Effet inhibiteur à la longues chaînes et de dérivés thiazolés sur la corrosion du laiton Amirauté.optimale des petites stations d'épuration à boues activées

Dans cette étude, des mesures électrochimiques ont été réalisées pour caractériser le comportement du laiton Amirauté dans une solution de chlorure de sodium 0,5 M en l'absence d'inhibiteur et en présence d'un mélange d'amines à longue chaîne et de dérivés thiazolés. Cette formulation est utilisée pour le traitement des eaux des circuits de refroidissement. Les courbes courant-tension stationnaires et les diagrammes d'impédance électrochimique ont été obtenus avec une electrode tournante.La première partie de cette étude présente les résultats obtenus pour deux concentrations du mélange et deux temps d'immersion préalable au potentiel de corrosion. Les essais électrochimiques montrent que l'effet inhibiteur est d'autant plus marqué que la concentration augmente. Une légère diminution de la protection de la surface du laiton Amirauté est observée avec l'augmentation du temps de maintien au potentiel de corrosion.La deuxième partie de l'étude compare les effets inhibiteurs de chacun des constituants du mélange, d'une part, pour les valeurs de concentration utilisées lors du traitement des eaux des circuits de refroidissement (0,1 mg/l de solution contenant les dérivés thiazolés et 1 mg/l de solution contenant les alkylamines) et, d'autre part, pour des valeurs de concentration comparables (5 mg/l).Pour la concentration de 0,1 mg/l l'action inhibitrice des dérivés thiazolés n'a pas été clairement mise en évidence. Ainsi, la protection contre la corrosion des circuits de refroidissement en laiton Amirauté avec le mélange est apportée principalement par les alkylamines. Celles-ci forment un film compact très protecteur à la surface de l'électrode.Pour des valeurs de concentration plus importantes, l'addition de 0,5 mg/l de dérivés thiazolés à 5 mg/l d'alkylamines améliore la protection du matériau.In this study, electrochemical measurements were carriet out to characterize the behaviour of Admiralty Brass in a 0.5 M sodium chloride solution in the absence of inhibitors and in the presence of a mixture of alkylamines and thiazol-derived products. This formulation is employed for water treatment in cooling circuits.The steady-state current voltage curves and the impedance diagrams were obtained with a rotating disc electrode in order to control the hydrodynamic conditions.The first part of this study deals with the results obtained for two concentrations of the mixture and for two immersion times at the corrosion potential. It has been shown that the inhibitive effect is more marked when the concentration increases from 10 to 50 mg/l. A slight decrease of the protection of the brass surface is observed when the immersion time increasesThe second part of this study is a comparison of the inhibitive effects of each compound of the mixture, on one hand, for concentration values used in the water treatment (0.1 mg/l of tbe solution containing the thiazol-derived products and 1 mg/l of the solution containing the alkylamines) and on the other hand, for identical concentration values (5 mg/l ). For 0.1 mg/l, no inhibitive action of thiazol-derived products could be detected. Thus, the corrosion protection of cooling circuits in Admiralty brass is attributed essentially to the alkylamines. They form a thick, protective film at the electrode surface. For higher concentration values, the addition of 0.5 mg/l of thiazol-derived products to 5 mg/l of alkylamines improves the corrosion resistance of brass

Inhibition de la corrosion d'un acier au carbone par des produits dérivés de phosphonates en association avec des sels de zinc

Dans cette étude, des mesures électrochimiques ont été utilisées pour caractériser l'efficacité inhibitrice de produits dérivés de phosphonates associés à des sels de zinc, employés pour le traitement des eaux des circuits de refroidissement. L'influence de la concentration de cette formulation ainsi que l'effet du pH du milieu ont été étudiés.Les courbes courant-tension stationnaires et les diagrammes d'impédance électrochimique ont été obtenus avec des électrodes tournantes en acier au carbone dans une solution de chlorure de sodium à 200 mg l-1. Ce milieu a été choisi car sa faible conductivité électrique est proche de celle rencontrée dans les eaux naturelles.La méthode stationnaire (relevé des courbes courant-tension) a permis de déterminer la vitesse de corrosion en l'absence et en présence de l'inhibiteur et par conséquent, le taux de protection. Ainsi, le composé présente une très bonne efficacité dès les faibles concentrations (50 mg · l-1). Entre 50 et 200 mg · l-1, l'efficacité inhibitrice augmente de 95 à 98 %. Pour la concentration de 100 mg · l-1 il est efficace dans un large domaine de pH (de 5,5 à 9). Cette efficacité apparaît légèrement supérieure à pH = 7 et à pH = 8.Les valeurs des résistances de polarisation mesurées à partir des diagrammes d'impédance confirment les résultats obtenus à partir des courbes stationnaires.En outre, l'efficacité inhibitrice du composé a été comparée à celle de produits déjà testés au Laboratoire pour des utilisations identiques. Le chlorure de zinc, le monofluorophosphate de zinc et l'association d'une amine grasse et d'acide phosphonique présentent des efficacités moindres que le mélange testé ici à base de produits dérivés de phosphonates associés aux sels de zinc.In this study, electrochemical measurements were carried out to characterize the inhibitive efficiency of the association of phosphonate-derived products with zinc salts, employed for water treatment in cooling circuits.The influence of parameters such as the concentration of the formulation and the effect of the solutions pH on the protection of the metal were studied.Steady-state current-voltage curves and electrochemical impedance diagrams have been obtained for a carbon steel rotating disc in a 200 mg · l-1 NaCl solution. The choice of this medium is based upon the following criteria :(i) its low electrical conductivity is close to that encountered in natural saline waters ;(ii) its corrosivity is fairly high ;(iii) it Is formed by an easily reproducible baseline solution.The inhibitive efficiency has been determined tram the plotting of the cathodic potentiostatic curves. It is important to note that in low conductivity media, the current-voltage curves are distorted by a non-negligible uncompensated ohmic drop (I.Re), Re being the electrolyte resistance between the working and the reference electrodes. The interpretation of these curves (i.e. corrosion rate evaluation, Tafel slopes determination) is only possible if they have been corrected according to the following relationship. Eapparent = Etrue + ReIIn this study, the electrolytic resistance value has been determined from electrochemical Impedance measurements : the high frequency limit of the impedance gives Re.The ohmic drop is then automatically compensated by the potentiostat to obtain the corrected steady-state curve.The inhibitive efficiency is evaluated by the relationship :Ei = (icorr0-icorr / icorr0) x 100in which iocorr and icorr represent the current densities without and with inhibitor, respectively.In addition to the determination of the current densities obtained from the steady-state current-voltage curves, the polarization resistance, Rp, has been measured from the impedance diagram : the low frequency limit of the impedance gives the sum Re + Rp ; Rp is equal to the slope of the steady-state current voltage curve.In this study, only the evolution of this value as a function of concentration has been examined.It has been shown from the steady-state technique that the compound presents a very good efficiency for low concentrations (50 mg · l-1). Between 50 and 200 mg · l-1, the inhibitive efficiency increases from 95 to 98 %. For 100 mg · l-1 it is effective over a wide pH range (5.5 to 9) with a better protection for pH = 7 and pH = 8.The measurements of the polarization resistance corroborate these results.In a second part, the inhibitive efficiency of the compound has been compared to different inhibitors used for similar uses and tested in the laboratory. Thus, zinc chloride, zinc fluorophosphate and the association of fatty amine and phosphonic acid present a lower efficiency than the product tested here

Integrating ASCAT surface soil moisture and GEOV1 leaf area index into the SURFEX modelling platform: a land data assimilation application over France

The land monitoring service of the European Copernicus programme has developed a set of satellite-based biogeophysical products, including surface soil moisture (SSM) and leaf area index (LAI). This study investigates the impact of joint assimilation of remotely sensed SSM derived from Advanced Scatterometer (ASCAT) backscatter data and the Copernicus Global Land GEOV1 satellite-based LAI product into the the vegetation growth version of the Interactions between Soil Biosphere Atmosphere (ISBA-A-gs) land surface model within the the externalised surface model (SURFEX) modelling platform of Météo-France. The ASCAT data were bias corrected with respect to the model climatology by using a seasonal-based CDF (Cumulative Distribution Function) matching technique. A multivariate multi-scale land data assimilation system (LDAS) based on the extended Kalman Filter (EKF) is used for monitoring the soil moisture, terrestrial vegetation, surface carbon and energy fluxes across the domain of France at a spatial resolution of 8 km. Each model grid box is divided into a number of land covers, each having its own set of prognostic variables. The filter algorithm is designed to provide a distinct analysis for each land cover while using one observation per grid box. The updated values are aggregated by computing a weighted average. <br><br> In this study, it is demonstrated that the assimilation scheme works effectively within the ISBA-A-gs model over a four-year period (2008–2011). The EKF is able to extract useful information from the data signal at the grid scale and distribute the root-zone soil moisture and LAI increments throughout the mosaic structure of the model. The impact of the assimilation on the vegetation phenology and on the water and carbon fluxes varies from one season to another. The spring drought of 2011 is an interesting case study of the potential of the assimilation to improve drought monitoring. A comparison between simulated and in situ soil moisture gathered at the twelve SMOSMANIA (Soil Moisture Observing System–Meteorological Automatic Network Integrated Application) stations shows improved anomaly correlations for eight stations

Quantum Hall resistance standards from graphene grown by chemical vapor deposition on silicon carbide

Replacing GaAs by graphene to realize more practical quantum Hall resistance standards (QHRS), accurate to within $10^{-9}$ in relative value, but operating at lower magnetic fields than 10 T, is an ongoing goal in metrology. To date, the required accuracy has been reported, only few times, in graphene grown on SiC by sublimation of Si, under higher magnetic fields. Here, we report on a device made of graphene grown by chemical vapour deposition on SiC which demonstrates such accuracies of the Hall resistance from 10 T up to 19 T at 1.4 K. This is explained by a quantum Hall effect with low dissipation, resulting from strongly localized bulk states at the magnetic length scale, over a wide magnetic field range. Our results show that graphene-based QHRS can replace their GaAs counterparts by operating in as-convenient cryomagnetic conditions, but over an extended magnetic field range. They rely on a promising hybrid and scalable growth method and a fabrication process achieving low-electron density devices.Comment: 12 pages, 8 figure

Study of the microstructure resulting from brazed aluminium materials used in heat exchangers

Re-solidification of AA4343 cladding after brazing as well as the related precipitation in the modified AA3003 core material have been investigated. Analysis of the re-solidified material showed that partial dissolution of the core alloy occurs in both the brazing joints and away of them. Far from the brazing joints, the dissolution is, however, limited and diffusion of silicon from the liquid into the core material leads to solid-state precipitation in the so-called “band of dense precipitates” (BDP). On the contrary, the dissolution is enhanced in the brazing joint to such an extent that no BDP could be observed. The intermetallic phases present in the resolidified areas as well as in the core material have been analyzed and found to be mainly cubic alpha-Al(Mn,Fe)Si. These results were then compared to predictions made with available phase diagram information

Use of a stimulated echo sequence in the MRI study of the brain and spine

We describe in this paper how the STEAM sequence can be an efficient tool to obtain images free of flow artifacts in anatomical situation where the spin echo failed. The simplest way to eliminate flow artifacts is to exploit the dephasing induced by motion in magnetic field gradients and to reduce to zero the signal from moving tissues. This can be achieve by increasing the time elapsed between the spin excitation and the signal observed. Because of T2 relaxation, such an increase results in a signal decrease when the spin echo sequence is used. The STEAM sequence has the unique property that the time elapsed between observation and excitation can be increased without change in T2 value and so allows a good suppression of signals from the moving spins with short TE. Our results demonstrate that, although the stimulated echo intensity is only half that of a spin echo taken at the same read out time, the advantages of STEAM imaging can compensate for this partial loss in signal to noise in some particular clinical situations. The influence of mixing time on contrast has been evaluated using thoracic spine imaging and it has been shown that contrast between spine and CSF can be significantly improved (+ 60%) when TM is increased (from 17 ms to 50 ms). In the same time, the contrast between spine and fat issue decreases (40%). This last effect facilitates the adjustment of contrast window. Suppression of motion artifacts has first been evaluated with thoracic spine imaging, using a whole body coil. Suppression of artifacts was better than that obtained with a flow compensated spin echo sequence, especially in the case of kyphotic patients when a presaturation band was inefficient. In a second step suppression of motion artifacts has been evaluated from posterior fossa examination after injection of a paramagnetic contrast agent. The images obtained with the stimulated echo sequence show a dramatic reduction of signal from blood in the lateral sinus, and therefore an increase of quality by elimination of motion artifacts

From Research to Operational Biomonitoring of Freshwaters: A Suggested Conceptual Framework and Practical Solutions

International audienceThe contradictory demands of managers (quick relevant operational responses) and ecologists (need time for in-depth research) involved in freshwater biomonitoring are still relevant today. To contribute to solving this dilemma, we are proposing a novel biomonitoring approach, which among many others, could be used in this field and further developed in the future. Biomonitoring actions are integrated in conceptual schemes, in which hydrology, chemistry, hydrogeology and geomorphology bear as much importance as biology. Among biomonitoring tools, a harmonization system allows end-users to use a set of qualitative indicators (various biotic indices) and integrate the information given by individual biotic indices. Functional traits and calculation of an ecological potential in porous aquatic habitats (surficial coarse sediments and the hyporheic system) are regarded as a basis for assessing ecological functioning of streams and rivers. This last methodology takes into account the dynamics of water exchanges between surface water and groundwater. Objectives of ecological quality, ecological potentials and resilience capacity that need to be preserved or rehabilitated in aquatic habitats are established. In lakes, a similar approach was followed and a general typology of lake functioning was proposed, including that for urban lakes. All those biomonitoring tools are transferred to end-users and subject to further research. The final purpose is to promote practical high-tech tools which are continually and interactively connected with ongoing research