Electrochemical formation of highly pitting resistant passive films on a biomedical grade 316LVM stainless steel surface

The results discussed in the paper demonstrate that a significant improvement in pitting corrosion resistance of a biomedical grade 316LVM stainless steel can be achieved by electrochemically forming highly-protective passive oxide films on the material's surface, under cyclic potentiodynamic polarization conditions. The film formed in a sodium nitrate electrolyte is completely resistant to pitting corrosion in simulating physiological solutions even at high temperatures (60 °C), and after sterilization. The high pitting resistance of the electrochemically-formed films was explained on the basis of their semiconducting properties. Namely, the enrichment of the outer part of the electrochemically formed passive film with Cr(VI)-species results in a decrease in the density of oxygen vacancies, which act as pitting initiation sites, and their ‘replacement’ by metal vacancies formed by the electrochemical oxidation of Cr(III) to Cr(VI). In this configuration, the outer Cr(VI)-rich oxide layer behaves as cation selective, which results in the increased pitting corrosion resistance of the film. The simple electrochemical passivation technique discussed in the paper can be efficiently used to form highly pitting resistant passive films on 316LVM-built medical implant devices of any geometry.     

The effect of surface roughness on the efficiency of the cyclic potentiodynamic passivation (CPP) method in the improvement of general and pitting corrosion resistance of 316LVM stainless steel

The influence of surface roughness on the efficiency of a cyclic potentiodynamic passivation (CPP) method employed to increase the general and pitting corrosion resistance of 316LVM stainless steel was investigated. The results show that a decrease in surface roughness of both the surface on which the passive film was formed naturally and by the CPP method, results in an increase in general corrosion resistance of the material, while for the CPP-modified surface, a notable increase in pitting corrosion resistance was also observed. It was further demonstrated that the CPP method is highly effective in increasing the general and pitting corrosion resistance of 316LVM, and that its efficiency does not depend on the surface roughness.     

Effect of Cl- on the Properties of the Passive Films Formed on 316L Stainless Steel in Acidic Solution

The corrosion behavior of 316L stainless steel （31 6L SS） has been investigated in solutions containing various concentrations of chloride ions by using potentiodynamic polarization, capacitance measurement and Mott- Schottky relationship analysis （M-S）. The result indicates that passive currents change slightly with the addition of chloride ions. The pitting potential （Epit） decreases linearly with Iog[CI-]. Correspondingly, the point defect diffusion coefficient （Do） of the passive film increases linearly with increasing Iog[CI-]. The results also indicate that the pitting corrosion of 316L SS follows the adsorption mechanism in NaCI solution.     

高氮奥氏体不锈钢耐点蚀性能研究

目前产于高氮不锈钢的研究多集中于理论基础、制造工艺和力学性能等方面,有关耐蚀性方面的研究有限。通过循环极化、Mott-Schottky曲线以及电化学阻抗(EIS)等方法,研究了Cr23Mo1N奥氏体不锈钢(高氮钢,HNSS)和316L不锈钢在Cl-溶液中的耐点蚀性能。结果表明:与316L不锈钢相比,高氮钢具有更正的自腐蚀电位,更小的维钝电流密度。阻抗谱表明高氮钢的钝化膜比316L更加稳定,且电荷转移电阻更大。Mott-Schottky曲线表明高氮钢的点缺陷施主浓度比316L不锈钢低一个数量级,钝化膜的绝缘性更好。循环极化曲线表明高氮钢的点蚀敏感性更小,钝化膜的自修复能力更强,耐蚀性能更加优越。     

铁氧化菌作用下316L不锈钢点蚀电化学特性的研究

采用电化学测量、交流阻抗技术、扫描电镜观察和能谱分析等实验方法,研究了316L不锈钢在铁氧化菌(IOB)溶液中的腐蚀电化学行为,分析了炼油厂冷却水系统微生物腐蚀的特征及机制,结果表明,在含有IOB溶液中的自腐蚀电位(Ecorr)、点蚀电位(Epit)和极化电阻(Rp)均随浸泡时间的增加呈现出降-升-降的变化趋势;在含有IOB溶液中的腐蚀速率均大于在无菌溶液中;IOB的生长代谢活动及其生物膜的完整性和致密性影响了316L不锈钢表面的腐蚀过程,使不锈钢表面的钝化膜层腐蚀破坏程度增加,加速了316L不锈钢的点蚀.     

Pitting initiation of 316L stainless steel in the media of sulfate-reducing and iron-oxidizing bacteria

Pitting corrosion behavior of stainless steel 316L in the presence of aerobic and anaerobic bacteria isolated from cooling water system in oil refinery was investigated using open circuit potential measurement, electrochemically impedance spectroscopy, scanning electron microscopy examinations, and energy dispersive spectrum analysis. The results show the corrosion potential (E _cor) and polarization resistance (R _p) decrease in the presence of sulfate-reducing bacteria (SRB), iron-oxidizing bacteria (IOB), and a combination of SRB and IOB, in comparison with those observed in the sterile medium for the same exposure time. The presence of SRB demonstrated higher corrosion rates than IOB. The combination of SRB and IOB created the highest corrosion rate. The metabolic activity of bacteria and the integrality and compactness of biofilm influenced the pitting corrosion process, increased the corrosion damage degree of the passive film, and accelerated the pitting corrosion. It is suggested that SRB and IOB in influencing the pitting corrosion of 316L SS is highlighted. The text was submitted by the authors in English.     

Corrosion behavior and passive film chemistry of 216L stainless steel in sulphuric acid

Corrosion behavior and chemical structure of the passive film of a newly developed 200 series austenitic stainless steel (216L) were studied in sulfuric acid (H₂SO₄) and compared with 316L. From potentiodynamic polarization studies it was found that the corrosion behavior of 216L closely follows that of 316L. The breakdown of passivity was evaluated by addition of sodium chloride (NaCl). The immersion tests revealed that the corrosion rate of 216L in various concentrations of H₂SO₄ at ambient temperature is equivalent to 316L. X-ray photoelectron spectroscopy (XPS) analysis of the passive film formed on 216L revealed enrichment of Cr ions on the surface while Mo and N compounds were also present. Ni and Mn ions were conspicuous by their absence in the passive film.     

Electrochemical and analytical investigation of passive films formed on stainless steels in alkaline media

Passive films were grown in potentiodynamic mode, by cyclic voltammetry on AISI 316 and AISI 304 stainless steels. The composition of these films was investigated by X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour and the chemical composition of the passive films formed by cyclic voltammetry were compared to those of films grown under natural conditions (by immersion at open circuit potential, OCP) in alkaline solutions simulating concrete. The study included the effect of pH of the electrolyte and the effect of the presence of chloride ions.The XPS results revealed important changes in the passive film composition, which becomes enriched in chromium and depleted in magnetite as the pH decreases. On the other hand, the presence of chlorides promotes a more oxidised passive layer. The XPS results also showed relevant differences on the composition of the oxide layers for the films formed under cyclic voltammetry and/or under OCP.     

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.     

Electrochemical properties of 316L stainless steel with culturing L929 fibroblasts.

Potentiodynamic polarization and impedance tests were carried out on 316L stainless steel with culturing murine fibroblast L929 cells to elucidate the corrosion behaviour of 316L steel with L929 cells and to understand the electrochemical interface between 316L steel and cells, respectively. Potential step test was carried out on 316L steel with type I collagen coating and culturing L929 cells to compare the effects of collagen and L929 cells. The open-circuit potential of 316L steel slightly shifted in a negative manner and passive current density increased with cells, indicating a decrease in the protective ability of passive oxide film. The pitting potential decreased with cells, indicating a decrease in the pitting corrosion resistance. In addition, a decrease in diffusivity at the interface was indicated from the decrease in the cathodic current density and the increase in the diffusion resistance parameter in the impedance test. The anodic peak current in the potential step test decreased with cells and collagen. Consequently, the corrosion resistance of 316L steel decreases with L929 cells. In addition, collagen coating would provide an environment for anodic reaction similar to that with culturing cells.     

Corrosion and stress corrosion cracking behavior of 316L austenitic stainless steel in high H2S–CO2–Cl− environment

In oil and gas production environments, H₂S and Cl^? can coordinate to cause pitting or stress corrosion cracking (SCC) of stainless steels. There has been limited work conducted on corrosion and SCC of autenitic stainless steels in high H₂S–CO₂–Cl^? environments. In this paper, by four-point bending test method and scanning electron microscopy analysis, SCC of 316L steel was investigated under high H₂S–CO₂ pressures with 150,000 ppm Cl^? at 60 °C. The effect of high H₂S–CO₂ pressure was discussed. The results indicated that the higher H₂S–CO₂ pressure can accelerate anodic dissolution process, deteriorate passive films, and aggravate SCC sensitivity. Using cyclic potentiodynamic polarization measurements, the corrosion behavior of 316L steel was studied in high H₂S–CO₂–Cl^? environments. The effect of pH on pitting corrosion was discussed. Lower pH can promote both cathodic and anodic actions on 316L steel and facilitate passive film breakdown.     

几种超级不锈钢在模拟烟气脱硫环境中的点蚀行为

目前,针对904L,254s Mo和2507等几种主要备选超级不锈钢在烟气脱硫环境中的耐点蚀性能缺乏系统研究。在温度分别为20、40、70℃的死亡绿液溶液中,利用循环伏安曲线和扫描电镜(SEM)法,对316不锈钢和超级不锈钢904L、254s Mo及2507的极化行为和点蚀形貌进行了研究。结果表明:在该环境中,升高温度可降低4种不锈钢表面钝化膜稳定性并提高其点蚀敏感性;在不同温度环境下,316不锈钢均有严重的点蚀现象发生,而254s Mo和2507不锈钢表面均无明显点蚀迹象;在20℃时,904L不锈钢表面无明显点蚀迹象,40℃时,其表面出现典型的点蚀形貌,但点蚀坑尺寸较小,在70℃的高温下,其点蚀坑尺寸明显增大,点蚀损伤严重;254s Mo和2507均适合作烟气脱硫设备材料,而316、904L在该环境中需谨慎使用。     

土壤环境中钢的杂散电流腐蚀研究

杂散电流可以造成金属的电解腐蚀侵害,在实验室模拟装置中,采用动电位扫描和恒电流极化法模拟杂散电流,研究了其对土壤环境中钢材的电解腐蚀行为,表征了其腐蚀产物及其表面钝化膜的形貌,探讨了腐蚀机理。结果表明,A3、16Mn和X70钢在土壤环境中的动电位扫描极化过程变化趋势基本相同;在恒电流阳极极化反应初期钢发生阳极溶解过程,待反应达到一定程度后,金属电极表面生成钝化膜,阳极极化电压发生突跃,钝化膜的生成与溶解交替过程造成阳极极化电压的振荡。     

Enhancement of corrosion protection efficiency of iron by poly(aniline-co-amino-naphthol-sulphonic acid) nanowires coating in highly acidic medium

Nanowires of copolymers film based on aniline and 1-amino-2-naphthol-4-sulphonic acid were electrochemically synthesized on the iron electrode by cyclic voltammetry using oxalic acid as a supporting electrolyte. Protective properties of copolymer film on the iron surface in 1.0 M HCl solution was investigated by chronoamperometry, potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results showed that the copolymer film showed the significant shifting in the corrosion potential and greater charge transfer resistance. Moreover, the copolymer showed the larger degree of surface coverage onto the iron surface, reflecting the higher protection for corrosion of the iron in acidic medium. In addition, the film constitutes a physical as well as a chemical barrier layer due to the presence of -OH and -NH groups in ANSA unit, which provides passivity protection in polymer coatings. The mechanism of corrosion protection of iron by these copolymers was investigated by surface morphology and EIS techniques. In addition, by using scanning electron microscopy, the effect of morphology of copolymer on corrosion protection of metal was investigated.     

Pitting Corrosion Behaviour of Monel-400 Alloy in Chloride Solutions

1-IntroductionPittingcorrosionisthemostdestructiveformamongthedifferentformsoflocalizedcorrosionofmetals.Thebreakdownofthepassivefilmbyag-gressiveionssuchaschlorideionscanleadtohighpenetrationrates.Copper-nickelalloysarewidelyusedascorrosionresistantmaterialsinmarineengineering.Theircor-rosionratesdecreasesharplywithincresingNicon-tent.AseriesofCu-Nialloyshavebeenwidely.tudi.d[1~12]innaturalseawaterandinNaClsolu-tionsusingdifferentelectrochemicalmethods.Con-tradictoryresultshavebeenobtained…     

亚硝酸钙阻锈剂对钢筋钝化膜的影响

为深入揭示亚硝酸盐阻锈剂提高钢筋混凝土结构耐久性的机理,采用动电位极化技术、X射线光电子能谱(XPS)和原子力显微镜(AFM)研究了亚硝酸钙阻锈剂对钢筋表面生成的钝化膜的影响。动电位极化研究结果表明:未添加阻锈剂时,钢筋发生点蚀的临界氯离子浓度在0.05~0.06 mol/L之间,添加亚硝酸钙阻锈剂后,钢筋发生点蚀的临界浓度增大至0.18~0.20 mol/L,表明亚硝酸钙阻锈剂提高了钢筋表面钝化膜的抗点蚀能力。X射线光电子能谱的研究结果表明:钢筋表面生成的钝化膜的成分均是由铁的氧化物(Fe_(ox))和铁的氢氧化物(Fe_(hydrox))组成,亚硝酸钙阻锈剂降低了钝化膜中Fe_(hydrox)的含量。原子力显微镜的研究结果表明:亚硝酸钙阻锈剂的添加使得钝化膜的表面更加光滑平整。     

温度对X80管线钢在0.5mol/L Na_2CO_3+1.0mol/L NaHCO_3溶液中电化学腐蚀性能的影响

目前,有关温度对CO_3~(2-)-HCO_3~-环境下X80管线钢腐蚀行为的影响规律尚无统一的认识。为了探究高强度钢在不同温度的0.5 mol/L Na_2CO_3+1.0 mol/L NaHCO_3溶液中的腐蚀行为,采用动电位极化、电化学阻抗技术,并结合金相显微镜观察研究了温度对X80管线钢在0.5 mol/L Na_2CO_3+1.0 mol/L NaHCO_3溶液中电化学腐蚀行为的影响规律,并通过Mott-Schottky曲线对不同温度下钝化膜的半导体性质进行探讨。结果表明:温度从30℃上升至75℃时,X80钢的点蚀电位和电荷转移电阻均逐渐减小,腐蚀现象越明显;当温度达到90℃时,点蚀电位和电荷转移电阻反而增大,腐蚀程度有所减缓;在0.3~0.7 V内,钝化膜呈现出典型的n型半导体特征;随着温度的升高,钝化膜内的施主电流密度和平带电位呈现先降低后增加的趋势,钝化膜稳定性先减弱后增强;在75~90℃之间存在一个临界温度,此温度下钝化膜的缺陷密度最大,保护性最差。     

Effect of chromium on the corrosion behavior of iron aluminides in thiosulfate-chloride solution

Aqueous corrosion characteristics of iron aluminides in thiosulfate-chloride solution were studied as a function of chromium addition. Four kinds of iron aluminides, namely, FA-61, FA-77, FA-72 and FA-78, were prepared by arc melting followed by thermomechanical treatment. The corrosion behavior in thiosulfate-chloride solution for the prepared alloys were investigated by electrochemical tests (potentiodynamic test, potentiostatic test and electrochemical impedance spectroscopy (EIS) measurement) and surface analyses. The results of the potentiodynamic test indicated that the breakdown potential increased with increasing Cr content. Cr additions were found to prevent passive film from undergoing pitting corrosion. In EIS measurement, the depression angle was inversely related to pitting resistance, and decreased with increasing chromium content. The SEM observations of the sample surfaces reveal the different forms of pit as a function of chromium content. The AES results give evidence that the thiosulfate ions are reduced on the metallic surface, which inhibits the repassivation process.     

Austenitizing treatment influence on the electrochemical corrosion behavior of 0.3C-14Cr-3Mo martensitic stainless steel

Effects of austenitizing treatment temperatures on aqueous corrosion properties of martensitic stainless steels were investigated by electrochemical tests (potentiodynamic test, potentiostatic test and electrochemical impedance spectroscopy), and surface analyses (optical microscopy and XRD). The results of potentiodynamic test revealed that the breakdown potential increased with the increased austenitizing temperature, indicating increased relative resistance to initiation of localized corrosion. EIS measurements showed that MSS3 (1030 °C) exhibits larger polarization resistance value than MSS1 (970 °C) and MSS2 (1000 °C) at passive and breakdown states. This was caused by decreasing the amount of Cr-rich M₂₃C₆ carbide which acts as preferential sites for pitting corrosion.     

Compatibility of ferritic and duplex stainless steels as implant materials: in vitro corrosion performance

The pitting corrosion, crevice corrosion and accelerated leaching of iron, chromium and nickel of super-ferritic and duplex stainless steels, and for effective comparison the presently used 316L stainless steel, have been studied in an artificial physiological solution (Hank's solution) by the potentiodynamic anodic polarization method. The results of the above studies have shown the new super-ferritic stainless steel to be immune to pitting and crevice corrosion attack. The pitting and crevice corrosion resistances of duplex stainless steel were found to be superior to those of the commonly used type 316L stainless steel implant materials. The accelerated leaching study conducted for the above alloys showed very little tendency for the leaching of metal ions when compared with 316L stainless steel. Thus the present study indicated that super-ferritic and duplex stainless steels can be adopted as implant materials due to their higher pitting and crevice corrosion resistance.