Long-term Corrosion Performance Research Articles

Role of anodic precursor layer thickness on PEO coatings: Energy consumption and long-term corrosion performance

PEO coatings with different thickness of anodic precursor films (5, 10, 20 and 40 μm) were successfully developed on AA2024 with the aim of determining how the thickness of anodic films affects the development of PEO film, structural growth, surface morphology, phase composition, and associated long term corrosion resistance properties. Compared to direct PEO treatment, reductions in the energy consumption (kW.h.m2.μm−1) of 71 %, 41 %, and 17 % are obtained at similar PEO processing conditions for the pre-anodized specimens of 40 μm, 20 μm, and 10 μm film thickness, respectively, while the time to current drop for above specimens reduced to 86.2 %, 63.3 % and 33.3 %, associated to the early formation of the “soft sparking” regime. The results suggest the effectiveness of pre-anodization on the PEO coatings for minimum energy consumption, developed explicitly on 20 and 40 μm anodic film, whereas overall PEO on anodic precursors exhibited a thicker oxide layer, homogenous pore size distribution, and long-term corrosion protection comparable to the original PEO layer. Based on the energy consumption and corrosion resistance of PEO on anodic precursor, a model of PEO coating growth is proposed, which can be considered a thorough insight towards highly developing energy-efficient PEO for practical applications.

Enhancement of corrosion resistance and bond strength in rebars employing abrasives-infused soy-protein isolate coatings

While epoxy coatings effectively prevent rebar corrosion, they can sustain damage during transportation, making them susceptible to localized corrosion during service. Additionally, these coatings can reduce the bond strength with concrete by over 20%, necessitating an increase in development length. Although soy-protein coatings could potentially repair damaged epoxy coatings in the field, they may further reduce the bond strength. This study aims to enhance the corrosion resistance of soy-protein isolate (SPI) coatings without undermining their bond with concrete. To achieve this, five new coating formulations were prepared by blending chemically inert oxide abrasives into SPI coatings in varying proportions. These modified soy-protein coatings were then assessed through physical, chemical, mechanical, and electrochemical analyses to measure their improvements. Adding abrasives beyond a certain weight proportion increased the viscosity and thickness of the coatings, improving their mechanical properties, including abrasive resistance and lap shear strength. Potentiodynamic polarization tests and macrocell analyses revealed a 94% and 78% improvement in short-term and long-term corrosion performance respectively. Moreover, when compared to conventional SPI coatings, the bond strength of the modified soy-protein coatings improved by up to 90.41%. In conclusion, SPI coatings infused with abrasives outperform traditional SPI coatings and could serve as superior secondary coats. They could even be considered as stand-alone coatings for rebars.

Synergistic enhancement of corrosion protection of carbon steels using corrosion inhibitors and biocides: Molecular adsorption studies, DFT calculations and long-term corrosion performance evaluation

Corrosion of carbon steel (CS) water pipelines is a major concern worldwide today, which causes leakage of precious water, damage valuable assets, interruption of the water supply, and pose the danger of contamination. In the present work, we demonstrate synergistic enhancement of corrosion protection of CS using biocides (BC) and corrosion inhibitor (CI) combinations of zinc chloride (ZnCl2), phosphoric acid (H3PO4), sodium molybdate (Na2MoO4) and an ionic liquid, 1-Butyl-3-methylimidazolium chloride (IL). 25 ppm of biocides (BC) such as benzalkonium chloride, bronopol, and isothiazoline showed excellent antimicrobial activity against the slime formers and manganese and iron-oxidizing bacteria (Mn/IOB). Electrochemical analysis showed nearly 98% corrosion inhibition efficiency of mixed CI and the anticorrosion mechanism of these CI on iron was further studied by quantum chemical calculations and adsorption studies. Molecular adsorption of the inhibitors onto the Fe(110) surface, modeled from first principle calculations, showed that adsorption energies of the ZnCl2, H3PO4, Na2MoO4 and the IL inhibitor molecules were − 1.94 eV, − 9.73 eV, − 2.14 eV and − 2.46 eV, respectively, in the order of H3PO4 >IL>Na2MoO4 >ZnCl2 indicating thermodynamically favorable interactions which was in good agreement with the experimental data. The long term efficiency of these BC and CI combinations was also tested under accelerated conditions in a pilot scale cooling tower. Nearly 92% corrosion inhibition efficiency was shown by a combination of all CI and BC when compared to corrosion inhibitors alone (81%). These findings are very promising for addressing the corrosion issues in carbon steel water pipelines.

Corrosion and wear resistance of coatings produced on AZ31 Mg alloy by plasma electrolytic oxidation in silicate-based K2TiF6 containing solution: Effect of waveform

In this research, plasma electrolytic oxidation coatings were prepared on AZ31 Mg alloy in a silicate-based solution containing K 2 TiF 6 using bipolar and soft sparking waveforms with 10, 20, and 30% cathodic duty cycles. The coatings displayed a net-like surface morphology consisted of irregular micro-pores, micro-cracks, fused oxide particles, and a sintered structure. Due to the incorporation of TiO 2 colloidal particles and the cathodic pulse repair effect, most of the micro-pores were sealed. Long-term corrosion performance of the coatings was investigated using electrochemical impedance spectroscopy during immersion in 3.5 wt.% NaCl solution up to 14 days. The coating grown by the soft sparking waveform with a 20% cathodic duty cycle having the lowest porosity (6.2%) and a sharp layer concentrated in F element at the substrate/coating interface shows the highest corrosion resistance. The friction coefficient of this coating has remained stable during the sliding even under 5 N normal load, showing relatively higher wear resistance than other coatings. The coating produced using the equivalent unipolar waveform, as the reference specimen, showed the highest friction coefficient and the lowest wear resistance despite its highest micro-hardness.

Comparison on long-term corrosion performance of WC-CoCr and Al2O3-TiO2 ceramic coatings in sulphide-containing 3.5 wt% NaCl solution

In this study, the WC-CoCr coating and Al2O3-TiO2 coating were deposited by high-velocity oxygen-fuel (HVOF) spraying and atmospheric plasma spraying (APS), respectively. Both coatings were immersed in 3.5 wt% NaCl solution with 20 ppm Na2S to investigate their long-term corrosion resistances in the simulated seawater environment. The corrosion behaviors of both coatings for different times were investigated by potentiodynamic polarization, EIS, XRD, EDS and SEM. The electrochemical measurement results showed that the corrosion resistance of both coatings decreased obviously after long-term immersion in sulphide-containing solution, while the Al2O3-TiO2 coating exhibits more stable corrosion performance during the whole immersion process compared with the WC-CoCr coating. The corrosion resistance of the WC-CoCr coating in sulphide-containing solution after long-term immersion was inferior to that of the Al2O3–40TiO2 coating.

Effect of Molybdate on Corrosion Performance of Oxide Coating Produced on 7075 Al Alloy Using PEO

In this research, plasma electrolytic oxidation (PEO) coatings were prepared on 7075 Al alloy in a silicate-based solution with Na2MoO4 additive using a unipolar waveform at constant current density. The coatings displayed micro-pores, micro-cracks, pancake-like and crater-like features, and also solidified molten oxide particles on the surface. The coatings were majorly composed of Al2O3 (γ, δ, and α), SiO2 (amorphous), and MoO3 phases, which confirms the incorporation of molybdenum in the case of additive-containing coatings. Molybdenum species were transported through cracks, channels, and micropores, as the ready access pathways into the coating and partly sealed the coating pores. The EIS technique was used to evaluate the long-term corrosion performance of the coatings up to 168 h of immersion in 3.5 wt.% NaCl solution. The results showed that the barrier action of the PEO coatings was highly enhanced by adding Na2MoO4 due to the higher resistance that alumina achieved to chlorine absorption and also its higher stability by the incorporation of MoO3. The coating formed in the presence of 5 g L−1 Na2MoO4 showed the highest thickness and the lowest porosity percent (15.15%), which provided the highest corrosion performance at long immersion times.

Effect of variation in oxygen concentration in static Pb–Bi eutectic on long-term corrosion performance of Al-alloyed austenitic steels at 500 °C

Aluminium-alloyed austenitic steels Fe-14Cr-2Mn-20Ni-0.5Cu-3Al and Fe-14Cr-5Mn-12Ni-3Cu-2.5Al were tested at 500 °C in static Pb-Bi eutectic for 10,000 h. The concentration of oxygen in the liquid metal was changed in a controlled way over the course of the test from ∼10−6 to ∼10−9 mass% which provided conditions for oxidation and dissolution, respectively. Both steels showed slight oxidation of surface. Steel with higher Ni content revealed also initiation of dissolution corrosion in the view of rare pit-type damages. The structural and compositional features of oxide films, sub-oxide zones and corrosion damages are discussed.

The effect of zinc oxide coating morphology on corrosion performance of Ti-6Al-4 V alloys

The release of aluminum and vanadium is one of the major issues affecting the service life of permanent orthopedic devices made of Ti6Al4V. This study aims to improve the corrosion resistance of Ti6Al4V using electrodeposited zinc oxide coatings. Moreover, the effects of bath temperature and applied potential on the morphology, roughness, porosity, wettability, and corrosion performance of zinc oxide coatings were evaluated. The results showed that by controlling the process parameters, zinc oxide coatings with various morphologies including spherical, worm-like, irregular porous network and flower-like were created. The coating changed the hydrophilic nature of Ti6Al4V substrate (wettability of ~46°) to a hydrophobic one. The wettability of the zinc oxide films varied from ~83° for the spherical to ~67° for the flower-like morphology. The long-term corrosion performance of the zinc oxide coatings was estimated in phosphate-buffered saline solution using electrochemical impedance spectroscopy. The results revealed that the spherical morphology provides higher corrosion performance at the initial stage of immersion, however, the corrosion behavior of both spherical and worm-like morphologies became the same after 4 weeks. On the other hand, zinc oxide coating with an irregular porous network of nanoflakes and flower-like morphologies reduced the corrosion performance of Ti6Al4V substrate.

Corrosion of Aluminium and Zinc in Concrete at Simulated Conditions of the Repository of Low Active Waste in Sweden

The corrosion performance of Aluminium (Al) and zinc (Zn) is of interest in repositories for radioactive waste as the production of hydrogen gas during their anoxic corrosion may create open pathways for the transport of radioactive ions. Al and Zn rods were embedded in concrete cylinders and immersed in artificial groundwater at anaerobic conditions for 2 weeks and up to 2 years in laboratory conditions. Corrosion rates were determined to enable predictions and estimations of risks for gas evolution and the assessment of the potential impact of corrosion on the structural integrity of concrete in the final repository of low and intermediate level metal-containing waste from dismantled nuclear power plants. Samples were collected after 2, 4, 12, 26, 52 and 104 weeks. The observed corrosion rates were higher for Al compared with Zn, as expected, but both materials revealed comparatively high initial corrosion rates that decreased with time, reaching steady state after 26–52 weeks. Some of the Al containing concrete cylinders were cracked as a result of the corrosion processes after 2 years of exposure, thereby providing free passage between the embedded metal and the surrounding environment. No such effects were observed for Zn. Comparative studies were performed on non-concrete-embedded Al and Zn immersed in artificial groundwater. Observed long-term corrosion rates (1–2 years) were similar to corresponding corrosion rates in concrete. The results indicate that immersion studies in artificial groundwater can be used to estimate the long-term corrosion performance of Zn and Al in concrete.

The multi-effects of K2TiF6 additive on the properties of PEO coatings on AZ31 Mg alloy

Plasma electrolytic oxidation of AZ31 Mg alloy was performed in an alkaline silicate-based solution containing various concentrations of K2TiF6 using unipolar waveform at a constant voltage. The surface morphology of all coatings was rough and contained a micro-pore network, micro-cracks, and granules of oxide compounds in different diameters and micro-pore levels. The coating is composed of MgO, MgF2, Mg2SiO4, SiO2 (amorphous), and TiO2 (crystalline and amorphous) phases. The average thickness of the coatings was increased by adding the K2TiF6, where EDS results showed that a skinny fluoride-rich passive layer forms. With increasing time and reaching the final potential, the TiO2 colloidal particles absorbed physically by the oxide erupted into the discharge channels allowing the formation of a thicker and more compact layer coating along with the pore sealing. Incorporation of silicate ions develops amorphous SiO2 in the coating that also partially seals the pores in the coating. Long-term corrosion performance of the coatings was investigated using EIS during 7 days of immersion in 3.5 wt% NaCl solution. It was found that the barrier performance of the PEO coatings was improved by adding K2TiF6 up to 5 g l−1. The coating produced in the presence of 5 g l−1 K2TiF6 displayed the lowest porosity percent (13.04%) with an appropriate thickness, which provided the highest barrier performance at both short- and long-immersion times.

Long-term corrosion performance of T91 ferritic/martensitic steel at 400 °C in flowing Pb-Bi eutectic with 2 × 10−7 mass% dissolved oxygen

Long-term corrosion behavior of T91 ferritic/martensitic steel in oxygen-doped flowing Pb–Bi eutectic is investigated by exposure for up to 20,000 h at 400 °C, 2 m/s and 2 × 10−7mass% dissolved oxygen. The corrosion phenomena and kinetics of interaction are characterized qualitatively and quantitatively. The steel shows major oxidation resulted in the formation of a bilayer Fe3O4 / Fe(Fe,Cr)2O4 scale. After 20,000 h, the scale thickness averages 12.6 (±2.7) μm. The metal recession due to oxidation does not exceed 5 (±1) μm. Besides oxidation, the localized dissolution of the steel is observed reaching of ∼100 μm in depth after 20,000 h.

Role of Substrates in the Corrosion Behaviors of Micro-Arc Oxidation Coatings on Magnesium Alloys

Micro-arc oxidation (MAO) was performed on AZ31 and AZ91 Mg alloys to explore the relationship between Mg substrates and corrosion behaviors of resultant coatings. The microstructure and long-term corrosion performance of the two coatings were investigated. Results showed that MAO coating on AZ91 alloy provided a longer-term corrosion protection to substrate than that on AZ31 alloy, despite having similar microstructure and phase composition. However, once corrosion occurred, the corrosion area of MAO coating on AZ91 alloy enlarged at a faster rate compared to that on AZ31 alloy during immersion tests, and their corrosion morphologies were different. Based on the corrosion features of Mg substrates and MAO coatings, roles of substrates on the corrosion processes of coatings were analyzed.

Characterization of Long-Term Corrosion Performance of TI15MO Alloy in Saline Solution

Characterization of Long-Term Corrosion Performance of TI15MO Alloy in Saline Solution

Challenges and opportunities in corrosion of steel in concrete

This paper summarizes the grand societal, economic, technological, and educational challenges related to corrosion of steel in concrete, and presents the state-of-the-art of the most relevant issues in the field. The enormous financial impact of infrastructure corrosion seems to be inadequately balanced by educational and research activities. This presents a unique opportunity in many countries for maintaining or improving their competitiveness, given the major technological challenges can be solved. The main technological challenges are (1) the ever-increasing need to cost-effectively maintain existing, ageing reinforced concrete structures, and (2) designing durable, thus sustainable new structures. The first challenge arises mainly in industrialized countries, where there is a need to abandon conservative, experience-based decision taking and instead move to innovative, knowledge-based strategies. The second challenge regards mainly emerging countries expanding their infrastructures and where thus a major beneficial environmental impact can still be made by providing long-lasting solutions. This means to be able to reliably predict the long-term corrosion performance of reinforced concrete structures in their actual environments, particularly for modern materials and in the absence of long-term experience. During the second half of the last century, civil engineers, materials scientists, and chemists have in many countries made considerable attempts towards understanding corrosion of steel in concrete, but many of the approaches got bogged down in empiricism. From reviewing the state-of-the-art one can conclude that transport modeling in concrete is relatively well-advanced, at least in comparison with understanding corrosion initiation and corrosion propagation, where many questions are still open. This presents a number of opportunities in scientific research and technological development that are discussed in this paper.

Versatile protection of exterior coatings by the aid of graphene oxide nano-sheets; comparison with conventional UV absorbers

Abstract In this study, graphene oxide nanoparticle was introduced as a versatile additive to enhance weathering and long-term corrosion performance of polyurethane (PU) coatings. For comparison purpose, the weathering performance of graphene oxide was compared with that of a typical organic UV absorber. The results demonstrated that graphene oxide could significantly improve the weathering and corrosion resistance of the coating. It was also revealed that while organic UV absorber could stabilize the coating for a limited time of weathering (temporary), graphene oxide stabilized the coating for a long time (permanent). The mechanisms of such permanent UV stabilization were also discussed.

Role of particle type and concentration on characteristics of PEO coatings on AM50 magnesium alloy

Composite ceramic coatings were formed on a magnesium alloy by AC plasma electrolytic oxidation using a phosphate-based electrolyte with α-Al2O3, monoclinic ZrO2 or CeO2 particles in suspension. Effects of particles concentration (2, 5 and 10g/L) on the electrical response, composition/morphology and corrosion behaviour of the coatings were investigated. Findings revealed successful incorporation of particles, which were preferentially located in the outer coating layer. Due to high temperatures at the locations of microdischarges, zirconia particles underwent transformation from monoclinic to tetragonal structure. The majority of alumina and ceria particles remained unaffected, although some of the alumina particles possibly formed MgAl2O4 by reaction with the substrate. Porosity and thickness of the coatings tended to decrease with increasing particles concentration in the electrolyte. Coatings formed in the electrolytes containing CeO2 particles revealed the best long-term corrosion performance in 0.5wt% NaCl solution.

Long-Term Corrosion Performance of Stainless Steel 316 in Molten LiCl-Li2o-Li

Introduction The electroreduction of used oxide nuclear fuel in a LiCl-Li­2O electrolyte is a necessary step for incorporating light water reactor fuel into a pyroprocessing based fuel cycle.1 During the electrolytic reduction of UO2, significant quantities of metallic Li are generated at the cathode due to the close reduction potentials of UO2 and Li2O, and the overpotential necessary to ensure a complete reduction of UO2.2 Due to the non-zero solubility limit of Li in Li­Cl, some of the Li thus generated dissolves into the electrolyte.3 The effects of this tertiary LiCl-Li2O-Li electrolyte on the degradation of structural materials have not been thoroughly studied for long exposure periods. Thus this work focuses on the long-term corrosion behavior of Stainless Steel 316 (SS316) in this system. Experimental Exposure testing of SS316 coupons in LiCl containing either 1 or 2 wt%Li2O and 0, 0.3, 0.6 and 1.0wt%Li were performed for 500 and 1000 hour exposure periods at each salt composition, for a total of 16 unique conditions. Due to the depletion of Li over time caused by both evaporation and reaction, the salt in which the samples were submerged in was replaced every 96 hours. Post exposure surface analysis was performed using Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, micro-Vickers hardness testing, and optical microscopy. Inductively coupled plasma – optical emission spectrometry was used to quantify the rate at which alloying elements were dissolved into the molten LiCl-Li2­O-Li solution. Results The presence of lithium chromite surface films was detected on SS316 samples exposed to molten LiCl-Li2O solutions containing no metallic Li. However, samples exposed to LiCl-Li­2O containing Li showed significantly thinner or no surface oxide, indicating that protective chromium oxide surface films are not stable under the reducing conditions caused by metallic Li. Additionally, significant degradation of the Ni crucibles used to contain the molten solutions was observed when metallic Li was present, while minimal degradation was observed when no metallic Li was present in the molten salt. These observations indicate that there is a marked change in corrosion mechanism when metallic Li is added to the LiCl-Li2O system. Acknowledgements: This work was performed under the auspices of the Department of Energy (DOE) under contracts DE-NE0008262 and DE-NE0008236, and the US Nuclear Regulatory Commission (NRC) under contracts NRCHQ-11-G-38-0039 and NRC-HQ-13-G-38-0027. W.P. acknowledges the Fellowship Award from the NRC. Dr. Kenny Osborne serves as the program manager for the DOE award and Ms. Nancy Hebron-Isreal serves as the grants program officer for the NRC awards.

Long-term corrosion performance of blended cement concrete in the marine environment – A real-time study

Blended cement is widely used in critical structures mainly because of its enhanced corrosion resistance concerning its durability. This paper presents the long term corrosion performance of blended cements namely; Portland pozzolana cement (PPC) and Portland slag cement (PSC) concrete under the three marine exposure conditions such as, atmospheric zone (AZ), immersion zone (IZ) and splash zone (SZ). Offshore Platform Marine Electrochemistry Center (OPMEC), Tuticorin, Tamil Nadu, India was selected as an exposure station. The concrete cubes were exposed over the period of 10years and their physicochemical properties such as compressive strength, alkalinity, free chloride content and sulphate content, bio-fouling attachment and electrochemical properties like, AC-impedance and potentiodynamic polarization were carried out and the results obtained were compared with Ordinary Portland Cement (OPC) concrete. XRD and SEM studies were also carried out for both OPC, PPC and PSC concrete samples exposed under various zones. It was observed that the strength and alkalinity of the blended cement concretes were relatively equal to that of OPC concrete. In addition, the pH values of the blended cement concretes are above the threshold limit recommended for depassivation. Furthermore, the resistance to chloride ion penetration was significantly reduced for blended cement concretes than that of OPC concrete and also exhibited very high amount of bio-fouling attachment. The electrochemical studies revealed that the blended cement concretes are having higher corrosion resistance in all three exposure zones than that of OPC concrete. From the results it is observed that the blended cement concretes are technically viable from the durability point of view and highly recommended for aggressive marine environments rather than OPC concrete.

The photoelectrocatalytic activity, long term stability and corrosion performance of NiMo deposited titanium oxide nano-tubes for hydrogen production in alkaline medium

In this study, titanium oxide nano-tubes are doped with Ni and Mo particles with various chemical compositions, in order to put forth the efficiency of single and binary coatings on hydrogen evolution reaction (HER) in 1M KOH. The characterization was achieved by cyclic voltammetry, scanning electron microscopy and energy dispersive X-ray analysis. The water wettability characteristics of electrode surfaces were investigated using contact angle. The long-term catalyst stability and corrosion performance were determined by current–potential curves and electrochemical impedance spectroscopy. Furthermore, photoelectrochemical behavior was determined via linear sweep voltammetry. Results showed that, nano-structured Ni and Mo deposited titanium oxide nano-tubes decrease the hydrogen over potential and increase HER efficiency, it is stable over 168h electrolysis and it exhibits higher corrosion performance.

Corrosion Performance of Fe-Based Alloys in Simulated Oxy-Fuel Environment

The long-term corrosion of Fe-based alloys in simulated oxy-fuel environment at 1023 K (750 °C) was studied. Detailed results are presented on weight change, scale thickness, internal penetration, microstructural characteristics of the corrosion products, and the cracking of scales for the alloys after exposure at 1023 K (750 °C) for up to 3600 hours. An incubation period during which the corrosion rate was low was observed for the alloys. After the incubation period, the corrosion accelerated, and the corrosion process followed linear kinetics. Effects of alloy, CaO-containing ash, and gas composition on the corrosion rate were also studied. In addition, synchrotron nanobeam X-ray analysis was employed to determine the phase and chemical composition of the oxide layers on the alloy surface. Results from these studies are being used to address the long-term corrosion performance of Fe-based alloys in various coal-ash combustion environments and to develop methods to mitigate high-temperature ash corrosion.