Aluminium corrosion studies. IV. Pitting corrosion

1978 ◽  
Vol 31 (5) ◽  
pp. 943 ◽  
Author(s):  
RT Lowson
Keyword(s):  
Open Circuit Potential ◽  
Chloride Concentration ◽  
Open Circuit ◽  
Aluminium Chloride ◽  
Bulk Solution ◽  
Pitting Potential ◽  
Functional Relationships ◽  
Corrosion Studies ◽  
Thermodynamic Equilibrium Condition ◽  
Chloride Activity

Measurements are reported for the variation of the open-circuit potential, Er, of aluminium in oxygen-saturated sodium salt solutions. The value of Er was independent of SO42- and NO3- concentrations and similar to the value obtained for water (0.04 (s.h.e.)). Er was a function of chloride concentration given by ������������������� Er = -0.475-0.060log[Cl-] V (s.h.e.) at 25�C. There was a less well defined relationship between Er and NO2-, I- and Br-, and a complex relationship with F-. ��� The potentiodynamic characteristics are reported for aluminium in 1-0.01 mol l-1 Cl- oxygen-saturated solutions. Functional relationships were found for E0, Ep, Es and E0' with chloride activity at 5, 25, 50 and 75°C. Hysteresis effects are reported. ��� The experimental results are interpreted in terms of a thermodynamic equilibrium condition between the surface oxide and soluble aluminium chloride. As the system oscillates across the equilibrium conditions the surface will passivate or pit. A critical bulk solution chloride concentration is necessary to maintain the growth of the pit; the experimental value was 1.6 mol l-1 Cl- and the corresponding open-circuit potential was Ecrit = -0.48 V (s.h.e.). The pitting potential, Ev, was interpreted as an overpotential, ηp, given by η = Ep,- Ep-Ecrit.

Experimental Study of Propagation Stage of Pitting Corrosion of 20Cr13 Steel

2008 ◽  
Vol 38 ◽  
pp. 238-247
Author(s):  
A.D. Davydov ◽  
V.S. Shaldaev
Keyword(s):  
Pitting Corrosion ◽  
Open Circuit Potential ◽  
Corrosion Potential ◽  
Ph Value ◽  
Open Circuit ◽  
Effect Of Temperature ◽  
Pitting Potential ◽  
Free Corrosion Potential ◽  
External Power Source ◽  
Corrosion Of Steel

The initiation and development of pitting corrosion of steel 20Cr13 in the NaCl solutions with various concentrations, temperatures, and pH values are studied under the potentiostatic conditions and at the free-corrosion potential. The pitting and repassivation potentials are determined using the method of cycling voltammetry. In spite of the fact that thus determined pitting potential is more positive than the corrosion potential (the open-circuit potential Eo.c.), the long-term experiments, which were performed at the free-corrosion potential, showed that pitting corrosion takes place without imposing a potential using an external power source. It is concluded that the probability of pitting corrosion of steel should be determined by comparing the corrosion potential (the open-circuit potential) with the repassivation potential Erp. Steel 20Cr13 is prone to the pitting corrosion, because Erp is more negative than Eo.c.. In the potentiostatic experiments, the variation of the depth and diameter of pits and their number with the time and the effect of temperature and electrode rotation on the pit propagation are studied. The results, which were obtained at the free-corrosion potential, are much less reproducible. In this case, in contrast to the potentiostatic conditions, the pit depth increased only slightly and the pit width increased to a larger extent. The effect of concentration, pH value, and temperature of NaCl solutions on the pit propagation is considered. It is concluded that the data on the development of pitting corrosion under the potentiostatic conditions can be hardly extended to the conditions of free corrosion potential.

scholarly journals The Effect of the Action of Impurities Present in Methanol as a Basis for Automobile Fuel and Their Impact on the Environment

2020 ◽  
Vol 70 (12) ◽  
pp. 4260-4265
Keyword(s):  
Air Pollution ◽  
Aluminum Alloy ◽  
Acid Chloride ◽  
Considerable Increase ◽  
Open Circuit Potential ◽  
Corrosion Potential ◽  
Open Circuit ◽  
Sulfur Oxides ◽  
Pitting Potential ◽  
Hydroxyl Ion

Corrosion of the tank made of aluminum alloy AlMg2,7Mn (5454) has been studied by electrochemical methods in methanolic solution containing different concentrations of acid, chloride, sulphate and water as impurities. In all these cases, the alloy exhibited a sponge passivity. Adding a 1mM solution in fuel leads to a considerable increase in corrosion potential, a 1 mM chlorine solution decreases the pitting potential, and a 1 mM solution of sulfate concentrations does not show any change. In the first phase, due to the hydroxyl ion that surrounds the aluminum, the present water leads to a decrease in the pitting potential.At the same time, the combustion of fuel remains the biggest source of air pollution. The air is polluted by impurities (acids, chlorides, sulphates and water) present in fuels, smoke (incomplete combustion) or nitrogen and sulfur oxides, so it is required to keep them within the limits set by the rules in force. Keywords: aluminium alloy, pitting potential, impurities, polarization curves, open circuit potential

scholarly journals Potentiometric Response of Ag/AgCl Chloride Sensors in Model Alkaline Medium

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Farhad Pargar ◽  
Hristo Kolev ◽  
Dessi A. Koleva ◽  
Klaas van Breugel
Keyword(s):  
Alkaline Medium ◽  
Open Circuit Potential ◽  
Dynamic Equilibrium ◽  
Chloride Concentration ◽  
Chloride Content ◽  
Cementitious Materials ◽  
Open Circuit ◽  
Potentiometric Response ◽  
Before And After ◽  
The Stability

The stability and reproducibility of an Ag/AgCl sensors’ response in an alkaline medium are important for the application of these sensors in cementitious materials. The sensors’ response, or their open circuit potential (OCP), reflects a dynamic equilibrium at the sensor/environment interface. The OCP response in an alkaline medium is affected by the presence of hydroxide ions. The interference of hydroxide ions leads to inaccuracies or a delay in the sensors’ response to a certain chloride content. In this article, the potentiometric response (or OCP evolution) of the chloride sensors is measured in model solutions, resembling the concrete pore water. The scatter of the sensors’ OCP is discussed with respect to the interference of hydroxide ions at varying chloride concentration in the medium. The deviation of the sensor’s response from its ideal performance (determined by the Nernst law) is attributed to dechlorination of the AgCl layer and the formation of Ag2O on the sensor’s surface. Results from the surface XPS analysis of the AgCl layer before and after treatment in alkaline medium confirm these observations in view of chemical transformation of AgCl to Ag2O.

Laser Welding Influence on Corrosion Rate of Galvanized Sheets of DP600 Automobilistic Alloy

2020 ◽  
Vol 1012 ◽  
pp. 436-440
Author(s):  
Viviane Teleginski Mazur ◽  
Sílvia Rosa Nascimento ◽  
Marilei de Fátima Oliveira ◽  
Willer Cézar Braz ◽  
Correard Gilson Carlos de Castro ◽  
...  
Keyword(s):  
Corrosion Rate ◽  
Open Circuit Potential ◽  
Scanning Speed ◽  
Open Circuit ◽  
Galvanized Steel ◽  
Beam Power ◽  
Laser Weld ◽  
Corrosion Studies ◽  
Laser Beam Power ◽  
Rate Behavior

Corrosion rate behavior of laser welded dual-phase galvanized steel, DP 600, has been assessed in comparison with the material without the laser weld, in 3.5% NaCl solution. Three combinations of both scanning speed and laser power parameters were selected, maintaining the thermal input of 30 J mm-1, calculated as the ratio between the laser beam power [W] and the scanning speed [mm s-1]. The corrosion studies included measurements of open circuit potential, micro and macro polarization, showing higher corrosion rates as scanning speed decreased. Optical microscopy showed the formation of a grain size refined morphology in the heat affected zone and fusion zone. A mechanism has been proposed to explain the corrosion behavior as a function of the laser parameters, which dictated the galvanized coating vaporization.

Influence of pH on the Electrochemical Bahavior of 00Cr15Ni7Mo2Cu2 Supermartensitic Stainless Steel in 3.5% NaCl Solutions

2012 ◽  
Vol 581-582 ◽  
pp. 1058-1061
Author(s):  
Jia Qun Rui ◽  
Jun Li ◽  
Hu Dai Sun ◽  
Kun Yu Zhao ◽  
Zhi Dong Li ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Open Circuit Potential ◽  
Electrochemical Impedance ◽  
Open Circuit ◽  
Pitting Potential ◽  
Supermartensitic Stainless Steel ◽  
Pitting Corrosion Resistance ◽  
Polarization Technique ◽  
Current Densities ◽  
Influence Of Ph

This objective is to study the influence of pH on the electrochemical behavior of 00Cr15Ni7Mo2Cu2 supermartensitic stainless steel in 3.5% NaCl solutions using potentiondynamic polarization technique, open circuit potential tests and electrochemical impedance spectroscopy (EIS).The study reveals that the pitting potential (Eb) is higher, the passivation current densities (ip) is lower and the electrochemical impedance increases with the pH. The results indicate that this stainless steel offer good pitting corrosion resistance with the pH increasing in 3.5% NaCl solutions.

scholarly journals Corrosion behavior of GeO2 and Sc2O3 Coatings on AZ31 Alloy

2021 ◽  
Vol 37 (2) ◽  
pp. 433-439
Author(s):  
L. Sutha ◽  
A. Cyril
Keyword(s):  
Open Circuit Potential ◽  
Corrosion Current ◽  
Az31 Alloy ◽  
Germanium Dioxide ◽  
Electrode System ◽  
Open Circuit ◽  
X Ray ◽  
X Ray Crystallography ◽  
Corrosion Studies ◽  
Surface Examination

In this work, GeO2 (germanium dioxide) and Sc2O3 (scandium trioxide) were developed as coatings on AZ31 alloy using polymer binder. The coatings were characterized using X-ray crystallography procedure (XRD), infrared spectrum of absorption or emission of a solid procedure (FTIR), Raman spectroscopy procedure, surface examination by FESEM. The corrosion studies were analyzed using a three electrode system in 3.5% NaCl electrolyte. The bare AZ31 alloy showed open circuit potential (Ecorr) of -1.7 V (SCE) and the corrosion current density (icorr) of 3.4 x 10-4 mA/cm2, while the Sc2O3 coated AZ31 alloy exhibited Ecorr of -1.4 V (SCE) and the icorr of 5.4 x 10-9 mA/cm2 and while the GeO2 coated AZ31 alloy exhibited Ecorr of -1.3 V (SCE) and the icorr of 2.59 x 10-9 mA/cm2. The results reveal that the GeO2 coated AZ31 alloy demonstrated higher corrosion resistance than of bare AZ31 alloy and Sc2O3 coated AZ31 alloy.

Corrosion Behavior of Sealed Films on Anodized Al Alloy

2011 ◽  
Vol 233-235 ◽  
pp. 1498-1501
Author(s):  
Qi Zhou ◽  
Chun Lin He ◽  
Qing Kui Cai
Keyword(s):  
Potentiodynamic Polarization ◽  
Open Circuit Potential ◽  
Corrosion Behaviour ◽  
Sol Gel ◽  
Open Circuit ◽  
Green Technology ◽  
Al Alloy ◽  
Corrosion Mechanism ◽  
Pitting Potential ◽  
Corrosive Solution

Alumina sol sealing is one of new green technology for anodized Al alloy. The corrosion mechanism of films sealed by sol and corrosion behaviour of films sealed by sol, Na2Cr2O7, boiling water were analyzed by their curves of open circuit voltage-time (E-T) and potentiodynamic polarization curve. It is found that corrosion tendency of sol sealing film is less than other sealed films by E-T inspection. Fluctuation of open-circuit potential is furious in the immersing prophase and slows down in the anaphase for anodized sealed films. At this time corrosive reactions gradually reach steady state. Open-circuit potential greatly waves for the rough sealed films. Potentiodynamic polarization curves of sealed films show that passive area is the longest for films sealed by sol which has the minimum corrosive current , the passivate current, anodic current and cathode current, but the maximum pitting potential and open-circuit potential. Corrosion parameters are the second for the film sealed by dichromate. Anodic reactions are strongly inhibited by sol sealing films in Cl- corrosive solution. Sol sealing films weaken cathode O2 depolarize reaction. Cl- ions erode anodized Al material on which covered with sol film and produce corrosion. The corrosion of sol-gel film goes through two periods: pitting induced phase and pitting corrosion period.

Activity of chloride in absorptive cells of Amphiuma small intestine.

1977 ◽  
Vol 232 (6) ◽  
pp. E553
Author(s):  
J F White
Keyword(s):  
Small Intestine ◽  
Activity Coefficient ◽  
Chloride Concentration ◽  
Bulk Solution ◽  
Intracellular Chloride ◽  
Absorptive Cells ◽  
Intracellular Chloride Concentration ◽  
Intracellular Chloride Activity ◽  
Chloride Activity ◽  
Parallel Measurements

Double-barreled chloride-selective microelectrodes constructed by a new method have been used to determine intracellular chloride activity (aic1) in the absorptive cells of isolated, stripped proximal and distal segments of Amphiuma small intestine. Chloride was passively distributed across the mucosal membrane in fall and winter animals and aic1 is about 20 mM. In contrast summer animals actively accumulated chloride in both proximal and distal segments. Parallel measurements of intracellular chloride concentration (Cic1) reveal a very low apparent chloride activity coefficient (aic1/CiC1) indicating that all of the chloride is not free in the cytoplasm. The chloride activity in the bath immediately adjacent to the mucosa is higher than in the bulk solution.

Galvanic Interactions between Fe Electrodes in CO<sub>2 Saturated Solutions with Different pH

CORROSION ◽  
10.5006/3556 ◽  
2021 ◽  
Author(s):  
Angeire Huggins Gonzalez ◽  
Gerald Frankel ◽  
Jose Vera ◽  
William Durnie ◽  
Richard Woollam
Keyword(s):  
Photoelectron Spectroscopy ◽  
Driving Force ◽  
Open Circuit Potential ◽  
Oil And Gas Industry ◽  
Open Circuit ◽  
Bulk Solution ◽  
Co2 Corrosion ◽  
Galvanic Current ◽  
X Ray ◽  
The Difference

Localized CO2 corrosion is a very common problem in the oil and gas industry. Severe damage of the surface is attributed to the formation, and breakdown, of protective iron carbonate (FeCO3) scales. When the corrosion layer is compromised, the difference between the open circuit potential of the FeCO3-covered and non-covered regions act as the driving force for a galvanic interaction. Depending on the area ratio of the anodic and cathodic areas, the surface could suffer severe localized damage. The present study was focused on the galvanic interactions between iron samples in solutions with different pH. CO2 saturated 1% NaCl solutions with bulk pH of between 6 and 8 and temperature ranging from 20°C and 80°C were studied. A split cell allowed for customization of different environments in each of the half cells, along with simultaneous monitoring of the galvanic current and driving force as indicated by the difference in open circuit potential. Corrosion product layers were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The results indicated that the pH of the bulk solution plays a major role in the formation of protective FeCO3 scales. Fe exhibited passive-like behavior when immersed in a solution at 80°C with pH adjusted to 8. After reaching a passive-like behavior, Fe samples were cathodic when coupled to samples immersed in a solution with lower pH. The galvanic current decreased with increasing temperature and pH gradient.

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