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.     

Characterization and cytocompatibility of polydopamine on MAO‐HA coating supported on Mg‐Zn‐Ca alloy

Magnesium has been suggested as a potential biodegradable metal for the usage as orthopaedic implants. However, high degradation rate in physiological environment remains the biggest challenge, impeding wide clinical application of magnesium‐based biomaterials. In order to reduce its degradation rate and improve the biocompatibility, micro‐arc oxidation coating doped with HA particles (MAO‐HA) was applied as the inner coating, and polydopamine (PDA) film was synthesized by dopamine self‐polymerization as the outer coating. The microstructure evolution of the coating was characterized using scanning electron microscopy (SEM), atomic force microscope (AFM), X‐ray diffraction analyses (XRD), Fourier transform infrared spectroscopy (FT‐IR), and X‐ray photoelectron spectroscopy (XPS). The results showed that PDA film had covered the entire surface of MAO‐HA coating and the pore size of MAO‐HA coating decreased. The root mean square (RMS) roughness of PDA/MAO‐HA coatings was approximately 106.46 nm, which was closer to the optimum surface roughness for cellular attachment as compared with MAO‐HA coatings. Contact angle measurement indicated that the surface wettability had been transformed from hydrophobic to hydrophilic due to the introduction of PDA. The PDA/MAO‐HA coatings exhibited better corrosion resistance in vitro, with the self‐corrosion potential increasing by 150 mV and the corrosion current density decreasing from 2.09 × 10^?5 A/cm ² to 1.46 × 10^?6 A/cm ² . In hydrogen evolution tests, the corrosion rates of the samples coated with PDA/MAO‐HA and MAO‐HA were 4.40 and 5.95 mm/y, respectively. MTS assay test and cell‐surface interactions experiment demonstrated that PDA/MAO‐HA coatings exhibited good cellular compatibility and could promote the adhesion and proliferation of MC3T3‐E1 cells.     

The formation mechanism and biocorrosion property of CaSiO3/CaHPO4 · 2H2O composite conversion coating on the extruded Mg‐Zn‐Ca alloy for bone implant application·

In this work, a calcium silicate and calcium phosphate (CaSiO₃/CaHPO₄ · 2H₂O) composite coating was applied by a chemical reaction to an extruded Mg‐Zn‐Ca magnesium alloy. SEM observation showed that a flat and sand‐like conversion coating was formed. X‐ray diffractometer (XRD) analysis indicated that the conversion coating was composed of CaHPO₄ · 2H₂O and a little amount of CaSiO₃. The formation mechanism of CaSiO₃/CaHPO₄ · 2H₂O composite conversion coatings was discussed. The electrochemical polarization tests showed that the conversion coating markedly improved the biocorrosion resistance of Mg‐Zn‐Ca alloy in Hank's solution. Copyright © 2010 John Wiley & Sons, Ltd.     

Novel Sol–Gel Synthesis of Acidic MgF2−x(OH)x Materials

Novel magnesium fluorides have been prepared by a new fluorolytic sol–gel synthesis for fluoride materials based on aqueous HF. By changing the amount of water at constant stoichiometric amount of HF, it is possible to tune the surface acidity of the resulting partly hydroxylated magnesium fluorides. These materials possess medium‐strength Lewis acid sites and, by increasing the amount of water, Brønsted acid sites as well. Magnesium hydroxyl groups normally have a basic nature and only with this new synthetic route is it possible to create Brønsted acidic magnesium hydroxyl groups. XRD, MAS NMR, TEM, thermal analysis, and elemental analysis have been applied to study the structure, composition, and thermal behaviour of the bulk materials. XPS measurements, FTIR with probe molecules, and the determination of N₂/Ar adsorption–desorption isotherms have been carried out to investigate the surface properties. Furthermore, activity data have indicated that the tuning of the acidic properties makes these materials versatile catalysts for different classes of reactions, such as the synthesis of (all‐rac)‐[α]‐tocopherol through the condensation of 2,3,6‐trimethylhydroquinone (TMHQ) with isophytol (IP).     

One‐step immersion method for fabricating superhydrophobic aluminum alloy with excellent corrosion resistance

This work develops a facile one‐step immersion method for preparing the superhydrophobic aluminum alloy, i.e. the aluminum alloy is treated with stearic acid (STA)–ethanol–H₂O solution at 60 °C for 35 h. Results show that the aluminum alloy achieves flower‐like structure with both a great deal of pillars and pores, while the long hydrophobic alkyl chains are chemically grafted onto the hierarchical surface. Meanwhile, the water contact angle at the aluminum alloy surface gradually enhances with the decrease of the ethanol–H₂O volume ratio, and the water contact angle and rolling angle of 156.2° and 5°, respectively, are obtained when the ethanol–H₂O volume ratio is 1:3. Moreover, results show that the higher water contact angle at the aluminum alloy, the better corrosion resistance of the aluminum alloy. Consequently, the aluminum alloy with the superhydrophobic property has the best corrosion resistance, durability, and stability in corrosive environments. Copyright © 2016 John Wiley & Sons, Ltd.     

Process aspects of electroless deposition for nickel–zinc–phosphorous alloys

Electroless deposition of Ni–Zn–P thin film was considered as a barrier film on a galvanic Zn or Ni–Zn sacrificial layer in a multicomponent corrosion protective coating on steel. The incorporation of zinc on the chemical composition of electroless Ni–Zn–P coating was studied. The effect of operating conditions such as temperature, pH value and concentration of zinc sulphate was investigated. Some physical characteristics such as morphology, structure, corrosion properties of Ni–Zn–P coatings were assessed in parallel with those of Ni–P. Inclusion of Zn to Ni–P is accompanied by the transformation of the coating structure from amorphous to crystalline. The effect of adding nonionic surfactant to the plating solution on the composition and surface morphologies was also investigated. The results indicate that nonionic surfactant has no effect on the Zn % in the deposit layer, but it affects the surface morphology and improves the corrosion resistance of Ni–Zn–P layers. Copyright © 2005 John Wiley & Sons, Ltd.     

MgAuGa and MgAu2Ga: first representatives of the Mg–Au–Ga system

MgAuGa (magnesium gold gallium), the first ternary representative of the Mg–Au–Ga system, crystallizes in the space group P2m and adopts the Fe₂P structure type (Pearson symbol hP9). Various phases with the general composition AB₂ have been reported in the surrounding binary systems, viz. Mg₂Ga (hP18), MgGa₂ (hP6; CaIn₂ type), AuGa₂ (cF12; CaF₂ type), Au₂Ga (oS24; Pd₂As type) and Mg₂Au (oP12; Co₂Si type). In principle, MgAuGa can be obtained from each of them by partial replacement of the major element with the missing element. In fact, the structure of MgAuGa closely resembles hexagonal Mg₂Ga through a direct group–subgroup relationship. MgAu₂Ga (magnesium digold gallium) also crystallizes hexagonally in the space group P6₃/mmc and is isotypic with Na₃As. It adopts the structure of another binary compound, viz. Mg₃Au (hP8), but shows an unexpected distribution of Mg, Au, and Ga among the atomic positions of the asymmetric unit. Both MgAuGa and MgAu₂Ga can be described as formally anionic Au/Ga frameworks, with pseudo‐hexagonal tunnels around Mg in MgAuGa or cages in MgAu₂Ga.     

Effect of Cu in electroless Ni–Cu–P coating on passivation process

Electroless Ni–P and Ni–Cu–P coatings were passivated by chromate conversion treatment respectively. The anticorrosive performances of passivated coatings were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The passivated Ni–Cu–P coating exhibited a high corrosion resistance with the i_corr of 0.236 μA/cm,² while the value of passivated Ni–P coating was only 1.030 μA/cm,² indicating the passive film could improve the corrosion resistance of Ni–Cu–P coating to a significant extent. High‐resolution X‐ray photoelectron spectroscopy was used to determine the chemical states of elements detected in the passive film. Compared with passivated Ni–P coating, the passive film on Ni–Cu–P coating exhibited a higher ratio of Cr₂O₃ to Cr(OH)₃ with the value of 72:28, which was the main factor for passivated Ni–Cu–P coating showing excellent corrosion resistance. The effect of Cu in electroless Ni–Cu–P coating on passivation process was discussed by the contrast experiment. Copyright © 2016 John Wiley & Sons, Ltd.     

Micro‐arc oxidation and electrophoretic deposition of nano‐grain merwinite (Ca3MgSi2O8) surface coating on magnesium alloy as biodegradable metallic implant

Magnesium alloys are promising biomaterials as biodegradable implant for orthopedic applications. However, their low corrosion resistance and poor bioactivity have prohibited their implant applications. In order to enhance these two properties, a nano‐grain merwinite coating was prepared on magnesium alloy. Its corrosion and the bioactivity behavior were characterized with electrochemical and immersion tests. The results showed that the nano‐grain merwinite coating can improve both the corrosion resistance and the bioactivity of the magnesium alloy making it an appropriate material for biodegradable bone implants. Copyright © 2014 John Wiley & Sons, Ltd.     

Corrosion behavior of electroless Ni–P/TiO2 nanocomposite coatings

Composite Ni–P/nano‐TiO₂ coatings were prepared by simultaneous electroless deposition of Ni–P and nano‐TiO₂ on a low carbon steel substrate. The deposition was carried out from stirred solutions containing suspended nano‐TiO₂ particles. The Ni–P and Ni–P/nano‐TiO₂ coatings before and after heat treatment were characterized by X‐ray diffraction, scanning electron microscopy and energy dispersive X‐ray spectroscopy. The micro‐structural morphologies of the coatings significantly varied with the nano‐TiO₂ content. The corrosion resistance of as‐plated and heat‐treated Ni–P and Ni–P/nano‐TiO₂ coatings was investigated by anodic polarization, Tafel plots and electrochemical impedance spectroscopic (EIS) studies in 3.5% NaCl solution. Ni–P/nano‐TiO₂ coating exhibited superior corrosion resistance over Ni–P coating. Copyright © 2015 John Wiley & Sons, Ltd.     

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.     

Corrosion,wear, and cell culture studies of oxygen ion implanted Ni–Ti alloy

To increase the biocompatibility of nickel–titanium (Ni–Ti) alloy substrates, oxygen ions have been implanted by the plasma immersion ion implantation (PIII–O) technique at low temperature without affecting the substrate properties. The implanted Ni–Ti surface is characterized for microhardness and composition. Energy‐dispersive spectroscopy and X‐ray photoelectron spectroscopy investigations show the replacement of native oxide on the alloy by a compact oxide during the implantation process. The corrosion behaviors of untreated substrate and PIII–O samples are investigated using potentiodynamic polarization and electrochemical impedance spectroscopy in simulated body fluid (Hanks' solution). Polarization and electrochemical impedance spectroscopy studies reveal nearly ideal capacitor behavior with better passivation characteristics for the oxygen‐implanted substrate. Sliding wear studies reveal lower friction of coefficient for the implanted layers as compared with the substrate. The bare and surface modified Ni–Ti alloy samples are evaluated for biocompatibility using osteoblast‐like cells (MG‐63). Cellular behavior in terms of cell morphology along with the viability and proliferations is evaluated by using scanning electron microscopy and in vitro cell culture assay, respectively. The results clearly show that oxygen implantation by PIII–O provides a better compatible surface for cell attachment and growth. The modified surface exhibits a higher percentage of cell viability demonstrating the enhanced biocompatibility of the oxygen‐implanted surface compared with bare Ni–Ti alloy. Copyright © 2017 John Wiley & Sons, Ltd.     

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.     

Biocompatibility and osteoconduction of active porous calcium-phosphate films on a novel Ti-3Zr-2Sn-3Mo-25Nb biomedical alloy

The purpose of this study is to investigate the biocompatibility and osteoconduction of active porous calcium-phosphate films on the novel Ti-3Zr-2Sn-3Mo-25Nb biomedical alloy. The active porous calcium-phosphate films were prepared by the micro-arc oxidation method on the surface of a near β biomedical Ti-3Zr-2Sn-3Mo-25Nb alloy, and then activated in a hydroxyl solution followed by an aminated solution. The phase composition, surface micro-topography and elemental characteristics of the active porous calcium-phosphate films were investigated with XRD, SEM, EDS and XPS. The biocompatibility was assessed using corrosion testing, the in vitro osteoblast cultivation test and implantation in soft tissue (subcutaneous and musculature). The osteoconduction was evaluated using the simulated body fluid test and by implantation in hard tissue. The results show that the active porous films are mainly composed of TiO(2) anatase and rutile. The oxide layer is a kind of porous ceramic intermixture containing Ca and P. Immersion in simulated body fluid can induce apatite formation on the porous calcium-phosphate films resulting in excellent bioactivity. Cell cultures revealed that MC3T3-E1 cells grew on the surface exhibiting favorable morphologies. These results indicate that the Ti-3Zr-2Sn-3Mo-25Nb biomedical alloy coated with an active porous calcium-phosphate film has been shown to have excellent corrosion resistance, good biocompatibility and osteoconduction, which can promote cell proliferation and bone formation.     

Static SIMS studies of carboxylic acids on gold and aluminium–magnesium alloy surfaces

Static secondary ion mass spectrometry was used to study the surface reactions and lateral distributions of fatty carboxylic acid molecules on sputter‐deposited gold and aluminium surfaces, as well as commercial aluminium–magnesium alloy surfaces, cleaned using UV/ozone. Films were prepared by spin coating dilute solutions of stearic acid and lauric acid onto the above surfaces. These carboxylic acids were shown to react with the oxide formed on the aluminium and aluminum–magnesium alloy substrates to produce a deprotonated acid anion, stabilized by the formation of a magnesium soap on the aluminium–magnesium alloy surface. Secondary ion imaging of stearic acid films revealed the formation of C‐type crystals. Copyright © 2003 John Wiley & Sons, Ltd.     

Influence of zirconium doping on the growth of apatite and corrosion behavior of DLC‐coated titanium alloy Ti–13Nb–13Zr

Ti–13Nb–13Zr was coated with diamond‐like carbon (DLC) and zirconium‐doped DLC by plasma‐enhanced chemical vapor deposition and sputtering. The corrosion current of the substrate is not affected after coating, and corrosion potential shifts towards nobler values in Hanks' solution. Electrochemical impedance spectroscopy studies show that Zr‐DLC samples behave like an ideal capacitor. Field emission scanning electron microscopy (FESEM) images after 7 days of immersion show absence of apatite on DLC‐coated sample and its presence on Zr‐doped DLC, but to a lesser extent as compared with that on the uncoated substrate. XPS and Energy‐dispersive X‐ray spectroscopy (EDS) of samples immersed in Hanks' solution show presence of calcium, phosphorous and oxygen in hydroxide/phosphate form on the substrate and Zr‐DLC. Copyright © 2013 John Wiley & Sons, Ltd.     

Host–Guest [2+2] Cycloaddition Reaction: Postsynthetic Modulation of CO2 Selectivity and Magnetic Properties in a Bimodal Metal–Organic Framework

Simultaneous tuning of permanent porosity and modulation of magnetic properties by postsynthetic modification (PSM) with light in a metal–organic framework is unprecedented. With the aim of achieving such a photoresponsive porous magnetic material, a 3D photoresponsive biporous framework, MOF1, which has 2D channels occupied by the guest 1,2‐bis(4‐pyridyl)ethylene (bpee), H₂O, and EtOH molecules, has been synthesized. The guest bpee in 1 is aligned parallel to pillared bpee with a distance of 3.9 Å between the ethylenic groups; this allows photoinduced PSM of the pore surface through a [2+2] cycloaddition reaction to yield MOF2. Such photoinduced PSM of the framework structure introduces enhanced CO₂ selectivity over that of N₂. The higher selectivity in MOF2 than that of MOF1 is studied through theoretical calculations. Moreover, MOF2 unveils reversible changes in T_c with response to dehydration–rehydration. This result demonstrates that photoinduced PSM is a powerful tool for fabricating novel functional materials.     

Static SIMS studies of fatty alcohols,amines and esters on gold and aluminium–magnesium alloy surfaces

Static secondary ion mass spectrometry was used to study the chemical reactions and lateral distributions of fatty amines, alcohols and esters spin coated onto gold surfaces and commercial aluminium–magnesium (Al–Mg) alloy surfaces, cleaned using UV–ozone. The aim of this study is to develop an understanding of the interactions of model lubricants with metal surfaces, such as gold and aluminium. This static SIMS study of organic thin films has been able to identify specific reaction products on the aluminium surface for each functional group. This work demonstrates that organic molecules with alcohol, ester and amine functional groups undergo specific chemical reactions with oxidized Al–Mg alloy surfaces. For example, films composed of the fatty alcohol dodecanol were observed to emit monomers, dimers and trimers with discrete distributions. In addition, negative secondary ion mass spectra indicate that a surface carboxylate is formed from the alcohol. The formation of carboxylate reaction products was confirmed by Fourier transform infrared spectroscopy. On Al–Mg alloy surfaces, a direct interaction with the amine and aluminium oxide surface is observed by the detection of a molecular ion that corresponds to the mass of dodecylamine and AlO^?, characteristic of aluminium oxide. Ethyl laurate was shown to eliminate the ethyl group, leaving the laurate anion. This study demonstrates the ability of time‐of‐flight (ToF) SIMS to discriminate and detect chemical reaction products formed between model lubricant molecules and metal surfaces. As a result of this study, the use of ToF‐SIMS to identify reaction products of model lubricants can be extended to provide a better understanding of the interactions of lubricants and metal surfaces at high temperatures and pressures that more closely resemble the conditions encountered in industrial rolling processes. Copyright © 2005 John Wiley & Sons, Ltd.     

1‐Hexene Polymerization over Supported Titanium–Magnesium Catalyst: The Effect of Composition of the Catalytic System and Polymerization Conditions on Temperature Dependence of the Polymerization Rate

The effect of temperature on the rate of 1‐hexene polymerization over supported titanium–magnesium catalyst of composition TiCl₄/D₁/MgCl₂ + AlR₃/D₂ (D₁ is dibutyl phthalate, D₂ is propyltrimethoxysilane, and AlR₃ is an organoaluminum cocatalyst) is studied. The unusual data that the polymer rate decreases when temperature is increased from 30 to 70 °C are obtained. The 1‐hexene polymerization rate and the pattern of changes in polymerization rate with temperature depend on a combination of factors such as cocatalyst (AlEt₃ or Al(i‐Bu)₃) and presence/absence of hydrogen and an external donor in the reaction mixture. These factors differ in their effects on catalytic activity at different polymerization temperatures, so the temperature coefficient (E_eff) values calculated using the Arrhenius dependence of the polymerization rate on polymerization temperature vary greatly. The “normal” Arrhenius plot where polymerization rate increases with temperature is observed only for polymerization with the Al(i‐Bu)₃ cocatalyst in the presence of hydrogen and without an external donor. Formation of high‐molecular‐weight polyhexene at low polymerization temperatures results in catalyst particle fragmentation, which may additionally contribute to the increase in polymerization rate as polymerization temperature is reduced.     

Effects of Ca and Ag addition and heat treatment on the corrosion behavior of Mg-7Sn alloys in 3.5 wt.% NaCl solution

The effects of 1 wt.% Ca or 1 wt.% Ca + 1 wt.% Ag addition and heat treatment on the corrosion behavior of Mg-7Sn (wt.%) alloy in 3.5 wt.% NaCl solution were investigated by electrochemical measurements and immersion tests. The alloys were characterized by optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). It was found that all alloys were corroded by pitting corrosion and grain boundary corrosion and further corroded with time going. Loose layers of compounds, including Mg (OH)₂, MgO, SnO₂, and other compounds containing Ca and Ag elements, were calibrated on the surface of corroded Mg-7Sn-1Ca-1Ag alloy. The Ca addition improved the corrosion resistance of Mg-7Sn alloy due to the formation of relatively stable compounds containing calcium element and grains refinement. Furthermore, the solid solutioned alloys obtained a superior corrosion resistance due to the dissolve of eutectic Mg₂Sn phase and homogenization treatment. However, the aging treatment is slightly detrimental to the corrosion resistance of Mg-7Sn alloys with the formation of Mg₂Sn precipitates. In conclusion, the aged Mg-7Sn-1Ca-1Ag alloy exhibited a better corrosion resistance and a noticeable micro-hardness property compared with those of as-cast Mg-7Sn alloy. And this study provides an important idea for the research on the comprehensive properties of Mg-Sn alloys.