Influence of the preparation method on the pore spectrum of Pt?Cr/Al2O3 and Pt?Sn/Al2O3 catalysts

It is shown that, in contrast to classical impregnation methods, in bimetallic catalyst production the texture of the carrier is stabilized by introducing the promoting ion on the surface of Pt/Al₂O₃ with vapors of CrO₂Cl₂ or SnCl₄. This is shown by a relatively slower decrease of the specific area and the volume of the pores upon calcination.

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, Pt/Al₂O₃- CrO₂Cl₂ SnCl₄ . .

     

Dehydrogenation activity of H-Y and RE-Y zeolites in decomposition of tetrahydrothiophene

Dehydrosulfurization of tetrahydrothiophene in nitrogen on H-Y and RE-Y zeolites was accompanied by dehydrogenation to thiophene. Neither reaction was influenced by hydrogen and water in the feed. The selectivity was independent of catalyst coking, which suggests a common origin of both functions.

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H-Y RE-Y . , . , , .

     

SIMS studies of water vapor adsorption on polycrystalline rhodium

Studies of water vapor adsorption on polycrystalline Rh at T>315 K and P=(2–4)×10^–2 Pa indicate that water is adsorbed dissociatively to O_ads and O_ads through a molecularly adsorbed species. Desorption activation energy is 46 and 69 kJ/mol for molecular and dissociative species, respectively.

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Rh (2–4)·10^–2 . , O OH - . 46 /, -69 /.

     

Factors determining the increased activity of metal catalysts in comparison with non-metallic ones in hydrocarbon oxidation

Studies of the activation of hydrocarbons in their oxidation over metals and oxides permit to interpret the observed relations between the activities (r) of optimal metal and oxide catalysts and the slope of the lg r vs. q_s curves (qs is the bond energy of surface oxygen).

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, lgr–q_s (q_s- ).

     

Effect of α-methylstyrene of the curing behaviour of vinyl ester resins

The curing behaviour of bismethacryloxy derivative of diglycidyl ether of bisphenol A (vinyl ester resin) containing styrene as the reactive diluent (40% w/w) was studied using gel point determination method and DSC. Seven samples of styrene/-methylstyrene in the ratio 400, 355, 3010, 2515, 2020, 1525 and 040 were studied. Delayed curing was observed in samples containing increasing proportions of -methylstyrene. The energy of activation decreased from 869 kJ mol^–1 to 333 kJ mol^–1 as the concentration of -methylstyrene increased in the formulations. However, no difference in thermal stability was observed by replacement of styrene by -methylstyrene. It was concluded that in vinyl ester resin samples 10–15% -methylstyrene and 30-25% styrene can be used as reactive diluent.

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Zusammenfassung Mittels DSC und Bestimmung der Gelierungstemperatur wurde das Aushärteverhalften des Bismethakryloxyderivaten des Diglycidyläthers von Bisphenol A (Vinylesterharz) mit 40 Gewichtsprozenten Styrol als reaktives Streckmittel untersucht. Es würden sieben Proben mit einem Styrol/-Methylstyrol Verhältnis von 400, 355, 3010, 2515, 2020, 1525 und 040 untersucht. Mit steigendem Anteil an -Methylstyrol konnte eine Verzögerung der Aushärtung sowie ein Absinken der Aktivierungsenergie von 869 kJ · mol^–1 auf 333 kJ · mol^–1 beobachtet werden. Der Ersatz von Styrol durch -Methylstyrol veränderte jedoch die thermische Stabilität in keiner Weise. Vinylesterharzproben mit 10–15% -Methylstyrol und 30–25% Styrol können als reaktive Streckmittel in Vinylesterharzen verwendet werden.

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- - , 40 .% . /-, 400, 355, 3010, 2515, 2020, 1525 040. - . - 869 333 · ^–1. , .. , , 10–15% - 30–25% .

     

Kinetic study of the thermal dehydration of syngenite K2Ca(SO4)2·H2O under non-isothermal conditions

Different calculation methods applied to TG, DTG and DTA curves obtained with a Mettler Thermoanalyzer at one or several heating rates have been tested. It has been shown that the dehydration of syngenite can best be described by the Avrami equation I [–1n(1–)]^1/2=3.46·10²¹exp (–2.73·10⁴/T)·t where is the degree of decomposition,T the absolute temperature, andt the time.The mean value of the activation energy is 54 kcal·mole^–1. This is in good agreement with the results obtained under isothermal conditions. The method of atava and kvára, supplemented by the numerical tables of Zsakó, is most useful in obtaining the kinetic equations describing the thermal decomposition of solids.

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Zusammenfassung Mit verschiedenen Berechnungsmethoden wurde anhand der TG, DTG und DTA-Kurven, die bei einer und mehreren Aufheizgeschwindigkeiten der Probe im Thermoanalysator der Firma Mettler erhalten wurden bewiesen, daß die kinetische Gleichung zur Beschreibung des Dhydratisierungsprozesses des Syngenits folgende Gestalt hat: [–1n(1–)]^1/2=3.46·10²¹ exp (–2.73·10⁴/T)·t (-Zersetzungsgrad,T absolute Temperatur,t-Zeit) Der Mittelwert der Aktivierungsenergie beträgt: 54 kcal·mol^–1. Die Gleichung und die Werte der kinetischen Parameter stimmen gut mit den Ergebnissen der isothermen Experimente überein. Bei den Untersuchungen thermischer Reaktionen der Zersetzung von Festkörpern hat sich die Methode von atava und kvára, ergänzt durch die numerische Tabelle von Zsakó als besonders geeignet erwiesen.

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Résumé Divers procédés de calcul appliqués aux courbes TG, TGD et ATD obtenues à l'aide d'un thermoanalyseur Mettler, avec une ou plusieurs vitesses de chauffage, conduisent à l'équation cinétique suivante pour exprimer le processus de déshydratation de la syngénite: [–1n (1–)]^1/2=3.46·10²¹exp (–2.73·10⁴/T)·t où =degré de décomposition,T=température absolute,t=temps. La valeur moyenne de l'énergie d'activation est 54 kcal·mol^–1, en bon accord avec les résultats des études en conditions isothermes. La méthode de atava et kvára, combinée avec les tables numériques de Zsakó, s'est révélée la plus efficace pour l'obtention de l'équations décrivant la cinétique de la décomposition thermique des corps solides.

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« » -, , . , , : [–1n(1–)]^1/2=3.46·10²¹ exp (–2.73·10⁴/T)·t - ,— ,t — . , 54 . ^–1. , . , , -log() III III.

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The authors would like to thank Dr. E. M. Bulewicz of this Department for valuable discussions, and Dr. M. Szakowicz and Mr. B. Gawliczek for carrying out the measurements on the Mettler instrument at the Institute of Metallurgy at the School of Mining and Metallurgy in Cracow.     

Thermogravimetric and EPR study of the solid-state reactions between zinc chromate and zinc oxalate

The formation of some catalytically active Cr(V) and Cr(III) species is studied when the progressive thermal reduction of zinc chromate is enhanced by the addition of solid zinc oxalate, the reducing agent CO being formed in situ, during thermal analysis.When compared with the decomposition of pure ZnCrO₄, Cr(VI) reduction, as followed by EPR, is similar concerning the nature of the intermediate Cr species formed: Cr(V), Cr(III) in a Cr₂O₃-like bulk phase and Cr(III) dispersed in ZnO. However, the temperature range of Cr₂O₃ formation, as well as the magnitude of the Cr(III)-Cr(III) interaction in such a phase is found to be strongly dependent on the amount of ZnO formed. On the other hand, after the Cr(V) species resulting from progressive oxygen release have disappeared, some other stable Cr(V) species are formed again at higher temperatures. Their formation may be related to a further reduction of the remaining Cr(VI) species by CO stemming from the oxalate.

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Zusammenfassung Die Bildung einiger katalytisch aktiver Cr(V) und Cr(III) Species wird für den Fall untersucht, bei dem die progressive thermische Reduktion von Zinkchromat durch Zugabe von festem Zinkoxalat gefördert wird, wobei das Reduktionsmittel CO in situ, während der Thermoanalyse gebildet wird.Ein Vergleich mit der Zersetzung der reinen ZnCrO₄ ergibt die ÄhnIichkeit der durch EPR verfolgten Cr(VI)-Reduktion hinsichtlich der Beschaffenheit der gebildeten Cr Intermediärspecies: Cr(V), Cr(III) in einer Cr₂O₃-artigen Hauptphase und Cr(III) in ZnO dispergiert. Jedoch sind Temperaturbereich der »Cr₂O₃«-Bildung sowie der Umfang der Cr(III)-Cr(III) Wechselwirkung in einer solchen Phase stark von der Menge des gebildeten ZnO abhängig. Andererseits werden nach dem Verschwinden der durch die progressive Sauerstoff-Freisetzung entstandenen Cr(V)-Species wider einige andere stabile Cr(V)-Species bei höheren Temperaturen gebildet. Ihre Bildung mag mit einer weiteren Reduktion der noch vorhandenen Cr(VI)-Species durch aus dem Oxalat stammendes CO verbunden sein.

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Cr(V) Cr(III) , , , , . , Cr(VI), ZnCrO₄ . , Cr : Cr(V) Cr(III) , Cr₂₃, Cr(III) ZnO. , «Cr₂₃», Cr(III)-Cr(III) . , , Cr(V) , Cr(V) . Cr(VI) , .

     

Kinetics of p-xylene oxidation catalyzed by cobalt oxide

Kinetics of p-xylene oxidation in an aqueous system catalyzed by cobalt oxide have been studied at 140 °C under oxygen. The reaction is second order in p-xylene and first order in cobalt oxide concentration. The rate constant and product distribution are very close to those found for homogeneous catalytic reactions. Based on these findings, a reaction scheme describing the influence of oxide catalyst is formulated. - , , 140° C . - . , . , .     

Digital temperature programmer with two temperature sensors

A new temperature programmer has been developed to provide accurate and sharp temperature programs for different ovens and furnaces, including those of thermoanalytical instruments. Control is based on two temperature sensors (thermocouples or resistance thermometers); sensor A is situated in the working space of the furnace (in the vicinity of the sample), while sensor B is near the heating wire.The principle of operation and the effects of controls are discussed, and several examples are presented to demonstrate the use of the programmer with different heater assemblies.

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Zusammenfassung Ein neues Temperaturprogrammiergerät wurde zur Herstellung genauer und scharfer Temperaturprogramme für verschiedene Öfen, thermoanalytische Geräte mit inbegriffen — erarbeitet. Die Steuerung beruht auf zwei Temperatursensoren (Thermoelemente oder Widerstandsthermometer); der SensorA befindet sich im Arbeitsraum des Ofens (in der Nähe der Probe), der SensorB ist in der Nähe der Heizwicklung.Das Arbeitsprinzip und der Effekt der Steuerungen wird erörtert und mehrere Beispiele angeführt, um die Anwendung des Programmiergeräts mit verschiedenen Heizvorrichtungen zu zeigen.

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Résumé On a mis au point un nouveau programmeur de température afin d'obtenir des programmes de température exacts et nets avec divers fours, y compris ceux des instruments d'analyse thermique. Le contrôle repose sur deux senseurs de température (thermocouples ou thermomètres à résistance); le senseurA se trouve dans l'espace de travail du four (à proximité de l'échantillon), le senseurB se trouve près du fil de chauffage.Le principe de l'opération et l'effet du contrôle sont discutés; plusieurs exemples montrent l'application du programmeur avec différents dispositifs de chauffage.

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, , . , A ( ), B- . . , .

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Digital Temperature Programmer LP 839 has been developed at Budapest Technical University. It is manufactured by CHINOIN, and exported by METRIMPEX and AKADIMPORT Budapest, Hungary.     

Temperature-dependence of electric and photovoltaic properties of HgTe thin film

The I–V characteristics of an illuminated thin film of HgTe and of a dark sample were recorded. The high values of the photoelectric current of the illuminated sample as the distance decreased may be due to the impurity conductivity, that can be higher than the band conduction predominating at higher incident energy. In the dark, the impurity conductivity is always low compared to the band conductivity occurring at the higher incident energy of mercury light. The low mobility and the increase of the activation energy with increasing temperature suggest that more than one conduction mechanism is involved. The high density of acceptor centres in the thin layer of HgTe may affect the conduction current in certain temperature ranges.The dielectric constant of the HgTe thin film was measured at different temperatures. The increase of the dielectric constant might be due to point defects which are Hg-vacancy or Te-interstitial acceptors. HgTe has an excess of Te and the net hole concentration (p-n) can be altered by increasing the ionized acceptor defects which migrate through the cubic crystallites to accumulate at the electrodes, giving rise to the dielectric constant.

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Zusammenfassung Die Strom-Spannungs-Charakteristik eines dünnen HgTe-Filmes wurde bei Einfall von Licht und im Dunklen registriert. Die hohen Werte des photoelektrischen Stromes der beleuchteten Probe bei abnehmenden Abstand können der durch Verunreinigungen bedingten Leitfähigkeit zugeschrieben werden, die bei größerer Einfallsenergie größer als die Bandleitfähigkeit sein kann. Im Dunklen ist die durch Verunreinigungen bedingte Leitfähigkeit immer gering im Vergleich zur Bandleitfähigkeit beim Einfall größerer Energiemengen von Hg-Licht. Die geringe Mobilität und der Anstieg der Aktivierungsenergie mit ansteigender Temperatur deuten darauf hin, daß am Vorgang mehr als nur ein Leitungsmechanismus beteiligt ist. Die hohe Dichte der Akzeptorzentren in der dünnen HgTe-Schicht beeinflußt den Leitfähigkeitsstrom in bestimmten Temperaturbereichen. Die dielektrische Konstante des dünnen HgTe-Filmes wurde bei verschiedenen Temperaturen gemessen. Der Anstieg der dielektrischen Konstante kann punktförmigen Gitterfehlern, nämlich Hg-Vakanzen oder interstitionellen Te-Akzeptoren zugeschrieben werden. HgTe hat einen Te-Überschuß, und die Gitterfehlstellenkonzentration kann durch Vermehrung der ionisierten Akzeptordefekte verändert werden, die durch die kubischen Kristallite migrieren, sich an den Elektroden anhäufen und so das dielektrische Verhalten bewirken.

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(I–V) HgTe. , , , . , . , . HgTe . HgTe. , Hg- - . (-) , , , .

     

Kinetics of oxidation of ethanol by potassium permanganate in perchloric acid medium

The oxidation of ethanol by permanganate has been found to obey the rate law v=k[MeCHO][MnO ₄ ^– ][H⁺]. The results are compared with those found for chromium (VI) oxidation of the same substrate.

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V=k[MeCHO][MnO ₄ ^– ][H⁺]. , (VI).

     

Kinetics of formation of the mercury/II/-cyanide-bromide mixed ligand complex in dioxan-water solvent mixtures

The kinetics of formation of the mercury/II/-cyanide-bromide mixed ligand complex have been studied spectrophotometrically at 25°C, in dioxan-water mixtures of different compositions. The reaction can be described by the rate equation of a simple second-order reversible process. The rate constants of both the forward and reverse reaction vary periodically with the solvent composition, whereas the equilibrium constant of the reaction does not change to a large extent. The unusual behaviour of the rate constants is due to selective solvation of the reactants.

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- (ІІ) 25°C, - . . — — , . .

     

Characterization of Ni supported on alumina by hydrogen-oxygen titration

Hydrogen-oxygen titration was performed on Ni/-Al₂O₃ supported catalysts. Hydrogen chemisorption is used to determine the surface area. An excess in oxygen consumption was observed and related to NiO formed in the bulk. A model is proposed which takes into account the formation of an oxide in the subsurface layers of the metal.

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H₂–O₂ Ni/-Al₂O₃. H₂ . , NiO . , .

     

Influence of Cyclodextrins on the Kinetics of Oxidation of Amino Acids and BSA by Hydrazyl Radicals

The kinetics of oxidation of amino acids (Arg, His, Lys, Phe, Thr and Tyr), a dipeptide (Gly-His), and BSA (bovine serum albumin) by two persistent water soluble free radicals of the hydrazyl type has been studied.The rate decreases in the order Arg>Lys>Tyr>Thr>HisBSAPheGly-His with bothfree radicals. Addition to the reaction mixture of - and -cyclodextrin decreases the oxidation rate, probably due to amino acidencapsulation in the cyclodextrin cavity. -Cyclodextrin protects more efficiently against oxidation than -cyclodextrin.     

Acetylacetonate of indium: Structure and reactivity with 1,3-dienes

The reaction of isoprene and 2,3-dimethyl-1,3-butadiene with indium tris-acetylacetonate, afforded C- and O-al-kylation products together with an oligomeric mass. A mechanism of diene transformation is proposed in which -diene-metal species could be involved.

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2,3--1,3- – - . , --.

     

Thermal neutron activation analysis of Cu in its ores by using an241Am−Be neutron source

A thermal neutron activation method has been developed for the determination of Cu in Cu–Pb–Zn ores and chalcopyrite ore concentrates using the reaction⁶³Cu(N, )⁶⁴Cu. The samples were irradiated with thermal neutrons from an²⁴¹Am–Be neutron source and the annihilation -radiations of 0.511 MeV were counted on 3×3 NaI(T1) detector coupled with single channel pulse height analyzer. The method is nondestructive, economical and ideal for bulk analysis of ores with 1–16% Cu.     

Microthermogravimetric studies of the kinetics and thermodynamics of heterogeneous reactions in sulfur-containing atmospheres

A thermobalance for studies of the high-temperature sulfidation of metals and alloys is described. This apparatus permits the determination of mass changes in the sulfidized sample as functions of temperature and sulfur vapour pressure with an accuracy of 10^–6 g. Besides heterogeneous kinetics measurements, it has been shown that the chemical diffusion coefficients and deviations from stoichiometry of metal sulfides can also be studied as functions of temperature and sulfur pressure by means of equilibration measurements.

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Zusammenfassung Es wird eine Thermowaage zur Untersuchung der Hochtemperatur-Sulfidierung von Metallen und Legierungen beschrieben. Diese Apparatur ermöglicht die Bestimmung von MassenverÄnderungen der sulfidierten Proben in AbhÄngigkeit von der Temperatur und dem Schwefeldampfdruck mit einer Genauigkeit von 10^–6 g. Es wird gezeigt, da\ damit, sofern Gleichgewichtsmessungen ausgeführt werden, auch die chemischen Diffusionskoeffizienten und Abweichungen der Metallsulfide von der Stöchiometrie in AbhÄngigkeit von der Temperatur und dem Schwefeldampfdruck untersucht werden können.

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. 10^–6 . , , , .

     

Simulation of the molecular and electronic structure of C60 fullerene π-complex with twelve half-sandwich species FeC5H5

The problem of existence of ⁵--complexes of fullerenes and their derivatives is discussed. The stability of the ⁵--complex C₆₀(FeCp)₁₂ (viz., icosahedral C₆₀ fullerene coated with twelve FeCp groups, each coordinated to its own pentagonal face of the fullerene cage) was first estimated in the framework of density functional approach (PBE approximation). The molecular and electronic structure of a biradical complex of C₆₀ fullerene with ten FeCp groups, C₆₀(FeCp)₁₀ (D _5d symmetry), and a 2⁵--complex of substituted fullerene H₁₀C₆₀, H₁₀C₆₀(FeCp)₂ (D _5d symmetry) in which hydrogen atoms are attached to the C atoms in the -positions relative to the atoms of the polar five-membered cycles, was simulated. According to calculations, the coated complex, I _h-C₆₀(FeCp)₁₂, should be much more stable than the complex of naked fullerene with one or two polarly located FeCp groups and only slightly less stable than the ferrocene molecule FeCp₂. The existence of C₆₀(FeCp)₁₂ and H₁₀C₆₀(FeCp)₂ complexes was suggested.