kinetik der Reaktion von der Natur und dem Druck des Gases ab.

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(25– 1000°). () , . , . - , . - : Fe₂O₃+WO₃ Fe₂WO₆. , 800°, .