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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 17 (1973), S. 1795-1803 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The rates of sorption of water vapor and of methanol vapor in cellulose film were examined by stepwise increments of vapor pressure. In addition, the rates of sorption of the series of vapors water, methanol, ethanol, n-propanol, and n-butanol were studied at pressures just below the respective saturated vapor pressures. The results obtained from both parts of the study are explained in terms of a bimodal diffusion mechanism. This consists of the simultaneous diffusion of vapor into the microporous structure of the cellulose film and diffusion from the micropores into the polymer matrix.
    Additional Material: 6 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The thermal degradation of four different forms of cellulose in nitrogen has been studied by using a thermobalance. In TG experiments a total weight loss at 900°C was 80% in the cases of film and pulp samples and 83% for two powder forms. The results for the isothermal degradation of the four samples at 270°C are plotted as degree of degradation α against reduced time t/t0.5 and compared with the master plots of Sharp, Brindley, and Achar. The experimental data fit most closely the plot for the Avrami-Erofeev equation in the form kt = {-ln (1-α)}1/n where n = 2. An activation energy of 144 kJ/mole has been found for the degradation of one of the celluloses from the results of isothermal runs at six different temperatures. It is postulated here that the thermal degradation occurs by random nucleation and nucleus growth in the cellulose fibrils so as to yield a carbon whose microporous structure is a replica of the pore system in the parent cellulose.
    Additional Material: 4 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Résumé La cinétique de la transition polymorphe de la vatérite en calcite et celle de l'aragonite en calcite ont été suivies par ATD. Cette méthode élimine l'opération de broyage nécessaire avec les autres techniques analytiques, ce qui présente un avantage certain. Les deux transitions peuvent être décrites par l'équation cinétique suivante: $$\frac{{\partial \alpha }}{{\partial t}} = \frac{4}{3}k[ - \ln (1 - \alpha )]^{3/4} (1 - \alpha ).$$ Les valeurs de l'énergie d'activation ont été trouvées égales à 452±19 kJ mol−1et 208±8 kJ mol−1 pour les transitions respectives de l'aragonite et de la vatérite, par un procédé permettant le calcul des paramètres cinétiques à partir d'un essai effectué à température croissante.
    Abstract: Zusammenfassung Die Übergangskinetik der polymorphen Änderungen von Vaterit zu Calcit und Aragonit zu Calcit wurde unter Anwendung der DTA-Technik verfolgt. Bei der Methode erübrigt sich der bei anderen analytischen Verfahren notwendige Mahlprozess, was von gewissem Vorteil ist. Für die Beschreibung der Prozesse beider Übergänge wurde folgende kinetische Gleichung gefunden: $$\frac{{\partial \alpha }}{{\partial t}} = \frac{4}{3}k[ - \ln (1 - \alpha )]^{3/4} (1 - \alpha ).$$ Als Aktivierungsenergien wurden Werte von 452±19 KJ Mol−1 und 208±8 KJ Mol−1 für die Übergänge von Vaterit bzw. Aragonit gefunden. Hierzu wurde eine Methode eingesetzt, die die Berechnung der kinetischen Parameter aus einem Versuch mit steigender Temperatur gestattet.
    Notes: Abstract 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.
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  • 4
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Résumé On donne un aperçu sur l'utilisation des procédés thermoanalytiques en vue d'obtenir les paramètres thermodynamiques et cinétiques. On montre les avantages des techniques d'ATD pour établir les données thermodynamiques. Les données cinétiques calculées à partir des courbes TG conduisent au tracé du logarithme de la constante spécifique de vitesse de réaction en fonction de 1/T, T étant la température en degrés Kelvin. A partir de là, le calcul pour établir les paramètres cinétiques est le même, que les données aient été obtenues par TG dynamique ou isotherme. Les données relatives aux changements de densité et de surface spécifique des résidus solides au cours des réactions de décomposition permettent de conclure que le nombre de particules présentes change d'une façon importante pendant la décomposition. On insiste sur ce fait qui reste souvent négligé lors de l'établissement des modèles cinétiques de décomposition des matériaux solides.
    Abstract: Zusammenfassung Der Einsatz thermoanalytischer Verfahren zur Bestimmung sowohl thermodynamischer als auch kinetischer Parameter wird beschrieben. Der Vorteil der DTA-Techniken bei der Ermittlung thermodynamischer Daten wird gezeigt. Die aus TG-Daten berechneten kinetischen Daten führen zu graphischen Darstellungen der Funktion des Logarithmus des spezifischen Reaktionsgeschwindigkeitskonstante gegen 1/T (wobeiT die Temperatur in Kelvin bedeutet). Hiervon ausgehend ist die Berechnung der kinetischen Parameter dieselbe, ungeachtet dessen, ob die Daten aus TG-Messungen oder aus isothermen Untersuchungen erhalten worden waren. Die Information bezüglich der Änderungen der Dichte und Oberfläche fester Rückstände von Zersetzungsprozessen führt zu der Folgerung, daß die Zahl der anwesenden Teilchen sich während der Zersetzung wesentlich ändert. Es wird betont, daß dieser Faktor bei der Entwicklung zur Zersetzung von Festkörpern in vielen Fällen ausser Acht gelassen wird.
    Notes: Abstract The use of thermal analytical procedures to obtain both thermodynamic and kinetic parameters is outlined. The advantage of DTA techniques in establishing thermodynamic data is demonstrated. Kinetic data calculated from TG data is demonstrated. Kinetic data calculated from TG data leads to plots of the logarithm of the specific reaction rate constant against 1/T (whereT is the temperature in degrees Kelvin) and from this point onwards the calculation is the same to establish the kinetic parameters no matter whether the data was obtained from TG or isothermal studies. Information on changes in the density and surface area of solid residues in the decomposition process leads to the conclusion that the number of particles present changes significantly during the decomposition and it is pointed out that this factor is largely ignored in setting up kinetic models for the decomposition of solid materials.
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  • 5
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Résumé On communique les résultats de l'étude de 25 oxalates par analyse thermique différentielle, dans l'oxygène et dans l'azote. On montre que pour certains d'entre eux, dans l'azote, le métal se forme, et que pour d'autres l'oxyde correspondant à la valence la plus faible apparaît; d'autres encore donnent le même oxyde dans l'azote et dans l'oxygène. Dans l'oxygène, et pour le premier groupe, il se forme l'oxyde, tandis que l'oxyde supérieur apparaît pour le second groupe; dans le premier cas, une réaction ultérieure du métal avec l'oxygène de l'atmosphère est mise en jeu. Un autre groupe d'oxalates donne des enregistrements d'ATD caractéristiques en raison de la formation de carbonate comme produit de décomposition initial. Ces oxalates se déshydratent en donnant des pics endothermiques.
    Abstract: Zusammenfassung Es wurden 25 verschiedene Oxalate durch DTA in Stickstoff- und Sauerstoffatmosphäre untersucht. In einigen Fällen wurde in Stickstoff das Metall gebildet, in anderen das Oxyd von niedrigster Wertigkeit. Es kommt auch vor, daß das gleiche Produkt in beiden Gasen entsteht. Beide erwähnten Produkte werden in Sauerstoff entsprechend oxydiert. Bei einigen Oxalaten erhielt man charakteristische Spitzen, die zeigten, daß das erste Zersetzungsprodukt Karbonat war. Die Dehydration dieser Oxalate zeigte sich durch endothermische Spitzen.
    Notes: Abstract Differential thermal analysis (DTA) of some 25 oxalates are reported in atmospheres of oxygen and nitrogen. It is shown that in some cases in nitrogen the metal is formed, in other cases the oxide of lowest valency state is produced, while a third group give the same oxide product in nitrogen and oxygen. The production in oxygen of the oxide for the first group, and of a higher oxide in the second group is a phenomenon which in the first case involves a further reaction of the metal with the oxygen atmosphere. Another group of oxalates produce characteristic DTA curves due to the formation of carbonate as the initial decomposition product. The dehydrations of these oxalates are marked by endothermic peaks.
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  • 6
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die sich auf die Signifikanz gemessener kinetischer Parameter von Zersetzungsreaktionen fester Stoffe beziehende Unsicherheit wird kurz diskutiert. Es werden einige Vorschläge hinsichtlich der Vorkehrungen unterbreitet, die zu treffen sind, um unverfälschte Meßergebnisse zu erhalten. Einige Kriterien werden vorgeschlagen, die geeignet sind zu entscheiden, ob ain gemessenerE-Wert die übliche Bedutung hat. Ergebnisse einer Reihe von Experimenten werden angegeben, die ausgeführt wurden, um die nach verschiedenen Methoden, bei Anwendung unterschiedlicher Probenmengen und unter verschiedenen Versuchsbedingungen für die Aktivierungsenergie der Zersetzung von CaCO3 erhaltenen Werte zu vergleichen. Es wird gefolgert, daß es möglich ist, den Wert vonE reproduzierbar zu messen, und versuchsweise vorgeschlagen, diesen Wert als sinnvoll für das Energiebarrierenmodell der chemischen Reaktionskinetik anzusehen.
    Abstract: Резюме Кратко обсуждена нео пределенность измеренных значений кинетических параме тров реакций разложений т вердых тел. Высказаны предложения о тех пре досторожностях, которые должны быть п риняты во внимание с ц елью измерения неискажен ных результатов. Предлож ены некоторые критер ии для решения того, что изме ренное значение E может быть истинным. П редставлены результ аты ряда экспериментов, прове денных с целью измерения раз личными методами эне ргии активации реакции ра зложения карбоната кальция, изменяя разм еры образцов и экспериментальные у словия. Полученные результаты сопостав лены с литературными данными и сделано заключение о возможности измерить воспроизво димое значение энерг ии активации. Условно предложено, ч то такое значение являе тся средним в зависим ости от модели энергетическ ого барьера кинетики химической реакции.
    Notes: Abstract The uncertainty surrounding the significance of the measured kinetic parameters of solid state decomposition reactions is discussed briefly. Some suggestions are made about what precautions should be taken in order to favour the measurement of undistorted results. Some criteria are proposed for deciding whether a measuredE value can be considered to have its usual meaning. The results of a series of experiments aimed at measuring the activation energy of the decomposition of calcium carbonate using a variety of methods, sample sizes and experimental conditions are presented. These results are compared with results found in the literature and it is concluded that it is possible to measure a reproducible value forE and it is tentatively proposed that this value is meaningful in terms of the energy barrier model of chemical reaction kinetics.
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  • 7
    ISSN: 1572-8943
    Keywords: activated carbons ; gasification reaction ; TG-DTA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In this study gasification in air of activated carbons and carbon blacks is investigated using a simultaneous TG-DTA unit. It is found that a final acid or alkaline treatment can substantially alter their reactivity in the gasification reaction in air. To make a proper assessment of their solid state reactivity with respect to their gasification in air a simple method is advanced which has been used recently in assessing solid state reactivity of other materials. In this method a thermogravimetric (TG) plot is obtained on a reference carbon and then similar TG plots are obtained on the other samples of carbon using identical experimental conditions and the same TG unit. The solid state reactivity is assessed from plots of the αR (the value of αR, the extent of the gasification of the reference carbon) against the sample carbons values of the αS (labeled αS to denote the value of the various carbon samples). The values of appropriate couples of αR and αS at temperaturesT 1,T 2,T 3,...Tn allow an αR-αS plot to be constructed. If the solid state reactivity of the carbon samples matches exactly that of the reference carbon the result will be a linear plot, showing coincidence of αS and αR at all values of αR. If the solid state reactivity of a carbon sample exceeds that of the reference carbon then the lines plotted will be on one side of the coincidence plot, while if they are less than the carbon reference they will lie on the other side. The results show that treatment of a carbon with alkaline or acid may have a significant effect on the reactivity of the carbon sample which is only partly explained by observable differences in surface area.
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  • 8
    ISSN: 1572-8943
    Keywords: activation ; carbon ; corn cobs ; SEM ; TG
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Corn cobs obtained as waste from the corn industry, were analyzed by a TG-DTA unit in an atmosphere of flowing nitrogen. The carbonaceous products so formed were then produced on a preparative scale and activated chemically using potassium hydroxide. This resulted in the formation of a carbon with a very high surface area. The active carbon produced was then examined using thermal analysis in the temperature jump mode on a thermogravimetry unit. From this data the kinetics of degradation of the active carbon was determined using zero order rate kinetics. The pore structure of the active material was also examined using SEM. TheE a for activated corn cobs was found to be 106 kJ mol−1.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1572-8943
    Keywords: enthalpy of vaporization ; Ibuprofen ; zero order reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ibuprofen has been subjected to a TG/DTA study over the temperature range of 30 to 350°C in a flowing atmosphere of nitrogen. The heating rate and the flow rate were varied. The DTA shows a melting at around 80°C and boiling point range from 212 to 251°C depending upon the heating rate. The mass loss in the TG data confirms the evaporation of Ibuprofen between them.p. and the normalb.p. Evaporation is limited to the surface area, which is a constant in the crucible holding the sample. The DTG plot shows clearly a zero order process which is consistent with the process of evaporation. The enthalpy of vaporization (Δvap H) calculated by Trouton's rule is found to be in the range of 42.7–46.1 kJ mol−1. TheE act for the zero order reaction is in the range of 81.8–87.0 kJ mol−1 and is calculated by use of the derivative method. The value ofE act is about twice that for ΔH vap in Ibuprofen and differs from other compounds, whereE act ≈Δ H vap . It is suggested that the Ibuprofen molecule is existing as a dimer in the liquid state and dissociates to a monomer in the vapor state.
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  • 10
    ISSN: 1572-8943
    Keywords: alkylcyclohexanes ; binary phase diagrams ; DSC ; metastable solutions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Differential scanning calorimetry (DSC) was used to construct phase diagrams of binary mixtures of alkylcyclohexanes and to characterize metastable phases formed in the binary mixtures. The experimentally measured liquidus curves were compared to the liquidus curves calculated using ideal solution theory. The measured phase diagrams of pentadecylcyclohexane/nonadecylcyclohexane and octadecylcyclohexane/nonadecylcyclohexane binary mixtures are consistent with theoretical phase diagrams constructed based on the assumption that these mixtures form eutectic systems. It was also observed that a metastable phase formed in some binary mixtures of pentadecylcyclohexane/nonadecylcyclohexane under fast cooling conditions. It is hypothesized that this metastable phase recrystallizes into the eutectic phase upon heating.
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