Zur Kinetik der verschleißinduzierten Wasserstoffeffusion aus unlegiertem Stahl

Unter Anwendung elektrochemischer und massenspektrometrischer Methoden wird in der vorliegenden Arbeit versucht, sowohl die einzelnen Beiträge zur verschleißinduzierten Wasserstoffeffusion quantitativ zu erfassen wie auch den Zusammenhang zwischen der verschleißgeförderten Wasserstoffeffusion und der Wasserstoffanreicherung in oberflächennahen Bereichen zu erforschen. Haftungsverschleiß- und Furchungsverschleiß-induzierte Wasserstoffeffusionsmechanismen sind meistens auf die mechanische Abtragung der wasserstoffangereicherten Schichten bzw. auf die Thermodiffusion aus diesen Schichten zurückzuführen. Nach einem Anlaufstadium stellt sich ein Gleichgewicht zwischen dem effundierenden und dem eingefangenen Wasserstoff ein. In diesem Stadium erfolgt die Wasserstoffeffusion mit stationärer Geschwindigkeit.     

The effect of electrolyte temperature on the passivity of solid electrolyte interphase formed on a graphite electrode

The effect of electrolyte temperature on the passivity of solid electrolyte interphase (SEI) was investigated in 1 M LiPF₆-ethylene carbonate/diethyl carbonate (50:50 vol.%) electrolyte, using galvanostatic charge-discharge experiment, and ac-impedance spectroscopy combined with Fourier transform infra-red spectroscopy, and high resolution transmission electron microscopy (HRTEM). The galvanostatic charge-discharge curves at 20 °C evidenced that the irreversible capacity loss during electrochemical cycling was markedly increased with rising SEI formation temperature from 0 to 40 °C. This implies that the higher the SEI formation temperature, the more were the graphite electrodes exposed to structural damages. From both increase of the relative amount of Li₂CO₃ to ROCO₂Li and decrease of resistance to the lithium transport through the SEI layer with increasing SEI formation temperature, it is reasonable to claim that, due to the enhanced gas evolution reactions during transformation of ROCO₂Li to Li₂CO₃, the rising SEI formation temperature increased the number of defect sites in the SEI layer. From the analysis of HRTEM images, no significant structural destruction in bulk graphite layer was observed after charge-discharge cycles. This means that solvated lithium ions were intercalated through the defect sites in the SEI, at most, into the surface region of the graphite layer.     

Electrodissolution of aluminium thin film microband electrodes

This paper discusses the electrodissolution of aluminium thin films as microband electrodes (length = 5 × 10^–3 m) in terms of mass transfer determined by voltammetry and a.c.-impedance techniques as a function of bandwidth (20 to 2000 nm) in 0.1m NaOH solution. The anodic polarization curves of the aluminium microband electrodes show that current density is enhanced with decreasing bandwidth. The ac impedance response suggests that a steady-state diffusion layer appears the more markedly, the smaller the bandwidth. The anodic polarization curves are analysed on the basis of the combined Butler-Volmer high field approximation and the semi-cylindrical diffusion field approximation. As a result of the analysis, the electrodissolution proceeds by a mixed kinetic-mass transfer controlled reaction. The analysis also makes it possible to distinguish the semi-cylindrical diffusive mass transfer contribution to the electrodissolution from the kinetic contribution, i.e., mass transfer index linearly diminishes with decreasing bandwidth. The increased current density is attributable to the decreased mass transfer contribution, i.e., the more predominant semi-cylindrical diffusive mass transfer as compared to laminar diffusive mass transfer.Nomenclature k _a anodic kinetic constant - k _c cathodic kinetic constant - F Faraday constant - _s kinetic transfer coefficient for anodic reaction - _c kinetic transfer coefficient for cathodic reaction - c ^s surface concentration - V anodic polarization - D diffusion coefficient - d diffusion layer thickness - z number of electrons transferred - l length of microband electrode - w bandwidth of microband electrode - r radius of cylinder     

X-ray topographic study of β-NiAl upon growth of an α-Al2O3 film

The Berg-Barrett X-ray topographic method was employed as a microstructural technique to seek correlations of the metal substructure to the morphological features of -Al₂O₃ films grown on -NiAl. An analysis of diffraction micrographs using {112} and {002} reflections from individual grains in -NiAl revealed its subgrain structure to a depth of 30 . The dimensions of these subgrains were directly related to the density of oxide ridges in the -Al₂O₃ films and to the dimensions and shapes of cavities at the NiAl-Al₂O₃ interface.     

Multi-species measurements in 1-butanol pyrolysis behind reflected shock waves

The kinetics of 1-butanol pyrolysis were investigated by measuring multi-species time histories using shock tube/laser absorption methods. Species time histories of OH, H₂O, C₂H₄, CO, and CH₄ were measured behind reflected shock waves using UV and IR laser absorption during the high-temperature decomposition of 1% 1-butanol/argon mixtures. Initial reflected shock temperatures and pressures for these experiments covered 1250–1650 K and 1.3–1.9 atm. Measured OH and H₂O time histories are in good agreement with previous experimental studies; measured C₂H₄, CO, and CH₄ time histories are the first reported for this fuel in shock tube experiments.Production pathways and sensitivities for the measured species are analyzed using the recent Sarathy et al. (2012) [37] detailed mechanism. Simulations using this mechanism underpredict H₂O, OH, and C₂H₄ mole fractions, overpredict CH₄ mole fractions, and significantly underpredict CO mole fractions at early times. As discussed in past papers and confirmed in this study, the branching ratios of H abstraction rates from 1-butanol, which are not precisely known, can significantly affect H₂O time history simulations. These simulations show that H₂O is produced primarily through H-atom abstraction from 1-butanol by OH, and therefore H₂O time histories are extremely sensitive to 1-butanol decomposition channels that contribute to the OH radical pool. Simulations also show that more C₂H₄ would be produced by faster decomposition of 1-butanol through several channels that also affect H₂O production. Finally, simulations show that CO time histories are strongly sensitive to 1-butanol decomposition into nC₃H₇ and CH₂OH, especially at early times. Evidence is presented that indicates this decomposition pathway is too slow in the simulations by a factor of three to five at conditions of the current study.     

A Low Distortion and Low Dissipation Power Amplifier with Gate Bias Control Circuit for Digital/Analog Dual-Mode Cellular Phones

A power amplifier operating at 3.3 V. has been developed for CDMA/AMPS dual-mode cellular phones. It consists of linear GaAs power MESFET's, a new gate bias control circuit, and an output matching circuit which prevents the drain terminal of the second MESFET from generating the harmonics. The relationship between the intermodulation distortion and the spectral regrowth of the power amplifier has been investigated with gate bias by using the two-tone test method and the adjacent channel leakage power ratio (ACPR) method of CDMA signals. The dissipation power of the power amplifier with a gate bias control circuit is minimized to below 1000 mW in the range of the low power levels while satisfying the ACPR of less than ?26 dBc for CDMA mode. The ACPR of the power amplifier is measured to be ?33 dBc at a high output power of 26 dBm.     

Improvement of catastrophic optical damage (COD) level forhigh-power 0.98-μm GaInAs-GaInP laser

We investigate improvement of catastrophic optical damage (COD) level for Al-free 0.98-μm ridge waveguide laser diodes (LDs) using the impurity induced layer disordering (IILD) process applied near the facets. The IILD is used for the purpose of forming transparent windows near both facets of the LDs utilizing its ability to increase bandgap energy of the GaInAs-GaInAsP strained quantum-well (QW) active layer. Improvement of the cod level by at least 1.65 times compared to the conventional LDs is obtained for the LDs with Si⁺ implantation followed by annealing at 900°C for 10 min