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     

SIMS Investigations on the Distribution of Trace Elements in Modified Aluminium–Silicon–Magnesium Alloys

 Strontium modified aluminium–silicon cast alloys are well known for their outstanding mechanical properties as they combine excellent strength with good ductility that is due to a modification of brittle Si in the eutectic with traces of Sr (0.3–0.5 wt%). Although the level of Sr addition is very low, formation of ternary AlSiSr phases with deleterious effects on the ductility can take place. Consequently, there is a certain need of alternative modifying elements. Following the theory of Lu and Hellawell which predicts an optimal atomic size for good modification, Eu, which has an atomic radius close to that optimal size, was additionally used as a modifying element. This study presents SIMS (secondary ion mass spectrometer) investigations of the 3D-distributions of the main alloying and trace elements in Al–Si feedstock alloys for thixocasting modified with Sr and Eu, respectively. Received October 1, 2001; accepted May 21, 2002     

A case study of algorithm selection for the traveling thief problem

Many real-world problems are composed of several interacting components. In order to facilitate research on such interactions, the Traveling Thief Problem (TTP) was created in 2013 as the combination of two well-understood combinatorial optimization problems. With this article, we contribute in four ways. First, we create a comprehensive dataset that comprises the performance data of 21 TTP algorithms on the full original set of 9720 TTP instances. Second, we define 55 characteristics for all TPP instances that can be used to select the best algorithm on a per-instance basis. Third, we use these algorithms and features to construct the first algorithm portfolios for TTP, clearly outperforming the single best algorithm. Finally, we study which algorithms contribute most to this portfolio.     

Application of SIMS in Re-Technology Studies: Characterization of Trace-Element Distributions and Quantitative of Carbon-Determination

 The content and the three dimensional distribution of impurities play an important role in the production process of high purity rhenium powder (99.99% purity grade) and for its further use as alloying and coating agent in high temperature applications. In this paper the characterization of raw Re granulate, Re powder, cleaned by heat treatment, Re coatings, produced by most common preparation methods (PVD and VPS) and PM Re by means of SIMS is presented. The analysis of the three dimensional distribution of trace elements is performed by 3D SIMS. The quantification of carbon, which was not possible with other analytical techniques as a result of the high volatility of Re₂O₇ until now, has been carried out by SIMS depth profile analysis. It is discussed if internal standards, produced by introduction of defined amounts of carbon soot to the Re powder lead to useful results.     

AuICl-bound N-heterocyclic carbene ligands form MII4(LAuCl)6 integrally gilded cages

The incorporation of an N-heterocyclic carbene (NHC) moiety into a self-assembled MII4L₆ cage framework required the NHC first to be metallated with gold(i). Bimetallic cages could then be constructed using zinc(ii) and cadmium(ii) templates, showing weak luminescence. The cages were destroyed by the addition of further gold(i) in the form of Au^I(2,4,6-trimethoxybenzonitrile)₂SbF₆, which caused the reversibly-formed cages to disassemble and controllably release the Au^I-NHC subcomponent into solution. This release in turn induced the growth of gold nanoparticles. The rate of dianiline release could be tuned by capsule design or through the addition of chemical stimuli, with different release profiles giving rise to different nanoparticle morphologies.     

Car-parrinello molecular dynamics simulation of liquid formic acid

First-principles molecular dynamics has been used to investigate the structural, vibrational, and energetic properties of formic acid, formic acid-formate anion dimers, and liquid formic acid in a periodically repeated box with 32 formic acid molecules. We found that in liquid formic acid the hydrogen-bonded clusters mainly consist of linear branching chains. From our simulation, we got good agreement with the available structural and dynamical data. We also studied the proton transfer in the cis-formic acid-formate anion dimer, and we showed that this proton transfer does not have any potential barrier. The hydrogen bonding statistics as well as the mean lifetime of the hydrogen bonds are analyzed.     

Photoinduced 1,4-additions of indoles to enones

[reaction: see text] A photoinduced procedure for the 1,4-addition of indoles to enones is described. This reaction occurs with modest to excellent yield for cyclic and some acyclic enones. This reaction is experimentally simple, requiring only irradiation (UVA lamps, ca. 350 nm) of the reagents in a CH2Cl2 solution at room temperature, and avoids the necessity to use a Lewis acid. An important solvent effect was noticed, with CH2Cl2 and CHCl3 being the optimal solvents. Various substituents are tolerated on the indole moiety and an electronic trend was noticed, as electron-withdrawing groups can suppress this reaction. A mechanism involving single electron transfer between the enone triplet excited state and the indole is proposed and accounts for all experimental observations.