Beitrag zur Kenntnis des Systems Vanadin—Chrom—Stickstoff

The System V–Cr–N has been investigated at 1100 and 1400 °C and at nitrogen pressures between 1 and 1000 atmospheres by X-ray techniques. VN and CrN on the one hand and V₂N and Cr₂N on the other are forming complete series of solid solutions. The phase field of the mononitride solid solution is dependent on nitrogen pressure and temperature conditions.

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Auszug aus der Diplomarbeit des Herrn Dipl.-Ing. Dr.W. Schebesta.     

La luminescence différée du styrène en solution vitreuse dans le méthylcyclohexane

The trapping of electrons and styrene cations and anions has been studied in a methylcyclohexane glass by the techniques of deferred luminescence. Radiothermoluminescence curves consist of two peaks, at 90 and 95°K, in this matrix. The second peak increases linearly with styrene concentration up to 2 × 10^?2M when it reaches a constant value, whereas the first peak increases from 10^?4 to 10^?3M and then decreases at higher concentrations and is not discernible at concentrations above 10^?2M. We propose two mechanisms which are qualitatively consistent with this behavior and are based essentially on the recombination of styrene cations with thermally detrapped electrons in the first peak and with anions in the second peak. Photothermoluminescence (i.e., thermoluminescence after photoionization with ultraviolet light) similarly consists of the 90 and 95°K peaks for a 10^?3M solution and of the 95° peak alone for a 10^?d M solution. Radiophotoluminescence excitation spectra at 77°K, corresponding to absorption spectra of trapped electrons and styrene anions, show that anions are the predominant negative species in 10^?2 molar solution, and trapped electrons in 10^?3 molar solution. Spectral analysis of radiothermoluminescenece shows the presence of two emission bands, one of which is identical with styrene fluorescence excited by the 254 Nm mercury line (λ_max = 292, 302, 307, and 317 Nm). The other band has three fairly poorly resolved maxima at 474, 486 and 496 nm and seems to correspond to the fluorescence of C₆H₅?H-CH₃ radicals formed during radiolysis.     

Über die Präparation und die Eigenschaften von Molybdän-Wolfram-Carbonitriden

Molybdenum-tungsten-carbonitrides can be prepared by reacting prealloyed powders of Mo and W with carbon in the presence of nitrogen or ammonia. Single phase carbonitrides (Mo, W) (C, N) with the WC-type structure can be obtained. The nitrogen content of these carbonitrides increases with increasing molybdenum content. Flowing ammonia has a decarburizing effect, which has to be counterbalanced by an addition of a carbonaceous gas such as methane. Nitrogen instead of ammonia is equally effective and gives carbonitrides which have a nitrogen content only insignificantly lower than the carbonitrides obtained in flowing ammonia. The lattice parameters of the carbonitrides are found to be slightly smaller than the lattice parameters of the corresponding carbides.

     

Zur Kristallstruktur der Carbohydride von Übergangsmetallen

Zusammenfassung Mit Hilfe von Neutronenbeugungs-Aufnahmen an hydrierten und deuterierten Übergangsmetall-Carbiden wurden die Positionen der Kohlenstoff- und Wasserstoffatome ermittelt. In den ternären Phasen Zr₂C_1-x Hy y und Zr₂C_1-x D _y besetzen H bzw. D die tetraedischen Lücken des Anti-CdJ₂-Typs. In der kubischen Carbohydrid-Phase liegt der Kohlenstoff geordnet vor; der Wasserstoff füllt vorzugsweise die freien Oktaederlücken.

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The positions of H and D have been determined in hexagonal carbohydrides by means of neutron diffraction experiments, the H(D-)-atoms filling the tetrahedral voids of the Anti-CdI₂-type. Carbon and most of the hydrogen (deuterium) are filling the octahedral voids of the cubic carbohydrides.

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Mit 4 Abbildungen     

A new DMAP-catalyzed and microwave-assisted approach for introducing heteroarylamino substituents at position-4 of the quinazoline ring

We report herein a new methodology for synthesizing quinazoline derivatives bearing a heteroarylamino moiety at position-4 of the quinazoline ring. As an alternative to the Buchwald–Hartwig cross-coupling reaction, which appears, until now, as the only efficient way to react 4-chloroquinazolines with numerous amino nitrogen-containing heterocycles displaying poor nucleophilicity, we developed a DMAP-catalyzed reaction involving microwave irradiation. Optimization of the reaction conditions led to the use of 30 mol % of DMAP in toluene, using a monomode microwave reactor and sealed vials. Moreover, the S_NAr reaction intermediate salt was isolated and fully characterized. Finally, the procedure was extended to two different 2-substituted-quinazoline series and also to various anilines, demonstrating that this approach was a general efficient way to access to such 4-substituted quinazoline scaffolds of high pharmaceutical interest.     

Die Herstellung von Boriden der Übergangsmetalle aus dem Hilfsmetallbad

Zusammenfassung Das Hilfsmetallbadverfahren zur Herstellung von Hartstoffen—Reaktion der Ausgangskomponenten in einer inerten Metallschmelze und nachträgliche Entfernung des Hilfsmetalles—, —das sich für die Herstellung von Carbiden, Siliciden, Nitriden und Carbonitriden schon bewährt hat, ist nach den vorliegenden Versuchsergebnissen auch für die Herstellung von Boriden geeignet. Die im Vergleich zu anderen Hartstoffen etwas geringere chemische Beständigkeit der Boride bedingt größere Boridverluste beim Weglösen der Hilfsmetalle. Es konnten in Versuchen quantitative Angaben über die Beständigkeit von ZrB₂, TaB₂ und MoB₂ gegenüber verschiedenen wäßr. Medien erarbeitet werden. Es gelang, reines ZrB₂ und HfB₂ aus Kupfer-, Blei- und Zinnschmelzen herzustellen; ZrB und HfB scheinen nach den Versuchsergebnissen, wie schon früher von anderen Autoren vermutet, nur stabilisiert zu existieren. Ternäre, hilfsmetallhältige Phasen wurden nicht beobachtet.

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Preparation of transition metal borides from the auxiliary metal bath

The auxiliary metal bath process for the preparation of hard materials—reaction of the starting materials in an inert metal melt and subsequent removal of the auxiliary metal—which has already proved suitable for the preparation of carbides, silicides, nitrides and carbonitrides, is shown by the experiments described to be also suitable for preparing borides. Owing to the rather lower chemical stability of the borides compared with other hard materials, greater losses occur during dissolution of the auxiliary metals. Quantitative data concerning the stability of ZrB₂, TaB₂ and MoB₂ towards various aqueous media were obtained experimentally. Pure ZrB₂ and HfB₂ could be prepared from copper, lead and tin metls; experimental results indicate that ZrB and HfB exist only when stabilized, as previously supposed by other authors. Ternary phases containing auxiliary metals were not observed.

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Mit 3 Abbildungen     

Das kubische Tantalmononitrid (B 1-Typ) und seine Mischbarkeit mit den isotypen Übergangsmetallnitriden und-carbiden

The position of the recently detected cubic -TaN_1–x phase (B1 type) with respect to the other tantalum nitride phases in the system Ta–N is discussed and a tentative phase diagram for the partial system Ta–N is proposed. -TaN_1–x , a high temperature phase, is completely miscible with all isotypic mononitrides and monocarbides of the 4 a and 5 a group metals. Lattice parameters of the solid solutions are given.

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Mit 4 Abbildungen

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Herrn Prof. Dr.O. Hromatka zum 70. Geburtstag gewidmet.     

Herstellung der harten und hochschmelzenden Übergangsmetallcarbide aus dem Hilfsmetallbad

Zusammenfassung Das Carburieren der Übergangsmetalle der IVa-VIa-Gruppe des Periodensystems in Hilfsmetallbad stellt ein einfaches, schnellarbeitendes Verfahren zur Gewinnung Stickstoff- und Sauerstoffarmer hochgekohlter Carbide dar. Vorgebildete Carbide können so auch umgefällt und gereinigt werden, wobei der Stickstoff-und Sauerstoffgehalt auf etwa 1/10 abgesenkt werden kann.Als Hilfsmetall eignen sich bes. Reinkobalt und eine 70/30 Fe-Ni-Legierung. Neben WC, TaC, NbC und TiC wurden erstmals die Carbide ZrC, HfC, VC, Mo₂C und (Cr,Co)₇C₃ aus dem Hilfsmetallbad hergestellt und beschrieben.

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The carburising of the transition metals of the IVa-VIa group of the periodic system with the help of an auxiliary metal bath represents a simple rapidly working process for the production of carbides high in bound carbon and with a low content of oxygen and nitrogen. Prefabricated carbides can easily be reprecipitated and purified. Oxygen and nitrogen contents are lowered to about a tenth of the original values. The most suitable auxiliary metals are cobalt and a 70/30 Fe-Ni-alloy.Besides WC, TaC, NbC and TiC the carbides ZrC, HfC, VC, Mo₂C and (Cr, Co)₇C₃ are produced and described for the first time.

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Mit 1 Abbildung

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Frau Prof. Dr.Erika Cremer zum Geburtstag herzlichst gewidmet.     

Band-selective measurements of electron dynamics in VO2 using femtosecond near-edge x-ray absorption

We report on the first demonstration of femtosecond x-ray absorption spectroscopy, made uniquely possible by the use of broadly tunable bending-magnet radiation from "laser-sliced" electron bunches within a synchrotron storage ring. We measure the femtosecond electronic rearrangements that occur during the photoinduced insulator-metal phase transition in VO2. Symmetry- and element-specific x-ray absorption from V2p and O1s core levels (near 500 eV) separately measures the filling dynamics of differently hybridized V3d-O2p electronic bands near the Fermi level.