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Passive Film (passive + film)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

Influences of passivating elements on the corrosion and biocompatibility of super stainless steels

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2008
Young-Ran Yoo
Abstract Biometals need high corrosion resistance since metallic implants in the body should be biocompatible and metal ion release should be minimized. In this work, we designed three kinds of super stainless steel and adjusted the alloying elements to obtain different microstructures. Super stainless steels contain larger amounts of Cr, Mo, W, and N than commercial alloys. These elements play a very important role in localized corrosion and, thus, their effects can be represented by the "pitting resistance equivalent number (PREN)." This work focused on the behavior which can arise when the bare surface of an implant in the body is exposed during walking, heavy exercise, and so on. Among the experimental alloys examined herein, Alloy Al and 316L stainless steels were mildly cytotoxic, whereas the other super austenitic, duplex, and ferritic stainless steels were noncytotoxic. This behavior is primarily related to the passive current and pitting resistance of the alloys. When the PREN value was increased, the passivation behavior in simulated body solution was totally different from that in acidic chloride solution and, thus, the Cr2O3/Cr(OH)3 and [Metal oxide]/[Metal + Metal oxide] ratios of the passive film in the simulated body solution were larger than those in acidic chloride solution. Also, the critical current density in simulated body solution increased and, thus, active dissolution may induce metal ion release into the body when the PREN value and Ni content are increased. This behavior was closely related to the presence of EDTA in the simulated body solution. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source]

Monitoring the corrosion and remediation of reinforced concrete on-site: An alternative approach

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 4 2005
N. Birbilis
Abstract Difficulties associated with the interpretation of site data collected over long periods of time from commonly used electrochemical corrosion monitoring techniques often make it difficult to assess the corrosion of reinforcing steel. An alternative approach for the interpretation of data is proposed, based on a model of the quality of passive film upon the steel surface. This model leads to a representation of the corrosion state by means of the relationship, over a long period of time, of the corrosion potential and the logarithm of the Linear Polarization Resistance, since both are functions inter alia of corrosion rate. It is shown that for the reinforced concrete panels tested, data points representing this relationship closely fitted a family of results; allowing the development of a "monitoring control diagram", MCD. The MCD reveals that for a fixed geometry and experimental conditions, a relationship between the corrosion potential and polarization resistance of steel exists, facilitating a useful monitoring tool for assessment of both the corrosion and remediation of reinforced concrete structures. Particular emphasis is placed on the latter in this work. [source]

Characteristics of anodic coatings oxidized to different voltage on AZ91D Mg alloy by micro-arc oxidization technique

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2005
Y. Wang
Abstract With increasing applied voltage, three types of anodic coatings, passive film, micro-spark ceramic coating and spark ceramic coating were made by micro-arc oxidization (MAO) technique on AZ91D magnesium alloy in alkali-silicate solution. The structure, composition characteristics and the electrochemical properties of coatings were also studied with SEM, XRD and EIS (electrochemical impedance spectroscopy) technique, respectively. It is found that the electrochemical properties are closely related to the structure and composition characteristics of the anodic coatings. At the same time, the characteristics of the three types of anodic coatings differ significantly, among them, the micro-spark ceramic coating, prepared in the voltage range of 170~220V exhibits compact, homogeneous structure and highest corrosion-resistance. [source]

The wet corrosion of molybdenum thin film , Part II: Behavior at 85°C

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 9 2004
C. R. Tomachuk
Abstract In the past few years there has been increased interest in molybdenum thin films, which are commonly prepared by magnetron sputtering. There is a variety of novel applications of molybdenum such as, for example, components for soft X-ray optics based on Mo/Si multi-layers, the back contact in thin film solar cells, NO gas detection, and microelectronics. Molybdenum is, also, widely used as an alloying addition in stainless steels to facilitate the formation of the passive film and to improve resistance to pitting attack. Its corrosion behaviour is complex and many aspects still need to be clarified. During this study, the corrosion behaviour of the PVD-Mo thin film immersed in aerated sulfate and chloride solutions at 85°C was investigated with both polarization and electrochemical impedance spectroscopy (EIS) measurements. It is apparent that the Mo thin film exhibits increased susceptibility to corrosion in more alkaline environments. [source]

Initiation and propagation of stainless steel pitting corrosion under heat flux

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 12 2003
T. Pro
nichtrostender Stahl; Lochkorrosion; Wärmeübergang; Wärmefluss Abstract An effect of heat flux on initiation and propagation of pitting corrosion of austenitic stainless steel in chloride environment has been studied using electrochemical and exposure methods. The experiments were performed at constant surface temperature of 60°C and heat flux from , 15 to + 74 kW m,2. The presence of heat flux from metal to solution shifted the breakdown potential towards noble values and lowered the pit density, whereas the pit propagation rate increased. Presence of maximum heat flux caused, in comparison with isothermal conditions, increase of the breakdown potential by approx. 100 mV, reduction of pit density by 30% and increase of the average pit depth by 40%. The positive effect of heat flux from metal to solution was given mainly by improving the protective ability of the passive film, as the amount of oxygen available at the metal surface increased. With a smaller significance, the effect of intensified mass transfer, which made accumulation of the chloride ions on the surface more difficult, occurred. Entstehung und Fortschreiten der Lochkorrosion von nichtrostendem Stahl bei Wärmefluss Der Einfluss von Wärmefluss auf die Entstehung und das Fortschreiten der Lochkorrosion bei austenitischen nichtrostenden Stählen in chloridhaltiger Umgebung wurden unter Verwendung elektrochemischer Methoden und in Auslagerungsversuchen untersucht. Die Versuche wurden bei einer konstanten Oberflächentemperatur von 60°C und einem Wärmefluss von , 15 bis 74 kWm2 durchgeführt. Ein Wärmefluss vom Metall hin zur Lösung verschob das Durchbruchspotential hin zu edleren Werten, es verringerte sich die Lochdichte, während eine Zunahme der Lochbildungsrate erfolgte. Ein Maximum des Wärmeflusses bewirkte im Vergleich mit isothermen Bedingungen eine Zunahme des Potentials um ca. 100 mV, eine Verringerung der Lochdichte um 30% und eine Zunahme des Wertes für die Lochtiefe um 40%. Der positive Einfluss des Wärmeflusses in Richtung vom Metall zur Lösung ergab im wesentlichen eine Verbesserung der Schutzwirkung des Passivfilms, da sich die verfügbare Menge Sauerstoff an der Metalloberfläche erhöhte. Weniger signifikant war der Effekt eines erhöhen Stofftransportes, der eine Akkumulation von Chlorid-Ionen an der Oberfläche erschwerte. [source]

Comparison of the corrosion protection of mild steel by polypyrrole,phosphate and polypyrrole,tungstenate coatings

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008
M. G. Hosseini
Abstract The electrodeposition of polypyrrole,phosphate (PPy,P) and polypyrrole,tungstenate (PPy,W) on mild steel (MS) were achieved in an oxalic acid medium with cyclic voltammetry techniques. Adherent and homogeneous PPy,P and PPy,W films were obtained. The corrosion behavior of mild steel with phosphate (PPy,P) and tungstenate (PPy,W) composite coatings in 3.5% NaCl solutions were investigated through a potentiodynamic polarization technique, open-circuit potential,time curves, and electrochemical impedance spectroscopy (EIS). On the basis of a physical model for corrosion of mild steel composites, Zview (II) software was applied to the EIS to estimate the parameters of the proposed equivalent circuit. It was found that the PPy,W coatings could provide much better protection than the PPy,P and polypyrrole coatings. The effects of the phosphate and tungstenate process parameters on the morphology and structure of the passive films were investigated by scanning electron microscopy and electron dispersion X-ray analyses. The results reveal that the PPy,P and PPy,W coated electrodes offered a noticeable enhancement in protection against corrosion processes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Effects of Hf content and immersion time on electrochemical behavior of biomedical Ti-22Nb- xHf alloys in 0.9% NaCl solution

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 5 2009
B. L. Wang
Abstract The aim of this study was to investigate the effects of Hf content and immersion time on the electrochemical corrosion behavior of the Ti-22Nb- xHf (x,=,0, 2, 4, and 6 at%) alloy samples in 0.9% NaCl solution at 37,°C and neutral pH range, utilizing the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. From the polarization curves, all these alloys exhibited typical passive behavior, which was indicated by a wide passive region without the breakdown of the passive films and low corrosion current densities. In addition, the values of the corrosion current densities and passive current densities decreased with increase in the Hf content. The EIS results, fitted by RS(QPRP) model, exhibited capacitive behavior (high corrosion resistance) with phase angles closed to ,80° and high impedance values at low and medium frequencies, indicating the formation of a highly stable film on these alloys in the test solution. The resistance of the passive films improved with increase in the Hf content and immersion time. All these observations suggested a more noble electrochemical behavior of the Ti-22Nb- xHf alloys compared to the Ti-Nb binary alloy. [source]

Mechanical and corrosion behaviour of a Ti-Al-Nb alloy after deformation at elevated temperatures

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 12 2008
M. V. Popa
Abstract The mechanical properties of Ti6Al7Nb alloy deformed and heat treated at elevated temperatures were correlated with its microstructure and corrosion behaviour in Ringer (of different pH values: 2.49, 6.9 and 8.9) and Ringer,Brown solutions. Microstructural analysis revealed a Widmanstatten structure for the alloys deformed at 1100,°C (, field) and structure with , grains at 930,°C (,,+,, field). The thermo-mechanical processing improved the electrochemical behaviour of Ti6Al7Nb alloys, especially their passive state. Open circuit potential variations in time reflected more compact, stable, resistant passive films on the surface of the treated alloys. Open circuit potential gradients simulating the non-uniformities of pH along the implant surface have very low values that cannot generate galvanic corrosion. Corrosion rates and ion release are very much reduced. Impedance spectra were fitted with a two time-constants equivalent circuit for some alloys and with three time-constants equivalent circuit for other alloys. [source]