47 research outputs found
Corrosion Protection of Magnesium Alloys: From Chromium VI Process to Alternative Coatings Technologies
Get PDFMagnesium and its alloys present several advantages such as a high strength/weight ratio and a low density. These properties allow them to be used for many aeronautical applications but they are very sensitive to corrosion. In order to solve this problem, chromium VI conversion coatings (CCC) are deposited on the surface before a protective top coat application. This process is now limited by several environmental laws due to the high toxicity of hexavalent chromium. However the chemical mechanisms of CCC deposition will be detailed in this chapter in order to understand the chemical properties of this coating. Pre-treatment steps allow cleaning and preparing the surface for improving the coating deposition. A final layer of chromium (III) oxide and magnesium hydroxide composes the coating allowing the protective properties. Orthorhombic potassium chromate clusters trapped on the coating surface give self-healing property to the coating.
Alternative conversion coatings are based onto solutions containing chromium (III), permanganate, phosphates, Rare Earth Elements (REEs) or vanadium. The second part of this chapter will detail the deposition and the protection mechanisms of these promising processes of CrVI substitution. Among them, permanganate/phosphate-based coating presents a better corrosion resistance than CCC and REEs have very efficient self-healing properties
Random sequential adsorption on a dashed line
Full text linkWe study analytically and numerically a model of random sequential adsorption
(RSA) of segments on a line, subject to some constraints suggested by two kinds
of physical situations:
- deposition of dimers on a lattice where the sites have a spatial extension;
- deposition of extended particles which must overlap one (or several)
adsorbing sites on the substrate.
Both systems involve discrete and continuous degrees of freedom, and, in one
dimension, are equivalent to our model, which depends on one length parameter.
When this parameter is varied, the model interpolates between a variety of
known situations : monomers on a lattice, "car-parking" problem, dimers on a
lattice. An analysis of the long-time behaviour of the coverage as a function
of the parameter exhibits an anomalous 1/t^2 approach to the jamming limit at
the transition point between the fast exponential kinetics, characteristic of
the lattice model, and the 1/t law of the continuous one.Comment: 14 pages (Latex) + 4 Postscript figure
Adsorption of Line Segments on a Square Lattice
Full text linkWe study the deposition of line segments on a two-dimensional square lattice.
The estimates for the coverage at jamming obtained by Monte-Carlo simulations
and by -order time-series expansion are successfully compared. The
non-trivial limit of adsorption of infinitely long segments is studied, and the
lattice coverage is consistently obtained using these two approaches.Comment: 19 pages in Latex+5 postscript files sent upon request ; PTB93_
La politique économique de François Hollande (2012-2014). Trahison électorale, ralliement économique, rupture politique
No full textEn mai 2012, François Hollande est élu à la présidence de la République. Un gouvernement socialiste se met en place et décide, 6 mois après son élection, de mettre en oeuvre une politique économique aux accents libéraux en parfaite contradiction avec les engagements de campagne du candidat Hollande. Même si l'évolution du socialisme économique laissait présager ces choix économiques, il n'en reste pas moins que la politique de compétitivité de François Hollande constitue une véritable trahison électorale. A travers une analyse du personnel dirigeant et du changement des modes de gouvernement de l'économie, ce mémoire analyse les ressorts de la décision prise par le gouvernement socialiste en 2012
RANDOM SEQUENTIAL ADSORPTION OF LINE SEGMENTS - UNIVERSAL PROPERTIES OF MIXTURES IN 1, 2 AND 3D LATTICES
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RANDOM SEQUENTIAL ADSORPTION OF LINE SEGMENTS - UNIVERSAL PROPERTIES OF MIXTURES IN 1, 2 AND 3D LATTICES
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