Abrasive wear is a principal cost in mining and mineral processing operations. High chromium white cast iron (WCI) further reinforced with niobium carbide (NbC) shows promise to increase component wear lives. This work investigates the effect of niobium macro-additions on microstructure, hardness and high-stress abrasive wear behaviour of Nb-containing high-Cr WCIs. Eight alloys with Nb between 0 and 10.7 wt% were produced by sand casting. Increasing niobium carbide volume fraction (Nb-CVF) increased hardness from 724 to 812 HV (7.3 HV per 1% Nb-CVF). Abrasive wear resistance, assessed using the ball mill abrasion test in basalt (less competent) and quartzite (competent rock), showed clear beneficial effect of NbC macro-addition up to 11.4 and 7 vol% in basalt and quartzite, respectively. These correspond to life improvements of 37% and 7% per 1% Nb-CVF in the optimum range of Nb macro-addition, in basalt and quartzite respectively. Micro-mechanistic observations of worn surfaces showed that NbC particles not only protrude from the matrix but do so more than Cr-rich M7C3 carbides. In deep wear grooves created by quartzite, M7C3 particles were cut flush with the matrix, whereas NbC protruded, visibly impeding the progress of the abrasion event.

White cast iron (WCIs) alloys were development by adding Nb, Mo, and a combination of both (~3 wt% Nb, ~3 wt% Mo, ~1 wt% Mo-2 wt% Nb) through melting and casting. The objective was to analyze the microstructural characteristics of the alloys, as well as the impact of reinforcing carbides on their mechanical and tribological properties. The alloy containing the highest percentage of niobium exhibited a refined microstructure, tending towards a eutectic structure, unlike the Mo-containing materials with totally hypoeutectic microstructures. The microstructural characteristics of the alloys and morphology of niobium carbides, as well as the percentage of M7C3 eutectic carbides produced were affected by the varying percentages of Nb and the Mo-Nb combination. Moreover, thermodynamic simulations revealed that the NbC carbide precipitated before the M7C3 eutectic carbides, austenite dendrites, and the MC (mostly composed of Mo-bound Nb) carbide resulting from the Mo-Nb combination. The alloys containing Mo had similar bulk hardness values, while the alloy with the highest percentage of Nb showed a higher bulk hardness value. This was attributed to the effect of Nb on microstructure refinement and on the production of M7C3 eutectic carbides from the alloy. Although there were different reinforcing carbides (NbC, MC and M2C), the differences in microstructural characteristics had no noticeable influence on the Charpy impact energy. Micro-scale abrasive wear test (conducted with SiC abrasive slurry) demonstrated that the reinforcing carbides MC and mainly NbC had a beneficial effect in blocking and preventing the progression of continuous micro-cuttings and formation of grooves. The M7C3 and M2C carbides were less effective at protecting the matrix against the high-hardness SiC abrasive.

In the current study, sol-gel technology was used to produce organic-inorganic hybrid coatings onto AISI 1045 carbon steel as a means of corrosion protection. The organic-inorganic hybrid coatings were prepared using tetraethylorthosilicate (TEOS) and 3-(trimethoxysilyl)propyl methacrylate precursors. The coatings were thermally treated and the effect of temperature and time was studied. The results of scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrated that the coatings possess homogeneous morphologies and that their thickness decreases with increasing heat treatment temperatures. At the highest treatment the coating was 20% thinner and more than 25% more scratch resistant compared with the untreated coating. According to thermalgravimetric analysis the coating mass loss was approximately 15% up to 150 degrees C and 2.7% between 150 and 400 degrees C. The electrochemical measurements, in 3.5% NaCl aqueous solution, determined that the coatings treated at 100 degrees C have polarization resistance values on the order of 60 k omega cm2 after 72 h of exposure time in saline solution. The phase angle at high frequency (close to - 90 degrees at 103-105 Hz) demonstrated that the coating presented capacitive behavior related to less aggressive corrosion in this electrolyte. Further increasing the temperature beyong 100 degrees C reduced the performance of the coatings as demonstrated by a decrease of the polarization resistance by about one order of magnitude and the shift of the corrosion potential to more negative values.

In this work, alternating current (AC) voltage ( V AC ) is applied to Ti–6Al–4V alloy in aqueous oxalic acid dihydrate solution to grow passive oxide films. The oxide layers are formed with V AC values in the range of 10–80 V. The resulting surface oxide layers have estimated thicknesses in the 100–500 nm range and are expected to have a two-layer structure consisting of a porous outer layer and a compact inner layer. The AC anodization process is demonstrated to have a slight effect on the surface roughness. Porous regions are observed on the films formed at lower and high AC voltages (i.e., V AC 10–30 and 80 V). The corrosion behavior in Ringer’s solution over 48 h of exposure is studied with electrochemical impedance spectroscopy. The AC anodized samples have higher impedance values than the untreated alloy by more than an order of magnitude. The oxides formed at V AC = 40 − 70 V exhibit optimal resistance to corrosion as demonstrated by the overall impedance values, the polarization resistance values, and the capacitive behavior.

•Electrochemical analyses showed that there is enhanced protection using blends when compared to pure PANI coatings.•The porosity of the PANI/PVC 1/1 blend was lower than in the pure PANI coatings.•The blend showed a distribution of PVC and PANI domains that contributed to its better protection performance.•Blended coatings with thickness of 26.3 ± 0.95 μm have better corrosion protection of the AA7075-T6 aluminum alloy.

This article presents the corrosion protection ability of blended polyaniline (PANI) and polyvinyl chloride (PVC) polymers applied on 1010 steel. The PANI/PVC blends, as well as pure PANI coatings, were fabricated via a casting method and characterized using infrared spectroscopy. Carbon steel substrates protected with the coatings, were subjected to 40day exposure tests in saline (3%.NaCI) and acidic (0.1 M HCI) environments and subsequently analyzed using electrochemical methods Electron microscopy (SEM) and spectroscopic methods (EDS and XPS) were used to study the corroded surface of the 1010 steel underlying the protective coating, as well as the polymer coating itself. The PANI/PVC blends demonstrated superior corrosion protection in both environments as compared to pure,PANI and pure PVC coatings. The PANI/PVC blend with a 1/1 proportion offered the most effective corrosion protection in acidic and saline environments based on high charge transfer resistance values and corrosion potential values that approach zero volts. The corrosion protection abilities of the blended coatings are attributed to a combination of barrier protection from the PVC and the formation of a protective oxide layer at the steel-to-polymer interface that is facilitated by the conductivity of PANI. (C) 2017 Elsevier B.V. All rights reserved.

In polymer electrolyte membrane fuel cells (PEMFCs), the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) take place on the surface of platinum nanoparticles (Pt-NPs) residing on carbon support. Polycrystalline platinum (Pt(poly)) serves as a model polyoriented system due to its randomly oriented grains separated by grain boundaries, and research using Pt(poly) creates important background knowledge that is used to identify and understand electrochemical phenomena occurring in fuel cells. In this study, we report new results on the electrochemical behavior of Pt(poly) in 0.50 M H2SO4 aqueous solution saturated with reactive gases, namely O2(g) and H2(g). We analyze the influence of the potential scan rate over a broad range of values (1.00–50.0 mV s−1) on the cyclic voltammetry (CV) behavior of Pt(poly). A comparative analysis of the impact of dissolved O2 and H2 on the electrochemical behavior of Pt(poly) is performed using CV profiles and capacitance transients. Their analysis reveals the existence of new features that are observed in the potential range corresponding to the Pt surface oxide formation and reduction. The results indicate that the Pt surface oxide reveals catalytic duality because it acts both as an inhibitor and a catalyst in both the ORR and HOR. In the case of the ORR, the anodic-going transients reveal that the process becomes inhibited as the Pt surface oxide develops, while in the cathodic-going transients, the reduction of Pt surface oxide significantly (ca. 65%) increases the reaction rate. In the case of the HOR, the anodic-going transients also reveal that the process becomes inhibited as the Pt surface oxide develops, while in the cathodic-going transients, the reduction of Pt surface oxide increases (ca. 15%) the reaction rate. The catalytic effect can be attributed either to changes in the surface electronic structure that accompanies the surface oxide reduction or to short-lived increase in the electrochemically active surface area.

In this contribution, which is the final paper in a topic-focused series of three papers, we report on the development of experimental methodology that is applied to acquire cyclic voltammetry (CV) profiles for hemispherical Pt(111), Pt(110), and Pt(100) as well as polyoriented monocrystalline Pt electrodes. The paper describes an effective, multi-step procedure for cleaning of electrochemical and annealing glassware. The procedure comprises a four-step process for cleaning glassware and a three-step process for cleaning Viton and Teflon parts to minimize any contamination that can originate from these setup components. The contribution also outlines general laboratory practices that need to be followed in order to maintain clean conditions for conducting electrochemical experiments. The paper discusses a thermal treatment methodology that consists of two steps, namely flame-based annealing and induction-based annealing. The application of this approach produces reproducible, clean, defect-free, and atomically-ordered Pt surfaces. The complete procedure of Pt electrode annealing, cooling in a controlled atmosphere, protecting with a droplet of water, and transferring to an electrochemical cell allows one to conserve a metallic character of the electrode surface (it does not form any oxide during the transfer) while maintaining an atomic order. In addition, the paper describes the design and operation of a multi-component electrochemical workstation, which is employed in measurements on platinum electrochemistry and electrocatalysis. The paper presents and discusses the hanging meniscus configuration that is used to maintain an electrolytic contact between a monocrystalline Pt electrode and an aqueous electrolyte solution. Finally, the contribution presents CV profiles for hemispherical Pt(111), Pt(110), and Pt(100) as well as polyoriented, monocrystalline Pt electrodes, which are characteristics of high-quality electrodes and clean experimental conditions. These results validate the instrumentation described in the series of papers and the laboratory practices developed in the course of our research.

Platinum‐nanoparticle‐functionalized, ordered, porous support electrodes are prepared and characterized as a potential new class of oxygen reduction reaction (ORR) electrocatalysts. This study aims to develop electrode materials that enhance the effective utilization of Pt in electrocatalytic reactions through improved mass transport properties, high Pt mass specific surface area, and increased Pt electrochemical stability. The electrodes are prepared using modular sacrificial templates, producing a uniform distribution of Pt nanoparticles inside ordered porous Au electrodes. This method can be further fine‐tuned to optimize the architecture for a range of characteristics, such as varying nanoparticle properties, pore size, or support material. The Pt‐coated Au, ordered, porous electrodes exhibit several improved characteristics, such as enhanced Pt effective utilization for ORR electrocatalysis. This includes a nearly twofold increase in Pt mass specific surface area over other ultrathin designs, superior mass transport properties in comparison to traditional catalyst layers of C black supported Pt nanoparticles mixed with ionomer, good methanol tolerance and exceptional stability toward Pt chemical and/or electrochemical dissolution through interfacial interactions with Au. The methods to prepare Pt‐coated ordered porous electrodes can be extended to other architectures for enhanced catalyst utilization and improved performance of Pt in electrochemical processes.

Polyaniline coatings of various controlled thicknesses are applied to 7075-T6 aluminum alloy substrates and evaluated for their corrosion protection ability in a corrosive saline environment using electrochemical techniques. The coating thicknesses are in the range of approximately 5 to 35 pm and they increase linearly with increasing quantities of PANI solution deposited on the substrate. The relationship between the coating thickness, roughness, and hydrophilicity is examined. Coatings ranging from 12 to 23 pm in thickness have the lowest roughness values and highest contact angles with water. The PANI-coated 7075 alloy electrodes with low roughness and high contact angles show better corrosion protection properties in saline solution (3.5% NaCl), as determined by electrochemical impedance spectroscopy (EIS) and voltammetric polarization measurements. Scanning electronic microscopy (SEM) images demonstrate the homogenous surface morphology of the PANI coatings on the micrometer scale. Even after prolonged exposure to corrosive media, no cracks were found. (C) 2017 Elsevier Ltd. All rights reserved.

Anodic polarization of Pt electrodes in aqueous H2SO4 leads to the formation of a surface oxide (PtO). Herein, the surface oxide growth is accomplished using three different approaches: (i) chronoamperometry (CA); (ii) chronocoulometry (CC); and (iii) a combination of cyclic voltammetry (CV) and CA. The PtO reduction is accomplished potentiodynamically using voltammetry. The oxide growth takes place at defined polarization potentials (E(p)), polarization times (t(p)), and temperatures (T). The oxide charge density (q(ox)) is determined for both the formation (q(ox,form)) and reduction (q(ox,red)) processes. The oxide reduction CV profiles are integrated to determine the charge density values for oxide reduction (q(ox,red,CV)) which are compared with the q(ox,form,CA) and q(ox,form,CC) values. The values of q(ox,form,CC) are greater than those of q(ox,form,CA), but both potentiotatic methods (CA and CC) produce q(ox,form) values that are consistently lower than those of q(ox,red,CV). In the case of oxide formation with combined CV and CA, the values of q(ox,form,CV+CA) are found to be lower than the values of q(ox,red,CV), although the difference is small. Electrochemical quartz crystal nanobalance (EQCN) is used to monitor the mass variation at the electrode surface during the oxide formation and reduction process at E(p) = 1.20 V with various t(p) values. Equal mass changes during oxide formation and reduction are detected by the EQCN. The nature of the differences in q(ox,form) and q(ox,red) encountered with the different experimental methods are discussed in terms of instrumental limitations.

Mechanistic and kinetic details of the ethanol oxidation reaction using a nickel electrode in sodium hydroxide solution under well-controlled experimental conditions that include the variation of solution temperature and scan rate are discussed. Electrochemical analysis of ethanol oxidation is presented for the first time corresponding to the low temperature range (-15 degrees C <= T <= 25 degrees C) and demonstrates that the reaction proceeds even at 15 degrees C. Cyclic voltammetry (CV) analysis demonstrates that the ethanol oxidation reaction occurs through a mechanism that involves a chemical reaction between the ethanol molecule and the beta-NiOOH species formed electrochemically on the electrode surface at potentials greater than 1.3 V. Decrease of temperature affects the kinetics of this reaction resulting in a decrease in the peak current density U) and causes a shift in the peak potential of the ethanol oxidation toward less positive values. Arrhenius plots demonstrate that the ethanol oxidation reaction has a high apparent activation energy (E-a(app)), corroborating with the proposed mechanism that involves the reaction between the ethanol molecule and beta-NiOOH in the rate-determining step. The j of ethanol oxidation at -15 degrees C is slightly affected by variation of the potential scan rate and rotation of the electrode. However, the potential scan rate has a considerable influence on the j of beta-NiOOH formation and reduction reactions. Analysis of in situ FTIR spectroscopic data shows that this alcohol is converted selectively to the corresponding carboxylate (acetate) under the conditions of the study. (C) 2015 Elsevier B.V. All rights reserved.

The electrochemical formation of α-Ni(OH)2 and NiOOH in the presence of adsorbed oxalate in alkaline media is studied under well-controlled experimental conditions that include the variation of the system temperature (T = −10 to 20 °C), the scan rate (v = 20, 150, and 200 mV s−1), and the concentration of supporting electrolyte (0.10 and 0.50 M KOH). The studies are carried out using cyclic voltammetry (CV) with polycrystalline bulk nickel and nickel foams. In situ infrared spectroscopy with voltammetry confirms the adsorption of oxalate to the surface of nickel in the 0.10 to 0.30 V potential window, concurrent with the formation of the α-Ni(OH)2 species. The presence of oxalate in the system increases the charge density (Q) for the formation of both the α-Ni(OH)2 and NiOOH surface oxides. The Q values calculated under various conditions indicate that the presence of oxalate in the system encourages the formation of a full single monolayer (ML) of NiOOH in the first CV scan. Measurements carried out at room temperature demonstrate that an increase in v decreases the Q values for NiOOH in the presence of oxalate to minimum values achieved at v ≥150 mV s−1. An increase of KOH concentration results in the formation of a thicker layer of NiOOH both in the presence and absence of oxalate. The Q values of NiOOH reduction in conditions that favor the formation of one complete monolayer of NiOOH are used to calculate the specific surface areas of open-cell nickel foams. The calculation of electrochemical surface area using this method is discussed and evaluated with respect to calculations based on the charge of α-Ni(OH)2 formation.

In this study, a nickel foam electrode is used for the anodic conversion of isopropanol to acetone. The process is studied under well-defined experimental conditions including variation of the concentration of isopropanol, variation in the strength of the supporting electrolyte (aqueous KOH), different cyclic voltammetry scan rates, and different temperatures. The outcome of these experiments demonstrates that the isopropanol oxidation reaction is dependent on the presence of the beta-NiOOH surface species, which is generated at potentials near the potential of the isopropanol oxidation reaction. However, the two processes do not occur at the exact same potential and their respective behaviors under the various experimental conditions can be understood independently. Nickel foams are successfully applied as the anode material for controlled-potential electrolysis of isopropanol to form acetone. The Ni foam anode sustains a current density of 2.6 mA cm(-2) for the electrolysis time of 600 min without significant loss of activity. Isopropanol is converted to acetone at a rate of 5.6 mM per hour. (C) 2013 Elsevier B.V. All rights reserved.

Platinum is deposited on open-cell nickel foam in low loading amounts via chemical reduction of Pt cations (specifically, Pt(2+) or Pt(4+)) originating from aqueous Pt salt solutions. The resulting Pt-modified nickel foams (Pt/Ni foams) are characterized using complementary electrochemical and materials analysis techniques. These include electron microscopy to examine the morphology of the deposited material, cyclic voltammetry to evaluate the electrochemical surface area of the deposited Pt, and inductively coupled plasma optical emission spectrometry to determine the mass of deposited Pt on the Ni foam substrate. The effect of potential cycling in alkaline media on the electrochemical behavior of the material and the stability of Pt deposit is studied. In the second part of this paper, the Pt/Ni foams are applied as electrode materials for hydrogen evolution, hydrogen reduction, oxygen reduction, and oxygen evolution reactions in an aqueous alkaline electrolyte. The electrocatalytic activity of the electrodes toward these processes is evaluated using linear sweep voltammetry curves and Tafel plots. The results of these studies demonstrate that nickel foams are acceptable support materials for nanoscopic Pt electrocatalysts and that the resulting Pt/Ni foams are excellent electrocatalysts for the hydrogen evolution reaction. An unmodified Ni foam is shown to be a highly active electrode for the oxygen evolution reaction.

High surface area platinum electrodes with an ordered porous structure (Pt-OP electrodes) have been prepared and characterized by electrochemical methods. This study builds a foundation upon which we can seek an in-depth understanding of the limitations and design considerations to make efficient and stable Pt-OP electrodes for use in electrochemical applications. A set of Pt-OP electrodes were prepared by controlled electrodeposition of Pt through a self-assembled array of spherical particles and subsequent removal of the spherical templates by solvent extraction. The preparation method was shown to be reproducible and the resulting electrodes were found to have clean Pt surfaces and a large electrochemical surface area (A ecsa) resulting from both the porous structure, as well as the nano- and micro-scale surface roughness. Additionally, the Pt-OP electrodes exhibit a surface area enhancement comparable to commercially available electrocatalysts. In summary, the Pt-OP electrodes prepared herein show properties of interest for both gaining fundamental insights into electrocatalytic processes and for use in applications that would benefit from enhanced electrochemical response.

Nickel-based metallic foams are commonly used in electrochemical energy storage devices (rechargeable batteries) as both current collectors and active mass support. These materials attract attention as tunable electrode materials because they are available in a range of chemical compositions, pore structures, pore sizes, and densities. This contribution presents structural, chemical, and electrochemical characterization of Ni-based metallic foams. Several materials and surface science techniques (transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), focused ion beam (FIB), and X-ray photoelectron spectroscopy (XPS)) and electrochemical methods (cyclic voltammetry (CV)) are used to examine the micro-, meso-, and nanoscopic structural characteristics, surface morphology, and surface-chemical composition of these materials. XPS combined with Ar-ion etching is employed to analyze the surface and near-surface chemical composition of the foams. The specific and electrochemically active surface areas (A(s), A(ecsa)) are determined using CV. Though the foams exhibit structural robustness typical of bulk materials, they have large A(s), in the range of 200-600 cm(2) g(-1). In addition, they are dual-porosity materials and possess both macro- and mesopores.

Bisphenol A (BPA) is an endocrine disrupting chemical that has the potential to harm humans. Electrochemical oxidation was successfully applied as an environmentally sustainable method for degrading this compound. Compared with high-cost anode materials such as Pt and Ti, low-cost Ni electrodes are an attractive material for the oxidation of organic molecules. The Ni electrode displays relevant catalytic properties, specifically the ability to dissociate water and break C-O and C-C bonds. This study examined the active surface area of an open-cell Ni foam. Chronoamperonietry (CA) and cyclic voltammetry (CV) were then employed to study the electrooxidation of BPA.

We investigate the influence of micro-sandblasting and electrochemical passivation on properties such as corrosion rate and surface roughness, which are important to the biocompatibility of titanium (Ti), using surface analysis techniques and electrochemical measurements. Results of microscopy and surface profilometry experiments reveal roughened but uniform surface topography with an average surface roughness in the 0.87–1.06 μm range, depending on the alternating current passivation voltage applied to the micro-sandblasted samples. Open circuit potential versus time measurements in Hank’s Balanced Salt Solution (HBSS, a simulated body fluid) allow determination of the corrosion potential (Ecorr) and reveal a shift of Ecorr toward higher values upon passivation, thus pointing to increased corrosion stability. Corrosion rates in HBSS range between 0.049 and 0.288 μm year−1 for micro-sandblasted and passivated Ti, as compared to that for the micro-sandblasted and non-passivated surface that is 0.785 μm year−1. Results from this study demonstrate that micro-sandblasting coupled with electrochemical passivation provides a roughened surface with increased corrosion stability and a low corrosion rate in HBSS. Application of this technique to Ti in medical and dental applications may be expected to result in an improvement of biocompatibility.