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Aluminium alloys forming the remnants of Lockheed P38 of Antoine de Saint-Exupery was identified as the 24S aluminium alloy developed in 1930s. After 60 years in sea water, thick corrosion layers c...

This study reports the use of zinc heptanoate (ZC7) and zinc decanoate (ZC10) as pigments for the corrosion inhibition of mild steel in NaCl medium. Their improvements compared to the widely used zinc phosphate (ZP). These pigments synthesized by co-precipitation method. X-ray-diffraction characterizations confirm the obtaining of these compounds. Stationary and dynamic electrochemical measurements (EIS) revealed that the both carboxylate pigments exhibit inhibition efficiency higher than that of reference ZP pigment. Besides, the EIS analysis along with XRD characterizations, carried out on substrates surfaces after electrochemical tests, showed the development of a protective layer based on iron carboxylate.

The electrodeposition of zinc from an acidic sulphate bath was studied in the presence of nettle (Urtica dioica L.) extract at room temperature and with relative low zinc concentration. Different electrochemical measurements show that the nettle extract allows a reduction of hydrogen adsorption on steel and zinc and therefore a decrease in hydrogen evolution, due to the specific adsorption of molecules of the extract. Scanning electron microscopy (SEM) observations and X-ray diffraction (XRD) measurements reveal that the addition of nettle extract induces a very fine grain size with a random crystallographic orientation. Finally, the nettle extract constitutes an interesting and low cost additive for all processes based on zinc electrochemical reduction in acidic sulphate electrolytes.

To prevent the premature tarnishing of zinc-coated products in moist atmosphere or during wet-dry climatic cycles, new surface treatments of zinc are developed in this study. For that, electrochemical behaviour of pure zinc in this media was studied versus pH and potential by using electrochemical impedance spectroscopy and potentiodynamic techniques. Then, different coatings constituted by zinc heptanoate or zinc hydroxyheptanoate were synthesized by electrochemical oxidation on zinc-coated steel and tested in climatic chamber. The coatings mainly constituted by zinc heptanoate trap the OH− anions and delay the alkalinisation of the zinc surface during the wet-dry cycle. This coating constitutes an environmentally friendly alternative to the usual conversion treatments, to inhibit the formation of hydrozincite (white rust) in atmospheric corrosion.

The anodizing of AS12 alloys in various alkaline media is investigated over a large potential range (0–600 V) in order to provide a deep understanding of the mechanisms involved and judiciously chose chemical conditions enabling efficient micro-arc anodizing. Combined in situ stationary electrochemical methods, electrochemical impedance spectroscopy and TEM observations reveal that silicon in the aluminium matrix modifies the composition and the electrochemical properties of the duplex nanostructure grown at the early stages of the anodizing, therefore hindering micro-arc anodizing initiation. The addition of fluorides to the electrolyte, or silicates to a lesser extend, reinforces the resistive properties of the internal anodic layer and favors the efficiency of the anodizing process. The corrosion resistance of AS12, evaluated in NaCl 0.1 M by electrochemical techniques and salt spray test, is improved by the presence of the oxide coating and the nature of the additive incorporated compounds as well.

In order to fine tune the morphology of an anodic network, the understanding of the basic electrochemical mechanisms involved is required. The purpose of the present paper is to study the formation of the anodic aluminum oxide (AAO) on 5657 aluminum alloy in H3PO4 when varying the electrolyte concentration (0.1 M – 2 M) and the applied voltage (0–300 V) using a combination of in situ electrochemical investigations and SEM morphological observations.Even if the anodizing voltage and the electrolyte concentration enhance the anodizing rate, the thickness of the anodic film remains limited to 13 µm whatever the electrochemical conditions. The presence of alloying elements induces morphological specificities: the cyclic accumulation/dissolution of the noble elements leads to the formation of regularly spaced transversal pores in the alumina wall. Finally, by selecting appropriate chemical and electrochemical conditions, the fabrication of AAO layer with large and regular pores (until 150 nm of diameter) is possible with a suitable growth rate (0.2 µm min−1 at 90 V in 1 M H3PO4) on the considered commercial complex aluminum alloys.

The control of the corrosion phenomenon occurring at the metal interface requires the development of new non-toxic anticorrosion additives. For this purpose, zirconium orthophosphate compounds (Zr(HPO 4 ) 2 ,H 2 O noted α-ZrP) were synthesized by both hydrothermal and refluxing methods The Ca 2+ -cationic exchange in the layered structure is kinetically favoured by low crystallinity of α-ZrP synthesized by refluxing process, and leads to the formation of CaZr(PO 4 ) 2 ,4H 2 O, noted Ca 2+ -ZrP. The H + /Ca 2+ exchange mechanism is mainly triggered by acid-base considerations, and especially the pKa of α-ZrP/Ca 2+ -ZrP acid-base couple (evaluated to 2.5). Both compounds are acidic compounds by internal exchangeable H+ for α-ZrP and surface protons for Ca 2+ -ZrP, and can be used as potential inhibitors of zinc corrosion. Electrochemical measurements show that Ca 2+ -ZrP compounds dispersed in the NaCl electrolyte buffer the pH value over a long time and therefore allow controlling the corrosion rate of zinc.

New smart corrosion-inhibitive pigment, based on fibrous palygorskite clay (Pal), was developed. The beforehand grafted aminopropyltriethoxysilane (APTES) to Pal was used to anchor inhibitor heptanoate (C 7 − ). In presence of C 7 -APTES-Pal, the electrochemical study of steel immersed in NaCl (0.1 M) showed good inhibition efficiency. Corrosion products characterizations revealed an iron heptanoate protective layer at the metal surface. Impedance measurements denoted the enhancement of the corrosion protection of steel in NaCl (0.51 M). These improvements can be due to the progressive release of heptanoate from Pal and to the fibrous morphology of Pal in improving the barrier properties of the polymer coating.

International audience; The sparking initiation during the anodizing of metals in passivating electrolytic media is highly dependent on the physico-chemical properties of the evolving dielectric interface. The present paper focuses on magnesium alloy AZ91 and describes its anodizing in KOH 3 M over the potential range 0 to 40 V by combining in situ ellipsometric and electrochemical methods. In a first step, a thin and compact MgO anodic film is formed by ionic migration with a rate of 0.4 nm V−1. At 4 V to 5 V, the growth stresses lead to a sharp cracking of this MgO layer and the precipitation of a porous external Mg(OH)2 layer. Under this overlayer acting as a membrane, a defective MgO film grows with a higher growth rate (1.1 nm V−1), inducing a new passivation state. This inner MgO layer is characterized by a relatively high dielectric constant and a large thickness (100 nm at 40 V) and is probably responsible for the low dielectric breakdown voltage observed during the anodizing process of magnesium alloy.

International audience; The electrochemical behavior of aged corrosion layers (CL) on artefact was studied, in corrosive reference water without and with non-toxic corrosion inhibitors such as decanoate ions and flavonoids compounds, constituting the condensed tannins, such as catechin. Electrochemical impedance spectroscopy measurements on the metal/CL system and voltammetric studies of FeOOH phases on carbon paste electrode show that the corrosion inhibition mechanism is mainly based on the blocking of the dissolution of FeOOH-type phase and the decrease of the diffusion of ionic species in the pores network of CL. Indeed, the formation of iron decanoate, revealed by X-ray diffraction and microscopic observation, inhibits the electrochemical activity of FeOOH-type phases and blocks the electrochemical dissolution of FeOOH into Fe2+ cations. On the other hand, the catechin compound modifies the surface of rust compounds into a blue-black compound, but this modification has a poor influence on the electrochemical activity of FeOOH-type compounds.

In order to fix colouring pigments in the decoration domain, to trap anticorrosion inhibitors or to heal structural defects in the field of protection and durability, the clogging or sealing of the nanoporous network of aluminium anodic oxides is required. It is classically achieved by the formation of nanometric overlayers throughout chemical impregnation. The purpose of the present work is to investigate the sealing mechanism and the composition of the clogging materials by impregnation in a Cr3+/ZrF62− solution. As shown by in situ electrochemical measurements, the upper part of the anodic layer firstly dissolves by a reaction of fluoride-hydroxide exchange between ZrF62− salt and the alumina anodic layer. Due to the resulting local pH increase, measured thanks to a micro-pH electrode in the diffusion zone, Cr3+ and ZrF62− salts precipitate into Cr(OH)2.5(SO4)0.25 and Zr(OH)4-xFx respectively, as revealed by SEM/TEM analysis and XPS measurements. Finally, the ingress of the metallic elements is limited and only fluorides diffuse in-depth within the nanoporous network. A part of Cr(III) cation is oxidized into Cr(VI) in the top layer, which might explain the process efficiency in anticorrosion applications.

Shear force-based scanning electrochemical microscopy is applied for pH monitoring during a sealing reaction at the interface between anodized 7175 aluminium alloy and a solution containing Cr(III) and Zr(IV) species. pH measurement is carried out with the electrode positioned near enough to the surface to be in the diffusion zone of the liquid/solid interface, in the reach of the surface-generated pH modulating chemical species. The pH electrode is accurately positioned at the surface of the metal with shear force detection before the solution is loaded into the electrochemical cell at room temperature and the pH is monitored for 20 minutes. After a rapid increase, a maximum pH is reached. A good correlation is found between this in situ measured pH and the precipitation pH of metallic species contained in the solution. Interpretation of the results from in situ pH monitoring and open-circuit potential of the treated surface allows to propose three distinctive steps during the sealing process: an activation of the alumina layer by its dissolution during the first minutes, which induces an increase of the interfacial pH, followed by a precipitation of the sealing products as soon as the precipitation domain is reached and finally a consolidation of the sealing layer during the next 20 min.

The anodized layer growth in H2SO4 2 mol L−1 on three different aluminium alloys (1050, 7175, 2618) is investigated by in-situ electrochemical methods and ex-situ characterization techniques. SEM observations of the anodic films indicate that they contain defects related to the size and the composition of the intermetallic phases precipitated within the aluminium matrix. The electrochemical resistances of both the porous and the barrier layer are reduced in presence of defects, depending on their size. In-situ electrochemical measurements enable to monitor the anodizing process. Moreover, the comparison of in-situ and ex-situ electrochemical impedance spectroscopy measurements consistently reveals that the barrier layer is greatly affected by the microstructure of the aluminium alloy.

International audience; Electrochemical behaviour of pure titanium was studied in KOH-based media over a large voltage range (0-700 V) in order to understand the micro-arc phenomenon occurrence, leading to the formation of a “ceramic-like” oxide layer. The influence of various KOH concentrations in the electrolytic bath (from 0.01 to 0.2 M) was investigated on titanium substrate by a potentiodynamic scan. Whatever the concentration, the electrochemical behaviour of titanium in KOH media can be described in three steps according to voltage: i) a “conventional anodizing” step controlled by the solid-state diffusion of O2− and Ti4+ ions under the electric field effect, ii) a voltage range during which the micro-arc phenomenon occurs, named “micro-arc region”, iii) a “sharp current rise” induced by the increase of oxide conductivity. After anodizing in galvanostatic conditions, XRD and EDS analyses combined with SEM observations show that all samples have similar morphology with a dense internal layer and a porous external one, constituted by titanium dioxide under anatase and rutile crystallized forms. The electrochemical behaviour of anodized layers was investigated by electrochemical impedance spectroscopy measurements. A Mott-Schottky analysis reveals a n-type semi-conducting behaviour of the oxide layers with a very high donor concentration between 1022 and 1023 cm−3.

International audience; Chemical compounds of orange peel extracts were identified and their antioxidant activities were determined. The inhibiting effect on acidic steel corrosion brought by the extract and selected antioxidant compounds (neohesperidin, naringin, ascorbic acid) was evaluated separately by electrochemical methods. Whatever the extract concentration, a significant inhibition is observed, whereas selected antioxidant compounds show only a slight effect. Both electrochemical impedance spectroscopy results and scanning electron microscopy observations after immersion reveal that the inhibiting efficiency of orange peel extract is not only due to the antioxidant activity of its compounds but also to the precipitation of a surface film.

In order to improve the chemical and electrochemical resistance of titanium as well as its potential bioactivity, coatings were formed by using plasma electrolytic oxidation under galvanostatic conditions in a phosphate containing electrolyte. The grown anodized layers were characterized at different stages of the oxidation process, corresponding to different voltages. The structure and composition of the coatings were investigated by XRD, SEM-EDS and μ-Raman spectroscopy. The electrochemical behaviour of the coated materials was evaluated in acidified artificial saliva by using classical stationary methods and electrochemical impedance spectroscopy. Before the initiation of sparks, an inner layer is formed by a classical anodizing mechanism. This layer plays the role of barrier, improving the corrosion resistance of titanium in artificial saliva. As soon as the sparking phenomenon starts, a more compact overlayer grows. Due to the presence of large cracks, the corrosion resistance is no more improved.

Materials made of aluminium alloys are nowadays encountered in museum collections, especially in air and space museums. Due to their size, these materials have been exposed for decades to climatic changes, allowing the development of thick corrosion layers. To improve the conservation of such collections, curators need information on the physico-chemical characteristics of the thick corrosion layers. To achieve this, samples collected on aircrafts were characterized. μXANES investigations (Al-K edge) have allowed us to determine aluminium local chemical environment in amorphous corrosion products. Electrochemical measurements were realised to establish correlation between the composition and the electrochemical behaviour of such Al alloys.

International audience; This paper focuses on the potential corrosion protection of steel in presence of three polyphenolic model molecules (rutin, esculin, esculetol) in a weak acidic medium (pH = 4). From an electrochemical point of view, the cathodic inhibition was attributed to the oxygen scavenger role of the considered antioxidant compounds. SEM observations, Raman spectroscopy and Synchrotron X-ray absorption spectroscopy revealed furthermore the formation of a surface film by precipitation of iron polyphenolate conversion products, in which iron III is likely coordinated with free-catechol groups. Glycosylated catechol groups are rather adsorbed on a FeOOH layer.

International audience; The electrochemical behaviour of AA1050 and AA2214 alloys was studied in a KOH/silicate in order to investigate the first stages of the coating formation during MAO process (by SEM and electrochemical measurements). Before the sparking initiation, occurring around 300 V for both alloys, a thin inner layer of aluminium oxide grows by a classical anodizing mechanism, and induces a great enhancement of the electrochemical resistance. Then, the micro-arc regime beyond 300 V leads to the formation of a dense, thicker but cracked external aluminium oxide layer. Afterwards, from 400 V, a sharp increase of current density named ``current wall'' and due to an increase of oxide conductivity, leads to a significant oxygen release and the occurrence of large and energetic sparks. Microscopic analyses reveal that the presence of copper-rich intermetallic phases in the multi-phased alloy (AA2214) induces the incorporation of copper nanoparticles in the gamma-alumina layer formed by the sparking phenomenon. These copper particles increase the reaction of water oxidation during the classical anodizing stage, and result in a delay of the sparking initiation during the galvanostatic anodizing and in a lower electrochemical resistance of the anodized layers.

The corrosion inhibition performances of zinc immersed in 0.1 M NaCl solution with and without CaCl2, Na+ and Ca2+ exchanged beidellite (BDT) clay mineral picked up from Agadir bassin (Morocco) was studiedby potentiodynamic measurements and electrochemical impedance spectroscopy. The chemical and microanalysis of Na+-BDT and Ca2+-BDT by different techniques reveal basal distances of clays, of about 1.22 and 1.48 nm respectively, consistent with the saturation of beidellite interlayer spaces with Na+ and Ca2+ ions surrounded by one and two equivalent layers of water respectively. EIS results and surface analysis show that Ca2+-BDT acts as a smart inhibitor on zinc surface by modifying the physicochemical parameters of electrolyte near the surface. The exchange reaction in BDT involves the concentration decrease or the “suppression” of Na+, CO 3 2 - and Cl− ions near the zinc surface.

This work shows the interest to use a real time, white laser-based ellipsometer to characterize a complex electrolyte|electrode interface during an electrochemical process in an aqueous-based medium. This method is proposed to probe electrochemical interfaces that are usually not suitable to the full extent application of ellipsometry due to great disturbance of the reflected light flux provoked by gas evolution or roughness. In situ spectroelectrochemical ellipsometry combining such a visible super continuum fiber laser-band source was not previously reported to the best of the authors’ knowledge. The setup was employed to monitor an electrochemical process whose mechanism was previously incompletely described: the prespark anodization regime of the plasma electrolytic oxidation process of the Mg alloy AZ91D in the 3M KOH electrolyte. Above the anodization voltage of 4 V, the side water oxidation reaction induced light diffusion that reduces reflected light beam intensity. The process is monitored in an extended voltage range from 4 to 40 V and in an extended spectral range (495–800 nm). In the presented case, the use of a visible super continuum fiber laser-band source enhanced the signal-to-noise ratio giving access to a deeper picture of the triplex layer structure during surface repassivation by monitoring the evolution of the outer, inner, and interfacial layers.This work shows the interest to use a real time, white laser-based ellipsometer to characterize a complex electrolyte|electrode interface during an electrochemical process in an aqueous-based medium. This method is proposed to probe electrochemical interfaces that are usually not suitable to the full extent application of ellipsometry due to great disturbance of the reflected light flux provoked by gas evolution or roughness. In situ spectroelectrochemical ellipsometry combining such a visible super continuum fiber laser-band source was not previously reported to the best of the authors’ knowledge. The setup was employed to monitor an electrochemical process whose mechanism was previously incompletely described: the prespark anodization regime of the plasma electrolytic oxidation process of the Mg alloy AZ91D in the 3M KOH electrolyte. Above the anodization voltage of 4 V, the side water oxidation reaction induced light diffusion that reduces reflected light beam intensity. The process is monitored in an ...

This study deals with the development of a novel inhibitor based on heptanoate anions encapsulated within chitosan-modified beidellite. Included in coating, this inhibitor ensured efficient protection of metals against wet corrosion via permanent controllable release of the heptanoate inhibitor. The interlayer Na + ions of beidellite from Agadir basin (Morocco) were exchanged with chitosan cations. The modified beidellite was studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), thermogravimetry (TG) analysis coupled to mass spectrometry (MS) and, X-ray diffraction (XRD) analysis. The expansion of the interlayer space of beidellite by ≈ 1.16 nm, evidenced by XRD, was consistent with the arrangement of chitosan bilayer. Exceeding positively charged sites of the biopolymer were compensated by heptanoate anions. Electrochemical impedance spectroscopy (EIS) measurements were carried out on galvanized steel immersed in a 3 mass% NaCl solution. The measurements revealed improvement of corrosion inhibition by chitosan-heptanoate modified beidellite in comparison with commercially available triphosphate aluminium (TPA) anti corrosion pigments. The improved corrosion inhibition was due to the continuous leaching of hepatanoate anions as inhibitors. However, the barrier properties of coatings containing chitosan-heptanoate modified beidellite were not as high as those of TPA-based coatings, probably due to insufficient dispersion of the modified beidellite particles within the polymeric matrix.

Nanoporous and self-organized layers of aluminium alloys are used in many applications as membranes, templates for nanometric objects or corrosion protection for aluminium alloys. The use of this nanometric structure widely remains empirical, especially in the case of very small pores ( In contact with water electrolyte, the hydrolysis of AlO 4 into AlO 6 cluster and a partial release of sulphate ions are an important chemical transformation of the amorphous structure. This structural transformation defines the chemistry (pH and surface charge) inside the nanopores, the ageing behaviour and the possible incorporation or diffusion of chemical species in the nanostructure.

The (bis aqua)(sebacato)magnesium Mg((κ2)-(κ1-κ1)-μ3-C10H16O4)(H2O)2 was synthesized by hydrothermal route. The structure was solved ab initio using optimisation methods from powder X-ray diffraction (PXRD) laboratory data. The structure crystallises in the monoclinic space group P21/c with a = 17.336(1) A, b = 7.456(1) A, c = 9.573(1) A, β = 96.43 (1) °, V = 1229.61(9) A3, Dx = 1.407 g cm−3 and Z = 4. Rietveld refinement from 399 reflexions leads to a reliability factor Rbragg = 0.06. The structure consists of double sheets of Mg2+ centred O-octahedra linked by H-bonds and bridged by sebacate anions along [100], building a 3D metal-organic framework ‘MOF’. Heating at 100 °C provokes the condensation of the octahedra in an anhydrous compound Mg(C10H16O4).

Rust converters are chemical formulations that can be applied to corroded surfaces to convert residual rust on iron/steel surfaces into harmless and adherent chemical compounds. The known hazardous effects of most synthetic rust converters have led to a search for safer, more environmentally friendly natural products. Tannins, a class of natural, non-toxic and biodegradable polyphenolic compounds, extracted from plant sources have been proposed as an alternative. The transformation of rust in the presence of 5 g L−1 tannins extracted from mangrove (Rhizophora apiculata) barks was studied. Three different methods of pre-rusted sample preparations were tested. The rust composition of the steel was dependent of sample preparation. The pre-rusted samples prepared formed predominantly lepidocrocite and magnetite. Transformation of rust components to ferric-tannates, particularly lepidocrocite, in the presence of mangrove tannins that could be observed via Fourier transform infrared spectroscopy, X-ray ...

AZ91 Mg alloys were anodized by PEO under galvanostatic regime in order to evaluate the role of the different constituents of a KOH + KF + Na 3 PO 4 containing electrolytic bath. The morphology of the anodized coatings was observed by scanning electron microscopy and the composition was evaluated by energy dispersive X-ray spectroscopy. The corrosion resistance of the grown films was studied by electrochemical methods such as impedance spectroscopy, voltammetry and chronoamperometry. It was shown that 10 min anodizing is sufficient to grow a protective layer by PEO under galvanostatic conditions (10 mA cm − 2 ), with a relatively low voltage (50 to 70 V). Fluoride anions act as “sparking initiators” in KOH electrolyte. So a threshold content of fluoride anions (0.2 M) is necessary to form an initial insulating layer and therefore reach the sparking phenomenon. Then, the addition of phosphate anions to a KOH/fluorides electrolyte allows the “sealing” or “the densification” of the coating, and promotes the growth of thicker films, without increasing the corrosion resistance of the coating.

New zinc–cerium alloys (up to 5 wt.%) was synthesized and their corrosion behaviour was studied in a reference corrosive media. Metallographic analyses show that cerium is exclusively present in a Zn11Ce intermetallic phase, homogeneously dispersed in the zinc matrix. With an optimal concentration at around 1.5 wt.%, the Zn11Ce phase acts as a tank of cerium to form a protective Ce-enriched passive layer. Nevertheless, at high Ce content, the benefit in terms of corrosion resistance obtained by the incorporation of Ce in the corrosion layer is shaded by the galvanic coupling between the intermetallic phase and the matrix.

Zinc-based metal–organic frameworks (MOFs), binary zinc carboxylates ZnCnCn′ with Cn and Cn′ = CH3(CH2)n – 2COO–, have been synthesised and characterised for anti-corrosion applications. The crystallographic structures of ZnC10C14 and ZnC10C16 were determied from synchrotron powder diffraction data and refined by the Rietveld method. Protective coatings on electrogalvanised steel composed of ZnC12C16 have been developed by formulating a particular “carboxylating” bath. The ZnC12C16 coating exhibits better anti-corrosion behaviour than the pure Zn(C16)2 and Zn(C12)2 coatings, according to electrochemical and non-electrochemical measurements. The crystallographic results and corrosion measurements demonstrate the great flexibility of the zinc carboxylate lamellar structures in modifying the insolubility and hydrophobicity of the protective coatings. In addition, the conditions for the ZnC12C16 coating process fulfil the specifications for the surface treatment of zinc. Finally, these new compounds, which can be easily synthesised in water, provide a new and environmentally friendly anti-corrosion treatment for metals.

Atomic emission spectroelectrochemistry (AESEC) was used to monitor the dissolution of alloying elements during the anodization process of AA7050-T74 alloy. This technique coupled with metallographic analysis of the alloy lead to the identification of defects formed in the anodized layer due to the dissolution of strengthening intermetallic compounds (Al2CuMg and MgZn2) and coarse compounds (Al7Cu2Fe). The rates of the dissolution phenomena were measured independently as a function of the applied voltage. Keywords: AESEC, Anodization, Aluminum alloys, Dissolution

The anticorrosion performances of new non-toxic inhibitors based on carboxylic acids extracted from vegetable oil have been evaluated for the protection of iron artefacts. Electrochemical measureme...

Magnesium alloys are often used in as-cast conditions. So, the aim of this work is to characterize the corrosion protection of as-cast AZ91D alloys coated with simple chemical conversion (phosphate–permanganate, and cerium-based coatings). With the two coatings, the electrochemical measurements show that the corrosion protection is due to both the inhibition of cathodic and anodic reactions, because of the presence of stable CeO 2 or manganese oxides in basic pH. Nevertheless, the non-electrochemical tests of corrosion are required to bring to light the healing effect of phosphate–permanganate coating compared to Ce-coating and to describe the corrosion behaviour completely. Finally phosphoric and soda pickling associated to phosphate–permanganate conversion treatment or cerium coating are ecologically efficient alternatives to fluoride-based pickling and the chromating treatment.

In the field of corrosion protection, the research of environmentally friendly coating processes is one of the research topics. The use of gaseous atmospheric plasma, especially dielectric barrier discharge (DBD) plasma is an interesting way to rapidly form a thin protective coating. The aim of this work is to characterize the electrochemical behaviour of a SiOxCyNz film, formed from different organosilicon precursors, in neutral corrosive environment on copper. The film morphology and composition were determined by transmission electron microscopy (TEM) observations and X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour of the different treated copper was studied by stationary techniques and electrochemical impedance spectroscopy (EIS). With the same plasma parameter, the kind of organosilicon precursor determines the chemical stability of the coatings in water, then their protective properties. When the SiO2-like structure contains a low carbon level, the SiOxCyNz films present a good stability in water, and acts clearly as an O2 barrier membrane.

From technical and industrial heritage, curators are in charge of numerous and important collections of metallic items which are representative of the industrial and technical development of our societies. The diagnosis of the conservation state and the choice of the restoration treatment are important questions that have to be solved by curators to avoid expensive restoration works. This paper proposes to show how simple electrochemical techniques can be used as an efficient tool to contribute to the diagnosis of the conservation state of metallic artefacts and to monitor the restoration treatment through three examples. In the case of the very-corroded aluminium alloys of aircraft belonging to the Air and Space Museum (Le Bourget, France), stationary electrochemical measurements are able to characterise the allowable electrochemical effect of thick corrosion layer on the corrosion rate of metal but are not sufficient to give a complete diagnosis. In contrary, for the bronze part of the miner's lamp collection of the Mining History Centre of Lewarde, France and the nickel-plated steel of an ancient typewriter of the Musee des Arts et Metiers, Paris, France, an inhibition treatment based on sodium carboxylate within the framework of temporary conservation treatment was applied with success, on the basis of the electrochemical results obtained in the present study.

When ash-forming oils or contaminated distillate oils are used as fuels in land-based, marine or aero gas turbines, the hot gas path components, mainly the partition vanes and the blades of the expansion turbine are subjected to the deposition of slags that are corrosive at high temperature due to their low liquidus temperature. This hot corrosion process - if not properly inhibited - entails a dramatic life reduction of the hot gas path parts. MgO is a traditional, efficient inhibitor. Recently, it has been found that NiO also suppresses the corrosiveness of the (Na,S,V) melts by trapping vanadium in a refractory vanadate (Ni3V2O8); this compound is friable and does not tend to accumulate on turbine blades. The use of inhibitors entails losses in both machine performance and availability. Moreover, other metals can interfere with the inhibition process. In particular, zinc and iron are often inadvertently introduced in gas turbines fuels during their transportation or storage and they can significantly interact with nickel. This paper distinguishes the interactions between NiO on one hand and both ZnO and Fe2O3 on the other hand in the general complex chemistry of ash. The thermochemical study of (Na,S,V) melts in presence of Ni confirms that nickel is a good "trapper" of vanadium oxide at high temperature. However, they also show that nickel can react with iron to form the very stable ferrite NiFe2O4 and a low melting point vanadate phase. On the contrary, the presence of zinc affects to a lesser extent the reactivity of NiO versus V2O5 despite the formation of Ni1-xZnxO solid solutions.

The inhibitive action of mangrove tannins, extracted from mangrove barks and phosphoric acid, on pre-rusted steel in a 3.5% NaCl solution was evaluated and the inhibitive efficiency was compared with that of mimosa tannins. From the electrochemical studies, the inhibition efficiency of solutions containing 3.0 g L −1 tannins depended upon the concentration of phosphoric acid added and the pH of the solution. At pH 0.5 and pH 2.0, inhibition was greatest with mangrove and mimosa tannins alone, while at pH 5.5 the addition of phosphoric acid alone gave the highest inhibition.

Corrosion phenomenon of magnesium alloys is one of the limits for using magnesium alloys in automotive and aerospace industries. The aim of this study is the development of Sn-containing protective oxide coating by a simple plasma electrolytic oxidation in KOH/KF/Na3PO4 electrolyte on AZ91D magnesium alloy in galvanostatic mode. The film morphology and composition were analysed by SEM coupled with EDS, XRD and Raman spectroscopy. In the oxide, tin is mainly incorporated as crystallised MgSn(OH)6 compound in the layer. The main properties of Sn-containing oxide coating on AZ91D are both keeping the corrosion rate at open-circuit conditions at an acceptable value, and providing a sufficient passivation plateau to reduce the pitting sensibility. The lather characteristic, revealed by pitting tests, addresses the major drawback of magnesium alloys which often undergo important galvanic coupling in service. Consequently, the addition of low stannate concentration in the electrolyte to form Sn-rich anodic oxide on magnesium alloys represents an interesting way to synthesize protective coatings by PEO in a short time of anodization.

During the transport or the storage, galvanized steel products undergo the wet storage stain phenomenon, leading to the formation of unsightly and extensive white rust of zinc. In the context of development of temporary protection to replace mineral oils, the present study is focused on the combined action of sodium heptanoate (CH 3 (CH 2 ) 5 COONa, noted NaC 7 ) and 3-methyl benzotriazol (named tolutriazol, TTA) on zinc corrosion. Stationary and dynamic electrochemical measurements have shown that the association of NaC 7 and TTA provokes the formation of insoluble and hydrophobic passive layer, and lead to a positive synergy between the anodic and cathodic inhibiting actions of the two respective compounds. According to XPS and MEB analysis, the protective material is a layer containing zinc cation, heptanoate anion and TTA molecules, formed by a mechanism of precipitation on the zinc surface. In accordance with the coordination properties between Zn 2+ and TTA determined by pH titration, the TTA molecules is trapped in a zinc soap, probably in a compound, Zn(TTA) 2 (C 7 ) 2 , which explains the efficiency of this formulation in the climatic chamber test.

Depolymerisation of mangrove Rhizophora apiculata bark extracts in the presence of phloroglucinol nucleophiles in ethanol was carried out. The flavan-3-ols and their phloroglucinol adducts were separated using reversed phase liquid chromatography (HPLC). The HPLC analysis of mangrove R. apiculata showed that catechin was the most common component of the flavanoid monomers. The antioxidant activities of these mangrove tannins were evaluated and compared with several commercial tannins by using reducing power, DPPH and ABTS assays with butylated hydroxytoluene, BHT and l -(+)-ascorbic acid as standards. All tannins had reducing power and percentage scavenging activities similar to the (+)-catechin and l -(+)-ascorbic acid standards. In the DPPH assay, >90% of the maximum scavenging activity was attained at 30 μg ml −1 . Mangrove tannins had stronger antioxidant activity than the BHT standard in the DPPH assay. The results of the ABTS assay were correlated with the DPPH assay. Scavenging activity in the ABTS assay increased as the tannin concentration increased, up to a plateau at 50 μg ml −1 .

Anodic coatings formed on magnesium alloys by plasma anodization process are mainly used as protective coatings against corrosion. The effects of KOH concentration, anodization time and current density on properties of anodic layers formed on AZ91D magnesium alloy were investigated to obtain coatings with improved corrosion behaviour. The coatings were characterized by scanning electron microscopy (SEM), electron dispersion X-ray spectroscopy (EDX), X-ray diffraction (XRD) and micro-Raman spectroscopy. The film is porous and cracked, mainly composed of magnesium oxide (MgO), but contains all the elements present in the electrolyte and alloy. The corrosion behaviour of anodized Mg alloy was examined by using stationary and dynamic electrochemical techniques in corrosive water. The best corrosion resistance measured by electrochemical methods is obtained in the more concentrated electrolyte 3 M KOH + 0.5 M KF + 0.25 M Na 3 PO 4 ·12 H 2 O, with a long anodization time and a low current density. A double electrochemical effects of the anodized layer on the magnesium corrosion is observed: a large inhibition of the cathodic process and a stabilization of a large passivation plateau.

The inhibitive behaviour on steel of flavanoid monomers that constitute mangrove tannins namely catechin, epicatechin, epigallocatechin and epicatechingallate was investigated in an aerated HCl solution via electrochemical methods. The monomers were found to be mainly cathodic inhibitors and the inhibition efficiency was dependent on concentration. To explain the adsorptive behaviour of the molecules on the steel surface, a semiempirical approach involving quantum chemical calculations using HyperChem 6.0 was undertaken. The HOMO electronic density of the molecule was used to explain the inhibiting mechanism. The most probable adsorption centers were found in the vicinity of the phenolic groups. In a second part, the use of mangrove tannin, extracted from the mangrove barks as steel corrosion inhibitors in acidic media was investigated and its inhibitive efficiency was compared with that of commercial mimosa, quebracho and chestnut tannins. The inhibitive performance of mangrove tannins was comparable to the other tannins investigated, indicating their potential in corrosion protection.

International audience; Electrochemical behavior of pure zinc was studied in alkaline KOH-based media over a large range of voltage (0-300 V) in order to investigate the occurrence of the micro-arc phenomenon, responsible for the formation of ``ceramic-like'' oxide layer. According to electrolyte composition, three anodizing steps can be observed, first, a classical anodizing process at low voltage, a voltage range of micro-arc phenomenon with a more or less intense water oxidation, and a sharp current rise corresponding to an increase of electronic conductivity of ``metal/oxide/electrolyte'' interface. Both KOH concentration and presence of additives in the electrolytic bath control the micro-arc voltage range, and the composition of anodized layer. Nevertheless, the internal layer of the coating remains mainly constituted by crystallized ZnO, formed by a mechanism of solid-state diffusion of O2- under electric field. Despite the significant coating thickness (several microns), the electrochemical characterization of the corrosion behavior in NaCl electrolyte only shows a slight improvement of the performances of the zinc anodized in presence of additives in KOH electrolyte, compared to an untreated one.

Since several years, lead calcium-based alloys have supplanted lead antimony alloys as structural materials for positive grids of lead-acid batteries in many applications, especially for VRLA batteries. Nevertheless, the positive grid corrosion probably remains one of the causes of rapid and premature failure of lead-acid batteries. The objective of the present study is to present a comprehensive study of the PbCaSn alloy corrosion in function of their composition, metallographic state and voltage conditions (discharge, overcharge, floating and cycling conditions). For that, four alloys PbCaSn x wt.% (x = 0, 0.6, 1.2, 2) were synthesized in two extreme metallurgical conditions and tested by four electrochemical lab-tests. Weight loss measurements and analyses by SEM, EPMA and XRD allowed to monitor the oxidation tests and to characterize the corrosion layers after the oxidation tests. The results show that the tin level in PbCaSn alloys should be adapted on the calcium concentration and the rate of overageing process, to maintain the beneficial effect of tin in service during the battery lifetime. According to our results, a Sn/Ca ratio of 2.5 gives good corrosion resistance in all potential conditions. Nevertheless, when tin level is too high, the corrosion layers can peel off from the metal, which involves a lack of cohesion between the collector and the paste, in cycling conditions. The anodic potential undergone by the metal is a second main factor determining the corrosion, especially the floating conditions and the frequency of deep discharge and overcharge. Thus the adjustment of the charge controller parameters of a battery system is a necessity to increase the lifetime of the grids and maintain a good rechargeability.

The efficiency of linear sodium decanoate, CH3(CH2)8COONa (noted NaC10), as corrosion inhibitor of lead was determined by electrochemical techniques in two corrosive mediums: ASTM D1384 standard water and acetic acid-enriched solutions. Best results were obtained with 0.05 mol l−1 of NaC10 solution. In these conditions, the inhibition efficiency can be estimated of 99.9%. The corrosion inhibition effect was confirmed by cyclic atmospheric tests in a climatic chamber in two different conditions: water saturated vapour, and acid acetic enriched vapour simulating the atmosphere in the wooden displays in museums. Surface analyses by SEM and X-ray diffraction indicate that the metal protection is due to the formation of a protective layer mainly composed of lead decanoate Pb(C10)2 (metallic soap). This inhibition treatment was applied on objects of metallic cultural heritage: gallo-roman sarcophagus in lead. Electrochemical methods confirm the efficiency of treatment on archaeological materials. In conclusion, this inhibitor treatment seems to be very promising against the atmospheric corrosion and the corrosion by organic acid vapour in museums.

This study is devoted to a new surface treatment of zinc, called “carboxylating”, which could be an environmentally friendly alternative to the usual conversion treatments. Carboxylating requires use of both n-alkyl carboxylic acid and peroxoborate as oxidizing agent, in a water–ethanol mixture. As in the phosphating process, the carboxylating one is carried out in four steps: the activation step, oxidation of the zinc substrate at an acidic pH, germination and growth of zinc carboxylate crystals. Influence of the activator content, treatment time, oxidizing agent concentration, and chain length of the carboxylic acid was successively examined. Carboxylates covered zinc samples were tested in corrosion conditions. The longer the carbon chain length, the more corrosion resistant the coating; its layered structure easily allows exchanging anions and a hydroxocarboxylate of zinc is stabilized during the corrosion test then delays the white rust formation.