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Environmentally assisted cracking (EAC) behavior of two Mg-rare earth (RE) alloys such as Mg–Zn–Gd–Nd–Zr (EV31A) and Mg–Y–Nd (WE43C) alloys was investigated by using U-bend specimens. Open circuit potentials (OCP) of the U-bend specimens were monitored during the EAC tests in 0.1 M NaOH solution with different chloride concentrations at room temperature. EV31A (as-received, and peak aged) and WE43C (peak aged) specimens failed by SCC in 80 ppm chloride containing 0.1 M NaOH solution at OCP. When the EAC initiation occurred, the OCP decreased continuously. Irregular fluctuations of the OCP were observed in the absence of EAC. The OCP versus time profile could be used for monitoring EAC failure of the Mg–RE alloy components in real life service. Applied potentials did not cause cracking of the EV31A alloy in 80 ppm Cl− containing 0.1 M NaOH. Accelerated cracking was observed on the WE43C alloy in peak-aged condition under the applied potentials in the transpassive region when compared to that of OCP condition. Overaging decreased the susceptibility to cracking.

Aging of graphite-based materials results in slower heterogeneous electron transfer (HET) kinetics and limits their conducting and catalytic performance. A thermal treatment protocol reportedly maintained a high HET kinetics of graphite by at least nine weeks. The present report investigates the consequences of such HET increases on graphite stabilities. Raman 2D peak evolution, potential windows, EIS, optical AFM, chronoamperometry and potentiodynamic polarization studies were employed to investigate electrochemical, structural and corrosion stabilities and mechanisms of the pristine and thermally treated graphite as they relate to its HET kinetics. Structure-induced electronic changes are suggested to trigger improved tunneling paths through the interfaces from the bulk layer. This tunneling improves and sustains HET kinetics by orders of magnitude in the treated graphite. Except for the graphite fibers, thermal treatment increased HET kinetics without compromises to electrochemical, structural and corrosion stabilities. In most instances, these properties improved over the pristine graphite. Thermal treatment transforms the pristine graphite into well-ordered lattices. AFM images show visual indifference between the pristine and treated graphite. However, their electronic structures and resultant electrochemistry are different. Despite minimal energy differences between both structures, a large thermodynamic barrier hinders the reversal of the treated to the pristine-like state.

Iron (Fe) and chromium (Cr) powders at various concentrations of Cr (6, 9, 12 and 14 wt%) were mechanically alloyed via high-energy ball milling for 10 h. The milled Fe–Cr alloy powders were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD) for understanding the impact of varying chromium content on the characteristics of the milled powder. The powder samples were then consolidated via spark plasma sintering (SPS) at 1000 °C for 45 min at 80 MPa pressure. The density of the consolidated samples was measured and found to reach a maximum of 98%. Microstructural characterization of the spark plasma sintered samples was performed using SEM and XRD. Electrochemical corrosion tests were performed on spark plasma sintered samples in 0.5 M H2SO4, 0.05 M NaH2PO4 and 1 M NaOH solutions using potentiodynamic polarization, electrochemical impedance spectroscopy and Mott–Schottky analysis. The corrosion behavior of the spark plasma sintered materials was compared with that of a wrought HT-9 steel (12Cr based ferritic–martensitic steel). The work presented here is a comparative study of microstructural evolution and corrosion behavior between the different spark plasma sintered Fe–Cr model alloys and wrought HT-9 steel.

Stainless steel (SS) canisters used for storing spent nuclear waste are prone to chloride-induced stress corrosion cracking. Friction stir welding (FSW), being a low heat input process, can be used for repair welding of these canisters. In this study, an artificial crack was introduced on the 304L SS coupons by an electric discharge machining process. The artificial crack was repair-welded by FSW by maintaining the tool temperature a constant at two levels (725 and 825 °C). Friction stirring significantly reduced the grain size of the stirred zone (SZ) from about 47 to 2–4 μm. The fraction of low-angle grain boundaries increased in the SZ from 2 to 37–43%. On the other hand, the fraction of special grain boundaries (Σ3 and Σ9) that was ~ 50% in the base metal reduced to

In recent time, solid state crack repair techniques in spent nuclear fuel dry storage canisters (SNF-DSC) have garnered significant interest. Plates of austenitic stainless steels are usually arc welded to fabricate the cylindrical canisters which are prone to chloride-induced stress corrosion cracking. Friction stir welding (FSW) is considered to be a potential candidate for damage repair. In this work, electrical discharge machining was used to simulate cracks in 304L stainless steel plates of 12.7 mm thickness. Subsequently, isothermal FSW was carried out at two different temperatures (725 and 825°C) in order to repair the simulated crack. Microstructure-mechanical property correlations in FSWed plates were studied in detail. Significant grain refinement observed in the stir zone (SZ) was attributed to dynamic recrystallization occurring during FSW. A comparison of Vickers microhardness showed higher hardness and homogeneity in the 725°C SZ than its 825°C counterpart. The fraction of Σ3 boundary is found to be low in the SZ as compared to base metal (BM). Yield strength of the joints was found to be approximately 100 MPa higher than that of the BM accompanied by a drop in ductility by a factor of 2. Residual stress profile across 825°C weld was measured using x-ray diffraction.

This study examined the effects of silica addition on electrochemical behavior of rebar in native pH 12.5 saturated solutions prepared by leaching of Portland Type-II cement, and in solutions reduc...

Mg-RE alloy Electron717 (ZE10A, UNS M11600) has a nominal composition of 1.2wt % Zn, 0.25wt% Zr

Commercial purity Mg, Mg-RE alloys ZE10A (UNS M11600), and EV31A (UNS M12310) were evaluated in the as-received condition for potential application as anode for Mg-air battery. Anodic and cathodic polarization studies were performed in 0.6 M NaCl, 0.5 M NaNO3 and 0.1 M Na2SO4 electrolytes. Hydrogen evolved during anodic polarization was measured at different potentials. Electrochemical impedance spectroscopy was carried out at open circuit conditions. The results showed that commercial purity magnesium had higher corrosion resistance than the Mg-RE alloy specimens in all the electrolytes tested. All the specimens showed negative difference effect (NDE) where the rate of hydrogen evolution increased with increased anodic polarization. The NDE was more pronounced on ZE10A than on other materials. The rate of hydrogen evolution was about three times higher in NaCl solution than in other two solutions. The results suggest that ZE10A could be a potential anode material for Mg-air battery due to its high anodic activity in spite of the observed NDE.

Friction stir welding was performed on 304L SS plates in order to heal simulated cracks created by electrical discharge machining. Two different tool temperatures (825 and 725 °C) were chosen for this study. Both neutron diffraction and X-ray diffraction techniques were employed to evaluate the residual stresses along two orthogonal reference directions, longitudinal (σyy) and transverse (σxx). The former technique was also used to measure residual stresses at various depths. It was found that, at 1 mm depth from the top surface inside the stir zone (SZ), the longitudinal component was tensile in nature while the transverse component was compressive. The nature and magnitude of the residual stress fields, and the position of the peak residual stresses were found to vary with the weld depth. The SZ of the 725 °C weld exhibited higher peak stress than 825 °C weld mainly due to a lack of stress relief at the lower temperature.

Novel electrode coating materials are needed for coal-fired magnetohydrodynamic (MHD) direct-current extraction power plants. Addition of potassium salt to increase the conductivity of coal plasma combined with high temperature render the service conditions extremely arduous. Therefore, the electrode coating materials must possess certain properties including high-temperature corrosion resistance, high-temperature oxidation resistance, and adequate electrical conductivity. In this work, those very properties of three different compositions of transition metal diboride solid solutions of HfB2-ZrB2 are studied. Two main approaches of oxidation mitigation methods were employed: adding chemical dopants, such as Hf and La, and performing pre-anodization on the samples to create a protective oxide coating. Thermogravimetric experiments were run at different partial pressures of oxygen to determine the high-temperature oxidation resistance of these boride ceramics. In addition, two different salt coatings (KCl and K2SO4) were applied to the surface of the samples to test their hot corrosion resistance. High-temperature polarization resistance tests were also conducted to measure the electrical resistivity. The addition of lanthanum aided in long term oxidation and corrosion protection, with a parabolic rate constant, Kp = 1.33 × 10−5 kg2/m4 s, a 40% improvement over the sample without the addition of lanthanum under the same conditions. Anodization, however, proved disadvantageous when combined with either lanthanum or a corrosive environment.

Passivation kinetics of two Mg-RE alloys, such as Mg-Nd-Gd-Zn-Zr (EV31A), and Mg-Y-Nd-Gd-Zr (WE43C) were investigated in two different heat treated conditions (solution treated and overaged) in 0.01 - 1.0 M NaOH solutions under potentiostatic conditions. Negative reaction order was observed in dilute NaOH which transitioned to positive values as the passivation time increased and in the 1 M NaOH as well. The passive layers showed platelet morphology and the size of the platelets decreased with increase in the NaOH concentration. The hydrogen evolution reaction (HER) kinetics was not improved on the passive layer covered surface of the Mg-RE alloys in contrast to the improvements reported on the hydroxide covered pure magnesium. The electrochemical impedance increased with increase in the NaOH concentration in the solution treated condition of both Mg-RE alloys, whereas the overaged EV31A alloy showed a reverse trend. The passive layer of EV31A showed almost 100% higher charge carrier density than the film formed on the WE43C in the overaged condition. A better passivation behavior was observed in the solution treated condition than that in the overaged condition which could be attributed to the uniform distribution of the RE elements in the solution treated specimens. The WE43C alloy revealed better corrosion resistance in the alkaline solution than the EV31A alloy. Keywords: Magnesium rare earth alloy, Passivation, Alkaline solution, Hydrogen evolution

Several solid solutions mixtures of ZrB2 and HfB2 with and without additives were investigated for corrosion behavior in aqueous solutions in a wide range of pH. The samples were prepared through ball milling followed by spark plasma sintering (SPS). In addition to the single component diborides and mixtures thereof, additives of Hf, Zr, and Ta pure metals as well as LaB6 and Gd2O3 were mixed in to test for corrosion improvements. Several electrochemical methods were employed including potentiostatic polarization, potentiodynamic polarization and electrical impedance spectroscopy (EIS). The results showed that mixed diboride solid solutions had better corrosion resistance than their unmixed counterparts. ZrB2-rich compositions performed better in the high pH solutions; whereas HfB2-rich compositions showed better corrosion resistance under acidic conditions. Metal-rich compositions and Ta additions did not show improvements in the corrosion resistance, the addition of LaB6 to the Hf0.5Zr0.5B2 solid solution, however, exhibited enhanced corrosion resistance in non-acidic solutions.

Mg–Y–Nd alloy (WE43C or Elektron 43) is a heat treatable magnesium wrought alloy that can be used up to 250 °C for aerospace application. This alloy has excellent mechanical properties (UTS: up to 345 MPa at room temperature) and improved corrosion resistance. Electrochemical passivation studies were conducted on this alloy under different heat treatment conditions in 0.1 M NaOH solution with the addition of chloride from 0 to 1000 ppm. The passive potential range typically extended to more than 1.5 VAg/AgCl. The transpassive potential was not dependent on the heat treatment condition of the alloy when the chloride concentration increased up to 500 ppm. However, pitting protection potential varied with the heat treatment condition when the chloride addition was 500 ppm or more. The specimen surface was analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy to understand the passivation behavior of this alloy. The passivated surface of the WE43C specimens indicated that the surface layer consisted of MgO, Mg(OH)2, and rare earth oxide phases, and the heat treatment conditions did not significantly affect the composition of the surface film. Keywords: Elektron 43, Magnesium alloy, Corrosion, Passivation, Chloride

Electrochemical energy storage of TiO 2 anodic oxide with a novel honeycomb morphology was characterized and compared with that of standard TiO 2 nanotubes. The new morphology consists of several smaller-diameter (∼20 nm) nanotubes stacked inside of each honeycomb like hemisphere. The honeycomb like hemispheres are 160–200 nm in diameter with inter-wall thicknesses of 20–50 nm grown onto a planar barrier layer. The dual-layered honeycomb oxide has a total thickness of about 350–500 nm and high surface area. Cyclic voltammetry and galvanostatic charge-discharge tests were carried out on these oxide samples in as-anodized and thermally annealed conditions using 0.1 M NaOH and 0.1 M LiCl + 0.1 M HCl electrolytes. The honeycomb arrays showed an areal capacitance of 56 mF cm −2 at 100 mV s −1 scan rate, and 0.75 mF cm −2 at a current density of 0.1 mA cm −2 . The areal capacitance of the honeycomb structured samples were about 60% higher than that of the regular TiO 2 nanotubes. The honeycomb structured TiO 2 also showed 33% higher capacitance retention after 10,000 cycles than that of regular TiO 2 nanotubes. The higher capacitance retention could be attributed to the enhanced structural stability of the honeycomb structures.

Addition of glycerol as a viscosity modifier in concrete is proposed to decrease the permeability of corrosion-inducing ions such as chloride and sulfate. In addition to controlling the permeability of concrete, glycerol could perform as an inhibitor of corrosion of rebar steel. Cyclic polarization studies were carried out on metallographically polished rebar steel specimens in actual concrete solutions at two different pH conditions (pH 12.5 and 9.0) and different chloride concentrations. The threshold concentration of chloride for passivity breakdown at pH 12.5 was greater than 50 × 10−3 mol/L in the absence of glycerol addition. The threshold increased to 81 × 10−3 mol/L upon addition of 2 wt% glycerol. The threshold chloride concentration for passivity breakdown in pH 9.0 cement solution was 0.2 × 10−3 mol/L without glycerol addition. No beneficial effect of glycerol was observed in the low pH condition. However, glycerol enhanced the passivation kinetics of the rebar steel in saturated cement solution, but did not affect the electronic properties of the passive layer. The passive layers exhibited n-type semiconductivity with a charge carrier density in the range of 2–7.5 × 1020 cm−3. Polarization of the specimens to potentials is higher than oxygen evolution potential, resulted in transition top-type semiconducting character due to an accumulation of holes. This phenomenon could be related to the passivity breakdown.

Mg–Zn–Gd–Nd–Zr alloy (EV31A) is a heat-treatable magnesium (Mg) cast alloy that can be used up to 200 °C for automobile and aerospace applications. This alloy has excellent mechanical properties (ultimate tensile strength: 280 MPa at room temperature, and ~230 MPa at 200 °C) and improved corrosion resistance. Electrochemical corrosion studies were conducted on this alloy under different heat treatment conditions in 0.1 M NaOH solution with the addition of 0–1000 ppm of chloride. The alloy showed excellent passivity in the 0.1 M NaOH solution. The passive potential range typically extended to more than 1.2 VAg/AgCl. The transpassive potential was observed to be dependent on heat treatment condition of the alloy. More than 80 ppm of chloride was required to induce passivity breakdown in any heat treatment condition. Peak aging at 200 °C for 16 h imparted better resistance for localized corrosion than other heat-treated conditions. The alloy in the as-received condition showed the highest passivation kinetics due to its smaller grain size that possibly increased the diffusion of reactive elements to form protective oxide. The passive film of the EV31A alloy showed n-type semiconductivity with a charge carrier density of ~2 × 1021 cm−3 with no chloride addition. The charge carrier density increased with chloride addition in the electrolyte which could be correlated with the susceptibility to localized corrosion.

Spark plasma sintered transition metal diborides such as HfB 2 , ZrB 2 and their solid solutions were investigated as electrode materials for electrochemical hydrogen evolutions reactions (HER) in 1 M H 2 SO 4 and 1 M NaOH electrolytes. HfB 2 and ZrB 2 formed complete solid solutions when mixed in 1:1, 1:4, and 4:1 ratios and they were stable in both electrolytes. The HER kinetics of the diborides were slower in the basic solution than in the acidic solutions. The Tafel slopes in 1 M H 2 SO 4 were in the range of 0.15–0.18 V/decade except for pure HfB 2 which showed a Tafel slope of 0.38 V/decade. In 1 M NaOH the Tafel slopes were in the range of 0.12–0.27 V/decade. The composition of Hf x Zr 1−x B 2 solid solutions with x=0.2–0.8, influenced the exchange current densities, overpotentials and Tafel slopes of the HER. The EIS data were fitted with a porous film equivalent circuit model in order to better understand the HER behavior. In addition, modeling calculations, using density functional theory approach, were carried out to estimate the density of states and band structure of the boride solid solutions.

Cyclic voltammetry CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy measurements were carried out in 1 and 5 wt% TeCl4 containing LiCl-KCl eutectic molten salt at 450 °C using tungsten and glassy carbon as working electrodes. Reduction of Te(IV) to Te(0) occurred in three steps at potentials more negative than −0.4 VAg/AgCl. The Te(0) was further reduced to Te2− at more negative potentials. Formation of Te2− was observed at potentials more negative than −2.2 VAg/AgCl. Diffusivities of Te4+, Te2+, and Te2− and their formal potentials were estimated from the CV data. The diffusion coefficients of Te4+, Te2+ and Te2− were 0.9 × 10−5, 3.8 × 10−5, and 1.5 × 10−5 cm2 s−1, respectively in the 1 wt% TeCl4 containing LiCl-KCl molten salt. The diffusivity of Te species generally decreased with increase in the concentration of TeCl4.

Electrochemical corrosion tests were carried out on AZ31 magnesium alloy specimens in pH: 4.5, 9.5, and 13.0 solutions with 0-2000 ppm of chloride additions at room temperature. No passivity breakdown was observed during cyclic polarization in pH:13 solutions containing up to 1500 ppm of chloride. Addition of sodium sulfate and sodium dihydrogen phosphate as supporting electrolytes offset the chloride effect on the corrosion of AZ31 in pH 4.5 and 9.5 solutions. The Mott-Schottky analysis showed the presence of a duplex surface layer consisting of an n-type MgO1−x inner layer (x = 0.024-0.05), and a p-type outer layer which thickened with time at the expense of the inner layer.

CaB 6 has a tunneled framework lattice structure that is suitable for intercalation of ions. Electrochemical charge-discharge testing of CaB 6 in lithium containing non-aqueous electrolyte showed a specific capacitance of 35.7 F/g at 0.42 A/g current rating. Even though the specific capacitance was low, CaB 6 shows promise as a Li-ion intercalating material because of its higher diffusivity (3×10 −10 cm 2 /s), p-type semiconductivity, high conductivity, and low density.

Transition metal borides are being considered for use as potential electrode coating materials in magnetohydrodynamic direct power extraction plants from coal-fired plasma. These electrode materials will be exposed to aggressive service conditions at high temperatures. Therefore, high-temperature oxidation resistance is an important property. Consolidated samples containing an equimolar solid solution of ZrB2-HfB2 with and without the addition of 1.8 mol pct LaB6 were prepared by ball milling of commercial boride material followed by spark plasma sintering. These samples were oxidized at 1773 K (1500 °C) in two different conditions: (1) as-sintered and (2) anodized (10 V in 0.1 M KOH electrolyte). Oxidation studies were carried out in 0.3 × 105 and 0.1 Pa oxygen partial pressures. The anodic oxide layers showed hafnium enrichment on the surface of the samples, whereas the high-temperature oxides showed zirconium enrichment. The anodized samples without LaB6 addition showed about 2.5 times higher oxidation resistance in high-oxygen partial pressures than the as-sintered samples. Addition of LaB6 improved the oxidation resistance in the as-sintered condition by about 30 pct in the high-oxygen partial pressure tests.

This work presents novel photochemical reactors with integrated titania photocatalyst for the UV photodecomposition of gaseous methyl iodide present in simulated vessel off-gas (VOG) in a nuclear fuel reprocessing facility. Continuous flow reactors composed of fluorinated ethylene propylene (FEP) were designed and constructed to allow transmission of UV light into the reactor while also providing resistance to the corrosive nature of methyl iodide. Titania nanotube photocatalyst increases methyl iodide photolysis rate by two orders of magnitude compared to that with UV light alone. The rate constant for methyl iodide photolysis with and without catalyst directly depends on the intensity of the light at the location of the reaction, which is inversely proportional to the distance from the linear light source. The titania photocatalyst is significantly active at low light intensity where no detectable reaction occurs in absence of catalyst. For example, at an initial concentration of 400 ppb methyl iodide, a residence time of 9 s, and a light intensity of 0.5 mW/cm2, conversions with and without titania photocatalyst are >99% and 0%, respectively. The UV light source is a low-pressure mercury vapor lamp with primary emission at 254 nm, the wavelength that is in the range of highest cross-sectional absorbance for methyl iodide. Parameters investigated in this work include UV lamp to reactor distance (light intensity), impact of humidity, gas phase composition, and catalyst form (nanotube vs powder). This work also demonstrates that titania possesses a characteristic activation period on the order of approximately one hour to reach its full steady-state activity.

A new method for creating a honeycomb morphology of TiO2 nanotubular arrays has been proposed using a two-step anodization process. The first anodization step utilizes fluoride containing ethylene glycol as an electrolyte (EG-solution). The anodic oxide formed during the first anodization step was removed to expose hemispherical nanoindentations created on the substrate. These nanoimprints acted as templates for honeycomb morphology during the second step of anodization that was carried out in fluoride containing phosphoric acid solution (PA-solution). Several small diameter nanotubes were grown in each honeycomb cell during the second anodization step. The formation of such honeycomb morphology required a threshold concentration of Ti4+ in the anodization electrolyte. Below the threshold Ti4+ concentration (4 × 10−3 M in this investigation), a good honeycomb morphology was not observed. The formation mechanism proposed is based on weakly linear surface perturbation theory aided by compressive growth stresses and a decrease in surface energy due to the presence of [TiF6]2− species.

Electrochemical energy storage using nanostructured metal oxides has been a topic of intensive investigation among materials scientists and electrochemists. Several transition metal oxides such as TiO2, WO3, Fe2O3, and V2O5 in the form of ordered nanoporous or nanotubular structures have been considered as active electrode materials for battery and electrochemical capacitor applications. Bismuth oxide (Bi2O3), because of its reasonable conductivity, high dielectric constant, catalytic behavior, non-toxicity, and abundance finds applications in a wide range of areas like gas sensors, optical coatings, microelectronics, photocatalysts, solid state electrolytes, and superconductors. Electro-deposited bismuth oxide (on various substrates and in various morphologies) has been investigated as a super capacitor material. The specific capacitance of the electro-deposited Bi2O3 varies from 60 -160 F/g. In the present investigation, Bi2O3 nanoporous films were synthesized by electrochemical anodization in the electrolyte solutions containing citric acid, ethylene glycol and glycerol. Nanoporous bismuth oxide films were formed by anodizing bismuth circular discs of 3 mm thick and 12.7 mm diameter. Anodization was carried out at various potentials ranging from 3 V to 60 V for different time durations ranging from 0.5 to 2 h. After anodization, the samples were thermally annealed at 200 °C for 2h. The influences of anodization time, electrolyte concentration and applied voltages on morphology have been investigated in this study. The electrochemical energy storage of the anodic bismuth oxide was investigated by carrying out cyclic voltammetry, galvanostatic charge-discharge, electrochemical impedance spectroscopy (EIS), and Mott-Schottky measurements in different electrolytes in the pH range of 7-14. All the depositions were examined under a FEI Quanta 200F scanning electron microscope. Figure 1 shows the nanoporous morphology of the oxide layer formed at 3V for 30minutes in citric acid electrolyte. The diameters of the pores were in the range of 20 -50 nm and total thickness of the film was about 500nm. It was observed that pore diameter and film thickness changed with the change in applied potential, time and electrolyte concentration. The XRD analysis showed that the nanoporous anodic oxide film after annealing was tetragonal β-Bi2O3. The nanoporous Bi2O3 contained a defect concentration in the range of 7x1016 – 4x1018 cm-3 for various anodized conditions. Figure 2 shows the typical results of cyclic voltammetry of as-anodized bismuth oxide nanoporous in 1 M KOH at different scan rates in a wide potential range. Oxidation of Bi (III) was not observed until 1.0 VAg/AgCl. However, a reduction wave was observed at potentials more negative than -0.6 VAg/AgCl, which could be attributed to the hydrogen ion intercalation in the oxide. Figure 3 shows the potential transient profile during the galvanostatic charge-discharge that was carried out at 10 mA/cm2.The high current density resulted in a sharp potential drop. The capacitance was calculated to be 78 mF/cm2 and the charge retention efficiency was 92%. The capacitance reported for the electrodeposited α-Bi2O3 was in the range of 12 - 22 mF/cm2 [1]. The anodic nanoporous oxide layer showed at least four times higher capacitance than the electro-deposited bismuth oxide. A detailed discussion will be provided in the final presentation on the electrochemical behavior of the Bi2O3 nanoporous structure as a function of morphology, and defect and electronic structures. References 1. T.P. Gujar, V.R. Shinde, D. Lokhande, Sung-Hwan Han, Journal of Power Sources 161 (2006) 1479–1485

ZrO2–WO3 mixed oxide nanotubes were synthesized by a simple electrochemical anodization route. The oxide nanotubes contained a mixture of metastable hexagonal WO3 and monoclinic (and orthorhombic) ZrO2 phases, as well as a mixed-oxide ZrW2O8 phase that showed a metastable tetragonal symmetry. Evaluation of photo-activity of the materials showed generation of photo-potentials of −85 mV and −230 mV in the as-anodized and annealed conditions. Because of the mismatch in the band edge positions of the WO3 and ZrO2 phases and the resultant relaxation of photo-generated charge carriers, no significant photo-current density could be observed. The arrays of oxide nanotubes are considered for electrochemical capacitor application because of their morphology-assisted fast charge/discharge kinetics and large surface area. Presence of a large concentration of charge defects (on the order of 1021 cm−3) and the reported high proton conductivity of the ZrO2–WO3 mixed oxide rendered high capacitance, which decreased with an increase in the scan rate of cyclic voltammetry. The highest measured capacitance was 40.03 mF/cm2 at a scan rate of 10 mV/s and the lowest was 1.93 mF/cm2 at 1 V/s in 1 M sulfuric acid solution.

Growth of metal/oxide nanowires inside of semiconducting nanotubes has several applications for energy storage and energy conversion. In this study, the bottom-up growth of copper nanowires through electrodeposition techniques was studied as a method to fill TiO2 nanotube arrays. Specifically, emphasis was placed on the study of copper containing electrolyte solution kinetics through inhibitor and accelerator additives commonly used in the damascene process. It was observed that the electrical conductivity and wetting characteristics of the TiO2 nanotubes played significant roles in the bottom-up growth of copper nanowire deposition. The electrolytes commonly used in the damascene process were found not to be useful for direct copper deposition inside of the TiO2 nanotubes. Higher pH solution of CuSO4 with tartaric acid as a complexing agent and pulsed deposition conditions showed promising results for copper deposition within the TiO2 nanotubes.

Nanoporous oxide layer was formed on the NdFeB permanent magnets by a simple anodization process in fluoride containing ethylene glycol at 50 V for 15 minutes. The electrochemical polarization behavior of the commercial permanent magnetic material was evaluated in 0.1 M NaH2PO4 solution (pH: 4.75) containing 0–0.017 M of chloride at room temperature. The material was evaluated in magnetized and demagnetized condition with different surface preparation conditions such as: Ni-Cu-Ni coated, uncoated (bare), and anodized. The nickel coated magnetic sample showed reasonable pitting corrosion resistance up to 0.0017 M chloride addition. The uncoated samples showed passivity in chloride free phosphate solution. Chloride additions caused pitting and the pitting protection potential was equal to the corrosion potential with 0.0017 M chloride addition. Demagnetization did not alter the electrochemical polarization. However, the passive film formed on the magnetic sample showed higher charge carrier density than the film formed on the demagnetized sample.

ZrO2-WO3 mixed-oxide nanostructures are created by anodizing a Zr-20 wt% W metal alloy at different potentials followed by annealing at various temperatures. The nanostructures are analyzed via SEM/TEM, X-ray diffraction, and XPS. Phases of h-WO3 and t-ZrW2O8 are found in both the as-anodized form and the annealed form. Also several electrochemical tests including cyclic voltammetry, EIS, and Mott-Schottky analysis are performed in electrolytes of different pHs. The maximum capacitance was determined to be ~45 mF/cm2. The defect concentration in the material was calculated by using the slopes of the Mott-Schottky curves. Finally, the mixed-oxide nanostructures were tested in a two-electrode apparatus which cycled the potential of the system between 0 V and 1 V. The charge and discharge times of the tests increased as cycling continued but the rate of increment changed with pH, annealing temperature, and, to a lesser degree, nanostructure.

Formation of ordered arrays of nanoporous or nanotubular oxides of Al, Ti, and other valve metals during anodization has been reported extensively. These nanostructured oxides could find applications in solar energy conversion, energy storage, photocatalysts for environmental remediation, sensors, templates for nanowire growth, and supports for various catalysts because of their unique geometry and resultant physical properties. Various theories on the formation mechanism of the ordered nanostructures have been proposed in the literature including the field assisted dissolution mechanism[1], localized dielectric breakdown model[2], comparison of the Gibb's free energies of the compact oxide formation and chemical dissolution[3], and morphological instability of the oxide due to ion migration and oxide dissolution[4]. In this presentation, formation of ordered nanoporous anodic oxides of different substrate materials such as pure Ti, Ti-Mn alloy, Zr-W alloy, and bismuth will be analyzed based on the I-t plots and surface perturbation model proposed by Asaro and Tiller[5]. Compressive stresses are developed due to thickening of oxide layer and electrostriction. This compressive stress undulates the barrier film which leads to the surface perturbation. The perturbation releases strain energy of the oxide layer which is balanced by the increase in the surface area. These surface undulations affect the local chemical potentials because of the curvature effect. The presence of surface active species in the anodization electrolyte such as [MeF6]2- helps enhance the surface perturbation. The formation of ordered nanostructure could be explained based on the interaction between electrostatic strain energy and surface energy during anodization in specific environments. [1] Z. Su and W. Zhou, Adv. Mater., 2008, 20, 3663–3667. [2] Z. Su, W. Zhou, F. Jiang and M. Hong, J. Mater. Chem., 2011, 22, 535–544. [3] M. Wang, Y. Liu and H. Yang, Electrochim. Acta, 2012, 62, 424–432 [4] K. R. Hebert, S. P. Albu, I. Paramasivam and P. Schmuki, Nat. Mater., 2012, 11, 162–166. [5] R. J. Asaro and W. A. Tiller, Metall. Trans., 1972, 3, 1789 – 1796.

Spent nuclear fuels are stored in stainless steel canisters. The containers are cooled naturally by a convective airflow through the annulus between the overpack and the canister. This air flow draws dust into the overpacks, and the surfaces of containers are covered with dust. Salts carried by the dust will deliquesce as heat generated by radioactive decay declines over time. The deliquescence of salt deposit could induce various forms of corrosion attack such as pitting and chloride-induced stress corrosion cracking (SCC). In this study, the corrosion behavior of 304L SS - a typical dry storage container material, is evaluated by simulating the deliquescence of salt deposit using a thin electrolyte test condition. Electrochemical corrosion test was performed on 304L Stainless Steel in 3.5 wt% NaCl solution at 20 OC. The tests were carried out in a newly fabricated electrochemical cell with exposed surface area of test specimen being 1 cm2. The cell has a movable PTFE wall which houses a Pt foil as a counter electrode. The adjustable wall enables the thickness of electrolyte to be varied between the SS specimen and the counter electrode. The thickness of the electrolyte was maintained at 1 mm in all the tests. This resulted in the volume of the electrolyte to be 10 ml. Open circuit potential, cyclic polarization and potentiostatic tests at different passivation potential were carried out. The potentiostatic passivation tests were followed by electrochemical impedance spectroscopy and Mott-Schotky analysis in order to understand the initiation of localized corrosion. For comparison, the electrochemical tests are being performed by using bulk electrolytes. The electrochemical polarization behavior in the thin film electrolyte was more or less similar to that in the bulk electrolyte. However, the pitting protection was shifted in the negative direction by about 80 mV in the thin electrolyte as compared to that of bulk electrolyte. Potentiostatic tests conducted at potentials below the pitting protection potential did not show pit initiation. Relatively a quick pit initiation event was observed when the applied potential was 60 mV anodic to the pitting protection potential. Bulk electrolytes showed no passivity breakdown at this potential. The results will be analyzed based on the EIS data, semiconducting properties of the passive film, and UV-Vis absorption of the test electrolytes.

Fluorine doped tin oxide (FTO) is a transparent conducting oxide which is widely used in different applications ranging from sensors, digital displays, smart window coatings, catalysts supports, and electrode substrates for various electrochemical applications. The FTO coated glass slides were evaluated for their chemical stability in different pH solutions at room temperature by carrying out potentiodynamic polarization and cyclic voltammetry (CV). Accelerated stress tests were carried out in 0.1 M HCl and 0.1 M NaOH solutions by scanning the potential from -2 V to 2 VRHE at a scan rate of 1 V/s. Ex-situ vibrational spectroscopy and in-situ photo absorption spectroscopy were carried out to evaluate the material degradation when electrochemically polarized. The FTO was more stable in 0.1 M HNO3 and 0.1 M NaCl solutions under both anodic and cathodic polarization conditions. Oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) were the cathodic reactions observed during cathodic polarization of the FTO. The activity of FTO for HER was higher in the acidic solutions than that in the neutral or alkaline solutions. Cathodic polarization in 0.1 M HCl solution resulted in a reduction of SnO2 to lower valent species. The semiconductivity of FTO, which was n-type at low anodic potentials, was p-type at high anodic potentials possibly due to the formation of a SnO-type surface layer by the removal of lattice oxygen during the oxygen evolution reaction. Cyclic stability of the FTO was evaluated by conducting CV between -2.0 and vbn 2.0 VAg/AgCl at 1 V/s. Intergranular corrosion was observed and the stability was completely lost after 215 cycles in the 0.1 M HCl solution, as seen in Fig. 1. The stability of FTO was better in the 0.1 M NaOH solution, wherein the electro-catalytic activity degraded after 500 cycles, the electrical connectivity was maintained even after 4500 cycles. Figure 1

Friction stir welding (FSW) is being considered as a potential repair welding technique for nuclear spent fuel dry storage canisters. The heat affected zones (HAZ) of the fusion welded regions of the canisters become prone to stress corrosion cracking (SCC) due to chlorides in the environment. Pitting corrosion is usually observed in the welded regions which is the precursor for SCC. The goal of the present work is to understand the effect of chloride on the atmospheric corrosion behavior of FSW 304L stainless steel. A simulated crack was introduced into hot rolled and annealed 304L plates by electric discharge machining, and FSW was performed at two different temperatures, 725 and 825 °C in order to repair the simulated crack. Figure 1(a)-(c) shows the optical images of the 825 °C FSWed 304L alloy. Electrochemical corrosion tests are being performed on FSWed 304L alloy in 3.5 wt% NaCl aqueous solution at 20 OC as a thin-layer electrolyte. A comparison will be made between the corrosion behaviors of the base metal, HAZ region and the weld nugget region for both FSWed specimen types. The electrochemical tests are carried out in an in-house designed electrochemical cell with less than 10 ml of electrolyte and variable electrolyte thicknesses in the range of 0.5 – 2 mm. Open circuit potential, cyclic polarization and potentiostatic tests at different passivation potentials are being conducted to understand the pit initiation and growth events as a function of FSW microstructures. Electrochemical impedance spectroscopy and Mott-Schottky analysis are carried out to understand the semiconducting properties of the passive film and their correlation with the passive film breakdown. This presentation will discuss the effect of FSW microstructures on the passivity breakdown in thin electrolytes containing chloride ions, and the results will be compared with that of tests conducted in the conventional bulk electrolyte arrangement. Figure 1