Dielectric differential thermal analysis

Dithionates (CaS₂O₆·4H₂O, SrS₂O₆·4H₂O, BaS₂O₆·2H₂O, MnS₂O₆·4H₂O, MgS₂O₆·6H₂O, CoS₂O₆·6H₂O, NiS₂O₆·6H₂O, ZnS₂O₆·6H₂O and CuS₂O₆·4H₂O) were subjected to thermodielectric analysis. The thermoanalytical curves show low temperature effects from 60 to 350°. These are related with the dehydration and decomposition of the dithionates, which could be fully correlated with the knowledge of the thermal behavior of these compouds obtained with other thermal methods.     

Dielectric differential thermal analysis

Thermodielectric analysis has been used to test some very well-characterized kaolins from Cuban deposits. The samples were analysed by thermal analysis, X-ray diffraction, infrared spectrometry, electron microscopy and chemical analysis.The dielectrical thermograms show that the most evident effect for the hydrated versions is the water peak. The second dielectric effect, at high temperatures, is related to the cationic conductions. A relation involving the K content of the sample was observed.

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Zusammenfassung Mittels thermodielektrischer Analyse wurden einige gut charakterisierte Kaoline aus kubanischen Lagerstätten untersucht. Die Proben wurden mittels Thermoanalyse (TA), Röntgendiffraktion (XRD), Infrarotspektroskopie (IR), Elektronenmikroskopie (EM) und Elementaranalyse untersucht. Die Dielektrothermogramme zeigen, daß bei den hydratierten Versionen der augenscheinlichste Effekt der Wasserpeak ist. Der zweite dielektrische Effekt bei höheren Temperaturen wird mit der Kationenleitung in Zusammenhang gebracht, wodurch es möglich wird, Informationen über den K-Gehalt der Proben zu erlangen.

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Dielectrical differential thermal analysis

Sodium faujasites with different Si/Al ratios were studied by means of thermodielectrical method.     

Dielectric differential thermal analysis

The present paper deals with the role of guest molecules in the moleculer sieves systems.     

Simultaneous photothermal and differential thermal analysis

Simultaneous photothermal analysis (PTA), and differential thermal analysis (DTA) curves of inorganic compounds and organic polymers are presented. While the two techniques reinforce each other and provide complementary information, light emanating from the sample and detected by a photomultiplier tube provides features in the PTA thermograms not present in the DTA thermograms.     

Square modulated differential thermal analysis

KMnF₃ and DKDP crystals have been studied around their phase transitions using a conduction calorimetry technique where a long periodical square thermal pulse (0.05 K in amplitude) is superposed to a heating or cooling ramp as low as 0.06 K h⁻¹. Specific heat data obtained in the dissipation and relaxation semiperiods of the square pulse become different inside the phase transition interval. The electromotive force developed by the heat fluxmeters at the end of the relaxation semiperiod (underlying signal) is compared with the DTA trace obtained in a second run with the same temperature ramp but without the modulated perturbation. The comparison between the DTA trace and specific heat data obtained in the first run allows us to determine the value of the latent heat and to obtain information about the kinetic of the phase transition.     

Topological aspects of differential thermal analysis

The most important calorimetric methods have been reviewed: the differential thermal analysis (DTA) as basic disposition and the scanning calorimetry (DSC) as well as the adiabatic rate calorimetry (ARC). The thermal circuits of these are expressed by bond diagrams as conceived by topological thermodynamics. It has been stated that the heat flux associated with the process of transformation is virtually (uncompensated) transferred in the DTA system, really transferred (compensated) in the DSC and ARC systems, between the two containers through a transfer medium assumed to be purely dissipative.

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Zusammenfassung Eine Übersicht über die wichtigsten kalorimetrischen Methoden, sowie die Differentialthermoanalyse (DTA) als Grundverfahren, die Abtastkalorimetrie (DSC) und die adiabatische Geschwindigkeitskalorimetrie (ARC) wird gegeben. Die thermischen Kreise derselben werden durch Bindungsdiagramme, wie sie an Hand der topologischen Thermodynamik erhalten werden, ausgedrückt. Es wurde festgestellt, dass die Wärmeströmung mit dem Umwandlungsprozess assoziiert scheinbar (unkompensiert) in das DTA-System, wahrhaftig (kompensiert) in die Systeme DSC und ARC übertragen wird, undzwar zwischen den zwei Behältern durch ein als rein zerstreuend angenommenes Transfermedium.

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Résumé Mise au point sur les méthodes calorimétriques les plus importantes: l'analyse thermique différentielle (ATD) comme technique de base, l'analyse calorimétrique différentielle à compensation de puissance (DSC) et la calorimétrie à vitesse adiabatique (ARC). Les circuits thermiques de ces techniques s'expriment par des diagrammes de liaisons comme ceux conçus par la thermodynamique topologique. On établit que le flux de chaleur associé au processus de la transformation est virtuellement transferré (sans compensation) en ATD et réellement transferré (avec compensation) en DSC et ARC, entre les deux conteneurs par un milieu de transfert supposé être purement dissipatif.

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Heterogeneous bulk nucleation and differential thermal analysis

The effect of the addition of Ag₂O on the mechanism of non-isothermal devitrification of Li₂O · 2 SiO₂ glass has been studied by differential thermal analysis. In both bulk and powdered samples, the presence of heterogeneous nuclei lowers the crystallization temperatures but not the value of the crystal growth activation energy.The influence of the catalyst on the crystallization mechanism is not affected by a pre vious heat treatment at the temperature of the maximum nucleation rate.

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Zusammenfassung Die Wirkung des Einflusses von Ag₂O auf den nicht-isothermen Entglasungsmechanismus von Li₂O · 2 SiO₂-Glas wurde durch Differentialthermoanalyse untersucht.Die Gegenwart heterogener Kerne setzt die Kristallisierungstemperaturen herab, jedoch nicht die Werte der Aktivierungsenergien des Kristallwachstums in grob- als auch in feinpulverisierten Proben.Die Wirkung des Katalysators auf den Kristallisationsmechanismus wird durch eine vorhergehende Wärmebehandlung bei der Temperatur der maximalen Keimbildungsgeschwindigkeit nicht beeinflusst.

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Résumé On a étudié, par analyse thermique différentielle, l'effet de l'addition d'Ag₂O sur le mécanisme de dévitrification non-isotherme du verre Li₂O · 2 SiO₂. La présence de noyaux hétérogènes abaisse les températures de cristallisation, mais pas la valeur de l'énergie d'activation de la croissance des cristaux, que les échantillons soient massifs ou pulvérisés.L'influence du catalyseur sur le mécanisme de la cristallisation n'est pas altérée par un traitement thermique préalable à la température de la vitesse maximale de nucléation.

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Quantitative thermal analysis,I Mathematical problems of quantitative differential thermal analysis

A highly simplified method for calculating heat of phase transitions from DTA data is presented. Two DTA curves are needed to calculate the heat of transition and the specific heat of the sample: one is for the original sample and one is for a sample prepared by mixing the original sample with some unreactive diluent the specific heat of which is known. The data of the DTA curves used in the calculations are the peak area, the rate of heating and the deviation of the DTA curve from the base line.

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Zusammenfassung Eine einfache Methode zur Errechnung der Werte der Phasenübergangswärme aus den DTA Daten wird besprochen. Die Kenntnis der spezifischen Wärme der betreffenden Substanz und zwei Thermogramme sind hierzu nötig, jenes der Originalprobe und jenes einer Mischung der zu prüfenden Substanz mit einem indifferenten Stoff von bekannter spezifischer Wärme. Die notwendigen DTA Daten sind die Spitzenflächen, die Erhitzungsgeschwindigkeit und die Abweichung der DTA Kurve von der Nullinie.

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Résumé On décrit une méthode simple pour caIculer les chaleurs des transitions de phase à l'aide des données d'analyse thermique différentielle. Il est nécessaire de connaître la chaleur spécifique et les thermogrammes de l'échantillon pur et en mélange avec une substance indifférente, de chaleur spécific connue. Pour les calculs, on se sert des données suivantes: surface des pics d'A. T. D., vitesse de chauffage et déviation de la courbe d'A. T. D. par rapport à la ligne de base.

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Camphor cryoscopy by differential thermal analysis

The determination of the freezing point depression of organic solutions with camphor as solvent was performed by means of DTA. Amounts of 50–100μg substance and 1–2 mg camphor were weighed on a platinum wire, the camphor being pressed to a pellet by a glass press. The temperature difference between the glass tubes with pure camphor and with solution was recorded versus temperature, while the samples were cooled in a previously heated aluminium block. The difference between the recorded deviations from a straight line was found to be a measure of the freezing point depression. Errors less than 5 % were computed for various samples.     

A new differential thermal analysis method

A new differential thermal analysis method has been developed which allows fast and accurate determinations of phase equilibria in condensed systems between 400 and 1100°. In this method the temperature is increased stepwise, heat effects being determined by analysis of the transient thermoelectric effects after each step. Between steps the temperature is kept constant until equilibrium is attained. The method has been tested in measurements of displacive solid-state transformations and melting points.

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Zusammenfassung Eine neue Methode der Differentialthermoanalyse wurde entwickelt, welche rasche und genaue Bestimmungen von Phasengleichgewichten in kondensierten Systemen zwischen 400° und 1100° ermöglicht. Bei dieser Methode wird die Temperatur stufenweise erhöht und die Wärmeeffekte durch Analyse der thermoelektischen Übergangseffekte nach jeder Stufe bestimmt. Zwischen den Stufen wird die Temperatur bis zum Erreichen des Gleichgewichts konstant gehalten. Die Methode wurde bei Messungen von Verschiebungsumsetzungen in festem Zustand und von Schmelzpunkten erprobt.

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Résumé Une nouvelle méthode d'analyse thermique différentielle a été mise au point. Elle permet de déterminer de façon rapide et exacte les équilibres de phases dans des systèmes condensés, entre 400 et 1100°. Selon cette méthode, on augmente graduellement la température en déterminant les effets thermiques par analyse des effets thermoélectriques intermédiaires après chaque palier. A chaque palier, on maintient la température constante jusqu'à ce que l'équilibre soit atteint. On a contrôlé la méthode par l'étude de changements de phases displacifs dans l'état solide et par mesure de points de fusion.

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Application of differential thermal analysis in mineralogy

In mineralogical research differential thermal analysis can be applied as either a single or a combined method for three purposes:

1. for the qualitative identification of minerals and the (semi-)quantitative determination of the components of rocks and soils,
2. for the characterization of crystal-physical and crystal-chemical properties, including the study of kinetics and the determination of thermodynamic data, phase and reaction equilibria,
3. for special petrogenetic investigations concerning the interrelation of mineralogical properties with the formation, decomposition or recrystallization of minerals.

The presented results were obtained under strongly standardized and reproducible conditions of analysis and by means of some methods recently developed by the author. They include the construction of key diagrams ofΔT versus peak temperatures to identify unknown minerals; the dependence of dehydration and decomposition peak temperatures on the partial pressure of gaseous reaction products (= PA curves); the determination of chemical and crystal-chemical parameters of minerals by using the dependence of dehydroxylation peak temperatures on solid solution (chlorites, smectites) or by using the interrelation between the peak temperatures of structural transformations and crystal-chemical substitutions (sulfides, carbonates, phosphates, silicates); the determination of the degree of disorder of minerals formed in sedimentary environments by using the dehydration or inversion peak temperature and peak shape dependence on the defect character of these crystal structures (clay minerals, quartz, cristobalite, hydroxides); the subdivision of mineral groups by using the interrelation of crystal chemistry and dehydration behaviour (zeolites, mixed-layer clay minerals); the characterization of ferromagnetic minerals by studying the Curie temperatures as a function of the chemical composition; the development of a DTA method to measure the degree of weathering of granitic rocks, etc. Data of 150 minerals are given.     

Periodic thermal instability during the differential thermal analysis of pyrite

The cause of oscillations in high resolution DTA curves was investigated using simultaneous TG supported by microscopic and XRD examination of quenched samples. The latter techniques showed the instability resulted from the sequential ignition of individual or small groups of particles. This behaviour was different to that observed in our earlier isothermal tests where the oscillations were caused by periodic cracking of the oxide film.

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Zusammenfassung Die Ursache von Oscillationen in hochaufgelösten DTA-Kurven wurde durch TG und gleichzeitige Ausführung von mikroskopischen und XRD-Untersuchungen von abgeschreckten Proben erforscht. Die zuletzt genannten Techniken lassen eine Instabilität erkennen, die auf eine regelmässig aufeinanderfolgende Verbrennung von individuellen oder kleinen Gruppen von Partikeln zurückzuführen ist. Dieses Verhalten unterscheidet sich von dem, das in unseren früheren isothermen Testversuchen beobachtet wurde, bei denen die Oscillationen durch periodisches Zerreissen des Oxidfilms verursacht wurden.

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Investigation of imidization by differential thermal analysis

The DTA method has been used to show that, in the imidization of polyamido acid in solution in dimethylformamide, there is not only dehydrocyclization but also interaction of the solvent with reactive groups of the polyamido acid.     

A high pressure differential thermal analysis apparatus

A high pressure differential thermal analysis apparatus is described which is capable of operation in the pressure range from 1-600 atm of nitrogen gas and at temperatures from 25 to 500°C. Use of the apparatus is illustrated by the deaquation reactions of CuCl₂·2H₂0 and CoSO₄·7H₂O at pressures from 1 to 69 atm.     

High-pressure differential thermal analysis (HP-DTA)

High-pressure differential thermal analysis results are used to describe dehydroxylation reactions for the clay materials of kaolinite, Na-rich montmorillonite, and K-, Ca-, and Mg-exchanged montmorillonite. Sealed capsules may be used to contain fluids and it is possible to evaluate the role of H₂O in these reactions. Furthermore, structural information is used with DTA data to develop atomistic models to understand these processes.     

High-pressure differential thermal analysis (HP-DTA)

High-pressure differential thermal analysis results are used to describe dehydration reactions for the clay-like materials of Na-rich montmorillonite, K-, Ca-, and Mg-exchanged montmorillonite, kerolite, and a high-pressure phase resembling talc/mica with excess water. Because sealed capsules may be used to contain fluids, it is possible to evaluate the role of H₂O in these reactions. A separate paper (Part II) addresses the use of HP-DTA to understand dehydroxylation reactions in these materials.