Passive Breakdown Potential Research Articles

Use of Multielectrode Arrays and Statistical Analysis to Investigate the Pitting Probability of Copper: Part II. The Effect of Sulfate and Bicarbonate

Copper and copper alloys have found applications in various industries. One of the main reasons Cu and its alloys are utilized widely is that they have sufficient corrosion resistance in key environments, such as seawater and anoxic solutions; however, localized corrosion processes might occur in the presence of aggressive anions, oxygen, or an increase in solution pH. In critical applications of Cu, the susceptibility of Cu to localized corrosion, specifically pitting, must be carefully considered, as it could lead to material failure. In this study, the pitting probability of Cu in unary (sulfate) and binary (sulfate + bicarbonate) solutions was investigated using electrochemical techniques in conjunction with statistical analysis. We determined pitting probabilities based on two different defining criteria for pitting susceptibility, one based on the probability that the corrosion potential, Ecorr, could exceed the passivity breakdown potential, Eb, and the other, a more conservative approach, based on the likelihood that Ecorr would be greater than the repassivation potential, Erp. The pitting probability of Cu did not change significantly with sulfate concentration at pH 8 but was found to increase with increasing [] up to 0.005 M at pH 9 and then to decrease with a further increase in [].

Effect of test media on the crevice corrosion of stainless steel by sulfate reducing bacteria

The potential for crevice corrosion of UNS30400 stainless steel in the presence of sulfate-reducing bacteria (SRB) was studied in different media. Immersion studies found crevice corrosion to occur in test media supplemented with high chloride levels and SRB present for crevice gaps of ~3 μm. Electrochemical measurements showed high susceptibility to corrosion in this particular medium, demonstrated by a negative shift of open circuit potential, increased corrosion current and the lowest passivity breakdown potential. Overall, the results showed that test media can play a critical role in the crevice corrosion of stainless steel in the presence of SRB.

Effect of Chloride on the Pitting Corrosion of Carbon Steel in Alkaline Solutions

The effect of chloride concentration on the passivity breakdown of carbon steel in deaerated pH = 13.5 alkaline solution was investigated. The results show that chloride plays an important role for the pitting corrosion of carbon steel. When NaCl the carbon steel is passive but for NaCl < 2 the carbon steel transfers from passive to passivity breakdown. When NaCl passive film breakdown occurs and the passivity breakdown potential (E b ) of carbon steel is linearly-dependent on the logarithm of the chloride activity in the alkaline solution. As predicted by the PDM, the near-normal distribution of is well indicated by the near straight line in the cumulative distribution probability. The analysis in this study gives us a method to calculate the of carbon steel in alkaline solution and its distribution for any given chloride concentration.

Influence of plutonyl ion on electrochemical characterization of zirconium in plutonium nitrate solutions

Abstract With the aim of evaluating the corrosion behavior of a Pu evaporator made from Zr in the Rokkasho Reprocessing Plant (RRP), the electrochemical characterization of Zr was investigated in Pu nitrate solutions. Before and after experiments, spectra of Pu nitrate solutions were recorded, and Pu4+ was oxidized to PuO2 2+ by heating these solutions. The ratio of PuO2 2+ in 3 mol dm−3 HNO3 was higher than that in 7 mol dm−3 HNO3 in our experiments. The maximum open circuit potential of Zr in the Pu nitrate solution was approximately 1 V in the Pu nitrate solution containing 7 mol dm−3 HNO3. However, there were no significant changes at high PuO2 2+ concentrations, and this value remained below the passivity breakdown potential under our experimental conditions. In this study, Zr showed high corrosion resistance, even though many PuO2 2+ ions existed in the Pu nitrate solution containing 7 mol dm−3 HNO3.

Experimental design to study the influence of temperature, pH, and chloride concentration on the pitting and crevice corrosion of UNS S30403 stainless steel

Localized corrosion of stainless steel affects seriously the performance of these materials in service. In this paper, the design of experiment (DOE) is used to study the influence of temperature, pH and chloride concentration on the pitting and crevice corrosion of UNS S30403 stainless steel. DOE approach enables to reduce the number of tests (potentiodynamic polarization) necessary to study the effect of several parameters on the passivity breakdown potential. The use of DOE provided a regression equation that was analyzed by comparison with laboratory results. Among all these parameters, the temperature has the most significant effect on pitting corrosion resistance.

Passivity breakdown of 13Cr stainless steel under high chloride and CO2 environment

Herein, the effect of high chloride ion (Cl−) concentration on the corrosion behavior and passive film breakdown of 13Cr martensitic stainless steel under CO2 environment was demonstrated. The Cl− concentration was varied from 30 to 150 g/L and cyclic potentiodynamic polarization was conducted to investigate the influence of the Cl− concentration on the corrosion potential (Ecorr), passive breakdown potential (Epit), and repassivation potential (Erep). The results of the polarization curves revealed that 13Cr stainless steel is susceptible to pitting under high Cl− concentration. The passive breakdown potential and repassivation potential decreased with the increase of Cl− concentration. The semiconducting behavior of the passive film was investigated by Mott-Schottky analysis and the point defect model (PDM). It was observed that the iron cation vacancies and oxygen vacancies were continuously generated by autocatalytic reactions and the higher Cl− concentration resulted in higher vacancies in the passive film. Once the excess vacancies condensed at the metal/film interface, the passive film became locally detached from the metal, which led to the breakdown of the passive film.

Microstructures, mechanical properties and corrosion resistance of the Zr[sbnd]xTi (Ag) alloys for dental implant application

The ZrxTi (Ag) alloys were designed for the application of dental implants. The microstructures of Zr20Ti and Zr40Ti alloy were observed using optical microscope and transmission electronic microscope. The hardness and compressive tests were performed to evaluate the mechanical properties of the ZrxTi alloys. The electrochemical behavior of the ZrxTi alloys with and without 6% Ag was investigated in the acidified artificial saliva containing 0.1% NaF (pH = 4). For comparison, the electrochemical behavior of cp Ti was examined in the same condition. The results show that the quenched Zr20Ti and Zr40Ti alloy exhibit acicular martensite microstructures containing twin substructure. They display good mechanical properties with the hardness of ∼330HV, the yield strength of ∼1000 MPa and the strain to fracture of ∼25% at room temperature. Adding 6% Ag to Zr20Ti alloy enhances the passivity breakdown potential and the self-corrosion potential, but hardly affects the corrosion current density and the impedance modulus. 6% Ag in Zr40Ti alloy distinctly increases pitting corrosion resistance, which is attributed the formation of thick, dense and stable passive film under the joint action of titanium and silver. In comparison with cp Ti, Zr40Ti6Ag alloy possesses the same good corrosion resistance in the rigorous oral environment as well as the superior mechanical properties.

Exploration of the effect of chloride ion concentration and temperature on pitting corrosion of carbon steel in saturated Ca(OH)2 solution

Passivity breakdown on carbon steel, has been studied and the data are interpreted in terms of the point defect model. An increase in temperature from 25°C to 85°C results in a decrease in localized corrosion resistance according to a linear relationship between the critical breakdown voltage, Eb, and log (chloride activity) for all chloride concentrations. The linear dependence of the passivity breakdown potential on the square root of potential scan rate (ν1/2), as predicted by the PDM, yields an estimate of the critical areal concentration of condensed cation vacancies at the metal/film interface that leads to the passivity breakdown.

Localized Corrosion of Carbon Steel in Simulated Concrete Pore Solution: Influence of Chloride Ion and Temperature

Passivity breakdown on carbon steel, which is the reference candidate material for fabricating high-level nuclear waste containers in Belgium, has been studied and the data are interpreted in terms of the point defect model (PDM). The near normal distribution in breakdown potential, measured in deaerated simulated concrete pore water solution (pH 12.5) at different chloride concentrations and temperatures are in satisfactory agreement with prediction of the PDM. An increase in temperature from 25°C to 85°C results in a decrease in localized corrosion resistance according to a linear relationship between the critical breakdown voltage, Eb , and log(chloride activity) for all chloride concentrations. The linear dependence of the passivity breakdown potential on the square root of potential scan rate (ν1/2), as predicted by the PDM, yields an estimate of the critical areal concentration of condensed cation vacancies at the metal/film interface (ξ<=5.45×1014cm-2 at 85oC and <=1.07×1014cm-2 at 55oC ) that leads to the passivity breakdown. The experimental distributions in the breakdown potential for carbon steel at 55oC and 85oC are in satisfactory agreement with the relevant calculated distributions. Acknowledgment: The authors gratefully acknowledge the support of this work by ONDRAF-NIRAS of Belgium.

Stress Corrosion Cracking Behavior of Zirconium in Boiling Nitric Acid Solutions at Oxide Formation Potentials

Zirconium has been utilized in nuclear fuel reprocessing plants because of its superior corrosion resistance in nitric acid solutions. However, stress corrosion cracking (SCC) susceptibility of zirconium has been reported in boiling nitric acid solutions at the passivity breakdown potential. However, it has not been clear the SCC initiation and propagation behavior of zirconium. In this study, to clarify the SCC initiation and propagation behavior of zirconium, constant load tensile tests were carried out in boiling nitric acid solutions. From the results, many cracks were initiated under the oxide film and maximum crack led to rupture in the potentials that nobler than passivity breakdown potential. These results showed that the SCC of zirconium in boiling nitric acid solutions is due to the oxide formation. And this SCC behavior suggests that the SCC behavior of zirconium can be attributed to tarnish rupture model. [doi:10.2320/matertrans.M2012341]

A XPS study of the Mo effect on passivation behaviors for highly controlled stainless steels in neutral and alkaline conditions

The objective of this work is to study the effect of Mo additions on film passive properties of three different stainless steels (SS) types (austenitic, ferritic and duplex alloys). A comparison between Mo containing (3wt% Mo) and free Mo (0wt% Mo) grades of highly controlled laboratory heats was done considering their passive film formed in different aggressive conditions, from neutral to alkaline pH. The presence of oxidized Mo on the passive layer was confirmed by X-ray photoelectron Spectroscopy (XPS). The presence of Mo within the passive film improved the passivity breakdown potential for the duplex and ferritic SS, but seemed to have no effect for austenitic SS.

Copper corrosion in soil: influence of chloride contents, aeration and humidity

The corrosion of copper in a typical Portuguese soil was studied. The original soil was characterised, and modifications were produced by adding chloride, and HClO4 solutions, or by increasing its relative humidity. The aggressiveness degree of the various soil samples was determined. Copper coupons exposed for 3 months in the original and in the modified soil samples were analysed. The average corrosion rates determined from gravimetric data were in good correlation with the soil aggressiveness. The morphology of the corroded copper surfaces, with and without corrosion products, was analysed by visual observation, optical microscopy and scanning electron microscopy. Energy dispersive spectroscopy was used for the semi-quantitative analysis of the corrosion products and X-ray diffraction spectroscopy to identify the crystalline products. Cuprite has been identified on the copper samples corresponding to the interfaces Cu|S6 and Cu|S8, plus paratacamite on the copper coupon exposed to the soil with higher concentration of chloride (S6). Polarisation curves of copper samples in neutral solutions made by adding different amounts of chloride ions to the soil washing water, under deaereated conditions, were recorded and analysed. The passivity breakdown potential has shown, as expected, a displacement to the cathodic direction as the Cl− ion concentration increases.

An assessment of the corrosion behaviour of high-grade alloys in seawater at elevated temperature and under a high velocity impinging flow

Laboratory experiments were carried out to investigate the effect of elevated temperature (up to 60 °C) and a high velocity impinging flow on the corrosion behaviour of stainless steels and related Ni-base and Co-base alloys. DC-electrochemical techniques were employed in conjunction with microscopy to determine the extent and mechanisms of attack under the severe imposed conditions. Experiments demonstrated the clear effect of increased temperature in facilitating premature breakdown of passivity on all materials and the effect of the high velocity impinging flow was to further shift the passivity breakdown potential to more active values but not necessarily to result in greater depth of attack. In addition, the study has indicated that the relative resistances of the different materials to attack under static, ambient temperature conditions is altered significantly when they are subjected to elevated temperatures and/or high velocity seawater impingement.

Mechanism of Passivity Breakdown of High Purity Cadmium

The passivity breakdown of high purity cadmium in , , and aqueous solutions was studied. The pitting potential was measured by potentiostatic polarization techniques, surface scratching techniques, and galvanostatic techniques. The effect of pH and aggressive anion concentration on the pitting potential was investigated. The passivity breakdown potential of cadmium in solution (pH 11 and 12.5) and in solution (pH 9–12.5) was found to be due to localized acidification on the metal‐solution interface. No pitting potential was found for cadmium either in solution (pH 11) or in solution (pH 9). Thermodynamic considerations showed that no stable oxide film is formed in those solutions.

Pitting of High Purity Zinc and Pitting Potential Significance

Abstract The passivity breakdown of high purity zinc in aqueous solutions containing different aggressive anions (Cl−, I−, SO4=, and NO3−) was studied. A critical evaluation of different methods for measuring the breakdown potential was made. Reproducible passivity breakdown potential measurements were given only by those methods producing mechanical disruption of the passive film. The passivity breakdown potential of high purity zinc was found to be independent of the nature of the anions tested, except for nitrates, and very close to the equilibrium potential of the reaction Zn = Zn2+ + 2e. The passivity breakdown potential in all the cases studied was found to be equal to the corrosion potential of zinc in the acid solution formed inside the pits. It is concluded that the pitting potential is the minimum potential at which an acidified solution can be produced and maintained in contact with the dissolving metal.