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.     

Initial corrosion behavior of composite coatings obtained by co-electrodeposition of zinc with nanoparticles of Ti and Ce oxides

The present work reports the results obtained for the electrodeposition of composite Zn coatings on steel by using Ti and Ce oxides nanopowders, separately or in mixture, and a TiO₂·CeO₂ binary oxide. In an attempt to correlate the effects of nanoparticles on corrosion behavior of the composite deposits, the properties of Zn–TiO₂·CeO₂ layers were compared with those referring to similar coatings prepared by using a simple mixture of the two oxides or individual oxides. Corrosion measurements were performed in 0.2 g?L^?1 Na₂SO₄ solution (pH?=?5). The results of electrochemical measurements (open circuit potential measurements, polarization curves, and electrochemical impedance spectroscopy) were corroborated with those obtained by using X-ray diffraction, atomic force microscopy, scanning electron microscopy, and salt spray tests. The results indicate that the composite Zn–(TiO₂?+?CeO₂) coatings exhibit the highest corrosion resistance from all investigated Zn coatings.     

Structural and electrochemical characterization of sputter-deposited nitrided NiCr alloys

Nickel-based coatings are potential candidates for the protection of electrochemical dissolution of steel surfaces. Such coatings, elaborated by magnetron sputtering in a nitrogen atmosphere, offer good corrosion protection, good adherence as well as stability for metallic structures. NiCr alloys with almost constant composition have been deposited with different nitrogen contents on stainless steel and carbon steel surfaces. The coating uniformity, homogeneity, composition and crystallinity have been studied by scanning electron microscopy, energy-dispersive X-ray spectrometry, atomic force microscopy and X-ray diffraction techniques. The corrosion degradation behavior of all the samples was tested in NaCl and NaCl and CO₂ mixture exposures using electrochemical impedance spectroscopy measurements. Nitrided NiCr alloys on a stainless steel substrate resulted with better adhesion than carbon steel, by delaying the corrosion mechanism when exposed to NaCl and CO₂ solution. A comparison of the corrosion resistive behavior of the substrates (stainless steel, carbon steel) and the coatings is made by using the electrical capacitance concept from a double-layer model for the coating–metal interface.     

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.     

Corrosion resistance of electroless Cu–P and Cu–P–SiC composite coatings in 3.5% NaCl

The Cu–P and Cu–P–SiC composite coatings on carbon steel substrates were deposited via electroless plating. The anti-corrosion properties of Cu–P and Cu–P–SiC coatings were studied in 3.5% NaCl solution. The anti-corrosion properties of Cu–P and Cu–P–SiC coatings were investigated in 3.5% NaCl solution by the weight loss, potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. It has been found that the shift in the corrosion potential (E_corr) towards the noble direction, decrease in the corrosion current density (I_corr), increase in the charge transfer resistance (R_ct) and decrease in the double layer capacitance (C_dl) values indicated an improvement in corrosion resistance with the incorporation of SiC particles in the Cu–P matrix. The effects of varying the SiC concentration on the corrosion resistance of carbon steel were investigated and it was found that the best anti-corrosion property of Cu–P–SiC is at 5 g L^?1 SiC in the bath formulation.     

Inclusion of W in electroless Ni–B coating developed from a stabilizer free bath and investigation of its tribological behaviour

In the present study, tribological and corrosion behaviour of electroless Ni–B–W (ENB-W) coatings prepared from stabilizer-free baths and deposited on AISI 1040 steel substrates were examined. Three distinct coating bath temperatures (85 °C, 90 °C, and 95 °C) were varied for coating deposition. The coatings showed nodular morphology. Thermogravimetric study of ENB-W coatings revealed improved thermal stability attained at 95 °C bath temperature. The microhardness of ENB-W coating was 645, 690, and 720 HV₁₀₀ at bath temperatures of 85 °C, 90 °C, and 95 °C respectively. The inclusion of W to Ni–B coating enhanced the hardness by ∼150 HV₁₀₀. On a pin-on-disc tribometer, wear test was conducted. The precipitation of Ni (111) and its borides occurred post sliding wear at high temperatures (300 °C). Ni (111) crystallite size decreased because of high temperature sliding wear at 300 °C with an increase in coating bath temperature. With a reduction in crystallite size at high temperatures, both wear rate and COF decreases. The scratch hardness and first critical load of failure of the coatings was determined using a scratch tester. Using potentiodynamic polarization, corrosion resistance of ENB-W coatings in 3.5% NaCl was investigated. ENB-W coatings could provide shielding to AISI 1040 steel from corrosion. Though the corrosion resistance is poor with respect to lead stabilized coatings.     

Surface properties,adherence, and photocatalytic activity of sol–gel dip-coated TiO2–ZnO films on glass plates

In this study, TiO₂–ZnO nanostructured films prepared from different Ti/water mole ratios were deposited on glass plates by a sol–gel dip-coating method. The structural and surface properties, adherence, and photoactivity of synthesized TiO₂–ZnO coatings in methylene blue degradation were investigated. Among the as-prepared TiO₂–ZnO coatings from sols with different Ti/water mole ratios (1, 0.66, 0.5, and 0.4), the highest sol concentration (Ti/water mole ratio of 1) showed the highest methylene blue photodegradation of almost 80% after 400 min of UV irradiation. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Energy-dispersive X-ray (EDX), and UV-vis diffuse reflectance spectra (DRS) confirmed that at high sol concentrations (Ti/water mole ratios of 1 and 0.66), a mixed phase of anatase and rutile is formed, whereas at a Ti/water mole ratio of 0.5, just pure rutile is formed. In detail, decreasing the sol concentration increases the cracks, degree of agglomeration, and the thickness of coatings. UV-vis DRS studies also confirm that decreasing the sol concentration in synthesized TiO₂–ZnO films leads to a shift in the absorption region of the coating to the UV region. Moreover, decreasing the sol concentration declines the coating adherence onto glass plates. TEM images of the TiO₂–ZnO coating synthesized from sol with a Ti/water mole ratio of 1 revealed the formation of ZnO nanorods around a spherical TiO₂, which indicates the presence of strong interaction between TiO₂ and ZnO nanoparticles. The TiO₂–ZnO coating synthesized from sol with a Ti/water mole ratio of 1 was then evaluated at different methylene blue concentrations, pH values, and number of coatings. After five consecutive runs, no significant decrease in the photodegradation efficiency was observed. Scanning electron microscopy (SEM) picture of used coating showed a smooth and stable layer without any detachment. Thermogravimetric analysis (TG) and sonication test confirmed thermal and mechanical stabilities of this coating as well.     

水热法制备TiO_2纳米线薄膜的光生阴极保护性能

应用水热法在钛箔表面制备TiO2纳米线薄膜,采用场发射扫描电子显微镜、X射线衍射和紫外-可见分光光度法对薄膜进行表征,用电极电位和电化学阻抗谱考察TiO2光生阴极保护性能.结果表明:薄膜由纵横交错的锐钛矿型TiO2纳米线组成,纳米线的直径约10nm.在150℃下反应6h生成的TiO2纳米线薄膜在0.3mol·L-1 Na2SO4溶液和0.3mol·L-1 Na2SO4+0.5mol·L-1 HCOOH混合溶液中对与TiO2薄膜耦连的403不锈钢均有良好的阴极保护效应.TiO2膜所在溶液中含有HCOOH时,可使耦连的403不锈钢在0.5mol·L-1 NaCl溶液中电极电位负移约545mV,界面反应电阻显著变小,表明电解质溶液加入HCOOH可以增强TiO2纳米线薄膜对403不锈钢的光生阴极保护效应.     

Effect of thermal annealing of poly(3-octylthiophene) films covered stainless steel on corrosion properties

The effect of thermal annealing of poly(3-octylthiophene) (P3OT) coatings on the corrosion inhibition of stainless steel in an NaCl solution was investigated. P3OT was synthesized by direct oxidation of the 3-octylthiophene monomer with ferric chloride (FeCl₃) as oxidant. P3OT films were deposited by drop-casting technique onto 304 stainless steel electrode (304SS). 304SS coated with P3OT films were thermally annealed during 30 h at different temperatures (55°C, 80°C, and 100°C). The corrosion resistance of stainless steel coated with P3OT in 0.5 M NaCl aqueous solution at room temperature was investigated by using potentiodynamic polarization curves, linear polarization resistance, and electrochemical impedance spectroscopy. The results indicated that the thermal treatment at 80°C and 100°C of P3OT films improved the corrosion resistance of the stainless steel in NaCl solution; the speed of corrosion diminished in an order of magnitude with regard to the 304SS. In order to study the temperature effect in the morphology of the coatings before and after the corrosive environment and correlate it with corrosion protection, atomic force microscopy and scanning electron microscopy were used. Morphological study showed that when the films are heated, the grain size increased and a denser surface was obtained, which benefited the barrier properties of the film.     

Sol-enhanced triple-layered Ni–P–TiO2 composite coatings

A novel coating process, TiO₂ sol enhanced Ni–P electroless composite coatings on carbon steel, is presented in this paper. Transparent TiO₂ sol was added into the electroless plating Ni–P solution at a controlled rate, leading to in situ synthesis of a triple-layered Ni–P–TiO₂ composite coating, i.e. the inner, transition and outer layers. The inner layer has a thickness of ~3 μm, mainly composed of Ni and P elements. The transition layer of the coating has a relatively high content of TiO₂ with a thickness of ~500 nm and a columnar-structure. The thickness of the outer layer was ~7 μm, with almost evenly distributed Ni, P and TiO₂. The hardness and Young’s modulus of the composite coating were greatly improved to ~10 and ~200 GPa, respectively, compared to ~6 and ~110 GPa of the traditional Ni–P coating.     

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.     

EIS study on the corrosion performance of a Cr(III)-based conversion coating on zinc galvanized steel for the automotive industry

The corrosion performance of a new industrial Cr(III)-based conversion coating on zinc galvanized FeP04 steel for the automotive industry was studied. For comparison, the zinc galvanized steel submitted to a Cr(VI)-based passivation treatment was also examined. The corrosion behavior was assessed by means of potentiodynamic polarization and electrochemical impedance spectroscopy measurements in aerated 0.1 M NaCl solution. The behavior of untreated zinc galvanized FeP04 steel in aerated 0.1 M NaCl solution was also studied. The results obtained indicate that with the same thickness, the coating generated in the Cr(III) treatment bath exhibits better corrosion properties compared to the coating formed in the Cr(VI) treatment bath. The difference in the corrosion protection given by the two conversion coating types can be ascribed to the difference in the chromium content and coating composition.     

Investigations on SnO2–TiO2 composite photoelectrodes for corrosion protection

Different compositions of SnO₂–TiO₂ composite electrode coatings were prepared on conducting ITO glass substrates and photoelectrochemical measurements were carried out on the coated substrates under illumination with ultraviolet light. Photopotential as well as polarization measurements were made on the samples to evaluate their performance with regard to application for cathodic protection of metals against corrosion. A composite electrode bearing SnO₂ and TiO₂ in a 1:1 molar ratio was found to exhibit the maximum photocurrent and a maximum lowering of potential under illumination when compared to the other compositions. A possibility of using a pure SnO₂ coating for cathodic protection of metals against corrosion under dark conditions was also explored.     

Chemical and electrochemical characterization of hybrid PVD + ALD hard coatings on tool steel

In the last 30 years, thin hard coatings were intensively investigated due to their high-performance characteristics: high wear resistance, low friction coefficient and good thermal stability. Performances were furthermore improved using multilayer configurations, although often limited by feasibility or cost considerations. One of the main problems to overcome was the low corrosion protection that these coatings assure to the tool steel substrates on which they are applied. To assure high performances and corrosion protection it is possible to employ a completely new approach, suitable either as a pre-treatment of the substrate or as top coating, by using materials of different nature in the form of nano-layers.Monolayer and multilayer coatings obtained by PVD (Physical Vapor Deposition, using reactive arc evaporation) and by PVD + ALD (Atomic Layer Deposition) were studied and compared. Both in-depth composition and corrosion resistance properties were investigated using SEM–EDXS, GDOES (Glow Discharge Optical Emission Spectrometry) and polarization curves in a 0.2 M NaCl solution. The coatings studied were a TiAlN/TiN bi-layer and a TiCN monolayer obtained by PVD and an Al₂O₃ nano-layer obtained by ALD.     

Electrodeposition and characterization of Cu-TiO2 nanocomposite coatings

Cu-TiO₂ nanocomposites were prepared by electrodeposition method onto copper substrate using an acid copper plating bath containing dispersed nanosized TiO₂. The composition of codeposited TiO₂ nanoparticles in the composite coatings was controlled by the addition of different concentrations of TiO₂ nanoparticles in the bath solution. The average crystallite size was calculated by using X-ray diffraction analysis and it was ~32 nm for electrodeposited copper and ~33 nm for Cu-TiO₂ composite coatings. The crystallite structure was fcc for electrodeposited copper and Cu-TiO₂ nanocomposite coatings. The surface morphology and composition of the nanocomposites were examined by scanning electron microscopy and energy dispersive X-ray spectroscopy analysis. The effect of TiO₂ content on the corrosion and wear resistance properties of the nanocomposite coatings was also presented. The codeposited TiO₂ nanoparticles in the deposit increased the corrosion and wear resistance, which were closely related with TiO₂ content in the nanocomposites. The wear resistance and microhardness of the Cu-TiO₂ nanocomposite coatings were higher than electrodeposited copper. The corrosion resistance property of the electrodeposited copper and Cu-TiO₂ nanocomposite coatings was evaluated by electrochemical impedance and Tafel polarization studies. Cu-TiO₂ composite coatings were more corrosion resistant than electrodeposited copper.     

Incorporation of Reactive Corrosion Inhibitor in Waterborne Acrylic Polyurethane Coatings and Evaluation of its Corrosion Performance

Hydroxyl-epoxy phosphate (HEP) as a reactive corrosion inhibitor was innovatively synthesized by the reaction of bisphenol A epoxy resin with phosphoric acid. HEP was mixed with hydroxyl acrylate resin, and crosslinked with waterborne isocyanate curing agent, which was used to form waterborne HEP/acrylic polyurethane composite (HEP-APU) coatings on Q235 steel surfaces. Electrochemical impedance spectroscopy and polarization curves were applied to analyze the corrosion behavior of the HEP-APU coatings in 3.5wt% NaCl solutions. The results indicated that the HEP-APU coatings show a superior passivation property and efficient corrosion protection of Q235 steel. The waterborne acrylic polyurethane coating containing 0.5wt% HEP exhibited the best corrosion performance among all the coating specimens. The improved flash-rust resistance can be attributed to the introduction of the phosphate group which could form phosphate film on the steel substrate.     

Electropolymerized coatings of poly(o‐anisidine) and poly(o‐anisidine)‐TiO2 nanocomposite on aluminum alloy 3004 by using the galvanostatic method and their corrosion protection performance

Poly(o‐anisidine) (POA) and poly(o‐anisidine)‐TiO₂ (POA‐TiO₂) nanocomposite coatings on aluminum alloy 3004 (AA3004) have been investigated by using the galvanostatic method. The electrosynthesized coatings were characterized by FT ‐ IR spectroscopy, XRD, SEM ‐ EDX and SEM. The corrosion protection performance of POA and POA‐TiO₂ nanocomposite coatings was investigated in the 3.5% NaCl solution by using potentiodynamic polarization technique and electrochemical impedance spectroscopy. The results show that the corrosion rate of the nanocomposite coatings is about 900 times lower than the bare AA3004 under optimal conditions. Copyright © 2013 John Wiley & Sons, Ltd.     

Potential of zinc based-graphene oxide composite coatings on mild steel in acidic solution

This study introduces varying concentrations of graphene oxide (GO) as a filler into zinc chromate in forming composite coatings to improve the corrosion protection of mild steel. The purity of synthesized GO was inferred through the application of complementary characterization techniques, including FT-IR, XRD, Raman, SEM-EDX, and TEM analyses. GO doped zinc chromate coatings were deposited on the surface of mild steel through the brushing method. Electrochemical studies, i.e., electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PD) were conducted to elucidate the anticorrosion properties of the coated mild steel exposed to 0.5 ​M HCl solution. It was revealed that the highest anticorrosion protection was attained at low doping amount of 0.5% of GO with a corrosion rate of 0.036 mpy. Surface analyses revealed that incorporating GO into zinc chromate coating can effectively improve the anticorrosion properties and adhesion strength.     

Characterization and anticorrosive properties of poly(2,3‐dimethylaniline)/nano‐Al2O3 composite synthesized by emulsion polymerization

Poly(2,3‐dimethylaniline)/nano‐Al₂O₃ composite (PAC) was synthesized by emulsion polymerization using dodecyl benzene sulfonic acid as emulsifier and dopant. The structure of PAC was characterized by Fourier fransformation infrared spectroscopy, UV–visible adsorption spectroscopy, and field emission scanning electron microscopy. The thermal stability was studied by thermogravimetric analysis, and the electrochemical performances were studied by cyclic voltammetry measurements. Epoxy coatings containing PAC and poly(2,3‐dimethylaniline) (P(2,3‐DMA)), respectively, were painted on steel, and accelerated immersion tests were performed to evaluate the anticorrosion property of the coatings in 3.5% NaCl solution. The results showed that the addition of PAC and P(2,3‐DMA) could improve the anticorrosion performance of epoxy coating significantly and the PAC coating had higher corrosion resistance than that of P(2,3‐DMA). Copyright © 2013 John Wiley & Sons, Ltd.     

Superior corrosion protection and in vitro biocompatibility of Na-HAp/CS composite coating on PoPD-coated 316L SS

The synthesis and development of sodium (Na)-substituted hydroxyapatite (HAp)/chitosan (CS) composite using poly (O-phenylenediamine) (PoPD) coating on 316L SS substrate for improving bioactivity and corrosion protection was studied. The surface of Na-HAp/CS/PoPD bilayer coatings on 316L SS substrate was characterized by diverse analytical techniques. The open circuit potential (OCP) measurement, potentiodynamic polarization, and impedance test revealed that the bilayer coating provides excellent protection to the substrate against the corrosion in the simulated body fluid (SBF) solution. This interior layer of the coating acts as a barrier against the release of metal ions from the substrate, which was confirmed by inductively coupled plasma-atomic emission spectroscopy. Besides, the mechanical properties of the coatings were analyzed. From the obtained results, the bilayer coating exhibited greater mechanical strength than the individual coating. An in vitro bioactivity of the coatings was assessed by immersion in the SBF solution at 7–28 days. The apatite formation of bilayer coatings on 316L SS substrate is found to be more bioactive compared with the Na-HAp, PoPD, and Na-HAp/CS. The in vitro biocompatibility test showed no adverse effects, which was proved by the enhanced biocompatibility of the bilayer coating on 316L SS.