M. Jeannin

Efficient solvent-free microwave phosphorylation of microcrystalline cellulose

Environmentally friendly microwave phosphorylation of microcrystalline cellulose is herein described for the first time. Microwave irradiation is found to offer an efficient solvent-free procedure for cellulose modification without its pre-treatment (swelling in appropriate solvent).

Mechanisms of Formation and Transformation of Ni-Fe Hydroxycarbonates

The mechanisms of the transformation of (Ni,Fe)(OH)2 precipitates in carbonated aqueous solutions were studied. The reactions were monitored by measuring the redox potential of the aqueous suspension, and end products were studied by Mossbauer spectroscopy, X‐ray diffraction and Raman spectroscopy. The oxidation processes were compared to those occurring without Ni, that is when the initial hydroxide is Fe(OH)2. Schematically, the oxidation of Fe(OH)2 involves two intermediate compounds, the carbonated GR of formula Fe4IIFe2III(OH)12CO3 ⋅ 2H2O, and ferrihydrite, before to lead finally to goethite α‐FeOOH. It proved possible to prepare Ni(II)‐Fe(III) hydroxycarbonates with ratios Fe/Ni from 1/6 to 1/3. When the Fe/Ni ratio is larger than 1/3, a two stage oxidation process takes place. The first stage leads to a Ni(II)‐Fe(II)‐Fe(III) hydroxycarbonate. The second stage corresponds to the oxidation of the Fe(II) remaining inside the hydroxycarbonate and leads to a mixture of Ni(II)‐Fe(III) hydroxycarbonate wi...

Elaboration and microstructural characterization of calcareous/ceria based composite on zinc substrate

Cerium conversion coatings were prepared by cathodic electrodeposition from a low concentrated aqueous solution of Ce(NO3)3 with KNO3 addition to insure the conductivity of the electrolyte. The cerium oxide film was characterized by Scanning Electronic Microscopy (SEM). Although the deposit is uniform with current density of 2 mA/cm2, it shows cauliflower morphology with a crack network, giving rise to bad mechanical and electrochemical behaviour. Elaboration of a calcareous deposit inside crack network of the cerium coating by cathodic polarization from artificial seawater is investigated at different applied potential, in order to increase the quality of the cerium coating formed. For cathodic potentials lower than–1.5 V/SCE, zinc corrosion products (gordaite) were observed inside the cerium oxide film instead of calcareous deposit although the current density decrease during the deposition suggesting a partially blocked surface. A pure calcareous compound was observed at–1.5 and–1.6 V/SCE. SEM and EDX cartography of the cross section revealed that open cracks in the cerium oxide structure are filled by calcium. Calcium was also detected inside the CeO2 film not only all around the cracks but also in all the porosity of the CeO2 film. It has precipitated as CaCO3 (aragonite form) as revealed by micro-Raman spectroscopy and XRD.

Artificial coral reefs, electrochemistry and calcium carbonate: electrodeposited coral-like aragonite

Global warming’s largest influence on coastal ranges remains massive erosion. Artificial reinforcements often suffer instable basements, in particular on large and sandy beaches. One potentially large-scale approach to consolidate such coasts rely in the use of electrodeposition of conglomerates of calcium carbonate, substituting the weak mechanical loci, at no environmental cost. In this approach, natural sea-water provides the necessary elements (Ca and CO2) for the precipitation of calcium carbonate around the working electrode that can be easily adapted to the local geometry, with no a priori limit in scale (Géocorail ®). The calcium carbonate deposits on metallic electrodes and on extended regions around them, ages and creates bonds between mineral sediments coming from sea waves carriage, and then makes a mechanically resistant agglomerate “Géocorail”. The deposited calcium carbonate is the aragonite polymorph, one of the most present biominerals in the oceans, in mollusc shells and corals. It is then important to compare our Géocorail with biominerals in order to optimize our elaboration process for eventual neo-fauna colonisation of the reinforcements. In this work, we selected few dead specimen of coral species from Noumea, Nouvelle Calédonie, Cancun, Mexico and Saint François, Guadalupe, and compared them with the artificially grown electrochemical samples, with the help of x-ray diffraction and SEM imaging.

Propriétés de l’interface d’infrastructures métalliques portuaires : facteurs d’impact corrosion/anticorrosion

Resume : L’exposition d’aciers a des conditions maritimes portuaires (immersion, marnage, eclaboussures...) conduit rapidement a la formation d’un depot sur la surface metallique Ce depot est constitue d’un melange de produits de corrosion de l’acier et de composes mineraux et organiques. La presence de ces depots peut se reveler protectrice ou nefaste vis-a-vis des phenomenes de corrosion selon leurs caracteristiques (nature, repartition, conductivite, ...). Cette etude vise a ameliorer les connaissances des proprietes d’interfaces acier/environnement des infrastructures metalliques portuaires afin d’optimiser la mise en place et le dimensionnement d’un systeme de protection cathodique. Ces travaux sont bases sur l’analyse des caracteristiques physico-chimiques et electrochimiques des depots formes sur des coupons d’acier au carbone exposes 6 a 7 ans en zone des basses eaux en conditions naturelles portuaires au sein des Grands Ports Maritime de NantesSaint-Nazaire et du Havre. Ces coupons ont ete places dans differentes conditions d’essais : sous protection cathodique permanente ou differee, a l’abandon ou sous rupture de protection. Les resultats de ce travail de recherche a permis de mettre en evidence, quel que soit le site pilote (estuarien ou strictement maritime), la formation de produits de corrosion selon le mecanisme generalement attendu sur des coupons d’acier a l’abandon. La protection cathodique permet une diminution significative de la cinetique de corrosion. Elle ne modifie pas fondamentalement la nature des produits de corrosion mais favorise la formation d’un depot plus protecteur que celui obtenu a l’abandon. Mots cles : Corrosion marine – Protection cathodique – Electrochimie – Raman – DRX