Aluminium based alloys were deposited on glass substrates by electron-beam evaporative PVD techni... more Aluminium based alloys were deposited on glass substrates by electron-beam evaporative PVD technique which is compatible with a roll to roll process on large flat substrates because of high deposition rates. Alloying elements (Cr, Gd) are added in order to improve both mechanical and corrosion behaviours of aluminium. This approach aims to develop sacrificial protection of steel flat products. Because
ABSTRACT Pitting corrosion of carbon steel electrodes in 0.1 mol L−1 NaHCO3 + 0.02 mol L−1 NaCl s... more ABSTRACT Pitting corrosion of carbon steel electrodes in 0.1 mol L−1 NaHCO3 + 0.02 mol L−1 NaCl solutions was induced by anodic polarisation. The evolution of the breakdown potential Eb with NO2− concentration was investigated by linear voltammetry. Eb increased from −15 ± 5 mV/SCE for [NO2−] = 0 up to 400 ± 50 mV/SCE for [NO2−] = 0.1 mol L−1. During anodic polarisation at potentials comprised between Eb([NO2−] = 0) and Eb([NO2−] ≠ 0), the behaviour of the whole electrode surface, followed by chronoamperometry, was compared to the behaviour of one single pit, followed via scanning vibrating electrode technique (SVET). Addition of a NaNO2 solution after the beginning of the polarisation led to a rapid repassivation of pre-existing well-grown pits. In situ micro-Raman spectroscopy was then used to identify the corrosion products forming inside the pits. The first species to be detected in the presence of NO2− were mainly dissolved Fe(III) species, more likely [FeIII(H2O)6]3+ complexes. Iron(II) carbonate FeCO3, siderite, and carbonated green rust GR(CO32−) were also detected in the active pits, as in the absence of nitrite. But they were accompanied by maghemite γ-Fe2O3, a phase structurally similar to the passive film, that forms from the Fe(III) complexes. The Raman analyses then correlate with the SVET observations and confirm that the main effect of nitrite ions is to oxidize iron(II) into iron(III). The passive film would then form from the Fe(III) species still bound to the steel surface.
Pitting corrosion of carbon steel electrodes in 0.1M NaHCO3+0.02M NaCl solutions was induced by a... more Pitting corrosion of carbon steel electrodes in 0.1M NaHCO3+0.02M NaCl solutions was induced by anodic polarisation. The evolution of the breakdown potential Eb with the phosphate concentration was investigated by linear voltammetry. Eb increased from −15±5mV/SCE for [HPO42−]=0 to 180±40mV/SCE for [HPO42−]=0.02molL−1. During anodic polarisation (E=50mV/SCE), the behaviour of the whole electrode surface, followed by chronoamperometry, was compared to the behaviour of one single pit, followed via the scanning vibrating electrode technique (SVET). The addition of a Na2HPO4 solution after the beginning of the polarisation did not lead to the repassivation of pre-existing well-grown pits. The corrosion products forming in the pits were identified in situ by micro-Raman spectroscopy. They depended on the phosphate concentration. For [HPO42−]=0.004molL−1, siderite FeCO3 was detected first. It was oxidised later into carbonated green rust GR(CO32−) by dissolved O2. The beginning of the process is therefore similar to that observed in the absence of phosphate. Finally, GR(CO32−) was oxidised into ferrihydrite, the most poorly ordered form of Fe(III) oxides and oxyhydroxides. Phosphate species, adsorbing on the nuclei of FeOOH, inhibited their growth and crystallisation. For [HPO42−]=0.02molL−1, siderite was accompanied by an amorphous precursor of vivianite, Fe2(PO4)3·8H2O. This shows that, in any case, phosphate species interact strongly with the iron species produced by the dissolution of steel.
Aluminum coatings are widely studied for the cathodic protection of steel structures. However, al... more Aluminum coatings are widely studied for the cathodic protection of steel structures. However, aluminum has poor mechanical properties and its passivation trend could favor localized degradation in chlorine environment, increasing largely the coating dissolution. In order to improve the sacrificial protection and the mechanical properties provided by the aluminum coatings, several alloying elements have been tested as monolayers, in particular Mo, Mg, and Mn. The use of a single alloying element cannot improve both mechanical and corrosion properties. As a consequence, multilayer configuration appears as a promising solution. Different multilayer configurations have been synthesized associating two elements or alloys: one with good mechanical properties and one with a good sacrificial behavior. This study is focused on the impact of the multilayer configuration on the mechanical and electrochemical properties. Several configurations have been tested: the periodicity Λ was varied bet...
Aluminium based alloys were deposited on glass substrates by electron-beam evaporative PVD techni... more Aluminium based alloys were deposited on glass substrates by electron-beam evaporative PVD technique which is compatible with a roll to roll process on large flat substrates because of high deposition rates. Alloying elements (Cr, Gd) are added in order to improve both mechanical and corrosion behaviours of aluminium. This approach aims to develop sacrificial protection of steel flat products. Because
ABSTRACT Pitting corrosion of carbon steel electrodes in 0.1 mol L−1 NaHCO3 + 0.02 mol L−1 NaCl s... more ABSTRACT Pitting corrosion of carbon steel electrodes in 0.1 mol L−1 NaHCO3 + 0.02 mol L−1 NaCl solutions was induced by anodic polarisation. The evolution of the breakdown potential Eb with NO2− concentration was investigated by linear voltammetry. Eb increased from −15 ± 5 mV/SCE for [NO2−] = 0 up to 400 ± 50 mV/SCE for [NO2−] = 0.1 mol L−1. During anodic polarisation at potentials comprised between Eb([NO2−] = 0) and Eb([NO2−] ≠ 0), the behaviour of the whole electrode surface, followed by chronoamperometry, was compared to the behaviour of one single pit, followed via scanning vibrating electrode technique (SVET). Addition of a NaNO2 solution after the beginning of the polarisation led to a rapid repassivation of pre-existing well-grown pits. In situ micro-Raman spectroscopy was then used to identify the corrosion products forming inside the pits. The first species to be detected in the presence of NO2− were mainly dissolved Fe(III) species, more likely [FeIII(H2O)6]3+ complexes. Iron(II) carbonate FeCO3, siderite, and carbonated green rust GR(CO32−) were also detected in the active pits, as in the absence of nitrite. But they were accompanied by maghemite γ-Fe2O3, a phase structurally similar to the passive film, that forms from the Fe(III) complexes. The Raman analyses then correlate with the SVET observations and confirm that the main effect of nitrite ions is to oxidize iron(II) into iron(III). The passive film would then form from the Fe(III) species still bound to the steel surface.
Pitting corrosion of carbon steel electrodes in 0.1M NaHCO3+0.02M NaCl solutions was induced by a... more Pitting corrosion of carbon steel electrodes in 0.1M NaHCO3+0.02M NaCl solutions was induced by anodic polarisation. The evolution of the breakdown potential Eb with the phosphate concentration was investigated by linear voltammetry. Eb increased from −15±5mV/SCE for [HPO42−]=0 to 180±40mV/SCE for [HPO42−]=0.02molL−1. During anodic polarisation (E=50mV/SCE), the behaviour of the whole electrode surface, followed by chronoamperometry, was compared to the behaviour of one single pit, followed via the scanning vibrating electrode technique (SVET). The addition of a Na2HPO4 solution after the beginning of the polarisation did not lead to the repassivation of pre-existing well-grown pits. The corrosion products forming in the pits were identified in situ by micro-Raman spectroscopy. They depended on the phosphate concentration. For [HPO42−]=0.004molL−1, siderite FeCO3 was detected first. It was oxidised later into carbonated green rust GR(CO32−) by dissolved O2. The beginning of the process is therefore similar to that observed in the absence of phosphate. Finally, GR(CO32−) was oxidised into ferrihydrite, the most poorly ordered form of Fe(III) oxides and oxyhydroxides. Phosphate species, adsorbing on the nuclei of FeOOH, inhibited their growth and crystallisation. For [HPO42−]=0.02molL−1, siderite was accompanied by an amorphous precursor of vivianite, Fe2(PO4)3·8H2O. This shows that, in any case, phosphate species interact strongly with the iron species produced by the dissolution of steel.
Aluminum coatings are widely studied for the cathodic protection of steel structures. However, al... more Aluminum coatings are widely studied for the cathodic protection of steel structures. However, aluminum has poor mechanical properties and its passivation trend could favor localized degradation in chlorine environment, increasing largely the coating dissolution. In order to improve the sacrificial protection and the mechanical properties provided by the aluminum coatings, several alloying elements have been tested as monolayers, in particular Mo, Mg, and Mn. The use of a single alloying element cannot improve both mechanical and corrosion properties. As a consequence, multilayer configuration appears as a promising solution. Different multilayer configurations have been synthesized associating two elements or alloys: one with good mechanical properties and one with a good sacrificial behavior. This study is focused on the impact of the multilayer configuration on the mechanical and electrochemical properties. Several configurations have been tested: the periodicity Λ was varied bet...
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Papers by C. Berziou