Effects of serum proteins on corrosion behavior of ISO 5832–9 alloy modified by titania coatings

Stainless steel ISO 5832–9 type is often used to perform implants which operate in protein-containing physiological environments. The interaction between proteins and surface of the implant may affect its corrosive properties. The aim of this work was to study the effect of selected serum proteins (albumin and γ-globulins) on the corrosion of ISO 5832–9 alloy (trade name M30NW) which surface was modified by titania coatings. These coatings were obtained by sol–gel method and heated at temperatures of 400 and 800 °C. To evaluate the effect of the proteins, the corrosion tests were performed with and without the addition of proteins with concentration of 1 g L^?1 to the physiological saline solution (0.9 % NaCl, pH 7.4) at 37 °C. The tests were carried out within 7 days. The following electrochemical methods were used: open circuit potential, linear polarization resistance, and electrochemical impedance spectroscopy. In addition, surface analysis by optical microscopy and X-ray photoelectron spectroscopy (XPS) method was done at the end of weekly corrosion tests. The results of corrosion tests showed that M30NW alloy both uncoated and modified with titania coatings exhibits a very good corrosion resistance during weekly exposition to corrosion medium. The best corrosion resistance in 0.9 % NaCl solution is shown by alloy samples modified by titania coating annealed at 400 °C. The serum proteins have no significant effect onto corrosion of investigated biomedical steel. The XPS results confirmed the presence of proteins on the alloy surface after 7 days of immersion in protein-containing solutions.     

Oxidation of electrodeposited cobalt electrodes in an alkaline electrolyte

The oxidation of electrodeposited Co electrodes has been studied in 0.1 M KOH_aq at potentials more negative than ?880 mV vs. Hg|HgO by means of electrochemical quartz crystal microbalance (EQCM) and rotating ring disk electrode coupled with cyclic voltammetry (CV) and chronoamperometry (CA). Dissolution of cobalt was found to be insignificant and does not constitute a step in the overall process of formation of the oxidised layer. The irreversibility of the oxidation process depends on the electrode potential and oxidation time. The composition of the oxidised layer depends on the oxidation potential: Co(OH)₂ is formed at more negative potentials, while at more positive potentials CoO is the prevailing product. The results obtained by means of three techniques (CV, CA and EQCM) reveal that at potentials not higher than ?880 mV, the oxidation of Co follows a direct logarithmic law. The mechanism of the process is discussed.     

Surface characteristics of AZ91D alloy anodized with various conditions

Anodic oxidation of an AZ91D magnesium alloy was carried out in an attempt to increase the corrosion resistance. The alloy was placed in an electrolyte containing 0.1 M sodium silicate (Na₂SiO₃), 2.0 M sodium hydroxide (NaOH) and 0.1 M sodium phosphate (Na₃PO₄), and treated with a current density of 100–400 mA/cm² for 1 to 4 min. After the anodic oxidation treatment, the surface characteristics were analyzed by SEM, X‐ray diffraction (XRD) and a surface roughness tester. The corrosion resistance was determined by measuring the corrosion potential and corrosion current density using potentiodynamic polarization in a 3.5 wt% NaCl electrolyte solution. Although the anodic oxidation treatment with the base electrolyte resulted in an arrival voltage ranging from 60 to 70 V, the addition of silicate tended to reduce this arrival voltage by approximately 10–20 V and decrease the critical voltage required for the formation of a porous oxide film. The pore size and film thickness increased with increasing applied current and treatment time. The addition of silicate to the electrolyte resulted in films with a homogeneous pore size and a film thickness increasing with the increasing applied current and treatment time. XRD showed the formation of a new MgO and Mg₂SiO₄ phase. The formation of Mg₂SiO₄ was attributed to the presence of SiO₄^4? in the film. After the addition of silicate, the corrosion potential increased and corrosion current decreased, resulting in improved corrosion resistance. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of Nb alloying additions on the characteristics of anodic oxide films on zirconium and their stability in NaOH solution

The characteristics of oxide films on Zr and Zr–Nb alloys (with Nb content of 2.5, 5, and 10 at.%) galvanostatically formed (at a current density of 100 μA cm^?2) in 0.5 M H₂SO₄ solution were investigated by means of electrochemical impedance spectroscopy. Electrochemical impedance spectroscopy spectra were interpreted in terms of an “equivalent circuit” with the circuit elements representing the electrochemical properties of a single layer oxide. The resistance of the oxide films was found to increase with increased Nb content in the alloy while the capacitance showed an opposite trend. The stability of the anodic oxide films grown in the sulfuric acid solution on Zr and Zr–Nb alloys was investigated by simultaneously measuring the electrode capacitance and resistance at a working frequency of 1 kHz as a function of exposure time to naturally aerated 3 M NaOH solution. Analyses of the electrode capacitance and resistance values indicated a decrease in chemical dissolution rate of the oxide films with the increase of Nb content in the alloy.     

Study on corrosion resistance of electroplating zinc–nickel alloy coatings

Electrodeposited zinc–nickel alloy coatings have been widely adopted for surface treatment of automobile body steel sheet for high corrosion resistance. The corrosion behavior of the coatings has been related with the components of nickel, and the zinc–nickel alloy passive coatings have much higher corrosion resistance than that of zinc–nickel alloy coatings. In the present paper, the corrosion resistance behavior of the zinc–nickel alloy coatings obtained by new process and formulation has been studied by means of the electrochemistry test and neutral salt spray test. And it is discovered that the properties of corrosion resistance of zinc–nickel alloy passive coatings were better than that of zinc passive coatings, Cadmium passive coatings and alloys of electrodeposited cadmium–titanium. The components of corrosion productions, in terms of X‐ray diffraction (XRD), are mainly ZnO, ZnCl₂ · 4Zn(OH)₂ and small quantity of 2ZnCO₃· 3Zn(OH)₂. The component of zinc–nickel alloy coatings has been investigated with Glow Discharge Optical Emission Spectrometry (GDA‐750). And it is found that as the thickness of zinc–nickel alloy coatings increases, the component of zinc increases from beginning to end, but the peak value of nickel appears and an enrichment of nickel in the coatings comes into being. Because the electrodeposited zinc–nickel alloy coatings exhibit different alloy phases as a function of their alloy composition, in this paper, the crystal structure changing with the different component of nickel has been studied in terms of XRD. The result shows that electrodeposited zinc–nickel alloy has different phases: α‐phase, a solid solution of zinc in nickel with an equilibrium solubility of about more than 79% nickel; γ‐phase, an intermediate phase with a composition Ni₅Zn₂₁; η‐phase, a solid solution of nickel in zinc with less than 5% nickel; and δ‐phase (Ni₃Zn₂₂) appeared from η‐phase to α‐phase with increasing content of nickel. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of nano-Al2O3 particles and of the Co concentration on the corrosion behavior of electrodeposited Ni–Co alloys

Incorporation of nano-Al₂O₃ particles into a Ni–Co alloy by electrodeposition influences the corrosion properties, morphology, and structure of the layers. The resistance against corrosion of Ni–Co/Al₂O₃ composite films deposited on stainless steel was investigated in a 0.1-M NaCl solution by potentiodynamic polarization. The presence of nanoparticles improves the corrosion resistance of Ni–Co/nano-Al₂O₃ deposits when compared to pure Ni–Co alloy. Moreover, by increasing the pH of the electrodeposition bath and the content of Co in the alloy, the resistance against corrosion is furthermore improved. The morphology of the deposits before and after their corrosion was analyzed by scanning electron microscopy. The presence of the embedded alumina particles in the Ni–Co alloys was one of the key factors that limited further propagation of corrosion on the metallic surface. Preferential corrosion attack, in the form of a pitting corrosion, was located mainly at the grain boundaries.     

酸性介质中丙烯基硫脲对铜阳极溶出和阴极沉积过程影响的EQCM研究

采用循环伏安(CV)和电化学石英晶体微天平(EQCM)方法研究了酸性介质中铜阳极溶出和阴极沉积过程以及丙烯基硫脲(AT)对该过程的影响. 结果表明, 铜阳极溶出和阴极沉积过程的M/n分别为32.0和34.2 g/mol, 都是两电子过程, 其间未检测到Cu(Ⅰ)中间产物. AT改变了铜阳极溶出和阴极沉积的历程. 在含AT的溶液中, 铜阳极溶出和阴极沉积过程的M/n分别为61.9和65.4 g/mol, 可指认铜阳极溶出产物为CuAT+, 并提出了AT存在下Cu阳极溶出和阴极沉积过程的反应机理; 从电极表面质量定量变化的角度提供了Cu阳极溶出和阴极沉积过程的新数据.     

Electrochemical behavior of polypyrrole-coated AZ31 alloy modified by fluoride anions

The electrochemical polymerization of polypyrrole (Ppy) films on AZ31Mg alloys was carried out using cyclic voltammetery in 0.5 M sodium salicylate solution containing 0.25 M pyrrole and different concentration of sodium fluoride (NaF). Corrosion performance of the Ppy film was assessed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests in 3.5 % NaCl solution. It was observed that Ppy coatings doped in the presence of 100 ppm NaF provide the best corrosion protection for magnesium and the corrosion potential shifted about 290 mV toward nobler potentials and decrease the corrosion current density about one order of magnitude. The surface analysis of the coatings showed that the addition of F^? dopant anions led to an improvement in the smoothness, thickness, and adhesion quality of the synthesized Ppy coating on the Mg surface. The scanning electron microscopy (SEM) studies of the fluoride-doped Ppy films revealed that the synthesized coating has a closely packed globular structure which was composed of nanoparticles of Ppy.     

Electrodeposition of Al-Ti alloy on mild steel from AlCl<Subscript>3</Subscript>-BMIC ionic liquid

The electrodeposition of Al-Ti alloy on a mild steel substrate is examined in a Lewis acidic 66.7–33.3 mol% AlCl₃-1-buthyl-3-methylimidazolium chloride ionic liquid containing TiCl₄. Dense and compact Al-Ti alloy coatings with Ti content ranging from 5.3 to 11.4 at.% can be obtained under optimized conditions. The applied current densities and TiCl₄ concentration are found to play central roles in controlling the alloy compositions and surface morphologies of the resultant Al-Ti alloy coatings. Ti content in Al-Ti alloys increases with initial increase in the current density and decreases when the current density is beyond 5 mA cm^?2. In addition, the enhanced corrosion resistance of the mild steel substrate by the deposited Al-Ti alloy layers is evaluated via electrochemical techniques. The Al-Ti alloy coatings show much higher corrosion resistance than single Al coating, and this performance is improved with the increase of the Ti content.     

Highly increased capacitance and thermal stability of anodic oxide films on oxygen-incorporated Zr-Ti alloy

Heat treatment of Zr-24 at% Ti alloy with barrier-type dielectric anodic oxide films was conducted at 473 K in air to examine the thermal stability of the dielectric oxide films for possible electrolytic capacitor application. The anodic oxide film was formed by anodizing of the alloy at 50 V for 30 min in 0.1 mol dm^?3 ammonium pentaborate electrolyte. The anodic oxide film of 125 nm thickness was crystalline, containing both monoclinic and tetragonal ZrO₂ phase. It was found that marked thickening of the oxide film with generation of cracks occurred during heat treatment at 473 K. Thus, the dielectric loss was largely increased along with the capacitance increase. In contrast, the anodic oxide film formed on the oxygen-incorporated alloy remained uniform, and no significant increase in dielectric loss was observed even after the heat treatment. The capacitance of the anodic film became as high as 4.8 mF m^?2, which was nearly twice that on Ta. The high capacitance was associated with the preferential formation of tetragonal ZrO₂ phase in the anodic oxide film on the oxygen-incorporated alloy. Findings indicated that the oxygen-incorporated Zr-Ti alloy is a promising novel material for capacitor application.     

Properties of Ni-W alloy coatings on steel substrate

Ni-W alloy coatings were prepared on the steel substrate at the temperature of 60°C. The content of tungsten in coatings was increased with the growing cathodic current density. The increase of the corrosion resistance of Ni-W alloy coatings with the rising content of tungsten was confirmed by the measurement of anodic polarization curves. Annealed coatings showed better antioorrosion properties than the non-annealed ones. The properties of annealed coatings including their corrosion resistance depend on the tungsten content, too.     

Electrochemical and microgravimetric characterization of magnetron-sputtered Fe–Cr–Ni–Ta and Fe–Cr–Ni alloy films in neutral and strongly acidic media

The Fe–Cr–Ni and Fe–Cr–Ni–Ta alloy films were deposited on quartz substrates by magnetron-sputtering using targets of AISI 316 stainless steel and in combination with pure tantalum. The conventional melting of the Fe–Cr–Ni–Ta alloy formed is virtually impossible because the melting point of tantalum is higher than the boiling points of the other components. Elemental content of the films was determined by XPS analysis. Corrosion behaviour of both alloy films was studied in 5% NaCl and 10 M HCl by electrochemical quartz crystal microgravimetry (EQCM), electrochemical impedance spectroscopy (EIS) and dc-voltammetry. The corrosion resistance of Fe–Cr–Ni–Ta appeared to be significantly higher than that of Fe–Cr–Ni in both neutral (5% NaCl) and strongly acidic (10 M HCl) media. The Fe–Cr–Ni–Ta specimen exhibited an extremely high corrosion resistance in 10 M HCl, where the corrosion rates were about one order of magnitude lower than those of Fe–Cr–Ni in neutral solution. EQCM measurements in NaCl solution indicated accumulation of corrosion products on the Fe–Cr–Ni–Ta surface, which was evident from a distinctive increase in electrode mass. By contrast, the mass of the tantalum-free alloy film decreased with a constant rate, which indicated alloy dissolution to prevail. The corrosion current calculated from the mass decrease was in good agreement with that derived from voltammetric measurements. The EQCM data showed that the corrosion resistance of the Fe–Cr–Ni–Ta alloy film in 10 M HCl was about two orders of magnitude higher than that of the Fe–Cr–Ni.     

Preparation and characterization of anticorrosion Ormosil sol–gel coatings for aluminum alloy

Organically modified silicate (Ormosil) coatings have been synthesized through the sol–gel method for corrosion protection of aluminum alloy. Silica-based unmodified coatings were also designed to investigate the effect of tetraethoxysilane (TEOS) content on the properties of the coatings. The surface morphology of the coatings was characterized by scanning electron microscopy. The corrosion resistance was evaluated by immersion test, electrochemical impedance spectroscopy and potentiodynamic polarization measurements. In addition, the surface potential differences of the coated samples were determined by scanning Kelvin probe. The results showed that a better corrosion resistance of unmodified coating was prepared by controlling the TEOS/EtOH/H₂O molar ratio of 0.109/1/1.52. Ormosil coatings provided excellent barrier properties and corrosion resistance in comparison with the unmodified sol–gel coatings. The Ormosil coating modified with triethoxyoctylsilane exhibited corrosion resistance properties superior to the other Ormosil coatings after exposure to 3.5 wt% NaCl solution for 10 days.     

Construction of a novel electrochemical sensor for the determination of tellurium in soil and water samples by Co nanoparticles-modified electrode

ABSTRACT

The spherical Co nanoparticles (Co-NPs) were successfully fabricated through a facile one-step reduction approach. Due to the large specific surface area and excellent electronic conductivity, Co-NPs displayed excellent electrochemical performance and exhibited high sensitivity towards the detection of Tellurium (IV). The electroanalysis of Tellurium (IV) on the modified electrode was investigated by differential pulse anodic stripping voltammetry. The peak currents of Tellurium (IV) increased proportionally within the range of 0.02–1.8 and 1.8–400 mg L^?1 in the 0.1 M H₂SO₄ solution, under the optimal conditions. The detection limit was 0.2 μg L^?1 (S/N = 3). Moreover, the proposed method was successfully applied to determine Tellurium (IV) in real samples with satisfactory results. The Co-NPs/GCE not only showed good reproducibility, stability and anti-interference but also supplied a viable way for designing low toxic, environment-friendly and low-cost sensors to detect Tellurium (IV).     

Influence of pyridazine derivative on corrosion inhibition of mild steel in acidic media

The inhibition behavior of 6-methyl-4,5-dihydropyridazin-3(2H)-one (MDP) on corrosion of mild steel in 1 M HCl and 0.5 M H₂SO₄ was investigated using weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) measurements. The results indicated that the corrosion inhibition efficiency depends on concentration, immersion time, solution temperature, and the nature of the acidic solutions. It is also noted that MDP is at its the most efficient in 1 M HCl and least in 0.5 M H₂SO₄. The effect is more pronounced with MDP concentration. It is found that the inhibition efficiency attains 98 % at 5 × 10^?3 M in 1 M HCl and 75 % at 5 × 10^?2 in 0.5 M H₂SO₄. Polarization measurements showed that the MDP acts as a mixed inhibitor. EIS diagrams showed that the adsorption of MDP increases the transfer resistance and decreases the capacitance of the interface metal/solution. From the temperature studies, the activation energies in the presence of MDP were found to be superior to those in uninhibited medium. Finally, a mechanism for the adsorption of MDP was proposed and discussed.     

EIS investigation of a Ce-based posttreatment step on the corrosion behaviour of Alclad AA2024 anodized in TSA

In the aircraft industry, anodizing and posttreatment steps use Cr (VI) compounds, which, despite offering good corrosion resistance and self-healing properties, are highly toxic and carcinogenic. Ce compounds are recognized as efficient corrosion inhibitors for Al alloys, and several works report self-healing ability for these chemicals. In this investigation, the corrosion resistance of Alclad AA2024-T3 alloy anodized in tartaric-sulphuric acid (TSA) bath and posttreated in a solution comprising cerium nitrate without and with hydrogen peroxide was evaluated. The purpose is to investigate the potentiality of using hydrothermal treatment in Ce nitrate solution as candidate to replace Cr (VI) posttreatment. The aim is to provide a posttreatment step which, while improving the corrosion resistance, does not plug the mouths of the pores maintaining the adhesion properties of the porous anodic layer. Microstructural characterization was carried out by SEM-EDS whereas corrosion resistance was evaluated by EIS. The surface analysis showed that the posttreatments, all performed at 50°C, kept the open structure of the pores. EIS analysis showed that the posttreatments performed in the H₂O₂ solution for short immersion times were the most effective in improving the corrosion resistance of the samples, whereas electrical equivalent circuit (EEC) fitting of the data indicated sealing of the porous layer during the immersion of the different samples in the test solution. SEM-EDS analysis of the samples posttreated in the H₂O₂ containing solution, prior and after the corrosion test, showed the presence of Ce oxy-hydroxide randomly deposited on the sample surface, indicating that Ce could be incorporated/stored in the anodic layer.     

Poly(3-octylthiophene) and polystyrene blends thermally treated as coatings for corrosion protection of stainless steel 304

The effect of thermal annealing of poly(3-octylthiophene) (P3OT) and polystyrene (PS) blend coatings on the corrosion inhibition of stainless steel in a 0.5 M NaCl solution was investigated. P3OT was synthesized by direct oxidation of the 3-octylthiophene monomer with ferric chloride (FeCl₃) as oxidant. Stainless steel electrodes with mirror finish were coated with P3OT/PS blend by drop-casting technique. In order to study the temperature effect on the function like physical barrier against the corrosive species of P3OT/PS polymeric blend, the coatings were thermally annealed at three different temperatures (55?°C, 80?°C, and 100?°C). The corrosion behavior of P3OT/PS-coated stainless steel was investigated in 0.5 M NaCl at room temperature, by using potentiodynamic polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy. The LPR values indicated that, at 100?°C, P3OT/PS coatings showed a better protection of the 304 stainless steel in 0.5 M NaCl; the corrosion rate diminished in two orders of magnitude with regard to the bare stainless steel. The superficial morphology of the coatings before and after the corrosive environment was researched by atomic force microscopy, optic microscopy, and scanning electronic microscopy. Morphological study showed that the increased temperature benefited the integration of the two polymeric phases, which improved the barrier properties of the coatings. The coating/metal adhesion and the coating thickness were evaluated. The temperature increases the adhesion degree coating/substrate; thus, the coating annealed at 100?°C showed the best adhesion.     

Characterization of electrodeposited Co + Ni alloys by application of the ALSV technique Professor Aleksandar Despic to commemorate his 70th birthday

Anomalous codeposition of Co and Ni onto a gold RDE was investigated in a solution containing simple sulfate salts with the addition of sodium citrate. It was shown that the dependence of the percentage of Co in the deposit on the percentage of Co in the bath follows the shape found in the literature, with the percentage of Co in the deposit being slightly higher than in electrolytes containing pure simple salts. Alloy layers of different composition, electrodeposited at constant charge Q_dep = 1 C cm⁻² (thickness 0.34 μm) were submitted to anodic dissolution at a sweep rate of 1 mV s⁻¹ (ALSV technique) in a solution of 1 M NaCl, pH 2. All samples were found to dissolve through a single anodic peak, indicating that both constituents of the alloy dissolve simultaneously. Alloys with higher Ni content (above 40at.%) were found to dissolve at potentials more positive than the potential of pure Ni dissolution as a consequence of the Gibbs energy change of formation of electrodeposited solid solution type Co + Ni alloys. The composition of electrodeposited alloys was determined by the atomic absorption technique. An attempt was made to obtain a correlation between the peak potentials of anodic dissolution of alloy samples and the composition of alloys, to determine the composition of the alloy from the peak potential of its dissolution. It is found that such a correlation can be used only for strictly defined conditions of alloy deposition and dissolution, caused by the contribution of the Gibbs energy change of formation of electrodeposited alloys. Also, the presence of a CoNi₃ ordered structure in the system is not detected as a separate ALSV peak, but its existence could be the cause of the shape of the Gibbs energy change with composition of the alloy for alloys electrodeposited at low current density.     

Characterisation of five coins from the archaeological heritage of Portugal

This paper reports a study carried out on three Roman and two Portuguese coins found in the archaeological site of São Pedro, in Fronteira (Alentejo, Portugal). The three Roman coins have been identified as a Follis, an AE 2 and an AE 3 (bronze alloys), while the Portuguese coins have been identified as a Ceitil (copper) and the “6 vinténs” (Ag–Cu alloy). Scanning electron microscopy (SEM) coupled to energy dispersive spectroscopy (EDS) has allowed the semi-quantitative determination of the elemental composition of both the corrosion products and the alloy used in the manufacture of the coins. The crystalline corrosion products constituents of the patinas were identified by X-ray powder diffraction spectroscopy (XRD). The more deteriorated coin, the AE 3, was submitted to electrochemical studies in Na₂SO₄ aqueous solution and the corresponding data analysed. After 3 weeks, the E _OCP was still quite stable, ranging between ?0.050 and ?0.070 V vs. SCE; the corrosion resistance, R _p, was of the order of 5 to 3?×?10³ Ω. Chemical treatment of the sample by 1-h immersion in 0.1 M NaOH produced a more active surface, with R _p showing a decrease of a factor of about ten. On the other hand, it was concluded from voltammetric data that polarisations of E _a?≥?0.050 V vs. SCE led to copper oxidation, with no reduction of the other corrosion products.     

Mechanical and corrosion behavior of amorphous and crystalline electroless Ni–W–P coatings

Two types of electroless Ni–W–P coatings: nanocrystalline with low P and amorphous with higher P content are investigated. Scanning probe microscopy is applied to study their morphology. Textured nanocrystalline coatings consist of coarse pyramids built of nanometer thick lamellas. The surface morphology of amorphous coatings is much finer and uniform. Nanohardness of all coatings depends on W content. Microhardness is increasing during the heat treatment up to 350 °C due to nickel phosphide precipitation affected by tungsten also. The wear resistance of nanocrystalline Ni–W–P coatings is much higher than that of amorphous in spite of the similar tungsten content in both. Lower corrosion resistance of amorphous Ni–W–P coatings is found by weight loss method during long-term immersion in 5 % NaCl. Electrochemical tests by potentiodynamic polarization curves in two model corrosion media—solutions of 0.5 M H₂SO₄ and 5 % NaCl—are performed. The corrosion of bi-layered Ni–W–P/Ni–P and Ni–W–P/Ni–Cu–P deposits on mild steel is also investigated. The results prove that an electroless Ni–W–P coating on mild steel extremely improves its mechanical and corrosion behavior. It is demonstrated that in addition to deposit’s structure and composition, the distribution and chemical state of alloy ingredients are also responsible for its properties.