Neuere Untersuchungen zur Aluminiumbestimmung mit Chromazurol S

Die photometrische Bestimmung von Aluminium im Stahl mit Chromazurol S unter Zusatz von Polyvinylalkohol als Schutzkolloid wurde untersucht. Der Aluminium-Komplex wird bei pH 6 gebildet, die Extinktion bei 620 nm gemessen. Störende Elemente werden durch eine Natronlaugefällung in Gegenwart von Zinkchlorid und Borsäure entfernt. Die Nachweisgrenze des Verfahrens liegt bei 0,0008% Al. Die Standardabweichung bei der Bestimmung von 0,0032% Al beträgt 0,00028% Al. Der Extinktionskoeffizient liegt bei 73 400 l/Mol · cm.     

Growth of Boric Acid Crystallites on the Surface of Boron-Doped Silicon Carbide Samples

White crystallites were visually observed on fractured or polished surfaces of SiC samples (grain sizes below ∼500 nm) during exposure to air at room temperature for several days. Characterization of the crystallites by scanning electron microscopy, secondary ion mass spectroscopy, and X-ray diffraction identified B(OH)₃ crystals with a strong (002) texture. The rate of boric acid formation was determined by a gravimetric experiment. The rate of weight gain increased significantly after an incubation period of 1 week. Nucleation is initially the rate-limiting process. Subsequently small B(OH)₃ crystals form on the surface, whose growth rate is determined by grain boundary diffusion of boron to the SiC surface. An estimated grain boundary diffusion coefficient of boron in SiC was many orders of magnitude higher than extrapolated literature values.     

Kinetic Process of Reoxidation of Base Metal Technology BaTiO3-Based Multilayer Capacitors

Base metal technology, mainly using Ni electrodes in multilayer ceramic capacitors (MLCCs), is now well established. This technology requires a so-called reoxidation treatment after sintering the MLCCs in a reducing atmosphere to guarantee a sufficient electrical reliability. Large numbers of electrodes, and production of physically larger components for high-voltage components, are two technological trends that make the control of the reoxidation process rather difficult. The reoxidation process has been studied to determine oxygen diffusion pathways into commercial MLCCs, using ¹⁸O tracer diffusion and finite element calculations. In MLCCs oxygen diffusion mainly occurs along the Ni electrodes. Furthermore, the reoxidation process is mostly controlled by the thermodynamic potential of the Ni/NiO equilibrium in the interior of the capacitor, but it is the short circuit diffusion along the interface of the electrode that controls the kinetics of the oxygen transport into the interior of the capacitor device.     

Hydroxyl Defect Effect on Reoxidation of Sc‐Doped (Ba,Ca)(Ti,Zr)O3 Fired in Reducing Atmospheres

The behavior of grain and grain‐boundary conductivity of acceptor (Sc)‐doped (Ba,Ca)(Ti,Zr)O₃ ceramics sintered in moist reducing atmosphere and subsequently reoxidized in dry and moist atmosphere was investigated by means of impedance spectroscopy (IS). In moist firing atmosphere, water vapor was found to react with oxygen vacancies, forming positively charged hydroxyl defects on regular oxygen sites in the crystal lattice. Proton hopping is considered to raise the ionic conductivity significantly. Therefore, hydroxyl defects in turn influence the grain conduction. Hydroxyl defects are also considered to be responsible for alternations of the dielectric maximum at the Curie point.     

Detection of Wear in One-Cathode Plasma Torch Electrodes and its Impact on Velocity and Temperature of Injected Particles

Wear at the electrode surfaces of a one-cathode plasma torch changes the characteristic fluctuation pattern of the plasma jet. This affects the trajectory of the particles injected into the plasma jet in a non-controllable way, which degrades the reproducibility of the process. Time-based voltage measurements and Fourier analysis were carried out on a one-cathode F4 torch at different wear conditions to determine the evolution of wear dependant characteristics. A significant correlation is observed between increasing torch wear and decreasing voltage roughness and high frequency noise. Furthermore, by means of particle diagnostic systems, the change in the particle velocity and temperature has been measured. The variations of the particle characteristics are significant and thus an influence on the sprayed coating microstructure is to be expected. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Correlation between spraying conditions and microcrack density and their influence on thermal cycling life of thermal barrier coatings

It is generally known that the porosity of thermal barrier coatings is essential to guarantee a sufficiently high strain tolerance of the coating during thermal cycling. However, much less is known about the influence of the specific morphology of porosity, such as microcracks and typically larger pores, on the performance of the coatings. Both features are usually formed during plasma spraying of yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs). In this investigation, the influence of microcracks on the thermal cycling behavior was studied. The amount of microcracks within YSZ thermal barrier coatings was changed by changing the powder-feeding rate. Only small changes of the total porosity were observed. Mercury porosimetry served as a tool to investigate both the amount of microcracks and pores in the coating. Additionally, microcrack densities were determined from metallographical investigations. A linear dependence between the amount of fine pores determined by Hg porosimetry and the crack density was obtained for one set of coatings. Thermal cycling TBC specimens with different microcrack densities were produced and tested in a gas burner test facility. At high surface temperatures (above 1300 °C), failure occurred in the ceramic close to the surface. Under these conditions, the samples with increased horizontal microcrack densities showed a significant increase of thermal cycling life.     

Safety of oleochemical products derived from beef tallow or bone fat regarding prions

Bovine bone fat and beef tallow are widely used as raw material for oleochemical processes. Due to high temperature and pressure these processes are supposed to have an excellent inactivation potential for prions, i.e. the agent of BSE and other transmissible spongiform encephalopathies. To experimentally prove the destruction of the pathogenic prion protein aggregates under technically relevant conditions, oleochemical processes were emulated in the laboratory in reduced scale. Fat samples were spiked with highly infectious ex vivo prion rods and aliquots were taken before and after the processes. From these aliquots, undegraded prion protein was precipitated and determined by a sensitive Western blot assay. Degradation factors of 2 ?10³ ‐ 10⁴ for catalytic fat hydrogenation and 10⁷ for fat hydrolysis represent acceptable safety limits. With these experimental prion protein degradation factors the risk of human exposure to oleochemical products of bovine origin can be assessed. Assuming worst‐case scenarios, the annual risk for human consumption of hydrogenated beef tallow is less than 6.8 x 10^‐7 and for skin application of fatty acid derivatives is less than 7.0 x 10^‐10. Both values are smaller than the background risk of contracting sporadic Creutzfeldt‐Jakob disease (1 x 10^‐6 per annum).     

Deletion of glycine transporter 1 (GlyT1) in forebrain neurons facilitates reversal learning: Enhanced cognitive adaptability?

Local availability of glycine near N-methyl-D-aspartate receptors (NMDARs) is partly regulated by neuronal glycine transporter 1 (GlyT1), which can therefore modulate NMDAR function because binding to the glycine site of the NMDAR is necessary for channel activation. Disrupting GlyT1 in forebrain neurons has been shown to enhance Pavlovian conditioning and object recognition memory. Here, the authors report that the same genetic manipulation facilitated reversal learning in the water maze test of reference memory, but did not lead to any clear improvement in a working memory version of the water maze test. Facilitation in a nonspatial discrimination reversal task conducted on a T maze was also observed, supporting the conclusion that forebrain neuronal GlyT1 may modulate the flexibility in (new) learning and relevant mnemonic functions. One possibility is that these phenotypes may reflect reduced susceptibility to certain forms of proactive interference. This may be relevant for the suggested clinical application of GlyT1 inhibitors in the treatment of cognitive deficits, including schizophrenia, which is characterized by cognitive inflexibility in addition to the positive symptoms of the disease. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An inverse approach to the numerical design of the process sequence of tailored heat treated blanks

While in industries lightweight construction gain an increasingly significant role and as weight reduction is often done with aluminum sheets, advanced production technologies have to be developed to be competitive for this evolution. Since steel sheet metal parts cannot be substituted directly with aluminum due to its minor formability, the usage of so called tailored heat treated blanks (THTB) is presented in this work. THTB are locally heat treated aluminum blanks from the 6,000-series alloy which exhibit a specific strength pattern optimized to the forming operation leading to a significantly improved formability for the manufacturing of complex aluminum car body parts. The enhancement of the formability is reached by a local heat treatment before the forming process. Due to the strong interdependency of heat treatment and forming operation, a numerical investigation of the process sequence is a prerequisite for a cost-effective usage of the THTB. An inverse approach on basis of a finite element simulation enables the determination of process parameters for an optimized THTB, thus having an effective and efficient engineering method for this technology. The investigations presented in this paper were carried out within the project CRC 396 B4 “Robust, shortened process sequences for lightweight sheet parts” sponsored by the German Research Foundation (DFG).