Electrochemical behaviour of Mo‐containing austenitic stainless steels in buffer solution

The effect of pH on the electrochemical behavior of austenitic stainless steels in naturally aerated and nitrogen‐deaerated buffer solutions has been studied. Potentiodynamic and ac impedance techniques were used. The results indicate that corrosion current (I_corr) decreases with pH. By examining the impedance data for the seven tested steels under various conditions, it seems that the total resistance (R_T) value is a suitable indication parameter for explaining the role of molybdenum and the other supplementary alloying additions (Ni, N, Cu and Mn) on the passive film behaviors as a function of pH of the forming solutions. As a general trend, the R_T values for all steels tended to be lower in the basic buffer than in the acidic solutions.     

Effect of pH on the formation-dissolution processes of anodic films on bismuth

Interrupted polarization measurements indicate that among Na₂SO₄, buffer (pH 7) and NaOH, the most passivating anodic film is formed on bismuth in the buffer solution. Under opencircuit conditions, film growth occurs on the metal surface in buffer solutions of pH 1.81 to 11.25. The rate of growth increases with decrease in pH. The passive metal undergoes dissolution in buffer solutions according to a zero-order mechanism; the most effective pH values for film dissolution lie between 8 and 10. The results indicate the simultaneous importance of the anion type and pH of the electrolyte in determining anodic film stability.     

含H2S的NaCl溶液中溶解氧对PH13-8Mo钢腐蚀性能的影响

为研究新型马氏体沉淀硬化不锈钢PH13-8Mo在含饱和H_2S的NaCl溶液中的腐蚀行为,利用极化曲线、电化学阻抗谱等电化学测试和浸泡实验相结合的方法,通过扫描电子显微镜(SEM)和X射线光电子能谱分析技术(XPS),观察了该高强钢在含H_2S的除氧和不除氧的NaCl溶液中的腐蚀形貌,并对其腐蚀产物的成分进行了分析.结果表明:在除氧的NaCl溶液中,阳极极化曲线的形状发生了明显的变化,电化学阻抗谱的容抗弧的幅值也较未除氧的溶液中变小;在除氧的NaCl溶液中浸泡7 d后,由于H_2S水解后的S~(2-)或HS~-离子侵入到钝化膜的内部,并与钝化膜或金属基体发生反应,使得试样表面发生全面腐蚀,腐蚀产物主要为Fe、Cr、Ni、Mo的氧化物和硫化物;而在未除氧的NaCl溶液中浸泡后,试样表面仅发生局部腐蚀.     

On structural and high temperature electrochemical properties of ZrO2 thin film coating on Zr metal produced by carbonate melt

Melt of NaCO₃ can favor oxidation of Zr to form ZrO₂ thin film on Zr surface, which is used to make Zr/ZrO₂ oxidation/reduction electrode of pH sensor for testing elevated temperature aqueous solutions. Using SEM, EPMA, XPS, EXAFS and HRTEM, we found that ZrO₂ film is tightness and solid with 20 μm thickness composed by nanometer-sized monoclinic crystals. Zr/ZrO₂ interface is characterized of zoning structure according to topography and chemical composition in five zones: oxygen-rich ZrO₂, ZrO₂, oxygen-rich Zr metal, oxygen-bearing Zr and Zr from outmost to center. Melt oxidation process of Zr involved oxidation time, air and temperature. The air is important effect on structural and electrochemical properties of ZrO₂ thin film for making elevate temperature electrochemical sensor. If oxygen air largely presented in carbonate melting process, ZrO₂ thin film is not tightness and not for oxidation/reduction electrode.     

Study of electrical and micro-structural properties of high-κ gate dielectric stacks deposited using pulse laser deposition for MOS capacitor applications

The electrical properties of hafnium oxide (HfO₂) gate dielectric as a metal–oxide–semiconductor (MOS) capacitor structure deposited using pulse laser deposition (PLD) technique at optimum substrate temperatures in an oxygen ambient gas are investigated. The film thickness and microstructure are examined using ellipsometer and atomic force microscope (AFM), respectively to see the effect of substrate temperatures on the device properties. The electrical J–V, C–V characteristics of the dielectric films are investigated employing Al–HfO₂–Si MOS capacitor structure. The important parameters like leakage current density, flat-band voltage (V_fb) and oxide-charge density (Q_ox) for MOS capacitors are extracted and investigated for optimum substrate temperature. Further, electrical studies of these MOS capacitors have been carried out by incorporating La₂O₃ into HfO₂ to fabricate HfO₂/La₂O₃ dielectric stacks at an optimized substrate temperature of 800 °C using a PLD deposition technique under oxygen ambient. These Al–HfO₂–La₂O₃–Si dielectric stacks MOS capacitor structure are found to possess better electrical properties than that of HfO₂ based MOS capacitors using the PLD deposition technique.     

Surface analysis and electrochemical behavior of Ti–20Zr alloy in simulated physiological fluids

An advanced Ti–20Zr alloy was obtained by double vacuum melting in a semi-levitation furnace with cold crucible. The alloy shows fully lamellar α + β microstructure. Cyclic potentiodynamic polarization curves revealed that the alloy passivated easier, more rapid than Ti, having a more stable passive film in Ringer solutions of different pH values, simulating severe functional conditions of an implant. In neutral and alkaline Ringer solutions, the alloy passive film improved its properties in time (1500 h) by the deposition of protective hydroxyapatite, as was demonstrated by XPS, SEM, EDX, Raman and FT-IR measurements. Alloy presented lower corrosion rates and higher polarization resistances (from linear polarization measurements) than those of Ti (tens of times) proving a more resistant passive film. Alloy open circuit potentials had more electropositive values in comparison with Ti and tended to nobler values in time, which denote better passive state and its enhancement in time, due to the new depositions from the physiological solutions. Nyquist and Bode spectra depicted a more protective passive film on the alloy surface than on Ti surface. The passive film is formed by two layers: an inner barrier layer and an outer porous layer. An electric equivalent circuit with two time constants was modeled.     

Electrochemical repairing of pitted 18-8 stainless steel

In order to clarify the reaction essential of electrochemical repairing method, which was developed to repair the passive film on pits and suppress pitting corrosion on passive 18-8 stainless steel (18-8ss) after occurrence of pitting, the electrochemical characteristics, morphology and composition of passive film after different treatments were investigated by electrochemical impedance spectroscopy (EIS), Cyclic Voltammogram (CV), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The dynamic behavior of reactions occurred at lower potential (E _L = −200 mV) and higher potential (E _H = 1000 mV) of alternating electric filed was discussed respectively and the correlation between those reactions was analyzed. Based on above results, reaction essence of electrochemical repairing for pitted 18-8ss electrode was proposed: during the periodic action of alternating current, recycle reactions take place on the surface and the pit area of pitted electrode, i.e., metal dissolves into cations (occurs at E _L and form hydrous hydroxide, the hydrous hydroxide turns into metal oxide (occurs at E _H), a ‘bipolar mode’ passive film forms and Cr content is increased in repaired passive film. At the pit area, enclosed state of the pit is destroyed by the perturbing effect of alternating current in 1.0 M H₂S0₄ solution, thus the pit area will be repaired through above-mentioned process.     

Effect of hafnium addition on the electrical properties of indium zinc oxide thin film transistors

This study reports the performance and stability of hafnium-indium zinc oxide (HfInZnO) thin film transistors (TFTs) with thermally grown SiO2. The HfInZnO channel layer was deposited at room temperature by a co-sputtering system. We examined the effects of hafnium addition on the X-ray photoelectron spectroscopy properties and on the electrical characteristics of the TFTs varying the concentration of the added hafnium. We found that the transistor on-off currents were greatly influenced by the composition of hafnium addition, which suppressed the formation of oxygen vacancies. The field-effect mobility of optimized HfInZnO TFT was 1.34 cm² V⁻¹ s⁻¹, along with an on-off current ratio of 10⁸ and a threshold voltage of 4.54 V. We also investigated the effects of bias stress on HfInZnO TFTs with passivated and non-passivated layers. The threshold voltage change in the passivated device after positive gate bias stress was lower than that in the non-passivated device. This result indicates that HfInZnO TFTs are sensitive to the ambient conditions of the back surface.     

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.     

Investigation of the Passivity of Tin in Neutral Media by cyclic galvanostatic polarization

In order to throw more light on the passivity of Sn in neutral media, two types of measurements have been performed in aerated unstirred KCl, Na₂SO₄ solutions (both 0.1, 0.5, 1.0, and 2.0 M) and in phosphate buffer (pH 6.6–6.7 for all), namely open-circuit measurements and cyclic galvanostatic polarization. The direction of change of the open-circuit potential with time in both KCl an Na₂SO₄ solutions indicates film repair and passivation (positive shift in potential). Addition of either KCl or Na₂SO₄ to phosphate buffer produces two opposite effects: (i) a positive potential shift in the case of chloride, and (ii) a negative potential shift in the case of sulphate (film destruction and activation). The behaviour of cyclic galvanostatic results (at 0.8 mA/cm²) differs considerably in phosphate buffer than in chloride and sulphate solutions. Thus, while in phosphate buffer the anodic half-cycle shows a passivation arrest and an anodic peak, the same half-cycle is manifested by a plateau in both chloride and sulphate solutions. Moreover, two cathodic arrests have been detected in the cathodic half-cycle in phosphate buffer, while three cathodic arrests are observed in the same half-cycle in chloride and sulphate solutions. The presence of cathodic arrests in chloride and sulphate solutions indicates the reduction of oxidized species originally formed during the anodic plateau. Data are compiled for the potential and duration of the arrests and plateaus in all three solutions, and the effects of electrolyte concentration and the number of successive cycles on these parameters are discussed. Although the combination of electrochemical results and thermodynamic calculations can only serve as an approximate indication to the possible occurrence of stoichiometric Sn(IV), Sn(II) oxides and hydroxides in the passive film such as in the case of phosphate buffer, yet the exact composition of the film can only be ascertained by surface analysis (eg XPS). However, electrochemical and thermodynamic means have been helpful in the present work in predicting the possible occurrence of species other than oxides and hydroxides (such as incorporated anions and oxy-salts) in the anode film formed in chloride and sulphate solutions in agreement with our previous potentiodynamic work. Although surface analysis can indicate the presence of elements and their oxidation states, yet no work has been cited in the literature on the calculations relevant to the presence of oxysalts in the film, and hence electrochemical and thermodynamic means are more helpful in this respect.     

模拟混凝土孔隙液中钢筋电化学腐蚀行为及pH值的影响作用

应用极化曲线法和电化学阻抗技术,结合扫描电子显微镜方法,测试钢筋在模拟混凝土孔隙液中的钝化与去钝化行为,以及溶液pH值对钢筋电化学腐蚀行为的影响作用.结果表明,钢筋在pH值为12.50的模拟液中处于钝态,随着溶液pH值的降低,钢筋的耐蚀性下降.钢筋表面去钝化发生腐蚀的临界PH值在11.12-11.05范围内.     

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.     

Enhancement of corrosion resistance of a biomedical grade 316LVM stainless steel by potentiodynamic cyclic polarization

The paper discusses the results on the use of a simple cyclic linear potentiodynamic polarization technique as a method of improving corrosion properties of passive oxide films formed on a biomedical-grade 316LVM stainless steel surface in phosphate buffer. The results demonstrate that the modification of 316LVM surface by cyclic potentiodynamic polarization between the potential of hydrogen and oxygen evolution results in the formation of a passive film that offers significantly increased corrosion resistance (both pitting and general) when compared to the naturally grown passive film. The effect of number of cycles and anodic potential limit on the resulting corrosion properties is discussed. The capacitance analysis demonstrates that the major difference between the electrochemically formed and naturally grown passive film is in the type of semiconductivity in the potential region where pitting on the unmodified surface occurs. The XPS analysis shows that this is due to the presence of Cr(VI)-species in the electrochemically formed passive film, which contribute to the increased density of metal vacancies, and thus to the increased pitting corrosion resistance of the passive film.     

Dosimetry aspects of hafnium oxide metal-oxide-semiconductor (MOS) capacitor

This paper reports the investigation of hafnium oxide based metal-oxide-semiconductor capacitor for the detection of gamma radiation. The fabrication of the device involved deposition of hafnium oxide thin film on n-type Si wafer by electron beam evaporation technique followed by deposition of aluminum metal layer by thermal evaporation process. The device was irradiated incrementally to the cumulative dose of 480 Gy by gamma rays of 1.25 MeV (Co-60). The change in accumulation capacitance, effective oxide charge and interface trap density with cumulative gamma dose was examined at room temperature. As the creation of oxide charge and change in oxide capacitance are well correlated with radiation dose, the device can be useful for radiation dosimetry.     

EIS study of passivation of austenitic and duplex stainless steels reinforcements in simulated pore solutions

Stainless steel reinforcements have proved to be one of the most effective methods to guarantee the passivity of reinforced concrete structures exposed to highly chloride-contaminated atmospheres. In the present work, the corrosion behaviour of two traditional austenitic stainless steels (AISI 304 and 316L types), and one duplex type (2205) are compared with that of a low-nickel, much more economic, austenitic type (204Cu). Ribbed and ground bars of these four materials are studied in non-carbonated and carbonated, saturated Ca(OH)₂ solutions with different chloride contents, using electrochemical techniques. The low-frequency time constant represents the charge transfer resistance (R_t) in parallel with the double layer capacitance. The R_t value of the passive reinforcements seems to be related with the quality of the passive layer. R_t values increase with the immersion time in the testing solutions and decrease with the chloride content. Moreover, R_t tends to increase when the ribs of the bars are removed.     

Electrochemical behaviour of ion implanted Ti-6AI-4V in Ringer's solution

Abstract

The effect of ion implantation of various elements (C, N, O, Y, Hf, Pd, Ir, Pt, Au) with different energy–dose combinations on the electrochemical behaviour of the alloy Ti-6AI-4 V in Ringer's solution has been investigated using backscattering spectrometry and potentiodynamic polarisation measurements. After yttrium or iridium implantation, the rest potential was shifted in the positive direction. Non-implanted specimens and those implanted with carbon monoxide, carbon dioxide, hafnium, or noble metals were passive over a wide range of potentials. Implantation of carbon, nitrogen, or yttrium led to breakdown of the oxide film and pitting corrosion. The breakdown potentials decreased with increasing dose. Precipitates of TiC resulted in a more pronounced reduction of the breakdown potential than did TiN precipitates or continuous surface layers.     

Dissolution and repair of passive film on Cu-bearing 304L stainless steels immersed in H2SO4 solution

The antibacterial Cu-bearing 304L stainless steel is a new kind of structural and functional integrated metal material. In this work, evolution behavior of passive film of different heat treated Cu-bearing 304L stainless steel immersed in 0.5?M H₂SO₄ solution was investigated by using electrochemical measurements, atomic force microscopy (AFM) observation and X-ray photoelectron spectroscopy (XPS) analysis. The results show that the solution and aging treated samples have the similar polarization behaviors. The passive film impedance experiences an initial decrease within 7?days followed by a subsequent increase, while the defect density of passive film presents the opposite trend. Meanwhile, the evolution of surface morphology and the estimated thickness of the passive film confirm that it experiences initial dissolution and follow-up repair. Furthermore, the Cr³⁺ content in passive film undergoes sequential reduction to increase, however the variation tendency of Cu²⁺ content is just opposite, indicating that the content variation of Cr and Cu in passive film reflects the competitive process of film dissolution and repair. In addition, compared with solution treated samples, aged samples have a bigger i_corr value and the rougher passive film. This indicates that the passive film of solution treated steel is more compact and stable.     

Corrosion behaviour of β-Ti20Mo alloy in artificial saliva

To evaluate the potential of β-Ti20Mo alloy as a dental material, we tested its corrosion behaviour in artificial saliva in comparison to that of cp-Ti. Open-circuit potential (E_OC), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used as electrochemical methods to characterize the corrosion behaviour of Ti20Mo alloy and cp-Ti, respectively. Corrosion current and passive current densities obtained from the polarization curves showed low values indicating a typical passive behaviour for Ti20Mo alloy. The EIS technique enabled us to study the nature of the passive film formed on the binary Ti20Mo alloy at various imposed potentials. The Bode phase spectra obtained for Ti20Mo alloy in artificial saliva exhibited two-time constants at higher potential (0.5 V, 1.0 V), indicating a two-layer structure. According to our experimental measurements, Ti20Mo alloy appears to possess superior corrosion resistance to that of cp-Ti in artificial saliva.     

AM355不锈钢在酸性溶液中的腐蚀电化学行为

结合腐蚀形貌,通过极化曲线、交流阻抗谱(EIS)和莫特肖特基(MS)曲线的测定,分析了溶液pH值对AM355不锈钢腐蚀电化学行为的影响。结果表明:随溶液pH值的减小,腐蚀电位正移,腐蚀电流密度增大,致钝电位发生了正移,致钝电流密度、维钝电流密度增大。钝化膜由铬氧化物和铁氧化物组成,酸性增加使得铁氧化物施主浓度增大,钝化膜表面吸附氢离子电荷密度增加。钝化膜的厚度及其电阻随pH值的减小而减小,钝化膜更容易被破坏,酸性达到一定程度,钝化膜局部区域优先腐蚀。溶液pH值减小,AM355在溶液中保持自钝化性能降低,材料的腐蚀速率增加。