Annie Chaussé

Plasma-polymerized coatings using HMDSO precursor for iron protection

Abstract A large microwave plasma reactor was used for the deposition of plasma-polymerized coating from hexamethyldisiloxane (HMDSO)/oxygen (O 2 ) mixtures on iron samples. The plasma was characterized by optical emission spectroscopy as a function of the HMDSO to oxygen ratio. Infrared spectroscopy was used to investigate the coating structure. The variation of the HMDSO content in the feed provides a large wide of coatings, from silica (HMDSO content: 20%) to polymer (HMDSO content >80%). Electrochemical impedance spectroscopy was used to predict corrosion protective properties of the coating. Different HMDSO/O 2 ratios in the mixture provide varying degree of corrosion protection and the best protection was obtained for the plasma-polymerized coating from HMDSO 80% content precursor.

Experimental investigations on iron corrosion products formed in bicarbonate/carbonate-containing solutions at 90°C

The influence of initial oxygen level and bicarbonate content on iron corrosion was examined during the early stages of a storage at 90°C. The nature of corrosion products formed on iron surface was investigated through FTIR, Raman spectrometry and scanning electron microscopy. It has been shown that high bicarbonate content (1 M) promotes the formation of siderite whatever the initial oxygen level. Decreasing the bicarbonate content (from 0.1 to 0.001 M) will favour the formation of FeII(OH−)x(HCO3−/CO32−)y species with increasing x values and decreasing y values. FeII(OH−)x(HCO3−/CO32−)y species may suffer a series of transformations into green rust GR1(CO3) (intermediate species), FeII(OH−)n(HCO3−/CO32−)m gel-like precipitate, magnetite or lepidocrocite depending on the initial oxygen level.

Electrochemical formation of a new Fe(II)Fe(III) hydroxy-carbonate green rust: characterisation and morphology

Abstract Electrochemical behaviour of iron in deaerated 0.2 M carbonate/bicarbonate solution pH 9.6 and T =25°C was investigated. Oxidation of iron leads to the formation of green rust as intermediate product and ferrihydrite as ultimate product. Characterisation of green rust was done through FTIR, TEM, XRD and Mossbauer spectroscopy. Results point out differences in the structure and morphology, such as size of hexagonal crystal lattice, parameter c and Fe(II)/Fe(III) ratio, between our electrochemically formed GR and GR1(CO 3 2− ) obtained by oxidation of Fe(OH) 2 . Co-precipitation of Fe(II) and Fe(III) species during the electrochemical procedure leads to a new GR. We propose the following chemical formula for this GR, [Fe (II) 2 Fe (III) 2 (OH) 8 ] 2+ ·[CO 3 ] 2− . However, the possibility that incorporation of both CO 3 2− and Cl − ions could occur is not ruled out.

A Raman and infrared study of a new carbonate green rust obtained by electrochemical way

The occurrence of a new carbonate green rust (GR) obtained by electrochemical oxidation of iron in bicarbonate/carbonate solutions has been evidenced by infrared spectroscopy, Raman microprobe and coulometric titration. The Fe2+/Fe3+ ratio is 1 that corresponds to an iron oxidation state of 2.5. Under wet and dry aerial oxidation conditions, the 1/1 carbonate GR is significantly more stable than the 2/1 carbonate GR, reported in the literature by now. The ultimate oxidation product is ferrihydrite. From coulometric investigations, the mechanism of formation was found to involve both an oxidation of iron to Fe(II) complexes and a solution oxidation of Fe(II) to Fe(III) prior to the precipitation of 1/1 carbonate GR.

Study of oxidation products formed on iron in solutions containing bicarbonate/carbonate

Abstract Oxidation layers formed on iron in deaerated bicarbonate/carbonate solutions at potentials in the active range were investigated through electrochemical techniques, FTIR and scanning electron microscopy. Three oxidation products have been obtained, siderite, am-FeOOH with adsorbed carbonate or bicarbonate ions and green rust GR1(CO 3 ). It has been shown that the formation of either compound was strongly dependent on the concentration, temperature and pH of solutions.

Screen-printed electrografted electrode for trace uranium analysis

This paper reports the interest of the novel 4-carboxyphenyl-grafted screen-printed electrodes (4-CP-SPEs) for sub-nanomolar analysis of uranium in water samples. Electrodes were easily prepared via electrochemically reduction of the corresponding diazonium salt. The stability of the grafted layer has been clearly demonstrated. Uranium detection was then achieved by immersing the grafted electrode into the sample solution, followed by the electrochemical measurement of adsorbed U(VI) by square wave voltammetry. Adsorption time was investigated so as to find the best compromise between analysis time, repeatability and reproducibility. Limit of detection and quantitation reached 7 x 10(-10) and 2 x 10(-9) mol L(-1), respectively. Moreover, interference study was conducted with Zn(II), Cd(II), Pb(II) and Cu(II); no major interference was established. 4-CP-SPEs were finally applied for uranium determination in estuarine water demonstrating the convenience of these electrodes for environmental analysis.

Hexamethyldisiloxane (HMDSO)-plasma-polymerised coatings as primer for iron corrosion protection: influence of RF bias

Silicone-like coatings were prepared by plasma enhanced chemical vapor deposition on steel substrates using a hexamethyldisiloxane–oxygen (80 ∶ 20) precursor mixture, in a microwave reactor. The plasma composition, the structure and barrier properties of the coatings were studied as a function of the RF bias. OES was carried out in order to identify the excited species in the plasma. The coatings were characterized by several ex situ diagnostics including FTIR, SEM, gravimetry and EIS. OES, using argon as an actinometer, showed no modification in the HMDSO dissociation as the RF bias varies; but it indicated changes in the chemical recombination reactions. Coating analyses revealed that radio frequency (RF) bias induced a densification of the coatings associated with modifications in their morphology and chemical composition. Results were explained using the general mechanism in the literature relative to plasma-deposited thin films. EIS results indicated that the best barrier properties during immersion in NaCl solutions were obtained with coatings deposited under high RF bias.

Electrochemical deposition of thin films of green rusts 1 and 2 on inert gold substrate

Abstract Green rusts are layered Fe(II)–Fe(III) hydroxy-salts that play an important role in iron corrosion, soil chemistry, and environmental engineering. Successful electrochemical depositions of thin layers of green rusts incorporating anions such as carbonate or chloride (GRs1) or sulphate (GR2) on gold substrate are presented. As far as we know, it is the first time that such synthesis has been reported. The thin layers of green rusts were characterized by ex situ methods such as XRD, SEM, EDS and FTIR. This new way of synthesis allowed us to get green rust particles with sizes significantly larger than those obtained from the ways reported until now.

Ion–ion interactions and lithium stability in a crosslinked PEO containing lithium salts

Abstract The electrochemical properties of a solid polymer electrolyte prepared by chemical crosslinking of PEO 2000 and containing LiAsF 6 or LiCF 3 SO 3 were investigated for electrochemical window, lithium stability and lithium/electrolyte interface stability. FTIR spectroscopy of the salt anion (AsF 6 − and CF 3 SO 3 − ) was also used to determine the nature and the extent of ion pairing and ion aggregation in these crosslinked electrolytes. The lithium corrosion appears as a diffusion limited process as the coulombic efficiency of a lithium deposit decreases with the square root of the contact time of lithium with the crosslinked PEO. Impedance parameters are consistent with an increase of the passivating layer upon storage. Their values strongly differ with the salt anion.

Design of metal organic framework–enzyme based bioelectrodes as a novel and highly sensitive biosensing platform

Nanocomposites combining the mesoporous iron(iii) trimesate MIL-100(Fe) (MIL: Matériaux Institut Lavoisier) and platinum nanoparticles (Pt-NPs) have been used as immobilization matrices of glucose oxidase (GOx). Due to the physico-chemical properties of Pt-NPs (electroactivity) and MIL-100(Fe) (high specific surface area and pore volume, biocompatibility), the resulting GOx-MIL-100(Fe)-PtNP bioelectrode exhibits excellent electrocatalytic performances for glucose detection. This novel glucose biosensor presents a high sensitivity of 71 mA M-1 cm-2 under optimum conditions and a low limit of detection of 5 μM with low response time (<5 s). In contrast, substitution of iron by chromium or aluminum in MIL-100 leads to a much lower sensitivity and higher response time values, suggesting that the iron centres of MIL-100(Fe) may be involved in a synergistic effect which indeed enhances the catalytic oxidation of glucose and biosensor activity. Thus, this work extends the scope of MOF nanoparticles with engineered cores and surface to the field of highly sensitive, durable glucose biosensors.