Volume and heat capacity of model non-aqueous self-assembly systems

Blends of immiscible polymers are often stabilized by block copolymers which can form non-aqueous micelles and microemulsions in the liquid polymers. The phase diagrans, apparent volumes and apparent heat capacities of model non-aqueous binary and ternary systems were studied in order to investigate the conditions under which such self-assembly systems could form. 1,2-Hexanediol, which can cosolubilize hexane and ethyleneglycol, forms inverse micelles in hexane and weak microaggregates in ethyleneglycol. Genapol X-060, a commercial alcoholic surfactant containing on the average an aliphatic chain of 13 carbons and 6 oxyethylenes (C₁₃E₆), forms microaggregates in poly(ethyleneglycol) 400. These self-assembly systems are strengthen in the presence of a third component which has an affinity for the inner phase.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

The additivity principle in pyrolysis—gas chromatography of brown coal

Pyrolysis—gas chromatography of brown coal exhibits additive properties and it is therefore possible to construct the pyrogram of the original coal from the individual pyrograms of the bitumen, humic acids, lignin and humin fractions. The contents of phenols in the pyrograms are typical for all of the above classes except bitumen and are in agreement with the contents of the individual groups in the original coal. The results suggest that the separation does not bring about significant chemical changes in individual brown coal fractions.     

IAEA quality control studies on determining trace elements in bioindicators

Twenty laboratories from 17 countries around the world participated in two analytical quality control exercises, coded NAT-5 and NAT-6, on determining trace and minor elements in plant bioindicator samples. 1398 laboratory mean values for 51 elements were submitted for two lichen and two moss materials. The submitted measurement results were evaluated as interlaboratory comparison (IC) exercises and as proficiency tests (PT) following standard procedures developed by the International Atomic Energy Agency (IAEA). The evaluations confirmed good performance of the participating laboratories for many elements. Furthermore, the laboratories performance based on IC criteria improved from the first exercise to the second one. Subsequent NAT-5 evaluation revealed systematic differences between the analytical values obtained non-destructively or after the total sample dissolution and the measurements following nitric acid sample dissolution (without the use of hydrofluoric acid) for some elements. The most critical elements for this kind of discrepancies appeared to be Al, Ca, Cr, Fe, Na, Ni, and Pb. After changing analytical methodologies in the concerned laboratories, more consistent values for those elements were obtained in NAT-6. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analyse theoretique des lois cinetiques couramment utilisees en thermoanalyse pour l'etude des reactions solid-gaz. III. proposition d'une nouvelle methode d'approche en regime dynamique

Résumé Dans la première partie de ce travail, les auteurs mettent en évidence que la vitesse d'une réaction en régime non isotherme dépend d'un facteur supplémentaire: le régime de montée en température. Cette assertion est basée sur le fait que le taux de réactionx est une fonction de trois variables: températureT, tempst, et vitesse de chauffeT, variable qui n'avait pas été prise en considération jusqu'ici par les autres auteurs travaillant sur ce problème.Puis, se basant sur les deux hypothèses suivantes: a) l'équation de vitesse en régime isotherme est la forme limite de l'équation de vitesse en régime dynamique, b) la variation de température en régime dynamique affecte la fréquence d'apparition des germes de la nouvelle phase, une formulation théorique des loisg(x) est proposée pour le régime non-isotherme. Cette formulation est explicitée en fonction de l'écart, à une température donnée, entre les valeurs de Lnk _i (isotherme) et Lnk _d (dynamique) dans le diagramme Lnk = f(1/T).L'étude, par thermogravimétrie, de la décomposition du gypse, du sulfate de calcium semihydraté, et de l'oxalate de calcium monohydraté, réalisée en montée linéaire de température, permet de vérifier expérimentalement la formulation théorique proposée.Pour obtenir une bonne interprétation cinétique d'une réaction chimique en régime dynamique, la vitesse de chauffe ne doit pas excéder 20°/heure.

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In the first part of this paper, the authors point out that the rate of reaction with non-isothermal kinetics depends on a supplementary factor: the heating rate. This assertion is based on the fact that the degreex of reaction is a function of three variables:T (temperature),t (time) andT (heating rate); this was not taken into account by other authors concerned with the subject.Then from the two following hypotheses: a) the rate equation for isothermal conditions is the limit form of the rate equation for non-isothermal conditions, b) the temperature change under dynamic conditions affects the frequency of nucleus formation of the new phase, a theoretical formulation of non-isothermalg(x) laws is proposed. This formulation involves the value of the difference, at constant temperature, between Ink _i (isothermal) and In k_d (dynamic) in the Ink=f(1/T) diagram.The thermogravimetric study of the dehydration of gypsum, of calcium sulfate hemihydrate, and of calcium oxalate monohydrate, under non-isothermal conditions, allows experimental verification of the theoretical formulation proposed.For a good kinetic approach of a chemical reaction under dynamic conditions, the heating rate must not exceed 20°/hour.

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Zusammenfassung Im ersten Teil dieser Arbeit wird von den Autoren bewiesen, daß die Geschwindigkeit einer Reaktion unter nicht-isothermen Bedingungen von einem zusätzlichen Faktor, den Bedingungen des Temperaturenstiegs, abhängt. Diese Behauptung beruht auf der Tatsache, daß der Reaktionsverlauf eine Funktion dreier Variablen ist: der TemperaturT, der Zeitt und der AufheizungsgeschwindigkeitT, wobei letztere Variable bisher von den auf diesem Gebiet arbeitenden Autoren außer Acht gelassen worden ist.Nachfolgend wird an Hand der zwei Voraussetzungen, daß a) die Geschwindigkeitsgleichung unter isothermen Bedingungen die Grenzform der Geschwindigkeitsgleichung unter dynamischen Bedingungen ist und b) die Temperaturänderung unter dynamischen Bedingungen sich auf die Erscheinungsfrequenz der Keime der neuen Phase auswirkt, eine theoretische Formulierung der Gesetzeg(x) für nicht-isotherme Bedingungen vorgeschlagen. Diese Formulierung wird als Funktion der Abweichung ausgedrückt, welche bei einer gegebenen Temperatur zwischen den Werten von Lnk _i (isotherm) und Lnk _d (dynamisch) im Diagramm Lnk=f(1/T) besteht.Die bei linearem Temperaturanstieg thermogravimetrisch durchgeführte Untersuchung der Zersetzung von Gips, von Calciumsulfat Semihydrat und von Calciumoxalat Monohydrat ermöglicht die vorgeschlagene theoretische Formulierung experimentell zu bestätigen.Um unter dynamischen Bedingungen eine gute kinetische Interpretation einer chemischen Reaktion zu erhalten, darf die Aufheizungsgeschwindigkeit den Wert von 20° pro Stunde nicht überschreiten.

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, : . , : (),t () ' ( ), , . : ) ) t(x) . Lnk _j () Lnk _d ( ) Lnk=f(1/T) . , , . , 20° .

     

Use of x-ray fluorescence spectrometry in ion-exchange studies of leach liquors

Equilibrium and kinetic studies of ion exchange of a complex leach liquor from coal ash, with strongly basic resins and a liquid ion exchanger are reported. The multi-component system was studied by determining the composition of the effluents and by non-destructive analysis of the loaded ion exchangers by XRF spectrometry. In the case of column operation, the elution processes were investigated by the same method, which was very appropriate for non-destructive monitoring of resin regeneration steps done repeatedly with the same resin sample.     

On lower bounds of number of perfect matchings in fullerene graphs

Couting perfect matchings in graphs is a very difficult problem. Some recently developed decomposition techniques allowed us to estimate the lower bound of the number of perfect matchings in certain classes of graphs. By applying these techniques, it will be shown that every fullerene graph with p vertices contains at least p/2+1 perfect matchings. It is a significant improvement over a previously published estimate, which claimed at least three perfect matchings in every fullerene graph. As an interesting chemical consequence, it is noted that every bisubstituted derivative of a fullerene still permits a Kekulé structure.     

(CuBr)3P4Se4: A Low Symmetric Variant of the (CuI)3P4Se4 Structure Type

Bright orange (CuBr)₃P₄Se₄ is obtained from the reaction of CuBr, P, and Se in stoichiometric amounts (CuBr : P : Se = 3 : 4 : 4). The composition and the crystal structure of the compound were determined from single crystal X‐ray diffraction data. Lattice constants are a = 33.627(2) Å, b = 6.402(1) Å, c = 19.059(1) Å, β = 90.19(3) °, V = 4103.2(3) ų, and Z = 12. The compound crystallizes in a structure that is related to (CuI)₃P₄Se₄. Cages of β‐P₄Se₄ are stacked along the b‐axis and are separated by columns of copper(I) bromide. However, the coordination of the β‐P₄Se₄ cage molecules to the copper atoms in the CuBr columns in (CuBr)₃P₄Se₄ is quite different from (CuI)₃P₄Se₄. The monoclinic compound (space group: P2₁, no. 4) has an almost orthorhombic metric in combination with a threefold superstructure in [100]. Structural aspects of (CuBr)₃P₄Se₄ are discussed with respect to the heavier homologue (CuI)₃P₄Se₄.     

Possible Mechanisms of Intercalation

Recent knowledge of the kinetics and intercalation mechanisms are summarized and accompanied by examples of intercalation reactions of water and ethanol into anhydrous vanadyl phosphate and redox intercalation of alkali metal cations into vanadyl phosphate dihydrate. Three possible mechanisms of intercalation are presented which are based on: (i) a concept of exfoliation of layers; (ii) the formation of stages and randomly stacked layers; (iii) co-existence of intercalated and non-intercalated parts of crystals of the host separated by an advancing phase boundary. The corresponding kinetic curves are ascribed to mechanisms (ii) and (iii).     

Thermal decomposition of N2H6GeF6 · H2O,isolation and characterization of intermediates

The thermal behaviour of N₂H₆GeF₆ · H₂O was investigated by TG, DTG and DTA measurements. The decomposition proceeded in three steps, in which anhydrous N₂H₆GeF₆ and N₂H₅GeF₅; were isolated and characterized by chemical analysis and vibrational spectroscopy. The X-ray powder photographs of the intermediates were indexed, namely, for N₂H₆GeF₆ on the basis of a monoclinic cell with a = 8.86(9), b = 9.29(2), c =7.40(0) Å, β = 85° and for N₂H₅GeF₅ on the basis of an ortrhorhombic cell with a = 8.43(5),b = 9.19(9), c = 7.43(6) Å.