On the quantitative reliability of heat flux DSC

In an attempt to explain how the calibration factor of a heat flux DSC cell depends both on the standard utilized and on the experimental variables, a study has been undertaken of the entire DSC trace.This report deals with the second half of the peak and shows that, other experimental conditons being fixed, the peak area increases with increasing heating rate.This accounts for the observed decrease in the calibration factors with increasing heating rate.

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Zusammenfassung Die gesamte DSC-Kurve wurde untersucht, um zu klären, wie der Eichfaktor einer Wärmefluss-DSC vom verwendeten Eichstandard und von den Versuchsbedingungen abhängt. Der vorliegende Teil behandelt den zweiten Abschnitt eines DSC-peaks (vom Maximum an). Es wird gezeigt, dass bei Konstanthalten aller anderen Versuchsbedingungen die peak-Flächen mit steigender Aufheizgeschwindigkeit zunehmen. Das wird als Ursache für die beobachtete Verringerung des Eichfaktors mit steigender Aufheizgeschwindigkeit angesehen.

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, . . , - , . .

     

Characterization of platinum-nickel catalysts by hydrogen-oxygen chemisorption

The use of hydrogen-oxygen titration method to characterize platinum-nickel supported catalysts has shown that the number of oxidized or reduced nickel layers is dependent on the atomic composition. This phenome non involves dynamic changes of the surface probably by a spillover mechanism. A surface reaction scheme based on a previous work is proposed to explain the experimental results.

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- - , . , , . , .

     

Effect of the state of vanadium cations on the IR spectra of adsorbed carbon monoxide

ESR and IR-spectrosocpic studies of the effect of the state of vanadium ions on the IR-spectra of adsorbed CO have revealed complex formation of CO with V⁴⁺ (vCO at 2192 and 2205 cm^–1) and V³⁺ (vCO at 2178 and 2185 cm^–1) ions.

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-- - CO. CO V⁴⁺ (vCO 2192, 2205 cm^–1) V³⁺ (vCO 2178, 2185 cm^–1).

     

Hydrodesulfurization activity and transformations of nickel molybdate hydrate

Nickel molybdate hydrate has been found to be an effective precursor catalyst for the hydrodesulfurization of thiophene. Calcination of the hydrate at 300°C and presulfidation with H₂S are favorable treatments for higher activity.

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, . 300°C H₂S , .

     

Kinetic and mechanistic studies on the oxidation of arginine and histidine by chloramine-T in hydrochloric acid medium

The oxidation of amino acids by chloramine-T (CAT) in HCl medium at 30°C indicates simultaneous catalysis by H⁺ and Cl^– ions in the HCl concentration range of 0.04–0.12 M. The reaction is first order with respect to concentrations [CAT], [H⁺] and [arginine], but zero order with respect to [histidine]. The rate depends also on Cl^– concentration following 0.7th order. At HCl concentrations >0.12 M, the rate equation is:w=k[CAT] [amino acid]^0.6 and is independent of the [Cl^–]. A suitable mechanism has been suggested.

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-T (CAT) HCl (30°C) H⁺, Cl^– [HCl]=0,04–0,12M. [CAT], [H⁺] [] []. [Cl^–]^0,7. [HCl]>0,12M =k · [CAT][]^0,6 [Cl^–]. .

     

Ammonium nitrate changes during thermal analysis

A study was made of the difference occurring in ammonium nitrate during investigation by DTA and by DSC. The results show that the DTA of ammonium nitrate (p.a.) is accompanied by the crystal transformation IV III II I and melting. During DSC investigation of the same ammonium nitrate samples, the salt undergoes the transformations IV III and IV II in parallel; then follow the crystal transformations III II I and melting. The investigation conditions and the history of the samples do not essentially influence the crystal transformations during thermal analysis.

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Zusammenfassung Bei DTA und DSC von Ammoniumnitrat zu beobachtende Unterschiede wurden untersucht. Bei der DTA von p.a. Ammoniumnitrat verlaufen die Kristallumwandlungen IV III II I sowie der Schmelzvorgang. Während der DSC der gleichen Ammoniumnitratproben verlaufen die Übergänge IV III und IV II parallel, worauf die Kristallumwandlungen III II I und der Schmelzvorgang folgen. Die experimentellen Bedingungen und die Vorgeschichte der Proben hat keinen wesentlichen Einfluß auf die während der thermischen Analyse verlaufenden Kristallumwandlungen.

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. ( ..) IV III II I . , IV III IV II - , III II ar I . .

     

Coked reforming catalysts: Self-regeneration by residual hydrogen

The deactivation and subsequent self-regeneration of several Pt/–Al₂O₃/honeycomb reforming catalysts have been investigated. Catalytic activity in the dehydrogenation of methylcyclohexane (MCH), taken as reaction model, has been evaluated at 400 °C in a continuous flow microreactor. The determining role of surface chlorine during the H₂ self-regeneration of catalysts is discussed. A catalyst with ca. 0.5% C1 shows complete self-regeneration. A regeneration mechanism, involving the spillover of residual hydrogen, is proposed.

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Pt/–Al₂O₃ . , , 400°C . . . 0.5% Cl . , .

     

Frequencies, anharmonicities, and dissociation energies of OH groups in H-mordenite

Harmonic frequencies, anharmonicities and dissociation energies of surface hydroxy groups in H-mordenite have been determined. The application of the Lippincott-Schroeder potential function for similar problems is proposed.

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, -. - .

     

Hydrogenation of 4-tert-butylphenol over supported catalysts in different solvents

It has been established that in hydrogenation of 4-tert-butylphenol over Rh/-Al₂O₃ in isopropanol the addition of CH₃COOH increases the yield of 4-tert-butylcyclohexanol.

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, CH₃COOH -4- 4- Rh/-Al₂O₃ .

     

Study of the interaction of atomic oxygen and nitrogen with ruthenium by the bond interaction method

The heats of atomically adsorbed oxygen and nitrogen on Ru(0001) and Ru(1010) planes have been calculated by the semiempirical bond interaction method. The calculations show that oxygen is strongly adsorbed on ruthenium, while molecular nitrogen cannot be chemisorbed on ruthenium.

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- (000I) (I0I0) . , Ru , .

     

Pyroelectricity of Cd-doped telluride thin film

The crystalline structure, electrical conductivity and pyroelecricity of freshly prepared Hg_0.7Cd_0.3Te thin film have been investigated in detail.

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Zusammenfassung Kristallstruktur, elektrische Leitfähigkeit und Pyroelektrizität einer frisch präparierten Hg_0.7Cd_0.3Te Filmschicht wurden ausführlich untersucht.

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, Hg_0.7Cd_0.3Te.

     

Thermal analysis of complexes of cadmium chloride picoline

The thermal decomposition of the, and- picoline complexes of cadmium were studied by means of TG-DTG-DTA. In connection with the preparation of the complex compounds, it was established that the ligand number was influenced by the reaction medium. The thermal decomposition took place stepwise, and intermediates were formed which could be isolated with a derivatograph by the freezing-in method. The structures and properties of these previously unknown compounds were investigated by far-IR spectroscopy and X-ray powder diffraction.

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Zusammenfassung Der thermische Zersetzungsprozess der Komplexverbindungen von Cadmiumchlorid mit-, - oder-Picolin wurde durch simultane TG-DTG-DTA im Derivatograph untersucht. Die Ligandenzahl der Komplexverbindungen wird durch das Reaktionsmedium bei der Präparation beeinflusst. Die thermische Zersetzung erfolgt stufenweise, Zwischenprodukte konnten mittels Derivatograph durch die Einfriermethode isoliert werden. Struktur und Eigenschaften dieser bisher unbekannten Verbindungen wurden durch Fern-IR-Spektroskopie und Röntgenpulverbeugung untersucht.

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- -, -. , . , « ». .

     

Über die Strukturänderung der Söderberg-Anode im Laufe der Elektrolyse

Zusammenfassung Es wurde die Änderung der Struktur der Söderberg-Anode im Laufe der Elektrolyse mit Hilfe der thermischen und mikroskopischen Analyse untersucht. Die Anode wurde in 10 Teilen von oben bis zu ihrem Unterteil im Elektrolyt aufgeteilt und die Teile separat der Untersuchung unterworfen. Die Ergebnisse gaben ausreichende Informationen über die Bildung des Sekundärkokses und über die Ausbildung der Inhomogenität in der Länge der Anode.

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Transformation of the anode structure during the electrolysis process was studied by means of thermal analysis and microscopy. The DTA method was found to be a good complement to traditional microscopic analysis. The autors succeeded in differentiating the formation and development of a secondary coke structure. The secondary coke is formed over half the anode length in the direction of the melt.

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. , . . .

     

Rate of14N2 desorption from the surfaces of nitrides in the presence and absence of15N2 in the gas phase

The rates of¹⁴N₂ desorption from the surfaces of nitrides have been measured in the presence and absence of¹⁵N₂ in the gas phase. Whatever the adsorption heat and the form of surface species, the adsorption of¹⁵N₂ molecules does not affect the rate of¹⁴N₂ desorption.

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¹⁴N₂ ¹⁵N₂ . , ¹⁵N₂ ¹⁴N₂.

     

Deactivation of a high-silica ultrazet zeolite by steam treatment

The activity and selectivity of hydrogen forms of an Ultrazet zeolite, a counterpart of the ZSM-5 zeolite, was studied in the cracking of n-hexane+3-methylpentane. Zeolite modifications by 773 and 1023 K steam treatment are discussed.

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, ZSM-5, - +3-. , 773 1023 K.

     

Determination of organic- and carbonate-carbon in freshwater lake sediments by a microcombustion procedure

A microcombustion procedure specific for the determination of total-, organic- and carbonate-C in freshwater lake sediments is described. The procedure involves combustion of the sample at 650° to obtain organic-C. Total-C is obtained by combustion at 950° and carbonate-C calculated by difference. The procedure was evaluated by differential thermal analyses of representative sediments and known carbonate minerals. A procedure for the identification of dolomite in lake sediments by differential thermal analysis under CO₂ is also described.

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Zusammenfassung Es wurde über ein zur Bestimmung des Gesamt-, Karbonat- und organischen Kohlenstoffgehaltes von Süßwasserrückständen geeigneten Mikroverbrennungsverfahren berichtet. Durch Verbrennen bei 650° erhält man den organischen Kohlenstoff, durch Verbrennen bei 950° den Gesamtkohlenstoff. Der Karbonatkohlenstoff ergibt sich aus der Differenz. Die Methode wurde durch differentialthermoanalytische Prüfung von charakteristischen Sedimenten und bekannten Karbonatmineralien getestet. Ein Verfahren zur Identifizierung von Dolomit in Seesedimenten durch Differentialthermoanalyse unter CO₂ wurde ebenfalls beschrieben.

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Résumé On décrit une méthode spécifique de microcombustion pour déterminer la teneur en carbone total, organique et carbonate dans des sédiments des lacs à eau froide. On reçoit le C organique par combustion à 650°, le C total par combustion à 950° et le carbone à l'état de carbonate, par la différence. On a évalué le procédé par ATD des sédiments représentatifs et de minérais de carbonate connus. On a décrit une méthode pour identifier le dolomite dans les sédiments des lacs, par ATD sous CO₂.

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, , C . C 650° 950°C, , C . . , , CO₂.