Pure Chloride Solution Research Articles

Unveiling the self-healing behavior of marine exposed concrete: Nondestructive ultrasonic detection and Vickers hardness characterization

Cracking is a widespread phenomenon throughout the service of concrete structures for marine and offshore engineering. In this paper, the effect of sulfate ions and related cations on the crack closure behavior of cracked mortar in chloride-containing environments was studied. To this end, the mortars are cracked before transferring to the pure chloride solution as well as composite chloride and sulfate solutions (CNS and CMS series). The self-healing behavior is assessed by the evolution of crack width, water absorption, and nondestructive ultrasonic detection. The Vickers hardness test is applied to evaluate the micro-hardness of self-healing products generated in the crack gaps. Thermodynamic modeling of the phase volume expansion from the mortar matrix to the crack surface is conducted using Gibb’s free energy theory to explore the self-healing mechanisms. Experiment results suggest that the existence of sulfate ions in chloride-containing solutions is beneficial for crack closure, and self-healing could be more obvious if the cations that bind to sulfate are magnesium ions. The distributions of Vickers hardness on the mortar surface across the crack reveal that the brucite layer diminishes the overall Vickers hardness of the mortar matrix, whereas it is favorable for the micro-hardness enhancement of self-healing products in the CMS series. Thermodynamic modeling interprets the expansion rates relative to the original unhydrated cement under the action of different soaking solutions.

Investigating the effects of testing protocol factors on chloride binding capacity in cementitious materials

This study investigates the influence of testing protocol factors, such as the degree of saturation (DoS), exposure solution composition, sample shape, and the solid-to-exposure solution mass ratio (SLR), on the measured chloride binding capacity of cementitious systems. Samples underwent varying degrees of saturation, including vacuum-saturated, partially saturated, and oven-dried conditions. The exposure solution composition included calcium, potassium, and sodium ions, in addition to pure sodium chloride. Different sample forms (powdered, crushed, and disk-shaped) were explored. Three SLRs of 1:3, 1:6, and 1:10 were also examined for their impact on chloride binding. The results indicated that DoS significantly influences chloride binding, with vacuum-saturated samples exhibiting higher binding capacity than partially saturated and oven dried samples. Additionally, the findings showed that samples in solutions containing additional ions had reduced binding capacities compared to pure chloride solutions. Increasing the sample surface area by crushing or powdering it led to an increase in chloride binding capacity compared to solid, disk-shaped specimens. Lastly, the results demonstrated that increasing the SLR can enhance the binding capacity of the system.

Inhibition Mechanism of Phosphate Ions on Chloride-Induced Crevice Corrosion of Alloy 22

Alloy 22, a nickel-based alloy that belongs to the Ni-Cr-Mo family, shows an outstanding corrosion resistance in most environments. Alloy 22 was extensively studied regarding its crevice corrosion behavior both in pure chloride solutions and in solutions containing other ions such as nitrate, sulfate, and carbonate/bicarbonate. Electrochemical tests were performed to study uniform and localized corrosion of Alloy 22 in a deaerated aqueous solution of 1 M NaCl and 1 M NaCl with different amounts of phosphate additions at 90°C and at pH near neutral. Results show that the addition of phosphate to the solution increased the length of the passive potential range. Moreover, results from two type of electrochemical tests showed that the addition of 0.3 M phosphate and higher completely eliminated the susceptibility of Alloy 22 to crevice corrosion. The excellent inhibitive effect of phosphate is comparable to that of nitrate already reported in the literature. Elemental analysis of the corroded area suggests th...

The effect of dichromate ion on the pitting corrosion of AISI 316 stainless steel. Part I: Critical pitting temperature

This article provides a better understanding of dichromate effect on the critical pitting temperature (CPT) of 316 SS in chloride solution. Potentiostatic measurements revealed that dichromate effectively improves the CPT. In the presence of dichromate ion, a remarkable decrease in the anodic dissolution in simulated pit environment and a slight decrease in the saturation concentration of cations in pit solution were defined in pencil electrode experiments. Scanning electron microscopy showed that, in compare with pure chloride solution, the pits formed on the metal surface in dichromate containing solution, have finer lacy covers.

Molybdate inhibition of corrosion fatigue crack propagation in precipitation hardened Al–Cu–Li

Addition of molybdate (MoO42-) to aqueous chloride solution effectively inhibits environmental fatigue crack propagation (EFCP) in peak aged Al–2.6Cu–1.6Li (wt pct, C47A-T86) which also exhibits alloy-induced inhibition in pure chloride solution. MoO42- inhibits EFCP at frequencies below an upper bound and eliminates the effect of environment at sufficiently low loading frequencies by yielding crack growth rates equivalent to those for fatigue in ultra-high vacuum. Ion-assisted inhibition is attributed to MoO42- stabilizing a crack tip passive film which reduces H production and uptake due to a diffusion barrier film, reduced crack acidification by hydrolysis, and buffered pH. Inhibition is governed by the balance between passive film rupture by crack tip strain and repassivation. As such, inhibition is promoted by reduced loading frequency and potentials at or anodic to free corrosion; each of which favors passivity over film rupture. Alloy-induced inhibition is destabilized by addition of molybdate. This is likely due to molybdate inhibiting localized corrosion of Al2CuLi precipitates in the crack wake which otherwise leads to Cu enrichment required for alloy-induced EFCP inhibition in C47A-T86. The inhibiting effect of molybdate for this Al–Cu–Li alloy parallels chromate and molybdate inhibition of EFCP in 7075-T651, establishing molybdate as a viable chromate replacement inhibitor.

Phosphate Inhibition Effect on Chloride-Induced Crevice Corrosion of Alloy 22

ABSTRACTAlloy 22 has been extensively studied regarding its crevice corrosion (CC) resistance both in pure chloride solutions and in solutions containing different oxyanions that may act as inhibitors of crevice corrosion. The scope of this work was to study the general and localized corrosion behavior of Alloy 22 when phosphate ions were added to a 1 M NaCl solution at 90°C. Results from the electrochemical tests indicate that the size of the passive potential range and the localized corrosion repassivation potential value increased in the presence of phosphate ions. Results from creviced specimens showed a strong inhibition effect of phosphate ions on the chloride induced crevice corrosion of Alloy 22. The critical molar concentration ratio (RCRIT = [phosphate]/[Cl]) to inhibit crevice corrosion was 0.3.

Effect of Sulfate Ions on the Corrosion Behavior of Steel in Concrete Using Electrochemical Methods

The effect of sulfate ions on the corrosion behavior of steel in ordinary Portland concrete (OPC) and high performance concrete (HPC) were investigated. Steel corrosion was evaluated by means of corrosion potential (Ecorr), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP). The electrochemical results indicated that, compared to the pure chloride solution, the presence of sulfate ions in the chloride solution both reduced the time to corrosion initiation and lead to an increase in corrosion rate of steel in OPC specimens; however, the sulfate ions had negligible effect in HPC specimens. Furthermore, the corrosion rate of steel exposed to chloride solution was higher that to the sulfate solution both in OPC and HPC specimens.

Determination of Crevice Corrosion Susceptibility of Alloy 22 Using Different Electrochemical Techniques

AbstractAlloy 22 belongs to the Ni-Cr-Mo family and it is highly resistant to general and localized corrosion. It may suffer crevice corrosion in aggressive environmental conditions. This alloy has been considered as a corrosion-resistant barrier for high-level nuclear waste containers. It is assumed that localized corrosion may occurs when the corrosion potential (ECORR) is equal or higher than the crevice corrosion repassivation potential (ER,CREV). The latter is measured by means of different electrochemical techniques using artificially creviced specimens. These techniques include cyclic potentiodynamic polarization (CPP) curves, Tsujikawa-Hisamatsu electrochemical (THE) method or other non-standard methods, such as the PD-GS-PD technique.The aim of the present work was to determine reliable critical or protection potentials for crevice corrosion of Alloy 22 in pure chloride solutions at 90°C. Conservative methodologies (which include extended potentiostatic steps) were applied for determining protection potentials below which crevice corrosion cannot initiate and propagate. Results from PD-GS-PD technique were compared with those from these methodologies in order to assess their reliability. Results from the CPP and the THE methods were also considered for comparison. The repassivation potential resulting from the PD-GS-PD technique was conservative and reproducible, and it did not depend on the amount of previous crevice corrosion propagation.

Effect of Weak Acid Additions on the General and Localized Corrosion Susceptibility of Alloy 22 in Chloride Solutions

AbstractElectrochemical studies such as cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy (EIS) were performed to determine the corrosion behavior of Alloy 22 (N06022) in 1M NaCl solutions at various pH values from acidic to neutral at 90°C. All the tested material was wrought Mill Annealed (MA). Tests were also performed in NaCl solutions containing weak organic acids such as oxalic, acetic, citric and picric acids.Results show that the CR of Alloy 22 was significantly higher in solutions containing oxalic acid than in solutions of pure NaCl at the same pH. Citric and Picric acids showed a slightly higher CR, and Acetic acid maintained the CR of pure chloride solutions at the same pH. Organic acids revealed to be weak inhibitors for crevice corrosion. Higher concentration ratios, compared to nitrate ions, were needed to completely inhibit crevice corrosion in chloride solutions.Results are discussed considering acid dissociation constants, buffer capacity and complex formation constants of the different weak acids.

Effect of Fluoride Ions on Crevice Corrosion and Passive Behavior of Alloy 22 in Hot Chloride Solutions

Alloy 22 (UNS N06022) is a Ni-Cr-Mo-W alloy highly resistant to localized corrosion. Alloy 22 may be susceptible to crevice corrosion in pure chloride (Cl−) solutions under aggressive environmental conditions. The effect of the fluoride (F−) over the crevice corrosion induced by chloride ions is still not well established. The objective of the present work was to explore the crevice corrosion resistance of this alloy to different mixtures of fluorides and chlorides. Cyclic potentiodynamic polarization (CPP) tests were conducted in deaerated aqueous solutions of pure halide ions and in different mixtures of chloride and fluoride at 90°C and pH 6. The range of chloride concentration [Cl−] was 0.001 M ≤ [Cl−] ≤ 10 M and the range of fluoride to chloride molar concentration ratio [F−]/[Cl−] was 0.1 ≤ [F−]/[Cl−] ≤ 10. Results show that Alloy 22 was susceptible to crevice corrosion in all the pure chloride solutions but was not in the pure fluoride solutions. Fluoride ions showed an inhibitor behavior only in mixtures with a molar ratio [F−]/[Cl−] > 2. For mixtures with a molar ratio [F−]/[Cl−] of 7 and 10, the inhibition of crevice corrosion was complete.

Influence of halide ions and alloy microstructure on the passive and localized corrosion behavior of alloy 22

Alloy 22 (N06022) is the current candidate alloy used to fabricate the external wall of the high-level nuclear waste containers for the Yucca Mountain repository. It was of interest to study and compare the general and localized corrosion susceptibility of Alloy 22 in fluoride and chloride solutions at 90 °C. Standard electrochemical tests such as cyclic potentiodynamic polarization, amperometry, and electrochemical impedance spectroscopy were used. Studied variables included the solution pH and the alloy microstructure (thermal aging). Results show that Alloy 22 is highly resistant to general corrosion in all the solutions tested. Thermal aging is not detrimental and even seems to be slightly beneficial for general corrosion at the higher solution pHs. Pitting corrosion was never observed. Crevice corrosion was found only for high chloride-containing solutions after anodic polarization. The presence of fluoride ions together with chloride ions seems to increase the susceptibility of Alloy 22 to crevice corrosion compared to pure chloride solutions.

Copper corrosion in buffered and non-buffered synthetic seawater: a comparative study

The electrochemical behaviour of copper in neutral buffered and non-buffered synthetic seawater and in pure chloride solutions has been studied by cyclic voltammetry, weight loss measurements, open circuit potential and scanning electron microscopy (SEM). Values of the repassivation potentials of Cu in non-buffered and buffered synthetic seawater, at 50 mV s−1, were 0.12 and 0.46 V vs. SCE, respectively. The sharpness, heights and location of the different peaks as well as their charges were shown to be influenced by the composition of the solution, buffering conditions, deoxygenation, polarization potential and time. High chloride concentrations lead to higher oxidation charges. The anodic and the cathodic charges were shown to increase as the chloride concentration increases. The open circuit potential transients of copper in non-deoxygenated, non-buffered synthetic seawater indicate pitting from the beginning of the exposure, while in buffered solutions the pitting appeared only after a quite long exposure period, i.e. after 40 days. Corrosion rates of Cu samples after 3 months of immersion were higher in solutions of pure chloride (0.5 M) than in synthetic seawater. After six months the differences were even more noticeable. SEM images have showed a somewhat higher density of pits on copper samples immersed in the chloride solution (0.5 M), in comparison with those in synthetic seawater.

The effect of some sulphur compounds on the pitting corrosion of type 304 stainless steel

The potentiodynamic anodic polarization behaviour of AISI 304 stainless steel (SS) in 0.1 M NaCl containing various concentrations of SO 4 2−, SO 3 2−, S 2− SCN − or S 2O 3 2− anions has been studied. In pure chloride solutions, the alloy exhibited pitting corrosion. The addition of low concentrations of the sulphur containing anions (except SO 4 2−) decreases the pitting potential. The sulphate anion appears to increase the pitting potential. The electric charges associated with the pitting initiation and propagation processes were calculated when the steel was immersed under potentiostatic potential of +320 mV for 10 min in 0.1 M NaCl without and with 10 −2 M of the cited anions. The results indicated that SO 3 2−, S 2−, SCN − and S 2O 3 2− anions promote the chloride-pitting propagation kinetics. The pitting potential of 304 SS decreases linearly with increasing chloride concentration while it was temperature independent in chloride and chloride containing sulphur anions in the range from 40 to 70°C. Scanning electron microscopy (SEM) observations indicated that open pit with 250 μm in diameter produced on the steel in 0.1 M NaCl under constant potential of +320 mV. While salt film formation inside open pits produced in the presence of sulphur containing anions with chloride. The pit morphology and its diameter depend on the type of sulphur containing anion present.

Pitting in Aluminum Thin Films: Supersaturation and Effects of Dichromate Ions

The growth of pits in 209 nm thick Al films in chloride solutions with and without dichromate ions was examined using image analysis of the growing pits to determine pit current density. In pure chloride solutions, the pit current density decreased at high potentials after reaching a maximum value, and then was almost independent of applied potential. A hysteresis in the pit current density‐potential behavior was observed during downward stepping of the potential from high values. This is a result of a combination of supersaturation of the pit electrolyte followed by salt film formation, and changes in mass transport from hydrogen bubbles that increase convection and lift the remnant passive film away from the dissolving surface. In solutions containing dichromate ions, the corrosion and repassivation potentials shifted in the noble direction, and rather large metastable pits formed at the open circuit. A large concentration of dichromate ions was needed to inhibit pit growth. In dichromate solutions, subsequent pit growth at higher potentials often initiated at the edge of the open‐circuit pits. The rate of pit growth was lower for these pits because the remnant passive film layer was not easily lifted up at these sites, and thus created a barrier for mass transport away from the dissolving pit edge.

Corrosion behaviour of Alloy 800 in high temperature aqueous solutions: Electrochemical studies

The anodic behaviour and passivity breakdown of Allot 800 in aqueous solutions of sodium chloride, sodium sulphate and sodium bicarbonate were studied by electrochemical techniques in the temperature range from 60°C to 280°C. The pitting resistance and pitting morphology of the alloy in chloride plus sulphate and chloride plus bicarbonate mixtures, at 60°C and 280°C, were also examined. Increasing bicarbonate or sulphate additions to chloride solutions shift the characteristic pitting potential of Alloy 800 to higher values, both at low and high temperatures. Changes in pitting morphology were observed in sulphate containing solutions while the morphology of the attack found in bicarbonate containing solutions was similar to that in pure chloride solutions. Finally, no localized or substantial generalized corrosion was detected in pure sulphate or bicarbonate solutions at any temperature.

The effect of chloride and sulfate ions on reinforcement corrosion

The effect of chloride, sulfate and chloride-sulfate solutions on corrosion of steel embedded in cement paste has been investigated. The reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density using D.C. linear polarization resistance technique. Results indicate that the corrosion activity was very minimal in specimens immersed in pure sulfate solution. The reinforcement corrosion activity was found to be higher in specimens immersed in chloride-sulfate solutions as compared to those immersed in pure chloride solution. The corrosion rate was observed to be doubled when the sulfate concentration in 15.7% Cl − solution was raised from 0.55 to 2.1%.

The effects of chromate on the transient repassivation potential of aluminium in chloride solution

The effects of chromate on the open-circuit repassivation of the guillotined aluminium electrode in chloride solutions are presented. The presence of chromate causes the entire transient to lie at higher potential, thereby accelerating repassivation. Reactivation of the repassivating surface observed in pure chloride solution is eliminated by the presence of chromate. Some implications of the results are discussed.

Corrosion Fatigue Behavior of Alloy 600 in High-Salinity Brine

Abstract The corrosion fatigue behavior of alloy 600 was studied as a function of applied potential and heat treatment in high-salinity brine (4 M NaCl) in the absence and presence of low concentrations (10−4 M) of sodium tetrathionate and sodium thiosulfate. It was found that the corrosion fatigue resistance of the solution-annealed material in pure chloride solution decreased by increasing the applied potential from −900 mVSCE (cathodic range) to −400 mVSCE (passive range) and to −100 mVSCE (above the pitting potential). The corrosion fatigue resistance was improved by heat treatment of the solution-annealed (SA) material at 800 C for 10 and 50 h. This improvement is attributed to the intergranular precipitation of chromium carbides. The addition of tetrathionate to the chloride solution did not change the fatigue life of the SA material with respect to that in pure chloride solution, while the addition of thiosulfate improved the corrosion fatigue resistance.