Breakdown Of Oxide Film Research Articles

Author Correction: Dielectric breakdown of oxide films in electronic devices

Author Correction: Dielectric breakdown of oxide films in electronic devices

Dielectric breakdown of oxide films in electronic devices

Dielectric breakdown of oxide films in electronic devices

Study on strontium doped bioactive coatings on titanium alloys surfaces by micro-arc oxidation

In order to improve the bioactivity of titanium alloy, hydroxyapatite coatings with different amounts of Sr doping were prepared on the Ti6Al4V surface by micro-arc oxidation (MAO) using electrolytes containing Ca(CH3COO)2, NaH2PO4, and different concentrations of Sr(CH3COO)2, and EDTA-2Na was used as a complexing agent to complex Ca and Sr ions. The coatings' thickness, phase composition, microstructure morphology, and elemental distribution were examined, and the hydrophilicity and bioactivity were evaluated by contact angle and MC3T3-E1 preosteoblasts proliferation experiments. The results show that the concentration of Sr(CH3COO)2 in the electrolyte has little effect on the anodic oxide film breakdown voltage. However, the higher the concentration, the smaller the stable value of the MAO voltage is. The thickness of the MAO coating decreases with the increase of Sr concentration in the electrolyte, and the coatings mainly consist of strontium-containing hydroxyapatite, rutile, and anatase phases. The rise in Sr content leads to a decrease in Ca content, and both Ca and Sr content on the surfaces of the coatings are higher than that on the interior. (Ca + Sr)/P in all coatings is close to 1.67, which is similar to human bone. Moreover, all coating surfaces have good hydrophilicity, the Sr-doped MAO coatings promote the proliferation of MC3T3-E1 preosteoblasts, and the cell proliferation is higher on the coatings with higher Sr content.

Formation and Breakdown of Oxide Films in High-Rate Anodic Dissolution of Chromium–Nickel Steels in Electrolytes for Electrochemical Machining

Formation and Breakdown of Oxide Films in High-Rate Anodic Dissolution of Chromium–Nickel Steels in Electrolytes for Electrochemical Machining

Formation and Breakdown of Oxide Films in High-Rate Anodic Dissolution of Chromium–Nickel Steels in Electrolytes for Electrochemical Machining

It is shown that, in high-rate pulsed galvanostatic anodic dissolution of type CSN17335 and AISI 304 chromium–nickel steels in electrolytes for electrochemical machining (ECM) (chloride, nitrate, and mixed chloride–nitrate solutions with a conductivity of 0.15 S/cm) using microsecond pulses with a duration of 20–2000 μs and current densities in the range of 1–100 A/cm2, a substantial fraction of charge (up to ~40%) is spent on the formation of a passivating oxide film with a semiconducting behavior. The electrochemical treatment therefore directly involves the oxide film, not the alloy. As a consequence, the current efficiency of ECM of these materials is ~60–70%, depending on the alloy composition. When using direct current, the rate of machining increases as a result of the oxide film breakdown due to its thermokinetic instability (“thermal explosion”) caused by a rise in the surface temperature.

Stochastic Local Breakdown of Oxide Film on Ni from Identical-Location Imaging: One Single Site at a Time.

The electrochemical breakdown of a metal oxide film can directly affect the performance of functional electrochemical devices. However, revealing the structural insight into the breakdown sites is challenging because of heterogeneity: different breakdown sites are spatially distributed over the surface. Herein, we combine scanning electrochemical cell microscopy with identical-location microscopies to reveal the heterogeneity in the breakdown of NiO film on Ni in a site-by-site manner. Local critical breakdown potential varies by ∼500 mV, corresponding to an excess energy of 0.02-0.12 J/m2. Correlative composition imaging using time-of-flight secondary ion mass spectrometry shows Ni crystal grains with thinner NiO films are more resistant to breakdown. This high resistance is explained using classical nucleation theory, where the electrical energy is affected by the film thickness through the local interfacial capacitance. The correlative imaging approach overcomes the issue of heterogeneity, providing conclusive insight into the stability of the electrochemical interfaces.

Strain rate dependence of the effect of intergranular carbides on the resistance to stress corrosion cracking initiation of alloy 690 in simulated PWR primary water

The stress corrosion cracking (SCC) initiation of alloy 690 in simulated PWR primary water was evaluated in constant extension rate tensile tests with different strain rates. The SCC initiation was inhibited by intergranular carbide precipitation. However, the carbide effect weakened with increasing strain rate. The SCC mitigation effect of carbides mainly arises from the carbides’ ability to impede the transfer of dislocations across grain boundaries and delay the local break-down of surface oxide films. However, dislocations accumulated near the grain boundary can promote intergranular oxidation which induces cracking after the oxide film fails.

Oxygen injection during fast vs slow passivation in aqueous solution

The typical defect reactions at the metal/oxide interface, which explain the growth and breakdown of passive oxide films in corrosion, include creating metal and oxygen vacancies. While the creation and coalescence of metal vacancies are well documented, there are relatively few observations on the nanoscale details of oxygen transport near the metal/oxide interface. We report here a new mechanism of oxygen injection into the metal. Fast and slow passivation (i.e., corrosion involving both oxide film growth and direct dissolution) of NiCr and NiCrMo alloys was performed by galvanostat experiments in 0.1 M NaCl (pH 4) deaerated solution. Localized regions of an unexpected nonequilibrium metal-based oxygen solid solution were observed beneath the outer (externally formed) oxides, and the saturated oxygen atoms distorted the fcc metallic lattices. Oxygen injection into the metal is more significant at a fast growth rate due to a large passivation current density for the NiCr alloy. In this case, there is a high volume of rock salt Ni(Cr)O nanocrystals in the O-rich Ni(Cr) substrate, which is consistent with greater susceptibility to chloride-induced breakdown found in potentiostat experiments. The addition of Mo promotes the formation of the corundum phase in the outer oxide layer for NiCrMo, which changes the transport mechanism as well as the diffusivity of oxygen through the oxide film and across the metal/oxide interface.

First-principles study of strain effect on oxygen vacancy in silicon oxide

The strain dependence of stability and diffusion barrier height of the O vacancy in Si oxide is examined using the first-principles calculation. It is found that the stability and the diffusion barrier height increase as the oxide is compressed. The analysis shows that the diffusion barrier height is determined by the Si–Si distance of the O vacancy. Based on these results, the dielectric breakdown of the gate Si oxide film in the three-dimensional structure metal-oxide-semiconductor field-effect transistor is also considered. It is suggested that the interfacial O-vacancy density increases because the interfacial oxide is subjected to compressive strain. On the other hand, the surface O-vacancy density decreases and the surface O-vacancy diffusion is promoted because the surface oxide is subjected to tensile strain. The reliability of the oxide film might be thus affected by the strain.

The corrosion behavior of Ti-6Al-3Nb-2Zr-1Mo alloy: Effects of HCl concentration and temperature

Investigation about the corrosion behavior of Ti alloys in different ambient environment is of great significance for their practical application. Herein, we systematically investigate the corrosion behavior of a newfound Ti-6Al-3Nb-2Zr-1Mo (Ti80) alloy in hydrochloric acid (HCl) ranging from 1.37 to 7 M, and temperature ranging from 25 to 55 °C, by means of electrochemical measurements, static immersion tests and surface analysis. Results manifest that increasing either HCl concentration or temperature can accelerate the corrosion of Ti80 alloy via promoting the breakdown of native protective oxide film and then further facilitating the active dissolution of Ti80 matrix. According to potentiodynamic polarization curves, Ti80 alloy displays a spontaneous passive behavior in 1.37 M HCl at 25 °C, compared to a typical active-passive behavior under the other conditions. As indicated by cathodic Tafel slope, the rate determining step for cathodic hydrogen evolution reaction is likely the discharge reaction step. The apparent activation energies obtained from corrosion current density and maximum anodic current density for Ti80 alloy in 5 M HCl solution are 62.4 and 55.6 kJ mol−1, respectively, which signifies that the rate determining step in the corrosion process of Ti80 alloy is mainly determined by surface-chemical reaction rather than diffusion. Besides, the electrochemical impedance spectroscopy tests demonstrate that a stable and compact oxide film exists in 1.37 M HCl at 25 °C, whereas a porous corrosion product film forms under the other conditions. Overall, the critical HCl concentration at which Ti80 alloy can maintain passivation at 25 °C can be determined as a value between 1.37 and 3 M. Furthermore, the corroded surface morphology characterization reveals that equiaxed α phase is more susceptible to corrosion compared to intergranular β phase due to a lower content of Nb, Mo, and Zr in the former.

Annealed microstructure dependent corrosion behavior of Ti-6Al-3Nb-2Zr-1Mo alloy

Corrosion resistance of titanium (Ti) alloys is closely connected with their microstructure which can be adjusted and controlled via different annealing schemes. Herein, we systematically investigate the specific effects of annealing on the corrosion performance of Ti-6Al-3Nb-2Zr-1Mo (Ti80) alloy in 3.5 wt.% NaCl and 5 M HCl solutions, respectively, based on open circuit potential (OCP), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), static immersion tests and surface analysis. Results indicate that increasing annealing temperature endows Ti80 alloy with a higher volume fraction of β phase and finer α phase, which in turn improves its corrosion resistance. Surface characterization demonstrates that β phase is more resistant to corrosion than α phase owing to a higher content of Nb, Mo, and Zr in the former; additionally, the decreased thickness of α phase alleviates segregation of elements to further restrain the micro-galvanic couple effects between α and β phases. Meanwhile, the influential mechanisms of environmental conditions on corrosion of Ti80 alloy are discussed in detail. As the formation of a highly compact and stable oxide film on surface, annealed Ti80 alloys exhibit a low corrosion current density (10−6 A/cm2) and high polarization impedance (106 Ω⋅ cm2) in 3.5 wt.% NaCl solution. However, they suffer severe corrosion in 5 M HCl solution, resulting from the breakdown of native oxide films (the conversion of TiO2 to aqueous Ti3+), active dissolution of substrate Ti to aqueous Ti3+ and existence of micro-galvanic couple effects. Those findings could provide new insights to designing Ti alloys with high-corrosion resistance through microstructural optimization.

Performance of protective oxide films on Fe–Ni alloy anodes in molten KF–AlF3–Al2O3 salts at 700 °C

An oxide film containing NiFe2O4 was prepared by oxidizing Fe–Ni alloy in hot air, and the performance of the protective oxide film in molten KF–AlF3–Al2O3 salts at 700 °C was characterized by electrochemical methods, including electrochemical impedance spectroscopy, capacitance measurements, linear sweep voltammetry, and chronoamperometry to clarify the breakdown and growth process of the oxide film. For the pre-oxidized 57Fe–43Ni, 50Fe–50Ni, and 43Fe–57Ni alloys, the oxide films, with a thickness of 5 μm, are composed of Fe2O3 and NiFe2O4, according to X-ray diffraction and scanning electron microscopy analysis. The transfer resistance of ions in the oxide film increases with increasing nickel content, and reaches its maximum value of 91.39 Ω⋅cm2 for the pre-oxidized 43Fe–57Ni alloy based on electrochemical impedance spectroscopy measurements. Moreover, the carrier density in the oxide film determined from Mott–Schottky plots decreases as the nickel content increases. Under anodic polarization, the breakdown of oxide film follows the generation of metal cation vacancies and condensation of excess cation vacancies. Concurrently, a new oxide layer forms along the substrate owing to the annihilation of oxygen vacancies and diffusion of oxygen anion in the oxide film. After oxygen evolution, a new oxide film layer containing NiFe2O4 forms on the alloy substrate, leading to the passivation observed in the anodic polarization curves. The maximum polarization resistance in the passivation region is 4.86 Ω⋅cm−2 for the pre-oxidized 43Fe–57Ni alloy, indicating that the pre-oxidized 43Fe–57Ni alloy possesses better corrosion resistance to molten fluorides than the other two pre-oxidized Fe–Ni alloys. Chronoamperometry measurements show that the oxide film on the 43Fe–57Ni alloy is in a dynamically stable state during oxygen evolution.

Microstructural investigation of the nodular corrosion of 304NG stainless steel in supercritical water

304NG stainless steel was exposed to deaerated 600 °C supercritical water for 300 h. The thin Cr-rich oxide film and corrosion nodules were characterized in detail by cutting edge techniques. The results show that the formation of MnCr2O4 is an important factor that deteriorates the protectiveness of the Cr-rich thin oxide film. Reaction zones ahead of the inner oxide are observed. The reaction zones are composed of oxide particles and remaining metal, indicating the occurrence of internal oxidation. The internal oxidation controls the further corrosion after the breakdown of Cr-rich thin oxide film, and subsequently the generation of corrosion nodules.

The influence of incorporation of Mn on the pitting corrosion performance of CrFeCoNi High Entropy Alloy at different temperatures

The electrochemical behavior and susceptibility to pitting corrosion of CrFeCoNi and CrMnFeCoNi high entropy alloys were studied in a 0.1 M NaCl solution at temperatures ranging from 25 to 75 °C. Electrochemical measurements revealed that CrMnFeCoNi is more susceptible to oxide film breakdown and localized corrosion compared to CrFeCoNi. Post corrosion microscopic observations showed severe pitting corrosion for CrMnFeCoNi in higher temperatures compared to CrFeCoNi. Based on in-depth XPS profile measurements on the remaining oxide films, this behavior was attributed to the depletion of Cr in the oxide film and detrimental presence of Mn in the matrix solid solution of CrMnFeCoNi.

Discharge Behavior and Dielectric Breakdown of Oxide Films during Single Pulse Anodizing of Aluminum Micro-Electrodes.

Micro-arc discharge events and dielectric breakdown of oxide films play an important role in the formation process of plasma electrolytic oxidation coating. Single pulse anodization of micro-electrodes was employed to study the discharge behavior and dielectric breakdown of oxide films deposited on aluminum in an alkaline silicate electrolyte. Voltage and current waveforms of applied pulses were measured and surface morphology of micro-electrodes was characterized from images obtained using scanning electron microscope (SEM). A feasible identification method for the critical breakdown voltage of oxide film was introduced. Different current transients of voltage pulses were obtained, depending on applied pulse voltage and duration. In addition, the active capacitive effect and complex non-linear nature of plasma electrolytic oxidation process is confirmed using dynamic electrical characteristic curves. A good correlation between the pulse parameters and shape of discharge channels was observed. Circular opened pores were found to close with increasing potential and pulse width. Finally, the characteristic parameters of a single discharge event were estimated.

The Breakdown of a 316L Stainless Steel Oxide Film in an AlCl3-EMIC Ionic Liquid

The Breakdown of a 316L Stainless Steel Oxide Film in an AlCl3-EMIC Ionic Liquid

Rapid Consolidation Mechanism of Titanium Aluminide Solid Compact via Electric Discharging Through Elemental Ti and Al Powder Mixture

Elemental Ti and Al powders were milled and mixed as starting materials for the synthesis of titanium aluminide solid compacts by using the electric discharge sintering (EDS) technique. The polycrystalline compact with near full-density (> 99.6%) and the main phase of Ti3Al was produced in 170 μs by the EDS. In the early stage of electric discharging, the generated heat at the interface of metal and oxide film created an explosive force, inducing a dielectric breakdown of inherent oxide film. Once the oxide film was removed and the metals were melt, the formation of necks at the clean contact points occurred and the inter-diffusion between Ti and Al in liquid phase was initiated at the metallic contact areas with sequent alloying into an amorphous Ti3Al. During the full alloying and substantial neck growth, the heat dissipated through the mold, causing the crystallization of Ti3Al. During the EDS, pinch pressure (24–68 MPa) was also generated, which can densify the EDS compact. The fine microstructure, higher density, and greater hardness of EDS compact were results of the shorter exposure time to a high temperature and the generated pinch pressure, causing a higher densification and constrained grain growth, compared to conventional powder metallurgy methods.

Revealing How Alkali Cations Affect the Surface Reactivity of Stainless Steel in Alkaline Aqueous Environments

Stainless steel is a ubiquitous structural material and one that finds extensive use in core-internal components in nuclear power plants. Stainless steel features superior corrosion resistance (e.g., as compared to ordinary steel) due to the formation of passivating iron and/or chromium oxides on its surfaces. However, the breakdown of such passivating oxide films, e.g., due to localized deformation and slip line formation following exposure to radiation, or aggressive ions renders stainless steel susceptible to corrosion-related degradation. Herein, the effects of alkali cations (i.e., K+, Li+) and the interactions between the passivated steel surface and the solution are examined using 304L stainless steel. Scanning electrochemical microscopy and atomic force microscopy are used to examine the inert-to-reactive transition of the steel surface both in the native state and in the presence of applied potentials. Careful analysis of interaction forces, in solution, within ≤10 nm of the steel surface, reveals that the interaction between the hydrated alkali cations and the substrate affects the structure of the electrical double layer (EDL). As a result, a higher surface reactivity is indicated in the presence of Li+ relative to K+ due to the effects of the former species in disrupting the EDL. These findings provide new insights into the role of the water chemistry not only on affecting metallic corrosion but also in other applications, such as batteries and electrochemical devices.

Improved fracture properties of Ni-Ti superelastic alloy under sustained tensile load in physiological saline solution containing hydrogen peroxide by hydrogen charging

We have attempted to improve the fracture properties of Ni-Ti superelastic alloy under a sustained tensile load in physiological saline solution containing hydrogen peroxide by charging with a small amount of hydrogen, which causes negligible hydrogen embrittlement. For hydrogen charged in the parent phase, no pitting potential is observed in anodic polarization curves for the present test solution; the time to fracture increases under an applied stress even in the elastic deformation region of the martensite phase. Upon aging after hydrogen charging, the pitting potential varies widely and the increase in the time to fracture slightly decreases. Hydrogen charging increases the time until a rapid shift of the corrosion potential in the less noble direction, corresponding to the breakdown of surface oxide films. The final fracture is mainly caused by overloading due to localized corrosion irrespective of hydrogen charging. For hydrogen charged in the martensite phase, i.e., the specimen not subjected to interactions between hydrogen and the stress-induced phase transformations, the time to fracture increases by more than that of the specimen subjected to the interactions. The present study indicates that a small amount of hydrogen charging is effective for inhibiting the localized corrosion of Ni-Ti superelastic alloy under applied stress in physiological saline solution containing hydrogen peroxide, thereby improving the fracture properties. In addition, changes in the hydrogen states and/or defects induced by the interactions between hydrogen and phase transformations probably play an important role in improving the fracture properties.

Electrochemical Behavior and Surface Characteristics of Pure Titanium during Corrosion in Simulated Desulfurized Flue Gas Condensates

Corrosion behavior of pure titanium in simulated desulfurized flue gas condensates in thermal power plant chimneys is investigated by electrochemical measurements and surface observations. Existence of fluoride ion leads to the breakdown of oxide film and promotes activation dissolution of Ti. Both anodic and cathodic reactions are enhanced by the increase of temperature, following an Arrhenius relationship. The participation of fluoride ion leads to low activation energy values. The corrosion process presents a two-step mechanism, in which dissolution of the adsorbed intermediate species is the rate determining step. Increase of temperature accelerates both of the two steps, especially the latter, and results in the low surface coverage of adsorbed species at high temperatures. Preferential dissolution occurs on specific grains and grain boundaries. Increase of temperature facilitates the crystallographic characteristics and aggravates the failure risk of the chimneys.