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 .% ).

     

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- - ( ), ( ) .

     

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.

     

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.     

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.     

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.

     

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.     

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.     

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.     

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.     

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.     

Synthesis and characterization of anhydride-functional polycaprolactone

Polycaprolactone-graft-maleic anhydride (PCL-g-MA) copolymer was prepared by grafting maleic anhydride onto PCL in a batch mixer and in an extruder using dicumyl peroxide as the initiator. The graft content was determined with the volumetric method by converting the anhydride functions to acid groups and then titrating with ethanolic potassium hydroxide. The grafted polymer was extracted with xylene to remove any unreacted monomer before the estimation step. The effect of temperature and the various concentrations of the initiator and monomer used for the grafting reaction were investigated. The presence of residual initiator in the reaction product was checked using thin-layer chromatography. Molecular weight determination was carried out for the pure and grafted polymer using gel permeation chromatography to determine if chain scission was present. Results indicate that maleic anhydride is grafted onto PCL using free radical initiators. The grafting reaction was confirmed by FTIR and NMR techniques. FTIR spectra showed absorption bands around 1785 and 1858 cm⁻¹. NMR spectra gave signals for methine proton at 3.47 ppm. For a given peroxide level, a higher temperature or residence (reaction) time gave higher percentage of grafted MA. There was an optimum temperature and initiator concentration after which the percentage of MA grafted on PCL decreased. The number-average molecular weight, tensile strength, and the percent elongation of PCL-g-MA were comparable to those of PCL before grafting. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1139–1148, 1997     

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.     

Zur Glucosebestimmung mit ?DTA

Ohne Zusammenfassung     

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.