Simulation of synergism phenomena in inhibition of styrene oxidation by organic phosphite and chromium(III) acetylacetonate

The rate constants for the reaction of styrene peroxy radicals with free and complexed phosphite molecules have been determined together with the rate constant for complex formation of Cr³⁺ with phosphite.

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(Cr⁺³) .

     

Temperature-dependence of electromechanical coupling and strain in barium titanate hafnate transducer

The electromechanical coupling factor and ferroelectric hysteresis loops were investigated at different temperatures for BaTi_0.85Hf_0.15O₃ transducer. Maximum polarization and strain were obtained near the transition of the crystal structure. This correlated with increases in the ease and extent of ferroelectric domain boundary motion. The change in the crystal structure varied the unit cell volume, leading to higher strain.

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Zusammenfassung Der elektromechanische Kopplungsfaktor und die ferroelektrische Hysteresisschleife wurde für BaTi_0.85Hf_0.15O₃-Transducer bei verschiedenen Temperaturen untersucht. Polarisation und Deformation nehmen in der Nähe des Umwandlungspunktes der Kristallstruktur maximale Werte an. Dies korreliert mit Leichtigkeit und Außmaß der Grenzbewegung im ferromagnetischen Bereich. Die mit der Umwandlung der Kristallstruktur zusammenhängende Veränderung des Elementarzellenvolumens führt zu größerer Verformung.

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BaTi_0.85Hf_0.15O₃ . . . , .

     

Kinetics of the selective hydrogenation of phenol to cyclohexanone over a Pd-alumina catalyst

The most suitable kinetic equation for the selective hydrogenation of phenol to cyclohexanone on a 0.96wt.% Pd-9.63wt.%CaO-alumina (Harshaw AL-3965) catalyst is determined among a series of models based on Langmuir-Hinshelwood-Hougen-Watson theory.

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0,96 . %Pd-9,63 .%CaO/Al₂O₃ (Harshaw AL-3965). , ---.

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Electrocatalytic oxidation of cyclohexane by molecular oxygen in non-aqueous solvents in the presence of perchloric acid and perchlorates

Several new electrocatalytic systems are described for the oxidation of cyclohexane by molecular oxygen at room temperature. The solvent is acetonitrile. Perchloric acid and perchlorates are used as supporting electrolytes. The maximum electrochemical yield amounts to 9.6% and is observed in the presence of perchloric acid.

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, . , — . 9,6% — .

     

Modifying action of carbon dioxide in catalytic oxidation of ethylene on silver

Carbon dioxide exerts a strong inhibitory effect on oxygen adsorption and complete oxidation of ethylene on silver but has little effect on the rate of ethylene oxidation to ethylene oxide.

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.

     

AES studies on a Pd-modified silver catalyst

Silver crystals electrodeposited from AgNO₃ (8%) and Pd²⁺ (250 mg/dm³) electrolyte before and after exposing to the conditions of the methanol to formaldehyde oxidation process were investigated by AES. Carbon, sulfur, oxygen and palladium on the surface were observed. Higher Pd concentration on the silver surface than in the bulk was found. Its amount on the surface decreased with the temperature increase.

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, - , AgNO₃ (8%) Pd⁺² (250 /), AES. , , - . , - Pd , , .

     

A stochastic analysis of catalyst deactivation in presence of external transfer limitations

The paper analyzes the simplest case of concentration independent deactivation of a catalyst surface in the presence of external transport limitations and accounts for the variations around the mean value of the activity of the catalysts leading to a stochastic formulation. The results reveal interesting features which would not be evident from the conventional deterministic analysis.

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- , , . , .

     

A metal reactor for the diaphragm method with chambers providing complete mixing

A new metal reactor with two chambers in which complete mixing of gases is achieved has been developed for use in the diaphragm method. This apparatus is suitable for the determination of the effective diffusion coefficient and its temperature dependence. It can also be used to determine the type of transport, the gas permeability coefficient and to investigate the macrokinetics of catalytic processes.

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. : ; ; .

     

X-ray photoelectron (ESCA) spectra of some fluorine containing aluminas

The binding energies of the F(1s) and Al(2p) electrons in fluorine containing alumina catalysts are reported. The X-ray photoelectron peaks confirm the formation of a bulk phase of AlF₃ at higher fluorine contents, whereas the fluorine signals at lower percentages originate from surface groups which are substituted by fluorine. By comparing X-ray photoelectron spectroscopy with X-ray diffraction we conclude that the combination of these techniques is a potential tool in detecting crystals on a catalyst surface which have a size under the detection limit of X-ray diffraction.

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F(1s) Al(2p) , . AlF₃ , , . , , , .

     

Isomerization, dehydrogenation and cracking of methylcyclohexane over HNaY zeolites

On HNaY zeolites the fractions of acid sites which are active for cracking, isomerization and dehydrogenation of methylcyclohexane do not increase linearly with increasing degree of exchange. Isomerization and dehydrogenation seem to involve a similar activated complex, while cracking proceeds through a different one and requires stronger acid sites. Activation energies are independent of exchange degree.

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HNaY, , . , . .

     

Anwendung der Momentenmethode bei thermophysikalischen Messungen

Zusammenfassung Es wird die Anwendung der Momentenmethode zur Auswertung von instationären Versuchen zur Bestimmung der spezifischen Wärmekapazität und der Temperaturleitfähigkeit beschrieben und anhand von eigenen Untersuchungen illustriert.

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Moment equations have been derived for the evaluation of non-stationary thermophysical measurements for determining the specific heat capacities and thermal conductivities of solids. For specific examples the application of these equations is shown, with evaluation of temperature response curves of a solid in an agitated vessel for the cases of a step change in the surrounding gas, a rectangular thermal pulse and linear temperature rise (DTA).

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Résumé On a utilisé la méthode des moments pour dépouiller les résultats des expériences en régime non-stationnaire afin de déterminer la chaleur spécifique et la conductibilité thermique des corps solides. La méthode est illustrée à l'aide d'exemples spécifiques.

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. , ( ).

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Calorimetric studies of adsorptive properties of metallic carbides and nitrides of transition elements. Adsorption of H2, CO and O2 on titanium nitrides

Adsorption heats of hydrogen, oxygen and carbon monoxide on titanium nitrides have been measured calorimetrically in the temperature range from 473 to 673 K. With increasing Me/N ratio, the adsorption heat of oxygen grows.

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, 473–673 . Me/N.

     

Cyclohexane conversion on nickel mordenite

Two series of nickel mordenite catalysts have been prepared on the basis of Na-mordenite and H-mordenite. Their catalytic activity in cyclohexane conversion has been studied. It has been found that the properties of the catalysts are strongly dependent on the acidity of mordenite.

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NaM HM. .

     

Synthesis and structure of (pyridine) bis(acetylacetonato) (1-methyl-1-phenylethylperoxo) cobalt (III)

Synthesis and structure of (pyridine) bis(acetylacetonato) (1-methyl-1-phenylethylperoxo) cobalt(III) complex are described.

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() () (III).

     

Materials testing by Dynamic mechanical analysis

Applications of the new 980 Dynamic mechanical analyser (DMA) to the study of thermoplastic polymers, thermosetting polymers and metal glasses have been discussed in this paper. This instrument has also been used to study impact modified thermoplastics [2] elastomers [3] and metals. DMA is one of the thermo-analytical thechniques available to the research or quality control chemist for evaluating the mechanical properties of materials. With the introduction of the 980 it is anticipated that the disadvantages due to long operation time and complexity inherent in older instrumentation will no longer hold back progress towards the full realisation of the technique.

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Zusammenfassung Der Einsatz des neuen 980 Dynamic Mechanical Analysers zur Untersuchung thermoplastischer und auf Hitzeeinwirkung fest werdender Polymere, sowie Metallgläser, wird in dieser Veröffentlichung beschrieben. Dieses Instrument wurde auch zur Untersuchung von durch Stoss modifizierten thermoplastischen Stoffen [2], Elastomeren [3] und Metallen verwendet. Die dynamische mechanische Analyse ist eine der für den Forschungsoder Kontrollchemiker bei der Bewertung der mechanischen Eigenschaften der Stoffe nützlichsten zur Verfügung stehenden thermoanalytischen Techniken. Die Einführung des Modells 980 gestattet die Folgerung, daß die bei den früheren Instrumenten als Nachteil verzeichnete lange Arbeitsdauer und Komplexität nunmehr dem Fortschritt in Richtung vollständiger Realisierung dieser Technik nicht mehr im Wege stehen werden.

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Résumé L'application du nouvel analyseur mécanique 980 à l'étude des polymères thermoplastiques, des polymères thermodurcissables et des verres métalliques est discutée. L'instrument a également été utilisé pour l'étude des thermoplastiques traités par percussion [2], des élastotnères [3] et des métaux. L'analyse mécanique dynamique est l'une des techniques d'analyse thermique les plus utiles pour évaluer les propriétés mécaniques des matériaux, aussi bien en recherche que pour les opérations de contrôle de qualité. Avec l'introduction du modèle 980, il est prévisible que les inconvénients des instruments précédents, dus à la durée et à la complexité des opérations, n'entraveront pas le développement de cette technique.

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980 , . , , . , . 980 , , , , .

     

Thermal degradation of some polymers based on ethylene glycol dimethacrylate

Thermogravimetric analysis and pyrolysis in combination with gas chromatography were used to study the thermal behaviour of some cross-linked polymers of ethylene glycol dimethacrylate. The investigated polymers show a complex thermal degradation mechanism. The complexity of the reaction increases together with increase of the ethylene glycol chain in the macromolecule and with increase of the pyrolysis temperature. At low temperature, the thermal decomposition products of the analyzed polymers are mainly the constituent monomers. At high temperatures, besides the monomer, other decomposition products are formed as a result of thermal cracking reactions, i.e. secondary reactions of decomposition and recombination.

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Zusammenfassung Zur Untersuchung des thermischen Verhaltens einiger quervernetzter Polymere auf Äthylenglykoldimetacrylatbasis wurden thermogravimetrische Analyse und Pyrolyse in Zusammenhang mit der Gaschromatographie angewendet. Die untersuchten Polymere zeigten einen komplexen thermischen Zersetzungsmechanismus. Die Komplexizität der Reaktion nimmt mit Zunahme der Anzahl der Äthylenglykolketten im Makromolekül und mit Zunahme der Pyrolysentemperatur gleichermaßen zu. Bei niedrigeren Temperaturen stellen die Hauptzerfallsprodukte der analysierten Polymere hauptsächlich deren Monomere dar. Bei höheren Temperaturen werden als Ergebnis thermischer Krackreaktionen, z. B. sekundäre Zersetzungs- und Rekombinationsreaktionen, neben den Monomeren auch andere Zersetzungsprodukte gebildet.

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. . . . , , , .

     

The Stevens rearrangement of methylenedimethyloxonium ylide: A quantum chemical study

The conversion of methylenedimethyloxonium ylide to ethyl methyl ether was investigated by the semiempirical MNDO method. An activation energy of 51 kJ/mol suggests that this rearrangement is a possible elementary reaction in the well-known MTG process.

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. 51 /, , .

     

Comparative thermal analysis (CTA) of thermally-stable polymers and model compounds. Polyimides and model compounds

The method of comparative thermal analysis has been used to determine the thermal stability of polyimides and their model compounds. The extent of defects in the investigated polyimides was determined by gas chromatography. The dependence of the extent of the defects on the chemical structure of the initial components and the supermolecular structure of the polyimides was established.

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Zusammenfassung Die Methode der vergleichenden Thermoanalyse wurde zur Bestimmung der Hitzestabilität von Polyimiden und ihren Modellverbindungen eingesetzt. Das Ausmass der Defekte in den untersuchten Polyimiden wurde gaschromatographisch bestimmt. Die Abhängigkeit des Umfangs der Defekte von der chemischen Struktur der Ausgangskomponenten und der supermolekularen Struktur der Polyimide wurde festgestellt.

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Résumé La méthode d'analyse thermique comparée (CTA) a été utilisée pour étudier la stabilité thermique des polyimides et de leurs composés modèles. On a déterminé par chromatographie en phase gazeuse l'étendue des défauts dans les polyimides étudiés. On a établie de même les rapports qui existent entre l'étendue des défauts dans la structure chimique des composants initiaux et la structure supermoléculaire des polyimides.

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, . . .

     

The question of thermal decomposition of pyrite

The thermal decomposition of monomineral pyrite was studied in an inert atmostphere. From an analysis of the values of the thermal effects, an interpretation of the hree physicochemical processes recorded in the thermoanalytical curves is proposed.

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Zusammenfassung Die thermische Zersetzung von monomineralem Pyrit wurde in inerter Atmosphäre untersucht. An Hand der Analyse der Werte der thermischen Effekte wird eine Beschreibung dreier, in den thermoanalytischen Kurven festgehaltener physikalischchemischer Vorgänge vorgeschlagen.

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Résumé On a étudié la décomposition thermique de la pyrite, en atmosphère inerte. On propose une interprétation des trois processus physicochimiques enregistrés sur les courbes thermoanalytiques, qui repose sur l'analyse des effects thermiques.

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- , .