Investigation of the formation and properties of protective oxide layers on high purity chromium with SIMS imaging techniques

Spallation of the protective oxide layer formed during hot gas oxidation is the main reason for the corrosion of high purity powder metallurgically produced chromium[1]. To explain the formation and occasional spallation of the oxide layer a chromium sample subjected to two consecutive oxidation processes in¹⁶O and¹⁸O atmosphere at high temperature was characterised by 2D and 3D SIMS.The formation of the protective oxide can be described by the diffusion of chromium from the bulk to the surface and the reaction of the chromium atoms with the oxygen from the gaseous phase. The very low solubility of nitrogen in chromium oxide indicates its inability to diffuse through the growing oxide layer and explains the enrichment of nitrogen (same mechanism applies for chlorine) in the interface metal/oxide. The accumulation of trace elements within the interface during the oxidation process explains the reduced adhesion power of the passivation layer and its spallation.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Übergangsmetall-Carben-Komplexe,CXXXVII Darstellung zweikerniger Gold(I)-Biscarben-Komplexe durch Carbenübertragungen von Wolfram auf Gold

The binuclear tungsten(0) biscarbene complexes3 and4 react with tetrachloroauric acid (stöchiometric ratio 1 : 2) to give the corresponding gold(I) complexes5 and6 involving the transfer of biscarbene ligands from two tungsten to two gold fragments. Preparation and spectroscopic data are described.

Herrn Prof. Dr.K. Schlögl zum 60. Geburtstag gewidmet.     

Binding energies of CO on gold cluster cations Au n + (n=1-65): a radiative association kinetics study

Room temperature CO adsorption on isolated gold cluster cations is studied over a wide size range (Au(n) (+),126), with notable exceptions at n=30, 31 and 48, 49 which manifest local binding energy maxima. For the smallest sizes (3相似文献   

Raman spectroscopy of individual single-walled carbon nanotubes from various sources

Resonance Raman spectroscopy/microscopy was used to study individualized single-walled carbon nanotubes (SWNTs) both in aqueous suspensions as well as after spin-coating onto Si/SiO2 surfaces. Four different SWNT materials containing nanotubes with diameters ranging from 0.7 to 1.6 nm were used. Comparison with Raman data obtained for suspensions shows that the surface does not dramatically affect the electronic properties of the deposited tubes. Raman features observed for deposited SWNTs are similar to what was measured for nanotubes directly fabricated on surfaces using chemical vapor deposition (CVD) methods. In particular, individual semiconducting tubes could be distinguished from metallic tubes by their different G-mode line shapes. It could also be shown that the high-power, short-time sonication used to generate individualized SWNT suspensions does not induce defects in great quantities. However, (additional) defects can be generated by laser irradiation of deposited SWNTs in air, thus giving rise to an increase of the D-mode intensity for even quite low power densities (approximately 10(4) W/cm2).     

Weak Interionic Interactions in 2‐Haloimidazolium Hexahalotellurates(IV) [1]

The 2‐haloimidazolium salts [C₁₁H₂₀N₂X]X [ 1 ; X = Cl ( a ), Br ( b )] react with TeX₄ to give the salts [C₁₁H₂₀N₂X]₂[TeX₆] [ 2 ; X = Cl ( a ), Br ( b )]. The crystal structure analyses of 2a and 2b · CH₂Cl₂ reveal the presence of ionic pairs linked by weak halogen to halogen interactions.     

Stereoselektive Synthese von Pyrrolizidin-Alkaloiden aus Nitroalkanonen

Stereoselective Synthesis von Pyrrolizidin Alkaloids from Nitroalkanones Reduction of 5-nitropentadecane-2,8-dione ( 11 ), synthesized by a Michael reaction from nitromethane, methyl vinyl ketone, and dec-1-en-3-one, gave, depending on the conditions, two epimeric 3-heptyl-2,3,5,6,7,7a-hexahydro-5-methyl-1H-pyrrolizines as the main products: Catalytic hydrogenation (Pd/C) afforded the expected 7aα-hydro epimer 1b with cis-orieted H-atoms at C(3), C(5), and C(7a). NaBH₃CN/NH₄OAc reduction of the nitrodione 11 yielded all four diastereoisomers with the 7aβ-hydro epimer 1a as the predominant component; 1a is a pheromone of the cryptic thief ant Solenopsis sp. The N-atom of the pyrrolizidine ring stems from NH₄OAc exclusively as shown by reduction of 11 with NaBH₃CN/(¹⁵N)H₄OAc.     

Reactive polymer blends with thermoplastic polyurethan

The paper presents the concept of reactive coupling of thermoplastics and describes the technological preconditions and the present state of development. The examples of developments of blends of thermoplastic polyurethan (TPU), and polyethylene terephthalate (PET) serve to show that different mechanisms of reactive coupling of the blend components permit to produce high-quality blends.