Zero Resistance Ammeter Research Articles

Corrosion behavior of additively manufactured M300-CuCr1Zr by multi-material laser-based powder bed fusion

Additive manufactured parts of thermally-conductive CuCr1Zr and high-hardness M300 tool steel were fabricated via a single step multi-material Laser-based Powder Bed Fusion (PBF-LB). The corrosion properties of two interface configurations, CuCr1Zr built on M300 and M300 on CuCr1Zr, were evaluated using the electrochemical polarization resistance measurement, weight loss method and galvanic corrosion current measurement via a Zero Resistance Ammeter. The interface microstructure of the dissimilar bi-metallic parts fabricated by multi-material PBF-LB is tunable. The printing configuration influences the defect size and density and interface microstructure, which affect the global corrosion rate of the fabricated parts. Electrochemical measurements were performed on the fabricated parts in oxygen-saturated and chloride-containing water at elevated temperature, complimented by post-mortem characterizations. The interface configuration with M300 on CuCr1Zr has a slightly lower corrosion rate than that of CuCr1Zr on M300. Unexpectedly, galvanic corrosion occurred only locally in the interface region between M300 and CuCr1Zr materials. Beyond the interface regions, there is no clear sign of galvanic corrosion. Pitting and intergranular corrosion in CuCr1Zr material is the dominant corrosion mechanism. Both base materials beyond the interface region underwent localized pitting, particular in CuCr1Zr. Intergranular corrosion in CuCr1Zr is governed by sub-surface defects like pores and microcracks formed during printing.

Effective Corrosion Inhibition of Galvanic Corrosion of Cu Coupled to Au by Sodium Dodecyl Sulfate (SDS) and Polyethylene Glycol (PEG) in Acid Solution

This study investigates the effects of sodium dodecyl sulfate (SDS) and polyethylene glycol (PEG) on the galvanic corrosion behavior of copper (Cu) coupled to gold (Au) in a printed circuit board (PCB) etching solution. Galvanic corrosion tests using ZRA (zero resistance ammeter) were performed to determine the optimal SDS concentration for corrosion inhibition. The corrosion current between Cu and Au decreased significantly with the addition of SDS, from 3.26 mA/cm2 to 0.248 mA/cm2 at 4 mM SDS, achieving an inhibitor efficiency (IE) of 92.3%. However, at 15 mM SDS, the corrosion current increased, and IE decreased to 80.5%. This phenomenon is attributed to the critical micelle concentration (CMC) of SDS, where surfactant molecules aggregate and reduce surface adsorption properties. Similarly, ZRA tests were conducted to analyze the effects of PEG on galvanic corrosion. The corrosion current significantly decreased with PEG addition, achieving 98.1% IE at 1 g/L and 99.5% IE at 2 g/L. Beyond this concentration, no significant change in IE was observed, indicating saturation. Potentiodynamic polarization tests were also conducted to study the individual effects of SDS and PEG on Cu and Au. The results showed that SDS effectively inhibited Cu corrosion but had a minimal impact on Au. In contrast, PEG significantly reduced the corrosion current density for both Cu and Au, with reductions of 99.5% and 95.1%, respectively.

Prediction of hardmetal corrosion based on the binder response

For 100 years WC-Co has been the quintessential hardmetal, finding extensive application whenever high hardness and wear resistance are required. However, recent concerns regarding health and economic factors have motivated both industry and academia to explore alternative composites. Consequently, numerous hard phases and metallic binders are currently under evaluation. To expedite and streamline the development process, a crucial question arises: “Can the corrosion resistance of hardmetals be predicted based on the electrochemical behavior of their binders?”. To help answer this question, this work compares the corrosion resistances of various hardmetal composites (WC-Co, WC-Ni, WC-CoNi, WC-CoCr, WC-NiCr, WC-CoNiCr, WC-NiCrMo, and WC-FeCoNi) to the corrosion resistances of binder analogues (Co, Ni, CoNi, CoCr, NiCr, CoNiCr, NiCrMo, and FeCoNi) in a 0.5 M NaCl solution using electrochemical techniques: open circuit potential monitoring, polarisation curves and galvanic current between WC and binder measured with zero resistance ammeter (ZRA).

Predicting Galvanic Corrosion of Aluminum Using Accelerated Laboratory Electrochemical Experiments

Aluminum (Al) alloys are the most commonly used non-ferrous metals (approximately 25 million tons per year) for various technical applications and is the second most commonly used metal alloy after steel. Al alloys are also used in combination with other metals or materials to get specific desirable properties for applications such as transportation, construction, electrical appliances, and consumer goods. However, a system of dissimilar materials can lead to potential corrosion problems such as galvanic and crevice corrosion. In this work, atmospheric galvanic corrosion of Al alloy was predicted by combining electrochemical techniques and accelerated laboratory corrosion tests. Three different galvanic couples were analyzed where 6061-T6 Al alloy was coupled with a passivating metal (304 stainless steel), noble metal (copper), and a carbon fiber-reinforced polymer matrix composite (CFR PMC). The galvanic current flowing between the anode and cathode was measured using the zero-resistance ammeter (ZRA) technique in the humidity-chamber setup, cyclic corrosion test chamber following a modified GM9540P cycle, and an outdoor exposure test site. Electrolytes with varying amounts of chloride contents were used to simulate different atmospheric conditions. Four separate equations based on Faraday's law were developed to calculate the corrosion rate in grams per meter square per day (gmd) by relating the time of wetness (TOW) to the galvanic current measured from the accelerated laboratory experiments. The total exposure time was divided into wet periods (Twet) and dry periods (Tdry). The surface morphology of Al samples from the galvanic couples was studied using a scanning electron microscope (SEM), and elemental surface analysis was conducted using energy-dispersive X-ray Spectroscopy (EDXA). Figure 1

Role of Fe oxide in the underdeposit corrosion of pipeline steel in oilfield produced water containing SRB

AbstractThe corrosion behavior of C20 pipeline steel was studied under Fe oxide and sand deposits in oilfield produced water containing sulfate‐reducing bacteria (SRB) via electrochemical techniques and surface analyses. A galvanic current of about 2 μAcm−2 was detected when the Fe oxide deposited sample and the bare steel were coupled in zero resistance ammeter (ZRA) mode, with the former being the anodic member of the couple. The Fe oxide deposited steel recorded severe localized corrosion after 14 days of testing in the SRB inoculated oilfield produced water. Corrosion severity decreased on the sand‐deposited steel, with general corrosion as the dominant morphology of surface attack. The development of product film was a vital factor in steel corrosion under the Fe oxide deposit.

Inhibition of Localized Corrosion Propagation on Carbon Steel: A Potentiostatic Study

The occurrence of localized corrosion in carbon steel pipelines, even when the uniform corrosion rate remains low, is a major concern in the hydrocarbon production and transmission industry. The propagation of these pits, caused by the galvanic coupling between the inhibited surface and the active pit, can lead to serious consequences such as financial loss, environmental damage, production interruption, and even loss of life. To better understand this phenomenon, this work focuses on using the potentiostatic technique to evaluate the tendency of localized corrosion propagation. The experiments were conducted using a primarily imidazolinium-based corrosion inhibitor in produced water conditions (5 wt% NaCl, pH 4.5, CO2-saturated) at 55°C and 80°C. The baseline results were obtained through linear polarization resistance and potentiodynamic polarization tests. The potentiostatic experiments were then conducted to artificially simulate different levels of galvanic coupling that could exist in case of active localized corrosion. The results showed that, at certain anodic potentials, increased inhibitor dosage was necessary to significantly decrease the current. However, at high current levels, further injections were insufficient, indicating that substrate dissolution may affect the adsorption of the inhibitor. This work provides insights into the role of inhibitors and important factors in stopping the propagation of localized corrosion of carbon steel. Further research, such as designing a proper zero-resistance ammeter setup, will be necessary to fully understand this complex phenomenon. The results show that the potentiostatic methodology can be a rapid and easy alternative to obtain electrochemical information and improve understanding of localized corrosion propagation.

Galvanic corrosion mechanism of Ti-Al coupling: the impact of passive films on the coupling effect

The light metals of titanium and aluminum are often used together, so the risk of galvanic corrosion is inevitable. However, the passive films on both metals will change during the galvanic corrosion process, which affects the coupling effect. Thus, this work aims to investigate the variation of passive films with increasing galvanic corrosion time, and further clarify their impact on galvanic corrosion rate. Motto-Schottky (M-S) curves, electrochemical impedance spectroscope (EIS), zero charge potential and XPS were used to characterize the state of the passive films, potentiodynamic polarization and zero resistance ammeter (ZRA) were utilized to analyze the cathodic and anodic reactions on Ti-Al coupling. The results indicate that during galvanic corrosion process the passive film on cathode titanium alloy is transformed from titanium dioxide to low-valent titanium oxide and titanium hydroxide due to hydrogen adsorption behavior, resulting in the increase of defect density in passive film. The passive film on anode aluminum alloy degrades rapidly in the initial galvanic corrosion stage due to the action of Cl− accumulation by non-electrostatic action, also the cathodic reaction on anode aluminum alloy is relatively high under coupled condition, which plays an important role in the high corrosion rate of anode aluminum alloy.

Research Progress of Macrocell Corrosion of Steel Rebar in Concrete

Macrocell corrosion of steel rebar in concrete induced by corrosive environments has attracted widespread attention in the engineering community due to its rapid corrosion rate, diverse forms, and multiple incentives. Potential differences between dissimilar coupled rebar or different parts of the same rebar mainly cause macrocell corrosion of steel rebar. The more significant the potential difference, the faster the corrosion rate of the macrocell. Based on the existing research reports on macrocell corrosion of reinforced concrete, this review paper comprehensively discusses the macro- and micro-corrosion behavior of various types of steel rebar, and a variety of induction factors, such as dissimilar metals and concentration differences of the service environment, development rules. and electrochemical mechanisms for corrosion of rebar macrocells are summarized. ZRA (zero-resistance ammeter), micro-area electrochemical testing technology and evaluation techniques commonly used in the laboratory, and electrochemical testing techniques used in engineering testing are listed. Common experimental models for corrosion of rebar macrocells are briefly introduced. Based on the internal characteristics of macrocell corrosion of reinforced concrete, this paper further proposes the control strategy of macrocell corrosion, starting from the improvement of the corrosion resistance of the rebar and regulating the service environment of the reinforced concrete structure (RCS). Meanwhile, the future direction of macrocell corrosion of steel rebar is also preliminarily prospected.

Contribution of galvanic coupling with TiN, TiAlN, and CrN to the corrosion of steel in neutral and acidic chloride solutions

AbstractThe inherent defective morphology of the physical vapor deposition (PVD) hard coatings limits their corrosion protective ability. We examined the impact of nitride‐based PVD coatings, including TiN, TiAlN, and CrN deposited on inert substrates by cathodic arc PVD method (CA‐PVD), on the galvanic corrosion of carbon steel. Their contribution was evaluated by zero‐resistance ammeter (ZRA) and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl at pH 2 and 6, with and without aeration. The results indicated the prominent role of the coating type and the coupling environment on the generated galvanic currents. Immersion tests for the TiN‐, TiAlN‐, and CrN‐coated steel cross‐sections visually verified these results. The galvanic current contribution was distinct in environments where oxygen reduction is the dominant cathodic reaction. However, the layers' contribution to galvanic corrosion was minimal in deaerated acidic solutions, which is attributed to the high bonding strength of adsorbed intermediates to the coating surfaces.

Mechanistic Insight into Al-Zn, Mg, and Al-Mg-Rich Primer Design for Enhanced Cathodic Prevention on Sensitized Al-Mg Alloys

Three Al-Zn, Mg, and Mg/Al-rich primers (RPs) were evaluated for their ability to suppress intergranular corrosion (IGC) and intergranular stress corrosion cracking (IG-SCC) on highly sensitized aluminum alloy 5456-H116 by sacrificial anode-based cathodic prevention and chemical deposition effects. Tests were conducted in a 0.6 M NaCl solution under full immersion. These evaluations considered the ability of the primer to attain an intermediate open-circuit potential (OCP) such that the galvanic couple potential with bare 5456 resided outside a range of potentials where IGC prevention is observed. The ability of the primer to achieve OCP’s negative enough so that the 5456-H116 could be protected by sacrificial anode-based cathodic prevention and the ability to sustain this function over time were evaluated. The primers consisted of epoxy resins embedded with either (1) spherical Al-5 wt% Zn, (2) spherical Al-5 wt% Zn and spherical Mg, or (3) Mg flake pigments. A variety of electrochemical techniques evaluated the performance specified including OCP, electrochemical impedance spectroscopy, diagnostic cycle testing, as well as zero resistance ammeter tests with simultaneous pH measurement. Electrochemical cycle testing demonstrated that Al-5%Zn did not activate or provide cathodic prevention. Mg-RP had a suitable OCP for cathodic protection of 5456 but the time to primer activation as well as the activated potential both decreased upon utilization of Mg flake content in the primer. The pure Mg-RP activated quickly but ceased to achieve protective potentials after 1 to 11 cycles of DC/AC/OCP cycle testing. Cross-sectional analysis demonstrated that some flakes dissolved while uniform surface oxidation occurred on the remaining Mg flakes, which in combination led to impaired activation. The composite Mg plus Al/Zn-RP mixed primer maintained a suitably negative OCP over time, remained activated, dispensed high anodic charge, and remained an anode in zero-resistance ammeter testing. Chemical stability modeling and zero-resistance ammeter testing suggest that Mg corrosion elevates the pH which activates the Al-5 wt% Zn pigments, thereby providing a secondary pathway for sacrificial anode-based cathodic protection which supports the long-lasting cathodic protection achieved by the Al-5 wt% Zn/Mg primer. These analyses set a baseline for the consideration of Al-Zn/Mg-based coatings to establish effective cathodic protection on highly sensitized 5456-H116 in an aggressive alternate immersion environment and illustrate the merit of using Al/Mg-RP.

Prediction of stress-corrosion cracking using electrochemical noise measurements: A case study of carbon steels exposed to H2O-CO-CO2 environment

At 45 °C, the stress-corrosion cracking (SCC) threshold was determined using current response measurements when carbon steels were exposed to a 50 %CO-50 %CO2-H2O environment. These measurements were performed by introducing an external “crack wall” surface and measuring a fraction of the current flow between the crack tip and this external surface. The current flow was measured between this external surface and the crack tip, by insulating most of the double cantilever beam samples, and using a zero-resistance ammeter (ZRA) to measure the current. These measurements showed that the threshold for cracking determined with this method corresponded well with the KISCC value measured for the same system. Crack tip activity was also measured, but it was difficult to correlate the current response data with the crack propagation rates, because of the crack length measurement resolution. However, it was possible to indicate the increased crack tip activity when the stress intensity showed slight variations, or for threshold stress intensity increase rates. The technique confirms the estimation of stress-corrosion thresholds and can be used to evaluate the influence of parameters on cracking in the absence of high-resolution crack length detection instrumentation.

Corrosion behavior of wire arc additive manufactured and wrought 309 stainless steel in acidic solution

In this study, 309 stainless steel (309SS) was fabricated by wire arc additive manufacturing (WAAM) process and characterized using optical microscopy and X-ray diffractometry. Corrosion behavior of WAAM 309SS in 1 mol/L H2SO4 solution at room temperature was investigated in comparison to that of wrought 309SS using electrochemical impedance spectroscopy, pontentiodynamic polarization, and immersion test. Mott-Schottky analysis, double loop electrochemical potentiokinetic reactivation (DLEPR) test and galvanic corrosion test using zero resistance ammeter (ZRA) technique were also conducted. The results showed that WAAM 309SS exhibited lower corrosion resistance than AISI 309SS due to microstructural differences engendered by the additive manufacturing process. Galvanic corrosion test showed that galvanic effect between the two stainless steels was minimal despite the microstructural differences while DLEPR test revealed the absence of chromium-depleted zones in both WAAM 309SS and AISI 309SS.

Corrosion-resistant metallic coatings for aluminum alloys by cold spray

An Al-V alloy powder produced by high-energy ball milling has been cold sprayed on an AA2024-T3 substrate. The corrosion resistance of cold sprayed alloy, represented by the corrosion current density and pitting potential, was significantly higher than the substrate. Furthermore, a zero-resistance ammeter test revealed that the coating was anodic to the substrate, which would provide cathodic protection in any event of coating breakdown. The wear resistance of the coating was almost four times higher than that of the substrate.

Micro‐galvanic corrosion of duplex stainless steel annealed at different temperatures evaluated by experiments and a numerical simulation model

AbstractIn this study, micro‐galvanic corrosion of SAF 2205 duplex stainless steel (DSS) annealed at different temperatures with different phase ratios (α/γ) in a 1 M H2SO4 + 1 M NaCl solution is analyzed by zero resistance ammeter (ZRA), immersion and numerical simulation model. COMSOL Multiphysics is used to solve the numerical simulation model and predict the local current density, potential distribution, and morphology of DSS annealed at different temperatures with different phase ratios. The modeling results are in good agreement with the immersion test results, which indicate that the micro‐galvanic corrosion depth of SAF 2205 DSS annealed at different temperatures initially decreases and then increases with the increase in the phase ratios (α/γ). The best micro‐galvanic corrosion resistance is obtained at an annealing temperature of 1100°C.

Investigation of the Corrosion Mechanism for Sulfate Reducing Bacteria (SRB) Using a Split-Chamber Zero Resistance Ammetry Technique

Microbiologically influenced corrosion (MIC) is one of the most aggressive forms of corrosion leasing to infrastructure and equipment damage in various industries, including oil and gas, water systems, medical devices, marine environments, nuclear waste storage facilities, and aviation fuel systems and storage. During the last 10 year, PHMSA estimates that MIC has caused 503 internal corrosion incidents at a reported property damage of $188 million and a loss of 53,000 barrels of oil. Some common bacteria associated with MIC are sulfate-reducing bacteria (SRB), iron and CO2 reducing bacteria and iron and manganese oxidizing bacteria. SRB are generally considered the most aggressive group of bacteria in pipeline systems that causes MIC and pitting, especially of carbon steel in the oil and gas industry. SRB are facultative anaerobes and thrive in anoxic environments, using sulfate as a terminal electron acceptor and producing hydrogen sulfide (H2S) as a metabolic byproduct. Furthermore, SRBs also can reduce both nitrate and thiosulfate and obtain their energy from organic nutrients, such as lactate.Electrochemical techniques to monitor for MIC focus on studying the electrochemical characteristics of the interface or mass transport properties of a system that are modified by the microbiological activities. Polarization sensors, such as the BIOX system or BioGeorge, use polarization based on a galvanic couple between a stainless steel electrode and a sacrificial anode. The measured galvanic current is proportional to biofilm that has grown on the electrode surface. Other electrochemical sensors use electrochemical impedance spectroscopy (EIS) or amperometry to measure biofilm thickness by comparing the electrochemical signatures of a reference channel (without bacteria) to a measurement channel (exposed to bacteria); while sensors based on electrochemical resistance use linear polarization measurements to determine the amount of biofilm on an electrode surface. Electro hydrodynamical impedance has also been used to measure the diffusion coefficient in a biofilm and correlate to biofilm growth and thickness. While these approaches can accurately predict the presence and/or thickness of a biofilm on a metal surface, they cannot determine the risk of MIC associated with biofilm formation, as the presence of a biofilm does not necessarily mean that a surface experiences MIC. Additionally, many of the techniques are destructive or require visual examination of the surface after analysis.This work presents a split-chamber zero resistance ammetry (SC-ZRA)-based approach to overcome the limitations to MIC monitoring described above and serve as a screening system to determine the risk of MIC associated with certain microorganisms or groups of microorganisms. Previous work using a split-chamber approach to assess MIC was used by Daumus for the study of stainless steel corrosion in the presence of sulfate reducing bacteria, and subsequently used by Miller et al to evaluate MIC under aerobic, Fe (III)- and nitrate-reducing conditions. In this approach, two identical electrochemical cells (chambers) are separated by an ion-transport membrane. Each chamber contains an identical electrode of the same material which are electrically connected through a zero-resistance ammeter. When one of the chambers is inoculated with microorganisms, the galvanic current between the two electrodes is measured through the zero ammeter. This configuration mimics the microbiologically induced development of localized anodic and cathodic patches on a metal surface that leads to corrosion. The flow of electrons (difference in corrosion current between the two chambers) depends solely on the microbiological activities of bacteria in one of the two chambers, so the influence of the microorganisms on MIC, as well as the extent of corrosion, can be quantified.Using the SC-ZRA technique we were able to characterize the mechanism and electrochemical signatures of SRB corrosion. Specifically, we found that in split-chamber incubations containing an electron donor, electrons flow from the inoculated to the uninoculated chambers. While the current direction could be interpreted as electron transfer such as in a microbial fuel cell, these systems deploy inert graphite electrodes. When used for MIC characterization, the SC-ZRA uses reactive carbon steel electrodes. Indeed, when positive current was detected, greater corrosion was detected on WE1, which is consistent with redox couples, as well as previous work to characterize MIC using SC-ZRA measurements. After depletion of an electron donor, SRB uses electrons from the metals surface as an electron donor reversing the flow of electrons from the uninoculated to the inoculated chamber. In future work, this technique can be used to provide a mechanistic understanding and a monitoring tool for corrosion of metals that are exposed to SRB under a variety of redox regimes.

Galvanic Coupling of Copper and Carbon Steel in the Presence of Bentonite Clay and Chloride

The long-term containment plan for Canada’s used nuclear fuel employs copper-coated carbon steel (CS) containers encased in compacted bentonite clay buffer boxes. In the hypothetical case of a through-coating defect, galvanic interactions between the Cu coating and the CS vessel are dependent on the conditions at the container surface. A zero-resistance ammeter was used to measure the galvanic current between Cu and CS electrodes at various area ratios in the presence of aerated 1 M NaCl and obstructive layers of bentonite slurry. The presence of bentonite resulted in an order of magnitude decrease in the corrosion rate of the steel. As shown by scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis and Raman spectroscopy, the extent of steel corrosion decreased significantly in the presence of bentonite slurry, favouring mild surface etching over oxide growth. Electrochemical impedance spectroscopy (EIS) measurements showed that the total impedance on carbon steel generally increased with bentonite layer thickness, but the total impedance on Cu plateaued when the layer exceeded 6 mm, consistent with trends in galvanic current density on carbon steel. The benign conditions produced by the bentonite slurry are attributed to the slightly alkaline pH and the hindrance of O2 diffusion.

Corrosion behavior of 316 stainless steel, copper, and brazed joint in lithium bromide solution at different temperatures

Abstract Lithium bromide (LiBr) corrosion on austenitic 316 stainless steel (AISI 316) and copper will largely determine the overall performance of refrigeration compression systems. In this work, the corrosion behavior of AISI 316, copper, and brazed joint was studied in LiBr solution at different temperatures by using the polarization curve and electrical impedance spectroscopy. The morphology and chemical composition of the samples before and after corrosion were characterized to elucidate the corrosion mechanism. The passivation film of AISI 316 stainless steel is more prone to breakdown as the temperature increases, and the corrosion resistance of copper and brazed joint also decreases with the increasing temperature. Zero-resistance ammeter technology was employed to analyze the effect of temperature on galvanic corrosion. The degree of galvanic corrosion increases with temperature for all galvanic pairs (AISI 316-Cu, AISI 316-brazed joint, and Cu-brazed joint). For AISI 316-Cu and AISI 316-brazed joint galvanic pairs, AISI 316 functions as the cathode, while copper or brazed joint serves as the anode. For the Cu-brazed joint pair, the brazed joint is preferred to be corroded at room temperature, whereas at 50 and 75 °C, copper corrosion occurs in priority.

An investigation on galvanic corrosion in frictionstir-welded AA 5083 aluminum alloy

Friction-stir welding (FSW) is a well-known solid-state technology for manufacturing high-quality aluminum welds. However, corrosion may become an issue due to the changes in the microstructure within the stir zone, perhaps creating a local galvanic couple. In this work, AA 5083-O aluminum plates were joined by FSW, and corrosion analyzes were undertaken. Therefore, corrosion behavior was investigated using an immersion test, open circuit potential (OCP), and zeroresistance ammeter (ZRA) measurements. The stirred material was found to be more resistant to pitting nucleation than the AA5083-O alloy base material on immersion test and OCP analyzes. Nevertheless, deeper pits were more significant in the stirred material. The ZRA test showed similar results for both regions, indicating this system’s low galvanic couple effect.

Insight into the Elemental Sulfur Corrosion of Carbon Steel in Chloride Bearing Media Using Electrochemical and Non-electrochemical Techniques

This paper studies elemental sulfur-induced corrosion of carbon steel in chloride bearing media. The issue is of great importance in industries dealing with sour gas environment and its mechanism is yet not entirely understood. The aim of this study was sought using various electrochemical (such as potentiodynamic polarization, linear polarization resistance technique, electrochemical impedance spectroscopy and zero resistance ammeter technique) and non-electrochemical techniques (such as scanning electron microscopy and Raman spectroscopy). It was found that reduction of dissolved oxygen is not the main cathodic reaction in the process of the sulfur-induced corrosion. Besides, severe corrosion primarily occurs at near peripheral region of sulfur deposition, leading to formation of a ring of FeS. However, the FeS accumulation reduces the corrosion rate, over the time. In the long term, a galvanic couple is established between the near peripheral and remote regions of the sulfur deposition. Occurrence of the consequent galvanic corrosion could cause severe corrosion at the regions which are far from the sulfur deposition and are not influenced by the sulfur-based species.

(Corrosion Division Morris Cohen Graduate Student Award Address) Galvanic Corrosion of Copper-Coated Carbon Steel for Used Nuclear Fuel Containers

Carbon steel vessels coated with ∼3 mm of Cu have been proposed for the permanent disposal of used nuclear fuel in a deep geological repository (DGR) in Canada. In the event that a container is emplaced in the DGR with an undetected defect in the Cu coating that exposes the steel substrate, galvanically accelerated corrosion of steel is, in principle, possible. To investigate this scenario, the progression of steel corrosion at the base of novel simulated through-coating defects was monitored electrochemically and imaged non-destructively using X-ray micro-computed tomography (micro-CT) as a function of time, O2 availability (including anoxic conditions), and coating method (cold spray deposition (with and without heat treatment) and electrodeposition). The corrosion products and surface damage were analyzed using Raman spectroscopy and scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDX). These analyses showed how the corrosion damage to steel evolved over time and how it was affected by the method used to coat steel with Cu and the amount of O2 available. The results showed that steel exposed at the base of a through-Cu coating defect corroded and became covered by corrosion products, while there was no visible loss of Cu. The supply of O2 to the sample surface governed the corrosion rate, while the distribution of damage to steel at the base of the defect depended on the Cu coating method and the resulting quality of the Cu/steel interface. Cold spray Cu-coated steel specimens exhibited a radial spread of corrosion along the Cu/steel interface, while electrodeposited Cu/steel specimens experienced preferential interfacial corrosion in the direction in which the steel substrate was machined prior to the electrodeposition of Cu. An example of the progression of corrosion observed by micro-CT is shown in Figure 1. Less extensive corrosion along the Cu/steel interface was observed on samples that were shown by electron backscatter diffraction (EBSD) and adhesion tests to have a less stressed, more uniform, and more well-adhered interface. However, less extensive corrosion was typically at the expense of deeper penetration into the steel. In the absence of O2, the quality of the Cu/steel interface greatly affected both the overall amount of corrosion damage to steel and the distribution of damage. The corrosion rates were significantly lower under anoxic conditions than under oxic conditions, and tended to decrease over time. The influence of a wide range of cathode:anode area ratios and Cl− concentrations, and the availability of O2, was evaluated by monitoring the galvanic current passing between separate Cu and steel electrodes, connected through a zero-resistance ammeter (ZRA), and the galvanic potential of the couple. The galvanic corrosion of steel was most severe when it was exposed to air-sparged solution with a moderate [Cl−] as part of the couple with the largest Cu:steel area ratio. Figure 1