Aspects physico-chimiques du nettoyage de surface par laser : critères de choix de la longueur d'onde

Le procede de decapage de surface par faisceau laser impulsionnel est actuellement envisage comme une technique de substitution a des procedes de nettoyage chimique afin de reduire les risques sur l'environnement ou a des procedes mecaniques afin de reduire dans ce cas les risques d'endommagement du substrat a nettoyer. Si les sources lasers choisies peuvent etre regroupees dans le domaine des lasers impulsionnels (temps d'interaction de l'ordre de la nanoseconde), le choix de la longueur d'onde est rarement justifie a partir d'une etude physico-chimique de l'interphase substrat-contaminant a expulser. Differents exemples sont presentes illustrant le besoin de developper des bases de donnee…

Corrosion in amine solvents used for the removal of acid gases

International audience; Processes using amine solvents for the removal of CO 2 have long been used for the treatment of natural gas. More recently, developments in the field of post-combustion CO 2 capture have gained considerable interest for greenhouse gas mitigation. Even though the nature of the amine is different for both applications, the process flow diagrams are very similar. The raw gas is contacted with the amine solvent in an absorber column, and the CO 2 is absorbed by the solvent. The rich solvent containing the CO 2 then circulates to a regenerator, where the temperature is increased to strip the CO 2. The lean solvent then returns to the absorber for a new cycle. For these pr…

Passivity Breakdown: Development and Application of Local Chemical and Electrochemical Probe Methods

Abstract The most identified classes of phenomena at the origin of the passivity breakdown and the electrochemical and chemical factors controlling the induced localized corrosion are summarized before introducing the scientific concepts at the origin of the design of the local probe techniques used in recent advances in understanding localized corrosion processes. Examples concerning the surface reactivity of aluminium alloys are presented to support a final discussion on the needs for experimental developments with capabilities to support modelling.

Mechanism of brittle fracture in a ductile 316 alloy during stress corrosion

Abstract The ductile f.c.c. 316 alloy is shown to exhibit brittle transgranular (and intergranular) stress corrosion cracking in a 153°C MgCl2 solution at free corrosion potential. Tests on smooth and pre-cracked specimens are performed to identify the mechanisms of fracture. Transgranular cracking is related to both a discontinuous microcleavage mainly on {100} planes and a microshearing on {111} planes. A new physical modelization is proposed to explain the brittle transgranular cracking. It is based on the influence of the localized anodic dissolution on the enhancement of the plasticity at the crack tip. The formation of dislocation pile-ups and the conditions of restricted slip induce …

Électrochimie et corrosion à l'échelle des microstructures

Resume. Dans ce chapitre, on montre que le role de la microstructure sur les processus de corrosion localisee, par exemple la sensibilite d’un precipite par rapport au reste de la matrice, peut etre evalue et simule en tenant compte des processus de couplage galvanique et de transport des especes chimiques, grâce a l’evolution recente d’un ensemble de methodes d’analyses chimiques, electrochimiques et electriques dont la resolution spatiale est adaptee a l’echelle micronique qui caracterise la microstructure des alliages metalliques. Il est possible de disposer, a cette echelle, d’informations comme la difference de potentiel de surface intrinseque a la coexistence d’une phase et de sa matr…

Distribution pattern of river blennies in the Júcar River basin (eastern Spain)

Salaria fluviatilis in the Jucar river basin was found only in the Jucar River itself, the tributaries Cabriel and Escalona, and the irrigation channel Acequia Real. Blenny density varied from 0.2 to 3.1 ind m -2 Sites with blennies had significantly lower coliform counts than those without blennies.

Environmental Variables and Planktonic Communities in Two Ponds of El Hondo Wetland (SE Spain)

The annual cycle of physical and chemical variables and plankton dynamics was studied in two shallow ponds (East and West Ponds) of the El Hondo wetland, an ecosystem of international importance. Water conductivity increased up to 31-49 mS cm -1 as water level decreased due to high evaporation and minimal water inputs. Initially considered mesohaline, the waters were reclassified as polyhaline during the hot season. EP was subject to successive desiccation-flooding cycles, and flooding of the dried sediment caused the release of high concentrations of nitrogen and phosphorus compounds, which quickly depleted. The algal species composition was typical of eutrophic ecosystems, and the chlorop…

Laser assisted particle removal from Silicon wafers

We have studied the removal of submicrometer particles from silicon wafers by the steam laser cleaning (SLC) and dry laser cleaning (DLC) processes. These processes are currently being investigated as new promising cleaning technologies for complementing traditional methods in industrial applications. For SLC a thin liquid layer (e.g. a water-alcohol mixture) is condensed onto the substrate, and is subsequently evaporated by irradiating the surface with a short laser pulse. The DLC process, on the other hand, relies only on the laser pulse, without application of a vapor jet. Using well-characterized monodisperse polystyrene and silica particles as well as irregularly shaped alumina particl…

Effect of surface microcracks on pitting susceptibility of manganese sulfide containing stainless steels

Corrosion in alcanolamines for natural gas treatment - High temperature experiments in lean and rich conditions

International audience; In the oil and gas industry, acid gas removal is required for the treatment of natural gas. New applications were also recently pushed forward for CO 2 capture from the flue gas of power plants. For both applications, the most widespread industrial processes use absorption-desorption by an alcanolamine solvent. In such amine units for acid gas removal, corrosion represents an important operational concern. Influent parameters governing corrosion are temperature and acid gas loading, amine nature, and the presence of degradation by-products. Some of these parameters were studied with corrosion experiments in autoclave. Test temperature was between 110°C and 120°C, i.e…

In-situ characterisation of organosilane films formation on aluminium alloys by electrochemical quartz crystal microbalance and in-situ ellipsometry

Abstract Organosilane pre-treatments have been studied intensively during the last years in order to replace hexavalent chromium conversion treatments. The aim of this study is to follow in-situ the formation of this organosilane layer in solution. Two in-situ techniques, spectroscopic ellipsometry and electrochemical quartz crystal microbalance, were used to investigate the mechanism and the kinetics of this protective film formation. In-situ measurements highlight that the organosilane film observed after the drying process is not formed into the solution, but during the emersion and drying step. Hence, it has been possible to characterise the presence of a very thin organosilane layer in…