A flow microdevice for studying the initiation and propagation of a single pit

International audienceA novel experimental setup in which a glass microcapillary can be precisely positioned close to a metallic electrode has been developed to locally inject aggressive solutions at will. It has been used for studying the pitting corrosion of a 316L stainless steel in 0.5 M H2SO4 medium. The amount of chloride ions released by the capillary could be controlled and the analysis of the corrosion products by scanning electron microscopy and energy dispersive X-ray spectroscopy showed there was no selective dissolution of the 316L stainless steel. This device was shown to be an efficient tool for understanding localized corrosion. (c) 2012 Elsevier Ltd. All rights reserved

Determination of mass transfer coefficient in flow assisted corrosion of steel in liquid Pb Bi. Rotating cylinder geometry

International audienceThe aim of this experimental and numerical work is to determine the mass transfer at the wall of a steel cylinder rotating within liquid Lead-Bismuth blend. This is a crucial parameter for the analysis of corrosion tests performed in the CICLAD experimental setup for the investigation of flow assisted corrosion of steel by liquid metals. As a reliable numerical modelling must rely on experimental validation, and since no direct wall mass transfer measurement is possible in CICLAD, a scaled electrochemical model has been achieved. Modelling the turbulence in this rotating configuration is shown to require the use of a Reynolds-Stress Model. A sensitivity to the Schmidt number is observed in the numerical simulations representing the measured mass transfer in the electrochemical model. Simulations dedicated to liquid Pb-Bi are thus presented in addition to those dedicated to the aqueous solution used in the electrochemical model. Following correlations are proposed for the prediction of Fe mass transfer at the wall of a steel rotating cylinder in liquid Pb-Bi: Sh=1.9x10-1 (Re 2 Sc) 0.31 for 2x10 9 <Re 2 Sc<5.3x10 10 ; Sh=1.4x10-3 (Re 2 Sc) 0.51 for 5.3x10 10 <Re 2 Sc<8.5x10 11

Corrosion of T91 and pure iron in flowing and static Pb-Bi alloy between 450&#8239;°C and 540&#8239;°C: experiments, modelling and mechanism

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Single pit initiation on 316L austenitic stainless steel using scanning electrochemical microscopy

International audienceScanning electrochemical microscopy was used to locally release a controlled amount of chloride ions close to a 316L austenitic stainless steel (SS) substrate in sulphuric acid medium to generate a single pit. Then, usual electrochemical techniques were applied for studying the early stages of pit initiation and propagation. The amount of chloride ions needed to reach the requisite threshold concentration for pit initiation was determined. It was found to be higher for SS than for pure iron. The amount of dissolved cations was also determined as a function of the substrate potential. Different pit shapes and depths were observed depending on the potential applied to the substrate. Following the pit repassivation, it was observed that a part of the dissolved products precipitated at the bottom of the pit

Initiation and growth of a single pit on 316L stainless steel: Influence of SO42− and ClO4− anions

International audienceIn this paper, an ion micro dispenser (IMD) was used to initiate a single pit by generating chloride anions above a 316L stainless steel electrode in either H2SO4 or HClO4 electrolyte. The current variations with respect to time provided an unambiguous characterization of the single pit evolution. Different pit shapes were observed depending on both the nature of the electrolyte and potential applied to the electrode. Substituting SO42− for ClO4− gave smaller (in diameter) but deeper pits at the early stage of pitting. However, when using a different setup that allows the sustaining of the pit propagation with a continuous supply of Cl−, the deeper pits were observed in HClO4 rather than H2SO4. The formation of an iron sulphate salt film at the bottom of the pit by precipitation of dissolution products in H2SO4 slowed down the corrosion rate. At high potentials, the repassivation mechanism outweighed the metal dissolution in the ClO4− containing solution

Oxidation mechanism of a Fe–9Cr–1Mo steel by liquid Pb–Bi eutectic alloy (Part I)

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