Korrosionsverhalten austenitischer Stähle bei der Prüfung nach Huey in Abhängigkeit vom Verformungsgrad

Einfluß von Probenlage und Verhältnis Querschnittsflächen/Gesamtfläche sowie Verformungsgrad beim Schmieden auf die Massenverlustrate bei der Prüfung des Stahles X 2 CrNiMoN 18 13 auf Beständigkeit gegen Kornzerfall nach Huey. Bedeutung von Zeilenbreite und Ausmaß der Seigerungen der Legierungselemente sowie Ableitung einer Beziehung zur Beherrschung der Beständigkeit gegen Kornzerfall.     

Ermittlung der zum Überlaufen von Sauerstoffaufblaskonvertern führenden Aufblasgeschwindigkeiten sowie der Größe fluider Partikeln in Gasströmen

Analogien zwischen dem Schäumen im Sauerstoffaufblaskonverter und dem Verhalten von Wirbelschichten. Quantitative Untersuchung der Höhe der Schaumschlacke. Aufstellung eines Nomogramms zur Ermittlung der Schaumschlackenhöhe bei Vorgabe der Sauerstoffaufblasgeschwindigkeit oder umgekehrt. Angabe von Maßnahmen zur Verminderung der Gefahr des Überlaufens. Abschätzung der Partikelabmessungen unter Berücksichtigung von Gasströmen als Zerkleinerungsmittel. Erörterung des Einflusses des entweichenden Kohlenmonoxids auf die Größe der fluiden Tropfen in der Schaumschlacke. Aussagen über bei Blasbeginn durch den Sauerstoffstrahl erzeugte Partikeln, deren Größe mit denen des braunen Rauches vergleichbar ist. Die Erzeugung der ?richtigen? Größe der Fluidpartikeln in der Schaumschlacke als Optimierungsproblem.     

Characterization and properties of metallic iron nanoparticles: spectroscopy, electrochemistry, and kinetics

There are reports that nano-sized zero-valent iron (Fe0) exhibits greater reactivity than micro-sized particles of Fe0, and it has been suggested that the higher reactivity of nano-Fe0 may impart advantages for groundwater remediation or other environmental applications. However, most of these reports are preliminary in that they leave a hostof potentiallysignificant(and often challenging) material or process variables either uncontrolled or unresolved. In an effort to better understand the reactivity of nano-Fe0, we have used a variety of complementary techniques to characterize two widely studied nano-Fe0 preparations: one synthesized by reduction of goethite with heat and H2 (Fe(H2)) and the other by reductive precipitation with borohydride (Fe(BH)). Fe(H2) is a two-phase material consisting of 40 nm alpha-Fe0 (made up of crystals approximately the size of the particles) and Fe3O4 particles of similar size or larger containing reduced sulfur; whereas Fe(BH) is mostly 20-80 nm metallic Fe particles (aggregates of <1.5 nm grains) with an oxide shell/coating that is high in oxidized boron. The FeBH particles further aggregate into chains. Both materials exhibit corrosion potentials that are more negative than nano-sized Fe2O3, Fe3O4, micro-sized Fe0, or a solid Fe0 disk, which is consistent with their rapid reduction of oxygen, benzoquinone, and carbon tetrachloride. Benzoquinone-which presumably probes inner-sphere surface reactions-reacts more rapidly with FeBH than Fe(H2), whereas carbon tetrachloride reacts at similar rates with FeBH and Fe(H2), presumably by outer-sphere electron transfer. Both types of nano-Fe0 react more rapidlythan micro-sized Fe0 based on mass-normalized rate constants, but surface area-normalized rate constants do not show a significant nano-size effect. The distribution of products from reduction of carbon tetrachloride is more favorable with Fe(H2), which produces less chloroform than reaction with Fe(BH).     

Structural characterization of octadecyl modified MCM-41 silica by NMR and FTIR

Mesoporous MCM-41 silica spheres were prepared via the pseudomorphic route, using commercial prontosil silica spheres. Surface modification offers a great opportunity to adjust both the pore structure and surface properties of MCM-41 type materials which results in materials of improved hydrothermal and mechanical stability to make them promising candidates for chromatographic applications. In the present context, the obtained MCM-41 silica spheres were surface modified with octadecyl (C₁₈) alkyl chains, by using direct grafting and surface polymerization methods, in order to vary the degree of surface hydrophobicity. The resulting materials were characterized before and after surface modification using various characterization techniques, with special emphasis on NMR and FTIR spectroscopies, for studying the attachment, mobility and the conformational order of the attached alkyl chains.     

Photokatalytische Bildung von Wasserstoff aus Thiolen in Gegenwart von Vitamin B12-Modellverbindungen mit Azid als photochemischem Opferliganden

Photocatalytic Hydrogen Formation from Thioles in the Presence of Vitamin-B₁₂ Model Complexes with Azide as Photochemical Sacrificial Ligand The photolysis of [N₃Co(chelat)B] complexes ( 1–3 ) (chelat = dimethylglyoxime, dmg; N,N′-o-phynylenebis(salicylidenimine), salphen; N,N′-ethylene-bis(salicylidenimine), salen; B = pyridine) leads by homolytic cleavage of the Co–N₃ bond to both coordinatively unsaturated cobalt(II) chelates [Co(chelat)B] and N₃ ligand radicals that undergo fast decay to dinitrogen. The photolysis of the cobalt (III) complexes 1–3 in the presence of thiophenole and other thioles proceeds catalytically and yields the corresponding disulphides and dihydrogen. The mechanism of this photocatalytic generation of dihydrogen is due to the catalytic activity of the coordinatively unsaturated cobalt(II) species formed photochemically. A photocatalytic cycle is proposed describing the generation of hydrogen. Possible photochemical and thermal steps of that cycle are discussed.     

Chromatographische Untersuchungen zur Polydispersität von Hydroxyethylstärke

Chromatographic Studies on the Polydispersity of Hydroxyethyl Starch. A representative sample of clinically used hydroxyethyl starch was separated by semipreparative HPSEC into narrow fractions in the range of approx. 3.000 to 800.000 D. The original sample and selected fractions were characterised by gaschromatographic methylation analysis according to their substitution degrees MS and DS, which were differentiated by the substitution positions at C2, C3 and C6 of the anhydroglucoses and their kind of glycosidic bonding α-1, α-1,4 or α-1,4,6, respectively. Furthermore, polydispersity in relations to the degree of branching was determined. Mark-Houwink and molecular weight distribution parameters determined by multi-detection HPSEC are reported. The presented data demonstrate a extensive homogeneity of the original sample. The clinical relevance is discussed.