Corrosion Protection of Magnesium Alloys: From Chromium VI Process to Alternative Coatings Technologies

Magnesium 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

Elaboration d'une nouvelle formulation de bains de satinage du verre en vue d'une résolution de la pollution à la source

Le dépolissage chimique du verre, appelé satinage , est couramment utilisé dans l industrie comme méthode de décoration des emballages en verre. Ce traitement se fait par trempage dans des bains très concentrés en ions ammonium et en acide fluorhydrique, espèces qui se retrouvent par la suite dans les eaux de rinçage des pièces et dont le traitement pose problème. Afin de contourner ce problème, la solution envisagée a été de réduire la pollution à la source et de remplacer les ions ammonium par des ions potassium moins toxiques. Dans le cas général, le relief de surface obtenu, responsable de l aspect satiné, présente des structures pyramidales et constitue une empreinte de la couche de précipités formée après l attaque du verre par l acide fluorhydrique. Les principaux composants de cette couche sont des hexafluorosilicates dont la faible solubilité, la nature passivante et le mode de cristallisation influent sur les formes et les tailles des pyramides microscopiques de surface. Afin d obtenir l aspect désiré et d augmenter la solubilité de l hexafluorosilicate de potassium, la présence d acide sulfurique est indispensable dans la nouvelle formulation. Un ajout de poudre de sulfate de baryum inerte, en quantité et granulométrie contrôlées, s est aussi avéré nécessaire pour améliorer la qualité du dépoli. En respectant le même procédé de dépolissage utilisé avec les formulations à base de bifluorure d ammonium, l efficacité de la nouvelle formulation a pu être validée d abord en laboratoire puis par des essais pilote à l échelle semi industrielle et une gestion rigoureuse des bains a été mise en place grâce à un suivi analytique simple des principes actifs.Frosting glass is widely used as a decorating method in the industry of glass packing. To obtain this surface aspect, the pieces of glass have to be immersed into a frosting bath made of ammonium bifluoride and hydrofluoric acid. These species are then found in waste water and can t be removed by any efficient chemical treatment. To resolve this problem, the solution is to reduce the pollution at the source by replacing the ammonium ions by less toxic potassium ions. The obtained surface relief, responsible for the frosted aspect, generally presents pyramidal structures and constitutes a print of the layer of precipitates formed after the attack of hydrofluoric acid on glass. The principal components of this layer are hexafluorosilicates of which low solubility, passivating nature and crystallization mode influence the shapes and the sizes of the microscopic pyramids observed on the glass surface. In order to obtain the desired aspect and to increase the solubility of the potassium hexafluorosilicate, the presence of sulphuric acid is essential in the new formulation. An addition of inert barium sulphate powder, in controlled quantity and granulometry, is also necessary to improve quality of the frosted aspect. Respecting the same process of frosting, with the formulations containing ammonium bifluoride, the effectiveness of the new formulation was initially validated in laboratory then by pilot tests on a semi industrial scale. A rigorous monitoring of the baths was also elaborated by a simple analytical follow-up of the active ingredients.PAU-BU Sciences (644452103) / SudocSudocFranceF

From hexafluorotitanate waste to TiO2 powder: Characterization and evaluation of the influence of synthesis parameters by the experimental design method

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New investigations on the LGT crystal intended for time and frequency applications

cited By 0International audienceMaterials of the langasite family are of current interest for both Bulk Acoustic Wave and Surface Acoustic Wave devices. In particular, they could be promising solutions to Frequency and Time applications due to their g/product, two to three times higher than for the quartz crystal [1]. We have shown that this encouraging result is strongly linked to the crystal quality [2] and to the post thermal treatment which has been submitted the device. Among the numerous crystals belonging to the LGS family, LGT seems more interesting because of the best combination of quality of growth and material parameters [3, 4]. © 2010 IEEE

Glass formation in the GexTe100x binary system: Synthesis by twin roller quenching and co-thermal evaporation techniques

International audienceThe Ge–Te system exhibits one main composition domain where glasses can be easily prepared by melt quenching technique; this domain is centered on the eutectic composition Ge15Te85. In this work, bulk flakes and films of composition GexTe100x with x 6 50 at.% were prepared by two different quenching techniques: (i) the twin roller quenching for bulk flakes and, (ii) the co-thermal evaporation for films (with thickness comprised between 2 and 14 lm). Electron Probe Micro-Analysis was used to check the composition of the materials while X-ray diffraction allowed identifying the amorphous state and/ or the crystalline phases present in the GexTe100x samples. Thermal properties for both types of materials were investigated by differential scanning calorimetry. The glass-forming regions were: 11.7– 22.0 at.% Ge for bulk flakes and 10.2–35.9 at.% Ge for films. A similar thermal behavior of bulk flakes and thick films was highlighted by Differential Scanning Calorimetry

Couplage photocatalyse-oxydation par le ferrate (VI) pour le traitement du colorant rhodamine 6G

Un facteur limitant de l’oxydation photocatalytique du dioxyde de titane (TiO2) sous irradiation UV est la recombinaison des électrons de la bande de conduction (e-cb) avec les trous d’électron (h+vb) à la surface de TiO2. Le couplage du ferrate(VI), Fe(VI), connu comme un oxydant respectueux de l’environnement, avec la photocatalyse UV/TiO2 pourrait conduire à une synergie oxydative de par le piégeage de e-cb par Fe(VI) et la consécutive formation de l’espèce hautement réactive Fe(V). Cette étude décrit les résultats du couplage TiO2 commercial P25 avec Fe(VI) sous forme pure ou sous forme d’une matière synthétisée dans notre laboratoire (produit solide nommé Fe(VI) matter) pour l’abattement du colorant rhodamine 6G (R6G). Les cinétiques de transformation de R6G ([R6G]0 = 10‑5 M; pH = 8,00 ± 0,05), en présence de TiO2 ([P25] = 0,1 g∙L‑1) illuminé sous UV et/ou de Fe(VI) ([Fe(VI)]0 = 10‑4 M) sont suivies par spectrophotométrie. Une synergie est mise en évidence lors du traitement de R6G par UV/TiO2/Fe(VI) pur, conduisant à une accélération de la transformation de R6G et à une minéralisation plus importante. Cependant, cet abattement n’est pas atteint lors du couplage UV/TiO2/Fe(VI) matter. Une étude de l’impact de sels inorganiques présents dans Fe(VI) matter sur l’activité photocatalytique est présentée. Le sulfate, SO42‑, et le Fe(OH)3 en particulier mènent à une forte inhibition de l’activité de TiO2. Le suivi de la production des radicaux hydroxyles (OH•) montre une inhibition physique de leur production due à la formation d’une couche de sels inorganiques à la surface de TiO2 et au piégeage de radicaux OH• dans la solution.A limiting factor in photocatalytic oxidation using UV irradiation of titanium dioxide (TiO2) is the recombination of conduction band electrons (e-cb) with electron holes (h+vb) on TiO2 surface. Coupling ferrate(VI), Fe(VI), known as an “environmentally friendly” oxidant, with UV/TiO2 photocatalysis may involve an oxidation synergism arising from the Fe(VI) scavenging of e-cb and the corresponding beneficial formation of highly reactive Fe(V). This study describes the results of coupling P25 TiO2 and Fe(VI) (pure or Fe(VI) matter synthesized in our laboratory) to remove the dye rhodamine 6G (R6G). Abatement kinetics for R6G, ([R6G]0 = 10‑5 M; pH = 8.00 ± 0.05), in presence of TiO2 ([P25] = 0.1 g∙L‑1) illuminated under an UV source and/or Fe(VI) ([Fe(VI)]0 = 10‑4 M) were followed by spectrophotometry. A synergism was highlighted during the treatment of R6G by UV/TiO2/pure Fe(VI), leading to a faster abatement and a better mineralization. However, this abatement was not reached when coupling Fe(VI) matter with UV/TiO2. A study of the impact of the inorganic salts present in the Fe(VI) matter on the oxidative activities is presented. Sulfate, SO42‑, and Fe(OH)3 in particular lead to a high inhibition of TiO2 activity. The monitoring of hydroxyl radical (OH•) production highlighted a physical inhibition of the formation of OH•, probably due to the formation of an inorganic salt layer at the surface of TiO2 and also to the scavenging of OH• in the bulk solution

Approach to spatialize local to long-range atmospheric metal input (Cd, Cu, Hg, Pb) in epiphytic lichens over a meso-scale area (Pyrénées-Atlantiques, southwestern France)

International audienceGeographically based investigations into atmospheric bio-monitoring usually provide information on concentration or occurrence data and spatial trends of specific contaminants over a specified study area. In this work, an original approach based on geographic information system (GIS) was used to establish metal contents (Hg, Cu, Pb, and Cd) in epiphytic lichens from 90 locations as atmospheric bio-monitors over a meso-scale area (Pyrénées-Atlantiques, southwestern France). This approach allows the integration of the heterogeneity of the territory and optimization of the sampling sites based on both socioeconomical and geophysical parameters (hereafter defined as urban, industrial, agricultural, and forested areas). The sampling strategy was first evaluated in several sites (n = 15) over different seasons and years in order to follow the temporal variability of the atmospheric metal input in lichens. The results demonstrate that concentration ranges remain constant over different sampling periods in “rural” areas (agricultural and forested). Higher variability is observed in the “anthropized” urban and industrial areas in relation to local atmospheric inputs. In this context, metal concentrations in lichens over the whole study show that (1) Hg and Cd are homogeneous over the whole territory (0.14 ± 0.04 and 0.38 ± 0.26 mg/kg, respectively), whereas (2) Cu and Pb are more concentrated in “anthropized” areas (9.3 and 11.9 mg/kg, respectively) than in “rural” ones (6.8 and 6.0 mg/kg, respectively) (Kruskall-Wallis, K(Cu) = 13.7 and K(Pb) = 9.7, p < 0.00001). They also showed a significant local enrichment for all metals in many locations in the Pays Basque (West) mainly due to metal and steel industrial activities. This confirms the local contribution of this contamination source over a wider geographic scale. A multiple linear regression model was applied to give an integrated spatialization of the data. This showed significant relationships for Pb and Cu (adjusted r2 of 0.39 and 0.45, respectively), especially with regards to variables such as industry and road densities (source factors) and elevation or water balance (remote factors). These results show that an integrated GIS-based sampling strategy can improve biomonitoring data distribution and allows better differentiation of local and long-range contamination

Determination of the chromium(III) reduction mechanism during chromium electroplating

International audienceThe reduction mechanism of Cr(III) depends on the nature of the complexing agent present in electroplating solutions. In pure water solutions and without any other additives, Cr (III) is complexed with water molecules, creating a stable [Cr(H2O)6]3+ complex. [Cr(H2O)6]3+ can be reduced to Cr(0) in two steps via a chromium(II) intermediate species. However, this reduction is not quantitative, and the Cr(0) coating is difficult to grow. The destabilization of the [Cr(H2O)6]3+ complex via the addition of an organic complexing agent allows the formation of a reducible Cr(III) complex. The different complexes obtained with the addition of oxalate, formate or acetate were characterized by UV–visible spectroscopy and HPLC-ICP/AES. The nature of the ligand, the [Cr]/[L] ratio and the pH of the solution influence the chemical mechanism of the Cr(III) reduction. Independently of the complex nature, the reduction of Cr(III) to Cr(0) occurs in one step with the three studied complexing agent. Moreover a more quantitative reduction can be obtained by using an organic complexing agent, low [Cr]/[L] ratios and a pH of approximately 3.5

Oxydation des Hydrocarbures Aromatiques Polycycliques (HAPs) et de leurs sous-produits par injection de ferrate de potassium dans la zone saturée

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Oxidation of PAHs and their by-products (polar PACs) in the saturated zone of DNAPL-contaminated sub-soils after pumping

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