Phase Stability and Oxidation Behavior of an Alumina Scale-Forming NiCrAlY Alloy

The phase constitution and associated oxidation behavior were determined for an alloy of composition (in wt%) Ni–31.5Cr–11.5Al–0.61Y. The identity, relative amount, and approximate composition of each phase were determined after equilibration at 700, 900, and 1100°C using SEM/EDS, XRD, and image analysis. The CALPHAD method was used to predict the phase equilibria in this system, and the results showed good agreement with experiment. Cyclic oxidation behavior at 900, 1050, and 1100°C in air was determined and assessment of the results was aided by CALPHAD predictions in conjunction with dilatometric measurements.     

Combining impedance spectroscopy with cyclic voltammetry: measurement and analysis of kinetic parameters for faradaic and nonfaradaic reactions on thin-film gold

The technique of time-resolved impedance spectroscopy can be combined with dc cyclic voltammetry (CV) to study mechanisms and kinetics of electrochemical reactions at solid-liquid interfaces. Utilization of these techniques in a combined framework, however, is based on a number of specific considerations of measurement procedures and data analysis. The present work discusses certain essential elements of this topic, focusing primarily on the analysis of time-resolved impedance spectra where interdependent dc and ac effects of parallel faradaic and nonfaradaic reactions are present under potentiodynamic conditions. A thin gold film is used as a model experimental system where oxidation and reduction of the sample surface is voltage-controlled both in the presence and in the absence of specifically adsorbing Cl- ions in neutral background electrolytes of NaF. Impedance spectra are recorded under transient conditions of CV, and kinetic parameters based on electrode-equivalent circuit models are obtained as functions of CV scans.     

Analysis of the Reactive Element Effect on the Oxidation of Ceria Doped Nickel

The effects of external doping with CeO₂ on the oxidation of nickel have been evaluated. The materials studied were pure Ni and Ni with the surface doped with CeO₂ by pulsed laser deposition. The oxidation kinetics were measured using thermogravimetric analysis. The oxidation microstructures were observed by scanning electron microscopy and cross-sectional transmission electron microscopy. Compositional analysis was performed with energy dispersive X-ray analysis and sputtering neutrals mass spectrometry. Phase identification was performed using X-ray diffraction. Doping with CeO₂ resulted in a significant decrease in the NiO growth rate at intermediate temperatures, e.g. 800?°C. The scales on doped Ni grew primarily inward whereas those on the undoped Ni grew primarily outward. Deposition of the CeO₂ dopant onto Ni with a thin, preformed NiO layer produced a similar reduction in the subsequent NiO growth rate. The CeO₂ dopant did not reduce the growth rate at high temperature (1,300?°C). The results indicate that the CeO₂ dopant influences grain boundary transport in the NiO. Mechanisms are presented to attempt to describe the above observations.     

A modified model for the Lobula Giant Movement Detector and its FPGA implementation

Bio-inspired vision sensors are particularly appropriate candidates for navigation of vehicles or mobile robots due to their computational simplicity, allowing compact hardware implementations with low power dissipation. The Lobula Giant Movement Detector (LGMD) is a wide-field visual neuron located in the Lobula layer of the Locust nervous system. The LGMD increases its firing rate in response to both the velocity of an approaching object and the proximity of this object. It has been found that it can respond to looming stimuli very quickly and trigger avoidance reactions. It has been successfully applied in visual collision avoidance systems for vehicles and robots. This paper introduces a modified neural model for LGMD that provides additional depth direction information for the movement. The proposed model retains the simplicity of the previous model by adding only a few new cells. It has been simplified and implemented on a Field Programmable Gate Array (FPGA), taking advantage of the inherent parallelism exhibited by the LGMD, and tested on real-time video streams. Experimental results demonstrate the effectiveness as a fast motion detector.     

Are Current Theories of Panic Falsifiable?

The authors examine 6 theories of panic attacks as to whether empirical approaches are capable of falsifying them and their heuristic value. The authors conclude that the catastrophic cognitions theory is least falsifiable because of the elusive nature of thoughts but that it has greatly stimulated research and therapy. The vicious circle theory is falsifiable only if the frightening internal sensations are specified. The 3-alarms theory postulates an indeterminate classification of attacks. Hyperventilation theory has been falsified. The suffocation false alarm theory lacks biological parameters that unambiguously index dyspnea or its distinction between anticipatory and panic anxiety. Some correspondences postulated between clinical phenomena and brain areas by the neuroanatomical hypothesis may be falsifiable if panic does not depend on specific thoughts. All these theories have heuristic value, and their unfalsifiable aspects are capable of modification. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hot-Corrosion Resistance of Ni–Cr–Al–Y and Ni–18% Si Alloys in Sulfate Eutectic and Sulfate Plus Vanadate Melts at 973 K

The hot-corrosion resistance of Ni–Cr–Al–Y and Ni–17.8 wt.% Si was examined in sulfate and sulfate plus vanadate melts at 973 K. Two salt-deposit compositions were considered: (a) sodium sulfate+50 mole% magnesium-sulfate eutectic and (b) sodium sulfate plus 20 mole% sodium meta-vanadate. Both types of deposit were molten at the test temperature. Cyclic hot-corrosion tests were conducted in a gas mixture consisting of oxygen, sulfur dioxide, and 0.0240 vol.% sulfur trioxide. The hot-corrosion kinetics were evaluated using weight change and the corrosion mechanism deduced from post-test metallography. The results indicate that the nickel–silicon alloy had much better hot corrosion resistance than Ni–Cr–Al–Y under all test conditions considered. The sample preparation process is outlined, the test procedure summarized, and the experimental results are presented and discussed.     

Effect of surface preparation on the durability of NiCoCrAlY coatings for oxidation protection and bond coats for thermal barrier coatings

A principal concern with alumina‐forming coatings for high‐temperature oxidation protection and bond coats (BCs) for ceramic thermal barrier coatings (TBCs) used in gas turbines is the spalling of the alumina scales during service. This paper describes the effects of BC surface preparation on the durability of NiCoCrAlY coatings exposed under thermal cycling conditions. State‐of‐the‐art TBC systems deposited by electron beam physical vapor deposition (EBPVD) with NiCoCrAlY overlay BCs were found to fail as the result of defects which included transient oxides, defects in the BC surface, defects in the as‐deposited microstructure of the TBC, and excessive oxidation of reactive element additions. In some instances, the TBC life was greatly extended by surface treatments, such as fine polishing. The oxidation behavior of NiCoCrAlY coatings, absent a TBC, was found to be sensitive to Y content and to surface preparation. This paper describes how a variety of surface treatments affected coating lives and failure mechanisms.