Etude du comportement thermique d'une mousse isolante Uree-Formol

The thermogravimetric curves of an urea-formaldehyde insulating foam were obtained at selected times after their formation (from six hours to thirty five days). They showed three intervals of weight loss depending on the temperature, and were different according to the foam ageing.The kinetics of weight loss has been studied. Formaldehyde was mainly produced during the first interval independent of the stage of foam ageing. At ambient temperature, formaldehyde formation was only achieved after four days following the foam formation. After this period of, time, the formaldehyde evolution was only observed when the temperature reached 60 °C.

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Zusammenfassung Thermogravimetrische Kurven eines Harnstorf-Formaldehyd-Isolierschaums wurden zu verschiedenen Zeiten nach dessen Bildung (von 6 Stunden bis 35 Tagen) aufgenommen. Drei Gewichtsverlustintervalle wurden mit steigender Temperatur beobachtet, die abhängig von der Schaumalterung sind. Die Kinetik des Gewichtsverlustes wird angegeben. Formaldehyd wird bei allen Schaumalterungszeiten hauptsächlich während des ersten Intervalls gebildet. Bei Raumtemperatur wird Formaldehydbildung nur während der ersten 4 Tage nach der Bildung des Schaumes beobachtet. Nach längeren Alterungszeiten setzt die Abgabe von Formaldehyd erst bei einer temperatur von 60 °C ein.

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- 6 35 . . . , , . . , 60°.

     

Kinetics and mechanism of isomerization of alkyl radicals in solution

It has been shown that in alkyl radicals the 1, 5-rearrangement of hydrogen atoms takes place. The isomerization rate constants for radicals of various structure have been estimated. There is a compensation effect for their Arrhenius parameters.

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, 1,5- . . .

     

Hydrogen adsorption on Dy and Tm films

Variations in resistivity R and work function of thin Tm and Dy films due to H₂ adsorption on their surface at 77 K have been studied. It is suggested that on most surfaces hydrogen is strongly adsorbed as H^–, and only below 10% monolayer is its weakly adsorbed form H ₂ ⁺ . The observed decrease of is attributed to H^– penetrating into lattice vacancies and surface cavities.

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R Tm Dy, H₂ 77 K. , H^–°, 10% H ₂ ⁺ . H^– .

     

Thermoanalytische Untersuchungen zur Zersetzung von MgCl2 · 6 H2O unter quasiisobaren Bedingungen

Zusammenfassung Vergleichende thermoanalytische Untersuchungen der thermischen Zersetzung von MgCl₂ · 6 H₂O bis 400° C bei p=1 bar unter quasiisothermen und temperaturdynamischen Bedingungen bei simultaner Gasanalyse (EGA) und Variation des H₂O- und HCl-Partialdrucks über der Substanz. Die H₂O- und HCl-Abspaltung erfolgt in Stufen, deren Temperatur vom H₂O-HCl-Partialdruck beeinflußt wird. In Abhängigkeit von den Bedingungen ist die Überführung in MgCl₂ · 4 H₂O direkt aus dem Feststoff oder aus einer Schmelze in einem nichtisothermen Schritt möglich. Die Zersetzung von MgCl₂ · 4 H₂O vollzieht sich unter quasiisobaren Verhältnissen in weiteren drei isothermen Reaktionen über MgCl₂ · 2 H₂O und thermisch stabile basische Magnesiumchloride.

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The decomposition of magnesium chloride hexahydrate was followed by differential thermal analysis and thermogravimetry in combination with evolved gas analysis. The examinations were carried out by means of a Q-derivatograph (temperature range 20–400°; pressure 1 bar) under quasiisothermal and dynamic heating conditions, with variation of the crucible type. The temperatures of the stepwise decomposition of H₂O and HCl are influenced by the partial pressures of H₂O and HCl. Depending on the conditions, it is possible to remove 2 moles of water from solid MgCl₂ · 6 H₂O or from a melt in a nonisothermal step. Under quasiisobaric conditions MgCl₂ · 4 H₂O is transformed in isothermal steps to MgCl₂ · 2 H₂O and stable basic magnesium chlorides.

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Résumé On a étudié la décomposition du chlorure de magnésium hexahydraté par analyse thermique différentielle et par thermogravimétrie combinée avec l'analyse des gaz dégagés. On a effectué les examens avec un dérivatographe-Q (entre 20 et 400°, sous une pression de 1 bar) en conditions de chauffage quasi-isotherme et dynamique, en changeant le type de creuset. La température de l'élimination étagée de H₂O et HCl est influencée par le pression partielle de H₂O et HCl. Suivant les conditions, il est possible d'éliminer deux moles d'eau de MgCl₂ · 6H₂O solide ou fondu, en une étape non-isotherme. En conditions quasi-isobares, MgCl₂ · 4H₂O réagit, par étapes isothermes, pour donner MgCl₂ · H₂O et des chlorures basiques de magnésium stables.

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. Q- ( 20–400°, 1 ) . H₂O HCl H₂O HCl. , , 2 MgCl₂ · 6H₂O , . MgCl₂ · 4H₂O MgCl₂ · 2H₂O .

     

DTA-Untersuchungen zur Kinetik der Karbonatzersetzung

Zusammenfassung Die Zersetzung mehrerer Karbonate wurde mittels DTA untersucht. Die DTA-Kurven dienten zur Bestimmung der AktivierungsenergieE und der Reaktionsordnungn. Verschiedene Auswertungsmethoden wurden miteinander verglichen. Die Aktivierungsenergie der Zersetzung von CaCO₃ beträgt 42.3 kcal mol^–1 als Mittelwert, ausgewertet nach verschiedenen Methoden. Der entsprechende Wert für CaC₂O₄ · H₂O ist 43.3 kcal mol^–1. Zusätzlich wurde die Kinetik der Entwässerung von CaC₂O₄ · H₂O mittels DTA untersucht. Die erhaltenen Werte:n=1 undE=21.7 kcal mol^–1 stimmen mit Literaturwerten überein. Es wurde gezeigt, daß eine einzige DTA-Aufnahme mit einer Aufheizgeschwindigkeit von 10 °C min^–1 eine befriedigende Auswertung der Aktivierungsenergien und Reaktionsordnungen ermöglicht. Der Verlauf der DTA-Kurven bei der Karbonatentsäuerung ist von der Art der Meßköpfe und der Versuchsatmosphäre abhängig. Diese Tatsache wurde am Dolomit unter verschiedenen Versuchsbedingungen bestätigt.

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The dissociation of several carbonates has been investigated by the DTA method. The curves have been used for the calculation of the activation energy and reaction order. Different evaluation methods have been assessed. The average activation energy for dissociation of CaCO₃ is 42.3 kcal mol^–1. The corresponding value for CaC₂O₄ · H₂O is 43.3 kcal mol^–1. The experimental values for the dehydration of CaC₂O₄ · H₂O,E=21.7 kcal mol^–1 andn=1 are in agreement with literature data. It was shown that a single DTA experiment at a heating rate of 10° min^–1 is sufficient for the evaluation of the apparent activation energy and reaction order as measured by thermoanalytical methods. The shape of DTA curves is dependent on the experimental conditions as shown by the dissociation of dolomite.

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Résumé On a étudié par ATD la décomposition de divers carbonates. Les valeurs de l'énergie d'activation et de l'ordre de la réaction ont été calculées d'après les enregistrements d'ATD. Les différentes méthodes utilisées pour ces déterminations ont été comparées. Elles ont donné comme valeur moyenne de l'énergie d'activation 42.3 kcal mol^–1 pour CaCO₃ et 43.3 kcal mol^–1 pour CaC₂O₄ · H₂O. L'étude de la cinétique de la déshydratation de CaC₂O₄ · H₂O par ATD a conduit aux valeurs den=1 et de E=21.7 kcal mol^–1. Une seule courbe d'ATD, enregistrée avec une vitesse d'échauffement de 10° min^–1, suffit pour évaluer avec entière satisfaction l'énergie d'activation et l'ordre de la réaction. L'exemple de la dolomite illustre l'influence des conditions expérimentales sur le tracé de la courbe d'ATD.

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() . . ₃ 42,3 / . ₂₄. ₂ - 43,3 /. , CaC₂O₄. ₂, E=21,7 / n=1, . , () 10°/ . , () .

     

Reduction kinetics of benzylideneaniline over Pd/SiO2?AlPO4 and Pd/sepiolite catalysts

The liquid-phase hydrogenation of benzylideneaniline over various Pd catalysts, using gaseous hydrogen has been studied. We have synthesized several Pd catalysts (3 wt.%) over SiO₂–AlPO₄ and sepiolite supports, and determined their metal surface area by X-ray diffraction. The study performed shows that the process follows a Langmuir-Hinshelwood kinetics with zero order in benzylideneaniline, r_i=k_okP_H2 (1+KP_H2)^–1.

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Pd, . Pd (3 .%) SiO₂–AlPO₄ . - . , - , r_i=k_okP_H2 (1+KP_H2)^–1.

     

The determination of kinetic parameters for some solid state reactions

The kinetics of many solid state reactions can best be explained in terms of an order of reaction; this is particularly true in the case of polymer degradation. The methods currently available for the determination ofn andk, from isothermal data, are either limited in the range of which can be used or are difference-difference techniques where the data must of necessity be highly accurate. This paper presents a review of these methods and introduces a new approach by whichn andk can be obtained directly, giving results which are unique and objective in that they provide a best fit to the experimental data.

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Zusammenfassung Die Kinetik vieler Reaktionen in fester Phase kann am besten an Hand einer Reaktions-Ordnung erklärt werden; dies besteht besonders bei dem Abbau von Polymeren. Die für die Bestimmung vonn undk aus isothermen Daten zur Verfügung stehenden Methoden sind entweder auf den verwendbaren Bereich von beschränkt oder sind Differenz-Differenz-Methoden, bei welchen es äußerst genauer Angaben bedarf. Die vorliegende Veröffentlichung gibt eine übersicht dieser Methoden und führt eine neue Annäherung ein, durch welchen undk unmittelbar erhalten werden können. Diese Methode ergibt einzigartige und zielgerechte Ergebnisse, indem diese sich den Versuchsdaten am besten anpassen.

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Résumé Pour de nombreuses réactions dans l'état solide l'ordre de réaction constitue un très bon moyen pour exprimer leur cinétique; c'est le cas, en particulier, de la dégradation des polymères. Les différentes méthodes dont on dispose pour déterminern et k à partir des données isothermes sont limitées à l'intervalle d'utilisation de ou opèrent par différences successives ce qui nécessite des données très précises. L'article présente une revue de ces méthodes et introduit une nouvelle approche oùn etk peuvent Être obtenus directement, en donnant des résultats uniques et objectifs qui assurent un meilleur accord avec les données expérimentales.

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; . , n ,k . , « — », . , n k. .

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The calculations presented in this paper were performed on an ICL 4130 computer using the program SOLITER. This program was written in ALGOL 60.     

Configuration analysis and electronic states properties

The excited-states electronic properties of unsaturated small-ring hydrocarbons with four- and six--electrons have been studied by the Molecules in Molecules method and compared with experimental data and PPP results interpreted through a configuration analysis procedure. The results show that the MIM method is applicable with good reliability.

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Zusammenfassung Die elektronischen Eigenschaften der angeregten Zustände von ungesättigten kleinen Kohlenwasserstoffringen mit vier und sechs -Elektronen wurden mit Hilfe der Molekül- im-Molekül-Methode untersucht und die Ergebnisse mit experimentellen Daten und PPP Resultaten, die durch eine Konfigurationsanalyse interpretiert wurden, verglichen. Die Ergebnisse zeigen, daß die MIM-Methode mit großer Zuverlässigkeit anwendbar ist.

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Financial aid from the Italian C.N.R. is gratefully acknowledged.     

Investigation of the thermal decomposition of potassium benzoate in the presence of cadmium and zinc compounds

It was established by thermogravimetric measurements that the thermal decomposition of potassium benzoate in the presence of inorganic cadmium or zinc salts results in the formation of the easily decomposing cadmium or zinc benzoate. These carboxylates are presumably the catalysts of the transcarboxylation of potassium benzoate to terephthalate.

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Zusammenfassung Es wurde durch thermogravimetrische Messungen festgestellt, da\ die thermische Zersetzung von Kaliumbenzoat in Gegenwart von anorganischen Kadmiumoder Zinksalzen zur Bildung des leicht zersetzbaren Zink- oder Kadmiumbenzoats führt. Diese Carboxylate spielen möglicherweise eine katalytische Rolle bei der Transcarboxylierung von Kaliumbenzoat zu Terephthalat.

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Résumé L'étude thermogravimétrique de la décomposition thermique du benzoate de potassium en présence de sels minéraux de zinc ou de cadmium montre la formation de benzoates de cadmium ou de zinc facilement dissociables. Ces carboxylates sont probablement les catalyseurs de la transcarboxylation du benzoate de potassium en téréphtalate.

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, . , , .

     

Use of a Packed Minicolumn Connected to a Syringe for Determination of Trace Elements in Biological and Water Samples by Flame Atomic Absorption Spectrometry

In this study, a syringe-connected minicolumn resin was used for the separation and enrichment of cadmium, copper, nickel and zinc prior to their determination by flame atomic absorption spectrometry. The proposed technique was compared with classical batch and column techniques in terms of rapidness, simplicity, enrichment and risk of contamination. The minicolumn was filled with Chromosorb-103 resin and connected to a syringe. If the samples were treated with ammonium pyrrolidine dithiocarbamate or 8-hydroxyquinoline, the analytes were quantitatively retained at pH2 and pH5 on the resin, respectively. On the other hand, if no chelating agent was added, the analytes were quantitatively retained at pH10. The analytes retained by the resin were quantitatively eluted by drawing and discharging nitric acid in acetone. The analytes in spiked river-water samples and in certified standard reference Bovine-Liver (NIST SRM 1577 b) were quantitatively (94%) recovered. The relative standard deviations for the determinations were found to be 1.0–10%.     

Stereochemical dependence and dependence on structural factors of the spin-spin coupling constants3JCOHβ in conjugated ω-amino-, alkoxy-, alkyl-, dialkyl-, phenyl-α-carbonyl-, and α,α′-dicarbonyl-containing compounds

We measure the cis and trans constants³J_CO, H and we discuss the effect on them from the structural factors in the¹³C spectra of 76 conjugated -amino, alkoxy-, alkyl-, dialkyl-, phenyl--carbonyl-, and ,-dicarbonyl-containing compounds. We show that the³J_CO, H are stereospecific [³J_CO, H (cis) (trans)] in all the studied compounds. On the basis of the stereo-specificity of the constants, we determine the configuration of the trisubstituted , double bond in ketones, ketoesters, and imides of different structures.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 356–365, February, 1990.     

Reversed phase liquid chromatographic retention behavior of polystyrene homopolymers

Summary Isocratic and gradient elution high performance liquid chromatographic measurements of the retention behavior of polystyrene homopolymers with molecular weights ranging from 2 kD to 390 kD were performed using mixed methylene chloride-methanol mobile phases of varying composition and a C-18 chemically bonded stationary phase supported on either 100 Å or 300 Å mean pore diameter silica. Isocratic measurements of the capacity factor, k, for different molecular weight homopolymers as a function of the volume fraction of methylene chloride, , permit determination of the critical composition, _c, which renders k=1 and the local slope, S=–lnk/_c of the lnk- isotherm at =_c, and also the dependence of _c and S on the degree of polymerization, M. Linear gradient elution measurements of _c and S were also performed and compared to the corresponding isocratic measurements. The general retention behavior and the dependence of _c and S on M compare favorably to the predictions of the theory of homopolymer retention and fractionation developed by Boehm, Martire, Armstrong, and Bui (BMAB). Comparison is also made between the present work and the experimental observations of other workers on related chromatographic systems involving hompolymer retention.     

Influence of SO 4 2− doping and Y-irradiation on the thermal decomposition of barium bromate

The effects of SO ₄ ^2– doping and Y-irradiation on the isothermal (563 K) decomposition of barium bromate have been investigated gasometrically with a vacuum apparatus. Plots of the fraction decomposed avs. timet for pure, doped and irradiated crystals exhibited characteristic stages: initial gas evolution (initial puff), an induction period, linear reaction, an acceleratory period and decay. The data are considered in the light of various kinetic models, e.g. linear rate equation, Prout-Tompkins and Avrami-Erofeev. The plausible mechanism of the reaction and the effects on this of anion vacancies and Y-irradiation are discussed briefly.

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Zusammenfassung Die Wirkung von Versetzen mit SO ₄ ^2} - und -Bestrahlung auf die isotherme (563 K) Zersetzung von Bariumbromat wurde gasometrisch untersucht. Es zeigte sich, daß die Zeitcharakteristiken für die reinen, die versetzten und bestrahlten Kristalle verschiedene Stufen durchlaufen, nämlich anfängliche Gasentwicklung (Aufblähen), Induktionsperiode, lineare Reaktion, Beschleunigung und Abklingen. Die Daten wurden unter dem Gesichtspunkt verschiedener kinetischer Modelle betrachtet, z. B. lineare Geschwindigkeitsgleichung, das Modell von Prout-Tompkins und Avrami-Erofeev. Es werden kurz ein einleuchtender Reaktionsmechanismus und der Einfluß von Anionengitterlücken und -Bestrahlung darauf diskutiert.

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- (563 ) . , ,-, «t» , , , , , . , - -. .

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The authors thank the Department of Atomic Energy, Government of India, for financial support. M.K.S. also gratefully acknowledges the award of a Research Fellowship by the same agency, which made the work possible.     

Stabilized zeolites of Y-type. Their adsorption and catalytic properties

The stabilized decationized form of a Y-type zeolite has been prepared by the self-steaming calcination method. The temperature of the stabilization process influenced the nature of the interaction with ethylene.

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Y . .

     

Magnetic effects in the reaction of benzyl chloride with triethylgermyl derivatives of alkali metals

The reaction of benzyl chloride with triethylgermyllithium and its analogs have been studied by the¹H-CIDNP method. A reaction mechanism is suggested. Benzyl and triethylgermyl free radicals have been found to be the precursors of main products. The magnetic field effects on the ratio of the main reaction products indicate that the radical path of their formation is predominant. The assumption is made that the ethylgermyl radicals take part in the reaction in the associated state.

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¹H . . , . , . , .

     

Multiple rate resonance phenomena in the forced composition cycling of the Fischer-Tropsch synthesis over a supported cobalt oxide catalyst

Experimental investigation of hydrocarbon synthesis from a mixture of CO and H₂ over a supported cobalt oxide catalyst showed pronounced resonance of the rate of formation of individual hydrocarbons with respect to the frequency of the feed compositon changes. When the measured concentrations of the synthesis products are time-averaged, the mean rate of formation for methane increases fivefold when compared with rate at the mean composition of the feed at steady state for a cycling frequency of 0.017 c/s. Another maximum occurs at about 0.00056 c/s, where the mean rate is about twice the steady-state rate. Rate resonance was also observed for higher hydrocarbons at similar frequencies but with smaller time-average rates. Resonance of rates of reaction has been observed for other catalysts, but rarely with multiple peaks and with such large magnitudes of the rate change.

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CO H₂ . , 0,017 /. 0,00056 /, . , , . , .

     

Condensation of 2-(1-ethoxyvinyl)oxiranes with sodiomalonic ester and decarboxylation of the reaction products obtained

-(1-Ethoxyvinyl)- and -(1-ethoxyvinyl)--ethoxycarbonyl--butyrolactones were obtained by the reaction of 2-(1-ethoxyvinyl)oxiranes with sodiomalonic ester. Decarboxylation of the -(1-ethoxyvinyl)--ethoxycarbonyl-butyrolactones in DMSO leads to -(1-ethoxyvinyl)--butyrolactones, the hydrolysis of which gives -acetyl-butyrolactones. Ethyl trans-3-acetyl-3-pentenoate was obtained by decarboxylation of -methyl--(1-ethoxyvinyl)--ethoxycarbonyl--butyrolactone in DMSO.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 22–25, January, 1992.     

Large volume sample application by a simplified “closed” on-column injector in capillary gas chromatography

Summary A new simplified version of a closed on-column injector is introduced. Because of its design isobaric injection conditions do not have to be followed and a wide range of injection temperatures above the boiling point of the sample solvent can be chosen for on-column injections in capillary gas chromatography. Also, when following certain basic injection rules, injections of large sample volumes (20 l or more) give accurate and reproducible results without further problems.Presented at the 17th International Symposium on Chromatography, September 25–30, 1988, Vienna, Austria.     

Nuclear quadrupole resonance spectroscopic studies of the structure of unsupported titanium-magnesium catalyst for olefin polymerization

The reaction of magnesium dichloride and titanium trichloride in the composition of an unsupported titanium-magnesium catalyst for olefin polymerization has been studied by nuclear quadrupole resonance spectroscopy.

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