Search results for "Surfaces"
showing 10 items of 2837 documents
Influence of the mode of introduction of a reactive element on the high temperature oxidation behavior of an alumina-forming alloy. Part I: Isotherma…
2004
Several routes of yttrium introduction were applied to test the high temperature oxidation performance of a FeCrAl alloy. Isothermal oxidation tests were described in a previous paper (Part I of this paper in this journal, 2004, 55, 352). Cyclic oxidation tests were performed in air under atmospheric pressure on blank specimens, Y 2 O 3 sol-gel coated-, Y 2 O 3 metal-organic chemical vapor deposited (MOCVD)-, yttrium ion implanted-alloys, as well as on a steel containing 0.1 wt.% of yttrium as an alloying element. For the 20 hours cycles, all the samples, except FeCrAl-0.1Y, exhibit weight losses after a few cycles, indicating drastic spallation of the oxide scales. The MOCVD coated specime…
Oxidation mechanism of the Inconel 601 alloy at high temperatures
2010
The Inconel 601 alloy oxidation was performed in air, in the temperature range 1000-1150 °C, during 90 h. Kinetic results show that the parabolic behavior is always followed in this temperature range. The Arrhenius plot of the kp values shows two different activation energies. Between 1000 and 1050 °C the activation energy is E a1 = 160 ± 10 kJ/mol. In the 1050-1150 °C temperature range a higher value is calculated E a2 = 252 ± 20 kJ/mol. The E a2 value and the X-ray diffraction (XRD) results and scanning electron microscope (SEM) energy dispersive X-ray spectroscopy (EDS) examinations are in accordance with a scale growth mechanism limited by a growing Cr 2 O 3 scale acting as a diffusion …
Metallic interconnects for solid oxide fuel cell: Performance of reactive element oxide coating during long time exposure
2011
One of challenges in improving the performance and cost-effectiveness of SOFCs (solid oxide fuel cells) is the development of suitable interconnects materials. Chromia-forming alloys and especially ferritic stainless steels, like Crofer22APU, are considered to be among the most promising candidate materials as interconnects in SOFC stacks. However, the performance of chromia-forming materials can be limited by the low electronic conductivity of the oxide scale (high ASR – area specific resistance – value). Such degradation are unacceptable regarding the long-term operation (>40 000 h). A previous study 1 demonstrated that in air, the addition of a nanometric reactive element oxide (La2O3) l…
High temperature alloy chloridation at 850°C
2007
The resistance of eight alloys against chloridation was tested at 850 °C in Ar/Cl 2 (2.5% Cl 2 ) for 15 min. Pre-oxidation treatments were performed for 1 h and 8 h at 850°C in order to produce a thin, adherent and protective oxide scale able to improve the chloridation behaviour of the tested materials. The chloridised sample morphologies were compared to the morphologies observed on the non pre-oxidised samples. The alloys containing a large amount of iron did not exhibit any chloridation resistance, even after pre-oxidation, and were severely damaged. The nickel based alloys gave interesting results but were also attacked by chloride, probably by the "active oxidation" mechanism. The dur…
High temperature alloy chloridation at 850°C. Part I: Comparison of Ni-based and Fe-based alloy behaviour
2007
Eight alloys were tested under Ar/Cl 2 atmosphere at 850 °C for 15 min and 1 h. Their gross and net weights were evaluated together with the base metal consumption. Macroscopic and microscopic micrographs, associated with chemical analyses and X-ray diffraction gave the composition and microstructure of the corrosion products. Huge differences were observed if one compared the nickel based alloy behaviour to that of the iron based alloy. Molybdenum and tungsten could also play a role, but it was not clearly defined until now. A tentative evaluation of the best candidates will be given, according the experimental conditions of this work and the chosen criteria. A corrosion index was establis…
White Etching Crack Root Cause Investigations
2014
White etching crack (WEC) failure is distinct to classical fatigue and driven by the composition of lubricants under special loading conditions; for example, slippage and electricity. The white etching area (WEA) within WEC contains carbon supersaturated ferrite (bcc-iron) and carbides, with a size of a few nanometers. This article presents investigations supporting the hypothesis that WEC processes start within a failure-free period by successive accumulation of a structural distortion. This can be measured by acoustic emission. Failure statistics show a steep ascent in the Weibull diagram (s values beyond 1) leading to the assumption that WEC processes start unsuspicious, as one would see…
Frictional behaviour of oxygen diffusion hardened titanium in dry sliding against Co–28Cr–5W–4Fe–3Ni–1Si cobalt alloy
2004
Abstract The results of conformal pin-on-disc tribological tests of a hard layer of the solid solution of oxygen in α-titanium sliding against a Co–28Cr–5W–4Fe–3Ni–1Si cobalt alloy counterspecimen are presented. The α-Ti(O) layer was diffusely produced over 2–8 h of oxidising in the superficial zone of a technical quality titanium specimen. The friction and wear responses of the system were recorded and the wear mechanisms were studied. Investigations of the material structure and chemical constitution in micro-areas of the titanium specimen, cobalt alloy counterspecimen and wear debris formed in dry sliding were performed with a Philips XL20 microscope equipped with an EDAX analyser. Crush…
A Magnetostrictive Electric Power Generator for energy harvesting from traffic: Design and experimental verification
2015
In the last decades, the growth in energy demand, the decrease of fossil fuels available in the market and the impact of anthropogenic factors on climate change has given new impulse to research on renewable energy systems, particularly those known as energy harvesting devices (EHDs) [1]. A large number of EHDs have been proposed, using different operating principle [1-4]. Among them, piezoelectric and magnetostrictive seem to be particularly suitable for the application in EHD. In these materials the application of external mechanical stress induces a change in the level of magnetization and therefore an electromotive force (emf) can be generated and collected in order to produce electrica…
Microsphere tensiometry to measure advancing and receding contact angles on individual particles
1999
In this paper, a method to measure the advancing and receding contact angles on individual colloidal spheres is described. For this purpose, the microspheres were attached to atomic force microscope cantilevers. Then the distance to which the microsphere jumps into its equilibrium position at the air-liquid interface of a drop or an air bubble was measured. From these distances the contact angles were calculated. To test the method, experiments were done with silanized silica spheres (4.1 μm in diameter). From the experiments with drops, an advancing contact angle of 101 ± 4° was determined. A receding contact angle of 101 ± 2° was calculated from the jump-in distance into a bubble. Both ex…
Rapid one-pot propargylamine synthesis by plasmon mediated catalysis with gold nanoparticles on ZnO under ambient conditions
2013
Surface plasmon excitation of gold nanoparticles on ZnO in the presence of an aldehyde, an amine and phenylacetylene led to rapid and selective formation of propargylamines with good yields (50-95%) at room temperature. Plasmon mediated catalysis is the best available route for this ternary coupling.