Barrier effect to charge injection in polyethylene by silver nanoparticles containing plasma polymer composites investigated by conductivity measurements

International audienceMain challenge in the development of HVDC polymeric insulation is to avoid the accumulation of space charge under electrical and/or thermal stresses which can significantly reduce the component reliability. Injection mitigation in low density polyethylene (LDPE) films by plasma processed silver nanoparticles (AgNPs) containing plasma polymer composites was recently reported through space charge measurements. The barrier effect has been assigned to the creation of permanent deep traps by introducing silver nanoparticles near the polyethylene surface. To substantiate the above findings, current measurements realized on composite layers and on polyethylene films with and without silver nanoparticles have been carried out. It is shown that in the presence of AgNPs in organosilicon layer, polarization/depolarization currents are one order of magnitude lower, transient currents decay faster and are not sensitive to multiple polarization. This can be understood if the AgNPs in the layer are acting as deep traps mitigating further injection with the result to decrease the apparent conductivity of the layer and to increase its breakdown strength. Similar trend is observed in polyethylene tailored by composite layer. These results strengthen the interpretation of the barrier effect based on space charge stabilized by deep traps formed by the AgNPs

Elaboration and characterization of Fe1–xO thin films sputter deposited from magnetite target

Majority of the authors report elaboration of iron oxide thin films by reactive magnetron sputtering from an iron target with Ar–O2 gas mixture. Instead of using the reactive sputtering of a metallic target we report here the preparation of Fe1–xOthin films, directly sputtered froma magnetite target in a pure argon gas flow with a bias power applied. This oxide is generally obtained at very low partial oxygen pressure and high temperature.We showed that bias sputtering which can be controlled very easily can lead to reducing conditions during deposition of oxide thin film on simple glass substrates. The proportion of wustite was directly adjusted bymodifying the power of the substrate polarization. Atomic force microscopy was used to observe these nanostructured layers. Mössbauer measurements and electrical properties versus bias polarization and annealing temperature are also reported

Quantifier l'effet de choix du site dans l'incertitude des jaugeages ADCP par transects

HMEM, Durham, New Hampshire, USA, 09-/07/2017 - 12/07/2017International audienceStage-discharge rating curves are used to relate streamflow discharge to continuously measured river stage readings to create a continuous record of streamflow discharge. The stage-discharge relationship is estimated and refined using discrete streamflow measurements over time, during which both the discharge and stage are measured. There is uncertainty in the resulting rating curve due to multiple factors including the curve-fitting process, assumptions on the form of the model used, fluvial geomorphology of natural channels, and the approaches used to extrapolate the rating equation beyond available observations. This rating curve uncertainty leads to uncertainty in the streamflow timeseries, and therefore to uncertainty in predictive models that use the streamflow data. Many different methods have been proposed in the literature for estimating rating curve uncertainty, differing in mathematical rigor, in the assumptions made about the component errors, and in the information required to implement the method at any given site. This study describes the results of an international experiment to test and compare streamflow uncertainty estimation methods from 7 research groups across 9 institutions. The methods range from simple LOWESS fits to more complicated Bayesian methods that consider hydraulic principles directly. We evaluate these different methods when applied to three diverse gauging stations using standardized information (channel characteristics, hydrographs, and streamflow measurements). Our results quantify the resultant spread of the stage-discharge Quantifying the uncertainty of discharge measurements (or "gaugings") is a challenge in the hydrometric community. A useful tool to empirically estimate the uncertainty of a gauging method is the field inter-laboratory experiment (Le Coz et al., 2016). Previous inter-laboratory experiments conducted in France (in 2009, 2010, 2011 and 2012) showed that the expanded uncertainty (with a probability level of 95%) of an ADCP gauging made of six successive transects is typically around 5% under optimum site conditions (straight reach, uniform and smooth streambed cross-section, homogeneous flow, etc.) and may be twice higher under poorer site conditions. In practice, the selected cross-section does not always match all quality requirements which may result in larger uncertainty. However, the uncertainty due to site selection is very difficult to estimate with predictive equations. From 9 to 10 November 2016, 50 teams from 8 different countries, using 50 ADCPs simultaneously, conducted more than 600 discharge measurements in steady flow conditions (~14 m3/s released by a dam). 26 cross-sections with various shapes and flow conditions were distributed over 500 meters along the Taurion River at Saint-Priest-de-Taurion, France. A specific experiment protocol, which consisted of circulating every team over half of the cross-sections, was implemented in order to quantify the impact of site selection on the discharge measurement uncertainty. Beyond the description of the experiments, uncertainty estimates are presented. The overall expanded uncertainty of a 6-transect ADCP gaugings (duration around 720 seconds) is estimated to be around 6%.The uncertainty of the discharge measurements varies among the cross-sections. These variations are well correlated to the expert judgment on the cross-section quality made by each team. First results seem to highlight a relation between uncertainty computed for each cross-section and criteria such as flow shallowness and measured discharge ratio. Further investigations are necessary to identify the criteria related to error sources that are possibly meaningful for categorizing measurement conditions and site selection. Moreover, experimental uncertainty and the uncertainty predicted by analytical methods such as QRev, QUant, OURSIN, RiverFlowUA or QMSys software will be compared

Valorisation of Biowastes for the Production of Green Materials Using Chemical Methods

With crude oil reserves dwindling, the hunt for a sustainable alternative feedstock for fuels and materials for our society continues to expand. The biorefinery concept has enjoyed both a surge in popularity and also vocal opposition to the idea of diverting food-grade land and crops for this purpose. The idea of using the inevitable wastes arising from biomass processing, particularly farming and food production, is, therefore, gaining more attention as the feedstock for the biorefinery. For the three main components of biomass—carbohydrates, lipids, and proteins—there are long-established processes for using some of these by-products. However, the recent advances in chemical technologies are expanding both the feedstocks available for processing and the products that be obtained. Herein, this review presents some of the more recent developments in processing these molecules for green materials, as well as case studies that bring these technologies and materials together into final products for applied usage

Inversion de données inclinométriques obtenues au cours de deux expériences de fracturation hydraulique

Deux expériences de fracturation hydraulique horizontale ont été effectuées à Tranqueville (Lorraine) grâce à des injections d’eau sous forts débits. Les déformations du sol induites ont été mesurées par des inclinomètres en silice très sensibles et présentant une très faible dérive instrumentale. Le modèle de fracture choisi est une zone de rupture circulaire horizontale. Une inversion probabiliste des inclinaisons a permis de vérifier la profondeur de propagation de la cassure et de déterminer les dimensions et la migration de la fracture créée. Lors de la deuxième manipulation, révolution du rayon de la rupture a été suivie grâce au traitement des mesures de trente-deux inclinomètres

Reactor Modelling and Analysis of Amorphous Hydrogenated Silicon Deposition by PECVD

The behaviour of plasma reactors is complex and affected by a large number of parameters (temperature, pressure, flow rates, power, frequency, etc...). In that context, modeling constitutes a very convenient theoretical approach to analyze the complex parameters influences on the reactors overall performances, in the particular case studied here, amorphous hydrogenated silicon deposition rate profiles on the substrates. This particular study is devoted to a detailed analysis of the reactor behaviour in higher electrical power conditions. It demonstrates that, if relatively simple mechanisms for electron-molecule interactions and gaz phase reactions can be used in low power conditions, this do not remain true in higher power conditions where a great number of reactions must be taken into account

Post-annealed silicon nanocrystal formation on substoichiometric SiO

In this work is presented a detailed physicochemical, structural and optical characterization of SiOxNy thin films. The films deposited using PECVD in SiH4-N2O-He discharges were thermally annealed at 1273 K for 1 hour in ambient nitrogen. The film stochiometry was measured by Rutherford Backscattering Spectroscopy. The chemical composition was dominated by silicon suboxide containing some Si-N and Si-H bonds. Raman scattering measurements suggest the formation of nanocrystallite silicon in the annealed films. The Raman observation is strongly supported by Transmission Electron Microscopy analysis which shows a high density of silicon nanocrystals, having a mean radius ranging between 3 and 6 nm. Using Spectroscopic Ellipsometry, we discussed the dielectric function evolution as a function of the deposition parameters

Sur l'efficacité des ions et des électrons dans un plasma froid venant en contact avec un polymère

An experimental set up recently achieved allows a target irradiation by the different species existing in a cold plasma. On the other hand electrical measurements in situ, under 10-4 Pa vacuum or atmospheric pressure in inert gas, characterize the effect of low energy ions and electrons (50-300 eV) working separately or in conjunction. Actually several materials are studied (polyimide, epoxy, resins, polyolefins), results on polypropylene are only presented. Complementary analysis carried out ex situ, such as ESR or leakage currents measurement confirm the ions efficiency and the combination of ions and electrons as well.Un dispositif expérimental mis au point récemment permet d'irradier une cible par les différentes espèces rencontrées dans un plasma froid. D'autre part, des mesures électriques pratiquées in situ soit sous vide de 10-4 Pa soit à la pression atmosphérique en atmosphère inerte caractérisent les conséquences de l'impact des ions et des électrons de faible énergie (50-300 eV) agissant séparément ou en conjugaison. Plusieurs matériaux sont actuellement étudiés (polyimide, polyepoxy, polyoléfines). Seuls les résultats concernant le polypropylène seront présentés ici. Des analyses complémentaires pratiquées ex situ, telles que la RPE ou la mesure de courants de fuite confirment l'efficacité des ions ainsi que celle de l'association des ions et des électrons