DTA of water-salt glasses

DTA investigations of glasses in the system Al₂(SO₄)₃-H₂O/55–65 mass% Al₂(SO₄)₃ revealed effects at the glass transformation (T _g), crystallization and melting temperature. During storage at ambient temperature,T _g increased, probably due to an annealing process; the increase was the least at the stability maximum for the glasses, at 61–63% Al₂(SO₄)₃.

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Zusammenfassung Gläser des Systems Al₂(SO₄)₃-H₂O mit 55–65 Masse-% Al₂(SO₄)₃ zeigen bei der DTA Effekte bei den Temperaturen von Glasumwandlung (T _g), Kristallisation und Schmelzen. Aufbewahren bei Raumtemperatur führt zum Ansteigen vonT _g, wahrscheinlich in Folge eines Temperprozesses; dieser Anstieg ist am geringsten bei der Zusammensetzung mit 61–63% Al₂(SO₄)₃, d. h. am Stabilitätsmaximum der Gläser.

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- 55–65 . % , _g, . _g, (61–63 .% ).

     

A DTA study of phenols

A comprehensive DTA study is reported of 17 halophenols and of the corresponding p-nitrobenzoylchloride 3,5-dinitrobenzoylchloride and p-phenylazobenzoylchloride derivatives, prepared “in-situ”by heating intimate mixtures of phenol and acid chloride in the DTA system. The thermal analysis data, in particular, the derivative formation temperatures, are interpreted in terms of the inductive, mesomeric and steric effects associated with the ring substituents of the phenol and acid chloride and the extent of inter- and intramolecular hydrogen-bonding existing in these systems. The DTA data collectively provide a reference base for the identification and characterization of halophenols via thermal analysis.     

A DTA study of phenols

A comprehensive DTA study is reported of ten polyhydroxy-phenols and eight naphthols and of the correspondingp-phenylazo benzoylchloride,p-nitrobenzoylchloride and 3,5-dinitrobenzoylchloride derivatives, prepared in situ by heating intimate mixtures of phenol and acid chloride in a conventional DTA system. The thermal analysis data and, in particular, the derivative formation temperatures, are interpreted in terms of the inductive, mesomeric and steric effects associated with the phenol and acid chloride and the extent of inter- and intramolecular hydrogen-bonding existing in these systems. The DTA data collectively, provide a comprehensive data base for the identification and characterisation of these phenols via DTA.

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Zusammenfassung Dies ist eine umfassende DTA-Untersuchung von zehn Polyhydroxyphenolen und acht Naphtholen sowie der entsprechendenp-Phenylazobenzoylchlorid-,p-Nitrobenzoylchlorid- und 3,5-Dinitrobenzoylchlorid-Derivate, die durch Erhitzen inniger Gemische des jeweiligen Phenoles und Säurechlorides in situ in einem herkömmlichen DTA-Gerät hergestellt wurden. Die bei der Thermoanalyse erhaltenen Angaben, insbesondere die Bildungstemperatur der Derivate wurde bezüglich des induktiven, mesomeren und sterischen Effektes bei Phenol und Säurechlorid sowie der Stärke der in diesem System existierenden inter- und intramolekularen Wasserstoffbrückenbindungen interpretiert. Die Gesamtheit der DTA-Daten bietet eine umfassende Datensammlung für Identifizierung und Charakterisierung dieser Phenole mittels DTA.

     

DTA/TG coupling

With the discovery of high temperature superconductivity an extraordinary field for investigations on new materials containing up to (more than) 8 or 9 components has been open. But, in addition to problems specifically related to superconductivity, we are faced with a prelimary difficulty: the preparation of well defined compounds which may have reproducible properties. This difficulty is smoothed out when the phase relations in the relevant systems are known. Differential Thermal Analysis (DTA) contributes to their establishment. However, in multicomponent systems, an isopletic line is expected to intercept various boundary surfaces and the analysis is obviously complicated, compared to low order systems. In addition, by the nature of high temperature superconductors the oxygen partial pressure used for their preparation is an important thermodynamic parameter which contributes to fix the oxygen content in the solid state. During heat treatments, the composition of the systems may change, due to oxygen or volatile oxides (Tl₂O₃, PbO₂ or HgO) release. A permanent composition control then requires thermogravimetric (TG) measurements associated to DTA.This paper attempts to demonstrate the efficiency of the assembly DTA/TG for the study of high temperature superconductors. Going beyond the frame of preparation and quality control, the system is also particularly useful for kinetic studies. Examples will be principally in the (Tl,Pb)-(Ba,Sr)-Ca-Cu-O systems.It is a pleasure to associate to this lecture my colleagues from research groups with which I collaborate from many years in the difficult field of elaboration and characterization of thalliumbased HTSC: T. K. Jondo, K. Lebbou. R. Abraham and M. T. Cohen-Adad in Lyon (Lab. PCM2), M. Couach and A. F. Khoder at the CEN in Grenoble (SPSMS), J. Muller and R. Flukiger at the DPMC in Geneva and of course C. Opagiste and Ph. Galez at the LSM in Annecy.     

The instrument constant in DTA. Theory of sensing units in DTA instruments

Volume-isothermal and surface-isothermal sensing units with a gas-phase thermal barrier are described. Use of the two-point method of DTA with the surface isothermal sensing unit permits experimental determination of the internal heat resistance of the sample holder (of the reaction zone), thereby allowing elucidation of the mechanism (topochemistry) of the reaction and the finding of more exact kinetic data via a novel method of split heat capacities.

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Zusammenfassung Volumen- und oberflÄchenisotherme Me\fühler mit thermischer Gasphasenbarriere werden beschrieben. Bei Verwendung von oberflÄchenisothermen Me\fühlern kann nach der DTA-Zweipunktsmethode der innere WÄrmewiderstand bestimmt werden, wodurch die AufklÄrung des Mechanismus (Topochemie) der Reaktion und die Ermittlung genauerer kinetischer Daten über eine neue SpaltwÄrmekapazitÄts-Methode ermöglicht wird.

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- . , 2- - ( ), ( ) .

     

The instrument constant in DTA. Theory of sensing units in DTA instruments

The theory of block-type sensing units is reviewed. The two-point method of DTA is described and appropriate computation formulae are derived. The failure of the existing blocktype sensing units to conform to the assumptions of the theory is demonstrated.     

DTA using single particles

A DTA sample holder for single particles was constructed using three thermocouples to hold the sample and reference material, respectively. The arrangement can be used to multiparticle samples too by setting a spherical-section sample holder on the three thermocouple junctions.The author is grateful to the National Science Foundation for its support of this work.     

A DTA study of phenols

A comprehensive DTA study is reported of eight methyl-phenols, 4-methoxy-phenol and four methyl-halo-phenols and of the correspondingp-nitrobenzoylchloride, 3,5-dinitrobenzoylchloride andp-phenylazobenzoylchloride derivatives, prepared in situ by heating intimate mixtures of phenol and acid chloride in a DTA system. The thermal analysis data, in particular, the derivative formation temperatures, are interpreted in terms of the inductive, mesomeric and steric effects associated with the ring substituents of the phenol and acid chloride and the extent of inter- and intramolecular hydrogen-bonding existing in these systems. The DTA data collectively, provide a comprehensive data base for the identification and characterisation of these phenols via DTA.

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Zusammenfassung An durch Erhitzen inniger Mischungen aus Phenol und Säurechloriden in einem DTA-System hergestellten acht Methylphenolen, an 4-Methoxyphenol, an vier Methylhalophenolen und an den entsprechendenp-Nitrobenzoylchlorid-, 3,5-Dinitrobenzoylchlorid- undp-Phenylazobenzoylchloridderivaten wurden ausführliche DTA-Untersuchungen durchgeführt. Thermoanalytische Ergebnisse, insbesondere die Bildungstemperatur der Derivate wurden als Ausdruck des induktiven, mesomeren und sterischen Effektes bezüglich der Substituenten am Phenolring und des Säurechlorides sowie des Ausmaßes der in diesem System existierenden inter- und intramolekularen Wasserstoffbrückenbindungen gewertet. Die Gesamtheit der DTA-Daten ist gleichzeitig eine ausführliche Datenreferenz zur Identifizierung und Charakterisierung dieser Phenole mittels DTA.

     

Correction in DTA purity determination

An equation for calculating the melted fraction (F) in purity determinations by DTA has been derived, which makes a correction for the thermal lag of the sample cell during the melting process. A set of samples of benzoic acid containing different quantities of anthracene has been tested. There are two peaks in the melting thermograms and the calculated impurity contents in these samples without using the correction are less than those prepared. This binary system is assumed to form an eutectic; its composition and melting point are estimated as X = 0.056 mole fraction of anthracene and T = 117.8°C respectively. Results obtained using naphthalene containing 0.415 mol% of fluorene show that the correction for the thermal lag of sample cell is necessary. In addition, a linear correction in the F calculation for the melting of eutectic and premelting of the main component is also desirable, giving a good straight line of the melting temperature T versus 1/F and a reasonable purity estimation.     

DTA study on lead chloride

The hydrolysis of lead chloride by residual water is responsible for the appearance of a second peak in the DTA curve, due to melting of the eutectic PbCl₂-PbO in repeated measurement runs on the same sample. This effect has previously been misinterpreted as a solid-solid transition in pure PbCl₂.     

DTA of Pt exchanged vermiculite mineral

DTA curves of Pt and Pd exchanged vermiculite mineral samples are presented. The minor structural changes brought by introduction of these cations in Mg and Ni vermiculites are explained. Results of chemical analysis and XRD are also discussed.

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Zusammenfassung DTA-Kurven von Pt- und Pd-versetzten Vermikulitmineralproben werden beschrieben. Es wird eine Erklärung für kleinere Strukturveränderungen gegeben, die durch den Einbau dieser Kationen in Mg- und Ni-Vermikulit auftraten. Ergebniße aus chemischer und röntgenografischer Analyse werden ebenfalls diskutiert.

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The authors are grateful to Dr H. Pezerat, Groupe cristallochimie CNRS, and Mmes D. Delafosse and Dr M. Kermarec, Laboratoire de cinétique des surfaces et des structures, Université de Pierre et Marie Curie, Paris, France for their valuable associations.     

Zur Glucosebestimmung mit ?DTA

Ohne Zusammenfassung     

Calculation of thermal effects in DTA

By considering that the temperature of the end of the thermal effect and the return of the thermal curve to the baseline do not coincide new calculation methods for the thermal effect become possible. Both the integral value of the thermal effect and its distribution over temperature may be calculated by processing only that part of the DTA curve which corresponds to the temperature interval of the transformation.It is demonstrated on the examples of non-variant transformation and transformation with an even distribution of the thermal effect over the temperature interval of the transformation that, under certain assumptions, the values of the thermal effect calculated by the suggested method and by the area of the peak are identical.

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Zusammenfassung Bei Berücksichtigung, daß die Temperatur des Endes des thermischen Effekts und die Rückkehr der thermischen Kurve zur Grundlinie nicht zusammenfallen, werden neue Methoden zur Berechnung des thermischen erschlossen. Sowohl der Integralwert des thermischen Effekts, als auch seine Verteilung in dem Temperaturbereich können durch Behandlung ausschließlich desjenigen Teils der DTA-Kurve berechnet werden, welcher dem Temperaturbereich der Umwandlung entspricht.Anhand von Beispielen der nicht-varianten Transformation und der Transformation mit gleichmäßiger Verteilung des thermischen Effekts im Temperaturbereich der Umwandlung wurde gezeigt, daß — unter gewissen Voraussetzungen — die Werte des durch die vorgeschlagene Methode und des aus der Peakfläche berechneten thermischen Effekts identisch sind.

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Résumé En considérant le fait que la température de la fin de l'effet thermique et le retour à la ligne de base de la courbe ATD ne coïncident pas, on a développé de nouvelles méthodes du calcul de l'effet thermique. La valeur intégrale de l'effet thermique ainsi que sa distribution dans l'intervalle de températures peuvent être calculées en ne considérant que la partie de la courbe ATD qui correspond à l'intervalle de température de la transformation.A l'aide d'exemples de transformations invariantes et de transformations à distribution uniforme de l'effet thermique dans l'intervalle de températures de la transformation, on a montré qu'avec certaines hypothèses, les valeurs de l'effet thermique calculées par la méthode proposée et à partir des surfaces des pics, sont identiques.

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. , -, . , , .

     

Kinetic data from DTA measurements

The theory of Borchardt and Daniels for the determination from the DTA curve of the fraction decomposed (α) is used. The probable mechanism, activation energy (E) and frequency factor (Z) can be found by the trial and error method from the plot ofα vs.T for a decomposition reaction which can be expressed by the equation $$\log g(\alpha ) = \log p(E/RT) + \frac{{ZE}}{{Rq}}$$ The use of tables of log g(α) for different mechanisms, and plots of the function logp(E/RT _α) vs. temperature for different activation energies is described. The influence is shown of the mechanism of the process, activation energy, frequency factor and heating rate (q) on the shape of the DTA curve. The kinetic data for the decomposition of several solids obtained by the described method are in good agreement with those obtained from literature sources.     

Polymorph transition kinetics by DTA

The polymorph transition kinetics of the changes vaterite to calcite and aragonite to calcite have been followed using a DTA technique. The method eliminates the grinding process present in other analytical techniques and so has certain advantages. For both transitions the kinetic equation describing the process is found to be: $$\frac{{\partial \alpha }}{{\partial t}} = \frac{4}{3}k[ - \ln (1 - \alpha )]^{3/4} (1 - \alpha ).$$ Values of activation energy were found to be 452±19 KJ mole^?1 and 208±8 KJ mole^?1 for aragonite and vaterite transitions respectively using a procedure which enabled the calculation of kinetic parameters from a rising temperature experiment.     

Physicochemical characterisation of degrading polycaprolactone scaffolds

A degradation study investigating the hydrolysis of different scaffolds of polycaprolactone suspended in phosphate buffer solution at 37 °C was performed over a three month period. Structures included electrospun fibres, held as 2D mats and 3D bundles, and solvent cast films. These structures and their surrounding solutions were physiochemically characterised using a range of techniques. Changes in scaffold physicochemical properties were observed over the course of the study, including significant loss in molecular mass, increases in thermal properties and crystallinity, and increases in tensile properties. The presence of degradation products, such as capronic acid containing compounds was also identified in the surrounding solution. 3D electrospun bundles - as a consequence of being the least crystalline scaffold and hence most susceptible to hydrolysis - demonstrated greatest reduction in molecular mass over the three months, followed by 2D electrospun mats, and the lowest mass loss was observed for solvent cast films.     

Degradation of polycaprolactone in supercritical fluids

The degradation of polycaprolactone (PCL) was studied in subcritical and supercritical toluene from 250 to 375 °C at 50 bar. The degradation was also investigated in various solvents like ethylbenzene, o-xylene and benzene at 325 °C and 50 bar. The effect of pressure on degradation was also evaluated at 325 °C at various pressures (35, 50 and 80 bar). The variation of molecular weight with time was analyzed using gel permeation chromatography and modeled using continuous distribution kinetics to evaluate the degradation rate coefficients. PCL degrades by random chain scission in subcritical conditions (250-300 °C) and by chain end scission (325-375 °C) in supercritical conditions in toluene. The degradation of PCL in other solvents at 325 °C was by chain end scission under both subcritical and supercritical conditions indicating that the mode of scission depends on the temperature and not on the supercriticality of the solvent. The thermogravimetric analysis of PCL was investigated at various heating rates (2-24 °C/min) and the activation energy was determined using Friedman, Ozawa and Kissinger methods. It was shown that PCL degrades by random scission at lower temperatures and by chain end scission at higher temperatures again indicating that the mode of scission is dependent on the temperature.