Protective Oxide Film Research Articles

Effects of chromium ion implantation voltage on the corrosion resistance and cytocompatibility of dual chromium and oxygen plasma-ion-implanted biodegradable magnesium

Magnesium is modified by chromium ion implantation at different voltages followed by oxygen ion implantation to improve the corrosion resistance and cytocompatibility. All the implanted samples exhibit improved corrosion resistance and the ones implanted at a lower voltage yield better results. The chromium-rich layer with chromium in the metallic state beneath the protective oxide film may undermine the electrochemical stability by inducing galvanic effects which lead to poorer corrosion resistance. Although dual Cr–O plasma immersion ion implantation promotes osteoblast adhesion and proliferation on the magnesium samples and produces a more favorable environment for osteoblast growth, optimal results require careful selection of the ion implantation voltage.

The localised corrosion of Mg alloy AZ31 in chloride containing electrolyte studied by a scanning vibrating electrode technique

The localised corrosion of AZ31 magnesium alloy immersed in chloride-containing electrolyte is characterised by the time-dependent evolution of dark, dendrite-like features comprising several mobile, focal anodes which are coupled with strong local cathodes situated at corroded regions left behind advancing anodes. The uncorroded, film-covered AZ31 surface is shown to be electrochemically inert in comparison. The number and intensity of the local anodes increase with time in proportion to the area of exposed local cathode, indicating that localised corrosion propagates under cathodic control. When the entirety of the exposed surface becomes affected by a network of dark dendritic corrosion features, the localised corrosion rate becomes time-independent although local anodes remain mobile local and traverse a cathodically activated corroded alloy surface. The source of this cathodic activation is proposed to be an enrichment in noble Al–Mn particles as anodic dissolution of the alpha Mg phase occurs. Localised corrosion rates are largely insensitive to pH in the 4≤pH≤10 range, but appreciably higher at pH 2 and markedly lower at pH values of 12 and above. The time taken for localised corrosion to initiate is independent of pH, an observation which appears inconsistent with the theories of elevated bulk pH acting to reinforce a protective (hydr)oxide film. Progressively lower post-breakdown local cathodic current density values are observed with increasing alkalinity, as a consequence of the pH dependence of the hydrogen evolution equilibrium potential.

Influence of Fe content on corrosion and hydrogen pick up behavior of Zr–2.5Nb pressure tube material

The effects of Fe addition in the range of 300–1250ppm in cold worked stress-relieved Zr–2.5Nb pressure tube on oxidation and hydrogen pick up behavior have been studied after 415°C steam autoclaving. Microstructure and micro-chemistry of second phase and precipitates were characterized using electron microscope. Addition of 800ppm Fe in Zr–2.5Nb alloy led to better oxidation resistance. With further addition of Fe no significant improvement of oxidation resistance was observed but hydrogen-pickup was found to increase. Zr–Nb–Fe bearing precipitates were observed in Zr–2.5Nb alloy containing 800ppm Fe. Further addition of Fe led to formation of Zr–Fe intermetallic. The chemical state of oxide has been determined by X-ray photo electron spectroscopy. Grazing Incidence X-ray Diffraction revealed that oxide in alloys with higher Fe, contained a higher fraction of tetragonal-Zirconia which is indicative of a protective oxide film and hence better oxidation resistance of the alloy.

Effects of Chromate and Molybdate Ions on Scratch Repassivation Behavior of Precipitation Hardened Aluminum Alloys

Scratch depassivation of AA2024-T351, AA7075-T6, and 99.999% aluminum in molybdate (MoO4 2-) and chromate (CrO4 2-) containing NaCl solutions was used to examine electrochemical repassivation kinetics over a range of potentials and inhibitor concentrations. Single frequency impedance measurements were taken in the capacitive region of frequency response. Capacitance measurements enabled the observation of the effects of inhibitor additions on oxide growth as protective oxide films formed on the scratched electrode surface. Chromate was found to suppress scratched electrode current transients at high potentials on both AA2024-T351 and AA7075-T6. Capacitance measurements revealed the rapid growth of a thick, protective oxide when concentrations as low 5 mM CrO4 2-E were in solution. Molybdate did not suppress transient current density in AA2024-T351 or AA7075-T6. In some cases the addition of molybdate increased the total charge passed after the scratch. However, capacitance measurements in the presence of molybdate indicate the rapid growth of a passive film.

(Invited) Metal Oxide Nano Film Characterization for CMP Optimization

This paper focuses on the planarization of metallic films in microelectronics manufacturing by CMP through investigation of metal oxide thin films forming as a result of the chemical component of the process. Tungsten planarization is discussed as a model to establish the role of metal oxide nano-films in achieving material removal through their formation characteristics during polishing. The findings indicate a protective oxide film formation on tungsten, which tends to nucleate at high concentrations of oxidizers and enables material removal through the interaction of nano-particles in the slurry with the surface oxide hillocks.

Formation of alumina films with nano‐dot structures by successive liquid phase deposition, anodizing, and substrate dissolution

A process based on successive anodizing, liquid phase deposition (LPD), re‐anodizing, and aluminium substrate dissolution to form alumina films with nano‐dot structures is demonstrated. Initially, a protective oxide film is formed on the aluminium surface to prevent further dissolution of the aluminium substrate during LPD processing. Because of heterogeneity in the protective oxide film, localized dissolution would otherwise occur under the film, resulting in pit formation during the LPD treatment. During re‐anodizing, these pits act as a mold for anodic oxide resembling a nano‐dot like structure. Optimization of LPD parameters, such as time and temperature, would make it possible to obtain alumina films with nano‐dot structures with sizes smaller than 1 µm. Alumina films with nano‐dot structures with hollow can be realized by controlling the LPD conditions. Copyright © 2013 John Wiley & Sons, Ltd.

Characterization of chemically modified thin films for optimization of metal CMP applications

ABSTRACTMetal CMP applications necessitate the formation of a protective oxide film in the presence of surface active agents, oxidizers, pH regulators and other chemicals to achieve global planarization. Formation and mechanical properties of the chemically modified metal oxide thin films in CMP determine the stresses develop at the interfaces delineating the stability and protective nature of the chemically altered films on the surface of the metal wafer. The balance between the stresses built in the film structure versus the mechanical actions provided during the process can be used to optimize the process variables and furthermore help define new planarization techniques for the next generation microelectronic device manufacturing. In this study, the preliminary studies were concentrated on the very well established tungsten CMP applications and furthermore, titanium CMP applications were presented as a part of surface nano-structuring methodology for biomedical applications by stressing the synergistic effect of protective metal oxide film of titanium in this advanced application.

Molecular dynamic simulation on iron corrosion-reduction in high temperature molten lead-bismuth eutectic

Molecular dynamic simulation on iron in high-temperature molten lead-bismuth eutectic has been carried out to investigate the iron corrosion and its mitigation. The aim of the work is to investigate the corrosion and evaluate proper oxygen content of injection for significant and effective reduction. To study the phenomena we calculated the diffusion coefficients, radial distribution functions and mean square displacement of iron, and also observed the micro-structure of iron before and after oxygen injection into coolant. The present calculation shows that a significant and effective reduction of corrosion can be achieved by injection of 7.68 \times 10^{-2}-1.55 \times 10^{-1} wt\% into coolant at temperature 750 °C. It is predicted that the lower limit of oxygen content, 7.68 \times 10^{-2} wt\%, is the minimum value to develop a self-healing stable protective oxide film for preventing high dissolution of iron; and that the upper limit of oxygen content, 1.55 \times 10^{-1} wt\%, is the maximum value in order to avoid the precipitation of coolant oxides. By injection of 7.68 \times 10^{-2} wt\% of oxygen, the corrosion rate has been reduced about 92.16\% at 750 °C, and reduced by 98.66\% at the lower temperature 550 °C, compared with the normal, oxygenless condition.

Sliding wear behavior of Fe-based bulk metallic glass at high temperature

In the past decade Fe-based bulk metallic glasses (BMGs) have attracted increasing attention due to their beneficial properties, including high glass forming ability (GFA), high strength and hardness and high fracture toughness in both fundamental science and engineering application. Most research using these materials has been conducted at room temperature environment, and research that assesses their behavior especially at high temperature has been scarce. We present the results of high temperature effect on the friction and wear behavior of Fe-based bulk metallic glass (BMG), and we tested that this material may satisfy wear and oxidation resistance at high temperature as well as to explore the high temperature wear mechanism of the Fe-based BMG. The dry sliding tribological behaviors of Febased BMG against Si3N4 ceramic were conducted with a pin-on-disc friction and wear tribometer. The morphology of the worn surfaces of Fe-based BMG was examined by scanning electron microscopy (SEM) and the chemical composition characterized with energy dispersive spectroscopy (EDS) to observe the wear characteristics and investigate the wear mechanisms. The overall average friction coefficient value generally decreased with increasing temperature, and the glass transition and the formation of protective oxide film played an important role in the tribological behavior of BMG. The wear resistance of Fe-based BMG was not only from their hardness but also from the formation protective oxide layer. Analysis of the worn surface revealed abrasion, plastic deformation and oxidation during sliding test.

Electrochemical behavior of aluminum in Grignard reagents/THF electrolytic solutions for rechargeable magnesium batteries

The electrochemical behavior of the aluminum current collector with a fresh surface (the scratched aluminum foil) in three kinds of Grignard reagents/THF electrolytic solutions has been studied by cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) analysis methods. The experimental results show that the passivating film on aluminum foils after five cycles of CV tests is mainly composed of Al2O3. The pitting potentials of scratched aluminum foils in three kinds of Grignard reagents/THF electrolytic solutions increase in the order of EtMgCl/THF<EtMgBr/THF<PhMgCl/THF, which indicates that the selection of electrolytic solutions species is important for the aluminum current collector to suppress the pitting corrosion. The corrosion behavior of three kinds of aluminum foils used as the current collector by different surface treatment processes, which include removal of the oxide film (the scratched aluminum foil), exposing at room temperature (the normal aluminum foil) and high temperature oxidation (the heated aluminum foil), in 1molL−1 EtMgBr/THF solution has been investigated by electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FT-IR) analysis methods. The pitting resistance of aluminum foils by different surface treatment processes in 1molL−1 EtMgBr/THF solution increases in the order of the scratched aluminum foil<the heated aluminum foil<the normal aluminum foil. These results demonstrate that a layer of dense protective oxide film is important for the aluminum current collector to suppress the pitting corrosion.

FeB and FeB/h‐BN based anti‐corrosive composite coatings for aluminium alloys

PurposeThe purpose of this paper is to investigate the corrosion behaviour of ferroboron (FeB) and FeB/h‐BN (hexagonal boron nitride) coatings deposited onto A383 substrates by atmospheric plasma spraying.Design/methodology/approachPotentiodynamic scanning (PDS) and electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion susceptibilities of the composite coatings. Microstructural characterizations were carried out by using scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS).FindingsIt was observed that the coatings resisted localized corrosion in NaCl solutions and protective oxide films on the coatings repaired themselves over the corrosion potential. Hexagonal‐BN is not only a limiting factor in the corrosion of the FeB based coatings. The corrosion morphologies of the coatings are strictly dependent on pores and micro‐cracks in the coating.Practical implicationsThe iron‐based borides act as solid lubricants and have a positive influence on tribological properties such as hardness, friction and corrosion of the coating.Originality/valueKnowledge of the effects of FeB on the corrosion behaviour of thermal spray coatings is still incomplete and this is the most important obstacle to the widespread use of the coatings in engineering applications. The paper reports electrochemical test results of the coatings and discusses the morphologic effects of h‐BN on the corrosion behaviour.

Predictions of Surface Electrochemistry of Saturated and Alkaline NH4Cl Solutions Interacting with Fe(110) from Ab Initio Calculations

Ammonium chloride (NH4Cl) precipitation can present deleterious effects on refinery surfaces when it combines with condensed water vapor to produce highly concentrated chloride and ammoniacal solutions. Herein, we have utilized density functional theory methods to compute the adsorption energies for various NHx, OHx, Cl, and H species on the lowest energy surface presented by iron. Adsorption energies are combined with thermodynamic analysis to develop phase diagrams for the various species that may dominate the surface adsorption coverage. Our results indicate that N, O, Cl, and H each possess regions of predominance on the surface Pourbaix diagram under conditions where a saturated NH4Cl solution is present. While N typically does not interfere with O adsorption except at very high anodic potentials, and is unlikely to depassivate any protective oxide films, Cl can compete with O surface stability, providing a competitive mechanism for hindering repassivation and/or accelerating the rate of metal dissol...

Selection and corrosion evaluation tests of candidate SCWR fuel cladding materials

Abstract Supercritical water cooled reactor (SCWR) is a promising Gen IV high performance reactor which can be developed for future large capacity electric power plants. However, the material selection for fuel cladding still remains one of the key issues. For a typical prototype SCWR design with outlet coolant temperature of 510 °C and pressure of 25 MPa, the hot spot temperature on fuel cladding exceeds 600 °C at normal operation conditions, and will be much higher during transients. Materials for fuel cladding should have good mechanical properties to meet the harsh working conditions in order to keep the integrity of fuel rod under normal and abnormal operational conditions, while corrosion in supercritical water and neutron irradiation damage will not lead to significant loss of strength and ductility, or lead to unacceptable deformation during service life. Materials for ultra-supercritical fossil fire plants, fast breeder reactor and jet air engines etc., are proposed as the candidate materials for SCWR fuel cladding. This paper reports the results based on corrosion screening tests of candidate materials exposed in supercritical water up to 650 °C. Results show that their corrosion rates increase significantly with the increase of temperature, and the protective oxide films of most candidate materials turn to be unstable above temperature of 600 °C. According to the present knowledge available, austenitic stainless steels with high Cr concentration show better performance and are more potential to be the references for developing the SCWR fuel cladding material.

Active oxidation of silicon carbide

The high temperature oxidation of silicon carbide occurs in two very different modes. Passive oxidation forms a protective oxide film which limits further attack of the SiC: SiC(s) + 3/2 O2(g) = SiO2(s) + CO(g) Active oxidation forms a volatile oxide and may lead to extensive attack of the SiC: SiC(s) + O2(g) = SiO(g) + CO(g) Generally passive oxidation occurs at higher oxidant pressures and active oxidation occurs at lower oxidant pressures and elevated temperatures. Active oxidation is a concern for reentry, where the flight trajectory involves the latter conditions. Thus the transition points and rates of active oxidation are a major concern. Passive/active transitions have been studied by a number of investigators. An examination of the literature indicates many questions remain regarding the effect of impurity, the hysteresis of the transition (i.e. the difference between active-to-passive and passive-toactive), and the effect of total pressure. In this study we systematically investigate each of these effects. Experiments were done in both an alumina furnace tube and a quartz furnace tube. It is known that alumina tubes release impurities such as sodium and increase the kinetics in the passive region [1]. We have observed that the active-to-passive transition occurs at a lower oxygen pressure when the experiment is conducted in alumina tubes and the resultant passive silica scale contains sodium. Thus the tests in this study are conducted in quartz tubes. The hysteresis of the transition has been discussed in the detail in the original theoretical treatise of this problem for pure silicon by Wagner [2], yet there is little mention of it in subsequent literature. Essentially Wagner points out that the active-to-passive transition is governed by the criterion for a stable Si/SiO2 equilibria and the passive-to-active transition is governed by the decomposition of the SiO2 film. A series of experiments were conducted for active-to-passive and passive-to-active transitions by increasing and decreasing oxygen pressure, respectively. For pure silicon a dramatic difference was found; whereas for SiC the difference was not as great. This may be due to the oxidation of the carbon in SiC which may break down the scale [3]. The third area is the effect of total pressure. In the literature, low oxygen potentials are achieved via either low total pressure or low oxygen pressure in an O2/Ar mixture. Both types of experiments are done in this study and the differences are discussed with regard to the presence or absence of a boundary layer.

Adhesion at oxide layer/substrate interface during sliding wear

Protective oxide film plays an indispensable role in reducing wear during metal-metal sliding contact, and its adherence to the substrate and stability is a major issue. This review examines some prevalent views proposed in literature on the adhesion between protective oxide layer formed during sliding wear and the steels and cast irons substrate under unlubricated condition. Attempt has been made to correlate some of them to be more connected and take them into account in a broader sliding condition in some sections in this review. Although this review is more relevant to the steels and cast irons as the tested materials during unlubricated unidirectional sliding, other alloys such as aluminium and Ni-based alloys would be hopefully to some extent associated.

Exploring the effect of alkaline silicate solution composition on the ac/dc spark anodization of Al–Cu Alloys

The ac/dc spark anodizing method has been used to form a protective oxide film on the Al–Cu alloy AA2219 in an alkaline silicate solution at 10 mA/cm 2. The composition of the anodizing bath is shown to have a crucial effect on the anodizing process and the oxide film characteristics. Various surface techniques showed that the oxide films are porous and consist of three main layers. In all solutions, the thickness of the outer layer increases with increasing silicate concentration and decreases with increasing solution pH. The degree of corrosion protection offered by the oxide layer has been investigated using linear sweep voltammetery in pH 7 borate buffer solution and electrochemical impedance spectroscopy in 0.86 M NaCl solution. Electrochemical studies show that there is a narrow range of anodization solution pH that is needed to achieve the most passive coating, and that the corrosion resistance increases with increasing bath silicate concentration.

人工模拟海洋大气环境下Sn-0.7Cu无铅焊料的点蚀行为及微量Ga的影响

The corrosion behaviors of Sn-0.7Cu and Sn-0.7Cu-0.01Ga alloys have been investigated by salt spray dry-wet test with artificial seawater to simulate marine atmospheric environment. The surface corrosion products were analyzed by SEM,XPS and XRD.The results show that,at the early stage of corrosion process,the pits easily form at the Cu enrichment area on the surface of Sn-0.7Cu alloy,then the pits propagate by the way of the tentacles.Latter the corrosion product cracks, laminates and falls off,so that it does not give resistance to the future corrosion.XRD result shows that the corrosion products are mainly composed of amorphous oxide of Sn and a few SnCl_2·2H_2O. The addition of trace Ga in the Sn-0.7Cu alloy can significantly improve the corrosion resistance of the alloy in the salt spray test.XPS result shows that trace Ga segregated highly on surface and existed a protective oxide film that can improve the corrosion resistance of the Sn-0.7Cu alloy.

Wear behavior of self-lubricating Fe-Cr-C-Mn-Cu alloys: Smearing effect of second phase particles

Newly developed self-lubricating Fe-Cr-C-Mn-Cu cast composite alloys were investigated to study the role of Cu-rich second phase particles which smear on the wear surface during sliding. The wear resistance of the material was improved with an increasing copper concentration. The improved wear resistance was probably obtained by forming a protective tribofilm, which prevented metal-to-metal contact through smearing of the embedded Cu-rich second phase particles. This formation of protective oxide films during sliding is likely to improve the wear resistance of austenitic Fe-Cr-C-Mn-Cu cast composite alloys.

Effect of loading force on the dissolution behavior and surface properties of nickel-titanium orthodontic archwires in artificial saliva

For orthodontic applications, equiatomic nickel-titanium (NiTi) wires are used to level and align the teeth under bending conditions in the oral environment for long periods. The aim of study was to investigate the influence of bending stress on the nickel release of commercial NiTi orthodontic wires in vitro, simulating the intraoral environment as realistically as possible. Two types of as-received orthodontic NiTi wires, free of performed internal stress, were immersed in artificial saliva. Half of the NiTi wires were exposed to continuous bending stress throughout the 14-day experimental period. The stressed NiTi wires exhibited substantial increases in the nickel release compared with the unstressed specimens during all experimental periods. The highest dissolution rate during the 0 to 1 day incubation period was observed for all stressed specimens. However, a slight increase of nickel released as a function of time was observed in the 3 groups of stressed specimens after 3 days of immersion. For the stressed specimens, it was hypothesized that the bending stress would induce buckling or cracking of the protective oxide film of the NiTi wires. In this study, the mechanism of nickel release was the underlying metal surface reacting with the surrounding environment. The results indicated that bending stress influences the nickel release of NiTi wires. The factor of loading condition with respect to corrosion behavior and passive film should be considered in view of the widespread use of NiTi wires for dental devices.

ANALYSES OF SURFACE OXIDE FILMS ON ELECTROPOLISHED ALLOY 690TT AFTER IMMERSION FOR DIFFERENT TIMES

The corrosion of Ni base alloys in high temperature and high pressure water is affected by samples surface statuses.The morphologies and structures of surface oxide films grown on electropolished(EP) alloy 690TT after immersion in the simulated hydrogenated primary water of pressured water reactors(PWRs) for different times were analyzed by AFM,SEM,TEM,EDS and XPS.After immersion for 15 and 35 h,the EP alloy 690TT samples were covered with columnar oxides. With the increase of the immersion time,the sample surfaces were covered with scattered big oxide particles and loose needle-like oxides.Regardless of the immersion time,the formed oxide films are composed of spinel oxides and metallic Ni.After immersion for 720,1440 and 2160 h,the oxide films are composed of three layers:the outmost layer is the separated big oxide particles which are rich in Fe and Ni:the intermediate layer is the loose needle-like oxides rich in Ni;the inner layer is the continuous and compact Cr oxides.The peak decomposition of the XPS revealed that the Cr oxides in the inner layer are probably Cr_2O_3.Only the inner layer in the oxide film could restrain the outward diffusion of metal atoms and also the inward diffusion of the oxygen atoms and then played the role of barrier layer well. Electropolishing treatment disadvantaged the fast growth of protective oxide film on alloy 690TT in the studied solution.The average corrosion rate of the inner layer does not decrease gradually with increasing the immersion time.After immersion for 2160 h,the oxide film still could not protect the matrix from further corrosion.