Film Breakdown Potential Research Articles

Effect of Sulfide and Chloride Ions on Pitting Corrosion of Type 316 Austenitic Stainless Steel in Groundwater Conditions Using Response Surface Methodology.

This study investigates the corrosion resistance of Type 316 stainless steel as a candidate material for radioactive waste disposal canisters. The viability of stainless steel is examined under groundwater conditions with variations in pH, bisulfide ions (HS-), and chloride ions (Cl-) concentrations. Utilizing response surface methodology, correlations between corrosion factors and two crucial response variables, passive film breakdown potential and protection potential, are established. Cyclic potentiodynamic polarization tests and advanced analytical techniques provide detailed insights into the material's behavior. This research goes beyond, deriving an equation through response surface methodology that elucidates the relationship between the factors and breakdown potential. HS- weakens the passive film and reduces the pitting corrosion resistance of the stainless steel. However, this study highlights the inhibitory effect of HS- on pitting corrosion when Cl- concentrations are below 0.001 M and at equivalent concentrations of HS-. Under these conditions, immediate re-passivation occurs from the destroyed passive film to metal sulfides such as FeS2, MoS2, and MoS3. As a result, no hysteresis loop occurs in the cyclic polarization curve in these conditions. This research contributes to the understanding of Type 316 stainless-steel corrosion behavior, offering implications for the disposal of radioactive waste in geological repositories.

SYNTHESIS AND PASSIVE PROPERTY OF NANOCOM-POSITE Ni-WC COATING

The metallic matrix composite with ceramic nano–particles has a wide prospect in many applications due to its superior properties. The nanocomposite Ni–WC coating has been synthesized by using DC co–electrodeposition of Ni with WC nano–particles. Its hardness was measured by using ultra–micro hardness tester. Its corrosion and passive properties were investigated in 0.05 mol/L H3BO3+0.075 mol/L Na2B4O7 buffer solution with pH=9.0 by using potentiodynamic polarization measurement. As compared to pure nanocrystalline (nc) Ni, nanocomposite refined remarkably, with average grain size about 21 nm and the hardness increase of 80%, reaching about 651 HV. The corrosion current density icorr is 1.29×10 −7 A/cm, approximately one magnitude order lower than that of nc Ni. With the similar passive film breakdown potential, nanocomposite exhibits a lower passivation potential Ep of 10 mV and a much lower passive current density ip of 1.79×10 −6 A/cm, about 1/7 that for nc Ni. According to the Mott–Schottky analysis together with point defect model, the passive film on the nanocomposite exhibits p–type semi–conducting behavior, similar to that on the nc Ni. The grain refinement of Ni is beneficial to the reduction of both the donor density and diffusion coefficient.

The Effect of Hydrogen on Pitting Corrosion of Superaustenitic and Austenitic-Ferritic Stainless Steels

Hydrogen entering into steel affects its electrochemical properties and may enhance the susceptibility to environmental degradation. The present work has been aimed at further clarifying the effect of hydrogenation on the corrosion behaviour and passivity of highly-alloyed stainless steels. The results were discussed by taking into account hydrogen charged samples and without hydrogen. The corrosion resistance to pitting was qualified with the cyclic polarization curves. The conclusion is that hydrogen may deteriorated the passive film stability and corrosion resistance to pitting of highly-alloyed stainless steel. Furthermore, the presence of hydrogen in passive films increases corrosion current density, decreasing the potential of the film breakdown and repassivation potential. It was also found that the degree of susceptibility to hydrogen-enhanced pitting corrosion was dependent on the type of steel.

Corrosion Inhibition of Stress Corrosion Cracking and Localized Corrosion of Turbo-Expander and Steam/Gas Turbines Materials

Stress corrosion cracking of 7050 aluminum alloys and ASTM A470 steel in the turbo expander and steam/gas turbine industry can cause expensive catastrophic failures, especially for turbo machinery systems performing in hostile, corrosive environments. Commercially available inhibitors were investigated for their effectiveness in reducing and controlling the corrosion susceptibility. Inhibitor effectiveness was confirmed with electrochemical corrosion techniques in different solutions. Polarization resistance increased with concentration of corrosion inhibitor due to film formation and displacement of water molecules. Cyclic polarization behavior for samples in the 1.0% and 5.0% inhibitors showed a shift in the passive film breakdown potential. The substantial increase in the passive range has positive consequences for neutralizing pitting and crevice corrosion cell chemistry. The strain to failure and tensile strength obtained from the slow strain rate studies for both alloys showed pronounced improvement due to corrosion inhibitor ability to mitigate SCC; the fractographic analysis showed a changed morphology with ductile overload as the primary failure mode instead of transgranular or intergranular cracking.

The role of inhibitors on the repassivation of pitting corrosion of carbon steel in synthetic carbonated concrete pore solution

The semiconductive properties and pitting susceptibility of passive films formed on carbon steel in synthetic carbonated concrete pore solution containing Cl − ions were studied by Mott–Schottky (M–S) plots and electrochemical noise (EN). The results show that both nitrite and tetraethylenepentamine (TEPA) can reduce the donor density in passive film, leading to a more positive film breakdown potential. Moreover, nitrite can rehabilitate metastable pits and passivate the broken passive film more quickly than TEPA. Polarization curves also show that nitrite can increase the pitting potential more than TEPA at same concentration. Atomic force microscopy (AFM) imaging shows that Cl − ions could induce large metastable pits on passive film, but the size of pits decreases and the density of pits increases with addition of nitrite. However, AFM imaging fails to detect the metastable pits under TEPA adsorbed film in spite of a smooth-like image on the steel surface is observed. The force curves of AFM indicate a stiffness (elasticity) order of films: nitrite oxidation film > original passive film > enamine adsorbed film.

Corrosion resistance of titanium-containing dental orthodontic wires in fluoride-containing artificial saliva

This study was to investigate the corrosion resistance of different Ti-containing dental orthodontic wires (including Ni–Ti, Ni–Ti–Cu, Ti–Mo–Zr–Sn, and Ti–Nb alloys) in acidic fluoride-containing artificial saliva using cyclic potentiodynamic polarization curve measurements. Different NaF concentrations (0%, 0.2%, and 0.5%), simulating the fluoride contents in commercial toothpastes, were added to the artificial saliva. Surface characterization was analyzed using X-ray photoelectron spectrometry. Cyclic potentiodynamic polarization curves showed that the presence of fluoride ions, especially 0.5% NaF, was detrimental to the protective ability of the TiO 2-based film on the Ti-containing wires. This might lead to a decrease in the corrosion resistance of the tested alloys, i.e. an increase in the corrosion rate and anodic current density and a decrease in the passive film breakdown potential. Among the tested Ti-containing wires, the Ni–Ti and Ni–Ti–Cu wires containing mainly TiO 2 on surface film were more susceptible to fluoride-enhanced corrosion, while the Ti–Mo–Zr–Sn and Ti–Nb wires containing MoO 3/ZrO 2/SnO and Nb 2O 5, respectively, along with TiO 2 on surface film were pitting corrosion resistant and showed a lower susceptibility to fluoride-enhanced corrosion. The difference in corrosion resistance of the tested commercial Ti-containing dental orthodontic wires was significantly dependent on the passive film characteristics on wires’ surface.

An irreversible dipping sealing technique for anodized ZE41 Mg alloy

Anodized coatings are porous and sealing has been considered to be an essential step for anodized magnesium alloys. In this study, a new sealing technique was proposed and validated. Anodized ZE41 was dipped in an E-coating bath solution for a few seconds. After baking, the specimen was found to have considerably improved corrosion resistance. The corrosion rate and polarization current densities were found to be more than 3 orders of magnitude lower and the film breakdown potential over 50 mV higher for the anodized ZE41 after sealing in the E-coating bath solution than for the as-anodized ZE41. An irreversible electroless E-coating deposition model and corrosion mitigation mechanism for a sealed specimen are proposed.

Investigation of surface oxide film on magnesium lithium alloy

Magnesium and its alloys are very chemically active metals. Oxide film can be spontaneously formed on their surface in an ambient atmosphere. The oxide film on the surface of Mg–8Li alloy was characterized by X-ray photoelectron spectroscopy (XPS) analysis and electrochemical measurements. The results indicated that the surface oxide film formed in the air exhibited multiple layer structure, which consisted of the elements of Li, Mg and O. The concentrations of Mg decreased and Li increased from the bottom layer to top layer of the oxide film. Lithium oxides mostly enriched in the outer oxide layer. The more the potential deviated from the E corr, the more severe the oxide film was destroyed. Below the film breakdown potential, the surface oxide film can slow down the corrosion of Mg–8Li alloy.

Corrosion behavior of copper alloys in chloride media

The potentiodynamic polarization behavior of copper alloys in chloride solutions (1 M NaCl) of different pH’s (6.5 and 10) was investigated. Three commercial alloys of nominal composition Cu–30Ni (Cu–Ni), Cu–30Zn (Cu–Zn) and 90Cu–8Al–2Fe (Cu–Al) were considered. Results at pH of 6.5 showed no evidence of passivity with polarization behavior being dominated by the Cu component. At pH of 10, however, some evidence of limited passivity was seen. Passivity was more evident in buffered chloride (pH 10), in particular for Cu–Zn which showed remarkable passive behavior over a wide potential range. A sudden increase in the current density occurred when the anodic potential exceeded a certain critical potential, i.e., film breakdown potential. The results of these experiments are discussed in reference to potential–pH (Pourbaix) diagrams of the alloying elements.

Effect of nitriding surface treatment on the corrosion resistance of dental nickel–titanium files in 5.25% sodium hypochlorite solution

This study investigated the effect of nitriding surface treatment on the corrosion resistance of commercial dental alloy, in the form of helical nickel–titanium (Ni–Ti) files, when treated with 5.25% sodium hypochlorite (NaOCl) solution. The surface of dental helical Ni–Ti files was modified using nitriding treatment at 200 °C, 250 °C and 300 °C in an NH 3-containing environment. The surface morphology and chemical composition of the Ni–Ti files were analyzed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. The corrosion resistance of the Ni–Ti files when treated with a clinical solution of 5.25% NaOCl was evaluated using the linear polarization method and by potentiodynamic polarization curve measurement. The nitriding treatments at different temperatures created titanium nitride (TiN) on the surface of the helical Ni–Ti files. The Ni–Ti files nitrided at 200 °C and 250 °C showed higher polarization resistance and higher passive film breakdown potential together with a lower passive current than untreated files. The presence of TiN on dental Ni–Ti files significantly increased the corrosion resistance of the files in the presence of 5.25% NaOCl solution.

The Influence of Fluoride on the Physicochemical Properties of Anodic Oxide Films Formed on Titanium Surfaces

The influence of fluoride (and its concentration) on the electrochemical and semiconducting properties of anodic oxide films formed on titanium surfaces was investigated by performing electrochemical measurements (potentiodynamic/pontiostatic polarization, open circuit potential (OCP), and capacitance measurements) for a titanium/oxide film/solution interface system in fluoride-containing 1.0 M HClO(4) solution. On the basis of the Mott-Schottky analysis, and with taking into account both the surface reactions (or, say, the specifically chemical adsorption) of fluoride ions at the oxide film surface and the migration/intercalation of fluoride ions into the oxide film, the changes in the electrochemical behavior of titanium measured in this work (e.g., the blocked anodic oxygen evolution, the increased anodic steady-state current density, the positively shifted flat band potential, and the positively shifted film breakdown potential) were interpreted by the changes in the surface and the bulk physicochemical properties (e.g., the surface charges, surface state density, doping concentration, and the interfacial potential drops) of the anodic films grown on titanium. The fluoride concentrations tested in this work can be divided into three groups according to their effect on the electrochemical behavior of the oxide films: < or =0.001 M, 0.001-0.01 M, and >0.01 M. By tracing the changes of the OCP of the passivated titanium in fluoride-containing solutions, the deleterious/depassive effect of fluoride ions on the titanium oxide films was examined and evaluated with the parameter of the film breakdown time. It was also shown that the films anodically formed on titanium at higher potentials (>2.5 V) exhibited significantly higher stability against the fluoride attack than that either formed at lower potentials (<2.5 V) or formed natively in the air.

Corrosion Resistances of Iron-Based Amorphous Metals with Yttrium and Tungsten Additions in Hot Calcium Chloride Brine & Natural Seawater: Fe48Mo14Cr15Y2C15B6 and W-Containing Variants

Yttrium-containing SAM1651 (Fe48.0Cr15.0Mo14.0B6.0C15.0Y2.0), has a critical cooling rate (CCR) of approximately 80 Kelvin per second, while SAM2X5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4) with no yttrium has a higher critical cooling rate of approximately 600 Kelvin per second. SAM1651's low CCR enables it to be rendered as a completely amorphous material in practical materials processes. Chromium (Cr), molybdenum (Mo) and tungsten (W) provide corrosion resistance; boron (B) enables glass formation; and rare earths such as yttrium (Y) lower critical cooling rate (CCR). The passive film stability of these Fe- based amorphous metal formulations have been found to be superior to that of conventional stainless steels, and comparable to that of Ni-based alloys, based on electrochemical measurements of the passive film breakdown potential and general corrosion rates.

Corrosion resistance of thermally sprayed high-boron iron-based amorphous-metal coatings: Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4

An iron-based amorphous metal, Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 (SAM2X5), with very good corrosion resistance has been developed. This material was prepared as a melt-spun ribbon, as well as gas atomized powder and a thermal-spray coating. During electrochemical testing in several environments, including seawater at 90 °C, the passive film stability was found to be comparable to that of high-performance nickel-based alloys and superior to that of stainless steels, based on electrochemical measurements of the passive film breakdown potential and general corrosion rates. This material also performed very well in standard salt fog tests. Chromium (Cr), molybdenum (Mo), and tungsten (W) provided corrosion resistance, and boron (B) enabled glass formation. The high boron content of this particular amorphous metal made it an effective neutron absorber and suitable for criticality control applications. This material and its parent alloy maintained corrosion resistance up to the glass transition temperature and remained in the amorphous state during exposure to relatively high neutron doses.

Corrosion Characteristics of TiN and ZrN Coated Ti-Nb Alloy by RF-Sputtering

In order to investigate the electrochemical characteristics of TiN and ZrN coated Ti-Nb alloys by using RF-sputtering method, the Ti containing Nb up to 3.0wt%, 20.0wt% and 40.0wt% were melted by using a vacuum furnace and then homogenized for 24hr at 1050°C. The specimens were coated with TiN and ZrN with few μm thickness, respectively, by RF-magnetron sputtering method. Ti alloy containing 3wt%, 20wt% and 40wt% Nb showed a, α+β and β phase. The corrosion current density of Ti-40Nb alloy was lower than that of other alloy in the 0.9% NaCI and corrosion potential of Ti-40Nb alloy were higher than that of Ti-3Nb and Ti-20Nb alloy. The corrosion resistance of Ti-40Nb was higher than that of Ti-3Nb and Ti-20Nb alloy in the 0.9% NaCI solution. The corrosion potential, passive film breakdown potential and repassivation potential of TiN and ZrN coated Ti-Nb alloy increased with increasing Nb content but the critical anodic current density at active region and the current density at passive region decreased. Therefore, The TiN and ZrN coated Ti-Nb alloy is a good corrosion resistance for dental implant compared with non coated Ti-Nb alloy.

A High-Performance Corrosion-Resistant Iron-Based Amorphous Metal - The Effects of Composition, Structure and Environment on Corrosion Resistance

ABSTRACTThe passive film stability of several Fe-based amorphous metal formulations have been found to be comparable to that of high-performance Ni-based alloys, and superior to that of stainless steels, based on electrochemical measurements of the passive film breakdown potential and general corrosion rates. Chromium (Cr), molybdenum (Mo) and tungsten (W) provide corrosion resistance; boron (B) enables glass formation; and rare earths such as yttrium (Y) lower critical cooling rate (CCR). The high boron content of this particular amorphous metal also makes it an effective neutron absorber, and suitable for criticality control applications, as discussed in companion publications. Corrosion data for SAM2X5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4) is discussed here.

Electrochemical conditions for environment-assisted cracking of 6061 Al alloy

We have investigated the influence of electrochemical conditions on environment-assisted cracking (EAC) of 6061 aluminum alloy in acidic chloride solutions. An EAC test was conducted by means of potential-controlled slow strain rate technique. In addition, thermal desorption spectroscopy (TDS) was employed to determine amount of hydrogen absorbed in the specimens under the same electrochemical conditions as those in the EAC tests. As a result, almost no EAC and very small amount of hydrogen absorption were found in a potential range lower than the film breakdown potential, while the higher potential induced severer EAC and much larger hydrogen absorption. The specimen pre-immersed in the chloride solution of pH 1, which derived voluntary breakdown of the oxide film, suffered preferential grain boundary attack. When the tensile test was conducted in air for the specimen with pre-immersion, the fracture strain became slightly smaller than that without pre-immersion. Moreover, the fracture strain drastically decreased and deep cracks was observed, namely the EAC occurred, when the pre-immersed specimen was examined by the EAC test under the cathodic condition which induced no EAC and very small hydrogen absorption for the specimen without pre-immersion.

Breakdown of ultrathin anodic valve metal oxide films in metal-insulator-metal-contacts compared with metal-insulator-electrolyte contacts

The anodic breakdown of thin valve metal oxide films on aluminium, hafnium, niobium, titanium, tantalum and zirconium in the system valve-metal/valve-metal-oxide/silver was investigated. For all systems valve metal wires covered by an anodically formed oxide with an evaporated silver film were used. For comparison three different types of oxide were used in the case of aluminium: anodic oxide, gas phase oxide and physical vapour deposited oxide. Due to an improved technique for the preparation a high reproducibility and reliability could be achieved. In the case of anodic oxide it is shown, that the formation field strength or reciprocal film formation factor and the breakdown field strength are equal. The initial step of anodic breakdown is clearly an ionic one. This was concluded from the strong correlation between film thickness and breakdown potential. An equation for the absolute quantitative calculation of tunnel currents is derived that takes the deformation of the barrier due to the image potential into account. The simulations are compared with the experimental results and the breakdown process is discussed in terms of ions which move into the tunnel barrier and deform the tunnel barrier.

ポアーフィリング法によるアルミニウムアノード酸化皮膜のブレークダウン電位上昇の試み

Aluminum covered with porous anodic oxide films was re-anodized in 0.5 kmolm-3-H3BO3 and 5×10-5kmolm-3-KOH solutions to examine the formation and breakdown of the oxide film.In H3BO3-solution, the pores were filled with new oxide during re-anodizing, resulting in the uniform thickening of the barrier layer until film breakdown started. The breakdown potential of the film formed by the “pore-filling” method was 200V higher at maximum than that formed by anodizing after electropolishing.In KOH solution, the pore-filling with new oxide was accompanied by local dissolution of oxide film, leading to the formation of rough interphase between oxide film and the substrate. The film breakdown potential of the film formed by the “pore-filling” was as high as that the the oxide film formed after electropolishing.Effects of the structure of porous anodic oxide films on the film breakdown potential during re-anodizing in H3BO3 solution are discussed.

Effects of Ni on Stress Corrosion Susceptibility of High-Cr Ferritic Stainless Steels in Hot Cl−Solution

Abstract Effects of nickel (Ni) on the stress corrosion susceptibility of high-chromium (Cr) ferritic stainless steels (SS) in boiling solution of 42% lithium chloride (LiCl) plus thiourea (NH2CSNH2) were investigated using a uniaxial tension-constant load tester. The influence of Ni on film breakdown potential, repassivation rate, creep behavior, and susceptibility to hydrogen (H)-induced failure of the alloys was evaluated. Commercial alloys of 29% Cr- 4% molybdenum (Mo) (UNS S44700) and 29% Cr-4% Mo-2% Ni (UNS S44800) ferritic SS were compared. The 29% Cr-4% Mo alloy was immune to stress corrosion cracking (SCC) at opencircuit potential (OCP) but became susceptible when polarized anodically to critical cracking potential (Ecc, −450 mVSCE) which was 20 mVSCE more noble to the stabilized corrosion potential (Ecorr, −470 mVSCE). Addition of 2% Ni to the 26% Cr-4% Mo alloy did not affect Ecc, but did induce susceptibility to cracking by increasing Ecorr to a value 80 mVSCE noble to Ecc. The 2% Ni addition ...

Influence of Chloride Ions on the Anodic Dissolution of Tin in Bicarbonate and Phosphate Solutions at pH 8

The influence of Cl− ions on passivated tin in 0.3M and 0.5M bicarbonate or phosphate solutions of pH 8 has been studied. The growth of a passive film was carried out in deaerated chloride free solution at to a constant thickness of 4 mC cm−2 and the film breakdown potential was determined potentiodynamically in Cl− containing solutions. The film breakdown potential was found to increase linearly with the potential scan rate. The critical pitting potential (breakdown potential at zero scan rate) decreased linearly with . The bicarbonate and phosphate ions inhibited the chloride attack, the effect being greater for bicarbonates. A rough, bare tin surface in the corrosion zones was observed in the phosphate solutions, whereas the pits were covered by corrosion products in the bicarbonate solutions. The current oscillations observed during experiments on the preoxidized electrode were very regular in the case of and : sine waveform with the same frequency of ∼0.3 Hz. However, the variations became chaotic when the applied potential was more positive than the breakdown potential.