Investigation of corrosion protection properties of an epoxy nanocomposite loaded with polysiloxane surface modified nanosilica particles on the steel substrate

In this study, it has been aimed to investigate the corrosion protection properties of an epoxy/polyamide coating loaded with different concentrations (ranged from 3 to 6% (w/w)) of the polysiloxane surface modified silica nanoparticles (nano-SiO₂). The nanocomposites were applied on the steel substrates. Field emission scanning electron microscope (FE-SEM) and UV–vis techniques were utilized in order to investigate the nanoparticles dispersion in the coating matrix. The effects of addition of nanoparticles on the corrosion resistance of the coating were studied by an electrochemical impedance spectroscopy (EIS) and salt spray test. The coating surface degradation was studied by optical microscope and Fourier transform infrared radiation (FT-IR) spectroscopy. Results obtained from UV–vis and FE-SEM analyses revealed proper and uniform distribution of surface modified nanoparticles in the epoxy coating matrix. It was shown that the coating corrosion protection properties were significantly enhanced in the presence of 5 wt% silica nanoparticles. Less degradation occurred on the surface of the coatings loaded with 5 wt% nanoparticles.     

The electrochemical studies of the corrosion resistance behaviour of hydroxyapatite coatings on stainless steel fabricated by electrophoretic deposition

HA was coated on stainless steel (SS) 316L by using electrophoretic deposition to impart corrosion resistance upon SS 316L. Consequently, corrosion behaviour of HA coated SS 316L deposited from applied voltages 10 V to 60 V (denoted as HA/SS316L-10V until -60V) was evaluated in comparison with pristine SS 316L by various electrochemical studies. As results, linear potentiodynamic polarisation result suggested that HA/SS316L-40V exhibits highest open circuit potential indicating that successful protection of HA coating. Additionally, cyclic polarisation studies revealed that HA coated SS 316L improves pitting corrosion resistance. Finally, EIS results demonstrated that higher polarisation resistance and lower capacitance values for HA/SS316L-40V.     

Spectrophotometric studies of photo-induced degradation of Tertrodirect Light Blue (TLB) using a nanostructure zinc zirconate composite

Zinc zirconate nanopowder (ZZN) photocatalyst was prepared by sol–gel method using zinc acetate and zirconium acetylacetonate as precursors. The optimal calcination temperature was 800 °C and ZnZrO₃ phase was formed. The structural and morphology properties of the nanocomposite were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDAX) and ultraviolet visible diffuse reflectance (UV-DRS). The SEM observation for ZZN showed the average grain size of 26 nm. UV–vis diffuse reflectance spectra (DRS) of the nanocomposite showed an absorption edge at 355 nm. The catalytic activity of ZZN was investigated by degradation of Tertrodirect Light Blue (TLB) dye in water using UV–vis spectroscopy (UV–vis) with an initial concentration of 20 mg/L dye. The influence of the catalyst concentration, time of irradiation and pH on photodegradation of dye was investigated. The results showed that degradation of TLB dye can be conducted in the photocatalytic process. Accordingly, a degradation of more than 97% of dye was achieved by applying the optimal operational parameters with 30 mg/L of catalyst, pH 9 at 1 h irradiation.     

Corrosion of mild steel with composite polyaniline coatings using different formulations

The protective abilities of composite coatings based on electrochemically and chemically formed polyaniline powder against the corrosion of mild steel were investigated. A polyaniline powder has been prepared in the form of an emeraldine base and benzoate salt through chemical dedoping and doping. The composite coatings using polyaniline powders, which were obtained through different routes, and base coatings, which were not corrosion-resistant, with different formulations were prepared and applied on mild steel samples. The corrosion was investigated using an electrochemical impedance technique in 3% NaCl, and the atmospheric corrosion was assessed in a humidity chamber. Emeraldine–benzoate salts, which are a chemically synthesized polyaniline, offer the best protection with an optimal polyaniline concentration of approximately 5 wt%. The different corrosion behaviors were assessed relative to the presence of aniline oligomers in the samples after characterization using UV–vis spectrophotometry. Upon comparison between the corrosion behavior in 3% NaCl with commercial primer paint for iron and that with a paint containing 5 wt% PANI, the composite coating has superior anticorrosion characteristics. The mechanism for the protection of mild steel from corrosion through composite polyaniline coatings was also considered.     

Nanostructure silver-doped zinc oxide films coating on glass prepared by sol–gel and photochemical deposition process: Application for removal of mercaptan

Silver-doped zinc oxide (SDZO) films have been grown on glass substrate by a novel combination of sol–gel and photochemical deposition processes (SGPD). The effect of sintering on structural, electrical and optical properties was investigated. The films were characterized by UV–vis absorption spectroscopy (UV–vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The result of X-ray photoelectron spectroscopy (XPS) revealed that the binding energy of Ag 3d_5/2 for SDZO shifts remarkably to the lower binding energy compared to the pure metallic Ag due to the interaction between silver and zinc oxide. The XRD spectra of the SDZO films indicate that silver was incorporated in the hexagonal crystal structure of zinc oxide. SEM micrographs show the uniform distribution of spherical grains of about 73 nm grain size for the pure zinc oxide thin films. The results indicated that silver doping photochemical deposition was a feasible method to tune the optical properties of zinc oxide nanostructures. SDZO films coated on glass were applied for the photodegradation of mercaptan in water. SDZO films were applied for degradation of mercaptobenzoxazole which reduced the mercaptan concentration to more than 98%.     

Formulation and performance evaluation of hydroxyl terminated hyperbranched polyesters based poly (ester–urethane–urea) coatings on mild steel

A low molecular weight, anticorrosive hyperbranched poly (ester–urethane–urea) [HB-P(EUU)] coatings were formulated using 2nd generation hydroxyl terminated hyperbranched polyesters (OH–HBPEs), isophorone di-isocyanate (IPDI) as a cross linking agent and dibutyltin dilaurate (DBTDL) as a catalyst with certain additives. First, NCO terminated prepolymers (HBPEUs) were formulated by reacting OH–HBPEs with IPDI at NCO:OH ratio of 1.1:1 for 4 h at 70–80 °C, then HBPEUs were mixed with DBTDL and various additives and finally coated on pretreated cold rolled mild steel (MS) substrates by dip coating method. Before applying on MS substrates, viscosity and volume solid of coatings were measured. The molecular structure of HBPEUs was characterized by ATR-FTIR and ¹H NMR analysis. Surface morphology of coated panels was characterized by atomic force microscopy (AFM) and found that coating components were homogeneously distributed and surface was smooth and crack free. Performance of coated substrates was evaluated by various tests such as cross hatch and pull off adhesion, abrasion resistance, scratch resistance, impact resistance, flexibility, and pencil hardness. UV stability of coated substrates was evaluated by UV-whether-o-meter and corrosion resistance property was evaluated by salt spray, humidity, polarization and electrochemical impedance (EIS) test. Results were also compared with polyurethane coating based on linear polyester. HB-P(EUU) coatings showed excellent enhancement in mechanical, durability as well as corrosion resistance properties than their linear counterpart.     

Corrosion inhibition by poly(N-ethylaniline) coatings of mild steel in aqueous acidic solutions

Poly(N-ethylaniline) (PNEA) coatings on mild steel have been electrodeposited from 0.1 to 0.5 M aqueous oxalic acid solutions containing 0.1 M N-ethylaniline (NEA) using potentiodynamic synthesis technique. The effect of oxalic acid concentration on the corrosion behavior of PNEA coated mild steel surfaces were investigated by DC polarization and electrochemical impedance spectroscopy (EIS) techniques in 0.1 M HCl and 0.05 M H₂SO₄ solutions. Corrosion test results showed that corrosion resistance of PNEA coatings decreases with increasing concentrations of oxalic acid in polymerization solution. Decreasing acidity of the polymerization solution causes more effective protection against corrosion in aqueous acidic corrosive medium.     

Novel method of fabrication of polyaniline–CdS nanocomposites: Structural,morphological and optoelectronic properties

Polyaniline–CdS nanocomposites have been synthesized by spin coating technique. The nanocrystalline CdS powder of particle size 40–50 nm was synthesized by sol–gel technique and the polyaniline was synthesized by chemical oxidative polymerization of aniline. The composite films were characterized by X-ray diffraction (XRD), field effect scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy and Four probe method. The results were compared with corresponding data on pure polyaniline films. The intensity of diffraction peaks for PANi–CdS composites is lower than that for CdS. The conductivity measurement shows that molecular chain constitution of polyaniline is the most important carrier in polyaniline–CdS nano composite. The optical studies showed that variation in band gap of polyaniline (3.40 eV) to 2.54 eV CdS which is attributed to the interaction of CdS nanoparticles with PANi molecular chains.     

Synthesis,characterization and optical properties of Zr+4/La+3/Nd+3 tri-doped yttria nanopowder by sol–gel combustion method

In this research, zirconium lanthanum and neodymium tri-doped yttria nanopowder was synthesized using the sol–gel combustion method. Citric acid (CA) and glycine (G) were used for the gel and fuel agent, respectively. The effect of CA:G:TM (TM=transition metal) mole ratios on the particle size and morphology of the product was evaluated. As-synthesized samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), energy dispersion spectrum (EDS), photoluminescence (PL) spectrum, Inductively coupled plasma (ICP), UV–visible (UV–vis spectroscopy), thermal gravimetric-differential thermal analysis (TG/DTA) and Fourier transform infrared (FTIR)analysis. The optimized sample synthesized with CA:G:TM mole ratio of (1.06:1.06:1) had the average particle size of 30–40 nm with a spherical morphology. Moreover, the optimized sample showed visible photoluminescence, at 400–800 nm.     

Comparative Study of Corrosion Protection of Sol–Gel Coatings with Different Organic Functionality on Al-2024 substrate

In this paper we have studied the effect of addition of amino silane and sulfur silane by 2 wt% into a reference coating solution by using two basic silane coupling agents methyl-tri-ethoxy silane (MTEO) and glycidoxy-propyl-tri-ethoxy silane (GPTS) in 1:1 molar ratio by sol–gel technique. The change in hydrophobicity due to the addition of amino group and thiol group was investigated by contact angle study and sol–gel kinetics was studied by Fourier transform infrared spectroscopy. The thermal resistance and surface morphology was analyzed by thermo gravimetric method and scanning electron microscope. The anti corrosion property of all three coatings were evaluated by potentiodynamic polarization study, AC impedance and salt spray method. X-ray photoelectron spectroscopic method was used to monitor the bonding mechanism of coating matrix with the metal surface. All type of investigations revealed that, addition of thiol group containing silane coating to the reference coating solution has caused remarkable improvement in hydrophobicity and corrosion resistance properties where as amine group rendred the surface less hydrophobic and showed no sign of improvement in corrosion protection. The most probable reason behind this improved performance is due to the additional hydrophobicity imparted by much less polar thiol group. But amino silane provided comparatively poor performance due to the presence of polar amine group.     

Preparation of zinc titanate nanoparticles and their photocatalytic behaviors in the photodegradation of humic acid in water

A series of zinc titanate nanoparticles was successfully synthesized using a simple sol–gel technique. The composites were characterized by thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD) patterns, scanning electron microscope (SEM), X-ray photoelectron spectra (XPS) and UV–vis diffuse reflectance spectra (UV–vis). The photocatalytic activity of samples was investigated by degradation of humic acid (HA) in water under xenon lamp. The sample calcined at 800 °C was found to exhibit much higher photocatalytic activity than the other samples. The investigation of photocatalytic mechanism indicates that the holes (h⁺) and OH radicals may be the major reactive species for the degradation of HA. Meanwhile, the processing parameters such as the light source and the dosage of catalysts play an important role in tuning the photocatalytic activity. The enhancement of photocatalytic activity for the zinc titanate nanoparticles calcined at 800 °C may be attributed to the higher redox ability, coordination of Ti ions and smaller particle size.     

Preparation of monodispersed magnesia coated silica particles through a surface-induced precipitation method

Monodispersed magnesia coated silica particles were prepared by the surface-induced precipitation method, in which a sol type of magnesium precursor was deposited on the surface of spherical silica particles via electrostatic attraction route, and then calcined at 700 °C for 90 min. The magnesium precursor was synthesized by the sol–gel technique, which employs ethanol as a solvent. The resulting particles were characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermal (TG/DTA) analysis, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). The results show the formation of a well-crystallized magnesia layer on the surface of the core silica particles. The resultant coated particles exhibited the spherical shape without the formation of a hard aggregate in spite of the heat treatment. XPS and FTIR investigations also confirmed that the magnesia coating layer and core silica particle were connected through the Mg–O–Si chemical bonding at the interface.     

Electrochemical synthesis of poly-2-aminothiazole on mild steel and its corrosion inhibition performance

2-Aminothiazole (AT) was polymerized by electrochemical technique on a mild steel (MS) electrode from 0.01 M monomer containing 0.3 M ammonium oxalate solution. Cyclic voltammetry was used for the synthesis. Poly-2-aminothiazole (pAT) film with a light-brownish color was obtained on the MS surface. The effectiveness of polymer film in preventing corrosion of MS was tested in 0.5 M HCl solution. For corrosion tests, anodic polarization curves, electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques were utilized. The results obtained indicated that, the polymer film adherent to the steel surface. The polymer film gives a good corrosion protection against the attack of corrosive environment.     

Effect of addition of surface modified nanosilica into silica–zirconia hybrid sol–gel matrix

An organic–inorganic hybrid sol (MZ) comprising a methacrylate functionalized silane matrix (M) and zirconium-n-propoxide (Z) was prepared using sol–gel technique. Two methodologies were adopted to modify the hybrid sol for generating nanocomposite coatings viz., (a) addition of acrylic surface modified silica nanoparticles (N) of diameter ～20 nm to the sol to enhance their compatibility with the hybrid sol–gel matrix and (b) in-situ formation of a three dimensional silica network by addition of tetraethoxy silane (T) to the sol MZ. In the first methodology, the sols were prepared with six different weight ratios of the nanoparticles to the sol, i.e. 0, 0.01, 0.05, 0.1, 0.25 and 1 which were labelled as MZ+Nx where x=0, 1, 2, 3, 4 and 5 respectively. The prepared sols were dip coated on 100 mm×100 mm polycarbonate substrates followed by thermal curing at 130 °C. The coatings were characterized for their mechanical properties like pencil scratch hardness, scratch resistance using scratch tester, nanoindentation hardness, and abrasion resistance as well as visible light transmittance. FT-IR studies were also carried out on heat-treated gels derived from the sols. A maximum pencil scratch hardness of 3H was obtained for the MZ+T coatings and these coatings withstood a critical load of 4.3±0.7 N before failure during scratch test. The maximum nanoindentation hardness of 3.8±0.01 GPa was obtained for the MZ+N5 coatings. The abrasion resistance of MZ+T coatings was higher when compared to MZ+N0 and MZ+N5 coatings. The scratch and nanoindentation hardness were seen to be better for an in-situ formed –Si–O–Si– network in the hybrid sol when compared to those obtained from coatings generated by external addition of acrylic surface modified silica nanoparticles. The difference in properties was attributed to the level of interaction between the nanoparticles and hybrid sol–gel matrix.     

Crack formation,exfoliation, and ridge formation in 500 °C annealed sol–gel silica coatings on stainless steel SUS304: Part II Spectroscopic and mechanical analyses and insights into mechanisms controlling coating characteristics

This report is a continuation of Part I of my studies of a non-aqueous sol–gel silica coating deposited on stainless steel SUS304. Part I discussed the microscopic observation of cracks, ridges and interlayers within the resulting silica coatings, and provided limited insight into their respective mechanisms of formation. This report provides further explanation for the mechanisms of these processes, as evidenced by spectroscopic and nano-indentation analyses of the coatings. Specifically, the coatings were analyzed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Auger electron spectroscopy. These results are discussed along with those obtained in Part I to further assess the mechanisms of crack formation in the coatings, and it was found that coating shrinkage and tension most likely caused crack formation. It seems that the O-deficient interlayers were formed under a mild oxidation condition existed around the silica/SUS304 interface during ～500 °C annealing. Additionally, nano-indentation analysis indicated that the coatings were compact, but the coatings’ hardness was intermediate. Suggestions for improvement of sol–gel silica coatings on stainless steel are also provided.     

Sol–gel hydrothermal synthesis of bismuth–TiO2 nanocubes for dye-sensitized solar cell

Bismuth–TiO₂ nanocubes were synthesized via a facile sol–gel hydrothermal method with titanium tetraisopropoxide as the precursor. The influence of the bismuth on the size, morphology, crystallinity and optical behavior of TiO₂ nanocubes were investigated. The samples were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), field emission scanning electron microscopy (FESEM) and UV–visible spectroscopy (UV–vis). Photovoltaic behavior of dye-sensitized solar cells (DSSCs) fabricated using Bi–TiO₂ nanocubes was studied. The DSSCs had an open-circuit voltage (V_oc) of 590 mV, a short-circuit current density (J_sc) of 7.71 mA/cm², and the conversion efficiency (η) of 2.11% under AM 1.5 illumination, a 77% increment as compared to pure TiO₂ nanocubes.     

Abrasion resistance of ceramic thin films of ZrO2/SiO2 on stretched grade polymethyl methacrylate substrates

Abrasion resistance of stretched grade polymethyl methacrylate (PMMA) was increased by using the sol–gel method to have it coated with a ZrO₂/SiO₂ thin film. Different molar ratios of Zr(OPr)₄/Si(OPr)₄ sols were prepared as precursors with propanol. These sols were used for dip-coating the stretched PMMA surfaces to establish very smooth thin films of amorphous Zr–O–Si. Fourier Transform Infrared spectroscopy (FT-IR) was employed to study vibrations of Zr–O–Si bonds within the thin film. The phase analysis was undertaken via X-ray Diffraction (XRD) method. The morphology and thickness of coatings on PMMA were investigated by means of Scanning Electron Microscopy (SEM). The results showed that coating had an amorphous structure with its thickness within the range of 80–100 nm. The water contact angle of PMMA substrates altered from 73° before coating to less than 64° after coating. Once coated, the PMMA substrate had its transparency characteristic (within the UV–vis region) increased. Furthermore, the influences of thermal treatment temperature and molar ratio of precursors (Zr(OPr)₄/Si(OPr)₄) on abrasion resistance of the coatings were studied.     

Optimized sol–gel thermal barrier coatings for long-term cyclic oxidation life

New promising thermal barrier coatings (TBCs) processed by the sol–gel route are deposited onto NiPtAl bond coated superalloy substrates using the dip and/or spray coating technique. In this study, the optimization of the process, including an appropriate heat treatment prone to densify the yttria-stabilized-zirconia (YSZ) top-coat and leading to the sintering and the development of a resulting crack network, is investigated. In particular, relevant information on internal strain evolution during the heat treatment are obtained using in situ synchrotron X-rays diffraction and confirm a stabilization of the TBC through the occurrence of the micro-cracks that beneficially releases the in-plane sintering stress. Such TBCs are subsequently reinforced using additional material brought within the cracks using sol–gel spray coating. The effect of various process parameters, such as the pre-oxidation of the bond-coat, on the sol gel TBCs consolidation and their cyclic oxidation resistance enhancement, is presented. Reinforced sol–gel TBCs are successfully oxidized up to more than one thousand 1 h-cycles at 1100 °C, without any detrimental spallation.     

The effect of zirconia ions on corrosion performance of sol–gel coated galvanized steel

Currently, galvanized steel is treated with hexavalent chrome passivation. Sol–gel coating has been found to be a potential replacement for the hazardous hexavalent chrome passivation treatment. The aim of this work is to study the effect of zirconyl nitrate on corrosion behavior of sol–gel coating. Aminopropyl-trimethoxysilane and 3-glycidoxypropyltrimethoxysilane were employed as precursors to prepare the sol–gel-based silane coating. The sol–gel film was deposited on galvanized steel sheet by dip coating method. The chemical properties of sol–gel solution and coated films were analyzed by infrared spectroscopy. Morphology of the film was characterized by scanning electron microscope. The corrosion resistance of the coated samples was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization curve, and salt spray test. The results indicated that zirconia-doped coatings have better corrosion resistance in comparison with their undoped counterparts. The coating doped with 0.5% zirconyl nitrate provides better corrosion protection due to the inhibitive action of zirconia ion.     

Formation of anatase TiO2 nanoparticles by simple polymer gel technique and their properties

Pure anatase nano-TiO₂ powders were successfully prepared by a simple polymer gel technique using poly-(vinylpyrrolidone) (PVP) as the polymer. The products were systematically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), UV–visible spectroscopy and photoluminescence studies. The XRD and XPS results indicate that the prepared powder had a pure anatase nano-TiO₂ structure with lattice parameters a and c of 0.378 and 0.951 nm, respectively. The particle size analysed by TEM ranged between 7 and 12 nm. The maximum UV absorption for the TiO₂ nanoparticles was below 400 nm with an estimated direct band gap (Eg) of 3.55 eV. The photoluminescence peaks of the nanopowder were observed at 391 and 468 nm. The nanosized materials were produced using a simple and cost effective polymer gel technique.