Effect of surface finishing on the formation of nanostructure and corrosion behavior of Ni–Ti alloy

In the present work, we have investigated the formation of nanostructured oxide layers by anodic oxidation on different surface finished (mirror finished, 600 and 400 grit polished) nickel–titanium alloy (Ni–Ti) in electrolyte solution containing ethylene glycol and NH₄F_. The anodized surface has been characterized by field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and X‐ray photoelectron spectroscopy (XPS). The corrosion behaviors of the Ni–Ti substrate and anodized samples have been investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization in simulated body fluid (Hanks' solution). The results show that the native oxide on the substrate is replaced by nanostructures through anodization process. XPS of Ni–Ti substrate shows the presence of Ni⁰, NiO, Ti⁰ and TiO₂ species, whereas Ni₂O₃ and Ni(OH)₂ and TiO₂ are observed in the samples after anodization. Corrosion resistance of the anodized sample is comparable with that of the untreated sample. Copyright © 2016 John Wiley & Sons, Ltd.     

Effects of Ti and Zr Substituted on the Electrochemical Characteristics of MgNi-Based Alloy Electrodes

Mg-based hydrogen storage alloys MgNi, Mg0.9Ti0.1Ni, and Mg0.9Ti0.06Zr0.04Ni were successfully prepared by means of mechanical alloying （MA）. The structure and the electrochemical characteristics of these Mg-based materials were studied. The X-ray diffraction （XRD） result shows that the main phases of the alloys exhibit amorphous structure. The scanning electron microscopy （SEM） photograph shows that the particle size of Ti and Zr substituted alloys was about 2-4 μm in diameter. The cycle lives of the alloys were prolonged by adding Ti and Zr. After 50 charge-discharge cycles, the discharge capacity of Mg0.9Ti0.06Zr0.04Ni was 91.74% higher than that of MgNi alloy and 37.96% higher than that of Mg0.9Ti0.1Ni alloy. The main reason for the electrode capacity decay is the formation of Mg（OH）2 （product of Mg corrosion） at the surface of alloy. The potentiodynamic polarization result indicates that Ti and Zr doping improves the anticorrosion in an alkaline solution. The electrochemical impedance spectroscopy （EIS） results suggest that proper amount of Ti and Zr doping improves the electrochemical catalytic activity significantly.     

Highly Active Nickel Nanoparticles Supported on TiO2 Nanotube Electrodes for Methanol Electrooxidation

Nickel nanoparticles/TiO₂ nanotubes/Ti electrodes were prepared by galvanic deposition of nickel nanoparticles on the TiO₂ nanotubes layer on titanium substrates. Titanium oxide nanotubes were fabricated by anodizing titanium foil in a DMSO fluoride‐containing electrolyte. The morphology and surface characteristics of titanium dioxide nanotubes and Ni/TiO₂/Ti electrodes were investigated using scanning electron microscopy and energy‐dispersive X‐ray spectroscopy, respectively. The results indicated that nickel nanoparticles were homogeneously deposited on the surface of TiO₂ nanotubes. The electrocatalytic behaviour of nickel nanoparticles/TiO₂/Ti electrodes for the methanol electrooxidation was studied by electrochemical impedance spectroscopy, cyclic voltammetry, differential pulse voltammetry and chronoamperometry methods. The results showed that Ni/TiO₂/Ti electrodes exhibit a considerably higher electrocatalytic activity toward the oxidation of methanol.     

Graphite felt modified with electroless Co-Ni-P alloy as an electrode material for electrochemical oxidation and reduction of polysulfide species

Electroless deposition of a Co?Ni?P alloy on the surface of graphite felt filaments was performed in a low-temperature pyrophosphate solution under flow-through conditions. The loading, composition, morphology, and structure of electroless the Co?Ni?P alloy deposit on the filaments of the modified graphite felt were investigated by gravimetric analysis, energy-dispersive X-ray spectroscopy, scanning electron microscopy and X-ray diffraction, respectively. Electrochemical characterization of a graphite felt electrode modified with electroless Co?Ni?P alloy was performed by cyclic voltammetry, chrono-techniques, and the electrochemical impedance spectroscopy test in an aqueous solution of polysulfide composed of the mixture of 1 M Na₂S, 1 M NaOH and 1 M S. It was found that the electroless Co?Ni?P alloy deposit on graphite felt has good cycling stability and high electrocatalytic activity toward reversible electrochemical redox reactions of polysulfide species. In comparison with the bare graphite felt electrode, the electrode modified with the electroless Co?Ni?P alloy showed five to seven times lower values of anodic and cathodic overpotentials in the aqueous solution of polysulfide. It is very likely that the good electrochemical performance of the modified graphite felt electrode is related to the high surface area of the electroless Co?Ni?P alloy deposit.     

Effect of TiO2–Ti and TiO2–TiN composite coatings on corrosion behavior of NiTi alloy

Two kinds of biocompatible coatings were produced in order to improve the corrosion resistance of nickel titanium (NiTi) alloy. A titanium oxide–titanium (TiO₂–Ti) composite was coated on NiTi alloy using electrophoretic method. After the coating process, the samples were heat‐treated at 1000 °C in two tube furnaces, the first one in argon atmosphere and the second one in nitrogen atmosphere at 1000 °C. The morphology and phase analysis of coatings were investigated using scanning electron microscopy and X‐ray diffraction analysis, respectively. The electrochemical behavior of the NiTi and coated samples was examined using polarization and electrochemical impedance spectroscopy tests. Electrochemical tests in simulated body fluid demonstrated a considerable increase in corrosion resistance of composite‐coated NiTi specimens compared to the non‐coated one. The heat‐treated composite coating sample in nitrogen atmosphere had a higher level of corrosion resistance compared to the heat‐treated sample in argon atmosphere, which is mainly due to having nitride phases. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization and corrosion properties of Ti‐O/HA composite coatings on Mg‐Zn alloy

Biodegradable magnesium alloys have been widely investigated in the field of biomaterials because they can be gradually dissolved and absorbed by the human body without long‐term existence. However, it was found that bare magnesium implants suffered from rapid corrosion. Surface modification is applied to improve the corrosion resistance and biocompatibility of magnesium implants. In this study, Ti‐O/HA composite coatings including typical flakes and nanofibers were fabricated on the Mg‐Zn alloy. The Ti‐O films were deposited on the magnesium alloy by direct current magnetron sputtering, and subsequently coated with HA flakes and nanofibers by electrochemical deposition, respectively. The obtained coatings were investigated by X‐ray diffraction, Fourier Transform Infrared spectroscopy and scanning electron microscopy. The corrosion resistance was evaluated by potentiodynamic polarization and hydrogen evolution tests in simulated body fluid at 37 °C. The results show that the compact Ti‐O films are composed of particles within the size of 100 nm, the outermost HA coatings are predominantly composed of HA and doped with Na⁺, Mg²⁺ ions and functional groups. The stronger diffraction and broader peak in nanofibers than typical flakes around 25.8° are ascribed to the preferential growth in orientation (002). The morphology of HA coatings changed from typical flakes into nanofibers with the addition of NaF, the mechanism to explain the difference is also discussed. The corrosion resistance was improved significantly by the coatings, the corrosion rates in the 10 days were 4.13, 1.77, 0.96 and 0.85 mm/y, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

(NaPO3)6对AZ91D镁合金微弧氧化陶瓷层电化学腐蚀特性的影响

在Na2SiO3-KOH电解液体系中添加一定量的(NaPO3)6, 利用微弧氧化(MAO)技术在AZ91D 镁合金表面制备了原位生长的陶瓷层. 采用动电位极化和电化学阻抗谱(EIS)技术研究了添加(NaPO3)6前后, 制备的陶瓷层在3.5%(w) NaCl溶液中的室温电化学行为. 结果表明, 添加(NaPO3)6后, 陶瓷层的自腐蚀电位显著上升, 自腐蚀电流密度明显减小. 这主要是由于(NaPO3)6增加了反应过程中基体镁合金表面的“氧空位”和溶液中PO3-4的含量, 促使元素Mg在金属/膜层(M/F)界面上快速形成相应氧化物, 从而增加了陶瓷层的厚度和致密性. 根据电化学反应体系和陶瓷层的特殊结构, 建立了合理的等效电路, 并结合EIS 数据, 分析了添加(NaPO3)6提高陶瓷层耐电化学腐蚀性能的机理.     

Effect of Nb,Ti, and W ion implantation on surface properties and cell compatibility of silicon carbide

Silicon carbide is considered as a bio-inert semiconductor material; consequently, it has been proposed for potential applications in human body implantation. In this study, we study the effect of implanting different metal ions on the surface properties of silicon carbide single crystal. The valence states of the elements and the surface roughness of implanted SiC were studied using X-ray photoelectron spectroscopy and atomic force microscope, respectively. Osteoblastic MG-63 cells were utilized to characterize the cytocompatibility of ion implanted SiC. The results show that after Nb ion implantation on the SiC surface, it mainly exists in the form of Nb–C bond, Nb–O bond, and a small amount of metallic niobium. The titanium implanted on SiC primarily forms Ti-C bond and Ti-O bond. The tungsten implanted on SiC mostly presents as metallic tungsten and W–O bond. The roughness of silicon carbide single crystal is improved by ion implantation of all three metal ions. Ion implantation of titanium and niobium can improve the cell compatibility and hydrophilicity of silicon carbide, whereas ion implantation of tungsten reduces the cell compatibility and hydrophilicity of silicon carbide.     

On Oxygen‐Containing Groups in Chemically Modified Graphenes

Reduced graphenes (belonging to the class of chemically modified graphenes, CMG) are one of the most investigated and utilized materials in current research. Oxygen functionalities on the CMG surfaces have dramatic influences on material properties. Interestingly, these functionalities are rarely comprehensively characterized. Herein, the four most commonly used CMGs, mainly electrochemically reduced graphene oxide (ER‐GO), thermally reduced graphene oxide (TR‐GO), and the corresponding starting materials, that is, graphene oxide and graphite oxide, were comprehensively characterized by a wide variety of methods, such as high‐resolution X‐ray photoelectron spectroscopy, electrochemical impedance spectroscopy, UV/Vis spectroscopy, transmission electron microscopy (TEM), and voltammetry, to establish connections between the structures of these materials that carry different oxygen functionalities and their electrochemical behaviors. This was followed by the quantification of the negatively charged oxygen‐containing groups (OCGs) by UV/Vis spectroscopy and of the electrochemically reducible OCGs by voltammetry. Lastly, a biofunctionalization with gold nanoparticle (AuNP)‐modified DNA sequences was performed by the formation of covalent bonds with the carboxylic groups (? COOH) on the CMG surfaces. There was an evident predominance of functionalizable ? COOH groups on the ER‐GO surface, as confirmed by a higher amount of Au detected both with differential‐pulse voltammetry and impedance spectroscopy, coupled with visualization by TEM. We exploited the DNA–Au bioconjugates as highly specific stains to localize and visualize the positions of carboxylic groups. Our findings are very important to clearly identify the presence, nature, and distribution of oxygen functionalities on different chemically modified graphenes.     

Changes in the surface morphology induced by 1.0‐MeV Au ion bombardment of Ti and Ti‐6Al‐4V

The effects of surface sputtering by 1.0‐MeV Au ion implantation in commercially pure Ti and its alloy Ti‐6Al‐4V have been studied. These materials are associated with applications in orthopaedic implants. There are few studies that try to explain the ion implantation process of Au in these materials when considering the effects generated on the surface by sputtering, especially at energies of the order of MeV. Discs of these materials were mirror polished and then implanted with 1.0‐MeV Au ions for 4.7 × 10¹⁷ ions/cm² at 45° incident angle with respect to the surface. Part of the eroded material was deposited simultaneously on glass slides to determine their spatial distribution. These discs and the slides were analysed by Rutherford backscattering spectroscopy (RBS), scanning electron microscopy (SEM), optical microscopy and atomic force microscopy. The implanted materials show the initial production of surface ripples that evolve into banded structures. Copyright © 2014 John Wiley & Sons, Ltd.     

Electrochemical impedance spectroscopy as a probe for wet chemical silicon oxide characterization

The kinetics of the chemical growth of silicon oxide in H₂O₂-containing ammonia solutions and its break-up by dilute ammonia solutions was investigated using electrochemical techniques and more specifically electrochemical impedance spectroscopy. The recording of the open circuit potential (OCP), complemented by successive impedance diagrams, demonstrates clearly the build-up of a silicon oxide passivating layer when hydrophobic Si surfaces are immersed in NH₃+H₂O₂ solutions. The thickening of the chemical oxide coating mainly results in the decrease of the capacitance value together with the enhancement of the ohmic surface resistance. On the other hand, pure ammonia dilute solutions lead to the progressive destruction of this hydrophilic passivating surface oxide, which is revealed by the simultaneous decay of the real component of the impedance. Finally, we observed the break-up of the passive layer, characterized by a sudden drop of the OCP to a value quite identical to that obtained with a bare Si surface. This process resulted in a dramatic corrosion of the substrate surface. Electronic Publication     

Improved Electrochemical Kinetic Performances of La-Mg-Ni-based Hydrogen Storage Alloy Modified by Ni-Polypyrrole Complex Surface Treatment

In order to improve the electrochemical kinetic performances of La-Mg-Ni-based alloy, complex surface modification of Ni with excellent catalytic activity and conducting polymer polypyrrole(PPy) was performed via electroless plating method. FESEM images revealed that the complex Ni-PPy treatment resulted in more micropores at the alloy surface, with Ni particles and cotton fiber-shape PPy microspheres attached. Both the larger surface area induced by the micropore and the higher catalytic activity and conductivity on account of the dispersed Ni particles/PPy microspheres promoted the electrode reaction, thereby increasing the discharge capacity of the modified alloy electrode. Electrochemical impedance spectroscopy(EIS) and linear polarization results showed that the Ni-PPy treatment decreased the charge-transfer resistance and increased the exchange current density greatly, far more than the single-component Ni or PPy treatment. Consequently, a notable improvement in high rate dischargeability(HRD) was observed, and at a high discharge current density of 1800 mA/g, the HRD of the modified electrode increased by 10.4% compared with that of the bare electrode.     

Interfacial and bulk processes during oxide growth on titanium in ethylene glycol-based electrolytes

Anodic oxidation has proven to be a promising route for the growth of self-ordering oxide nanotubes on Ti, the best results being obtained in ethylene glycol (EG)-based electrolytes with the addition of fluoride and small amounts of water. In the present paper, emphasis is put on the investigation of barrier film growth and dissolution on Ti in EG electrolytes with the addition of H₂O (0.3–2.4 M) and NH₄F (0.015–0.17 M) using electrochemical and surface analytical techniques. Steady-state current–potential curves and electrochemical impedance spectra as depending on potential (?0.1/5.0 V vs. AgCl/Ag), water and fluoride content have been registered. In addition, the chemical composition of the surface of the oxides obtained at 0.1 and 1.0 V has been estimated by X-ray photoelectron spectroscopy (XPS). XPS analysis revealed the presence of a non-stoichiometric oxide containing mainly Ti⁴⁺ and a certain amount of Ti³⁺, with a certain degree of hydroxylation. Estimates of the total thickness of the oxide from the XPS data using a dual layer model are also presented. A kinetic model of the process is advanced to quantitatively interpret the electrochemical and surface analytical results.     

Characterization of surface composition on Alloy 22 in neutral chloride solutions

The composition of anodically grown oxide films on Alloy 22, a Ni‐Cr‐Mo(W) alloy, has been investigated in 5 mol l^?1 NaCl at room temperature using X‐ray photoelectron spectroscopy and time‐of‐flight secondary ion mass spectrometry. For applied potentials up to 0.2 V (vs Ag/AgCl (saturated KCl solution)), a Cr(III) oxide barrier layer develops at the alloy/oxide interface accounting for the excellent passivity demonstrated to prevail in this potential region by previous electrochemical impedance spectroscopy measurements. At higher potentials, this layer is destroyed by defect injection as Cr(III) is oxidized to the more soluble Cr(VI). The overall oxide/hydroxide film thickness is, however, increased as Mo(VI)/W(VI) species accumulate at the oxide solution interface. The potential of 0.2 V at which the barrier layer switches from growth to destruction coincides with the previously demonstrated threshold potential for the initiation of crevice corrosion. Copyright © 2012 John Wiley & Sons, Ltd.     

纳米氧化物对MH/Ni电池负极电化学性能影响的研究

采用纳米氧化铜作为添加剂掺杂制备MH/Ni电池负极, 研究了氧化铜在电极内部的反应机理, 考察了修饰后电极储备容量的变化, 及电极的电化学性能, 并应用EIS方法探讨了电极性能改善的作用机理. 循环伏安测试表明, 氧化铜在首次充电时被还原成铜并沉积在合金颗粒表面. 电化学测试表明, 掺杂后合金电极的电化学性能显著提高. EIS分析表明, 掺杂后合金电极的导电性提高, 电化学活性增强.     

Electrochemical Behavior of Dental Ni‐Cr Wirolloy Coated with Eco‐friendly Films in Artificial Saliva

The electrochemical corrosion behavior of the non‐precious Ni‐Cr Wirolloy, being used in dentistry, was investigated before and after applying of two types of eco‐friendly coatings, polyvinyl silsesquioxane (PVS) and nano‐hydroxyapatite (nHAP) separately in artificial saliva solution at 37 °C for 14 d of immersion. The study aimed to investigate the effectiveness of the introduced coating films in enhancing the corrosion resistance of the alloy, and in decreasing the leaching of the toxic Ni ions from the alloy into the environment. The electrochemical corrosion investigation methods used are; open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The evaluated results revealed that the electrochemically coated alloy with PVS. prepared at cathodic potential showed higher corrosion resistance and more stable film compared to that prepared by conventional dip‐coating method. At the same time, the nHAP electrochemically coated film provided the best anti‐corrosion properties over all examined time intervals. The obtained results were confirmed via surface analysis, which assured the formation of the prepared coatings on the alloy surface. Chemical analysis of the corrosion product/solutions showed that the effect of electrochemically deposited nHAP and PVS. polymer films in suppression of Ni ions leaching is similar and slightly higher than that of the chemically coated PVS. one; however, all of them are efficient in decreasing the leaching of the risky Ni ions into the solution.     

Biocorrosion and biocompatibility of Zr–Cu–Fe–Al bulk metallic glasses

Owing to their unique chemo‐physical and structural characteristics, amorphous bulk metallic glasses (BMGs) are of great demand for fabrication of variety of advanced and innovative products including surgical and biomedical tools and devices. In this study, a series of Ni‐free Zr‐based BMGs in Zr–Cu–Fe–Al system are fabricated using copper‐mold casting technique, and their biocorrosion and biocompatibility are evaluated with respect to their corrosion behavior in the phosphate buffered saline (pH = 7.4) solution. Anodic polarization curves, scanning electron microscopy combined with energy‐dispersive X‐ray, and wettability analyses are conducted to characterize the surfaces of BMG samples. The biocompatibility of the BMG and control samples is studied by comparing cell–substrate interactions among different samples. It is found that Zr₆₀Cu₂₀Fe₁₀Al₁₀ displays a higher passive region compared with that of Zr₆₀Cu_22.5Fe_7.5Al₁₀, but both BMGs exhibit lower corrosion resistance compared with Ti–6Al–4V alloy. By addition of titanium to Zr–Cu–Fe–Al system (Zr₆₀Ti₆Cu₁₉Fe₅Al₁₀), a significant increase in the passive region of the polarization curve is detected. The cell culture experiments reveal that the number of attached and grown cells is significantly higher on the surface of the treated BMGs as compared with Ti–6Al–4V substrates and the culture plate as controls. There is no noticeable difference in cellular morphology among the BMG samples, and no cytotoxicity is detected. We speculate that the interaction of water molecules and matrix proteins with the surfaces of BMGs plays an important role in cell–substrate interactions and improved cell response. Copyright © 2013 John Wiley & Sons, Ltd.     

A Sensitive and Selective Nitrite Detection in Water Using Graphene/Platinum Nanocomposite

A glassy carbon electrode modified with reduced graphene oxide and platinum nanocomposite film was developed simply by electrochemical method for the sensitive and selective detection of nitrite in water. The electrochemical reduction of graphene oxide (GO) efficiently eliminates oxygen‐containing functional groups. Pt nanoparticles were electrochemically and homogeneously deposited on the ErGO surface. Field emission scanning electron microscopy (FE‐SEM), Raman spectroscopy, attenuated total reflectance‐fourier transform infrared spectroscopy (ATR‐FTIR), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were used to examine the surface morphology and electrocatalytic properties of the Pt‐ErGO nanocomposite film‐modified electrode surface. The fabricated nitrite sensor showed good electrochemical performance with two linear ranges; one from 5 to 100 µM (R²=0.9995) and the other from 100 to 1000 µM (R²=0.9972) and a detection limit of 0.22 µM. The proposed sensor was successfully applied for the detection of nitrite in tap water samples which proves performance of the Pt‐ErGO nanocomposite films.     

Glucose Electro‐oxidation on Graphite Electrode Modified with Nickel/Chromium Nanoparticles

In this study, an available and inexpensive graphite substrate, was easily modified with Ni/Cr nanoparticles via electrodeposition technique in a very short time (3 min) and used as an electrocatalyst for glucose oxidation in alkaline solution. Graphite electrode modified with Ni/Cr nanoparticles demonstrated an outstanding electrocatalytic performance to glucose oxidation in comparison to examined Ni‐based electrodes or even different materials in other reports. It is noteworthy to mention that adding a little Cr led to a synergistic effect with Ni; accordingly, the presence of Cr not only resulted in a greater adsorption of glucose molecules by chromium oxide but also boosted conductivity of the nickel oxide because of the enhancement of Ni(III) amount. The electrochemical studies were performed by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The morphology and structure of catalyst layer was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and energy dispersive x‐ray spectroscopy (EDS). The linear range of the electrode by cyclic voltammetry was between 2–31 mM with a high sensitivity of 2094 μA cm^?2 mM^?1. The repeatability and reproducibility of the proposed electrode was examined in glucose solution which were 0.3 % and 4.7 %, respectively. According to the low cost, ease and fast preparation, good repeatability and high sensitivity, this electrode can be a good candidate for nonenzymatic glucose oxidation.     

Enhancement of Methanol Tolerance in DMFC Cathode: Addition of Chloride Ions

In the operation of a direct methanol fuel cell, the modification by chloride ions on the surface of a Pt cathode can facilitate the extraordinary increase of power performance and long‐term stability. Analyzing the results of cyclic voltammograms and electrochemical impedance spectroscopy, the positive shift of Pt oxidation onset potential and the depression of oxidation current are observed, which results from the role of chloride as surface inhibitor. In addition, O₂ temperature‐programmed desorption and X‐ray photoelectron spectroscopy also reveal that the suppression of Pt surface oxide can be best understood in terms of lower binding of oxygen species by the alteration of electronic state of Pt atoms. Such a reduced surface oxide formation not only provides more efficient proton adsorption sites with high selectivity but also decreases the mixed potential by crossover methanol, resulting in higher performance and stability even under high voltage long‐term operation.