Potentiodynamic Anodic Polarization Curves Research Articles

Effect of chloride ions on the corrosion behaviour of steel in 0.1 M citrate

The corrosion behaviour of steel was studied in aerated near neutral citrate solutions without and with various concentrations of NaCl. The potentiodynamic anodic polarization curve in 0.1 M citrate solution exhibits four anodic peaks A1, A2, A3 and A4 prior to the oxygen evolution reaction. Addition of Cl − ions to the solution enhances the four peaks currents, specially A3, which is followed by pitting corrosion. The negative going scans of the cyclic voltammograms show two anodic reactivation peaks A5 and A6 and one cathodic plateau P1. A diffusion controlled process in the potential range of A1, A2 and P1 was detected by RDE experiments. The potentiostatic current time transients, at different concentrations of NaCl and applied potentials E a > A3, were studied. The pit nucleation rate ( t i −1) is found to increase with increasing the concentration of NaCl and the applied anodic potential. The impedance spectra exhibit four different behaviours depending on the potential range used. They were fitted with a single time constant circuit at E a < −700 mV. However, at −700 mV < E a < −480 mV, they were fitted with a circuit with two time constants. At E a > −480 mV, the second semicircle is replaced by negative polarization resistance which is disappeared at E a > −300 mV. The electrode impedance was found to decrease with the applied potential.

Passivity and passivity breakdown of a zinc electrode in aerated neutral sodium nitrate solutions

The passivation and pitting corrosion behaviour of a zinc electrode in aerated neutral sodium nitrate solutions was investigated by cyclic voltammetry and chronopotentiometry techniques, complemented by ex situ scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) examinations of the electrode surface. Measurements were conducted under different experimental conditions. The potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of thin film of ZnO on the anode surface. The passive region is followed by pitting corrosion as a result of breakdown of the passive film. SEM images confirmed the existence of pits on the electrode surface. The breakdown potential decreases with an increase in NO 3 − concentration and temperature, but increases with increasing potential scan rate. Addition of SO 4 2− ions to the nitrate solution accelerates pitting corrosion, while addition of WO 4 2− and MoO 4 2− ions inhibits pitting corrosion. The chronopotentiometry measurements show that the incubation time for pitting initiation decreases with increasing NO 3 − concentration, temperature and applied anodic current density. Addition of SO 4 2− ions decreases the rate of passive film growth and the incubation time, while the reverse changes produced by addition of either WO 4 2− or MoO 4 2− ions.

耐食・耐摩耗性を備えた肉盛材料の開発

For fluid machinery used in seawater, the overlaying technique is an effective means for the resistance to corrosion, erosion and abrasive wear in terms of cost, performance and repair. Therefore, we had attempted to combine the manufacturing technique of anti-wear resistant Co based KV powder and Crevelloy alloy with excellent crevice corrosion resistance. As the results, the overlayer containing 15%massVC, 35%massCr, and 15%massMo shows high hardness and excellent anti-corrosion property. High hardness of overlayer is mainly caused by matrix phase with lamellar structure consisting Ni-Cr-Mo-Fe alloy phase and carbide phase. Corrosion property was evaluated by cyclic potentiodynamic anodic polarization curve measurement in 3.0%NaCl aq. at 25°C, pitting potential measurement in 3.5%NaCl aq. at 80°C and 6-months immersion test in seawater. Erosion property was evaluated by slurry jet test and vibratory cavitation erosion test. From the evaluation results, developed material VCRMO is recommended as overlaied alloy for seawater applications.

Corrosion behaviour of 304 stainless steel in sulphuric acid solutions and its inhibition by some substituted pyrazolones

The corrosion behaviour of 304 stainless steel (SS) in 0.5 M H 2SO 4 solution was studied using potentiodynamic and galvanostatic polarization techniques. Three anodic peaks were observed in the potentiodynamic anodic polarization curves before oxygen evolution. The effects of acid concentrations and voltage scan rate were studied. The inhibitive effect of 4-substituted pyrazole-5-ones toward the corrosion of 304 SS in 0.5 M H 2SO 4 were studied. The inhibition action of these compounds was assumed to occur via adsorption on the steel surface through the active centres contained in their structure. The mechanism of inhibition was interpreted on the basis of the inductive and mesomeric effects of the substituents. There is a good agreement between the percentage inhibition efficiencies calculated from both techniques. The inhibition efficiencies increase with increasing the inhibitor concentrations.

Correlation between microstructure and properties of biocomposite coatings

A SiO2–CaO–Na2O (SCN) based bioactive glass was used to prepare glass–matrix/Ti particle composite coatings (SCNT). The coatings were obtained by vacuum plasma spray (VPS) on Ti–6Al–4V substrates. Two different deposition methods have been compared: (a) VPS of powders obtained by ball milling of sintered composites; (b) in situ plasma spray of mixed titanium and glass powders. For comparative purposes, pure SCN glass coatings were produced. The coating morphology and microstructure were observed by optical and scanning electron microscopy, compositional analyses by energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Comparative mechanical tests were carried out by shear tests and by Vickers indentations at the interface between the substrate and the coatings. The bioactivity of glass- and composite coatings was investigated in vitro by soaking them in a simulated body fluid (SBF) with the same ion concentration of the human plasma. All the layers retain their starting composition. The composite coatings obtained by VPS of the powdered presintered composites showed a better mechanical behaviour with respect both to the composite coatings obtained by the in situ method and to the pure glass coatings. Both the glass- and the two kind of composite coatings revealed to be bioactive by the growth of a thick apatite layer after 30 days of soaking in SBF. The electrochemical behaviour of the SCNT coatings was evaluated by means of potentiodynamic anodic polarization curves and free corrosion potential measurements in Ringer solution at 25 °C. For comparative purposes the same analyses were performed on analogous bioactive glass-matrix/Ti particle composite coated samples, based on the system TiO2–SiO2–CaO–B2O3 (TSCB), and obtained both by the in situ and by presintering method as well. The results of the electrochemical tests showed a better corrosion behaviour of the samples coated by VPS of powdered sintered composites with respect to those coated by in situ VPS composites.

Corrosion of AISI 304 stainless steel induced by thermophilic sulfate reducing bacteria (SRB) from a geothermal power unit

Corrosion behavior of AISI 304 stainless steel induced by two strains of thermophilic sulfate reducing bacteria (SRB) was analyzed. Inoculated bacteria were isolated from the surface condenser's tubes of “Los Azufres”, a geothermal electric field located in the State of Michoacan in Central Mexico. Anaerobic corrosion tests were carried out for two months in Czapek's medium at 50°C and 90°C inoculated with strains. The examination in scanning electron microscope (SEM) was accomplished to determine the type of corrosion, morphology, and preferential attacked zones. Measuring the corrosion potential and determining of anodic potentiodynamic polarization curves after two months of exposure in anaerobic conditions carried out an electrochemical study. Durch thermophile sulfatreduzierende Bakterien aus einem geothermischen Kraftwerk induzierte Korrosion von nichtrostendem Stahl 1.4301 Das durch zwei Arten thermophiler sulfatreduzierender Bakterien (SRB) induzierte Korrosionsverhalten von nichtrostendem Stahl 1.4301 wurde untersucht. Geimpfte Bakterien wurden von der Oberfläche der Verdampferrohre von „Los Azufres”︁, einem geothermischen, elektrischen Feld im Staat Michoacan in Zentralmexiko, isoliert. Anaerobe Korrosionsprüfungen wurden über zwei Monate in Czapeks-Medium, das mit den zwei Arten geimpft war, bei 50 und 90°C durchgeführt. Die Untersuchungen im Rasterelektronenmikroskop wurden vorgenommen, um die Art der Korrosion, die Morphologie und die bevorzugt angegriffenen Bereiche zu ermitteln. Die elektrochemischen Untersuchungen beinhalteten die Messung des Korrosionspotentials und die Ermittlung anodischer potentiodynamischer Polarisationskurven nach zweimonatiger Auslagerung.

Corrosion resistance in different environments and structural features of dental casting alloys for resin bonding

en

Stainless steel containers for the storage of low and medium level radioactive waste

Corrosion investigations have been performed on the austenitic structural steel AISI 304L, in comparison with the structural steel AISI 316L, in an aerated and a de-aerated solution, which was leached from low and medium level radioactive waste. On the basis of measured potentio-dynamic anodic polarization curves and the results of cyclic polarization tests, it was found that both types of steel, as well as the corresponding welds, had a high pitting potential and a high protective potential, which means that they have a strong tendency to form a compact and corrosion-resistant passive film. The repassivation capability of both types of steel prevents the occurrence of stress corrosion cracking at the level of concentration of chloride ions which corresponds to the described type of waste, whereas absorbed atomic hydrogen does not reduce toughness or cause hydrogen embrittlement. The results of the research work confirmed that it is possible to use AISI 304L structural steel for the construction of containers for the temporary, 30-year storage of low and medium level radioactive waste.

Anodic Behavior of Some Metals and Alloys in Dimethylsulfoxide and Dimethylformamide Solutions

In the present work, we propose the results of investigation of the anodic behavior of metals with different chemical and electrochemical characteristics in dimethylsulfoxide and dimethylformamide. We studied copper, silver, iron, molybdenum, platinum, aluminum, tin, titanium, 12Kh18N10T corrosionresistant steel, Cu‐Sn alloys with 5, 10, and 15% of tin, and Ag‐Cu alloys containing 45, 72, and 90% of silver. For this purpose, we recorded potentiodynamic anodic polarization curves at a scanning speed of 1.0 mV/sec with the help of a PI-50-1.1 potentiostat. We used a silver-chloride reference electrode and a standard thermostatically controlled cell (or a cell containing a source of ultrasonic field with a frequency of 50 Hz and intensity of 1 W / cm 3 mounted at the bottom). Metal specimens in the form of cylindrical rods were pressed into fluoroplastic cartridges. Prior to each test, the specimens were ground with an M-40 fine-grained emery cloth, degreased, and washed in acetone. As working media, we used reagent-grade 1 M LiNO 3 solutions in dimethylsulfoxide (DMSO) and dimethylformamide (DMFA). According to the anodic behavior of the investigated metals and alloys in DMSO and DMFA, they can be conventionally split into the following three groups: (1) electrochemically passive (aluminum, titanium, tin, and corrosion-resistant steel), (2) anodically insoluble (platinum), and

Dealloying and electroformation in high-Pd dental alloys

Objective. The corrosion of high-Pd dental alloys, depending on their composition, is postulated to be associated with dealloying and electroformation. The aim of this study was to obtain additional information to support these postulations. Methods. The corrosion characteristics of two commercial high-Pd alloys, Naturelle (79Pd–10Cu–2Au–9Ga wt%) and Rx 91 (54Pd–37Ag–9Sn), and their elemental components were evaluated in a phosphated buffer saline (PBS) solution. Indium, a common element in high-Pd alloys, was also included. The corrosion characteristics measured for each material were the 24 h open circuit potential (OCP) and the potentiodynamic anodic polarization curve. Additionally, the surface composition of the two alloys, before and after immersion corrosion in PBS for 2 months, was analyzed by X-ray photo electron spectroscopy (XPS). Results. Of the pure metals, Ga had the most electroactive OCP followed in order by In, Sn, Cu, Ag, Au, and Pd. The anodic polarization data showed all base metals to be unstable in PBS. The electroformation of AgCl was evidenced in the polarization curve of pure Ag. Both electrochemical characteristics of the PdCu-based alloy were very similar to that of pure Pd. The PdAg-based alloy displayed corrosion behavior resembling that of Ag. XPS data showed that the corrosion of the PdCu-based alloy was associated with a decrease in surface content of Cu and Ga but an increase in Pd and Au. The PdAg-based alloy surface during corrosion showed a decrease in Sn, an increase in Ag, and an unaltered Pd content. The behavior of the PdCu-based alloy is attributed to the operation of a galvanic interaction that causes dissolution of base metals and surface enrichment with primarily Pd. Dealloying, Ag-enrichment, and AgCl formation are thought to have contributed to the observed behavior of the PdAg-based alloy. These mechanisms are consistent with data from published ion release studies. Significance. The allergenic potential of any Pd alloy is dependent on its propensity to develop a Pd-rich surface and thus release Pd +2 ions. The present study, though limited, has shown that electrochemical characteristics, namely OCP and polarization curves, can be used to identify such alloys. Further studies are warranted to evaluate the widespread applicability of these characteristics in distinguishing between Pd alloys that are biologically safe and those that are not.

Corrosion behavior of nitrogen-implanted Zircaloy

Nitrogen implantation was applied to Zircaloy-4 sheet to improve corrosion resistance at 100 and 120 keV by varying the ion dose of nitrogen from 1 × 10 17 to 1 × 10 18 ions cm −2 . The influence of nitrogen dose and substrate temperature on the corrosion resistance of the alloy were examined by measuring potentiodynamic anodic polarization curves in deaerated NaCl solution at 80 °C. The corrosion resistance of Zircaloy-4 was significantly improved with nitrogen implantation, as confirmed by the distinct increase in the pitting potential from 235 mV (vs. saturated calomel electrode, (SCE)) for the unimplanted alloy to 685 mV(SCE) for the alloy implanted with 10 18 ions cm −2 , and by the gradual decrease in the passive current density with dose. This improvement in corrosion resistance of the implanted alloy is attributed to the formation of ZrN and ZrO 2 during the implantation. Corrosion resistance of nitrogen implanted Zircaloy-4 was found to be very sensitive to the substrate temperature; the maximum resistance to localized corrosion of the implanted alloy was obtained at about 293 °C.

Corrosion behavior of nitrogen-implanted zircaloy

Nitrogen implantation was applied to Zircaloy-4 sheet to improve corrosion resistance at 100 and 120 keV by varying the ion dose of nitrogen from 1 × 10 17 to 1 × 10 18 ions cm −2. The influence of nitrogen dose and substrate temperature on the corrosion resistance of the alloy were examined by measuring potentiodynamic anodic polarization curves in deaerated NaCl solution at 80 °C. The corrosion resistance of Zircaloy-4 was significantly improved with nitrogen implantation, as confirmed by the distinct increase in the pitting potential from 235 mV (vs. saturated calomel electrode, (SCE)) for the unimplanted alloy to 685 mV(SCE) for the alloy implanted with 10 18 ions cm −2, and by the gradual decrease in the passive current density with dose. This improvement in corrosion resistance of the implanted alloy is attributed to the formation of ZrN and ZrO 2 during the implantation. Corrosion resistance of nitrogen implanted Zircaloy-4 was found to be very sensitive to the substrate temperature; the maximum resistance to localized corrosion of the implanted alloy was obtained at about 293 °C.

Production of gas atomized bronze powder: B. Xinguo (Beijing Non-Ferrous Powder Factory, Beijing, China), PM Technology, Vol. 11, No 4, 1993, 189–192. (In Chinese).

The pitting corrosion susceptibility of pure Al and three Al-Si alloys, namely (Al-6%Si), (Al-12%Si) and (Al-18%Si) has been studied in 0.04 M KSCN solution. Measurements were carried out under the effect of various experimental conditions using cyclic polarization, potentiostatic and galvanostatic techniques. In all cases, the potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of a thin film of Al2O3 on the anode surface. The passive region is followed by pitting corrosion, at a certain critical potential, pitting potential (Epit), as a result of breakdown of the passive film by SCN− anions. Cyclic polarization measurements allowed the determination of the pitting corrosion parameters, namely the pitting potential and the repassivation potential (Erp). Alloyed Si decreased the passive current (jpass) and shifted both Epit and Erp towards more positive values. Thus alloyed Si suppressed pitting attack. The effect of illumination on passivity and the initiation of pitting corrosion on Al in KSCN solutions was also studied. It is observed that illumination of Al leads to an increase in its pitting corrosion resistance-apparent from jpass, Epit, and Erp measurements in aggressive KSCN solutions.

Electrochemical behaviour of titanium and dental alloys in artificial saliva

The electrochemical behaviour of titanium in artificial saliva was compared to those of a gold alloy, two CoCr alloys, and a non-gamma-2 dental amalgam. The potentiodynamic anodic polarization curve of Ti has an extremely weak passivation current density (= 1.5 μA cm −2) even at high polarization potentials. No breakdown potential has been observed, at least up to 1200 mV vs. sce. Repassivation of Ti is immediate, and its corrosion resistance is very high. The galvanic currents between Ti and CoCr alloys are extremely weak. Ti also shows a low sensitivity to crevice corrosion. When corrosion is uniform or localized, Ti has a nearly identical or better behaviour than CoCr alloys in artificial saliva.

Effect of microstructure on the corrosion behaviour of dental gold alloys

The effect of microstructure on the corrosion behaviour of Au-Cu-11 at % Pd, Au-Cu-11 at % Ag and (Au-Cu-11 at % Ag)-5 at % Pd alloys was studied by anodic potentiodynamic and potentiostatic polarization tests. The single-phase Au-Cu-11 at % Pd alloys had high corrosion resistance and their potentiodynamic polarization curves were simple. The high-nobility Au-Cu-11 at % Ag alloy displayed high corrosion resistance regardless of its microstructure. The two-phase Au-Cu-11 at % Ag and (Au-Cu-11 at % Ag)-5 at % Pd alloys had lowered corrosion resistance compared with the single-phase alloys. Anodic potentiodynamic polarization curves of the two-phase alloys were complex, but they were explained by superimposing the curves of each phase using the principle of additivity. The potential at which the current density sharply increased corresponded with that of each phase, and the value of current density was calculated as the sum of the current density of each phase and taking account of their volume fractions. In the anodic potentiodynamic polarization, there was little galvanic effect between the two phases.

Inhibition of pitting corrosion of Pb in alkaline chlorate and perchlorate solutions by some inorganic anions

The potentiodynamic anodic polarization curves for the lead electrode were obtained in 0.1 mol L‐1 KOH solution in the absence and presence of C103‐ or C104‐ as aggressive ions at different concentrations. Lower concentrations of these ions have no significant influence on the passive film, while higher concentrations raise the active dissolution current density, and cause destruction of passivity and initiation of pitting corrosion. The critical pitting corrosion potential varies with the concentration of the aggressive ions according to sigmoidal curves. These curves were explained on the basis of the formation of passivitable, active and continuously propagagting pits depending on the range of the aggressive ion concentration. Additions of increasing concentrations of chromate, phosphate, sulphate and carbonate ions cause a shift of the critical pitting potential in the noble direction accounting for increase resistance to pitting attack (inhibition). The pitting corrosion potential varies with the concentration of the inhibitive ions, in the presence of a constant concentration of the aggressive ions, according to curves of sigmoidal shape. From these curves one can determine the minimum concentration of the inhibitive ions necessary for inhibition of pitting corrosion to occur.

火山性環境におけるダイレクトCrめっきステンレス鋼の耐さび性

The atmospheric corrosion resistance of SUS 304·BA, SUS 430·BA, 430M·BA (modified SUS 430) and directly Cr-plated Stainless Steels were studied in volacanic Kagoshima district during three months, showing that SUS 304·BA and SUS 430·BA were strongly inferior in corrosion resistance to directly Cr-plated Stainless Steels. Juding from the potentiodynamic anodic polarization curves and the shapes of corroded surfaces measured by SEM, SUS 304· BA and SUS 430·BA had scarcely corrosion resistance against volcanic ashe attack, because the crevice corrosion was occurred under the ache and the corrosion reaction was promoted by extracted corrosive anion (especially F-) from the ashe. On the other hand, corrosion resistance of directly Cr-plated Stainless Steels were little influenced by the corrosive anion extracted from the ashe and quiet superior.

Corrosion behavior of Pd [sbnd]Cu and Pd [sbnd]Co alloys in synthetic saliva

Pd-based alloys are major alternatives to gold-based alloys for PFM applications. In electrolytes simulating oral fluids, these alloys exhibit electrode behavior similar to passivity of active metals, i.e., a potential region of almost constant current density up to a critical potential, above which the current increases. The objective of this study was to correlate the electrode behavior with the results of solution analyses and changes in the surface composition of the alloys. Binary alloys Pd-15 wt% Cu and Pd-19 wt% Co, as well as the pure components, were examined. Corrosion potentials vs. time, potentiodynamic anodic polarization curves, polarization resistances vs. time, and potentiostatic anodic charges were measured with synthetic saliva used as the electrolyte. The concentrations of Pd, Cu, and Co in the solution after various exposures were determined by atomic absorption. The surfaces of the alloys were examined by x-ray photoelectron spectroscopy before and after the exposures. The results show that selective dissolution of the less-noble components occurred on the surfaces of both alloys for all the exposures, leaving the surfaces highly enriched in Pd. This enrichment contributed to the potential changes and the passive-type behavior. Copper dissolved more than cobalt at longer exposures and higher potentials, in spite of its higher nobility. Dissolution of cobalt seemed to be limited by the formation of a surface film, which may be related to the transition character of this element.

Structural characterization and electrochemical behaviour of Fe-Ni-Mo-B Amorphous alloys

A series of amorphous alloys obtained by the “melt-spinning” technique, with variable nickel and molybdenum contents, have been examined. Potentiodynamic anodic and cathodic polarization curves have been obtained for each of these amorphous alloys in various environments (1N HCl, 1N H 2S0 4, 3% NaCl, 1N NaOH). Their electrochemical properties were correlated with the amorphous structure and with their composition, characterized by means of X-ray diffraction and Mössbauer spectroscopy. Surface morphology has been observed by Scanning Electron Microscopy (SEM). The nickel content, in amorphous Fe-Ni x-Mo 4-B 13 (balance iron) alloys enhanced the corrosion resistance in acid (IN H 2SO 4, 1N HCl), neutral (3% NaCl) and alkaline (1N NaOH) environments. The molybdenum content (from 4 to 8.5%) in the amorphous Fe-Ni 20-Mo x-B 13 (balance iron) alloys increased the corrosion resistance only in alkaline solutions. In the various environments tested, the corrosion potentials tend to ennoble on increasing the nickel content. While the alloys are in the active state in acid and neutral environments, they are passive in alkaline environments. A correlation has been found between the short range order in the alloys of the Fe-Ni-Mo-B type, of similar chemical composition, and the electrochemical behaviour.

Ion mixing effects on the electrochemical behavior of tin coated nickel

Nickel substrates were coated with a thin Sn layer and implanted with 100 keV xenon ions, leading to the formation of new surface phases, mainly Ni 3Sn. Electrochemical measurements were carried out on Ni samples submitted to each of the following surface modifications: Sn-deposition, Xe +-implantation, ion-mixing (combined treatment), and on untreated Ni. The test solution was 0.5 M NaCl. Both the potentiodynamic anodic and cathodic polarization curves show that the implantation on uncoated Ni improves the anodic passivation with respect to the Sn deposition on Ni; comparable results are obtained by surface alloying induced by ion-mixing. The cathodic behaviour is in agreement with the presence of both galvanic couples and active sites for H 2 evolution due to defect spreading. Only the alloyed surface shows a clearly different behaviour, i.e. a high hydrogen reduction overvoltage. The electrochemical measurements were repeated in the presence of sulphide ions.