Die Bestimmung von Sauerstoffisotopen

Ohne Zusammenfassung     

On the compensation of heterovalent ferric ions in the lattice of barium titanate single crystals

The introduction of heterovalent ferric ions into the titanium sites of the BaTiO₃-lattice of single crystals prepared by the fluoride process is due to the formation of oxygen vacancies and to the introduction of F-ions into the oxygen sites. Experimental results obtained by physical and chemical methods show the dependence of both mechanisms of compensation on the iron content of the crystals.     

Phenolische Antioxydantien

Ohne Zusammenfassung     

Radiometrische Ultramikrobestimmung von Harnstoff in Blut

Ohne Zusammenfassung     

Hochfrequenztitrimetrische Bestimmung von Eisen(III)-ionen und ihre Anwendung zur Bestimmung von Oxytetracyclin

Ohne Zusammenfassung     

О ВЛИЯНИИ НЕСТЕХИОМЕТРИИ КИСЛОРОДА НА ПЕТЛИ ГИСТЕРЕЗИСА BaTiO3

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The influence of oxygen non-stoichiometry on the hysteresis loops of BaTiO₃

     

Aminos?uren

Ohne Zusammenfassung     

On the identification of Wiener-Hopf factors

This note is concerned with the identification of the Wiener-Hopf factors of a function 1–f, wheref generates an aperiodic distribution on the integers with a negative mean. The general and rational cases are addressed. We give a concise summary of the main practical facts needed for calculations involving the Wiener-Hopf factors. The basic facts are cited from the literature, but a few aspects are briefly proven here.Supported by the European grant BRA-QMIPS of CEC DG XIII.     

Anwendung von d-Chirasil-Val bei der gas-chromatographischen Analytik von Enantiomeren

Zusammenfassung Der Anwendungsbereich der kommerziell erhältlichen chiralen stationären Phase l-Chirasil-Val wird durch die enantiomere Phase d-Chirasil-Val beträchtlich erweitert. Bei hoher Peakauflösung wird die Präzision der Bestimmung von Enantiomerenreinheiten verbessert, da einige systematische Fehler bei vertauschter Elutionsreihenfolge ausgeschlossen werden können. Unvollständige Peakauflösung infolge von Peaktailing kann verbessert werden, wenn die Hauptkomponente nach dem in geringen Anteilen vorkommenden Enantiomer eluiert wird. Die Zuordnung von Konfigurationsisomeren wird durch Vergleich der Elutionsreihenfolge auf enantiomeren Phasen erleichtert, da der Syntheseaufwand verringert wird.

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Application of d-chirasil-val in the analysis of enantiomers by gas-chromatography

Summary The utility of the commercially available chiral stationary phase l-Chirasil-Val is extended by the enantiomeric phase d-Chirasil-Val. Given high peak resolution, the precision of the determination of the enantiomeric purity is enhanced, excluding some systematic errors by reversing the order of peak emergence. Incomplete peak resolution caused by peak tailing is improved, when the minor enantiomer is eluted before the predominant enantiomer. The assignment of configuration isomers is simplified by correlation of the peak emergence on both enantiomers of the stationary phase, thus reducing the necessary synthetic effort.

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Herrn Prof. Dr. E. Stahl, Saarbrücken, zum 60. Geburtstag gewidmet     

CO<Subscript>2</Subscript> activation on single crystal based ceria and magnesia/ceria model catalysts

Novel multifunctional ceria based materials may show an improved performance in catalytic processes involving CO₂ activation and reforming of hydrocarbons. Towards a more detailed understanding of the underlying surface chemistry, we have investigated CO₂ activation on single crystal based ceria and magnesia/ceria model catalysts. All model systems are prepared starting from well-ordered and fully stoichiometric CeO₂(111) films on a Cu(111) substrate. Samples with different structure, oxidation state and compositions are generated, including CeO_2-x/Cu(111) (reduced), MgO/CeO_2-x/Cu(111) (reduced), mixed MgO-CeO₂/Cu(111) (stoichiometric), and mixed MgO-CeO_2-x/Cu(111) (reduced). The morphology of the model surfaces is characterized by means of scanning tunneling microscopy (STM), whereas the electronic structure and reactivity is probed by X-ray photoelectron spectroscopy (XPS). The experimental approach allows us to compare the reactivity of samples containing different types of Ce³⁺, Ce⁴⁺, and Mg²⁺ ions towards CO₂ at a sample temperature of 300 K. Briefly, we detect the formation of two CO₂-derived species, namely carbonate (CO₃ ^2-) and carboxylate (CO₂ ^-) groups, on the surfaces of all investigated samples after exposure to CO₂ at 300 K. In parallel to formation of the carbonate species, slow partial reoxidation of reduced CeO_2-x/Cu(111) occurs at large doses of CO₂. The reoxidation of the reduced ceria is largely suppressed on MgO-containing samples. The tendency for reoxidation of Ce³⁺ to Ce⁴⁺ by CO₂ decreases with increasing degree of intermixing between MgO and CeO_2-x. Additionally, we have studied the stability of the formed carbonate species as a function of annealing temperature.