Potentiostatic Polarization Techniques Research Articles

(General Student Poster Award Winner, 3rd Place) Corrosion Electrochemistry in Molten Flinak Salts

An existing knowledge gap in the field of molten salt (MS) corrosion is the lack of in situ, diagnostical and instantaneous measurements of the underlying corrosion system. Numerous investigations comparing the corrosion behavior of commercial alloys with complex microstructures and compositions in molten fluoride salts have been conducted during the past five years. A few of these have been expanded from exposure studies to those using electrochemical methods[1,2]. In essence, electrochemical techniques offer an in situ and diagnostical way to analyze the corrosion behavior of potential materials in real-time, either in open-circuit (static immersion) or polarized conditions. Investigations on MS corrosion have found few mechanistic insights that elucidate the fundamentals of electrode reactions and characteristics of the electrode-salt interface. However, fate of elements oxidized are not tracked. Nonetheless can be difficult to understand the electrochemical corrosion behavior of structural alloys in non-aqueous, aggressive media, such as molten LiF-NaF-KF (FLiNaK) salts, as they may be influenced by a wide range of parameters (such as microstructure, impurity, and potential).Understanding the mechanism of an alloy's most susceptible alloying constituent's dissolution and describing the rate-determining steps (RDS) of this process using the principles of thermodynamics, kinetics, and electrochemistry are fundamental initial steps in understanding the complexities of alloy corrosion. Chromium (Cr) is frequently referred to in molten fluorides research as an essential yet harmful alloying element in candidate molten salt reactor structural alloys (i.e.Ni-based superalloys and stainless steels) due to its high thermodynamic driving force to dissolve relative to other alloying elements. Because of that Cr is a crucial material for research because it serves as the basis for work on Fe-Cr, Ni-Cr, and Fe-Ni-Cr alloys as well as other alloys. However, published research does not consistently describe the mechanism relating to Cr corrosion in FLiNaK.The objective of this work was to explore the electrochemical corrosion behavior of pure Cr in molten FLiNaK salts at 600oC using electrochemical methods. In this study, we describe and clarify the regimes of Cr corrosion in FLiNaK at 600 oC that are potential-dependent, rate-limiting charge-transfer and mass-transport regulated.A range of measurements based on electrochemistry and material characterization, such as linear, cyclic, and potentiostatic polarization techniques, is presented. A key finding in this work was the attempt to establish a connection between the reactivity of Cr in an aggressive, non-aqueous electrolyte such as molten FLiNaK to electrochemical potentials and corrosion morphology predicted thermodynamically. It was found, that the corrosion mechanism of Cr in FLiNaK was dependent upon mixed potentials established by the anodic Cr/Cr(II) and/or Cr(II) /Cr(III) oxidations coupled with cathodic reactions by multiple oxidizer candidates whose predominance is a function of salt impurity level and Cr exposure times. Results suggest that the early stage of Cr dissolution is regulated by charge-transfer (or activation-controlled) in FLiNaK at 600oC. This type of mechanism can occur at low overpotential (i.e. lower driving force) and can be interrupted by the oversaturation of Cr at the surface. Its presence may be eliminated if the salt film is present. The electrochemical potential in which mass transport regime is rate-limiting falls within the phase stability field where CrF6 3- species dominates, and leading to the formation of a K3CrF6 salt film. The post-exposure SEM analysis revealed that Cr dissolution in this regime involves volume transport within each grain, resulting in the revelation of surface facets containing crystallographic features of cubic crystals.The application of electrochemistry enables a more straightforward way to identify potential RDS that control the rate of Cr corrosion and offers a temporal description of the corrosion mechanism. Such fundamental understanding, especially on the nature of cathodic and anodic reactions of Cr, can provide a baseline to understand the corrosion mechanism of complex alloys. The post-corrosion microstructure investigation, the XRD of the solidified salt combination, and the thermodynamic analysis of the stable phases present in each corrosion regime all corroborated these conclusions. Acknowledgments Research is primarily supported as part of the fundamental understanding of transport under reactor extremes (FUTURE), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Wang, Y. L., et al. Corrosion Science 109, 43–49 (2016).Chan, H.L., et al. NPJ Materials Degradation 6(1), 46 (2022).

Corrosion and Corrosion Protection of Copper Sculptures by Formation of Composite Barrier

Nitrogen dioxide, carbon dioxide and sulphur dioxide are acidic gas and they produce corrosive medium for copper sculptures. These gases absorb moisture to form nitric acid, carbonic and sulphuric acid. It forms corrosion cell on the surface of copper and accelerate corrosion reactions. The corrosion cell formation is written as: Cu|Cu2+||H+|H2 thus corrosion reactions start and copper is oxidized into Cu2+surface and it is oxidized into Cu2+ whereas H+ ion is reduced into H2 . Nitric acid environment copper exhibits galvanic, pitting, stress, crevice, blistering, embrittlement and intergranular corrosion. The corrosion reactions change physical, chemical and mechanical properties of corroded materials. Nanocoating compound tetrahydrodibenzo[a,d][7]annulene-5,11-disemicarbazone and SiC electrospray compounds used to control the corrosion of copper in nitrogen dioxide medium. For corrosion mitigation of copper metal interface was coated with tetrahydro-dibenzo[a,d][7]annulene-5,11-disemicarbazone and SiC. The coating compound tetrahydro-dibenzo[a,d][7]annulene-5,11-disemicarbazone was synthesized in laboratory. Nozzle spray techniques used for nanocoating and electrospraying. The corrosion rate of copper was determined by gravimetric loss method at different temperatures, concentrations and days in nitrogen dioxide medium. Potentiostatic polarization technique used for the determination of electrode potential, corrosion current and current density. Nanocoating and electrospraying compounds formed a composite barrier on the surface of base metal by chemical bonding. The nanocoating and electrospray compounds adhered on base metal by chemisorptions to confirm by activation energy, heat of adsorption, free energy, enthalpy and entropy. The nanocoating and electrospray deposited on copper confirmed by Langmuir, Frundlich and Temkin isotherm. Copper formed a complex compound to interact with tetrahydro-dibenzo[a,d][7]annulene-5,11-disemicarbazone and SiC. Electrospraying SiC blocked porosities of nanocoating compound and checked osmosis process of nitrogen dioxide. Thenanocoating and electrospray compounds decreased corrosion rate and increased surface coverage areas and percentage coating efficiencies.

Corrosion Behaviors of Fe-22Cr-16Mn-0.55N High-Nitrogen Austenitic Stainless Steel in 3.5% NaCl Solution

In this study, the corrosion behavior of the high-nitrogen austenitic stainless steel (HNS) Fe-22Cr-16Mn-0.55N before and after solution treatment (ST) in 3.5% NaCl solution has been investigated. The effect of a solution temperature of 1100 °C and heat preservation for 30 min on the corrosion resistance and passive film protection of HNS steel was studied. Open-circuit potential, potentiodynamic polarization and electrochemical impedance tests were used to assess the corrosion resistance of treated and untreated steels. In addition, potentiostatic polarization and XPS techniques together with Mott–Schottky curves were applied to determine the composition and properties of the passive films. The results showed that after solution treatment, the grain size of HNS decreased and the grain became more uniform. Although corrosion occurred on HNSs both before and after treatment, solution treatment resulted in greater compactness in passive films, leading to lower carrier density, lower corrosion current density and better corrosion resistance.

Superhydrophobic Stearic Acid Deposited by Dip-Coating on AISI 304 Stainless Steel: Electrochemical Behavior in a Saline Solutions

A superhydrophobic surface with excellent corrosion resistance was prepared on sandblasted AISI 304 stainless steel by applying stearic acid through dip-coating. Superhydrophobic surfaces have several advantages, such as self-cleaning, anti-icing, anti-adherent, and anti-corrosion. In this work, roughness and superhydrophobic properties were studied by contact angle, optical profilometry, electrochemical impedance spectroscopy, and potentiostatic polarization techniques. The lowest surface wettability was obtained in sandblasted samples (146.2°, due to the roughness change). The stearic acid coating response on sandblasted substrates was acquired by EIS analysis. The sample set with higher corrosion resistance at saline solution during the polarized potentiostat tests was the smoothly coated sandblasted samples. For comparison, corrosion current density of sample without coating was 3.13x10-7, whilst the coated sample was 1.34x10-8. Further, the passive current density was 6.02x10-7 for as-received samples and 2.16x10-8 for coated samples. The modified surface proved to be effective against corrosion when compared to smooth surfaces.

Investigation of the Microstructure Dependence of Critical Pitting Temperature and Pitting Potential in a 2205 Duplex Stainless Steel

Dependence of 2205 duplex stainless steel pitting resistance on its microstructure was investigated using microstructural examinations and potentiodynamic and potentiostatic polarization techniques. An as-received hot-rolled alloy was subjected to different heat treatments to understand how microstructural characteristics individually affect the corrosion resistance in terms of critical pitting temperature (CPT), pitting potential (E pit), and metastable pitting characteristics. Results revealed that there is a transition temperature interval for the 2205 DSS. By promoting pit initiation and pit propagation, the Widmanstätten structure significantly deteriorated both CPT, by 10 °C, and E pit, compared to the as-received hot-rolled specimen. The σ phase appearance was also associated with a minor drop in CPT, but a considerable reduction in E pit as it increased the occurrence frequency of metastable pits. The specimen having equiaxed grains had the highest CPT, underwent stable pitting at 47 °C, but still it had a low E pit compared to the hot-rolled specimen due to its higher occurrence frequency of metastable pits. The formation of the Widmanstätten austenite needles weakened the ferrite phase in terms of the pitting resistance by reducing the contents of Cr and Mo in it and made it more susceptible to pit propagation.

A Study on The Electrochemical Behaviour of 416 and 440C Martensitic Stainless Steels in Alcohols.(Dept.M)

The electrochemical behaviour of AISI 416 and 440 martensitic stainless steel in alcoholic solutions (ethanol, iso-propanol and t-butanol) containing different concentractions of sulfuric acid (0,1 to 2M) has been investigated using potentiostatic anodic-cathodic polarization techniques. An activ- passive transition behaviour were observed and the critical current density (CD) for passivity was found to be dependent on tile concentration of acid in alcohols. The effect of water additions (5, 10, 15%) to IM H2So4 alcohols has been also investigated. It was found that the presence of water strongly influences the passivation of both steels in IM H2SO4 - alcoholic solutions.

Tungsten Oxide Nanoparticles as Corrosion Inhibitor of Stainless Steel in Saline Medium

Tungsten oxide (WO3) nanoparticles at various concentrations of 1.7×10-2, 2.5×10-2 and 3.4×10-2 M were electrophoretic deposited onto stainless steel surface for corrosion inhibition investigations with respect to concentration as well as temperature by using potentiostatic polarization technique. Results obtained show that WO3 nano coating was used as a barrier layer for the corrosion protection of stainless steel in saline solution. The morphology of nanoparticles was examined using Scanning Electron Microscopy (SEM).The obtained results indicated that these nanoparticles are good inhibitors. All polarization curves yielded similar behavior pointing to stainless steel corrosion is controlled by the charge transfer process so that the stainless steel dissolution mechanism does not alter due to the presence of the nanoparticles. Generally, increasing the inhibitor concentration and temperatures leads to an increase in the inhibition efficiency. Thermodynamic parameters were calculated, and the energy of activation data obtained of the corrosion reaction was decreased with an increase of the concentration of nanoparticles. It is likely that the adsorption of WO3NP on the surface of stainless steel was chemical in nature.

Efficient gel-polymer electrolyte for sodium-ion batteries based on poly(acrylonitrile-co-methyl acrylate)

Efficient polyacrylonitrile-based gel-polymer electrolyte for sodium-ion batteries was prepared using commercially available copolymer poly(acrylonitrile-co-methyl acrylate), propylene carbonate as plasticizer, and NaClO4 or NaPF6 as electrolyte salts. Specific and molar conductivities were determined at different salt concentrations using the ac impedance technique with reversible rather than blocking electrodes. The cation transference numbers were measured using the potentiostatic polarization technique. The electrolytes showed high room-temperature ionic conductivities up to 1.8 × 10−3 S cm−1 and high cation transference numbers up to 0.89. The conductivity followed the Arrhenius behavior with the activation energy of 12–15 kJ mol−1. The polymer electrolyte was able to sustain over 700 charge-discharge cycles in full sodium-ion cells at room temperature and at −20 °C. The results indicate that polyacrylonitrile-based gel-polymer electrolytes are promising systems to replace liquid electrolytes in future sodium-ion batteries.

Pyrrolidinium Ionic Liquid Electrolyte with Bis(trifluoromethylsulfonyl)imide and Bis(fluorosulfonyl)imide Anions: Lithium Solvation and Mobility, and Performance in Lithium Metal–Lithium Iron Phosphate Batteries

A mixture of n-methyl-n-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [PYR13][TFSI] and n-propyl-n-methylpyrrolidinium bis(fluorosulfonyl)imide, [PYR13][FSI] ionic liquids (ILs) is investigated for lithium–metal batteries. Specifically, the relation among conductivity, solvation structure, and Li⁺ mobility is investigated in a Li/IL/IL type ternary mixture. Li⁺ anion coordination numbers with both [TFSI] and [FSI] in the ternary mixtures are derived from Raman analysis. The Li⁺ transference number was measured by a combination of potentiostatic polarization and electrochemical impedance spectroscopy (EIS) techniques. The electrochemical stability and transport property of the developed ternary mixture were confirmed with Li–Li symmetrical and Li–LiFePO₄ cells. The ternary system exhibited improved rate capability compared to binary parent electrolytes as well as the state-of-the art carbonate-based electrolyte at −20 °C, and slightly better cycling stability at 25 °C. This study demonstrates the flexibility in tailoring physical properties and the Li⁺ solvation environment by ternary Li/IL/IL mixtures for enhanced battery performance.

Cr(VI) Ion Reduction Reaction on Nickel and Stainless Steel Electrodes in Acid Medium

The reduction of Cr(VI) ion in 0.5 M H2SO4 deaerated solutions with different concentrations of K2CrO4 on nickel and 18Cr-10Ni stainless steel electrodes have been studied by potentiostatic polarisation technique depending on the chromate concentration in solution. The kinetic parameters -Tafel slope, charge transfer coefficient and limiting current density -were evaluated comparatively. For the solutions containing �5 mM K2CrO4 the Tafel slopes are higher on stainless steel than on nickel (around -135 mV�dec-1 for nickel and -165 mV�dec-1 for stainless steel). Moreover, by increasing the chromate concentration the Tafel slopes increase on nickel and decrease on stainless steel. The low Tafel slope values of -75 mV�dec-1 obtained on stainless steel electrode in the potential region -0.5� -0.75V vs. SCE could be due to a decrease of the charge transfer process rate because of the presence of a physical barrier. The values for the reaction rates are slightly higher for nickel than for stainless steel electrodes on all the studied potential range. The reaction product is soluble trivalent chromium, excepting the solution with 500 mM K2CrO4, when a Cr(OH)3 film may cover the electrode surface that determines the decrease of the reaction rate.

Electrode Scratching Technique As a Robust Way to Decouple Erosion-Corrosion Components

The substantial number of parameters and their interdependence makes the modelling and prediction of erosion-corrosion rates a rather challenging task, yet owing to increasing computational capacity one that is potentially solvable. To accurately estimate the rate of material loss, universally accepted explanations of the mechanisms of combined erosion and corrosion must be developed. The absence of reliable data can undermine safety and predictability of industrial processes, such as oil and gas transportation. The aim of this work is to demonstrate the application of an electrode scratching technique coupled with microstructural characterisation for improved understanding of synergy in erosion-corrosion. In this work, a rotating disc electrode scratching setup, with well-defined and controlled flow conditions, was developed to study individual contributions to erosion-corrosion. Linear potentiodynamic and potentiostatic polarization techniques were used to reproducibly monitor the kinetics of dissolution and repassivation of API X65 steel electrodes upon scratching. Samples characterized using high-resolution scanning electron microscopy (SEM) and white-light interferometry (WLI), confirm the synergy; the losses due to erosion-corrosion are larger than that of the summation of the separate contributions of erosion and corrosion. Focused Ion Beam (FIB) milling was implemented for in-situ lift-out of lamellae from scratched samples for Transmission Electron Microscopy (TEM) characterisation. We confirm distinct microstructural changes take place in the vicinity of scratches: with nanoscale grain refinement and orientation changes observed (See Figure 1). These results, coupled with electrochemical data and micro-hardness measurements, suggest time-dependent surface-hardening processes affect material loss rates during mechanical-electrochemical coupled corrosion. Figure 1

Ni/Ni-Cr-P and Ni/Ni-Mo-Cr-P Electrodeposited Coatings As Bipolar Plate in Polymer Electrolyte Membrane Fuel Cell Environment

Polymer electrolyte membrane (PEM) fuel cells are expected to play a major role in transporting humans and goods. However, one of major bottlenecks is the high materials and manufacturing cost. One way to lower the cost to a great extent is by replacing conventional graphitic bipolar plates with metallic bipolar plates (BPPs), as they costs around 30% of the total cost of stack1. That said, metallic BPPs have durability issues. Over time, they corrode and show higher interfacial contact resistance (ICR). In this work we attempt to engineer the surface of metallic BPPs, so that they perform for longer duration without degrading. To keep the process economical and commercially attractive, a bilayer coating of Ni followed by Ni-Cr-P alloy is pulsed electrodeposited on AISI 1020 low carbon steel. The electrodeposition process is optimized varying the process parameters, such as electrolyte composition, temperature and deposition current. Field emission scanning electron microscopy and energy dispersive x-ray spectroscopy are used to study the surface morphology and compositional analysis of coating, respectively. Variation in microstructure and composition the Ni/Ni-Cr-P coating is observed with change in process parameter such as pH and temperature. Corrosion studies were carried out on Ni/Ni-Cr-P coated samples using potentiodynamic technique in accelerated (0.5 M H2SO4 + 2 ppm HF) solution at 80ºC. Ni/Ni-Cr-P coated samples with higher Cr content exhibited better corrosion resistance behaviour in both cathodic (air-purging) as well as anodic (H2-purging) environment compared to the bare substrate. Long term durability of Ni/Ni-Cr-P coated samples and AISI 1020 low carbon steel samples were studied using potentiostatic polarization technique. Both coated and bare samples are placed in the accelerated electrolyte solution. Ni/Ni-Cr-P coated samples showed better durability with less change in current density, while bare samples completely disintegrate and precipitate into the solution within 2–3 hours in potentiostatic mode in both the environments. Ni/Ni-Cr-P coated sample show lower interfacial contact resistance (ICR) value than that of bare AISI 1020 steel samples. For better corrosion resistance and improvement in surface electrical property, Mo was included in the coating composition2. Ni/Ni-Mo-Cr-P coated samples show improved corrosion resistance than Ni/Ni-Cr-P coated samples and AISI 1020 low carbon steel bare samples in both anodic and cathodic PEM fuel cell environment. Reference: R. Taherian, J. Power Sources, 265, 370–390 (2014) http://dx.doi.org/10.1016/j.jpowsour.2014.04.081.H. Rashtchi et al., Fuel Cells, 16, 784–800 (2016) http://dx.doi.org/10.1002/fuce.201600062

Sol-gel synthesis, characterization and electrochemical corrosion behavior of S-N-C-doped TiO2 nano coating on copper

The aim of this study is the synthesis of S-N-C-Doped TiO2 nano coating which would provide corrosion resistance when deposited on copper substrate. Nano-titania coatings doped simultaneously with three atoms of nitrogen, sulfur and carbon have been provided on the surface of copper by sol–gel process via dip-coating technique. The characterization and morphology of the obtained coatings checked by scanning electron microscopy (SEM) and X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS).Different calcination temperatures (200, 300, 400 °C) and heating times (1, 2, 3 h) were used in the synthesis stages of the coatings. The performance of the coatings was examined via potentiostatic polarization and electrochemical impedance spectroscopy (EIS) techniques. Electrochemical results show that the nano coating synthesized at 300 °C with the heating time of 2 h is very efficient for the corrosion protection of copper.The corrosion current density of the coated-copper electrode significantly decreases and the corrosion potential shifted to positive values when compared with un-coated copper electrode. The obtained results show that the 300 °C for calcination temperature and 2 h for time heating are the optimum conditions that have created the homogeneous and non-cracked surfaces of S-N-C-doped TiO2 nano coating with improved anticorrosive efficiency.

Anti-corrosion Properties of Ethanol Extract of Acacia senegalensis stem on Al–Si–Fe/SiC Composite in Sulfuric Acid Medium

The potential of Acacia senegalensis stem extract for corrosion inhibition of aluminum alloy (Al–Si–Fe) reinforced with 15% SiC in 0.5 M H2SO4 was investigated using gravimetric and potentiostatic polarization techniques. The plant stems were characterized by both FT-IR and GC–MS with the aims of knowing the active components. The concentration of inhibitor, temperature and time were varied in the range of 0–10% v/v at 2% v/v interval, 30–70 °C at 20 °C interval and 12–72 h at 12 h interval, respectively. The surface morphology of the coupons before and after corrosion tests were characterized by scanning electron microscopy (SEM) techniques. The results of both weight loss and potentiostatic polarization indicated that the corrosion inhibition efficiency increased with an increase in inhibitor concentration at optimum of 8% v/v (92.66% at 30 °C) and decreased with an increase in temperature at 50 °C (89.61%) and at 70 °C (79.98%). Both the adsorption and physisorption followed Langmuir adsorption isotherm. SEM shows a smooth morphology for the specimens after immersion in 0.5 M H2SO4 solutions containing 8% v/v optimum of Acacia senegalensis. The FT-IR and GC–MS results revealed some elements (−N=C=S, C≡N), chemical bonds/functional groups (NH2) which were responsible for the protection of aluminum alloy (Al–Si–Fe) reinforced with 15% SiC in acid environment. High inhibition efficiency was obtained, which suggests that the extract could serve as an effective inhibitor of the composite in 0.5 M sulfuric acid.

Study of the Inhibition Effect of Carbendazim Towards Carbon Steel Corrosion in 0.50M HCl Solutions

The inhibition effect of carbendazim on the corrosion behavior of carbon steel in 0.50M HCl solution was investigated using weight loss, potentiostatic polarization and electrochemical impedance spectroscopy techniques. The inhibition efficiency increased as the concentration of the inhibitor was increased with a maximum achievable inhibition efficiency of almost 90 %. Electrochemical impedance spectroscopy technique was utilized to investigate the effect of temperature on corrosion inhibition and was found to be insignificant and thermodynamic parameters were calculated. The adsorption of the inhibitor on carbon steel surface obeys Langmuir adsorption isotherm.

Corrosion Protection of Iron Alloy Using <i> Peganum harmala </i> Extract as Inhibitor in Acidic Solution

This work describes the inhibition effect of different concentration of an aqueous extracted of Peganum harmala seed on the corrosion of carbon steel in 1 M H2SO4 solution using potentiostatic polarization techniques at the temperature range (298 - 328) K. The result showed that the inhibition efficiency increased with increasing of extract inhibitor concentration and temperature. The adsorption of inhibitor on carbon steel surface was fit into Langmuir adsorption isotherm. Kinetic and thermodynamic parameters governing the corrosion and the adsorption process were calculated and discussed.

Corrosion Analysis of AZ61 Alloy with Different Level of Ca Addition and Aging

The corrosion behavior of AZ61 alloyed with 0.5, 1.0, 1.5 and 2.0% Ca were studied by potentiostatic polarization technique in 3.5wt. % NaCl solution and the further effect of corrosion behavior have been studied after aging at different temperature in a controlled environment.The results show that the calcium addition enhances the corrosion resistance.Simultaneously when the alloy is aged at 180°C, the corrosion resistance has improved. This study also reveals the interesting microstructural change that isresponsible for the improved corrosion resistance. Themicrostructural characterization of this alloy was studied using Optical and Scanning Electron Microscopy (SEM).

Anticorrosion properties of an epoxy zinc-rich composite coating reinforced with zinc, aluminum, and iron oxide pigments

The effects of lamellar aluminum (Al) and micaceous iron oxide (MIO) pigments on the anticorrosion properties of an epoxy zinc-rich coating were studied. To this end, the epoxy zinc-rich coatings containing 70% w/w spherical Zn particles, 60% w/w Zn + 10% w/w MIO, and 60% w/w Zn + 10% w/w Al were prepared. The electrochemical noise (ECN), potentiostatic polarization technique, and salt spray test were employed in order to investigate the anticorrosion performances of the zinc-rich coatings. The zinc-rich coatings morphologies were studied by scanning electron microscope (SEM) before and after the salt spray test. The open-circuit potential values were also measured at different immersion times. Results showed that MIO particles could enhance the cathodic protection duration of the zinc-rich coating by enhancing its barrier properties and reducing the zinc particles oxidation rate. It was also shown that Al particles reduced zinc-rich coating sacrificial behavior at short immersion times and increased it at long immersion times. Unlike MIO particles, Al particles behaved both as barrier and sacrificial pigment.

Acceleration and quantitative evaluation of degradation for corrosion protective coatings on buried pipeline: Part II. Application to the evaluation of polyethylene and coal-tar enamel coatings

The pulsed potentiostatic polarization technique proposed previously has been applied to evaluate the electrochemical degradation of polyethylene and coal-tar enamel coated SS400 for buried pipeline. The degradation of coated systems was accelerated and evaluated using electrochemical techniques (pulsed potentiostatic polarization test, electrochemical impedance spectroscopy) and surface analyses (scanning electron microscopy and energy dispersive X-ray spectroscopy). It was found that polyethylene coating had better protective performance than coal-tar enamel coating due to its low porosity. It was confirmed that the electrochemically accelerated test is an effective technique in the evaluation of coating performance.

Corrosion Behavior of a Fe-25at%Sn Supersaturated Solid Solution in H3PO4 Solution

Corrosion resistance of iron can be drastically improved by addition of passivating alloying elements. A supersaturated solid solution of Fe-25at%Sn was produced by mechanical alloying of commercially pure iron and tin powders for 24 hours using a planetary ball mill. Electrochemical measurements were performed on cold compacted unsintered specimens.. XRD investigation on produced alloy showed the characteristics of a supersaturated solid solution. Corrosion behavior of the solid solution alloy was investigated in 0.1M H3PO4 employing potentiodynamic and potentiostatic polarization techniques. The anodic behavior of mechanically alloyed specimens was compared with specimens prepared from individually compacted iron, tin and appropriate admixture of tin/iron powders. Potentiodynamic polarization of supersaturated specimen featured a gradual decrease in anodic current density, indicating a feature of quasi passivation which was attributed to the tin surface enrichment as a result of preferential iron dissolution. Anodic current density from the result of potentiostatic polarization of the prepared alloy also showed a gradual decrease with time following i¥t-0.45 relationships indicating a characterization of passivity. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) examination of the specimen surface after potentiostatic anodic polarization test confirmed the presence of high tin content on the surface.