Synthesis of polyaniline nanofiber and anticorrosion property of polyaniline–epoxy composite coating for Q235 steel

Polyaniline (PANI) nanofibers were prepared by direct mixed oxidation in four kinds of inorganic acids. The characterization of scanning electron microscopy (SEM) showed that high quality PANI fibers with uniform diameter and several microns length can be obtained by direct mixed oxidation, especially in a sulfuric acid system. Structural characteristics of PANI products through IR and UV spectra indicated the consistent peak distribution with the classic spectrum of the doped PANI. In addition, composite coatings of PANI–epoxy resin were prepared by mechanical grinding. The effect of PANI’s content on anticorrosion property of the composite coatings for Q235 steel was studied by the electrochemical impedance spectroscopy (EIS). Results showed that the best shielding protective effect was obtained when the amount of PANI was around 0.5% (wt%). More importantly, the effects of four different inorganic acids on anticorrosion property of the composite coatings were studied by the EIS and Tafel polarization curve. Experiments showed that the different composite coatings of PANI doped by different inorganic acids provided different protective abilities for the Q235 steel. It can be concluded that both the morphology and counter-anion would impact the anticorrosion effect of the doped PANI.     

Multilayered polypyrrole–SiO2 composite coatings for functionalization of stainless steel: Characterization and corrosion protection behavior

Two different multilayered composite polypyrrole/SiO₂ coatings were synthesized on 304 stainless steel. Electrochemical and electrophoretic depositions were used to grow polypyrrole and SiO₂ layers, respectively. Coatings were characterized by glow discharge optical emission spectroscopy to observe repartition of elements within different layers, by scanning electron microscopy to observe surface morphology and by electrochemistry to investigate corrosion protection behavior. The electrophoretic approach enables good incorporation of SiO₂ particles. This incorporation was more extensive and more homogeneous than for coatings obtained with the mixing method related in previous works. Moreover, incorporation and repartition of SiO₂ particles are greatly enhanced when the silica layer is grown directly on the steel surface. Corrosion protection of the stainless steel substrate was improved when multilayered composite polypyrrole/SiO₂ coatings were used.     

Electrophoretic deposition of bioactive wollastonite and porcelain–wollastonite coatings on 316L stainless steel

Wollastonite and porcelain–wollastonite coatings on stainless steel were obtained by electrophoretic deposition using acetone as dispersive medium. A direct electric current of 800 V for 3 min was used for obtaining the single wollastonite coating. A well-sintered layer was observed after heat treatment at 1050 °C for 1 h in air. The two-layer coating was obtained by depositing dental porcelain at 400 V for 30 s followed by the deposition of wollastonite at 400 V for 3 min. After forming the two layers, this complex coating was heat treated at 800 °C for 5 min. Under these conditions, strong bonds of both the interface wollastonite–porcelain and that of porcelain–metallic substrate were observed. The in vitro bioactivity assessment of the coatings was performed by immersing the deposited substrates in simulated body fluid (SBF) for 21 days. All the materials showed to be highly bioactive through the formation of a homogeneous apatite layer.     

Study on cerium-doped nano-TiO2 coatings for corrosion protection of 316?L stainless steel

Many methods have been reported on improving the photogenerated cathodic protection of nano-TiO₂ coatings for metals. In this work, nano-TiO₂ coatings doped with cerium nitrate have been developed by sol–gel method for corrosion protection of 316 L stainless steel. Surface morphology, structure, and properties of the prepared coatings were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. The corrosion protection performance of the prepared coatings was evaluated in 3 wt% NaCl solution by using electrochemical techniques in the presence and absence of simulated sunlight illumination. The results indicated that the 1.2% Ce-TiO₂ coating with three layers exhibited an excellent photogenerated cathodic protection under illumination attributed to the higher separation efficiency of electron–hole pairs and higher photoelectric conversion efficiency. The results also showed that after doping with an appropriate concentration of cerium nitrate, the anti-corrosion performance of the TiO₂ coating was improved even without irradiation due to the self-healing property of cerium ions.     

Effect of cerium concentration on corrosion resistance and polymerization of hybrid sol–gel coating on martensitic stainless steel

Stainless steels are increasingly used in the aeronautics field for the manufacture of structural parts. One of them, the X13VD martensitic stainless steel (X12CrNiMoV12-3), known for its good mechanical properties, has a poor corrosion resistance in confined or severe environments. In the past years, Cr(VI) based pre-treatments have been currently used for corrosion protection of different metals, however, they are toxic and due to environmental regulations, they will be definitely banned in a near future. Alternatives to replace Cr(VI) show advantages and drawbacks considering key properties such as: corrosion resistance, adhesion of coatings, fatigue resistance, durability and reliability. However, some of their possible alternatives show high potential.     

A review on application of structural adhesives in concrete and steel–concrete composite and factors influencing the performance of composite connections

This paper chronicles the use of structural adhesives in civil engineering construction since its inception. The usage of structural adhesives as effective and popular strengthening agents has been discussed. The application of structural adhesives as connecting agents, especially in cases of steel–concrete composites has also been discussed in detail. Various factors influence the bond strength of interfaces, such as the physical, mechanical and chemical properties of structural adhesives and adherends, the shape of adherends, water immersion, adhesive layer thickness, bonded area geometry, relative humidity and temperature of the environment during curing and service life, the amount and type of fillers and surface finishing of adherends.     

Fabrication of ZnO–GO hybrid for enhancement of chemically bonded phosphate ceramic coatings corrosion protection performance on AISI304L stainless steel

In this paper, a solvothermal method is used to prepare nano-sized zinc oxide-graphene oxide (ZnO–GO) hybrid, and the ZnO–GO hybrid is characterized by X-ray diffraction analysis, Raman, Fourier transform infrared spectroscopy, and scanning electron microscopy. In addition, chemically bonded phosphate ceramics coatings with different content of ZnO–GO hybrid are prepared on the stainless steel through the sol-gel method. The corrosion performance of the coatings is evaluated by electrochemical properties and the analysis of the surface and cross morphology of the coating. Results indicate ZnO–GO hybrid significantly enhances the compactness and corrosive behavior of the coating because the overlapping structure of GO flake improves the barrier performance of the coating. Besides, ZnO nanoparticles on the surface of GO can react with aluminum dihydrogen phosphate binder, in that case the adhesion between GO and the coating is improved.     

Corrosion behavior of nanohybrid titania–silica composite coating on phosphated steel sheet

Corrosion resistance behavior of sol–gel-derived organic–inorganic nanotitania–silica composite coatings was studied. Hybrid sol was prepared from Ti-isopropoxide and N-phenyl-3-aminopropyl triethoxy silane. The structure, morphology, and properties of the coating were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermo gravimetric analysis. The corrosion performances of the sol–gel-coated samples were investigated by electrochemical impedance spectroscopy (EIS) and standard salt spray tests. The hybrid coatings were found to be dense, more uniform, and defect free. In addition, the coatings also proved its excellent corrosion protection on phosphated steel sheet.     

Synthesis and characterization of epoxy–silicone–polythiophene interpenetrating polymer network for corrosion protection of steel

Polymer alloys, particularly interpenetrating polymer networks (IPNs) exhibit excellent coating properties. Often combination of polymers result in IPNs with controlled morphologies and synergistic behavior. In this study, corrosion-resistant IPNs were prepared from immiscible resins (epoxy, silicone and thiophene) using a cross-linking agent and a catalyst. GPC, FTIR, NMR, TG, DTA and SEM studies used to fix the best performing IPN. Surface morphology studies using SEM confirm the incorporation of silicone and polythiophene in to the epoxy polymer to form homogeneously micro structured IPN. The heat-resistance of the IPN was determined as per ASTM 2485. The improved corrosion resistance of the IPN was evaluated by AC impedance measurements.     

Characterization and adhesion strength study of detonation-sprayed MoB–CoCr alloy coatings on 2Cr13 stainless steel substrate

A novel MoB–CoCr alloy coating was deposited onto stainless steel (2Cr13) substrate using a detonation gun (D-gun) spraying technique. Microstructures of the powder and coating were investigated by X-ray diffraction (XRD), scanning election microscopy (SEM), and transmission electron microscopy (TEM), and a quantitative determination of the adhesion strength of the coating was calculated by combination of modified four-point bending (4PB) test and finite element analysis (FEA) simulation. The results show that the coating mainly consists of ternary transition metal boride matrix phases (CoMo₂B₂, MoCoB) and binary borides (MoB and CrB). Nanocrystalline grains with a size of 50–100 nm were observed in the coating. The average energy release rate and phase angle are 191.2 J m⁻² and 41.7o, respectively, which show strong bond strength compared to other reported values.     

Deposition of zinc–zinc phosphate composite coatings on steel by cathodic electrochemical treatment

The present work aims at the development of an energy-efficient and eco-friendly approach for the deposition of zinc phosphate coatings on steel. The study describes the possibility of preparing zinc–zinc phosphate composite coatings by cathodic electrochemical treatment using dilute phosphoric acid as an electrolyte and zinc as an anode. The methodology enables the preparation of coatings with different proportions of zinc and zinc phosphate by suitably varying the applied current density, pH, and treatment time. Adhesion of the coating on mild steel and adhesion of paint film on the phosphate coating were found to be good. The surface morphology of the coatings exhibited platelet-type features and small white crystals (agglomerated at some places) which represented zinc and zinc phosphate, respectively. An increase in current density (from 20 to 50 mA/cm²) increased the size of the zinc crystals, and coatings prepared at 40 and 50 mA/cm² resembled that of electrodeposited zinc. Since the proportions of zinc and zinc phosphate could be varied with applied current density, pH, and treatment time, it would be possible to use this methodology to prepare coatings that would offer different degrees of corrosion protection.     

Corrosion resistance performance of cerium doped silica sol–gel coatings on 304L stainless steel

The aim of this work is the synthesis and investigation of silane based organic–inorganic hybrid coatings, which can be used to improve the corrosion performance of steel structures subjected to a marine environment. The silane based sol–gel coatings were prepared by dip coating 304L stainless steel in a solution of organically modified silica sol made through hydrolysis and condensation of 3-glycidoxypropyl-trimethoxysilane (GPTMS) as precursor and bisphenol A (BPA) as a cross-linking agent in an acid catalyzed condition. The influence of the addition of cerium and the use of bisphenol A as a cross-linking agent on the microscopic features and morphology as well as on the corrosion resistance of the coatings were examined using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), neutral salt spray tests, potentiodynamic polarization and electrochemical impedance techniques. Results show that cerium modified nano-hybrid coatings exhibit a superior corrosion inhibition performance to that displayed by silica hybrid coatings. Additionally, data showed that the bisphenol A as a cross-linking agent has a significant effect on the morphology and corrosion resistance of the cerium doped silica coating. Omitting the use of bisphenol A causes the creation of defects/cracks in the coating, thereby promoting diffusion of the aggressive electrolyte toward the substrate and decreasing the corrosion resistance of the coating.     

A kinetic study of in situ polyaniline–gold composite film formation

Chloroaurate acid (HAuCl₄) was used as an oxidant and aniline (ANI) was used as a reducing agent to prepare a polyaniline–gold (PANI-Au) composite film by in situ polymerization. The formation of the composite film was monitored using a quartz crystal microbalance (QCM). The effects of the concentrations of HAuCl₄ and ANI as well as the reaction temperature on the formation of the PANI-Au composite film are discussed. The kinetics of the reaction were investigated by the QCM technique. The results indicate that the kinetics of the reaction are of order 0.5 with respect to HAuCl₄ and 1.5 with respect to aniline. The film growth rate increased with increasing ANI, HAuCl₄ concentration and reaction temperature. The activation energy calculated from the temperature dependence of the growth rate was 40.32 ± 0.15 kJ/mol. In situ UV-visible spectra of the reaction process were obtained and compared to the reaction process using the QCM technique.     

Structure characterisation and mechanical properties of crystalline alumina coatings on stainless steel fabricated via sol–gel technology and fibre laser processing

The surface modification of stainless steel by coating with alumina (Al₂O₃) was carried out using sol–gel coating technology in combination with laser processing. Alumina coatings have been synthesised via a sol–gel route and deposited on stainless steel substrates by dip coating. The coated substrates were then treated with pulsed ytterbium fibre laser radiation (λ = 1064 nm) in continuous wave mode with different specific energies. The composition and structure of the coated surfaces after laser processing were characterised by ATR-FTIR, XRD, SEM and contact angle measurements, whilst the mechanical properties of modified surfaces were determined using nano-indentation. The results showed that the alumina xerogel films coated on the substrates are successfully converted into crystalline alumina ceramic coatings by the laser irradiation, the structure of resulting coatings being dependent on the irradiation conditions, with increase of laser specific energy leading to the formation of initially γ-Al₂O₃ with increasing amounts of α-Al₂O₃ at higher energy. Nano-indentation results reveal that the laser processing results in significant improvement in hardness and Young's modulus of the alumina-coated surface and, at optimum, can achieve the mechanical properties at the same level as pure α-alumina ceramic, much higher than those of the as-dried xerogel coating.     

The influence of polyaniline (PANI) coating on corrosion behaviour of zinc–cobalt coated carbon steel electrode

Zinc–cobalt alloy plating (ZnCo) was successfully deposited on carbon steel (CS) applying current of 2 mA with galvanostatic technique. Polyaniline film (PANI) was synthesized with cyclic voltammetry technique from 0.20 M aniline containing 0.20 M sodium tartrate solution on zinc–cobalt plated carbon steel (CS/ZnCo) electrode. PANI film characterized by scanning electron microscopy (SEM), was covered with a dark green-brown homopolymer film of strongly adherent homogeneous characteristic while the other one was plated with a porous light ZnCo one. The corrosion behaviour of zinc–cobalt deposited carbon steel electrodes with and without polyaniline (PANI) film in 3.5% NaCl solution was investigated with AC impedance spectroscopy (EIS) technique and anodic polarization curves. The results showed that PANI coating led to decrease of the permeability of metallic plating. The PANI homopolymer film provided an effective barrier property on zinc–cobalt coating and a remarkable anodic protection to substrate for longer exposure time.     

Preparation of polyaniline–palladium composite microflakes by one-step interface polymerization method

Polyaniline–palladium (PANi-Pd) composite microflakes were synthesized through an immiscible organic/inorganic biphasic system in the presence of poly(ethylene glycol) with molecular weight 4,000 (PEG4000). Aniline was oxidized by PdCl₂ in the interface polymerization system, yielding PANi microflakes and elemental Pd nanoparticles simultaneously. Palladium nanoparticles were uniformly dispersed in the microflakes of PANi. The results of FTIR spectra suggested that the oxidation degree of PANi was affected by the initial ratio of metal ions to monomer. The PANi-Pd composites were characterized using X-ray photoelectron spectroscopy and the conductivity of the composite was measured by conventional four-probe method. Scanning and transmission electron microscopy were used to show the morphology of the composites.     

Synthesize of polyaniline–multi walled carbon nanotubes composite on the glass and silicon substrates and methane gas sensing behavior of them at room temperature

In this study, fabrication of methane gas sensor using composites of multi-walled carbon nanotubes (MWCNT) and polyaniline (PANI) on glass and silicon substrates is reported. In this respect, 8 wt% of purified MWCNT by acid washing procedure, was combined with PANI by solution mixing method. The MWCNT–PANI composite was deposited on the surface of glass and Si substrates using spin coating technique. The methane gas sensing of composite films were evaluated by measuring the change of electrical resistance in the presence of methane gas at room temperature. It is observed that the MWCNT–PANI film on the Si substrate shows a higher sensitivity to methane gas in comparison to pure PANI on the glass substrate. The characterization of samples has also been investigated by Fourier transform infrared, transmission electron microscopy and scanning electron microscopy analyses.     

Characterization of sol–gel coated 316L stainless steel for biomedical applications

Silica based organic–inorganic hybrid coatings were deposited on 316L stainless steel by sol–gel technique. The hybrid sols were prepared by hydrolysis and condensation of 3-methacryloxypropyltrimethoxysilane (TMSM) and tetraethylorthosilicate (TEOS) at different molar ratios. Electrochemical experiments were performed to evaluate the corrosion resistance properties of the coatings. Structural characterization of the coatings was performed using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Contact angle measurement and cell morphology assay were performed to investigate the hydrophilicity and in vitro cytotoxicity of the coatings, respectively. The results indicate formation of a crack-free and highly adherent film acting as a protective barrier against the physiological medium. Corrosion resistance of hybrid coatings was influenced by the molar ratios of TMSM:TEOS. The best corrosion protection was obtained at TMSM:TEOS molar ratio of 1:1. Sol–gel coatings enhanced the hydrophilicity of 316L steel surfaces. Also, these coatings showed non-toxicity for L929 cells.     

Electro-deposition and characterizations of nickel coatings on the carbon–polythene composite

Nickel coating on the carbon–polythene composite plate was prepared by electrodeposition in a nickel sulfate solution in this work. The morphology and cross-sectional microstructure of the nickel coating were examined by scanning electron microscope (SEM) and optical microscope (OM), respectively. The influence of bath temperature on the nickel deposition rate was investigated experimentally. The adhesion between the coating and the substrate was evaluated by the pull-off test. The corrosion behavior of the coating in an aqueous solution of NaCl was studied by electrochemical methods. The results showed that the nickel electrodeposition rate could reach up to 0.68 μm min⁻¹ on average under conditions of cathodic current density of 20 mA cm⁻² and bath temperature of 60 °C. It was confirmed that increasing the bath temperature up to 50 °C had a positive effect on the nickel deposit rate, while an adverse effect was observed beyond 60 °C. The adhesion strength between the nickel coating and the substrate can be more than 2.3 MPa. The corrosion potential of the bright coating in the NaCl solution was more positive than that of the dull coating, and the anodic dissolution rate of the bright coating was also far lower at the same polarization potential compared with the dull coating.