Electrochemical behavior of Ni-Al-Fe alloys in simulated human body solution

An investigation about the corrosion resistance of Ni-Al-Fe intermetallic alloys in simulated human body fluid environments has been carried out using electrochemical techniques. Tested alloys included 57 (wt%) Ni-(20 to 30) Al-(12 to 23) Fe using the Hank's solution because the high corrosion resistance provided by protective Al₂O₃ external layer. For comparison, AISI 316L type stainless steel has also been used. Electrochemical techniques included potentiodynamic polarization curves, electrochemical impedance spectroscopy, and electrochemical noise measurements. The different techniques have shown that these alloys showed a similar or higher corrosion resistance than conventional AISI 316L type stainless steel, and this corrosion resistance decreased as the Al content in the alloy increased. The alloys were susceptible to pitting type of corrosion on the interdendritic Ni-rich phases.     

A zirconia-polyester glycol coating on differently pretreated AISI 316L stainless steel: corrosion behavior in chloride solution

The effect of zirconia and zirconia-polyester glycol hybrid coatings on the corrosion resistance of mechanically polished or anodized AISI 316 stainless steel (316L), was studied by potentiodynamic polarization and electrochemical impedance spectroscopy in 0.1 M NaCl and scanning electron microscope and atomic force microscopy examinations. The deposition of zirconia coatings was achieved by the sol–gel technique by immersing the samples in either the inorganic polymer or the organic–inorganic polymer mixture. From potentiodynamic and impedance measurements, the grade of protection is reduced with the exposure time to the electrolyte, which is mainly associated with lost of film adhesion and, consequently, detachment from the metal substrate. However, the uncoated anodized sample revealed an unexpected corrosion behavior; the anodic film formed during anodizing readily increased the corrosion resistance of the 316L stainless steel in 0.1 M NaCl, revealing a considerable reduction in the corrosion current density and an increase in the pitting potential.     

The effect of hydrostatic extrusion on resistance of 316 austenitic stainless steel to pit nucleation

The resistance to pit nucleation of an austenitic 316 stainless steel was investigated in an aggressive environment containing Cl⁻ ions in the as-received state, and after a heavy deformation by hydrostatic extrusion (HE) leading to nanostructurisation.XRD and TEM were used to examine structural changes introduced by HE treatment. The corrosion resistance of 316 stainless steel was investigated by potentiodynamic polarization in a borate buffer + 0.1 M NaCl. The results show that the HE processed material exhibits an extended stable passivity region by about 0.4 V or more, as compared to that of the as-received one.     

The electrochemical synthesis of poly(o-phenylenediamine) on stainless steel and its corrosion protection ability in 3.5 % NaCl solution

In this study, electrochemical synthesis of poly(o-phenylenediamine) (PoPDA) on 316L stainless steel and its corrosion inhibition effect were studied. Electropolymerization of o-phenylenediamine (oPDA) was carried out by a potentiodynamic method using 0.5 M H₂SO₄ solution containing 0.05 M oPDA monomer. The corrosion protection ability of the PoPDA in 3.5 % NaCl was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, and change of open circuit potential with immersion time (E_OCP ? t). The results showed that PoPDA acted as a protective layer on stainless steel against corrosion in 3.5 % NaCl solution.     

Assessment of corrosion resistance of surface-coated galvanized steel by analysis of the AC impedance spectra measured on the salt-spray-tested specimen

In the present work, corrosion resistance of surface-coated galvanized steel was quantitatively determined by an analysis of the alternating current (AC) impedance spectra measured on the salt-spray-tested specimen. To evaluate the corrosion resistance of the surface-coated galvanized steel, AC impedance spectroscopy was performed on the salt-spray-tested specimen previously exposed to salt-sprayed corrosive environment. From the analysis of the impedance spectra, the area fraction transient of white rust θ ₂(t) was theoretically derived from the equivalent circuit equation by using two fitting parameters. The values of the two fitting parameters were determined by fitting the empirical transient equations to the area fraction of the resin coating layer and to the total resistance obtained from the impedance spectra measured, respectively. From the analyses of θ ₂(t) for four kinds of surface-coated galvanized steels with various resin coating layers, it is indicated that as the values of the two fitting parameters decrease in the order of CP, GI, OD and OM (commercial trade names) specimens, the corrosion resistance increases in that order as well. Furthermore, from the quantitative comparison of the two fitting parameters with the polarization resistance of the upper resin coating layer R _p determined from the potentiodynamic polarization curve, it is suggested that the two fitting parameters decrease in value as well with increasing R _p.     

Impact of sensitization on dissolution process of AISI 304 stainless steel during intergranular corrosion evaluated using DEIS technique

The paper presents the results of instantaneous impedance changes measurements vs. reactivation potential performed by means of dynamic electrochemical impedance spectroscopy (DEIS) technique for AISI 304 stainless steel (SS) dissolution process during intergranular corrosion (IG) in 0.5 M H₂SO₄ + 0.01 M KSCN solution. With the use of DEIS method, it was possible to estimate dynamic changes of the examined system’s impedance in conditions of proceeding IG process. Furthermore, the paper proposes an alternative way of evaluating AISI 304 stainless steel dissolution rate during intergranular corrosion based on approximation to theory of iron dissolution in sulfuric acid medium. Simultaneously, based on the DEIS measurements, information about the degree of sensitization of the examined material were obtained. Performed research revealed the advantages of the DEIS technique over the classical double-loop electrochemical potentiokinetic reactivation tests when investigating intergranular corrosion process.     

EIS monitoring study of the early microbiologically influenced corrosion of AISI 304L stainless steel condenser tubes in freshwater

This study examined the early stages of tarnishing of American Iron Steel Institute (AISI) 304L austenitic stainless steel (SS) condenser tubes in contact with running freshwater from the Tagus River in Spain. The immersion time of the tubes was 569 days. Tarnishing originated by biofouling was assessed using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses in conjunction with argon ion sputtering. The EIS diagrams showed a semicircle that was better defined as the experimental time increased, indicating the decreasing tarnishing resistance of the immersed specimens. The EIS results were validated using Kramers–Kronig relationships. SEM micrographs of biofouling indicated that the number of microorganisms on the SS surfaces increased with immersion time. According to the XPS spectra, the main elements deposited on the tarnished AISI 304L SS layer were calcium, phosphorus, and nitrogen. A mechanism of biofouling and microbiologically influenced corrosion behavior of AISI 304L SS condenser tubes in freshwater is proposed.     

Corrosion sous contrainte de mono et polycristaux d'aciers inoxydables austenitiques en milieu MgCl2: Recherche d'ameliorations du comportement

The fractographic results of stress corrosion cracking of a 316L type austenitic stainless steel in MgCl₂ are in good agreement with the corrosion enhanced plasticity model. Based on the ideas of this model, the research of an improvement of the SCC resistance is attempted. It is shown that a cyclic prehardening can delay the initiation of the first microcracks and decrease the crack propagation velocity.     

EIS and XPS studies on passive film of AISI 304 stainless steel in dilute sulfuric acid solution

Electrochemical impedance spectroscopy and XPS studies on AISI 304 stainless steel in naturally aerated 0.5 M H₂SO₄ solution were carried out at room temperature. The valuable model of the metal/solution interphase was established, and the reliable equivalent electrical circuits in the solution were presented. The analysis of the chemical composition of passive film on AISI 304 stainless steel was carried out by XPS. The passive film of AISI 304 stainless steel is composed of oxyhydroxides, Fe₂O_3, FeO, Cr₂O₃, NiO, sulfate, sulfite, and sulfide (FeS, NiS). It is reported that the ferrous sulfide film formed on AISI 304 stainless steel in the dilute sulfuric acid solution. The possible process in which sulfuric acid is reduced to sulfite and sulfide is proposed. The galvanic interaction of sulfide inclusions with the base alloy is introduced. Copyright © 2011 John Wiley & Sons, Ltd.     

Electrochemical study on corrosion process characteristics of the high-strength low-alloy steels in NaHSO3 solution

Electrochemical methods were used to study the characteristics of corrosion process for the high-strength low-alloy steel and carbon steel used as a huge oil storage tank in NaHSO₃ solution. The polarization curve results show that both steel samples take place in active solution, and the high-strength low-alloy (HSLA) steel has higher i _corr value than carbon steel, which is due to the small grain size that provides high density of active sites for preferential attack. The electrochemical impedance spectroscopy (EIS) results make known that the corrosion process presents two stages. In the first 136 h, one-time constant in EIS diagrams can be shown. Both steels have similar corrosion resistance due to the combination effects of the grain size and microstructure. After 240 h of immersion, a complete passive film forms on the specimen surface, and two-time constants can be shown in EIS diagram. The HSLA steel exhibited improved corrosion resistance when compared with the carbon steel, which is due to the effect of the shape Fe₃C in microstructure and the deposition of FeSO₄ on the electrode surface. The scanning electrode microscopy analyses show that both steels take place in homogenous corrosion, and the carbon steel shows higher surface roughness and many Fe₃C residues. XRD results show that both steels have similar phase constitutes of corrosion products.     

Bioactive and Protective Sol-Gel Coatings on Metals for Orthopaedic Prostheses

The aim of this work has been the preparation and evaluation of sol-gel coatings for clinical applications. Research was focussed in the development of highly corrosion resistant and/or bioactive sol-gel coatings onto AISI 316L stainless steel. Hybrid SiO₂ sol-gel coatings inhibited corrosion and Fe diffusion, although no signal of bioactivity was detected. The inclusion of Ca- and P-alcoxides in the sol composition did not promote bioactivity. Bioactive coatings were obtained from suspensions prepared by adding glass (CaO·SiO₂·P₂O₅) particles to an hybrid organic-inorganic SiO₂ sol. The dissolution of glass particles promoted in vitro induction of apatite along with a slight reduction in the corrosion resistance of coated pieces. By combining an inner SiO₂ hybrid film acting as barrier against corrosion with an outer coating containing bioactive glass particles, a significant improvement in the electrochemical behaviour was observed. This double-layered coating showed in vitro signals of bioactivity, and preliminary in vivo tests gave promising results.     

Nanoindentation studies and modeling of surface layers on austenitic stainless steels by extreme electrochemical treatments

The nanoindentation studies were performed on two austenitic stainless steels, AISI 304L and 316L. The steel samples have undergone two different electrochemical treatments, standard (EP50) and a high‐current density electropolishing (EP1000). Firstly, the observations of the steels' surfaces were done with the optic images of the AISI 304L and 316L SS after these two treatments displayed. Presented in the paper results have shown clearly that the high‐current density close to 1000 A/dm² allows for obtaining the passive nanolayers with other mechanical properties than those obtained after a standard electropolishing (EP50). The prediction of these results has been confirmed by the preliminary XPS studies allowing for modeling of the steels' surface layers. The main finding of the study is revealing a new method of electrochemical treatment (EP1000) allowing to obtain the reduced Young's modulus of the stainless steels lower than that obtained after EP50. This feature is of high importance regarding the use of these steels as biomaterials. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of Sintering Temperature on the Corrosion and Wear Behavior of Protective SiO2-Based Sol-Gel Coatings

Sol-gel hybrid organic-inorganic and inorganic SiO₂-based protective coatings with and without added 3 m glass particles were developed and tested for their corrosion and wear behavior of an stainless steel substrate (AISI316L). The corrosion resistance greatly increases by incorporating glass particles in the sols. The incorporation of particles in the coatings allows the synthesis of thicker crack-free coatings. On the other hand, the corrosion resistance increases for coatings with a higher organic content obtained at lower sintering temperature. These coatings are also highly stable in saline aqueous solutions. However, the wear resistance is badly affected by the hybrid character of the SiO₂ matrix. The optimum coating process in terms of corrosion and wear resistance, appears to be a hybrid system with a dense SiO₂ network achieved at intermediate sintering temperatures.     

高温高压喷射湍流区中X70管线钢CO2腐蚀电化学特征

采用高温高压环路喷射装置并结合腐蚀微电极技术, 开展了湍流区中X70 管线钢CO₂腐蚀实验. 利用扫描电镜对不同实验时间的试样表面腐蚀产物微观形貌进行了观察和分析, 并进行了湍流区原位电化学测试和分析. 结果表明, 湍流区中X70 钢的CO₂腐蚀电化学特征与其表面所覆盖腐蚀产物膜层变化密切相关. 实验12 h内, 湍流区中X70钢表面从最初的基体与腐蚀产物共存, 转变为由疏松且不完整的膜层覆盖的特征. 实验12 h 后, 试样表面出现内外两层腐蚀产物膜, 内层膜堆垛致密, 外层膜疏松多孔, 同时湍流区中高切应力导致外层腐蚀产物脱落, 材料表面逐渐被完整致密的内层膜覆盖, 这是腐蚀速率持续下降的主要原因. 电化学结果表明, 实验12 h 内, 湍流区中X70 钢的腐蚀电位E_corr和线性极化电阻R_p不断下降; 电化学阻抗谱由高频容抗弧、中频容抗弧和低频感抗弧组成, 膜层电阻R_f缓慢增加, 电荷传递电阻R_t不断下降, 双电层电容C_dl和膜层电容C_f迅速下降; 12 h后, 腐蚀产物膜层对基体材料保护性随喷射时间延长逐渐增强, E_corr和R_p逐渐增大, 电化学阻抗谱中低频感抗弧逐渐收缩并在48 h 时消失, 最后转变为双容抗特征, R_f、R_t和C_dl随时间迅速增大, C_f趋于稳定.     

Determination of nickel in finished product alloys by instrumental neutron activation analysis and spectrophotometry

Nickel contents in different finished product alloys were determined using a k ₀-based internal monostandard instrumental neutron activation analysis (IM-INAA) method. Five stainless steels (SS) and three high nickel alloys were analyzed by IM-INAA. BCS CRMs 225/1 (low alloy steel) and 466 (austenitic SS) and NIST SRM 247 (high Ni alloy) were analyzed to evaluate the accuracy of the method. The results of CRMs and SS were found to be in good agreement with certified or specified values. The Ni contents in the high nickel alloys were also determined by relative method of NAA for verification. Nickel contents in BCS CRM 466 and SS 316M were determined by UV–Visible spectrophotometry and the values were found to be in good agreement with IM-INAA results.     

Cerium hybrid silica coatings on stainless steel AISI 304 substrate

AISI 304 Stainless Steel is widely used in different industrial fields because of its mechanical and corrosion properties. However, its tendency to corrosion in presence of halide ions limits the applications. One strategy to improve the corrosion resistance is the use of coatings barriers containing corrosion inhibitors in their formulation. The lanthanides present attractive green and corrosion properties for the substitution of chromates, which are the most common substances used as corrosion protection. However, these compounds are highly toxic, and an intense effort is being undertaken to replace them. Cerium is a good alternative because of its relatively low cost and abundance. It fulfils the basics requirements for being considered an alternative inhibitor: the ions form insoluble hydroxides and they present low toxicity. Inorganic and hybrid sol-gel coatings have been developed to increase the corrosion resistance of metals and they provide an excellent vehicle for the incorporation of secondary phases including particles and metal ions as cerium ions. The aim of this work was to study the influence of the incorporation of cerium ions in hybrid silica sol-gel coatings deposited on AISI 304 stainless steel as substrate as a potential replacement of chromate treatments. This system should combine the barrier protection effect of silica coating with the corrosion inhibitor effect of the cerium ions inside the coatings. After 7 days of immersion in NaCl, coated substrates showed lower current densities than the bare steel, although the coatings produced from Ce (III) salts experience a slight weakening in time and those obtained from Ce (IV) chemicals evidence an enhance in the coating performance, probably due to the plugging of corrosion products in the defective areas of the film.     

Adsorption and inhibitive properties of aminobiphenyl and its Schiff base on mild steel corrosion in 0.5 M HCl medium

Electrochemical measurements were performed to investigate the effectiveness and adsorption behaviour of aminobiphenyl (Aph) and 2-(3-hydroxybenzylideneamino)biphenyl (Aph-S), as corrosion inhibitors for mild steel (MS) in 0.5 M HCl solution. Potentiodynamic polarization, linear polarization resistance (LP) and electrochemical impedance spectroscopy (EIS) techniques were applied to study the metal corrosion behaviour in the absence and presence of different concentrations of Aph and Aph-S. In order to gain more information about adsorption mechanism the AC impedance technique was used to evaluate the potential of zero charge (PZC) from polarization resistance (R_p) versus voltage (E) plot. Potentiodynamic polarization measurements showed that Aph act as cathodic type inhibitor where as Aph-S act mixed type. The inhibition efficiency (IE%) increases with increasing concentration of compounds and reached 92.6% for Aph and 97.2% for Aph-S at 5 × 10⁻³ M. Double layer capacitance (C_dl) and polarization resistance (R_p) values are derived from Nyquist plots obtained from AC impedance studies. The experimental data fit Langmuir isotherm for both Aph and Aph-S, and from the adsorption isotherm some thermodynamic data for the adsorption processes are calculated and discussed. The effect of exposure time on the corrosion behaviour of mild steel in the absence and presence of inhibitor over 168 h was also studied.     

Electrochemical response of natural and induced passivation of high strength duplex stainless steels in alkaline media

The passivation of two high strength duplex stainless steels (HSSS) was investigated in alkaline solutions simulating the pore solution of concrete by the growth of natural and induced passive films. Induced passive films were generated both by cyclic voltammetry and by chronoamperometry. Natural passive films were spontaneously grown by the immersion of the steel in the alkaline electrolyte. These passive layers were characterised by electrochemical impedance spectroscopy, corrosion current density (i _corr) and corrosion potential (E _corr) monitoring. The effect of significant parameters, such as the pH in the HSSS/alkaline solution interface, the composition of the duplex stainless steels and the ageing of the passive layer, on the electrochemical performance of both induced and spontaneously grown passive films has been analysed. The increase of alkalinity highly influences the electrochemical performance of the passive film by promoting the formation of a passive layer with a less resistant electrochemical response. The electrochemical behaviour of the passive layer is also affected by the alloying elements like Mo or Ni. Both natural and induced passive films show similar electrochemical trend with respect to significant parameters such as the pH and the composition of the steel. The ageing of the spontaneously grown passive layer promotes a higher resistive electrochemical response which might be related to the enrichment of the passive layer in non-conducting (or semi-conducting) oxides.     

Study on the anodic behavior of AISI E52100 steel in two fluorine-containing ionic liquids

Ionic liquids have a number of excellent applications such as a kind of promising lubricants which have attracted considerable attention. In this work, we investigated corrosion properties which were found in the use of ILs formed by a 1-butyl-3-methylimidazolium cation and a fluorine-containing anion as lubricants of AISI E52100 steel. Electrochemical tests were used to study the anodic behavior of AISI E52100 steel, and surface analysis was performed to study the surface morphology. The electrochemical results showed that increasing temperature accelerates corrosion of the alloy in two kinds of ionic liquids. The data obtained from polarization curves and EIS suggested that the anodic process of the E52100 steel showed generally an active dissolution and increasing temperature can accelerate the corrosion of the steel. At the same time, the main difference as revealed by SEM–EDS plots was that localized corrosion with some irregular etch pits occurred in [Bmim]BF₄ ionic liquid; however, a product layer covered uniformly on the surface of metal in [Bmim]PF₆. The results of XPS spectrum indicated that the corrosion products formed on the surface of the AISI E52100 steel are mainly composed of FeO, Fe₂O₃, FeF₂ and FeF₃.

     

Corrosion Behavior of Biocompatible Stainless Steels in Physiological Medium for Non‐invasive Diagnosis of Small Fiber Neuropathies Applications

A non‐invasive device based on measurements of electrochemical skin conductance can detect small fiber neuropathy, a sweat gland dysfunction implicated in several diseases. The measurement is related to sweat composition and notably to chloride concentration. To optimize the electrode material, in vitro experiments are performed in mimetic sweat solutions. This work reports on the resistance to pitting corrosion of biocompatible stainless steels (AISI 304L, AISI 430, AISI 430T, D2205) in sweat mimicking electrolyte at pH 7 with variable chloride concentration, to determine the most sensitive material to sweat composition. AISI 430 is promising due to its high sensitivity to chloride concentration variations.