Examination of phase eouilibrium of the Ca(NO3)2-H2O system with quasi-isothermal-quasi-isobaric thermogravimetry and DTA

By means of the quasi-isothermal-quasi-isobaric thermogravimetry (Q-TG) technique ideal experimental conditions can be realized. This provides a possibility to compare the measured data with data from other phase equilibrium (solubility, tension) examinations.On the example of the Ca(NO₃)₂-H₂O system it is demonstrated that the phase diagrams can be used to interpret thermoanalytical (especially Q-TG) curves, or conversely, the results of thermoanalytical (Q-TG, DTA) examinations can serve for the control of equilibrium data of phase diagrams or to supply missing data.

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Zusammenfassung Mit Hilfe des quasi-isothermischen-quasi-isobaren thermogravimetrischen (Q-TG) Verfahrens können ideale Versuchsbedingungen realisiert werden. Das ermöglicht es, die gemessenen Daten mit von anderen Phasengleichgewicht-Untersuchungen (Lösbarkeit, Tension) stammenden Daten zu vergleichen.Durch das Beispiel des Ca(NO₃)₂-H₂O-Systems wurde es gezeigt, dass die Phasendiagramme zur Erklärung von thermoanalytischen (insbesondere Q-TG) Kurven können angewandt werden, oder umgekehrt, die Ergebnisse der thermoanalytischen (Q-TG, DTA) Untersuchungen als Kontrolle der Gleichgewichtsdaten der Phasendiagramme dienen können, oder die fehlenden Daten liefern können.

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- (Q-) . ( , ). Ca(NO₃)₂-H₂O , ( Q-) , .

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The authors are indebted to Prof. E. Pungor for valuable discussions, and thank Mrs. M. Kiss and Miss I. Fábián for their technical assistance.     

Investigations under quasi-isothermal and quasi-isobaric conditions by means of the Derivatograph

It is proved that under the conditions of dynamic thermoanalytical examinations the course of a decomposition reaction is determined primarily by the gas- and heattransfer partial processes, i.e. indirectly by the experimental conditions. This raises the question of whether it is justified to make kinetic calculations based on the shapes of similar curves. A new measuring technique is reported which uses a slightly modified Derivatograph. With this new method decomposition reactions can be examined under “quasi-isothermal” and “quasi-isobaric” conditions. The pernicious effects of the gas- and heat-transfer processes are thus eliminated, and the shapes of the curves obtained provide the possibility of studying the decomposition reactions in a new and more thorough way.     

Die Anwendung des Derivatographen zur Gleichzeitigen Dilatometrischen und Differential-Thermischen Analyse von Gläsern

Simultaneous DTA and dilatometric measurements were made and the derivatives of the dilatometric curves were taken for three glasses by means of a derivatograph. Glass blocks were used as test pieces with a boring for the thermoelement. A maximum was observed in the rate of length change, which can be explained by overheating phenomena. A comparison with DTA curves of glass powders published by Yamamoto showed that the break points in the DTA curves of glass blocks do not coincide with the Tg points, but under identical conditions they can serve for the rapid characterization of the transformation range.     

Derivative Dilatometrie

Zusammenfassung Die derivatographische Methode wurde weiterentwickelt. Mit Hilfe einer neuen Einrichtung kann man die Temperatur, die Gewichtsänderung und die Dilatation der Probe sowie auch die Geschwindigkeit der Enthalpie- und Gewichtsänderungen und die Geschwindigkeit der Dilatation messen. Die Vorteile der Einrichtung wurden an einigen praktischen Beispielen erläutert.

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Summary The derivatographic method was further developed. With the aid of a new apparatus it is possible to measure the temperature, the change in weight and the dilatation of the sample, as well as the velocity of the changes; in enthalpy and weight and the velocity of the dilatation. The advantages of the apparatus were demonstrated by means of several practical examples.

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Résumé On a élargi le domaine des méthodes dérivatographiques. A l'aide d'un nouveau dispositif, on peut mesurer la température, la variation de poids et la dilatation de l'échantillon, ainsi que la vitesse des changements d'enthalpie et de poids, et aussi la vitesse de la dilatation. On a montré les avantages de ce dispositif sur un certain nombre d'exemples pratiques.

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Bei der Ausführung der Versuche waren uns FrauM. Csonka und FrauE. Borsay behilflich, wofür wir ihnen auch an dieser Stelle danken.     

Determination of the pyrites content of bauxites by thermal methods

A derivatographic method has been developed for the identification and determination of the pyrites content of bauxites and clay minerals. If the sample contains at least 0.2% of pyrite, then at 400–450° a weight increase is indicated on the DTG curve, while a heat liberation is shown on the DTA curve. The amplitude of or the area under, these maxima is proportional to the pyrites content of the sample, although the correlation is not linear. In addition, the effect of experimental conditions on the thermal decomposition of pyrites has been studied.     

Influence of foreign materials upon the thermal decomposition of dolomite,calcite and magnesite part I. Influence of sodium chloride

The influence of sodium chloride on the course of thermal decomposition of calcite, magnesite and dolomite was studied partly under dynamic, and partly under quasi-isothermal heating conditions. Four different types of sample holders were applied in the experiment, i.e., the partial pressure of carbon dioxide was also different in the four cases. It was found that the presence of sodium chloride reduced the decomposition temperature in every case. The extent of this reduction amounted to about 10°C in the case of calcite, 40–80°C in the case of magnesite, and 10–40°C and 10–20°C for the first and second decomposition stages, respectively, of dolomite.     

Simultaneous thermogravimetric and thermo-gastitrimetric investigations under quasi-isothermal and quasi-isobaric conditions

The derivatograph has been modified to provide a new technique with the help of which the weight change of a sample and the amount of the evolving gases can be determined as a function of the temperature of the sample under quasi-isothermal and quasi-isobaric conditions. The thermal decompositions of potassium and sodium hydrogencarbonate were investigated; it was established that under special conditions the otherwise one-step thermal decomposition of the two materials becomes a two-step process. The phenomenon involves a change only from the point of view of kinetics, for the decomposition itself does not split into two consecutive processes.     

A simple device for continuous and selective detection of water vapour evolved during thermal decomposition reactions

A technique developed for the continuous and selective detection of water vapour formed during thermal decomposition reactions is described. The device can be connected to different types of thermoanalytical instruments without any difficulties. The detector can closely follow changes in the amount of water released during decomposition reactions, with negligible time delay. The signal curves obtained by the detector can be compared to the simultaneously recorded thermoanalytical curves and used to determine the step in which the water was released. The device as a free standing unit can be used to detect water plugs in different gas flows as well.     

Investigation on the thermal behaviour of Mg(NO3)2·6H2O

DTA, DSC and X-ray investigations of Mg(NO₃)₂ · 6H₂O revealed a lattice transformation at (71±2) C withH=12.5 J/g, and congruent melting at 90 C withH=150.3 J/g. The results of the DTA investigations on different Mg(NO₃)₂-H₂O samples are in good agreement with those of solubility investigations. The melting enthalpy of Mg(NO₃)₃ · 6H₂O is lowered considerably by deviation from the stoichiometric water content of the compound. The results allow conclusions as to the application of this salt hydrate as a latent heat-storage material.

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Zusammenfassung DTA-, DSC- und röntgenographische Untersuchungen von Mg(NO₃)₂ · 6H₂O zeigten die Existenz einer Gitterumwandlung bei (71±2) C mitH=12.5 J/g und ein kongruentes Schmelzen bei 90 C mitH=150.3 J/g. Die Ergebnisse der DTA-Untersuchungen an verschiedenen Mg(NO₃)₂-H₂O Proben stehen in guter übereinstimmung mit denen von Löslichkeitsuntersuchungen. Durch ein Abweichen vom stöchiometrischen Wassergehalt der Verbindung wird die Schmelzenthalpie von Mg(NO₃)₂ · 6H₂O beträchtlich vermindert. Die Ergebnisse ermöglichen Aussagen zur Anwendbarkeit dieses Salzhydrates als Wärmespeichermedium.

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, 71±2 H=12,5 · 90 H=150,3 ·^–1. Mg(NO₃)₂-H₂O . . .

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We thank Dr. Flammersheim, Department of Chemistry, FSU, Jena, for the DSC measueements.     

Influence of the aluminum alkyl co-catalyst type in Ziegler-Natta ethene polymerization on the formation of active sites, polymerization rate, and molecular weight

The influence of the concentration of the co-catalysts triethylaluminium (TEAL), tri-iso-butylaluminium (TIBAL), tri-n-octylaluminium on the polymerization rate for standard Ziegler-Natta catalyst systems was studied. By comparing the influence of monomeric TIBAL with TEAL co-catalyst on the polymerization activity, the effect of TEAL dimerization was described. The use of the Eley-Ridealadsorption model instead of Langmuir-Hinselwood model is proposed for the absorption of monomeric aluminiumalkyl species and for the formation of active centers C*. It is further proposed that steric hindrance from different co-catalysts, which results in a higher molecular weight (MW) of polymers, is caused by active centers with reduced space for chain transfer reactions.