Comparative study on corrosion behaviour of Nitinol and stainless steel orthodontic wires in simulated saliva solution in presence of fluoride ions

Localized corrosion and effects of pre-passivation treatment of Nitinol and SS304 orthodontic wires in simulated saliva solution in the presence and absence of fluoride ions were investigated by means of potentiodynamic and potentiostatic polarisations. Results revealed that Nitinol does not show pitting corrosion in saliva solution however, SS304 shows pitting corrosion. Meanwhile fluoride ion has deteriorative effect on pitting corrosion of Nitinol, while its effect on SS304 was marginally constructive. Additionally, the presence of artificial crevice has no effect on corrosion behaviour in the presence of fluoride. Pre-passivation treatment has positive influence on pitting corrosion of both alloys in the presence of F^? ions.     

Effect of sulfide ions on the stress corrosion behaviour of Al-brass and Cu10Ni alloys in salt water

The stress corrosion cracking (SCC) behavior of Al-brass and Cu10Ni alloys was investigated in 3.5% NaCl solution in absence and in presence of different concentrations of Na₂S under open-circuit potentials using the constant slow strain rate technique. The results indicated that the Cu10Ni alloy is more susceptible to stress corrosion cracking than as-received Al-brass at strain rate of 3.5 × 10^–6 s^–1 in 3.5% NaCl in presence of high concentration of sulfide ions (1000 ppm). The sulfide ions (up to 500 ppm) has no effect on the stress corrosion cracking of the annealed Al-brass in 3.5% NaCl at two strain rates of 7.4 × 10^–6 and 3.5 × 10^–6 s^–1. The results support film rupture for Al-brass and sulfide stress corrosion cracking assisted with pitting corrosion for Cu10Ni at slip steps as the operating mechanisms.     

Potentiodynamic Polarization Behavior and Pitting Corrosion Analysis of 2101 Duplex and 301 Austenitic Stainless Steel in Sulfuric Acid Concentrations

The corrosion behavior of 2101 duplex and 301 austenitic stainless steel in the presence of sulfate (SO₄ ^2?) anion concentrations was investigated through polarization techniques, weight loss and optical microscopy analysis. The corrosion rates of the steels were comparable after 3M H₂SO₄. Results confirm that the duplex steel displayed a higher resistance to pitting corrosion than the austenitic steel. Experimental observation shows that its pitting potential depends on the concentration of the SO₄ ^2? ions in the acid solution due to adsorption of anions at the metal-film interface. The duplex steel underwent stable pitting at relatively higher potentials and significantly higher corrosion current than the austenitic steel. The duplex steel exhibited lower corrosion potential values thus less likely to polarize in the acid solution. Solution concentration had a limited influence on the polarization behavior of the austenitic steel and hence its reaction to SO₄ ^2? ion penetration from analysis of the pitting potentials and observation of its narrower polarization scans compared to the duplex steel which showed wide scatter over the potential domain with changes in concentration.     

Influence of Cl-, Br-, NO 3 - and SO 4 2- ions on the corrosion behaviour of 6061 Al alloy

The effects of anions like Cl^-, Br^-, NO ₃ ^- and SO ₄ ^2- on the anodic dissolution of the monolithic Al 6061 alloy have been investigated at neutral pH through immersion testing and electrochemical techniques like potentiodynamic polarization and a.c. impedance spectroscopy. Scanning electron microscopy was employed to characterize the corroded surface and to observe the extent of pitting in different media. From the evaluated corrosion parameters it was found that the dissolution of the matrix was extensively reduced in presence of aqueous solutions containing Br^-, NO ₃ ^- and SO ₄ ^2- ions while Cl^- ions aggravated corrosion by penetrating into the barrier oxide film on the surface of the material. Pronounced effect of pitting was observed in presence of Cl^- and the level of pitting in NO ₃ ^- and Br^- were mild. In presence of SO ₄ ^2- ions passivity was extended over a wide potential range and breakdown of passivity occurs when the material was polarized beyond pitting potential. The departure of capacitive behaviour towards resistive behaviour was clearly observed through impedance measurements when investigations were conducted in Cl^- media and in presence of the other electrolytes. Corrosion rates were, however, controlled during prolonged exposure in the electrolytic media, specially in case of chloride media, due to the predominance of film repair kinetics.     

Interactions between nitrites and Fe(II)-containing phases during corrosion of iron in concrete-simulating electrolytes

The influence of sodium nitrite on the corrosion processes of iron in solutions simulating polluted concrete was investigated by means of electrochemical methods, such us potentiodynamic, galvanostatic and impedance spectroscopy tests, coupled with analyses of the corrosion layers by Mössbauer spectroscopy. NO ₂ ^? ions are anodic inhibitors and provoked consequently an important increase of the corrosion potential. The polarisation curves show that NO ₂ ^? ions increase the pitting potential value. The size of electrochemical impedance spectra obtained at the OCP increases with the concentration of nitrite, which confirms the decrease of the corrosion rate. Galvanostatic experiments allowed us to provoke active corrosion even in presence of NO ₂ ^? . When nitrite ions are not present, the corrosion products mainly consist of iron (II) compounds, FeCO₃ or Fe(OH)₂ depending on the pH, and iron(II)–iron (III) compounds, i.e. green rusts (GRs). The main effect of nitrite ions was to accelerate the oxidation of GRs into FeOOH phases, confirming their oxidizing role. While immersed for long periods in the nitrite containing solutions, the α-iron foils do not present any single trace of corrosion.     

Electroplating of zirconium and aluminum hydroxide thin films following anodic dissolution of corresponding metal anodes in organic medium

Zirconium (IV) hydroxide or hydrate oxide films, which are typically difficult to prepare by electrochemical methods using aqueous solutions, are easily fabricated in an acetone bath using Zr anodes as the metal sources and a metal-free solvent containing halide ions as the supporting electrolyte. This method is also confirmed to be applicable to aluminum anodes. In the early stage of electrolysis, anodic oxidation of the metal anode proceeds in the presence of water as an impurity in the solvent. Subsequently, pitting corrosion of the oxide film on the metal anode occurs as a result of the action of halide ions. The corrosiveness of the halogen additive appears to be an important factor determining the dissolution or deposition of metal species in this stage. That is, Br^– is more active for electrochemical dissolution of a passive oxide film on the anode compared to I^–. Finally, Zr species are deposited on the cathode surface via reactions with cathodically generated hydroxide ions. In these processes, the metal plate acts as a soluble anode and as a metal source for electrodeposition. The coating of Zr (IV) hydroxide film on a stainless steel substrate is shown to act as an effective barrier against electrolytic corrosion.     

Analysis of Copper Pitting Failure in Drinking Water Distribution System

Electrochemical tests, as well as surface and chemical analysis were used to investigate the cause of pitting failure of copper tubing in a drinking water distribution system. The results show that localized pitting was the cause of failure and copper corrosion problems were observed under a green deposit. The pitting corrosion was associated with the Cl⁻ and SO₄ ²⁻ ions introduced by the water softening treatment. These ions promoted the corrosion and the influence of Cl⁻ ion was much greater than that of the SO₄ ²⁻ ion.     

Short-term corrosion behavior of galvanized coatings in natural waters of the Greek territory

The corrosion behavior of hot-dip galvanized steel immersed in domestic and seawater was investigated after an exposure period up to 10 days. The examination of the coatings was accomplished with optical microscopy, scanning electron microscopy and X-ray diffraction. From this investigation it was deduced that the corrosion process in domestic water is slow and mainly proceeds through pitting corrosion, while the corrosion phenomena in seawater are more intense. The main mechanisms in this environment are pitting and intergranular corrosion. In both waters the Cl⁻ and the O²⁻ ions diffuse in the coating up to the Fe/Zn interface. Especially in seawater the Cl⁻ ions seem to be very aggressive.     

Chloride induced pitting corrosion of nickel in alkaline solutions and its inhibition by organic amines

Cyclic voltammetry, potentiodynamic and potentiostatic anodic polarization techniques complemented by SEM investigation are used to study the initiation and inhibition of pitting corrosion of nickel in NaOH solutions. The presence of Cl⁻ ions locally destroys the passive film formed on the nickel electrode at the pitting potentials, E_p, which are more active the higher the concentration of the Cl⁻ ions. E_p varies with the logarithm of Cl⁻ ions concentration according to sigmoidal S-shaped curves.     

Effect of fluoride on the corrosion behavior of nanostructured Ti-24Nb-4Zr-8Sn alloy in acidulated artificial saliva

The surface of titanium dental implants is highly susceptible to aggressive fluoride ions in the oral environment. Nanotechnology has proven an effective approach to improve the stability and corrosion resistance of titanium by applying a passive film. In this study, we investigated the effects of fluoride on the corrosion behavior of nanostructured(NS) Ti-24 Nb-4 Zr-8 Sn(Ti2448) alloy in acidulated artificial saliva(AAS)at 37 ℃, and then conducted comparisons with its coarse grained(CG) counterpart. Electrochemical techniques, such as potentiodynamic polarization and electrochemical impedance spectroscopy(EIS), as well as surface analysis including X-ray photoelectron spectroscopy(XPS) with argon ion sputtering, and scanning electronic microscopy(SEM) were employed to evaluate the effects of fluoride on sensitivity to pitting and the tolerance of Ti2448 to fluoride in AAS solution. The results demonstrate that corrosion current density increased with F-concentration. In all respects, the NS Ti2448 alloy presented corrosion resistance superior to that of its coarse grained(CG) counterpart at low F-concentrations(0.1%).Furthermore, a high content of F-(1%) was shown to promote the active dissolution of both alloys by increasing the rate of corrosion. Following immersion in the fluoridated AAS solution for 60 days, a tissuefriendly compound, Ca_3(PO_4)_2, was detected on the surface of the NS when F-= 0.01% and Na_2 TiF_6 was identified as the main component in the corrosion products of the CG as well as NS Ti2448 alloys when F-= 1%. High concentrations of F-produced pitting corrosion on the CG alloy, whereas NS Ti2448 alloy presented general corrosion in the form of lamellar separation under the same conditions. These findings demonstrate the superior corrosion resistance of the NS Ti2448 alloy as well as lower pitting sensitivity and higher tolerance to fluoride due mainly to grain refinement.     

Synergistic effect of 2-oleyl-1-oleylamidoethyl imidazoline ammonium methylsulfate and halide ions on the inhibition of mild steel in HCl

The effect of 2-oleyl-1-oleylamidoethyl imidazoline ammonium methylsulfate (ODD) and halide ions on corrosion inhibition of mild steel in HCl solution has been studied by experimental and molecular dynamics simulation methods. Synergistic effects were observed between ODD and the halides, and the inhibition efficiency was found to follow the trend ODD–Cl⁻ < ODD–Br⁻ < ODD–I⁻. In molecular dynamics simulation, the analysis of fractional free volume and diffusion coefficient showed that the synergistic effect increased in the order ODD–Cl⁻ < ODD–Br⁻ < ODD–I⁻. The molecular dynamics simulation analysis agreed with the experimental results.     

Effect of Cu Addition to 2205 Duplex Stainless Steel on the Resistance against Pitting Corrosion by the Pseudomonas aeruginosa Biofilm

The effect of copper addition to 2205 duplex stainless steel(DSS) on its resistance against pitting corrosion by the Pseudomonas aeruginosa biofilm was investigated using electrochemical and surface analysis techniques. Cu addition decreased the general corrosion resistance, resulting in a higher general corrosion rate in the sterile medium. Because DSS usually has a very small general corrosion rate, its pitting corrosion resistance is far more important. In this work, it was shown that 2205-3%Cu DSS exhibited a much higher pitting corrosion resistance against the P. aeruginosa biofilm compared with the 2205 DSS control, characterized by no significant change in the pitting potential and critical pitting temperature(CPT) values. The strong pitting resistance ability of 2205-3%Cu DSS could be attributed to the copper-rich phases on the surface and the release of copper ions, providing a strong antibacterial ability that inhibited the attachment and growth of the corrosive P. aeruginosa biofilm.     

Effect of pH, temperature and Cl− concentration on electrochemical behavior of NiTi shape memory alloy in artificial saliva

The cooperation of pH, temperature and Cl⁻ concentration on electrochemical behavior of NiTi shape memory alloy in artificial saliva was studied using orthogonal test method. The results showed that the pitting potential for NiTi in artificial saliva decreased at low and high pH; at 25^∘C, the pitting potential was the lowest compared to those at 10^∘C, 37^∘C and 50^∘C; when the Cl⁻ concentration was not less than 0.05 mol/L the pitting potential decreased with the increase of Cl⁻ concentration. The free corrosion potential of austenitic NiTi was lower than that of mixture of austenite and martensite.     

Copper nucleation and growth during the corrosion of aluminum alloy 2524 in sodium chloride solutions

Copper clusters, as nodules and micro dendritic masses, were observed to nucleate and grow on Al 2524 surfaces after corrosion immersion experiments for up to 5 days in 0.6 M NaCl solutions; with pH values ranging from 3 to 11. Cu clusters observed by SEM on the corroded surfaces and confirmed by EDX analysis were extracted or stripped from their original sites and examined in detail utilizing TEM and EDX spectrometry. These observations confirm a mechanism contributing to pitting corrosion in copper-rich aluminum alloys involving the plating or cementation of Cu²⁺ from solution as an electrochemical displacement reaction, resulting in nucleation and growth of Cu clusters on the aluminum alloy surface, and causing additional aluminum dissolution and pitting around the Cu deposits.     

Effects of pre-stretching on corrosion resistance of a creep-aged Al–5.87Zn–2.07Mg–2.42Cu alloy

In this experiment, the corrosion resistance of an Al–5.87Zn–2.07 Mg–2.42Cu alloy with different pre-stretchings (0, 2, 4, 6%) after creep aging (CA) was investigated. It is found that the corrosion performance reaches the optimal value at 4% pre-stretched sample, which owns the largest stress corrosion sensitivity factor r_tf (93.8%) and the shallowest intergranular corrosion depth (24.7 µm). When the degree of pre-stretching before CA rises, coarser and sparser intragranular precipitates (IGPs) are observed after CA. The average size of IGPs rises from about 2.2 to 5.8 nm while the density declines from about 5.4?×?10¹⁶ to 3.5?×?10¹⁶ cm^?3, and thus diminish the electron scattering effect and release the strain field. Moreover, the grain boundary precipitates (GBPs) become larger and more discontinuous and the precipitate-free zones (PFZs) broaden. The average size of GBPs rises from about 9.3 to 23.9 nm, and the average distance between GBPs increases from about 11.8 to 39.4 nm. Additionally, the segregation degree of Mg reduces and the content of Cu of GBPs rises with the increase of pre-stretching. These influence factors reduce the possibility of anodic dissolution and hydrogen-induced cracking (HIC). However, the expanding PFZ increases the potential difference between matrix and PFZ, promoting the anodic dissolution. Therefore, the corrosion resistance of an Al–5.87Zn–2.07 Mg–2.42Cu alloy can be improved by applying 4% pre-stretching before CA.

     

Stability of plasma electrolytic oxidation coating on titanium in artificial saliva

Bioactive PEO coating on titanium with high Ca/P ratio was fabricated and characterized with respect to its morphology, composition and microstructure. Long-term electrochemical stability of the coating and Ti⁴⁺ ion release was evaluated in artificial saliva. Influence of the lactic acid and fluoride ions on corrosion protection mechanism of the coated titanium was assessed using AC and DC electrochemical tests. The PEO-treated titanium maintained high passivity in the broad range of potentials up to 2.5 V (Ag/AgCl) for up to 8 weeks of immersion in unmodified saliva and exhibited Ti⁴⁺ ion release <0.002 µg cm^?2 days^?1. The high corrosion resistance of the coating is determined by diffusion of reacting species through the coating and resistance of the inner dense part of the coating adjacent to the substrate. Acidification of saliva in the absence of fluoride ions does not affect the surface passivity, but the presence of 0.1 % of fluoride ions at pH ≤4.0 causes loss of adhesion of the coating due to inwards migration of fluoride ions and their adsorption at the substrate/coating interface in the presence of polarisation.     

Inhibition of chloride pitting corrosion of Zircaloy-4 alloy in highly radioactive water by radiolytic nitrate and hydrogen peroxide

We report an investigation of the pitting corrosion susceptibility of Zircaloy-4 alloy in presence of radiolytic chloride, nitrate and hydrogen peroxide. The electrochemical behavior of Zircaloy-4 was essentially studied using cyclic voltammetry and electrochemical impedance spectroscopy to provide an indication of mechanisms and oxide layer modifications. The experiments have shown that the pitting corrosion behavior is dependent on the concentration of these radiolytic species in tritiated water. Nitrate shows pronounced inhibitory action due to adsorption of the ammoniac formed on the passive oxide layer buffering the pH, which stops pit initiation and assists repassivation of the oxide surface. The presence of both hydrogen peroxide and NO_{3 –} produces other effects. The passive oxide layer is thicker and its characteristics change in the bulk. Also, pit initiation is stopped whereas it is more difficult to obtain repassivation of existing pits. This can be explained by the capability of ³H₂O₂ to oxidize the surface and thus enhance passive oxide formation. But, in this case, NO_{3 –}/N³H⁺ ₄ adsorption should be hindered by the ³H₂O₂ present and consequently there is less buffering of the surface pH limiting repassivation of the existing pits. However, with these two combined effects: pH kept constant on the Zircaloy-4 surface and enhancement of the oxide layer intrinsic characteristics, less pitting is observed than in presence of chloride ions alone.     

Passivity,pitting and corrosion of anodically polarized Fe-Ni alloys in 0.5 M H2SO4 containing Cl−

Iron-nickel alloys containing 0, 20, 40, 60, 80 and 100% Ni (wt%) have been anodically polarized in 0.5 M H₂SO₄ containing Cl^?, and the conditions for passivity, pitting and corrosion with respect to alloy composition and Cl^? concentration broadly defined. Breaks occur in the values of the corrosion properties at about 30% and 70% Ni. It is considered that the corrosion properties of alloys containing up to 30% Ni are determined by the ferrite in the alloy and the low corrosion resistance of its surface film, that alloys containing 30 to 70% Ni have a corrosion resistant film probably similar to a nickel ferrite spinel, and that alloys containing over 70% Ni have properties similar to nickel and probably have a surface film based on a solid solution of iron in NiO.     

Overview on electrochemical parameters to assess the corrosion state of steel reinforcement in CAC mortar and concrete

Calcium Aluminate Cement (CAC) can be used successfully in mortars and concretes for special applications such as refractory and sulphate-resistant materials. However, some failures have been reported when used in reinforced concretes exposed to wet environments in presence of chloride ions. Chloroaluminates formation in either reinforced CAC mortar or concrete could be a way to reduce chloride ions in the pore solution of this material, thereby, decreasing the risk of corrosion. This paper presents the characteristic values of corrosion rate, corrosion potential and resistivity and the relationship between them. Assuming a significant corrosion state at corrosion rate values over 0.1 A/cm², we can establish a threshold level for corrosion initiation in reinforced mortar or concrete of –250 mV and 10⁴ ·cm. Therefore, lesser values constitue important corrosion rates.     

Long-term assessment of the implant titanium material—artificial saliva interface

This paper studies the long-term (20,000 exposure hours) behavior of titanium and Ti–5Al–4V alloy—Carter–Brugirard saliva interface and the short-term (500 exposure hours) resistance of titanium and Ti–5Al–4V alloy—Tani&Zucchi saliva interface. Potentiodynamic polarization method was applied for the determination of the main electrochemical parameters. Linear polarization measurements for to obtain the corrosion rates were used. Monitoring of the open circuit potentials (E _oc) for long-term have permitted to calculate the potential gradients due to the pH, ΔE _oc(pH) and to the saliva composition ΔE _oc(c) changes which can appear “in vivo” conditions and can generate local corrosion. Atomic force microscopy (AFM) has analyzed the surface roughness. Ion release was studied by atomic absorption spectroscopy (AAS). In Carter–Brugirard saliva both titanium and Ti–5Al–4V alloy present very stable passive films, long-term stability, “very good” resistance, low values of the open circuit potential gradients, which cannot generate local corrosion. In Tani&Zucchi artificial saliva, pitting corrosion and noble pitting protection potentials (which cannot be reached in oral cavity) were registered; titanium ion release is very low; surface roughness increase in time and in the presence of the fluoride ions, denoting some increase in the anodic activity.