Electrochemical Behavior of Sn‐Ag Alloys in Sodium Fluoride Solutions

Passivation and corrosion behavior on Ag, Sn and Sn‐Ag alloys were studied using various electrochemical techniques, i.e. open‐circuit, potentiodynamic polarization and impedance measurements. The specimens were polarized between –1000 and 500 mV vs. saturated calomel electrode (SCE) in naturally oxygenated NaF solution of different concentrations. The results of potentiodynamic polarization showed that each of i_corr and i_c increases with increasing either Sn% or F^‐ concentration. EIS measurements under open circuit conditions confirmed well this behavior. The effect of temperature was also studied in 0.5M NaF at temperature range of 291K to 333K. The corrosion current i_corr was observed to increase with temperature for the same electrode. The activation energy was calculated according to Arrhenius equation and its value was found to decrease considerably with increasing the Sn content in the alloy.     

Electrochemical characterization of the corrosion of a Mg-Li Alloy

The corrosion characteristic of a novel Mg-Li alloy with RE in alkaline NaCl solution was investigated by electrochemical means, such as open circuit potential vs time curves, potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS). The result showed that Cl⁻ concentration and pH value affected the corrosion of Mg-Li alloy, and in high Cl⁻ concentration solution Cl⁻ concentration was the major factor. Corrosion of the alloy was slighter in the stronger alkaline solution, because corrosion current(I_corr) reduced, corrosion potential (E_corr) turned to positive direction and the capacitive loops enlarged. When Cl⁻ increased, I_corr increased and capacitive loops shrinked, this means that corrosion of the alloy was more serious with the increase in Cl⁻ concentration.     

Comparative corrosion study of Ag-Pd and Co-Cr alloys used in dental applications

The electrochemical behaviour of two Ag-Pd alloys (Unique White and Paliag) used in dental prosthetics construction for crowns and bridges and one Co-Cr alloy (Vitallium 2000) was studied in artificial saliva using the polarization curves and electrochemical impedance spectroscopy (EIS). The corrosion resistance was evaluated by means of the corrosion currents value and by coulometric analysis. The open circuit potential of Ag-Pd are attributed to dealloying followed by surface enrichment with Ag and the possible formation of an insoluble AgCl surface film on the respective alloy surfaces. Our results have shown that these alloys have a somewhat good corrosion resistance in artificial saliva. The corrosion current densities of Unique White and Vitallium 2000 alloys were very low (∼100 nA/cm²). For Ag-Pd alloys, when increasing the content of Cu, corrosion resistance decreases. The passivation of all samples occurred spontaneously at the open circuit potential. The electrochemical properties of the spontaneously passivated electrodes at the open circuit potential were studied by EIS. The polarization resistance (R _p) and the electrode capacitance (C _dl) were determined. The polarization resistance of all the samples increases with the immersion time. The polarization resistances are largest for Unique White (Ag-Pd) and Vitallium 2000 (Co-Cr) alloys. Because the electrochemical behaviour of the Co-Cr alloy was compared with that of Ag-Pd alloy, this type of alloy may be a suitable alternative for use in the manufacture of fixed dental prostheses. The present study, though limited, has shown that electrochemical characteristics can be used to identify such alloys. Knowledge of the in vitro corrosion behaviour of these alloys may lead to better understanding of any biologically adverse effects in vitro.     

Extremely high pitting resistance of NiTi shape memory alloy thin film in simulated body fluids

In this paper the corrosion behavior of NiTi thin films fabricated by sputtering from Ni and Ti targets has been studied by cyclic potentiodynamic polarization tests in Hank's and Ringer's solution at 310 K. For comparison, bulk NiTi Shape Memory Alloy (SMA) has also been studied to elucidate the different corrosion behavior of bulk and thin film material. The electrochemical experiments reveal that thin film NiTi SMA has comparable corrosion current density (i_corr), much higher pitting corrosion potentials and wider passive range than the bulk NiTi. We show that NiTi SMA vapour deposited thin films are less susceptible to pitting corrosion than the bulk.     

Comparative Evaluation on the In Vitro Biological Performance of Ti45Al8.5Nb Intermetallic with Ti6Al4V and Ti6Al7Nb Alloys

The corrosion resistance of Ti45Al8.5Nb intermetallic alloy in artificial saliva and its cytocompatibility was studied via electrochemical tests, scanning electron microscopy, ion release measurement, and MTT assay, with contemporary biomedical Ti6Al4V and Ti6Al7Nb alloys as comparison. The results demonstrate that the corrosion potential (E_corr) and the corrosion current density (i_corr) of the three experimental alloy samples are similar and there is no statistically significant difference among them (p > 0.05). The Al³⁺ ion releasing concentration for Ti45Al8.5Nb intermetallic and Ti6Al7Nb alloy after anodic polarization are close. The relative cell proliferation rates of the three experimental alloy extract groups are all over 90% at various cultivation periods (1, 3, and 5 d), and there is no obvious difference for the MG63 cell morphologies comparing with that of the negative group, reaching confluence after 5 d culture and showing well stretched, which indicates that Ti45Al8.5Nb intermetallic alloy has a good cytocompatibility with the Grade 1 RGR value (no toxicity) according to ISO 10993‐5: 1999.     

Corrosion behavior of bulk amorphous Zr55Al10Cu30Ni5−xPdx alloys

Bulk amorphous Zr₅₅Al₁₀Cu₃₀Ni_5−xPd_x (x=0, 5at.%) alloys were produced by copper mould casting. The microstructure of samples was characterized by X-ray diffraction (XRD). The corrosion resistance of the bulk amorphous alloys was studied by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). The Pd-free alloy showed an active–passive transition by anodic polarization in 3.5% NaCl solution, it was spontaneously passive and had a wide passive region with significantly low passive current density. The 5% Pd amorphous alloy shows a single active state even with a limited passive region. X-ray photoelectron spectroscopy (XPS) analysis revealed that the spontaneous passive films formed on the alloys after immersion in 0.6 M NaCl solution for 72 h were composed of the oxidation of Zr, Al and Cu element. The Pd-free and 5% Pd alloys show excellent corrosion properties in 1 M NaOH solution.     

Corrosion behaviour of sintered 6061 aluminium alloy-graphite particle composites

The corrosion behaviour of sintered 6061 aluminium alloy and its composite dispersed with 7.0 vol% graphite particles is described. Techniques, namely immersion, tafel and impedance, were employed to study the corrosion behaviour. Immersion tests were performed in different media, namely HCl, NaCl and lubricating oil (used and fresh) while tafel and impedance tests were performed in 0.1 N HCl and 3% NaCl solution. Corrosion behaviour was monitored by measuring the weight change in immersion studies and corrosion current, i_corr, in tafel and impedance tests. The values of corrosion potential, E _corr, and i _corr were calculated from the tafel plots obtained at a scanning rate of 1 mV s^–1. In impedance study, i _corr was calculated from the value of polarization resistance, R _p, obtained from the Nyquist plot; the latter was obtained by merging the lock-in and FFT plots. Aluminium alloy and its composite suffered from corrosion in HCl and NaCl. However, the extent of severity was greater in the case of HCl. The i _corr values obtained by the impedance method also revealed a similar trend. The higher corrosion rate of the alloy and composites in HCl was due to the dissolution of the thin oxide (protective) film in the solution. The decreased corrosion rate of the composite and the base alloy in NaCl was attributed to the formation of stable corrosion product, Al (OH)₃, on the surface, which prevented further attack on the surface of the specimen. There was practically no evidence of corrosion attack on the alloy and the composite surface in used and fresh lubricating oil.     

Effects of phosphate on the chloride-induced corrosion behavior of reinforcing steel in mortars

The influence of phosphate as a corrosion inhibitor on the corrosion behavior of as-received and pre-rusted reinforcing steels in mortar specimens was investigated after 360 days exposure in 3.5% NaCl solution. This involved the use of electrochemical techniques for studying the steel surface reactions and microscopic observations of the steel–mortar interface. The electrochemical methods, including electrochemical impedance spectroscopy (EIS) and measurements of corrosion potential (E_corr) and linear polarization resistance (LPR), were employed to evaluate the corrosion tendency and general corrosion rate of steel. In addition, the pitting corrosion resistance of steel was also determined by cyclic polarization (CP) measurements. The results indicate that different from nitrite, which is generally accepted as an anodic inhibitor, phosphate may be a cathodic inhibitor according to its reduced corrosion rate and more negative E_corr at the same dosage as nitrite in mortar specimens. The study also reveals that the inhibiting efficiency of phosphate against general corrosion of both as-received and pre-rusted specimens is lower than 10%, which is inferior to nitrite in some respects. However, as indicated by cyclic polarization measurements, the presence of phosphate provides slightly higher pitting corrosion resistance in comparison to nitrite. Furthermore, it suggests that the corrosion inhibition mechanism of phosphate in mortars mainly depends on a dual effect occurring at the steel–mortar interface. Furthermore, it is confirmed that phosphate has little effect on the long-term mechanical properties of mortars.     

Impact of mechanical loading on the corrosion of steel reinforcement in concrete structures

This paper presents results of an experimental investigation on the effect of mechanical loading on the corrosion of steel reinforcement in concrete. Reinforced concrete beams were cast, subjected to mechanical loadings and then exposed to corrosive environment. Successive drying and wetting cycles using 3% sodium chloride salt solution were used to accelerate the corrosion attack. Electrochemical techniques such as macrocell corrosion current, linear polarization resistance (LPR), corrosion potential (E _corr ) and electrochemical impedance spectroscopic (EIS), were used to evaluate the corrosion behavior of the reinforcement. Also, chloride penetration profile and visual inspection of the beam rebars were obtained. The results shows that the pre-exposure mechanical load has no influence on the corrosion initiation or corrosion rate thereafter, unless it reaches to some limit where it develops connected cracks through which the chloride ions flow and depassivate the rebars. The load of 25% of the ultimate capacity seems to be the critical load limit where some microcracks onset to be connected, facilitate the chloride ions flow, and initiate the rebar corrosion.     

氧化铈膜制备及其耐腐蚀性能

采用不同的制备溶液及制备参数在X80钢表面制备出不同的氧化铈膜,并对其耐腐蚀性能进行了研究.利用扫描电镜、能谱仪、XRD、拉曼光谱、接触角测试仪对不同的氧化铈膜腐蚀前后的表面形貌、元素、物相及亲水性进行了分析,利用电化学工作站对不同的氧化铈膜在3.5wt.％NaCl溶液中的开路电位、线性极化电阻、交流阻抗、极化曲线进行...     

Influence of noble metals alloying additions on the corrosion behaviour of titanium in a fluoride-containing environment

Titanium alloys exhibit excellent corrosion resistance in most aqueous media due to the formation of a stable oxide film, and some of these alloys (particularly Ti-6Al-7Nb) have been chosen for surgical and odontological implants for their resistance and biocompatibility. Treatment with fluorides (F⁻) is known to be the main method for preventing plaque formation and dental caries. Toothpastes, mouthwashes, and prophylactic gels can contain from 200 to 20,000 ppm F⁻ and can affect the corrosion behaviour of titanium alloy devices present in the oral cavity. In this work, the electrochemical corrosion behaviour of Ti-1M alloys (M = Ag, Au, Pd, Pt) was assessed in artificial saliva of pH = 3.0 containing 910 ppm F⁻ (0.05 M NaF) through open circuit potential, E_OC, and electrochemical impedance spectroscopy (EIS) measurements. The corrosion behaviour of the Ti-6Al-7Nb commercial alloy was also evaluated for comparison. E _OC measurements show an active behaviour for all the titanium alloys in fluoridated acidified saliva due to the presence of significant concentrations of HF and HF₂ ⁻ species that dissolve the spontaneous air-formed oxide film giving rise to surface activation. However, an increase in stability of the passive oxide layer and consequently a decrease in surface activation is observed for the Ti-1M alloys. This behaviour is confirmed by EIS measurements. In fact, the Ti-6Al-7Nb alloy exhibits lower impedance values as compared with Ti-1M alloys, the highest values being measured for the Ti-1Au alloy. The experimental results show that the corrosion resistance of the studied Ti-1M alloys is similar to or better than that of Ti-6Al-7Nb alloy currently used as biomaterial, suggesting their potential for dental applications.     

Corrosion study of single crystal Ni–Mn–Ga alloy and Tb<Subscript>0.27</Subscript>Dy<Subscript>0.73</Subscript>Fe<Subscript>1.95</Subscript> alloy for the design of new medical microdevices

Once placed in a magnetic field, smart magnetic materials (SMM) change their shape, which could be use for the development of smaller minimally invasive surgery devices activated by magnetic field. However, the potential degradation and release of cytotoxic ions by SMM corrosion has to be determined. This paper evaluates the corrosion resistance of two SMM: a single crystal Ni–Mn–Ga alloy and Tb_0.27Dy_0.73Fe_1.95 alloy. Ni–Mn–Ga alloy displayed a corrosion potential (E _corr) of −0.58 V/SCE and a corrosion current density (i _corr) of 0.43 μA/cm². During the corrosion assay, Ni–Mn–Ga sample surface was partially protected; local pits were formed on 20% of the surface and nickel ions were mainly found in the electrolyte. Tb_0.27Dy_0.73Fe_1.95 alloy exhibited poor corrosion properties such as E _corr of −0.87 V/SCE and i _corr of 5.90 μA/cm². During the corrosion test, this alloy was continuously degraded, its surface was impaired by pits and cracks extensively and a high amount of iron ions was measured in the electrolyte. These alloys exhibited low corrosion parameters and a selective degradation in the electrolyte. They could only be used for medical applications if they are coated with high strain biocompatible materials or embedded in composites to prevent direct contact with physiological fluids.     

Fabrication of hydrophobic/super-hydrophobic nanofilms on magnesium alloys by polymer plating

Hydrophobic/super-hydrophobic nanofilms with improved corrosion resistance were fabricated on the surfaces of Mg-Mn-Ce magnesium alloy by a surface modification technique, named as polymer plating, which has been developed to modify superficial characteristics of magnesium alloys with polymeric nanofilms through synthesized organic compounds of triazine dithiol containing functional groups. The nanofilms were prepared by the electrochemical and polymerization reactions during polymer plating analyzed from characteristics of Fourier transform infrared spectrophotometer, X-ray photoelectron spectroscopy and scanning electron microscopy. The fabricated nanofilms changed the surface wettability of blank magnesium alloy from hydrophilic to hydrophobic with contact angle 119.0° of distilled water with lower surface free energy of 20.59 mJ/m² and even super-hydrophobic with contact angle 158.3° with lowest surface free energy of 4.68 mJ/m² by different functional nanofilms on their surfaces. Alteration of wettability from hydrophilic to hydrophobic and super-hydrophobic resulted from their low surface free energy and surface morphology with micro- and nano-rough structures. The corrosion behaviors from potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) show that the super-hydrophobic nanofilm has higher corrosion resistance and stability in 0.1 mol/L NaCl solution and lower corrosion current density (I_corr) with R_ct increasing two orders of magnitude of 16,500 Ω·cm² compared to that obtained for blank of 485 Ω·cm².     

Anticorrosion behavior of ultrafine-grained Al-26?wt% Si alloy fabricated by ECAP

Ultrafine-grained (UFG) Al-26 wt% Si alloy was obtained through multipass equal-channel angular pressing (EACP) procedure and subsequently tested in 3.5 wt% NaCl solution for the evaluation of electrochemical corrosion. The results show that the ECAPed alloy with increased number of pressing passes obtain lower mass-loss ratios, nobler E _corr and E _pit, lower I _corr values, and higher anode polarization. The improved corrosion resistance of the ECAPed alloy results from the homogeneous UFG structure with the breakage of brittle large primary silicon crystals, which contributes to a higher pitting resistance. The oxidation product with improved adhesion force and protection efficacy can be formed with greater ease on UFG alloys. It implies that grain refinement through severe-plastic-deformation can enhance anticorrosion behavior of hypereutectic Al–Si alloys, besides the well-known strengthening and toughening effects.     

Influence of glyoxal on localized corrosion of austenitic stainless steel in spring water

This paper presents the research regarding the influence of glyoxal on electrochemical and corrosion behaviour of austenitic stainless steel in water. For this purpose, model solutions containing glyoxal in water in concentrations ranging from 0.1 to 1 % were prepared. Spring water was used as control electrolyte. From the potentiostatic polarisation data (using the standard three‐electrode system), the corrosion current (i_corr), corrosion potential (E_corr) and polarisation resistance (R_p) were calculated. The research included also the conductivity, total dissolved soils, salinity, resistivity and pH, absolute potential, and relative potential of model solutions. The presence of glyoxal at the highest concentration of 1 % in the water solution has accelerating effect on corrosion.     

Effect of Y on the bio-corrosion behavior of extruded Mg–Zn–Mn alloy in Hank's solution

The bio-corrosion properties of Mg–Zn–Mn alloys with and without Y in Hank's solution at 37 °C were investigated by using electrochemical test and electrochemical impedance spectra (EIS). The results of open circuit potential (OCP) and polarization tests indicated that Y could reduce the cathodic current density. A passivative stage appeared in the Tafel curve of the Y containing magnesium alloy, indicating that a passivative film was formed on the surface of the Y containing magnesium alloy. EIS results showed that the Y containing alloy had higher charge transfer resistance and film resistance, but lower double layer capacity than the alloy without the Y element. The surface reaction product identification by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed that the surface corrosion products were hydroxide and phosphate (Mg₃Ca₃(PO₄)₄) for Mg–Zn–Mn alloy and phosphate (MgNaPO₄) for the Y containing Mg–Zn–Mn alloys. The XPS results also showed that a Y₂O₃ protective film was formed on the surface of the Y containing magnesium alloy which contributed mainly to the low cathodic current density and the high resistance.     

Corrosion behavior of SiC p /6061 Al metal matrix composites in chloride solutions

The corrosion behavior of silicon carbide particulates-aluminum metal matrix composites was studied in chloride solution by means of electrochemical techniques, scanning electron microscope (SEM), transmission electron microscope (TEM) and optical microscope. The materials under investigation were compocasting processed 6061 Al reinforced with increasing amounts of SiC particulates. Electrochemical tests such as potentiostatic polarization were done in 0.1 kmol·m^–3 NaCl solutions that were aerated and deaerated to observe overall corrosion behavior. In addition, pit morphology was observed after immersion tests. It was seen that the pitting potentials did not vary greatly or show definite trends in relation to the amounts of SiC _p reinforcement. However, the degree of corrosion increased with increasing SiC _p content; probably mainly due to galvanic couple. No intermetallics layer was found at the SiC _p /Al interface. Based on pitting potentials of Al-Si alloys, a pitting process around SiC particulate was proposed.Abbreviations SiC _p (silicon carbide particulates) - SiC _f (silicon carbide fibers) - SiC _w (silicon carbide whiskers) - E_pit (pitting potential) - E_prot (protection potential) - E _corr (corrosion potential) - i _galv (galvanic current density) - E _galv (galvanic potential)     

Spark plasma sintering behaviour of commercially pure titanium micro-alloyed with Ta-Ru

ABSTRACT

Spark plasma sintering (SPS) technology was used to consolidate Ti-Ta-Ru powders and the effects of sintering parameters on the densification, corrosion and wear performance of the sintered compacts were investigated. Results showed that addition of Ta with small amount of Ru had significant influence on densification, hardness and corrosion behavior of the sintered alloy. When 9 vol.% and 1 vol.% Ru were added, the sintered density and hardness were 92.07% and 330 HV_0.1 respectively. Furthermore, the addition of tantalum and ruthenium improve the corrosion and wear behaviours of Ti with a significant effect on the corrosion potential, E_corr, and corrosion current density, I_corr, in 1?M HCl solution. The COF trend decreases upon the addition of Ta-Ru with relative improvement in wear resistance in Ti-10Ta and Ti-9Ta-1Ru as compared with commercially pure Ti. This decrease in COF is more gradual which may be attributed to the solid solution hardening offered by Ta and Ru in the matrix.     

The influence of SiC particles on the corrosion resistance of electroless,Cu–P composite coating in 1 M HCl

The present paper aims to compare the corrosion resistance of the electroless Cu–P–SiC with Cu–P composite coating on carbon steel in 1 M HCl solution by the weight loss, potentiodynamic polarisation and electrochemical impedance spectroscopic (EIS) techniques. The study reveals that, the corrosion current density (I_corr) and the double layer capacitance (C_dl) values decrease, the charge transfer resistance (R_ct) and inhibition of efficiencies (IE %) increase with the incorporation of SiC particles in the Cu–P matrix indicating the improvement in corrosion resistance.     

Microbiologically influenced corrosion of titanium caused by aerobic marine bacterium Pseudomonas aeruginosa

Microbiologically influenced corrosion (MIC) is a big threat to the strength and safety of many metallic materials used in different environments throughout the world. The metabolites and bioactivity of the microorganisms cause severe deterioration on the metals. In this study, MIC of pure titanium (Ti) was studied in the presence of a highly corrosive aerobic marine bacterium Pseudomonas aeruginosa. The results obtained from electrochemical test showed that Ti was corrosion resistant in the abiotic culture medium after 14 d, while the increased corrosion current density (i_corr) obtained from polarization curves and the decreased charge transfer resistance (R_ct) from electrochemical impedance spectroscopy (EIS) indicated the accelerated corrosion of Ti caused by P. aeruginosa biofilm. For further confirmation of the above results, the surface of Ti was investigated using scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and X-ray photoelectron spectroscopy (XPS). According to the XPS results, TiO₂ was formed in both abiotic and biotic conditions, while unstable oxide Ti₂O₃ was detected in the presence of P. aeruginosa, leading to the defects in the passive film and localized corrosion. Pitting corrosion was investigated with the help of CLSM, and the largest pit depth found on Ti surface immersed in P. aeruginosa was 1.2 μm. Ti was not immune to MIC caused by P. aeruginosa.