The ironcorrosion rate is conditioned by the properties of the corrosion anodic and cathodic reactions. A better understanding of the corrosion mechanisms requires the identification of the limiting steps of these reactions. The major part of publications concerns the description of the anodic reaction. Studies involving the cathodic reaction are less common but its limiting steps are: transport inside the CPL of reducible chemical species in the electrolyte or electrons issued from the iron anodic dissolution.
-a more porous layer called transformed medium (TM) that presents soil compounds
(quartz, calcite, clays,…) mixed with ironcorrosion products, and the soil itself.
These different layers are presented on the schematic representation in Figure 3.
In some areas of the CPLs, the corrosion pattern indicates only ferrous carbonate matrix
The system has been altered in the Andra ’s Underground
Research Laboratory (URL) at Bure (Meuse/Haute-Marne,
France) for 2 years [ 5 ]. On the one hand, physicochemical
analyses are performed on the altered glass, in the Glass Alteration layer (GAL), and in the IronCorrosion Products (ICP) to describe the different alteration products and assess the preferential locations of iron-silicates precipitation. On the second hand, a comparative approach is led between iron-silicates found in the sample and phyllosilicate refer- ences in order to better understand the alteration of nuclear glass under geological disposal conditions.
The results presented here are obtained on samples (mix of nuclear glass and iron powder) altered in the underground Laboratory of Bure (France). Micro and Nanoscale investigations (Transmission Electron Microscopy, Scanning Transmission X-Ray Microscopy, nanoAuger electron spectroscopy) show presence of neoformed nanocristallized phases (iron silicates) inside GAL and in the ironcorrosion products (ICP). Several families of structured Si-Fe-O phases are identified (e.g. smectite in ICP, chlorite and iron sulfide in GAL) according to the localization and the valence of iron in CP. Moreveor study of the provenance of silicium and iron found in phyllosilicates was carried out in mass spectroscopy (TOF-SIMS). Thereby it is possible to know the proportion of silicon and iron arising from the glass, initially substituted for 29-silicium and 5-iron, to form these silicates.
3.4. Electrochemical activity of A. fulgidus on iron coupon 3.4.1. Effect of A. fulgidus on the free corrosion potential of iron
Electrochemical potential/time characterizations were carried out to assess deterioration of the metallic surface when it was immersed in A. fulgidus culture medium. Indeed, open circuit potential (E corr ) was monitored for 1 cm 2 immersed iron coupon in inoculated and abiotic culture medium in the presence or absence of lactate as an organic electron donor over 8 days ( Fig. 4 A). Under abiotic conditions (sterile electrolyte), the organic electron donor had no influence on the poten- tial. Therefore, we chose to present only curve of controls in medium containing lactate ( Fig. 4 A). Within the first few hours, the E corr curves of all conditions decreased to more electronegative potentials and increased to more positive values after one day. In A. fulgidus-inoculated media with lactate, lowest E corr potentials were observed after one day of stabilization in comparison to other conditions. The abiotic control reached, approximately, − 480 mV/SCE from day 3 and remained stable until day 5. It showed abrupt decrease to reach − 600mV/SCE. However, it increased at day 6 to gain the initial level of − 480 mV/SCE again. These abrupt decrease and increase corresponded to an artifact. A similar but smaller artifact was also observed few hours later in the A. fulgidus-inoculated assay without lactate; however, the artifact was not detected in the assay with lactate. In the absence of lactate as an
from 0 to 40 min, becoming important only after that. The polymeric coating can alter the reactivity of iron- 245
based particles due to (i) the blocking of reactive sites and (ii) the inhibition of mass transfer to the surface due to 246
Raman structural imaging can bring original information to answer new questions raised with the recent studies on iron and low alloy steel corrosion. Up to now, this technique has allowed the extraction of the qualitative distribution of the compounds constituting the corrosion product layers. We propose here a methodology to extract quantitative parameters from Raman hyperspectral maps, executed by a home- developed software: LADIR-CAT. Specifically developed for ironcorrosion quantitative component imaging, the approach and program operation are described. The LADIR-CAT is applied on ancient iron corroded samples originating from the Amiens cathedral (France) to establish the description and the composition of the corrosion system through quantitative compounds imaging. Moreover, the global phase quantities proposed supply data for calculating the so-called “protectivity ratio”.
The ironcorrosion rate is conditioned by the characteristics of the corrosion anodic and cathodic reactions. Therefore, for a better understanding of the corrosion mechanisms, the limiting steps both for the anodic and for the cathodic reactions need to be identified. As far as the corrosion mechanisms of iron are considered, the major part of publications concerns the anodic reaction study and there is a serious lack of data linked to the corrosion cathodic reaction. The limiting steps of this latter can be: transport inside the corrosion product layer (CPL) of the electrolyte, of the chemical species (such as H 2 ) or electrons issued from the iron
This paper gives the first results on ironcorrosion in a liquid UF 6 environment whereas the whole literature focuses on gas state. These results have been obtained thanks a dedicated reliable experimental setup and the associated procedure which have been developed in the framework of this study. Three experiments have been performed and have been presented here. These corrosion tests, analyzed by SEM/EDS and XRD, gave results on nature of corrosion products and their structure but also the trend of the corrosion kinetics for iron samples polished up to 1200# SiC. On the one hand, the iron fluoride formed at experimental conditions is FeF2, from nodules to a scale which present important cracks. The uranium fluoride resulting during the corrosion reaction, and mainly localized in cracks, is not clearly identified by EDS since it is highly porous leading to low EDS signal while XRD results tend to attribute the U 2 F 9 nature. On the other hand, the kinetics follows a parabolic law. Since the kinetics is obtained from only 3 experimental points, other experiments are currently running. Moreover, the use protective coating on sample parts will help to know the consumed iron and precise the corrosion monitoring. This could be performed with a Ni coating. Indeed Ni presents higher resistance to corrosion in UF6 than iron . This coating could act like a surface marker allowing estimation of the consumed iron thickness instead of the formed fluoride.
Water utilities use different criteria to assess the structural deterioration of pipes, among which the principal ones are breakage frequency or the growth rate of corrosion pits. The predominant deterioration mechanism on the exterior of metallic pipes is electro-chemical corrosion with the damage occurring in the form of corrosion pits in ductile iron (DI) and graphitized zones in cast iron (CI). Graphitization is a term used to describe the network of graphite flakes that remain behind after the iron in the pipe has been leached away by corrosion. Either form of metal loss will with time lead to a pipe break or leakage. The physical environment in which the pipe is placed has a significant impact on the deterioration rate. Factors that accelerate corrosion of metallic pipes are stray electrical currents, soil properties such as moisture content, chemical and microbiological content, electrical resistivity, aeration, and redox potential.
field effect inspection tools, which will help to de- termine the necessary sensor distribution in future field tools.
A final issue that needs to be explored is the ef- fect of the radial location of the sensors within the pipe. The measurements shown here where made close to the pipe surface on the outside of the pipe. Measurements in the field will not only be made on the inside of the pipe in the remote field zone, but will also be placed a significant distance from the interior pipe surface. Cast iron water pipes may contain significant tuberculation, which can impede or prevent the movement of the remote field inspec- tion tool along the pipe. Inspection is normally pre- ceded by cleaning, but only to the point where a 126 mm tool can pass through a 152 mm pipe. The sen- sor array is therefore highly unlikely to be located immediately adjacent to the interior pipe surface. Further work is therefore required to understand the effect of sensor location within the pipe on the abil- ity to accurately size corrosion pits.
Corrosion under Evaporating Salty Sessile Droplets
Evaporating corrosion droplet
Low salt concentration: c 0 = 10 -3 M NaCl
Evaporation of pinned salty sessile droplets causes peripheral salt enrichment Local chloride enrichment promotes the initiation of corrosion
In the frame of an ongoing project, the authors are presently investigating the preparation of multimetallic films by co-depositing Fe and Al with the MOCVD technique. Such intermetallic systems can be used for the processing of coatings containing iron alu- minides and more generally complex metallic alloys presenting unique combinations of properties. 5 To meet this objective, the se- lection of appropriate precursors is not simply limited to identifying metal complexes with similar volatilities and similar decomposition temperatures. Ideally, precursors for the chemical vapor deposition 共CVD兲 of metals should be selected and treated so as to be cleanly decomposed 共clean cleavage, stable ligands, ligand fragments, etc.兲 共see, for instance, Ref. 6 兲. Co-depositing several metals requires
- Oxidation of the steel elements (Fe, Cr, Ni, Mn, …) of the surface in contact with the liquid metal, if the oxygen content is high enough, then dissolution of the oxides and transfer of
corrosion products (reaction with other dissolved species) Oxygen concentration (concentration of impurities)
V-3 EFFET DE L ABRASION SUR LA CORROSION
Cette étude a été effectuée dans l acide phosphorique industriel à 30 % P 2 O 5
avec addition de 20 g/l de SiC. La vitesse du jet d abrasif choisie est de 5 m/s.
On constate que l abrasion rend la passivation du matériau plus difficile, effet qui se traduit par l apparition d un pic d activité pour les trois alliages (figure 51). Le courant critique est de l ordre de 1190, 790 et 990 µA/cm² respectivement pour les alliages FCr, 3127hMo et 5923hMo. Ce phénomène s accompagne d un élargissement du domaine d activité qui pourrait être dû à une dissolution active de l alliage.