Local and global electrochemical impedances applied to the corrosion behaviour of an AZ91 magnesium alloy

The electrochemical behaviour of an AZ91 magnesium alloy was investigated in a low aggressive medium by means of local and global electrochemical impedance measurements. The results were compared to those obtained on a pure magnesium sample. It was possible to show the individual contribution of each phase constituting the alloy, and it was observed that the corrosion mechanism of the two phases was the same, controlled by the Mg dissolution. However, local impedance diagrams clearly indicated that the kinetics dissolution of the b-phase was slower than that of the a-phase, which was in good agreement with SEM observations

Galvanic coupling between copper and aluminium in a thin-layer cell

The Al/Cu coupling was investigated in a thin-layer cell formed by a large Cu electrode and an Al microelectrode embedded in an insulator placed above the Cu electrode. By using a scanning electrochemical microscope (SECM) the thickness of the thin layer was perfectly controlledwith a precision in the micrometer range. A copper deposit on an electrochemical quartz crystal microbalance (EQCM) was also used as SECM substrate to quantify the copper dissolution rate. It was shown that such an experimental set-up allows to mimic the galvanic corrosion of intermetallic particles embedded in the aluminium matrix of the 2XXX series aluminium alloys. The combination of the SECM and the EQCM permitted the evaluation of the corrosion rate of copper at the corrosion potential of the 2024 Al alloy, whereas cyclic voltammetry performed on the SECM tip indicated the enrichment in Cu2+ ions in the thin electrolyte layer

Influence of flow on the corrosion inhibition of carbon steel by fatty amines in association with phosphonocarboxylic acid salts

This work was carried out to study the inhibition mechanism of a carbon steel in a 200 mg l−1 NaCl solution by a non-toxic multi-component inhibitor used for water treatment in cooling circuits. The inhibitive formulation was composed of 50 mg l−1 fatty amines associated with 200 mg l−1 phosphonocarboxylic acid salts. Steady-state current–voltage curves, obtained with a rotating disc electrode, revealed that the properties of the protective layer were dependent on the electrode rotation rate and on the immersion time. The cathodic process of oxygen reduction was not modified in the presence of the inhibitive mixture. As expected, the current densities increased when the rotation rate was increased. In the anodic range, original behaviour was observed: the current densities decreased when the electrode rotation rate increased. The morphology and the chemical composition of the inhibitive layers allowed the electrochemical results to be explained. Two distinct surface areas were visualised on the metal surface and the ratio between the two zones was dependent on the flow conditions. This behaviour was attributed to a mechanical effect linked to centrifugal force. XPS analysis revealed that the formation of a chelate between the phosphonocarboxylic acid salt molecules and the iron oxide/hydroxide was enhanced by the increase of the electrode rotation rate

Knowledge diffusion and innovation policies within the European regions: Challenges based on recent empirical evidence

This article builds upon empirical results concerning localised knowledge spillovers to highlight some policy implications within European regions. The analysis emphasises the role of regional innovation policies in supporting the institutions that generate knowledge and learning. However, the variety of regional features presented in the empirical literature suggests that the search for universal policy tools is unrealistic. From this perspective, we argue that original strategies must be generated to cope with the various dilemmas faced by regional innovation policies. Such specific strategies require accurate knowledge of local features. Improving data and indicators to diagnose and monitor regional innovation is therefore presented as a key issue for policy makersinnovation policy ; localised knowledge flows ; European regions ; knowledge-based economy

The determinants of innovation adoption

Using a sample of 46 000 EU firms from the Community Innovation Survey, this paper analyses the drivers of innovation adoption. In contrast to most empirical studies on innovation diffusion in which a specific technology is analyzed, this study covers several countries and industries in the European Union. Following Van de Ven and Van Praag (1981), Heckman's method is applied in a context of binary endogenous variable to explain the choices made by firms regarding innovation. Distinctions are made between the internal generation of innovation and the adoption of innovation produced by others, as well as between different types of adoption (product vs. process and cooperation-based adoption vs. isolated adoption). The study is focused on the impact of users' features and their cooperation with suppliers on the adoption choices. The results point out that cooperation is a key driver of adoption choices. Usual determinants such as firm size, absorptive capability or exports would foster generation of innovation instead of adoption.Innovation adoption; Innovation diffusion; Community Innovation Survey; Process adoption; Product adoption

CPE analysis by local electrochemical impedance spectroscopy

Constant-phase elements (CPE) are used extensively in equivalent electrical circuits for fitting of experimental impedance data. The CPE behavior is generally attributed to distributed surface reactivity, surface inhomogeneity, roughness or fractal geometry, electrode porosity, and to current and potential distributions associated with electrode geometry. In this work, different electrochemical systems showing the CPE dependence in the high-frequency range for the overall impedance were considered. Local electrochemical impedance spectroscopy was found to provide a good means for assessing the influence of local variations on the CPE behavior seen in global impedance measurements. A separation between 2D and 3D distributions could be easily observed. In the case of a 2D distribution (AZ91 Mg alloy), the origin of the CPE behavior was the distribution of high-frequency resistance associated with the geometry of the disk electrode; whereas, the capacitance was independent of position. In the case of the aluminium electrode, the CPE behavior could be attributed to a combination of 3D and 2D distributions. Geometric distributions can play a significant role in the impedance response of electrochemical systems, and these distributions can lead to CPE behavior

La société en mouvement : la Belgique sur une voie de développement durable?

Vingt ans après le Sommet de la Terre de Rio, la société belge est-elle sur une voie de développement durable ? Ou bien sommes-nous engagés sur la pente d’un inéluctable déclin ? Deux rédacteurs, tous deux de la « génération Rio » dans deux communautés de ce pays, ont relevé le défi d’explorer ensemble cette question dans la première partie de La société en mouvement. Cette même question a été posée aux personnalités issues de différents groupes sociétaux. Femmes, jeunes, immigrés, ong, autorités locales, travailleurs, employeurs, agriculteurs, ... : des co-auteurs représentant ces groupes ou les connaissant bien y commentent cette évolution, leurs expériences et leurs espérances. Dans la troisième partie, des experts se demandent si nous mesurons bien les enjeux de notre développement et comment les plus jeunes, aujourd’hui, sont préparés à l’avenir qui les attend. Les constats de La société en mouvement sont parfois surprenants mais ils sont convergents au moins sur un point: les défis sont colossaux et doivent d’urgence être relevés. Le titre de la dernière partie est éloquent : 'Appel à l’action urgente pour accélérer la transition'

LA PUISSANCE PUBLIQUE PROMOTEUR DE NOUVEAUX CRITERES DE DECISION DE FINANCEMENT DES ENTREPRISES

Ce texte est à paraître dans l'ouvrage E. Chatel, T. Kirat et R. Salais (Eds) : Action publique, L'Harmattan.La double nécessité à laquelle se trouve confrontée la puissance publique - dynamisation de la croissance au moyen de l'aide aux entreprises et renforcement des règles prudentielles transnationales - invite à se demander dans quelle mesure les divergences résultant de la mise en application simultanée de critères de sélection opposés peuvent être atténuées, voire compensées, par la mise en œuvre de modes de décision alternatifs. En d'autres termes, comment la puissance publique peut-elle promouvoir l'adoption d'un point de vue de financeur ni totalement soumis aux ratios de solvabilité habituellement privilégiés par les établissements financiers, ni exclusivement guidé par des considérations d'ordre territorial, souvent incarnées dans le nombre d'emplois créés, qui intéressent davantage les organismes d'aide et de subvention ? Cette interrogation vaut aussi pour les relations entre l'emprunteur et le prêteur, encore trop dominées par la volonté d'inciter le premier à mieux tenir compte des exigences du second sans que la réciproque ne soit vraie. Partant de l'hypothèse que la discrimination entre entreprises capables d'être pérennes et entreprise qui le seront moins dépasse le seul cadre de l'analyse financière, ce texte vise à mettre en évidence le rôle que peut jouer la puissance publique dans un contexte de démographie économique turbulent. Il apparaîtra que si l'objectif est la survie des entreprises et la stabilisation du parc, les outils d'évaluation ex ante de la qualité doivent différer de ceux qui guident les décideurs préoccupés par un objectif de création d'entreprises et d'accroissement de l'activité. Le changement de cadre d'analyse pouvant difficilement s'opérer de manière spontanée compte tenu des routines observées dans le domaine de l'évaluation de la fiabilité des entrepreneurs par les principaux organismes concernés, l'intervention de la puissance publique semble à même de faciliter la diffusion de critères différents de ceux actuellement utilisés pour décider de l'attribution de financements

Localized approach to galvanic coupling in an aluminum–magnesium system

The corrosion behavior of a pure aluminum/pure magnesium couple in a weakly conductive sodium sulfate solution was investigated. Potential and current distributions on the surface of the model couple at the beginning of immersion were obtained by solving the Laplace equation using a finite element method algorithm. Magnesium acted as the anode of the system while oxygen and water were reduced on aluminum. Calculations predicted a large current peak at the Al/Mg interface related to a local increase in both Mg dissolution and oxygen and water reduction on aluminum, leading to a local pH increase. Optical and scanning electron microscope observations confirmed the strong dissolution of magnesium concomitantly with depassivation of aluminum at the Al/Mg interface. Local electrochemical impedance spectroscopy showed the detrimental effects of the galvanic coupling both on aluminum and magnesium