Use of acoustic emission technique for the early detection of aluminium alloys exfoliation corrosion

International audienc

LASER SURFACE ALLOYING OF A MILD STEEL FOR CORROSION RESISTANCE IMPROVEMENT

Surface alloys were produced by laser melting of different predeposits into the outer part of a mild steel substrate. Three types of coatings were used : electroless nickel (containing phosphorous), electroless nickel in which chromium carbide particles were introduced during deposition and duplex coatings made of, first, a nickel layer (electroless or electrodeposited) and then, a chromium layer. The surface alloying treatments were performed using a cw high power CO2 laser and the multiple track melting technique with 60 % overlap between each track. A single laser scan was used. The obtained surface alloys show excellent adherence without porosity or cracking. A detailed microstructural investigation revealed a fine dendritic microstructure. Phosphorous, when present, is segregated in the interdendritic areas. The corrosion resistance of the surface alloys was tested by electrochemical techniques in various neutral or acidified saline media deaerated or naturally aerated. With the first type of predeposit, surface alloys exhibit a corrosion resistance similar to that of electroless nickel but with a much higher adherence of the coating to the substrate. With the second type of predeposit, the increase in corrosion resistance is limited due to the low chromium concentration obtained in solid solution. On the contrary with the third type of predeposits (duplex layers), surface alloys exhibit a high corrosion resistance especially when electrolytic nickel coating was used

Physico-chemical properties and photo-reactivity relationship for para-substituted phenols in photo-assisted Fenton system

The reactivity of phenolic compounds can be drastically affected by the electronic nature of the substituting groups. In this work, the effect of physico-chemical properties on the reactivity via photo-assisted Fenton catalysis is reported for several para-substituted phenols (p-nitrophenol (p-NO2), p-chlorophenol (p-Cl), p-hydroxybenzaldehyde (p-CHO), phenol (p-H), p-methoxyphenol (p-OCH3), p-hydroxyphenol (p-OH)) in order to cover a wide range of electronics effects. Electronic descriptors (Hammett constants (sigma). frontier molecular orbital energies (E-HOMO), electronic and zero point energies (E, E-ZERO)). electrochemical descriptor (half wave potential for the oxidation of phenols to phenoxyl radical (E-1/2)), and other descriptors (acidity constants (pK(a)), maximum absorption wavelength (lambda(max)), 1-octanol/water partition coefficient (K-ow)) were correlated with the initial Fenton and photo-Fenton degradation rates (r(0)). Linear relationships were obtained between the initial Fenton and photo-Fenton degradation rates and electronic descriptors. However p-Cl and p-CHO showed higher photo-Fenton degradation rates than ones predicted by the model implying the presence of weaker bonds in these molecules. The biodegradability increase due to the photo-Fenton process was strong but poorly selective suggesting that the produced intermediates present a similar biodegradability. (C) 2009 Elsevier B.V. All rights reserved

Comparative evaluation of polymer surface functionalization techniques before iron oxide deposition. Activity of the iron oxide-coated polymer films in the photo-assisted degradation of organic pollutants and inactivation of bacteria

The preparation of iron oxide-coated polymer films and their photocatalytic activity in organic pollutants degradation and bacterial inactivation is described. Polyvinyl fluoride (PVF), polyethylene (PE) and polyethylene terephtalate (PET) films were used as catalyst supports. Polymer surfaces were functionalized by vacuum-UV radiation (V-UV) and radio-frequency plasma (RF-P); and also by photo-Fenton oxidation (P-FO) and TiO2 photocatalysis (Ti-PC) in solution. These pre-treatments were performed to improve iron oxide adhesion on the commercial polymer surface. The functionalized polymers films (P-f) were afterward immersed in an aqueous solution for the deposition of iron oxide layer by hydrolysis of FeCl3. The photocatalytic activities of iron oxide-coated functionalized polymers films (P-f-Fe oxide) prepared by different methods were compared during hydroquinone degradation in presence of H2O2. RF-P and Ti-PC pre-treated polymers showed significantly higher photocatalytic activity and long-term stability during processes leading to pollutant abatement, if compared with not treated ones (NT), although similar leaching of iron was observed for all the materials. PET bottles (PETb) were used as reactor and catalyst supports. The produced PETbf-Fe oxide surfaces were efficient in photo-assisted bacterial inactivation in the presence of H2O2, and no dissolved iron species were detected in solution. (C) 2010 Elsevier B.V. All rights reserved

On the opportunity to use non-intrusive acoustic emission recordings for monitoring uniform corrosion of carbon steel and austenitic stainless steel in acid and neutral solutions

International audienceUniform corrosion of steels is responsible for the early damaging of many industrial parts and its control and monitoring prevent against significant economic and environmental failures. Yet, classical estimation of corrosion damage gives only the result of the average corrosion rate but not the 'instantaneous' value. In that context, acou stic emission (AE) technique, based on the rapid release of energy within a material generating a transient elastic wave propagation, was carried out to get quantitative information on corrosion evolution. Uniform corrosion conditions close to industrial ones were simulated with the use of a pilot device, allowing the simultaneous control and measurement of the temperature and pH of the saline and/or acidic solutions, as well as the amount of dissolved oxygen and the fluid velocity, together with AE recordings. Emission so urces during uniform corrosion of carbon steel and austenitic stainless steel were then identified as hydrogen release, friction of hydrogen bubbles and evolution of corrosion deposits, each of these mechanisms inducing the emission of AE signals with specific parameters. Moreover, it appears clearly that acoustic emission measurements are in good correlation with aggressiveness of the corrosive media, and a semi-quantitative correlation is obtained between AE activity and corrosion rate for austenitic stainless steel. Whereas initial surface conditions greatly influence the acoustic activity, AE monitoring appears to be a rewarding technique for detecting corrosion rate evolutions during process modifications

Loss-of-vacuum, loss-of-coolant, and loss-of-flow accident analysis for NET ITER

Analyses are presented οη hypothetical accidents in NET/ITER involving: -air ingress in the graphite-coated plasma chamber through a breach in the vacuum vessel (LOVA); -loss-of-coolant inside the vacuum vessel with water ingress in the plasma chamber (inside LOCA); -loss-of-coolant outside the vacuum vessel (outside LOCA); -loss-of-power with the worst case conditions of absence of any cooling by natural convection (total LOCA) , and with natural convection flow (total LOFA). Ιn this paper the modeling of these accidents and important results are shown

Loss-of-vacuum, loss-of-coolant, and loss-of-flow accident analysis for NET ITER

Analyses are presented οη hypothetical accidents in NET/ITER involving: -air ingress in the graphite-coated plasma chamber through a breach in the vacuum vessel (LOVA); -loss-of-coolant inside the vacuum vessel with water ingress in the plasma chamber (inside LOCA); -loss-of-coolant outside the vacuum vessel (outside LOCA); -loss-of-power with the worst case conditions of absence of any cooling by natural convection (total LOCA) , and with natural convection flow (total LOFA). Ιn this paper the modeling of these accidents and important results are shown