Precipitation Of Corrosion Products Research Articles

Comparison of microstructure, mechanical property, and degradation rate of Mg-1Li-1Ca and Mg-4Li-1Ca alloys.

Mg-1 wt.% Li-1 wt.% Ca (LX11) and Mg-4 wt.% Li-1 wt.% Ca (LX41) alloys share the same hexagonal closed-packed crystalline structure. However, the differences in microstructure, mechanical properties, and degradation rates between the two alloys are not well understood. Hereby, the above three aspects of LX11 and LX41 alloys were studied via optical microscopy, tensile tests, and electrochemical polarization and electrochemical impedance spectroscopy, together with hydrogen evolution. The concentration of the released Mg2+, Ca2+, and Li+ ions was analyzed using a flame atomic absorption spectrophotometer. Results demonstrated that the LX11 alloy was composed of finer α-Mg grains, fewer twins, and smaller volume fractions of the intermetallic phases Mg2Ca than the LX41 alloy. The increasing Li concentration generated a weak decrease in the yield strength of the Mg-Li-Ca alloys, a remarkable increase in elongation to failure, and a stable ultimate tensile strength. The LX11 alloy had better corrosion resistance than the LX41 alloy. The release rate of the cations (Mg2+, Ca2+, and Li+) varied significantly with time. The release rate of metallic ions in Hank's solution cannot reflect the true corrosion rate of Mg-Li-Ca alloys due to the formation of the precipitated corrosion products and their difference in solubility. The dealloying corrosion mechanism of the Mg2Ca phase in Mg-Li-Ca alloys was proposed.

Atomic-scale insights into the precipitation behaviors of copper atoms in liquid lithium

The precipitation of corrosion products in liquid lithium (Li) is one of the concerns in the compatibility of liquid Li with solid materials. In this work, molecular dynamics simulations are employed to investigate the precipitation behavior of copper (Cu) atoms in liquid Li at different temperatures. It is found that Cu atoms combine with Li atoms to form CuLix nanoalloy clusters during the precipitation process. The cluster analysis revealed that the low temperature environment not only facilitates the formation of large clusters but also promotes their transformation from amorphous structure to ordered Cu-Li solid solution. The phase transition occurs because the merger and growth of clusters reduces the potential energy of the internal atoms. In addition, the CuLix nanoalloy clusters bind the Li atoms through internal alloying and surface adsorption, which in turn increases the viscosity of liquid Li. The larger the cluster size, the greater the viscosity increment.

Corrosion mechanisms of AZ31 magnesium alloy: Importance of starting pH and its evolution

AbstractThis article aims at improving the understanding of the corrosion mechanism of AZ31 magnesium alloys during a long period of immersion in an aqueous electrolyte. In particular, the influence of the starting pH of the electrolyte on the oxidation of AZ31 alloy and its evolution due to corrosion phenomena were investigated. Several electrolytes with different pH values containing or not chlorides were used. The electrochemical properties of the metal substrate in these electrolytes were studied as a function of immersion time by electrochemical impedance spectroscopy. The kinetics of the reactions were determined by potentiodynamic polarization as well as dihydrogen evolution measurements by eudiometry. All these tests were carried out while the sample surface and electrolyte volume remained constant. The corrosion products generated on the alloy surface were analyzed by X‐ray photoelectrons spectrometry. This study has shown that the evolution of the corrosion rate and the corrosion products depends greatly on the initial pH and the nature of the used electrolyte. Alkaline electrolyte leads to a passive protective layer that can be locally destroyed by chloride ions. For a neutral chloride electrolyte, the strong increase of the pH due to the magnesium corrosion is not able to form a protective layer by precipitation of corrosion products. The kinetic and the corrosion extent are affected by the pH changes.

Application of focused ion beam-field emission scanning electron microscopy-X-ray microanalysis in the study of the surface alterations of archaeological tin-glazed ceramics

The historical evolution of tin-glazed ceramics is a subject that has attracted the attention of many scientists and, consequently, abundant archaeometrical studies can be found in the specialized literature. Nevertheless, a lesser number of studies aimed at the characterization of the alterations undergone by archaeological glazes has been reported. This work describes some unusual alteration processes found in tin-glazes depending on the environmental conditions surrounding the piece during centuries. For this purpose, focused ion beam-field emission scanning electron microscopy-X-ray microanalysis (FIB-FESEM-EDX), an advanced instrumental technique for surface analysis at the nanoscale, has been used for the first time, complementarily to optical microscopy (OM), FESEM-EDX and Fourier transform Infrared spectroscopy (FTIR). In the buried glaze the nanostructure of the outer lamellar corrosion layer due to humidity-dryness cycles is described. Unusual and selective erosion of the glaze matrix due to the silicification metabolism of diatoms is observed in a submarine glaze. A nanometric outer corrosion layer formed by precipitated corrosion products and unspecific organic matter that has been partially degraded to lead and calcium oxalates is found in a glazed tile subjected to an atmospheric environment.

THCM numerical simulations of the engineered barrier system for radioactive waste disposal

The final disposal of high-level radioactive waste in geological repositories envisages an engineered barrier system with a bentonite buffer, which will be subjected to strongly coupled thermal, hydrodynamic, geochemical and mechanical (THCM) processes. This paper presents coupled THCM numerical simulations of laboratory and in situ tests performed with compacted Full-scale Engineered Barrier Experiment (Febex) bentonite having different space and time scales. The simulations of the heating and hydration tests fit the measured temperature, water content and water intake data and reproduce the trends of the geochemical data. Although simulation results of the tests display similar trends, they show differences due to geometry and initial and confining conditions. The changes in porosity due to mineral dissolution/precipitation are not relevant in these tests but become relevant in long-term simulations, which show that the precipitation of corrosion products reduces significantly the porosity of the bentonite near the canister and causes pore clogging. The thickness of the bentonite alteration band is simulated to be smaller than 7 cm after 1 Ma.

Excellent long-term reactivity of inhomogeneous nanoscale Fe-based metallic glass in wastewater purification

Metallic glasses (MGs) have attracted great attention in wastewater treatment because of their high reactivity arising from amorphous structure, large residual stress and high density of low coordination sites. However, the reactivity of MGs would gradually slow down with time due to the passivation of active sites by corrosion products, resulting in limited long-term reactivity, which is also an unsolved key issue for established crystalline zero valent iron (ZVI) technology. Here, such problems are successfully overcome by introducing nanoscale chemical inhomogeneities in Fe-based MG (Fe-MGI), which apparently contributes to local galvanic cell effect and accelerates electron transfer during degradation process. More importantly, the selective depletion of Fe0 causes local volume shrinkage and crack formation, leading to self-peeling of precipitated corrosion products and reacted regions. Thereby fresh low coordination sites could be continuously provided, counteracting the mass transport and reactivity deteriorating problem. Consequently, Fe-MGI demonstrates excellent long-term reactivity and self-refreshing properties even in neutral solution. The present results provide not only a new candidate but also a new route of designing ZVI materials for wastewater treatment.

Effect of CaCO3-saturated solution on CO2 corrosion of mild steel explored in a system with controlled water chemistry and well-defined mass transfer conditions

The effect of Ca2+ on the corrosion product layers when the CO2-containing electrolyte is saturated with respect to CaCO3, as frequently observed in oil production systems, was studied by weight loss, electrochemical techniques, and surface characterizations. An improved experimental set up was used and all experimental parameters reported. Results show that precipitation of corrosion products in solutions with or without CaCO3 was due to the favorable water chemistry obtained at the steel surface compared to the bulk solution. The presence of Ca2+ did not jeopardize the final protectiveness of corrosion product layer, but seemed to delay its growth.

Investigation of corrosion mechanism of NiTi modified by carbon plasma immersion ion implantation (C-PIII) by electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) is conducted to investigate the corrosion behavior and mechanism of NiTi modified by carbon plasma immersion ion implantation (C-PIII) in 3.5% NaCl and simulated body fluids (SBF) solutions. The unstable native oxide formed on the pristine NiTi is easily corroded by aggressive ions leading to delamination of the surface structure. C-PIII enhances the surface stability by forming a smooth and crack-free coating with a thickness of 50 nm. Ni leaching is reduced and EIS reveals significantly improved corrosion resistance. The amounts of nickel ions released to SBF and 3.5% NaCl solution are 1.3724 and 4.1463 mg L−1 cm−2, respectively, and C-PIII decreases the amounts of nickel ions in SBF and 3.5% NaCl solution by 99.13 and 99.31%, respectively, after immersion for 96 h. The corrosion resistance mechanism depends on the inactive protection layer and functional carbon film on the NiTi surface. Formation of a homogeneous and uniform layer on the surface, precipitation of corrosion products from soluble compounds, especially in SBF, and formation of titanium oxide at local defects due to the penetration of corrosive ions such as Cl− and water absorption are the major mechanisms responsible for the improved corrosion resistance of the C-PIII NiTi.

Corrosion behavior of 20# steel at initial stage under the (CO2/aqueous solution) gas-liquid two-phase plug flow condition

The corrosion behavior of 20# steel at initial stage under CO2/H2O gas-liquid two-phase plug flow conditions was studied through weight loss, SEM, EDS, XPS methods. The corrosion rate results indicated that there was an obvious deceleration transition at the early stage of corrosion process. The difference of corrosion rate under different CO2 pressures decreased with the extension of corrosion time. The precipitation of corrosion products started from the defects area of the pipe wall surface or the crystal interface, and the corrosion products extended to contact each other with the extending time. The corrosion products grew into the flocculated corrosion products on the surface of acicular corrosion products layer deposited preliminary with the extending corrosion time. The corrosion products on the bottom pipe wall grew faster than that on the top pipe wall. The main phases among the corrosion products layer were Fe3C, FeCO3, FeOOH and Fe3O4, and there was no polygonal FeCO3 appeared.

Influence of calcium cations on the corrosion behavior of hot-dip galvanized steel in model concrete pore solutions

Abstract In this paper, the influence of calcium cations on the corrosion behavior of hot-dip galvanized steel in model concrete pore solutions is evaluated by means of conventional electrochemical methods (measurement of free corosion potencial and polarization resistance), surface analysis methods (optical and confocal microscopy) and XRD phase analysis of precipitated corrosion products. The results of these experiments confirm the conclusions of the current work on a similar topic, i.e. the crystalline calcium based corrosion products Ca[Zn(OH)3]2·2H2O are not able passivate effectively surface of hot-dip galvanized steel in model of concrete pore solutions (pH 12.6; 13.0). If passivation occurs, a mixed Ca[Zn(OH)3]2·2H2O, ZnO and Zn(OH)2 is involved.

Corrosion protection of steel cut‐edges by hot‐dip galvanized Al(Zn,Mg) coatings in 1 wt% NaCl: Part I. Experimental study

Corrosion of AlZnMg coated steel in chloride media is a complicated process, which progress is determined not only by the electrode reactions but also by the local pH and formation of soluble and insoluble corrosion products. In order to adequately describe and predict the corrosion behavior of steel/AlZnMg cut‐edge, a multi‐ion transport, and reaction model (MITReM) is built. Such model takes into account the transport of species in the solution together with their production/consumption in electrochemical and chemical reactions. The main aim of this work is the validation of a numerical model for describing and predicting corrosion of steel/AlZnMg cut‐edge in immersed conditions. This first part describes the experimental work done to obtain model input parameters and validation measurements. The metallic coatings are characterized experimentally with respect to their composition and microstructure, global and local electrochemical behavior (polarization curves, AESEC, and SVET). Local distribution of corrosion products and local pH are also characterized. No blocking effect of the precipitated corrosion products has been observed and dedicated measurements are performed to validate this observation. Based on the experimental input from this part, numerical models of cut‐edge corrosion with different levels of details are developed in Part II.

The kinetic competition between transport and oxidation of ferrous ions governs precipitation of corrosion products in carbonated concrete

Corrosion products, originating from steel corrosion and precipitating in the concrete pore system, can lead to concrete cracking and to spalling of the concrete cover. Related premature structural repair causes high costs. Thus, reliable quantitative models are needed, which currently do not exist. Here, we present a new conceptual model to describe the fate of ferrous ions that are released at the steel surface during the corrosion process. The key novelty of our approach can be found in explicitly considering the kinetics of oxidation and transport of Fe2+ in the pore solution. These two processes constantly dilute the Fe2+ concentration and are in competition with the supply of Fe2+ from the anodic iron dissolution reaction. We use a numerical model to elucidate which of the described processes is the fastest. The results find good agreement with experimental data and reveal that under natural corrosion conditions, Fe2+ hardly reach the saturation level, which permits the diffusion of corrosion products up to millimeters away from the steel without necessarily leading to expansive stresses. Under accelerated corrosion conditions, however, precipitation is forced immediately at the steel surface. This fundamentally changes the cracking mechanism and questions the relevance of such tests and related models.

X-ray microprobe characterization of corrosion at the buried polymer-steel interface

The simultaneous collection of x-ray fluorescence (XRF) intensity maps for several elements was combined with x-ray absorption near-edge spectroscopy (XANES) to perform a non-destructive study of polymer-steel interfaces exposed to high pH potash brine. Analysis of iron, manganese, potassium and chlorine XRF maps allowed the identification of anodic pits, disbonded areas containing precipitated corrosion products and several cathodic regions. Iron XANES was used to determine the phases of Fe corrosion products present. Our results confirm previous models of corrosion under polymer films where osmotic blisters are causally related to the spread of corrosion at the polymer-metal interface.

Predictive modelling of the corrosion rate of carbon steel focusing on the effect of the precipitation of corrosion products

ABSTRACTIn the frame of conceptual design for the long-term management of high level radioactive waste defined by Andra (France), it is assumed that carbon steel (C-Steel) overpack would be mainly affected by general corrosion. As it is widely accepted that precipitation of a corrosion product layer (CPL) can limit the corrosion rate, the aim of this work is to simulate the growth of a thick FeCO3 CPL and its impact on the evolution of the corrosion rate. We use a 1D finite element method numerical model based on the resolution of Nernst–Planck equation in free potential conditions. Two numerical models of the evolution of the corrosion rate of low alloy steel in anoxic conditions are developed. These models take into account the growth of a porous CPL assuming either a constant and homogeneous porosity or a varying and heterogeneous porosity and results are compared to experimental data.This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

Smeared crack modelling approach for corrosion-induced concrete damage

In this paper a smeared crack modelling approach is used to simulate corrosion-induced damage in reinforced concrete. The presented modelling approach utilizes a thermal analogy to mimic the expansive nature of solid corrosion products, while taking into account the penetration of corrosion products into the surrounding concrete, non-uniform precipitation of corrosion products, and creep. To demonstrate the applicability of the presented modelling approach, numerical predictions in terms of corrosion-induced deformations as well as formation and propagation of micro- and macrocracks were compared to experimental data obtained by digital image correlation and published in the literature. Excellent agreements between experimentally observed and numerically predicted crack patterns at the micro and macro scale indicate the capability of the modelling approach to accurately capture corrosion-induced damage phenomena in reinforced concrete. Moreover, good agreements were also found between experimental and numerical data for corrosion-induced deformations along the circumference of the reinforcement.

Electrochemical characteristics of bioresorbable binary MgCa alloys in Ringer's solution: Revealing the impact of local pH distributions during in-vitro dissolution

Biodegradable magnesium–calcium (MgCa) alloy is a very attractive biomaterial. Two MgCa alloys below the solid solubility of Ca were considered, as to solely investigate the effect of Ca content on the behavior of magnesium and the pH changes associated to metal dissolution. X-ray diffraction analysis and optical microscopy showed that both Mg–0.63Ca and Mg–0.89Ca alloys were solely composed of α(Mg) phase. Degradation characteristics and electrochemical characterization of MgCa alloys were investigated during exposure to Ringer's solution at 37°C by electrochemical impedance spectroscopy and scanning electrochemical microscopy. The impedance behavior showed both capacitive and inductive features that are related to the alloy charge transfer reaction and the relaxation of the absorbed corrosion compounds, and can be described in terms of an equivalent circuit. Scanning electron microscopy (SEM) was employed to view the surface morphology of the MgCa samples after 1week immersion in Ringer's solution showing extensive precipitation of corrosion products, whereas the substrate shows evidence of a non-uniform corrosion process. Energy dispersive analysis showed that the precipitates contained oxygen, calcium, magnesium and chlorine, and the Mg:Ca ratios were smaller than in the alloys. Scanning electrochemical microscopy (SECM) was used to visualize local pH changes associated to these physicochemical processes with high spatial resolution. The occurrence of pH variations in excess of 3 units between anodic and cathodic half-cell reactions was monitored in situ.

Corrosion Evolution of Low Alloy Steel in Deaerated Bicarbonate Solutions

Corrosion evolution during immersion tests (up to 43 days) of NiCu steel in deaerated 0.1 mol/L bicarbonate solutions was investigated by electrochemical measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results show that NiCu steel transformed from the anodic dissolution in the early stage of immersion to a metastable passive state in the final stage as the open-circuit potential value shifted positively, which was aroused by the precipitation of corrosion products. This process was mainly promoted by the trace amount of oxygen. Simultaneously, dominant cathodic reaction transformed from the hydrogen evolution in early stage to reduction processes of corrosion products in later stages. Possible corrosion processes were discussed with the assistance of a corresponding Pourbaix diagram.

Multiscale Electrochemical Investigation of the Corrosion Resistance of Various Alloys Used in Dental Prostheses

The electrochemical behavior of Ag-Pd (Paliag), Ni-Cr (Heraenium NA), and Co-Cr (Heraenium CE) alloys used in dental prosthetics construction of crowns and bridges was studied in 0.9 pct NaCl solution at 298 K (25 °C). The localized electrochemical characteristics related to corrosion resistance and eventual breakdown of the protecting oxide layers were investigated by scanning electrochemical microscopy (SECM), whereas potentiodynamic polarization and electrochemical impedance spectroscopy techniques were employed to establish oxide stability. When the corrosion resistance of the alloys was evaluated by means of the corrosion current value determined around their corresponding open circuit potential in 0.9 pct NaCl solution, good protection can be expected resulting from their spontaneous passivation (low current densities in the order of tenths of μA cm−2). The polarization resistance of all the samples increased with immersion time, in the sequence Ag-Pd < Heraenium NA < Heraenium CE. Yet, increased electrochemical activity was detected with SECM when the alloys were polarized at +0.40 V SCE, a value that may be eventually experienced in the human body. Although a passivation mechanism was still operating in the chromium-containing alloys, oxide dissolution and precipitation of corrosion products occurred on Ag-Pd instead.

Nanostructured Magnesium Composite Coatings for Corrosion Protection of Low-Alloy Steels

Corrosion of base metals represents a tremendous problem that has spurred a global search for cost-effective and environmentally friendly alternatives to current corrosion-inhibiting technologies. In this work, we report a novel sustainable hybrid Mg/poly(ether imide) (PEI) nanocomposite coating that provides corrosion protection to low-alloy steels at relatively low coating thicknesses and with reduced weight as compared to conventional metallic coatings. The coatings are constituted using Mg nanoplatelets dispersed within a polyamic acid matrix that is subsequently imidized on the steel substrate to form PEI. The coatings function through a combination of sacrificial cathodic protection (afforded by the preferential oxidation of the Mg nanoplatelets), anodic passivation through precipitation of corrosion products, and the inhibitive action of the PEI polymeric matrix. The use of nanostructured Mg allows for reduced coating thicknesses and a smoother surface finish, whereas the PEI matrix provides excellent adhesion to the metal surface. Based on potentiodynamic testing and prolonged exposure to saline environments, the novel coating materials significantly outperform galvanized Zn and Zn-rich primer coatings of comparable thickness.

Concrete cover cracking owing to reinforcement corrosion – theoretical considerations and practical experience

AbstractReinforcement corrosion might lead to cracking and spalling of the concrete cover owing to the volume expansion associated with the deposition of some of the possible corrosion products. This is not only aesthetically unpleasing, it might also accelerate deterioration processes or become a safety issue for passing traffic. The present paper discusses first the mechanisms of carbonation‐ and chloride‐induced reinforcement corrosion and considers the chemistry of aqueous iron in order to identify the type of corrosion products as well as their location of formation. Furthermore, practical examples are summarised in order to compare the documented behaviour of a number of real structures with the theoretical considerations made. It is shown that for the case of purely chloride‐induced (pitting) corrosion, precipitation of corrosion products is strongly delayed or may even not occur. Implications are discussed with respect to time‐to‐corrosion prediction models and visual inspection of reinforced concrete structures. Both the theoretical considerations and the practical experience illustrate that relying on outwardly visible signs to detect internally on‐going corrosion must be done with caution if localised reinforcement corrosion cannot be excluded.