Effect of nano-Al2O3 particles on the corrosion behavior of alkyd based waterborne coatings

A modification in the alkyd based waterborne coatings was studied with the addition of 0.05%, 0.1%, 0.2%, and 0.3% nano-Al₂O₃. Corrosion performance of the nano-composite coatings were evaluated by applying these nanocomposites on mild steel substrate and exposing them to salt spray, humidity, and accelerated weathering. Mechanical properties were studied by subjecting the coating to scratch and abrasion test. The results showed that, with an increase in the concentration of nano-Al₂O₃ there was an improvement in the corrosion resistance, UV resistance, and mechanical properties of the coatings indicating the positive effect of addition of nano-Al₂O₃ particles in the coatings. Further, the transparency of the coating was not altered, maintaining the optical clarity of the coating.     

Preparation and corrosion resistance studies of nanometric sol-gel-based CeO2 film with a chromium-free pretreatment on AZ91D magnesium alloy

Magnesium alloy, although valuable, is reactive and requires protection before it can be applied in many fields. In this study, a novel protective environmental-friendly gradient coating was performed on AZ91D magnesium alloy by non-chromate surface treatments, which consisted of phytic acid chemical conversion coating and the sol-gel-based CeO₂ thin film. The surface morphologies, microstructure and composition of the coatings were investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD), respectively. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. The effects of the concentration, layers, temperature of heat treatment of CeO₂ sol on the anti-corrosion properties of the gradient coating for magnesium were also investigated. The results showed that the gradient coating was mainly composed of crystalline CeO₂. According to the results of electrochemical tests, the corrosion resistance of AZ91D magnesium alloy was found to be greatly improved by means of this new environmental-friendly surface treatment.     

Electrochemical impedance spectroscopy (EIS) study of nano-alumina modified alkyd based waterborne coatings

A nano-composite coating was formed by dispersing nano-Al₂O₃ as pigments in different concentrations, to a specially developed alkyd based waterborne coating. The nano-Al₂O₃ based composite coatings were applied on mild steel substrate by dipping. The dispersion of particles in coating system was investigated by using SEM and AFM techniques. The effect of addition of these nano-pigments on the electrochemical behavior of the coating was investigated in 3.5% NaCl solution, using electrochemical impedance spectroscopy (EIS). It was found that coating modified with higher concentration of nano-Al₂O₃ particles showed comparatively better performance as it was evident from pore resistance (R_p) and coating capacitance (C_c) values after 30 days of exposure. In general, the study showed an improvement in the corrosion resistance of the nano-particle modified coatings as compared to the neat coating, confirming the positive effect of nano-particle addition in coatings.     

Zn–Ni/nano-TiO2 composite electrodeposits: surface modifications and protective properties

Zn–Ni composite coatings were obtained by electrochemical co-deposition of TiO₂ nano-particles (mean diameter 21 nm). Zn–Ni alloy coating was also produced under the same experimental conditions for comparison. The surface morphology, crystallographic structure, and the grain size of the deposits were investigated, along with the percentage of the embedded nano-particles in Zn–Ni matrix, as a function of concentration of TiO₂ nano-particles in the bath. As the titania incorporation percentage is increased, a grain refinement in the nanometer region was revealed followed enhanced microhardness values and an improvement of the content of the nickel in the alloy. Annealing of all coatings at 200 °C revealed the crystallization of the matrix accompanied by a decrease of microhardness followed by stability for 24 h. The corrosion behavior of Zn–Ni/nano-TiO₂ composite coatings with various amount of particle content was mainly studied by electrochemical impedance spectroscopy in 3 % NaCl. It was seen that Zn–Ni/nano-TiO₂ composite coatings exhibited higher corrosion resistances comparing to Zn–Ni alloy coating and corrosion protection improved with increasing nano-TiO₂ in coatings.     

Biocompatibility,corrosion resistance and antibacterial activity of TiO2/CuO coating on titanium

In this work, TiO₂/CuO coating was prepared on titanium (Ti) by combination of magnetron sputtering and annealing treatment. The microstructure, biocompatibility, corrosion resistance and antibacterial property of TiO₂/CuO coating were investigated in comparison with pure Ti and TiO₂ coating. The results show that TiO₂/CuO coating is mainly composed of TiO₂ and CuO. In vitro cytocompatibility evaluation suggests that no obvious toxicity appears on the TiO₂/CuO coating, and the coating stimulates the osteoblast spreading and proliferation. Compared with Ti and TiO₂ coating, TiO₂/CuO coating exhibits improved corrosion resistance and antibacterial ability against S.aureus. This study is the first attempt to apply the combination of magnetron sputtering and annealing treatment to introduce the Cu into TiO₂ coating for surface modification of Ti-based implant materials, which may provide a research foundation for further development of bioactive multifunctional coatings to meet the better clinical demand.     

Kinetics study of living microemulsion polymerization mediated by reversible addition-fragmentation chain transfer

The present work focuses on the development of functional polyurethane hybrids through the incorporation of surface modified TiO₂ nanoparticles. For improving the nano-particle dispersion and increasing possible interactions between nano-particles and polyurethane matrix, the surface of the nano-particles was modified with 1,3,5-triazine core silane coupling agent. The surface modification of nanoparticles was confirmed by FESEM, FT-IR and Raman spectroscopic techniques. The functionalized nanoparticles were then inscribed in 0, 1 and 2 weight percentages into polyurethane matrix. The as prepared composite coatings were investigated for various anti-microbial, thermo-mechanical and anticorrosive properties. The tensile strength of polyurethane was improved by 300 % upon addition of 2 wt% of modified TiO₂ nanoparticles as compared to neat polyurethane. Fog test and electrochemical polarization studies suggest that the corrosion resistance increases with increase of the modified TiO₂ content in the coating formulation. The composite coatings also have good resistance towards various bacterial and fungal stains as compared to the pure polyurethanes. The coatings substantially gain hydrophilic nature symbiotically with TiO₂ content suggesting its potential application as self-cleanable material.     

Surface modification of TiO2 nano-particles with silane coupling agent and investigation of its effect on the properties of polyurethane composite coating

Surface modification and characterization of TiO₂ nano-particles as an additive in a polyurethane clear coat were investigated. For the improvement of nano-particles dispersion and increasing possible interactions between nano-particles and polymeric matrix, the surface of the nano-particles was modified with amino propyl trimethoxy silane (APS). Equivalent amount of APS for monolayer formation on the nano-particles surface was determined by means of elemental analysis (CHN). The grafting of APS on the TiO₂ nano-particles surface was characterized with TGA and FTIR techniques. Mechanical properties of coatings containing various amount of TiO₂ nano-particles were evaluated with DMA technique and tensile strength measurement. UV–vis spectroscopy was employed to evaluate the absorbance and transmittance of the nano-TiO₂ composite coatings in the wavelength range of 230–700 nm.     

Incorporation of ZnO–ZrO2 nanoparticles into TiO2 coatings obtained by PEO on Ti–6Al–4V substrate and evaluation of its corrosion behavior,microstructural and antibacterial effects exposed to SBF solution

In this research, Plasma Electrolytic Oxidation technique was used to incorporate ZnO–ZrO₂ nanoparticles into TiO₂ ceramic coating on Ti6–Al–4V using sodium phosphate as an electrolyte. The effect of adding these nanoparticles on corrosion, morphology, wettability and antibacterial properties in the simulated body fluid (SBF) solution was investigated. The results indicated nanoparticles modified the microstructure of coating, which increased corrosion resistance 12 times higher than that of substrate. Besides, ZrO₂ nanoparticles had the most significant effect on increasing the contact angle. In addition, due to the compatibility of zirconium and zinc oxides with human body environment, the antibacterial properties of coatings were significantly improved.     

Corrosion resistance and photocatalytic activity evaluation of electrophoretically deposited TiO2-rGO nanocomposite on 316L stainless steel substrate

TiO₂-rGO nanocomposite coatings were obtained by electrophoretic deposition (EPD) technique of TiO₂ nanoparticles and graphene oxide (GO) on stainless steel substrate. First, GO particles were synthesized using a modified Hummers' method. GO was reduced electrochemically to form a coating in the presence of nano-sized TiO₂ particles. The influences of different parameters such as GO concentration, coupling co-electro-deposition parameters (electrophoretic duration and voltage) on thickness, surface morphology and, corrosion behavior of the as-synthesized TiO₂-rGO nanocomposite coatings were systematically surveyed. The morphology and microstructure were investigated by field emission scanning electron microscopy (FE-SEM), Raman spectra and X-ray diffraction (XRD) techniques. Atomic force microscopy (AFM) was harnessed to evaluate the topography of the as-prepared GO powder. The bonding characteristics of as-synthesized and as-reduced GO were examined after deposition, by Energy Dispersive Analysis of X-Ray (EDX) and Fourier-transform infrared spectroscopy (FT-IR). Corrosion behavior of coatings and that of the pure TiO₂ layer were evaluated by electrochemical impedance spectroscopy (EIS) and polarization techniques (by applying potentiodynamic polarization spectroscopy (PDS)). Detailed SEM studies showed that increasing EPD voltage brings about a coating with increased porosity and microcracks with higher thickness. In addition to that, the presence of rGO reduced corrosion current density (i_corr) and shifted corrosion potential (E_corr) toward more noble values in 3.5% NaCl at room temperature. Also, Analyses revealed that the optimum electrophoretically synthesized coating was obtained at GO concentration of 1 g/L, 30 V and 30 min at room temperature. The corrosion current density of the corresponding coating was remediated up to 0.2 μA cm⁻², which means an anti-corrosion ability of about 30 times compared to TiO₂-coated and bare 316L stainless steel. The results of impedance spectroscopic studies demonstrated that this coating renders as a barrier layer and resistance increased from 2.95 KΩ cm² for TiO₂-coated layer to 10.49 KΩ cm² for the optimized layer.     

A study on the N-, S- and Cl-modified nano-TiO2 coatings for corrosion protection of stainless steel

Nano-titania coatings doped with anions of nitrogen, sulfur and chlorine have been supplied on the surface of 316L stainless steel by a sol-gel process and dip-coating technique. The measurements of XRD, SEM, ATR-IR, Raman and XPS were carried out to characterize the chemical composition and structure for the prepared samples. The corrosion performances of the coating in 0.5 M NaCl were evaluated by electrochemical impedance spectroscopy (EIS) and polarization measurements. According to the measurements of EIS and electrochemical polarization, the N-modified TiO₂ nano-coatings show a highest corrosion resistance among the prepared coatings. It is revealed, from the SEM, XRD and Raman characterizations, that the surface of N-modified TiO₂ nano-coatings are more compact and uniform, relatively well-crystallized and able to act as an optimal barrier layer to metallic substrates. The XPS analysis confirms the presence of low concentration of N element in two forms, atomic β-N (interstitial state) and chemisorbed γ-N₂ on the surface of TiO₂ nano-coatings. It is suggested that the addition of nitrogen is beneficial to improve the compact structure and enhance the hydrophobic property.     

Preparation and properties of Ni-W-P-TiO2 nanocomposite coatings developed by a sol-enhanced electroplating method

Several Ni-W-P-TiO₂ nanocomposite coatings were developed by the sol-enhanced electroplating method. The phase and elemental compositions of coatings were determined, and the surface and cross-section morphology were characterized. The mechanical and corrosion performance were systematically tested. The results revealed the addition of 5 ml·L^-1 TiO₂ sol caused a compact coating surface, while higher concentrations of TiO₂ reduced the coating thickness and led to the inferior surface microstructure. The comparison in physiochemical properties of prepared coatings confirmed the superior performance of the Ni-W-P-TiO₂ nanocomposite coating at 5 ml·L^-1 TiO₂ sol addition. Under this condition, the best mechanical properties were achieved when abrasive wear was the dominating wear-resistance mechanism, and the best corrosion resistance was obtained due to its smooth and compact surface microstructure.     

Composite Ni/Al2O3 coatings and their corrosion resistance

Composite coatings Ni/Al₂O₃ were electrochemically deposited from a Watts bath. Al₂O₃ powder with particle diameter below 1 μm was codeposited with the metal. The obtained Ni/Al₂O₃ coatings contained 5-6% by weight of corundum. The structure of the coatings was examined by scanning electron microscopy (SEM). It has been found that the codeposition of Al₂O₃ particles with nickel disturbs the nickel coating's regular surface structure, increasing its microcrystallinity and surface roughness. DC and AC electrochemical tests were carried out on such coatings in a 0.5 M solution of Na₂SO₄ in order to evaluate their corrosion resistance. The potentiodynamic tests showed that the corrosion resistance of composite coating Ni/Al₂O₃ is better than that of the standard nickel coating. After 14 days of exposure the nickel coating corrodes three times faster than the Ni/Al₂O₃ coating. The electrochemical behaviour of the coatings in the corrosive solution was investigated by electrochemical impedance spectroscopy (EIS). An equivalent circuit diagram consisting of two RC electric circuits: one for electrode, nickel corrosion processes and the other for processes causing coating surface blockage, were adopted for the analysis of the impedance spectra. The changes in the charge transfer resistance determined from the impedance measurements are comparable with the changes in corrosion resistance determined from potentiodynamic measurements.     

The effect of concentration and source of calcium ions on anticorrosion properties of Ca-doped TiO2 bioactive sol-gel coatings

Titanium dioxide (TiO₂) coating with an enhanced anticorrosion properties and bioactivity was developed by doping it with calcium ions through a sol–gel method. The effect of annealing temperature, anions, as well as calcium ions concentration on microstructural and anticorrosion properties of Ca-doped TiO₂ coatings have been investigated. The phase composition and morphology of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion resistance of M30NW biomedical alloy coated with Ca-doped TiO₂ coatings was evaluated using electrochemical methods in conditions similar to the normal physiological environments (PBS solution, pH 7.4, temperature of 37 °C). The obtained results show that the annealing temperature and the source of calcium ions influence the anticorrosion properties of Ca-doped TiO₂ coatings. The best anticorrosion properties were registered for coatings with the highest concentration of Ca ions. At the same time all the examined coatings presented good bioactivity in SBF solution test.     

Effect of titania particles preparation on the properties of Ni–TiO2 electrodeposited composite coatings

In this paper, the effect of titania particles preparation on the properties of Ni–TiO₂ electrocomposite coatings has been addressed. Titania particles were prepared by precipitation method using titanium tetrachloride as the precursor. The titanyl hydroxide precipitate was subjected to two different calcinations temperatures (400 and 900 °C) to obtain anatase and rutile titania particles. These particles along with commercial anatase titania particles were separately dispersed in nickel sulfamate bath and electrodeposited under identical electroplating conditions to obtain composite coatings. The electrodeposited coatings were evaluated for their microhardness, wettability, corrosion resistance, and tribological behavior. The variation of microhardness with current density exhibited a similar trend for all the three composite coatings. The composite coating containing anatase titania particles exhibited higher microhardness and improved wear resistance. However, the corrosion resistance of the composite coating containing commercial titania powder was superior to that of plain nickel, Ni–TiO₂ composite coatings containing anatase and rutile titania particles. The poor corrosion resistance of these composite coatings was attributed to the higher surface roughness of the coatings. This problem was alleviated by incorporating ball-milled titania powders. The composite coatings with higher surface roughness were modified with a low surface energy material like fluoroalkyl silane to impart hydrophobic and superhydrophobic properties to the coatings. Among these coatings, Ni–TiO₂–9C coating exhibited the highest water contact angle of 157°.     

Electrolytic deposition of Ni-Co-Al2O3 composite coating on pipe steel for corrosion/erosion resistance in oil sand slurry

To improve the resistance of the hydrotransport pipe steel to corrosion and erosion in oil sand slurry, a Ni-Co-Al₂O₃ composite coating was fabricated by electrolytic deposition on X-65 pipe steel substrate. Potentiodynamic polarization curve and electrochemical impedance measurements show that the deposited coating significantly improves the corrosion resistance of the steel in water-oil-sand solution that simulates the chemistry of oil sand slurry. The corrosion resistance of the coating increases with the increasing Al₂O₃ particle concentration in electrolyte, cathodic current density, electrode rotating speed and temperature. However, a maximum value of corrosion resistance as a function of the depositing parameters is observed, indicating that the optimal electrodepositing parameters and operating conditions are essential to the maximization of the corrosion resistance of the coated steel in oil sand slurry. The optimal depositing conditions are suggested in the given system. The morphology, structure and composition of the coatings were characterized by scanning electron microscopy and energy-dispersive X-ray analysis. The Ni-Co-Al₂O₃ composite coating develops a compact, uniform, nodular structure with an average thickness of 50-200 microns. The Al₂O₃ amount in the coating increases with the increasing Al₂O₃ concentration in electrolyte, which also enhances the co-deposition of Ni and Co. The micro-hardness and wear resistance of the composite coatings are much higher than the steel substrate and increase with the increasing Al₂O₃ particle amount in the coating.     

Influences of electrolytes on tribocorrosion performance of MAO coating on AZ31B magnesium alloy in simulated body fluid

In this paper, the effects of electrolytes on the corrosion resistance and tribocorrosion performance of micro-arc oxidation (MAO) coatings on AZ31B magnesium (Mg) alloys in simulated body fluid (SBF) were studied. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were utilized to explore the microstructure, surface morphology, and phase components of the MAO coatings. Corrosion and tribocorrosion performance of MAO coated Mg alloys were evaluated by using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and a ball-on-disk tribotester. It was found that MAO coating produced in electrolyte containing both Na₂SiO₃ and Na₂B₄O₇ exhibited superior corrosion resistance and tribocorrosion performance in the SBF.     

Corrosion behavior of Zn-incorporated antibacterial TiO2 porous coating on titanium

Incorporation of antibacterial agents (e.g. Ag and Cu) at the surface of biomedical materials has evolved as a potentially effective method for preventing the bacterial infections. However, the antibacterial efficacy of medical device implants must necessarily be balanced by good corrosion resistance and the corrosion behavior of the antibacterial coatings has seldom been reported. In this work, Zn-incorporated antibacterial TiO₂ coating was produced on pure titanium (Ti) by micro-arc oxidization (MAO) and the electrochemical behavior was assessed. The results obtained from the antibacterial studies suggest that the Zn-incorporated TiO₂ coating provides bactericidal activity against both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) over 90%. The corrosion behavior of Zn-incorporated TiO₂ coating were investigated using a combination of complementary electrochemical measurement techniques such as open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that the Zn-incorporated TiO₂ coating move the OCP to the positive direction and increase the polarization resistance, thereby enhances the corrosion resistance of pure Ti. Collectively, the Zn-incorporated TiO₂ coating with both antibacterial ability and anti-corrosive properties might be more suitable for biomedical surfaces.     

WC的质量浓度对Ni-WC纳米复合镀层耐蚀性及硬度的影响

采用脉冲电沉积方法在304不锈钢基体上制备出Ni-WC纳米复合镀层。研究了WC的质量浓度对Ni-WC纳米复合镀层性能的影响。结果表明:随着WC的质量浓度的增加,Ni-WC纳米复合镀层的耐蚀性先增强后减弱,硬度先增大后减小;当WC的质量浓度为30g/L时,Ni-WC纳米复合镀层的耐蚀性最好,硬度最大。     

Microstructures and mechanical properties of wear-resistant titanium oxide coatings deposited on Ti-6Al-4V alloy using laser cladding

In this work, a freeze-dried TiO₂ nano-sized powder was used as the coating material and single tracks of TiO_x coating were cladded on Ti-6Al-4V substrates using a diode laser. The microstructure, chemical composition, and mechanical properties of the coatings were characterized and their relationships were explored. Coatings with structural and compositional gradients formed under a laser energy density (LED) of 20 kJ/m, while coatings with a relatively homogeneous microstructure were obtained using a LED of 30 kJ/m. The microstructure evolution was controlled by the molten pool lifetime and the intensity of convective flow during laser processing. The elastic modulus of the graded coating showed a decreasing trend from the top coating surface to the interface while that of the homogeneous coating remained constant. Our results also demonstrated that the hardness and wear resistance of the oxide coatings were up to four and ten times higher than that of the substrate.     

Corrosion behavior of titania films coated by liquid‐phase deposition on AISI304 stainless steel substrates

Fouling deposition and localized corrosion on the heat‐transfer surfaces of the stainless steel equipments often simultaneously exist, which can introduce additional thermal resistance to heat‐transfer and damage heat‐transfer surfaces. It is a good anticorrosion way to coat a barrier layer of certain materials on the metal surface. In this article, the TiO₂ coatings with nanoscale thicknesses were obtained by liquid‐phase deposition method on the substrates of AISI304 stainless steel (ASS). The coating thickness, surface roughness, surface morphology, crystal phase, and chemical element were characterized with the film thickness measuring instrument, roughmeter, atomic force microscopy, field emission scanning electron microscopy, X‐ray diffraction, and energy‐dispersive X‐ray spectroscopy analyzer, respectively. Corrosion behavior of the TiO₂ coatings was evaluated by potentiodynamic polarization, cyclic voltammograms scanning, and electrochemical impedance spectroscopy tests with the mixed corrosion solution composed of 3.5 wt. % NaCl and 0.05 M NaOH. It is shown that the TiO₂ coating is composed of the nanoparticles with smooth, crack‐free, dense, and uniform surface topography; the roughness of coating surface increases slightly compared with that of the polished ASS substrate. The anatase‐phase TiO₂ coatings are obtained when sintering temperature being varied from 573.15 to 923.15 K and exhibit better anticorrosion behavior compared with ASS surfaces. The corrosion current density decreases and the polarization resistance increases with the increase of the coating thickness. The corrosion resistance of the TiO₂ coatings deteriorates with the increase of the corrosion time. The capacitance and the resistance of the corrosion product layer between the interface of the ASS substrate and the TiO₂ coating are found after the corrosion time of 240 h. A corrosion model was introduced, and a possible new explanation on the anticorrosion mechanisms of the TiO₂ coating was also analyzed. The corrosion mechanism of the TiO₂ coating might comply with the multistage corrosion process. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1907–1920, 2012