466 research outputs found
Al-Pt MOCVD coatings for the protection of Ti6242 alloy against oxidation at elevated temperature
Results on isothermal oxidation at 873K for 90 h of Al-Pt coatings on Ti6242 coupons are reported. These coatings were obtained by low temperature, low pressure metalorganic chemical vapor deposition using Me3(MeCp)Pt(VI) and dimethylethylamine alane. Three coating architectures were investigated, namely pure Al, Pt and Al sequential sublayers, and co-deposited Al and Pt. Oxidation kinetics revealed a strong transient oxidation regime followed by a diffusion driven parabolic one. Such coatings allow to decrease oxidation kinetics more than one order of magnitude compared with those of the bare Ti6242. Scanning electron microscopy, second ion mass spectrometry, X-ray diffraction and transmission electron microscopy revealed that these coatings present a rough surface morphology. They are dense, they develop scales composed of γ-Al2O3 and δ-Al2O3 and they prevent titanium diffusion from the alloy to the surface. It is concluded that coatings produced by this process show promise for use as effective protection against oxidation of Ti6242 alloys and consequently they may raise the maximum operating temperature tolerated by corresponding parts in helicopter turboengines
Players or pawns? : "professionalism" and teacher disunity in the Western Cape, 1980-1990
Bibliography: pages 275-286.Focussing primarily on black teacher groups, this dissertation will describe the remarkable events within teacher politics in the Western Cape in the 1980s, following from the Soweto uprising of 1976. The decade of the eighties marked massive changes in the political and educational context within which teachers worked. After 1976, schools became the focus of opposition to the apartheid state. The atmosphere within schools changed as many students rejected the schooling proffered them by the state, and the "professional" implementation of state schooling by teachers. The liberation movement grew as the decade progressed, bolstered by a militant black trade union movement. The liberation struggle expanded and community-based protest drew schools into a broader, societal opposition to the state. The nature of schooling changed, as students and other elements of the liberation movement rejected apartheid education, and began fostering alternative education. Most notably, People's Education articulated both a rejection of state education and a desire for relevant, democratic schooling
Adolescent girls
This thesis describes the author\u27s two-year documentary photography project showing adolescent girls in two schools in New York City. It details the development of her photographic style and her approach to her subject. It also discusses work by other photographers that influenced her
Modelling the corrosion behaviour of Al2CuMg coarse particles in copper-rich aluminium alloys
The corrosion behaviour of 2024 aluminium alloy in sulphate solutions was studied; attention was focused on the influence of coarse intermetallic Al2CuMg particles on the corrosion resistance of the alloy. Model alloys representative of the aluminium matrix and of Al2CuMg coarse intermetallics were synthesized by magnetron sputtering. Open-circuit potential measurements, current–potential curve plotting and galvanic coupling tests were performed in sulphate solutions with or without chlorides. Further explanations were deduced from the study of the passive films grown on model alloys in sulphate solutions. The results showed that model alloys are a powerful tool to study the corrosion behaviour of aluminium alloys
Galvanic corrosion of aluminium–copper model alloys
Galvanic coupling between different α and θ phase-containing model Al–Cu alloys, deposited by magnetron sputtering, has revealed that the anodic α phase did not suffer corrosion and remained in the passive state in sulphate solution. Conversely, sulphate ions induced pitting of the cathodic θ phase. Pitting susceptibility of the cathode increased when the difference between the copper content of the anode and cathode increased. Similar observations were made for all the galvanic couples; further, the higher the copper content of a phase, then the greater its susceptibility to pitting
Ostracods and paleoambiental inferences in the Plottier Formation (Coniancian - Upper Cretaceous) of the Barreales Lake, Neuquén
Upper Cretaceous outcrops, at the northeast of Barreales lake, NeuquĂ©n, Argentina, has given in the last 20 years a rich vertebrate fauna including dinosaur, reptiles, fish and plants on different sites. In this contribution, rocks of the Plottier Formation at Babilonia Site at Proyecto Dino Geopaleontological Park have given, for the first time, an interesting microfauna composed by ostracods. The ostracofauna recovered is represented by the family Ilyocyprididae with four taxa, Neuquenocypris calfucurensis Musacchio, 1973, Neocyprideis zampalensis (Angelozzi, 1980), Neuquenocypris tenuipunctata Musacchio & Simeoni, 1991 and Neuquenocypris nahuelniyuensis Musacchio, 1989 and the family limnocytheridae, with one taxa Vecticypris sp. The ssociation of theses ostracod indicates a paleoenvironment characterized by a shallow meandering river with low energy, probably an abandoned oxbow lake. Palaeoecological analyses indicate a fresh water with fluctuating oligohaline salinities throughout deposition.Fil: Kihn, Romina Gisela. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Instituto de Ciencias de la Tierra y Ambientales de La Pampa. Universidad Nacional de La Pampa. Facultad de Ciencias Exactas y Naturales. Instituto de Ciencias de la Tierra y Ambientales de La Pampa; ArgentinaFil: Calvo, Jorge Orlando. Universidad Nacional del Comahue. Centro PaleontolĂłgico Lago Barreales; Argentin
Large scale production of multi-walled carbon nanotubes by fluidized bed catalytic chemical vapor deposition : a parametric study
A parametric study investigating the impact of temperature, run duration, total pressure, and
composition of the gaseous phase on the catalytic growth of multi-walled carbon nanotubes
(MWNT) has been performed. MWNT have been produced very selectively on the multi
gram scale by catalytic chemical vapor deposition from ethylene in a fluidized bed reactor.
The kinetics of MWNT growth is fast and, with the catalyst used, no induction period has
been observed. The kinetic law is positive order in ethylene concentration and the process is
limited by internal diffusion in the porosity of the catalyst. The formation of MWNT in the
macroporosity of the catalyst induces an explosion of the catalyst grains. Such a process, thanks to the absence of temperature gradient and to the efficient mixing of the grains allows a uniform and selective treatment of the catalyst powder leading to very high selectivity
towards MWNT formation. High purity MWNT have been obtained after catalyst dissolution.
Depending on the temperature of production, the specific surface area of this material ranged
between 95 and 455 m2/g
Electrochemical Behavior of Magnetron-Sputtered Al–Cu Alloy Films in Sulfate Solutions
Model alloys, generated by magnetron sputtering, have been employed to understand the role of copper on the corrosion behavior of aluminum alloys. Binary Al–Cu alloys, with copper contents between 0 and 100 atom %, were synthesized with well-controlled compositions, embracing single-phase alpha and theta alloys together with multiphase alloys. Electrochemical measurements confirmed the stability of the thin alloy films and revealed that the corrosion behavior of the alpha, theta, and eta2 phases differed strongly in the cathodic region. Further, in the anodic region, phases of high copper content suffered pitting in sulfate solutions, while the alpha phase remained passive
Why do corporations embrace the LGBTQ+ cause?
©2023 Authors. This manuscript version is made available under the Creative Commons Attribution–NonCommercial–NoDerivatives 4.0 International (CC BY–NC–ND 4.0) license, https://creativecommons.org/licenses/by-nc-nd/4.0/fi=vertaisarvioimaton|en=nonPeerReviewed
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