Polarization Resistance Measurements 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.

Corrosion of Copper, Cupronickel, Nickel Aluminium Bronze and Super-Duplex Stainless Steel Rotating Cylinder Electrodes in Seawater under Turbulent Flow Conditions

The corrosion of uncoated metals in a marine environment restricts the choice of suitable engineering metals and alloys. Anodic dissolution of metal and cathodic reduction of oxygen are important processes and formation of a surface oxide film can affect both electrode reactions. Charge transfer and mass transfer data can provide information on corrosion rate and mechanism. Several metals and alloys having a history of use in marine engineering are considered, including copper, two copper alloys (cupronickel and nickel aluminium bronze) plus a more recent addition to strong, corrosion resistant alloys (a super duplex stainless steel). The rotating cylinder electrode offers the benefits of a controlled, turbulent flow of electrolyte, facilitating controlled mass transfer in a compact cell geometry which is well-suited to bench-top operation. These features are illustrated using a variety of electrochemical techniques, including open-circuit potential vs time monitoring, linear sweep voltammetry, rotation speed step- or potential step current transients and linear polarisation resistance measurements. Seawater taken from Langstone Harbour, Hampshire, UK, was filtered, air-saturated, pH 8.0 and maintained at 25 °C. Dimensionless group correlations and graphical plots (using an analogous approach to the Koutecky-Levich equation for an RDE) enabled contributions of charge transfer-, mixed- and mass transfer- controlled data to be appreciated, allowing the Tafel slopes of electrode reactions, the diffusion coefficient of dissolved oxygen, the mass transfer coefficient for oxygen reduction and the mean corrosion rate to be estimated.

Investigation of Rosemary Oil as Environmentally Friendly Corrosion Inhibitor of Aluminum Alloy

The inhibitory effect of Rosemary oil on the corrosion of aluminum alloy EN AW-2011 in 1M H2SO4 solution was studied by weight loss and electrochemical methods such as open circuit potential (OCP), linear sweep voltammetry (LSV) and linear polarization resistance (LPR). The inhibition efficiency increases with increasing the concentration and shows maximum inhibition efficiency (70.7 %) at optimum concentration (0.05 g.L-1). The linear polarization resistance measurements show that the presence of Rosemary oil in 1M H2SO4 solution influences polarization resistance increasing and corrosion current decreasing. The voltammetric curve shows that Rosemary oil reduces the anodic process. Open circuit potential results confirmed that organic compounds present in Rosemary oil can form a protective layer on aluminum surfaces. The inhibitive effect was probably caused by the adsorption of organic compounds such as 1,8-cineole, α-pinene, borneol, limonene, and myrcene on aluminum surfaces which are non-toxic and environmentally friendly. This study showed that the essential oil of Rosemary could be used as an environmentally friendly inhibitor of the corrosion of alloy EN AW-2011 in an acidic medium.

Cathodic Protection of Carbon Steel in Soil: A Study of Induced Passivation

Two-month experiments were carried out with carbon steel electrodes buried in an artificial sand wetted at 50–55% of saturation with a 0.07 mol L−1 Na2SO4·10H2O solution. Various protection potentials (corrected from the ohmic drop) were applied from −0.60 to −1.13 V/Cu-CuSO4. In each case, the behavior of the electrode protected by cathodic polarization was compared with that of an unprotected electrode. The electrochemical study was performed using voltammetry, linear polarization resistance measurements, and EIS. Surface characterization of the coupons was carried out using optical microscopy and X-ray diffraction. First, cathodic protection was observed to induce a spreading of the electrolyte on the metal surface because of electrocapillary effects. The active area, or more precisely the wet area, of the electrode increased, leading to a decrease in soil electrolyte resistance Rs measured using EIS. This phenomenon was experimentally confirmed via visual observations of the surface of the coupons at the end of the experiments. Secondly, cathodic protection induced a passivation of the steel surface. The passive state persisted for 35 to 85 h after cathodic protection was stopped and could be studied during various periods of interruption of the protection. In each case, the OCP of the previously polarized coupons reached high values, actually 200–250 mV higher than those measured for the unprotected coupons, and was associated with high polarization resistance Rp values (~40 kΩ cm2). Depassivation of the metal finally occurred, a phenomenon revealed by simultaneous important drops of both OCP and Rp.

Chromium-Free Coating for Al Alloy Corrosion Protection Based on a Novel Ti/Mg Oxyfluoride

Chromium-free corrosion protection of aluminum alloys comparable to that of chromates (Cr(VI)) is demonstrated using a TiF6 2− fluoro-anion-based coating recipe containing boric acid and a Mg salt. Boric acid drove TiF6 2− hydrolysis enabling up to micrometer-scale thick coatings. The Mg salt led to deposition of a novel crystalline phase Ti/Mg oxyfluoride coating with an approximate composition of Ti5MgO7F8. Corrosion protection performance was characterized by polarization resistance measurements during immersion in 5% aqueous NaCl solution and neutral salt fog exposure following ASTM B.117. The performance is discussed in terms of the presence of fluoride in the coating enabling active behavior during its gradual depletion (in corrosion environments) toward a final composition approaching TiO2. This active corrosion protection mechanism may be more generally applicable for transition metal-based coatings that do not have high oxidation state oxo-anions, but do have stable fluoro-anions.

Vitamin B9 as a new eco-friendly corrosion inhibitor for copper in 3.5% NaCl solution

Folic acid salt (sodium folate) has been studied as an eco-friendly and non-toxic copper corrosion inhibitor in 3.5 % NaCl solution. Electrochemical impedance spectroscopy, polarization resistance, and weight-loss measurements show that the inhibitor efficiency increases with the concentration increase (the highest value- 96 % was reported for 16 mM sodium folate solution after 24 h). EIS data indicate that sodium folate is a barrier inhibitor. The standard Gibbs free energy of adsorption obtained using the Langmuir model (–27.5 kJ/mol) suggests that both chemisorption and physisorption may occur. The decrease in the inhibitor efficiency with temperature increase (the temperature coefficient of corrosion inhibition is –0.0045 1/oC) shows that the physical interactions between the inhibitor and metal surface dominate in the studied system. Potential chemical changes in the sodium folate solution were investigated using UV–VIS spectroscopy. Furthermore, the copper surface after immersion in the presence and absence of inhibitor was characterized with scanning electron microscopy, energy-dispersive X-Ray spectroscopy, and microscopic photographs. The protection of copper elements using sodium folate was found to be a promising method that is worth further development.

Understanding the corrosion and structural potential of 95Al-RHA-PSA composite for advance application

Material reinforcement has become popular in improving properties, such as corrosion, mechanical and wear behaviour. Aluminium-base composite has found usefulness in the technology of automobiles, aerospace, and marine and designs of a wide range of components. The use of reinforcement materials increases the efficiency of composites products and reduces overall expenses. Aluminium alloy composite provides low-cost advantages over many other matrix composites. The use of agro-based waste material as reinforcement alternatives is becoming very important because of its close to nothing cost and availability to produce nanoparticles. This study aim to use agro based processed rice hulls (RHA) and periwinkle shells (PSA) to improve aluminium properties in an attempt to gain prominence in today's automotive advancements. SEM imaging was conducted at a magnification of 15,000 at 20 kV to evaluate structural properties, while X-ray Diffractometer (XRD) images were utilized to observe the crystallography peaks and phases of the developed alloys. Rockwell hardness testing, in accordance with ASTM E18 standards, involved subjecting the samples to a 30 kg/f load for 30 s using a hardened steel ball for indentation. Corrosion properties were assessed via linear polarization resistance and open circuit potential measurements. From the results, there is a higher corrosion resistance from 95Al-RHA-PSA composite samples compared to the control (aluminium alloy) samples. The lower values of jcorr and higher values of Pr of the 95Al-RHA-PSA composite samples also indicated that the RHA and PSA content of the composite minimized the penetration of chloride ions into the active sites of the composite samples. The 95Al-2RHA-3PSA composite sample exhibited the lowest Cr of 1.4172 mm/year, lowest jcorr of 1.220E-04 A/cm2 and highest Pr of 70.02 Ω, which indicated the 95Al-2RHA-3PSA composite sample provided the most significant passivation, leading higher corrosion resistance. The XRD of the control sample has several crystallographic phases, with AlNi3Al2SiO8 exhibiting the most elevated peak intensity at about 550 a.u (2θ = 39°). In comparison, the peak intensity of the other crystals is less than 200 a.u. However, the 95Al-RHA-PSA composite samples exhibited crystallites of higher peak intensities and better morphological strengthening characteristics. The findings suggest promising prospects for the development of sustainable and long-lasting aluminium alloy for automotive use.

The Influence of Corrosion Processes on the Degradation of Concrete Cover.

In this work, two methods were used to accelerate the corrosion of concrete. In the first method, chloride ions were injected into the concrete using the migration method. The moment of the initiation of the corrosion process was monitored using an electrochemical method of measuring polarization resistance. In the next step, the corrosion process was accelerated by the electrolysis process. Changes on the sample surface were also monitored using a camera. In the second method, the corrosion process of the reinforcing bar was initiated by the use of the electrolysis process only. Here, changes occurring on the surfaces of the tested sample were recorded using two web cameras placed on planes perpendicular to each other. Continuous measurement of the current flowing through the system was carried out in both cases. It was assumed that in conditions of natural corrosion, a crack would occur when the sum of the mass loss of the reinforcing bar due to corrosion reached the same value in tcr(real) (real time) as it reached in the tcr (time of cracking) during the accelerated corrosion test. The real time value was estimated for C1 concrete with cement CEM I. The estimated value was tcr(real) = 1.1 years and for C2 concrete with cement CEM III, tcr(real) = 11.2 years. However, the main difference that was observed during the tests was the nature of the concrete cracks. In the case of the C1 concrete sample, these occurred along the reinforcing bar, while in the C2 concrete, the failures occurred on a perpendicular plane transverse to the direction of the reinforcing bar.

Unraveling the structure-property relationship of pyrimidine-derivatives as CO2 corrosion inhibitors: Experimental and periodic DFT investigations

CO2-containing environments commonly cause corrosion of carbon steel (CS) pipelines used in the oil and gas industry. In this work, the inhibition of corrosion by three derivatives of pyrimidine, namely 2-mercaptopyrimidine (MPY), 4-hydroxy-2-mercapto-6-methylpyrimidine (HMMP), and 4,5-Diamino-2,6-dimercaptopyrimidine (DDMP) for C1018 CS in CO2 saturated 3.5% NaCl brine was investigated. The corrosion rates and inhibition efficiency were investigated at 25 and 70 °C using open circuit potential, linear polarization resistance, potentiodynamic polarization and electrochemical impedance measurements. The post-immersion surface characterization of the exposed C1018 CS with and without the three molecules was carried out using SEM and 3D surface optical profilometer. Theoretical computation using DFT was further utilized to examine the role of the molecular structures and the mechanism of inhibition of the three molecules on steel surface at the atomic level. The experimental results indicate the following order of inhibition efficiency: MPY > DDMP > HMMP. Our experimental work proved that MPY molecule (the smaller one with the least number of heteroatoms) as the most efficient corrosion inhibitor. Surface characterization analysis confirmed the order of inhibition efficiency. The theoretical results revealed that the stability of molecules adsorbed on Fe (110) surface in the parallel orientation and on FeCO3 (104) is identical on both surfaces, which is completely consistent with the experiment. Our study provides a feasible strategy for developing new corrosion inhibitors by understanding how similar organic inhibitors work.

Investigation of the inhibiting effect of environmentally friendly cerium-containing conversion films on the corrosion of zinc coatings

In the present work, the inhibiting effect of environmentally friendly cerium and phosphorus-based conversion films on zinc corrosion in 5% NaCl and 1 N Na2SO4 test media was investigated. The films were prepared by immersion and stirring in the passivating/converting solution for time periods of 3,5,7, 10 min., respectively. The chemical composition of the films was determined by EDX analysis. The results of the electrochemical studies showed that in 5% NaCl medium, cerium- and phosphorus-based films exhibited high inhibition effect only during the first days of polarization resistance (Rp) measurement. In 1 N Na2SO4 medium, the Rp of the conversion films was up to 2.5 times higher than that of pure zinc coatings throughout the test period.

A novel methodology for monitoring low-temperature corrosion caused by hygroscopic salts using linear polarization resistance

A new methodology for monitoring low-temperature corrosion caused by hygroscopic salts was developed and tested with ZnCl2. First, deliquescence and efflorescence points of ZnCl2 were determined by electrochemical impedance spectroscopy and chronoamperometry measurements in the range of 10–35 vol % H2O. Then, low-temperature corrosion was monitored using a probe that combines linear polarization resistance and mass loss measurements. Suitable potential and scan rate for the linear polarization resistance measurements were experimentally determined. The feasibility of the probe was tested by monitoring the corrosiveness of ZnCl2 on P235GH steel under different temperatures (100–180 °C) and water vapor concentrations (15–35 vol %). With the developed corrosion probe, corrosion caused by hygroscopic salts during changes in testing conditions can be monitored and evaluated.

The Influences of Traces of Oxygen and Sulfide on the Corrosion of Copper Under Canadian Nuclear Waste Disposal Conditions

The Canadian repository concept for the permanent disposal of used nuclear fuel is to seal it in Cu-coated steel containers and dispose of it in a deep geological repository (DGR) surrounded by compacted bentonite clay. The Cu coating will be directly bonded on the steel vessel and lid using electro-deposition (ED-Cu), with the final container closure weld sealed with a cold-sprayed Cu deposit (CS-Cu). To assess the durability of such a container, long-term corrosion experiments have been performed on CS-Cu and ED-Cu specimens, and compared with those performed on wrought Cu specimens provided by the Swedish Nuclear Fuel and Waste Management Company (SKB-Cu).Experiments were conducted in 3 M NaCl solutions containing traces of sulfide (< 10- 6 M) for exposure periods of ≥150 days. These conditions reflect a generic groundwater that may influence container corrosion in a Canadian DGR Since conditions in a DGR will evolve from initially oxic to eventually anoxic, experiments were conducted under three sets of redox conditions: (i) aerated (oxic) conditions; (ii) Ar-purged (oxic to anoxic transition conditions (with a dissolved [O2] ~ 10- 6 M)); and (iii) anaerobic chamber (anoxic) conditions ([O2] < 1.3 × 10- 9 M). The exposure process was followed using open circuit (i.e., corrosion) potential and polarization resistance (RP) measurements. Specimens were analyzed before and after corrosion using optical microscopy, scanning electron microscopy on surfaces and focused ion beam cut cross sections, Raman spectroscopy, and X-ray photoelectron/Auger spectroscopy.In all environments, all three types of specimens (ED-Cu, CS-Cu, SKB-Cu) showed similar behaviour. Under anoxic conditions, minor corrosion, indicated by large RP values, leading to the deposition of traces of chalcocite (Cu2S) (identified by Raman spectroscopy) and observed by SEM, indicated that corrosion could be attributed to reaction with the trace amounts of sulfide present in NaCl. In Ar-purged solutions, the RP values were approximately one order of magnitude lower (i.e., the corrosion rate was one order of magnitude higher) than those measured under anoxic conditions, and significant corrosion damage was observed in SEM micrographs. Both Cu2O and Cu2S were detected by Raman spectroscopy. The detection of oxidized sulfur species (SO3 2 - and SO4 2 -) on the corroded surface by XPS/Auger confirmed that even trace amounts of dissolved O2 led to sulfide oxidation and the possible formation of potentially more corrosive species such as thiosulfate (S2O3 2 -). Under aerated conditions, extensive corrosion occurred leading to the formation of green CuII products (atacamite (Cu2(OH)3Cl)) with no detectable Cu2S formation.Within the DGR, corrosion of Cu under anoxic conditions will be limited by the available supply of sulfide, which may be produced remotely at the host rock/clay interface and/or in the porewater within the rock fractures. In the presence of even trace of dissolved O2, the corrosion process is significantly accelerated with the formation of potentially aggressive oxidized sulfur species. Under aerated conditions, extensive corrosion due to reaction with O2 leads to the deposition of CuII deposits. On the time scale of these experiments with only trace of sulfide present, no detectable conversion of copper oxide to Cu2S was observed. Keywords: Copper; Sulfide; Corrosion; Nuclear waste disposal

Understanding the Corrosion of Copper in Nitric Acid By Tuning the Solution Chemistry

The used fuel container (UFC) is a key engineered barrier to permanently contain and isolate used nuclear fuels underground in deep geological repositories (DGR) to be implemented in Canada, Sweden and Finland.1,2 Copper is used for corrosion protection in the current design of the UFC. Within a DGR, radiolysis of humid air will result in the formation of nitric acid.3 Recent studies showed that copper corrodes faster in nitric acid when oxygen is present, which will be the case for a short period after the UFC’s emplacement.4 When the oxygen becomes depleted in a DGR, the corrosion of copper will be minimal but can be affected by corrosion products such as Cu+, Cu2+, NO2 - and NO. Previous results suggest that the presence of copper ions in the solution surrounding the copper can activate nitrate as a cathodic reagent.5 A possible mechanism is that Cu+ reacts with nitrate through its oxidation to Cu2+, which then reacts with metallic copper through its comproportionation reaction, accelerating the corrosion process.5 Yet, a precise mechanistic understanding of the role of Cu+, such as the degree to which oxidation of Cu+ occurs in solution, or if Cu+ simply acts as a catalyst for nitrate reduction or decomposition, is missing. As a result, an improved understanding of the influence of solution parameters on the corrosion mechanisms of copper in nitric acid is needed, including the presence of oxidants and Cu+-chelating species such as chloride.Herein, the interplay between the dissolved redox couples, Cu+/Cu2+ and NO3 -/NO2 - and Cl- is explored, and their effect on the corrosion of copper is studied by linear sweep voltammetry and polarization resistance and Tafel analysis. The interpretation of linear polarization resistance measurements in the presence of multivalent ions and the role of corrosion products are discussed.1 P. G. Keech, P. Vo, S. Ramamurthy, J. Chen, R. Jacklin and D. W. Shoesmith, Corrosion Engineering, Science and Technology, 49, 2014, 425-430.2 F. King, L. Ahonen, C. Taxen, U. Vuorinen and L. Werme, Copper corrosion under expected conditions in a deep geologic repository (SKB-TR--01-23), 2001. Sweden.3 R. P. Morco, J. M. Joseph, D. S. Hall, C. Medri, D. W. Shoesmith and J. C. Wren, Corrosion Engineering, Science and Technology, 52, 2017, 141-147.4 J. Turnbull, R. Szukalo, M. Behazin, D. Hall, D. Zagidulin, S. Ramamurthy, J. Wren and D. Shoesmith, Corrosion, 74, 2017, 326-336.5 J. Turnbull, R. Szukalo, D. Zagidulin, M. Biesinger and D. W. Shoesmith, Materials and Corrosion, 72, 2021, 348–360.

Corrosion-Resistive ZrO2 Barrier Films on Selected Zn-Based Alloys.

This work presents the enhanced corrosion resistance of newly developed two-layer composite coatings deposited on low-carbon steel: electrodeposited zinc alloy coatings (Zn-Ni with 10 wt.% Ni (ZN) or Zn-Co with 3 wt.% Co (ZC), respectively) and a top ZrO2 sol-gel layer. Surface morphology peculiarities and anti-corrosion characteristics were examined using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), atomic force microscopy (AFM), water contact angle (WCA) measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) analyses, potentiodynamic polarization (PDP) curves, corrosion potential (Ecorr), polarization resistance (Rp) measurements (for a prolonged period of 25 days) and open-circuit potential (OCP). The results were compared with the corrosion peculiarities of usual zinc coating. The zirconia top coatings in both systems were amorphous and dense, possessing hydrophobic nature. The experimental data revealed an increased corrosion resistance and protective ability of the ZC system in comparison to that of ZN due to its smooth, homogeneous surface and the presence of poorly crystallized oxides (ZnO and Co3O4), both later playing the role of a barrier for corrosive agents.

Corrosion of carbon steel rebar in binary blended concrete with accelerated chloride transport

Samples with two different binary blended concrete mixes were prepared, one containing cement replacement of 50% slag (referred here as SL mix) and the other containing cement replacement of 20% fly ash (termed here as FA mix). The water to cementitious ratio used to produce concrete specimens was 0.41. On the top surface of each specimen, various reservoir lengths that ranged from 2.5 cm to 17.5 cm were fitted, and these reservoirs were filled with a 10% NaCl solution. Electromigration was used to accelerate the transport of chlorides, with an applied potential of 9 V at first, and subsequently reduced to 3 V after about a week. The electromigration was applied for a short period (few weeks to a couple of months). For a period of about 1100 days, the corrosion related parameters such as concrete solution resistance, rebar potential, and corrosion current were monitored via the rebar potential measurements, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) measurements, the latter used only to obtain the solution resistance. The corrosion current values determined through experimental observations were then converted to mass loss using Faraday’s law. The readings of corrosion current values (last 7 sets of readings) as well as the calculated mass loss values were found to be larger for the rebars embedded in specimens prepared with SL mix, followed by rebars embedded in specimens prepared with FA mix. Corrosion current and calculated mass loss values in general tended to increase with increasing solution reservoir lengths. No cracks or corrosion products that reached the surface of the concrete were observed on the specimens for the duration of the reported monitored propagation period. This study offers a framework for future studies on accelerated steel corrosion in concrete.

Electrochemical Study of Corrosion Inhibition of Carbon Steel During Oil/Water Intermittent Wetting

Application of corrosion inhibitors in production systems containing oil and water is an economic method to protect carbon steel against internal corrosion. This study investigates how intermittent oil/water wetting of such a steel surface, simulating multiphase flow phenomena, impacts corrosion inhibition in exploration-production (high salinity with CO2) and refinery (low salinity without CO2) environments. The employed corrosion inhibitor was a pyrimidinium-type model compound, its effectiveness against corrosion being characterized using linear polarization resistance measurements and electrochemical impedance spectroscopy. Experimental results demonstrated that the presence of an aliphatic oil promotes corrosion inhibition in the exploration production condition, but failed to do so in the refinery condition. Electrochemical impedance spectroscopy revealed two different protection mechanisms in the presence of oil between the two environments. The inhibitor layer in refinery condition with oil was different from in the simulated exploration production environment after oil wetting. Results also demonstrated that the inhibitor in this study was physically adsorbed on the surface steel via electrostatic attraction. Anions, identified as chloride ions, played a critical role in inhibitor adsorption.

Impedance analysis of electrolyte processes in a solid oxide cell

AbstractElectrochemical impedance spectroscopy and the distribution of relaxation times are powerful tools to study polarization processes in solid oxide cells (SOC). Commonly the measured polarization resistance is solely attributed to polarization phenomena in the electrodes whereas the electrolyte is assumed to act as purely ohmic series resistance.In this study an electrolyte supported SOC is investigated by impedance spectroscopy from the nominal operating temperature range of 700–900°C down to temperatures as low as 350°C. At such low temperatures the dielectric polarization of the electrolyte is shifted into the accessible frequency range, providing access to additional processes which are deconvoluted and quantified. It is discussed to which extent the additional layers like gadolinia doped ceria diffusion barrier and electrode layers influence the electrolyte processes as grain and grain boundary.

Corrosion Inhibition in CO2-Saturated Brine by Nd3+ Ions.

This study reports the use of an inorganic corrosion inhibitor to mitigate dissolved CO2-induced corrosion. Using electrochemical techniques (polarization curves, open circuit potential, polarization resistance, and electrochemical impedance), the effect of adding Nd3+ ions on the corrosion resistance of X52 steel immersed in CO2-saturated brine at 20 °C and 60 °C was evaluated. The polarization curves showed that the Icorr values tend to decrease with increasing Nd3+ ion concentration, up to the optimal inhibition concentration, and that the corrosion potential increases at nobler values. Open circuit potential measurements showed a large increase in potential values immediately after the addition of the Nd3+ ions. Similarly, polarization resistance measurements showed similar trends. It was observed that regardless of temperature, Nd3+ ions can reduce the corrosion rate by more than 97% at doses as low as 0.001 M. Electrochemical impedance measurements confirmed the formation of a protective layer on the steel surface, which caused an increase in the magnitude of the impedance module and phase angle, which indicates an increase in the resistance to charge transfer and capacitive properties of the metallic surface. The characterization of the metallic surface showed that the protective layer was formed by Nd carbonates, whose formation was due to a CO2 capture process.

Measurements on macrocells made of segmented reinforcement in concrete showing environmental impacts on corrosion of steel in concrete

AbstractCorrosion of steel in concrete can be characterized by measuring the galvanic current density when a macrocell is established. On nonpolarized steel, however, other electrochemical techniques like linear polarization resistance measurements may be used to characterize the electrochemical state of steel in concrete. On existing structures with their large dimensions and local differences in exposure conditions, local differences in the electrochemical state of the embedded reinforcement are established, leading to potential differences along the reinforcement and galvanic currents flowing. When it is possible to isolate anodic areas from the rest of the reinforcement, both galvanic current measurements, determination of polarization resistance on the separated anodic areas and the driving force between the anodic segments and the reinforcement are possible to obtain. In this work, this procedure is discussed and verified on a field structure on anodic areas caused by cracks in the concrete overlay and the results thereof are presented.

Corrosion behavior and immobilization of pure aluminum and Al−Mg alloy LLRW in magnesium potassium phosphate cements

Magnesium potassium phosphate cement (MKPC) is a candidate material to replace ordinary Portland cement (OPC) for the encapsulation of metallic low-level radioactive waste (LLRW) and improve the corrosion behavior of encapsulated reactive metals such as aluminum. The objectives of this research were to study the corrosion behavior of pure Al (A1050) and Al−Mg alloy (AA5754) embedded in MKPC and OPC mortars, to assess the effect of curing conditions on hardening properties and on the reactivity of Al and Al−Mg alloy. Results were obtained with measurements of compressive strength, X-ray diffraction and polarization resistance and the proposed interpretation was based on Faraday´s law. In the first 15 days of interaction in water immersion the corrosion rate and the volume of hydrogen evolved were seen to be at least one order of magnitude lower for AA5754 in MKPC than in OPC mortar, yielding average corrosion current density values of 1.85 and 109.0 × 10−6 A/cm2, and hydrogen volumes of 0.33 L/m2 and 17.8 L/m2 for AA5754/MKPC and AA5754/OPC, respectively. The pore pH was close to neutral and the hardening properties were highly dependent on the curing conditions.