Structure Of Passive Film Research Articles

Structure of passivation films on sintered titanium-molybdenum alloys: Y.Hayashi et al. (Kyushu University, Fukuoka, Japan.) J. Jpn Soc. Powder/Powder Metall., vol 46, no 3, 1999, 277–282. (In Japanese.)

Structure of passivation films on sintered titanium-molybdenum alloys: Y.Hayashi et al. (Kyushu University, Fukuoka, Japan.) J. Jpn Soc. Powder/Powder Metall., vol 46, no 3, 1999, 277–282. (In Japanese.)

Critical hydrogen charging conditions for martensite transformation and surface cracking in type 304 stainless steel

The hydrogen embrittlement susceptibility of two precipitation hardened nickel-based alloys was studied. Conventional slow strain rate testing results are compared against data obtained from a modified Rising Step Loading Test with interrupted hydrogen charging to determine the role of defects in the passive layer caused by local straining. The results obtained in these tests, show that the elongation to failure for most cases was independent of the testing methodology. XPS and EIS studies indicate changes to the passive film structure caused by CP. These results imply that during hydrogen charging, the passive film is partially dissolved facilitating hydrogen uptake.

Soft x-ray absorption spectroscopy study of electrochemically formed passive layers on AISI 304 and 316L stainless steels

The structure and composition of passive films electrochemically formed on AISI 304 and 316L stainless steels in a chloride-containing solution have been studied by soft x-ray absorption spectroscopy. Soft x-ray absorption spectra were taken at the oxygen 1s edge and at the transition metals (Cr, Fe, Ni) 2p edges, making it possible to determine the main contributions to the passive film's composition. The soft x-ray absorption spectra at the Cr 2p edges indicate that in all cases the passive film is mainly formed by Cr2O3. Spectra at the Fe and Ni 2p edges exhibit no significant contribution of Ni and Fe oxides to the passive layer composition. However, differences in spectral shape with respect to metallic Ni and Fe suggest the presence of a small amount of hydroxides, which is maximum for the AISI 304 stainless steel polarized at the lowest scan rate. The spectra at the O 1s edges confirm the results obtained at the transition metal edges.

In Situ Scanning Tunneling Microscope Study of the Passivation of Cu(111)

In situ scanning tunneling microscopy has been used to study the nucleation and growth mechanisms and the structure of passive films formed on Cu(111) surfaces in 0.1 M borate buffer solution (pH 9.3). A surface topography characterized by terraces with monoatomic steps is obtained after potentiodynamic reduction down to −1.12 V/standard hydrogen electrode (SHE), of the electropolished surface exposed to air. The formation of a single passive layer at 0.03 V/SHE proceeds first by a roughening of the steps assigned to a locally blocked step flow process due to a competition between dissolution and preferential nucleation of the oxide at the steps. The observed oxide nuclei are 2–3 nm wide and about one atomic plane high. This process leads to the complete coverage of the terraces by a grain‐like structure of the oxide film. The initial terrace topography is completely altered. Thickening of this oxide layer leads to unstable scanning tunneling microscope imaging, despite the presence of a subband in the bandgap of the oxide. Duplex passive films, , produced at 0.98 V/SHE, are characterized by a grain‐like structure with no detectable evidence of crystallinity. The lateral size of the grains ranges from 2 to 5 nm. The measured height difference is ≤1.5 nm. Stable imaging occurs via electron tunneling in the conduction band of the passive film. A metal surface topography can be recovered by potentiodynamic reduction of the oxide film down to −0.92 V/SHE. The smallest terraces are eliminated by step coalescence in these oxidation/reduction treatments, which leads to steeper surface profiles. © 1999 The Electrochemical Society. All rights reserved.

Ｔｉ‐Ｍｏ系焼結合金に形成される不働態被膜の構造

Ｔｉ‐Ｍｏ系焼結合金に形成される不働態被膜の構造

X‐Ray Photoelectron Spectroscopy and Scanning Tunneling Microscopy Study of Passive Films Formed on (100) Fe‐18Cr‐13Ni Single‐Crystal Surfaces

X‐ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) were combined to investigate the thickness, chemical composition, and structure of passive films formed in 0.5 M on (100)Fe‐18Cr‐13Ni. The XPS measurements show that aging under polarization at +500 mV/SHE causes a dehydration reaction of the outer chromium hydroxide layer of the passive film. This reaction results in a thickening of the mixed Cr(III) and Fe(III) inner oxide layer and increases the enrichment. This reaction consumes, in addition to chromium hydroxide of the outer layer, chromium from the metallic phase underneath the passive film. Only traces of nickel (hydroxide) are detected in the passive film, whereas Ni enrichment is observed in the alloy underneath the passive film. High‐resolution STM images reveal that aging under polarization causes a crystallization of the inner oxide layer in epitaxy with the substrate. The epitaxial relationship is with . The crystallization proceeds with a faster kinetics than on (110) Fe‐22Cr in the same conditions. The crystallization rate is modified by the presence of Ni in the alloy, which is enriched in the metallic phase underneath the film and slows down the formation of in the inner part of the film. This favors a more complete process of crystallization. Aging under polarization is beneficial to the further stability of the passive film in air.

Corrosion-resistant amorphous aluminum alloys and structure of passive films

The corrosion behavior of amorphous Al-Ti-Ni, Al-Cr-Ti and Al-Cr-Mo alloys in 1 M HCl and that of amorphous Al-Ti-Mg alloys in chloride containing neutral solution is investigated. The amorphous Al-Ti-Ni, Al-Ti-Cr and Al-Cr-Mo alloys are passivated spontaneously even in 1 M HCl and show lower corrosion rates and higher pitting potentials in comparison with Al-Ti and Al-Cr binary alloys. Al-Ti-Mg alloys containing relatively low concentration of magnesium possess a better resistance against pitting corrosion. X-ray photoelectron spectroscopy measurement reveals that titanium and chromium are enriched in the passive films formed on Al-Ti-Ni, Al-Ti-Mg and Al-Cr-Mo alloys, respectively. Angle-resolved XPS measurements were performed in order to characterize the in-depth distribution of constituents in the passive films formed on amorphous Al-Ti-Ni, Al-Ti-Mg and Al-Cr-Mo alloys in the passive films of which, passivating elements are enriched.

Structure and composition of passive titanium oxide films

The thickness and composition of several kinds of titanium oxide films formed on a titanium substrate were determined by surface analysis techniques: X-ray photoelectron spectroscopy, Rutherford back scattering, X-ray diffraction and atomic force microscopy. Most titanium oxide samples were prepared by anodisation, using a galvanostatic procedure. The films were shown to be composed of an amorphous TiO 2 outer layer (10–20 nm thick) and an intermediate TiO x layer, in contact with the TiO 2 layer and the metallic substrate. The outer layer is sensitive to the environment: its thickness usually decreases with ageing in a corrosive solution. A stabilisation procedure was proposed in order to improve its ability to withstand corrosion.

Silicon quantum well as passivation barrier on GaAs surface

Synchrotron radiation Si L-edge absorption spectroscopy is used to study the band structure of thin silicon passivation films on GaAs(100) surface. The measurements show that the Si L-edge, which measures the conduction band minimum (CBM), is shifted drastically to a higher energy as the Si film thickness is reduced to below 2.5 nm. This shift in the CBM is found to scale with the Si layer thickness L as 1/L1.7, indicating that the electronic states within the Si layer are quantum confined. Within a confined quantum well, the energy levels of all states including localized gap states will be shifted to higher energy. Quantum confinement effects in the thin Si layer is found responsible for its successful use for passivation of GaAs surfaces.

X‐Ray Photoelectron Spectroscopic Examinations of Electrochemically Formed Passive Layers on Ni‐Cr Alloys

The structure and composition of passive films electrochemically formed on Ni‐Cr alloys in 1 M NaOH and 0.5 M has been studied with x‐ray photoelectron spectroscopy. The passivation potential was varied within the passive range up to the transpassive range and the time of passivation from 10 ms to 1000 s. With angular‐resolved x‐ray photoelectron spectroscopy, the passive film was found to have a two‐layer structure with an inner oxide part formed directly at the metal surface and an outer hydroxide part in contact with the electrolyte. The metal surface underneath is enriched in Ni compared to the metal bulk composition. Except for potentials approaching the transpassive range, the hydroxide layer forms the dominant part of the passive film. Above 0.3 V in NaOH and 1.2 V in , Cr(VI) ions are found within the hydroxide layer. The maximum thickness of the passive layer is about 6 nm in NaOH and 3.5 nm in . The growth and the pronounced changes of the composition of the passive layers reflect the electrochemical behavior of the pure metal components. The results are in agreement with the thermodynamic data.

ChemInform Abstract: Electronic Structure of Passive Films Formed on Molybdenum‐Containing Ferritic Stainless Steels.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Electronic Structure of Passive Films Formed on Molybdenum‐Containing Ferritic Stainless Steels

The effect of molybdenum on the electronic structure of the passive films formed on ferritic (Fe‐Cr and Fe‐Cr‐Mo) stainless steels is examined by capacitance and photoelectrochemical measurements. The capacitance study is supported by a mathematical analysis of the Schottky barrier developed at the semiconductor‐electrolyte interface in the case of a semiconductor with multiple bulk electronic states in the bandgap. The numerical simulations, based on the more general Mott‐Schottky relation proposed, are in good agreement with the experimental results. It can be concluded that the capacitance behavior of the passive films is related to the contributions of a shallow donor level very close to the conduction band and a deep donor level at about 0.4 eV below the conduction band. The addition of molybdenum decreases the donor density of the deep level. Photoeffects observed for subbandgap photon energies reveal that this deep donor level behaves like a trapping electronic state situated in the space‐charge zone of the passive film. On the basis of the results obtained, the crystallographic factors determining the nature of the donor species are discussed.

XPS and STM Study of Passive Films Formed on Fe‐22Cr(110) Single‐Crystal Surfaces

X‐ray photoelectron spectroscopy and ex situ scanning tunneling microscopy measurements have been combined to investigate the thickness, the chemical composition, and the structure of passive films formed in 0.5 M on Fe‐22Cr(110). Aging under polarization at +500 mV/SHE causes a dehydration (anodic) reaction of the outer chromium hydroxide layer of the passive film. This anodic reaction results in a thickening of the inner mixed Cr(III) and Fe(III) oxide layer enriched in . It also causes a coalescence of the oxide nuclei of the passive film and a crystallization of the inner oxide layer in epitaxy with the substrate. The epitaxial relationship is with three different azimuthal orientations. Aging under polarization is beneficial to the stability of the passive film in air and prevents the dehydration reaction of the hydroxide coupled to an oxidation reaction of iron which are observed on freshly passivated surfaces. Polarization at +700 mV/SHE activates the dissolution of substrate terrace atoms whereas polarization at +300 or +500 mV/SHE activates the dissolution of substrate atoms at step edges only.

An X‐Ray Absorption Near‐Edge Spectroscopic Study of the Structure of Passive Films on Amorphous Al‐Fe‐Ce Alloys

We report on the composition and structure of passive oxide films of melt‐spun ribbons of amorphous (x = 3, 5, and 7) alloys using x‐ray absorption near‐edge structure (XANES) spectroscopy. The passive films were formed in an aerated solution of 0.9 weight percent (w/o) NaCl at constant potential in the passive region at −0.5 V vs. a saturated calomel electrode (SCE) for 60 min. The oxidation state of Fe in the passive films of these alloys is mainly +3, such as in and /or . Cerium in the passive film of alloy is present mainly in the +3 oxidation state as and/or , with only a small fraction as . In the passive film of alloy it is present in the +3 and +4 oxidation states (as and/or and ) while in alloy the passive film contains cerium in the +4 oxidation state as . The fact that the passive film may consist of mixed oxide phases containing Al, Fe, and Ce cannot be ruled out.

Influence of intrinsic electric fields on passive film chemistry and structure

Alloys and their oxides are a very important class of materials on which modern society depends. Yet, today we do not have an adequate fundamental physical-chemical model of how oxides evolve on alloys under oxidizing conditions. In a research program examining the parameters, temperature and O 2 activity, which control the driving potential for alloy oxidation, a new extended model for alloy oxidation has been developed that allows for prediction of the resulting passive layer structures.

The electronic structure of passive films formed on stainless steels

The capacitance behaviour of passive films formed on austenitic type 304 stainless steel and Fe-Cr alloys (0 ≤ Cr ≤ 30%) was studied using the Mott-Schottky approach. The results obtained show that the films behave as n-type and p-type semiconductors in the potential range above and below the flat band potential, respectively. This behaviour is assumed to be the consequence of the semiconducting properties of the iron oxide and chromium oxide regions which compose the passive films. This interpretation is supported by Auger analysis which enables the establishment of a direct relationship between the chemical composition of the two oxide regions and the Mott-Schottky plots. Based on the results obtained a model of the electronic structure of the passive films formed on stainless steels is proposed.

Atomic Structure and Mechanical Behaviour of Passive Film Formed on Stainless Steels

Atomic Structure and Mechanical Behaviour of Passive Film Formed on Stainless Steels

A Model for Oxide Film Evolution on Alloys and Prediction of Resulting Layer Structure

Alloys and their oxides are a very important class of materials on which modern society depends. Yet, today we do not have an adequate fundamental physical-chemical model of how oxides evolve on alloys under oxidizing conditions. This physical chemical understanding will effect our ability to design a wide range of materials from electronic devices to the improved protective oxide films on alloys. The fundamental progress, in both physics and chemistry, made on several critical questions, •What interface(s) control alloy oxidation and how? •What parameters provide the driving potential for oxidation? •How does this potential respond to temperature (T), pressure (P) and compositional changes? will be discussed. Progress on these questions have allowed models to be proposed to predict alloy oxidation behavior under any set of conditions. These models are already providing some predictive power in how the oxide overlayer and passive film structure develop. By using surface studies of the oxidation behavior of the following alloys and their thin films: Cu-Mn, Ag-Mn, Ni-Ti, Ni-Zr, Ti-Cu and Ti-Al, we have been able to delineate the factors which are most important to the oxide formation process and provide insight into the prediction of oxide layer structures. These will be illustrated with actual experimental results on selected alloys.

In situ synchrotron radiation X-ray techniques for studies of corrosion and protection

The importance of synchrotron radiation X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) as probes for the characterisation of corrosion products, surface films and protective layers is emphasised. In many cases, in situ studies may be carried out to elucidate structural information about the surface of an electrode in the presence of an intact surface film and the electrolyte under controlled potential conditions. The versatility of these X-ray techniques in corrosion and protection is illustrated by the following systems (and X-ray techniques): the phase composition of phosphate coatings on carbon steel ( ex situ XRD), phase transformation of lead dioxide films in 1 M H 2SO 4 during potential cycling ( in situ XRD) and the structure of passive films on iron in 0.1 M NaClO 4 at constant potential ( in situ XAS).

Electronic Properties and Defect Structure of Fe and Fe-Cr Passive Films

Abstract The electronic properties of passive films on Fe-Cr alloys were determined by the photoelectrochemical technique. Measurement of the flat band potential for the passive films on the different alloys indicated that the film is doped increasingly n-type as the Cr concentration in the base alloy is increased. This doping is due to a Cr oxide with Cr in the 4+ or 6+ valence state. The concentration of this doping species increases as the concentration of Cr in the Fe-Cr alloy is increased. The n-type doping has the effect of decreasing the number of oxygen vacancies in the Fe-Cr passive film. Since oxygen vacancies are the mobile point defect species in the Fe-Cr passive film, decreasing this species decreases the oxygen vacancy flux and ultimately the passive film growth kinetics. The contribution of film dissolution and cation transmission through the passive film was also analyzed. Film dissolution was shown to be the major contribution to the passive current density.