A DSC study of thermally treated and UV-treated low-density polyethylene

The melting behaviour of thermally and UV-treated polymer film was studied using DSC. The melting profiles was registered after periods of 24 hours of exposure. The melting profiles after the UV-exposure resembled those observed after heating at 60°. A weak shoulder was first recorded at about 50° and was observed to shift to higher temperatures with increasing exposure time. At the end of the experiments the shoulder was registered around 80°. The changes are compared with results from mechanical tensile tests.

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Zusammenfassung Das Schmelzverhalten eines thermisch und UV-behandelten Polymer-films wurde unter Anwendung der DSC untersucht. Das Schmelzprofil wurde nach 24-stündiger Behandlung registriert. Die Schmelzprofile nach UV-Behandlung ähnelten jeden, die nach Erwärmung auf 60° erhalten worden waren. Eine schwache Schulter wurde zuerst bei etwa 50° beobachtet, welche bei steigender Behandlungszeit in Richtung der höheren Temperaturen verschoben wurde. Am Ende der Versuche wurde die Schulter bei etwa 80° registriert. Die Änderungen wurden mit den Ergebnissen mechanischer Dehnteste verglichen.

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Résumé On a étudié par analyse calorimétrique différentielle (DSC) le comportement pendant la fusion d'un polymère en film soumis à un traitement thermique et par UV. Les profils de fusion ont été enregistrés après des périodes d'exposition de 24 h. Les profils de fusion après traitement UV ressemblent à ceux obtenus après chauffage à 60 °C. Un faible épaulement vers 50° est d'abord enregistré puis il se déplace vers les températures plus élevées, quand la durée d'exposition augmente. En fin d'expérience l'épaulement se situe vers 80°. Ces modifications sont comparées avec les résultats obtenus à partir des essais mécaniques de traction.

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, . , 60°. 50°, . 80°. .

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Valuable assistance from Mrs. E.-L. Svahn is greatefully acknowledged. This work was supported by the Neste Oy Foundation and the Foundation of Technology in Finland.     

Structure and reactivity of vanadium-phosphorus oxides

The contribution of thermal methods of analysis to the study of the structure and reactivity of vanadium-phosphorus oxides is examined. In particular, data are reported on the solid-state reaction VOHPO₄·1/2H₂O(VO)₂P₂O₇+2 H₂O for VOHPO₄·1/2H₂O prepared in different ways, on the redox properties of oxidation and reduction of vanadium for catalysts prepared with different PV atomic ratios in the range 0.9–1.3, and on the surface properties determined by TPD of catalysts with different PV ratios. The relationship between these properties and the catalytic properties in the selective oxidation ofn-butane and but-1-ene is discussed.

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Zusammenfassung Der Beitrag thermischer Analysenmethoden zur Untersuchung der Struktur und Reaktivität von Vanadin-Phosphor-Oxiden wird erörtert. Insbesondere werden sich auf die Festkörperreaktion 2VOHPO₄.1/2H₂O(VO)₂P₂O₇+2H₂O für auf verschiedene Weise dargestelltes VOHPO₄.1/2H₂O, auf die Redox-Eigenschaften von Vanadin in Katalysatoren mit P/V-Atomverhältnissen im Bereich 0.9–1.3 und auf durch TPD bestimmte Oberflächeneigenschaften von Katalysatoren mit unterschiedlichen P/V-Verhältnissen beziehende Angaben gemacht. Zusammenhänge zwischen diesen Eigenschaften und den katalytischen Eigenschaften bei der selektiven Oxydation von n-Butan und N-Buten werden diskutiert.

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- . , VOHPO₄ · 1/2H₂O, VOHPO₄ · 1/2H₂O(VO)₂P₂O₇ + 2H₂O, - PV 0,91,3. - 1-.

     

Nonsteady-state kinetic model of sulfur dioxide oxidation on vanadium catalysts

Rate constants and activation energies of individual steps for the previously suggested mechanism of SO₂ oxidation on vanadium catalysts have been determined from experimental data on nonsteady-state kinetics.

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Hydrogenolysis of n-butane on low-loaded Rh/TiO2, I. Catalysts obtained by ion exchange

The activity in n-butane hydrogenolysis of Rh/TiO₂ (0.6 wt.% Rh) catalysts prepared by ion exchange and reduced at different heating rates is reported. The heating rate has no major effect on the properties of the catalysts (similar dispersions and activities are achieved). Carbonaceous residues formed at high temperature are removed by hydrogen at room temperature, thus leading to recovery of the activity.

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Rh/TiO₂ (0,6 .% Rh), , -. : . , , , , , .

     

Correlation between the surface acidity and activity of bismuth tungstate catalysts

The surface acid strength distribution in bismuth tungstate catalysts with Bi/W ratios of 2/3, 1/1, 2/1 and 6/1 has been investigated. The results are interpreted attributing higher acidities to W–O–W bonds and lower acidities to W=O bonds. An apparent correlation is observed between the surface acidities of the catalysts and their activities in the oxidation and ammoxidation of propylene and 1-butene.

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Bi/W, 2/3, 1/1, 2/1 6/1. , W–O–W W=O. 1-.

     

ESR spectra of47Ti-enriched titanium catalysts for polymerization

For the first time ESR spectra of⁴⁷Ti-enriched Ziegler system Ti-TIBA in toluene have been studied. For the ratio Ti/Al1, more accurate h. f. s. constants have been found. For Ti/Al1/15 no h. f. s. have been observed, which is ascribed to ordering due to the cooperative Jahn-Teller effect.

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TiCl₄+ ⁴⁷Ti. Ti/Al1 . Ti/Al1/15 , -.

     

Thermal properties of binary polyolefin blends

The thermal properties of binary polyolefin blends (LDPE/HDPE, LDPE/PP, HDPE/PP) were examined by differential scanning calorimetry. The additon of a second polymer lowers the melting temperature although the melting temperature depression is not a defined function of the blend composition. DSC curves show two melting and two crystallization temperatures. The difference between crystallization temperatures for blends containing PP is smaller than the difference between melting temperatures. The enthalpies of fusion are nearly monotonic functions of blend composition.

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Zusammenfassung Die thermischen Eigenschaften binärer Polyolefinmischungen (LDPE/HDPE, LDPE/PP, HDPE/PP) wurden mittels DSC untersucht. Durch Zugabe eines zweiten Polymers wird die Schmelztemperatur erniedrigt, obwohl die Erniedrigung der Schmelztemperatur keine Funktion der Mischungszusammensetzung ist. Die DSC-Kurven zeigen zwei Schmelz- und zwei Kristallisationspeaks. Bei PP enthaltenden Mischungen ist der Unterschied zwischen den Kristallisationstemperaturen geringer als zwischen den Schmelztemperaturen. Die Schmelzenthalpie ist eine nahezu monotone Funktion der Mischungszusammensetzung.

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— , — , — . , . . , . .

     

Effect of acetylenic carbinol structure on hydrogenation selectivity

Quantum-chemical calculations of dimethylethynylcarbinol (DMEC) and dimethylvinylcarbinol molecules by CNDO/2 and MINDO-3 method indicate that a double bond is more reactive than a triple, which hinders the selective hydrogenation process. Dehydrolinalool and DMEC hydrogenation selectivity has been studied.

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() /2 /3; . , , , .

     

Determination of the strength of aprotic acidic centers on catalyst surfaces from the IR spectra of adsorbed carbon monoxide

Correlations between the adsorption heats of carbon monoxide on aprotic acidic centers and the v _CO values in IR spectra have been studied. In the case of aprotic centers formed by cations of non-transition metals, v _CO is shown to be linearly dependent on the adsorption heat.

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v _CO . , , , v _CO .

     

New models of monooxygenase on the basis of Sn(II) compounds

The data on the selectivity of various C–H bonds and the stereochemical course of the reaction in the known chemical systems simulating monooxygenase, do not agree with the oxenoid mechanism postulated for these reactions, but correspond to the interaction of saturated hydrocarbons with the OH radical intermediate. On the basis of organic compounds of Sn(II) in aprotic media, new systems have been developed which selectively oxidize alkanes to alcohols in the presence of O₂ in the coupled process and display many characteristics of the oxenoid reactions.

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C–H , , , , . (II) , .

     

Effect of the support on the coking of nickel catalysts in hydrocarbon steam reforming

Experiments on the coking rates of variously prepared nickel catalysts on TiO₂, Al₂O₃ and MgO in n-butane steam reforming show that changes in the relative coking rate at a rising steam excess in the gas phase depend mainly on the kind of support. The results obtained are accounted for by changes in the electron density at the site of nickel crystallite contact with the surface of various supports.

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, TiO₂, Al₂O₃ MgO, - , , , , , . .

     

The thermal decomposition temperatures of ionic metal oxalates

Previous investigations linking the thermal decomposition properties of metal oxalates to the nature of the bonding have been successful only in establishing qualitative relationships. A quantitative relation is now revealed permitting prediction of the thermal decomposition temperaturesT _d (°C) of metal oxalates:T _d =516–1.4006r _c /r _i I wherer _c /r _i is the ratio of the Pauling covalent radius and the ionic radius of the metal atom in hexacoordination, andI _i is the sum of the ionization potentials of the metal atom in kJ mol^–1.

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Zusammenfassung Frühere Untersuchungen über Beziehungen der Eigenschaften thermischer Zersetzung von Metalloxalaten in Bezug auf Bindungseigenschaften, waren nur hinsichtlich der Feststellung qualitativer Zusammenhänge erfolgreich. Es wurde ein quantitativer Zuhammenhang gefunden, welcher die Voraussage der thermischen ZersetzungstemperaturenT _d (°C) der Metalloxalate gestattet:T _d =516–1.4006r _c /r _i , I _i wobeir _c /r _i das Verhältnis der Pauling'schen kovalenten Radiusen und des Ionenradius des Metallatoms in sechsfacher Koordination ist undI _i die Summe des Ionisierungspotentials des Metallatoms in kJ·mol^–1.

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Résumé Les études antérieures qui reliaient les caractéristiques de la décomposition thermique des oxalates métalliques à la nature de la liaison sont restées limitées à des relations qualitatives. Une relation quantitative qui permet de prédire les températures de décomposition thermiqueT _d (°C) des oxalates de métaux est présentée ici:T _d =516–1.4006r _c /r _i , I _i oùr _c /r _i est le rapport du rayon covalent de Pauling au rayon ionique de l'atome métallique hexacoordonné etI _i la somme des potentiels d'ionisation de l'atome de métal en kJ·mol^–1.

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, , . , T _d (°) :T _d =516–1.4006r _c /r _i ,I _i r _c /r _i — , aI _i — , · ^–1.

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Excerpt from a Dissertation by I. A. Kahwa, in fulfilment of the requirements for the degree of M. Sc. at the University of Dar es Salaam.

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The authors wish to thank the University Research and Publications Committee for grants which enabled carrying out of the preliminary studies, and the Staff Development Committee of the University of Dar es Salaam for financial support to I. A. Kahwa.     

Etude cinetique non isotherme de la decomposition thermique du complexe dipyridinique de bromure de cadmium

Résumé Les paramètres cinétiques de la décomposition du complexe CdPy₂Br₂ ont été déterminés à l'aide de plusieurs méthodes nonisothermes à l'aide des données fournies par la thermogravimétrie et l'ATD. Les valeurs obtenues concordent de faÇon satisfaisante.

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Six nonisothermal thermogravimetric and DTA methods have been applied for determining the kinetic parameters of the decomposition of CdPy₂Br₂. The values obtained are in satisfactory agreement.

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Zusammenfassung Die kinetischen Parameter der Zersetzung des Komplexes CdPy₂Br₂ wurden durch verschiedene nicht-isotherme Methoden, durch Thermogravimetrie und Differentialthermoanalyse bestimmt. Die Resultate stimmten gut überein.

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6 CdPy₂Br₂. .

     

Influence of the gas phase on metallic reference electrodes used in work function measurements

Contact potential differences between electrodes of Pt, Au and Ta of different surface finishing were measured by the dynamic condenser method in propylene and oxygen. Propylene is irreversibly adsorbed, thus changing the work function. This renders the electrodes unsuitable as standard electrodes for work function measurements on catalysts in the atmosphere of hydrocarbons, but they may be used in adsorption studies on oxygen.

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Pt, Au Ta . , , . , .

     

Photochemical reactions of anthraquinone with hydrocarbons in the presence and absence of oxygen: Trapping of radical intermediates

Radical intermediates formed at 25°C in the presence and absence of oxygen during the photolysis of anthraquinone in aromatic, cyclic and aliphatic hydrocarbon solvents were trapped by 2,6-dichloronitrosobenzene, 2,6-dibromonitrosobenzene and 2,4,6-tribromonitrosobenzene. The resulting nitroxide radicals have been characterized in situ by ESR spectra.

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: 2,6-, 2,6- 2,4,6-— , , 25°C. .

     

Nature of intermediates in the synthesis of hydrocarbons from methanol

According to the GC-MS analysis of the composition of liquid hydrocarbons obtained in methanol conversion on ZSM-5 zeolites and the selectivity of cyclohexene conversion on these catalysts, the sequence of the aromatization reaction steps is discussed.

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-- , ZSM-5, .

     

Propagation of vibrational excitation in an adsorbed layer

Using a crystal model with an adsorbed layer, the propagation of vibrational excitation induced by an adsorbed particle is considered. The relaxation times of excitation have been estimated. The role of excitation transfer processes in adsorption-desorption phenomena is discussed.

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, . . - .

     

Dissociative adsorption of propene on chromium molybdate

TPD studies of the interaction of propene with oxidized chromium molybdate have revealed that propene is reversibly chemisorbed on the Cr(MoO₄)₃ surface. The kinetic order of propene desorption is close to 2, which indicates a dissociative character of adsorption. It permits to suggest the presence of a -allyl complex of propene on the surface.

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. , . , . - .

     

George Martine,M.D., F.R.S. (1700–1741) an early thermal analyst?

A study of the life and work of George Martine, who seems to have been the first to have used the principle of differential thermal analysis, reveals that his stature scientifically (and perhaps medically) has not as yet been fully appreciated. A complete bibliography of his writings is appended.

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Zusammenfassung Durch das Studium von Leben und Werk von George Martine, der augenscheinlich der erste Anwender der Prinzipien der Differentialthermoanalyse war, wird offenkundig, daß sein Wesen bisher wissenschaftlich (und möglicherweise auch medizinisch) nicht gebührend gewürdigt wurde. Eine komplette Bibliographie seiner Schriften ist beigelegt.

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. , , , , , ( ) . .

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The author expresses his sincere gratitude to Mr R. N. Smart of the University of St. Andrews Library, Mr A. J. Clark, Deputy Librarian of the Royal Society, Mrs. J. Currie and Ms. J. Archibald of Edinburgh University Library, Dr. H. MacDonald of the National Library of Scotland, Ms. J. A. Beavan of Aberdeen University Library and all those contacted regarding the existence of a portrait of George Martine for their information and assistance, without which this article could not have been compiled.     

Influence of water vapor on propylene oxidation on VMo catalyst

The dependence of reaction rates for acetone and acetic acid formation on the concentration of water vapor is determined on the basis of the participation of surface hydroxy groups and Brönsted acid centers of the catalyst.

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