Two thermoanalytical methods for the determination of GeO2 on germanium powders

Two thermoanalytical methods have been developed for determining GeO₂ on the surface of germanium. Possible errors and attainable accuracies are discussed. Both methods give the same results within the limits of error. The applicability of the determination is demonstrated in two ways:

1. in connection with the growth of the oxide layer in air,
2. in connection with the dissolution of the oxide layer in water.

The oxidation at room temperature proceeds at a practically constant velocity; the equilibrium thickness of the oxide layer on crystalline Ge powder in water proved to be about 5 Å.     

Utilization of the affine transformation of thermoanalytical curves for the determination of kinetic parameters

A method is suggested for the affine transformation of thermoanalytical curves, by means of which their comparison with one another becomes feasible. It is demonstrated that the results obtained by the traditional methods of non-isothermal kinetics depend on the heating rate, whereas the results attained by affine transformation are independent of the heating rate. They are consistent with the results obtained by Merzhanov's dmethod, which is also a non-aprioristic method.

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Zusammenfassung Eine Methode zur Affintransformierung thermoanalytischer Kurven wird vorgeschlagen, wodurch ihr Vergleich miteinandere rmöglicht wird. Es wird gezeigt, daß die durch traditionelle Methoden der nicht-isothermen Kinetik erhaltenen Ergebnisse von der Aufheizgeschwindigkeit abhängig sind, während die durch Affintransformierung erhaltenen von der Aufheizgeschwindigkeit unabhängig sind. Sie sind in Übereinstimmung mit den nach der Methode von Merzhanov erhaltenen Ergebnissen, die ebenfalls eine nicht-aprioristische Methode ist.

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Résumé On propose une méthode pour la transformation affine des courbes d'analyse thermique, qui permet leur comparaison. On montre que les résultats obtenus par les méthodes traditionnelles de cinétique non-isotherme dépendent de la vitesse du chauffage, tandis que les résultats obtenus par la transformation affine n'en dépendent pas. Ils sont en accord avec les résultats de la méthode de Merzhanov.

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The peak of the derivative thermoanalytical curve of diffusion

The conversion, the reduced rate of conversion dC/dΘ andΘ at the peak of derivative thermoanalytical curve of diffusion are estimated theoretically, solving the theoretical equation with an electronic digital computer. These values for chemical reactions including random degradation of polymers are also estimated and compared with those of diffusion. The conversion at the peak is utilized to elucidate preliminarily the mechanism of the process.     

Historical development of thermoanalytical methods

Thermal tests in antiquity and in the Middle Ages. Blowpipe tests. Measuring temperature and the development of thermometers. Latent heat. The nature of heat. Amount of heat. Differential thermal analysis. Differential scanning calorimetry. Heat treatment of precipitates. Thermobalances. Thermoanalytical methods associated with determination of evolved gas. Thermometry, enthalpimetry.     

The theory and practice of thermoanalytical kinetics of solid-state reactions

on kinetics have become a feature of ICTAC Congresses and are generally well-attended and result in lots of useful discussion. The Workshop at ICTAC 13 continued the tradition with about 50 attendees. The workshop was chaired by Haruhiko Tanaka and Michael Brown. Six introductory presentations were made on the subject, followed by the discussion summarized below. The six introductory speakers were: (1) Ranjit K. Verma; (2) Mike Reading; (3) Crisan Popescu; (4) Erwin Kaiserberger; (5) Mike Brown; (6) Haruhiko Tanaka.     

The problems of reaction kinetics calculations based on thermoanalytical curves

The work, results and estimations are summarized which are related to reaction kinetic calculations using thermoanalytical curves. Mathematical operations applied to the calculations are studied. Calculation methods are evaluated on the basis of our test results. The effect of test conditions on reaction kinetic parameters is analysed. Calculation of half-period is also investigated in the study.     

Organic-inorganic composite cation-exchanger: poly-o-toluidine Zr(IV) phosphate-based ion-selective membrane electrode for the potentiometric determination of mercury

A new heterogeneous precipitate of an organic-inorganic composite cation-exchanger poly-o-toluidine Zr(IV) phosphate was utilized for the preparation of a Hg(II) ion-sensitive membrane electrode for the determination of Hg(II) ions in real aqueous as well as in real samples. The electrode showed good potentiometric response characteristics, and displayed a linear log[Hg(2+)] versus EMF response over a wide concentration range of 1 x 10(-1) - 1 x 10(-6) M with a Nernstian slope of 30 mV per decade change in concentration with a detection limit of 1 x 10(-6). The membrane electrode showed a very fast response time of 5 s and could be operated well in the pH range 2 - 8. The selectivity coefficients were determined by the mixed-solution method, and revealed that the electrode was selective in the presence of interfering cations; however most of these did not show significant interference in the concentration range of 1 x 10(-1) - 1 x 10(-4) M. The lifetime of the membrane electrode was observed to be 120 days. The analytical utility of this electrode was established by employing it as an indicator electrode in the potentiometric titrations of Hg(2+) ions from a synthetic mixture as well as drain water.     

The nonadiabatic deactivation paths of pyrrole

Multireference configuration interaction (MRCI) calculations have been performed for pyrrole with the aim of providing an explanation for the experimentally observed photochemical deactivation processes. Potential energy curves and minima on the crossing seam were determined using the analytic MRCI gradient and nonadiabatic coupling features of the COLUMBUS program system. A new deactivation mechanism based on an out-of-plane ring deformation is presented. This mechanism directly couples the charge transfer 1pipi* and ground states. It may be responsible for more than 50% of the observed photofragments of pipi*-excited pyrrole. The ring deformation mechanism should act complementary to the previously proposed NH-stretching mechanism, thus offering a more complete interpretation of the pyrrole photodynamics.     

The application of thermoanalytical methods in the investigation of biological substances

The equilibria and thermodynamics of a number of naturally occuring isolated compounds (e.g. proteins, amino acids, carbohydrates) have recently been studied in several laboraties in different temperature ranges, and thermoanalytical methods have been used to study structural changes of biological materials, among them human tissues.In our investigations we succeeded in appling the derivatograph for the assay of glycosaminoglycans and for the characterization of the stability of crosslinked proteins in intact human and animal tissues. By means of this method age-related and pathological changes and repair reactions were studied in various connective and vascular tissues.Other temperature-dependent techniques (DSC, polarizing microscopy) were used successfully in another series of experiments. Alterations in the characteristic order-disorder transition temperatures of human serum lipoproteins could be demonstrated in pathological conditions; the altered physical structure of lipoproteins might give an additional explanation to the assumed mechanism of different metabolic disorders.

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Zusammenfassung Die Gleichgewichte und die Thermodynamik einer Reihe von natürlich vorkommenden isolierten Verbindungen (z. B. Proteine, Aminosäuren, Kohlenhydrate) wurden in verschiedenen Laboratorien in verschiedenen Temperaturbereichen untersucht. Hierbei wurden thermoanalytische Methoden zum Studium der Strukturänderungen von biologischem Material, u. a. von menschlichem Gewebe, eingesetzt.In unseren Untersuchungen gelang es den Derivatographen zur Prüfung von Glycosaminoglycanen und zur Charakterisierung der Stabilität quervernetzter Proteine in intakten menschlichen und tierischen Geweben einzusetzen. Durch diese Methode wurden altersbedingte und pathologische Änderungen sowie Reaktionen zur Wiederherstellung in verschiedenen Binde und Vasculärgeweben studiert.Andere temperaturabhängige Techniken (DSC, Polarisationsmikroskopie) wurden in anderen Versuchsserien mit Erfolg eingesetzt.

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Plenary lecture     

The application of thermoanalytical methods for the characterization of zeolite catalysts

Through the coupling of a DSC 111 (Setaram) with a gas dosing valve and a catharometer detector, equipment was developed for the investigation of adsorbents and catalysts. This equipment was applied for the determination of differential and integral heats of adsorption of C₂ to C₄ hydrocarbons on zeolites of the pentasile family. The proposed method has sufficient accuracy for the determination of adsorption heats for technical products. The advantages and the problems of the presented method are discussed.

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Zusammenfassung Durch Kombination eines DSC-Geräts (Setaram Typ 111) mit einem Gasdosierventil und einem Wärmeleitfähigkeitsdetektor wurde ein Gerät für die Untersuchung von Adsorbentien und Katalysatoren geschaffen. Dieses Gerät wurde zur Bestimmung difierentieller und integraler Adsorptionswärmen von C₂- bis C₄-Kohlenwasserstoffen an Zeolithen der Pentasil-Familie eingesetzt. Die vorgeschlagene Methode ist ausreichend genau, um Adsorptionswärmen technischer Produkte zu bestimmen. Vorzüge und Probleme der Methode werden diskutiert.

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A thermoanalytical assessment of an organoclay

High resolution thermogravimetric analysis (TG) has attracted much attention in the synthesis of organoclays and its applications. In this study, organoclays were synthesised through ion exchange of a single cationic surfactant for sodium ions, and characterised by methods including X-ray diffraction (XRD) and TG. The changes of surface properties in montmorillonite (MMT) and organoclays intercalated with surfactant were determined using XRD through the changes in the basal spacing. The TG was applied in this study to investigate more information of the configuration and structural changes in the organoclays with thermal decomposition. There are four different decompositions steps in differential thermogravimetric curves. The obtained TG steps are relevant to the arrangement of the surfactant molecules intercalated in MMT and the thermal analysis indicates the thermal stability of surfactant modified clays. This investigation provides new insights into the properties of organoclays and is important in the synthesis and processing of organoclays for environmental applications.     

The influence of an anionic additive on the properties of cation-exchanger based calcium-selective electrodes

Potentiometric and electrochemical impedance spectroscopic investigations of calcium-selective membranes containing poly(vinylchloride), dioctylphenylphosphonate, calcium (bis[4-(1,1,3,3-tetramethylbutyl)phenyl] phosphate) and different amounts of the lipophilic anionic additive tridodecylmethylammonium chloride were carried out. The addition of the lipophilic additive changes the properties of calcium-selective electrodes, e.g. slope and calcium selectivity. The selectivity for calcium in presence of H⁺, Na⁺, K⁺, NH₄ ⁺, Mg²⁺, Ba²⁺, Sr²⁺ and (C₂H₅)₄N⁺ was measured by three different methods, namely separate solution method, fixed interference method and matched potential method. Membranes with different concentration ratios between the calcium-exchanger and tridodecylmethylammonium chloride were investigated within half a year. The tendency of changing from cationic into anionic response for membranes containing nearly equivalent concentrations of cation- and anion-exchanger was shown. This inversion of the electrode response depends not only upon the concentration ratio of both ion-exchangers but also upon the total concentration of calcium-exchanger. Electrochemical impedance spectroscopy was used for monitoring the development of membrane resistances during a soaking period of one month. Based on these results dielectric constants for the calcium-selective membranes depending on the membrane composition were determined. Furthermore, the dependence of the membrane resistance on the membrane thickness and the concentration of tridodecylmethylammonium chloride was evaluated. Received: 21 July 1998 / Revised: 16 October 1998 / Accepted: 23 October 1998     

Characterization of snake skin by thermoanalytical techniques

Snake skin is a viable and readily available material as a model for human skin. Pharmaceutical applications use shed snake skin to study the effects of sunscreens on exposure to UV radiation (e.g. benzophenone on Boa integument). In order to understand the effects of radiation or drug transport through this model skin, one must determine its basic physical properties. This preliminary study evaluated two types of snake skin, namely Cuban Boa a 'dark' skin (Epicrates angulifer) and Green tree python a 'light' skin (Morelia viridis). Previous studies by other investigators have used pig, rabbit and snake skin as a human skin substitute. The structure of both snake skins was comparable based on IR spectroscopy and were functionally amino acids and moisture. Photomicrography by light and scanning electron microscopy revealed strong anatomic similarities. Morphologically there were two structures visible, namely a cellular and hinge-fibrous area. The thermal techniques indicated a phase transition at 35-75°C, which is associated with lipid melting. There was an 8 and 12% mass loss for the light skin and dark skin, respectively, which is interpreted, in part, as moisture loss at <100°C. The physical and analytical properties establish a base line that will be used in the future to differentiate various sunscreen types, such as benzophenone and octyl salicylate. Study was also done to determine the effect of an application of a commercially available sunscreen using SEM.This revised version was published online in November 2005 with corrections to the Cover Date.     

Studies of non-stoichiometric oxides by thermoanalytical methods

Non-stoichiometric oxides can be divided into metal-deficient and oxygen-deficient oxides, and a few examples of each type are given in order to show the materials of interest in this field. After a short review of the methods used in the study of these oxides, an account is given of the methods used in and the results obtained from a recent thermogravimetric investigation in atmospheres of controlled oxygen pressure on cerium oxides, plutonium oxides and mixed uranium plutonium oxides, which are all of special interest in research on fuels for nuclear power reactors.     

Concentration, separation and determination of scandium, zirconium, hafnium and thorium with a silica-based sulphonic acid cation-exchanger

A study has been made of the dependence of the sorption of scandium, zirconium, hafnium and thorium from aqueous solutions with a silica-based sulphonic cation-exchanger (SCE-SiO(2)) on the concentration and nature of the acid medium, time of contact, concentration of the element, and the ionic strength. The selectivity decreases in the order Zr approximately Hf > Th > Sc > Fe(III). The sorption characteristics of silica gel and SCE-SiO(2) have been compared, and the sorption mechanism is discussed. The SCE-SiO(2) exchanger has been used for 100-fold concentration of scandium, zirconium, hafnium and thorium from their 10(-8)-10(-7) M solutions, and a spectrophotometric method has been developed for their determination with a detection limit of 0.5 ng/ml for Zr and Sc and 0.1 ng/ml for Hf and Th. Zirconium and hafnium have been determined in the solvent phase by X-ray fluorescence and atomic-emission methods.     

The influence of an anionic additive on the properties of cation-exchanger based calcium-selective electrodes

Potentiometric and electrochemical impedance spectroscopic investigations of calcium-selective membranes containing poly(vinylchloride), dioctylphenylphosphonate, calcium (bis[4-(1,1,3,3-tetramethylbutyl)phenyl] phosphate) and different amounts of the lipophilic anionic additive tridodecylmethylammonium chloride were carried out. The addition of the lipophilic additive changes the properties of calcium-selective electrodes, e.g. slope and calcium selectivity. The selectivity for calcium in presence of H⁺, Na⁺, K⁺, NH₄ ⁺, Mg²⁺, Ba²⁺, Sr²⁺ and (C₂H₅)₄N⁺ was measured by three different methods, namely separate solution method, fixed interference method and matched potential method. Membranes with different concentration ratios between the calcium-exchanger and tridodecylmethylammonium chloride were investigated within half a year. The tendency of changing from cationic into anionic response for membranes containing nearly equivalent concentrations of cation- and anion-exchanger was shown. This inversion of the electrode response depends not only upon the concentration ratio of both ion-exchangers but also upon the total concentration of calcium-exchanger. Electrochemical impedance spectroscopy was used for monitoring the development of membrane resistances during a soaking period of one month. Based on these results dielectric constants for the calcium-selective membranes depending on the membrane composition were determined. Furthermore, the dependence of the membrane resistance on the membrane thickness and the concentration of tridodecylmethylammonium chloride was evaluated.     

A thermoanalytical study of treated wools

Previous studies of fibrous keratins have enabled assignments to be proposed for the endothermic processes identified in the relatively complex DTA curve. From this base, the influence of well defined chemical modifications to keratin on their observed DTA curves has been discussed. Wools are specifically treated commercially to improve shrink resistance and machine washability. To achieve these desired characteristics wools are treated, (a) by special oxidative processes, (b) with specific polymers, and (c) by combinations of (a) and (b). The DTA curves of wool samples which have been subjected to each of the three different treatments were reproducibly recorded. The significance of differences between these curves and that for the untreated fibre are discussed. Although characteristic differences in the DTA curves of wools after specific treatments can be distinguished, differential thermal analysis cannot be regarded as a general tool for such treatment characterisation. It is considered that thermogravimetry should offer a greater potential for this purpose.

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Zusammenfassung Vorangegangene Untersuchungen über faserige Keratine ermöglichten Zuordnungsvorschläge für die in der verhältnismässig komplexen DTA-Kurve befindlichen endothermen Vorgänge. Auf dieser Basis wurde der Einfluss gut definierter chemischer Veränderungen in Richtung Keratin auf ihre beobachteten DTA-Kurven erörtert. Die Wollen werden im Handelsmaßstab spezifisch behandelt um ihre Widerstandsfähigkeit gegenüber dem Eingehen zu erhöhen und ihre Waschbarkeit in der Maschine zu fördern. Um diese erwünschten Charakteristika zu erreichen werden die Wollen a) durch spezielle Oxidationsvorgänge, b) mittels spezifischer Polymere und c) mit kombinierten Verfahren von a) und b) behandelt. Die DTA-Kurven von jedem dieser drei verschiedenen Behandlungen unterworfenen Wollproben wurden reproduzierbar aufgezeichnet. Die Signifikanz der Unterschiede dieser Kurven gegenüber denen der unbehandelten Fasern wird erörtert. Obwohl sich charakteristische Unterschiede in den DTA-Kurven der spezifisch behandelten Wollen beobachten lassen, kann die Differentialthermoanalyse nicht als ein allgemein anwendbares Verfahren zur Charakterisierung solcher Behandlungen betrachtet werden. Es wird angenommen, dass die Thermogravimetrie für diesen Zweck grössere Möglichkeiten bietet.

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Résumé Des études antérieures sur les kératines fibreuses ont permis de proposer des interprétations sur les effects endothermiques identifiés sur la courbe ATD relativement complexe. Sur cette base, l'influence de modifications chimiques bien définies de la kératine sur les courbes ATD observées est discutée. Les laines, à l'échelle commerciale, sont traitées spécifiquement pour augmenter leur résistance au rétrécissement ainsi que pour améliorer leur faculté de lavage en machine. Afin d'atteindre ces caractéristiques, elles sont traitées soit par des procédés oxydants spéciaux, soit par des polymères spécifiques soit par les deux. Les courbes ATD d'échantillons de laines traitées par chacune de ces méthodes ont été enregistrées de façon reproductible. Les différences observées entre les courbes obtenues avec les fibres traitées et non traitées sont discutées. Malgré des différences caractéristiques, l'analyse thermique différentielle ne peut pas être considérée comme une méthode universelle pour caractériser de tels traitements. La thermogravimétrie pourrait être potentiellement plus adaptée.

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Paper presented at the 1^st ESTA, Salford U.K.

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We wish to thank Precision Processes (Textiles) Ltd., and the International Wool Secretariat for samples and information. Their co-operation is gratefully acknowledged. One of us (WMF) wishes to record her thanks to the I.W.S. for their support of a research studentship.