Investigation of effective parameters in improving corrosion resistance of silica coated stainless steel via sol–gel method

Abstract

The sol–gel method has been used to deposit oxide thin films. In the present study, silica was coated on 316L stainless steel substrate through sol–gel method via dipping process. Silica sol was made in a mixture of methyltriethoxysilane (MTES), tetraethyl orthosilicate (TEOS), pure water, absolute ethanol as solvent, nitric acid, and hydrochloric acid as catalysts. The corrosion resistance of samples was investigated in simulated body fluid by a potentiodynamic test and uniformity of the coating was evaluated by scanning electron microscope. We have assessed the effective parameters, such as wetting agent, number of layers, catalyst and different roughness of sublayers on corrosion properties of samples. The silica coating resulted in improvement of corrosion resistance of 316L stainless steel in body environment, and can be used as a proper coating on orthopaedic implants.     

Polyindole top coat on TiO2 sol–gel films for corrosion protection of steel

The protection efficiency of polyindole film on stainless steel was enhanced via titanium dioxide pre-coating. The characterization of coatings was achieved by nuclear magnetic resonance and Fourier-transform infrared spectra. The surface morphology of electrodes was monitored with scanning electron microscope. The corrosion performance was investigated in 3.5% NaCl solution by electrochemical impedance spectroscopy and potentiodynamic measurements. The quantum calculations were employed, and theoretical parameters were determined. Results showed that the correlation between experimental and theoretical parameters. The high protection efficiency was observed against corrosion on the steel surface via forming a protective polyindole top coated titanium dioxide film.     

Influence of outer rust layers on corrosion of carbon steel and weathering steel during wet–dry cycles

The influence of the rust layers of carbon steel and weathering steel on the corrosion were investigated. It was found that corrosion of carbon steel slows down when its outer rust layer is removed. This phenomenon might be attributed to the shortening of the wetting time in wet–dry cycles when the outer rust layers are removed. What is more, growth time of the corrosion products is shortened as well, which results in the formation of the fine corrosion products. However, the behavior of corrosion of weathering steel is not obviously influenced by the outer rust layer and the wetting time.     

Study of molybdate–phytic acid passivation on galvanised steel

Abstract

A combined molybdate–phytic acid passivation treatment on galvanised steel is studied in this paper. Both copper decoration drop tests and immersion mass loss tests indicated that the combined molybdate–phytic acid passivated samples showed better corrosion resistance than that of samples treated separately by molybdate or phytic acid. The electrochemical behaviours of the passivated samples were investigated using potentiodynamic polarisation and electrochemical impendence spectra in 0·5 mol L^?1 NaCl solution and showed corrosion current densities of 4·95×10^?5, 5·10×10^?5 and 1·19×10^?5 A cm^?2 respectively. Electrochemical impendence spectra also indicated that molybdate–phytic passivated samples exhibited better corrosion resistance. The mechanism of synergetic effect for molybdate–phytic acid passivation on galvanised steel is discussed in brief.     

Effect of the temperature of cerium nitrate–NaCl solution on corrosion inhibition of mild steel

In this study, the effect of temperature on corrosion inhibition is studied in the absence and presence of an optimal concentration of cerium nitrate (600 mg/L) as an inhibitor of mild steel in sodium chloride. Corrosion tests are carried out through electrochemical techniques such as impedance spectroscopy and d.c. polarization measurements. The surface morphology of the films is investigated by optical microscopy, white-light interferometry, and scanning electronic microscopy, coupled with energy-dispersive spectroscopy analysis for chemical composition. The results obtained show that the activation energy for the corrosion inhibition process to occur increases in the presence of a cerium nitrate inhibitor. However, the corrosion resistance of mild steel is somewhat lost upon increasing the solution temperature up to 55°C, which leads to more cracked films. The enthalpy and entropy values suggest a mixed mechanism of chemisorption and physisorption inhibition, with a major dominance of physisorption control.     

Fabrication of hydrophobic and antireflective coatings based on hybrid silica films by sol–gel process

This paper reports the synthesis of hydrophobic and antireflective coatings by sol–gel process at room temperature (25 °C), using tetraethylorthosilicate (TEOS) as a precursor and methyltriethoxysilane (MTES), phenyltriethoxysilane (PTES), vinyltriethoxysilane (VTES), and octyltriethoxysilane (OTES) as surface modifying agents. The silica sol was prepared by keeping the molar ratio of TEOS:RTES at 1:1, in acidic conditions with ethanol and 0.1 M HCl. All hybrid systems were enriched with titanium(IV) isopropoxide as the cross-linking agent. It was observed that the obtained silica films become hydrophobic with the introduction of the hydrophobic organic group. The higher value of static water contact angle (107 ± 3°) was obtained for the silica film prepared with TEOS + OTES. Under optimal synthesis condition, we obtained antireflection coatings, exhibiting a low reflection in the visible range.     

Preparation and characterisation of acrylic–polyurethane-based waterborne anticorrosion coating on galvanised steel

Four water-based organic composite coating solutions were prepared and applied on galvanised sheet samples producing a transparent film of about 5-µm thickness. Their corrosion performances were examined by Tafel polarisation, EIS, salt spray and cyclic corrosion tests. The primary coating formulation contained an acrylic emulsion and polyurethane dispersion mixture together with additives. The corrosion resistance properties of the primary formulation were enhanced by adding nano-ZnO particles, and further improved by adding corrosion inhibitors such as zinc phosphate and sodium phosphate. The final formulation on galvanised samples showed 720?h of salt spray resistance and 90 cycles of cyclic corrosion resistance, SAE J2334. The Tafel and EIS studies indicate that the coating possesses barrier protection properties. The electrolyte penetrates through the coating within 24?h but progress of corrosion depends upon the coating adhesion and its compactness, that is improved significantly by adding nano-ZnO and corrosion inhibitor to the coating formulation.     

Preparation and properties of atomic oxygen protective films deposited on Kapton by solvothermal and sol–gel methods

Due to a smooth hydrophobic surface of Kapton, it is very difficult for other materials to bond to it. In this study, using solvothermal method to modify the surface of Kapton substrates, the adhesion between silica film and Kapton substrate was greatly improved. Silica films were prepared on Kapton substrate via sol–gel method and the samples were irradiated by atomic oxygen (AO) in a ground-based simulation system. The AO erosion yield values of the samples after AO irradiation were tested. The surface morphology and the structure of silica films were investigated by scanning electronic microscope (SEM) and Fourier transformed infrared spectroscopy (FTIR). The results indicated that a uniform thin film was easily formed on the surface of Kapton. After AO exposure, the silica films become smoother and more uniform, without peeling off, and the AO erosion yield of coated Kapton was sharply down, equivalent to only 4.7% of pristine Kapton.     

Effect of heat treatment on corrosion behaviour of deposited Fe–40Al intermetallics

Abstract

A study using electrochemical techniques of the susceptibility to corrosion in 0·1M NaCl solution (pH 3) of atomised and deposited Fe–40Al (at.-%) intermetallic material at room temperature is reported. Specimens were heat treated at temperatures of 600 and 900°C for 24 and 72 h. Potentiodynamic polarisation, linear polarisation resistance, potential–time, and electrochemical current noise data were collected. The untreated material displayed higher corrosion resistance than the heat treated material. In the treated material, the corrosion resistance increased with both the time and temperature of heat treatment. Also, untreated material was more susceptible to pitting corrosion than heat treated material. As the temperature or the time of heat treatment was increased, the material became more resistant to pitting. This improvement in resistance to pitting was related to a decrease in surface defects, such as pores and cracks, and an increase in grain size. Thus, heat treatment lowered the number of active sites and helped the material to establish a more protective film.     

Comparison of selected inhibitor doped sol–gel coating systems for protection of mild steel

Current legislation around the use of antifouling and anticorrosion coatings has increased the need to find an environment friendly alternative to existing biocide containing pretreatments for steel structures exposed to sea water. Sol–gel technology offers a solution to fouling and corrosion inhibition since sol–gel chemistry lends itself ideally to functionalisation with a variety of components, for example, corrosion inhibitors. In this study, we have utilised the above mentioned approach in order to produce an inhibitor doped sol–gel protective coating on mild steel. The corrosion protection performance of three inhibitors, i.e. SD (Shieldex303), MOLY (Moly-White101ED-PLUS) and ZAPP (Heucophos ZAPP), added individually to a sol–gel, and applied to mild steel Q panels, were evaluated using electrochemical impedance spectroscopy. The inhibitor containing coatings were shown to protect against corrosion of mild steel; the coatings containing the inhibitors Moly and ZAPP were the most effective of the systems tested.

Highlights

? Sol–gel coatings are potential candidate systems for the protection of mild steel substrates.

? Sol–gel chemistry allows a variety of corrosion inhibitors to be incorporated into the sol–gel coating matrix.

? Evaluation of corrosion inhibition efficiency of sol–gel coatings can be assessed using electrochemical impedance spectroscopy (EIS).     

Glass-like CexOy sol–gel coatings for corrosion protection of aluminium and magnesium alloys

This work reports the preparation of glass-like, environmentally-friendly, cerium-based coatings for active corrosion protection of aluminium and magnesium alloys. It describes the production of cerium sol–gel sols from cerium nitrate and their deposition by immersion and automatic spray onto aluminium and magnesium alloys to produce uniform coatings with amorphous (glass-like) structures (Ce_xO_y). The coatings have been characterised by profilometry, scanning electron microscopy (SEM), spectral ellipsometry and UV–visible, in order to analyse the structure and density of the glass-like cerium coatings as well as their redox ratio Ce⁴⁺/Ce³⁺ as a function of pH and sintering temperature. Finally, electrochemical measurements (EIS) and standard corrosion tests (neutral salt spray, filiform corrosion, immersion–emersion test and adhesion on embossing and T-bend test) have been performed to study the corrosion behaviour of the cerium glass-like coatings on aluminium and magnesium alloys. EIS measurements confirm the healing or blocking of the defects by the corrosion inhibiting species. Excellent corrosion protection is provided by cerium glass-like coatings, satisfying the most demanding industrial requirements.     

Investigation of high concentration of benzotriazole on corrosion behaviour of titania–benzotriazole hybrid nanostructured coating applied on Al 7075 by the sol–gel method

Nowadays, surface modification with self-healing ability is a valuable technique to improve chemical stability, oxidation behaviour and corrosion resistance of materials without interference with its physical, chemical or mechanical properties of bulk material underneath. In this paper, hybrid organic amorphous titania coatings are deposited on 7075 aluminium alloy substrates by using the sol–gel method. A titania–benzotriazole (BTA) nanostructured hybrid sol–gel coating is impregnated with three different high concentrations of BTA, 1.4, 2.8 and 4.2%. The bonds existing in the hybrid coating, structure and morphology and coating corrosion behaviour have been studied using the FTIR, GIXRD, field emission scanning electron microscopy and electrochemical impedance spectroscopy (EIS) test in a 3.5?wt-% NaCl solution during different immersion times, 24, 48, 72, 96 and 120?h. EIS studies indicated that a higher coating resistance value was gained for titania–4.2% BTA even after 120?h of immersion and BTA acted mainly on the amorphous titania coating as a corrosion inhibitor and a healing agent that acts by two mechanisms: first, release of a healing agent to the formation of corrosion products, then finally blocking surface defects; second, release of a healing agent during 48?h of immersion and its adsorption to produce an insulating layer on the surface of the coating in contact with the solution.     

Effect of number of layers on erosion,corrosion, and wear resistance of multilayer Cr–N/Cr–Al–N coatings on AISI 630 stainless steel

In the present study, multilayered Cr–N/Cr–Al–N coatings were prepared by cathodic arc physical vapor deposition (PVD) with different numbers of layers and the same total thickness on AISI 630 steel in an attempt to improve the wear and erosion–corrosion resistance. Structural analysis of the coatings was performed by field scanning electron microscopy, X-ray diffraction (XRD), and energy-dispersive spectroscopy. Depth profiles and roughness parameters of worn surfaces were calculated after erosion and wear tests. XRD indicated that nitride compounds were formed in multilayer coatings by PVD. The Cr–N/Cr–Al–N coating exhibited superior corrosion resistance compared with AISI 630 substrate. The erosion–corrosion results revealed that the smoothest wear track with the minimum erosion rate and wear depth was obtained for five- and seven-layered coatings. The failure mechanism of the bare substrate was influenced by plastic deformation via cutting and plowing, while the failure mechanism for coated samples was chipping and delamination. According to the wear results, the multilayer coatings showed a lower friction coefficient and better surface morphology that demonstrated their high ability for wear protection.     

Effect of carbon dioxide on the atmospheric corrosion of Zn–Mg–Al coated steel

The atmospheric corrosion of line hot dip ZnMgAl coating was investigated at low and ambient concentration of CO₂ as a function surface chloride concentration and temperature and compared to conventional hot dip galvanised (GI) and Galfan coatings. The corrosion of zinc coatings was enhanced in low CO₂ conditions and ZnMgAl material was more affected than GI, and in the range of the Galfan coating. An obvious pH effect was underlined in low CO₂ conditions. Layered double hydroxide (LDH) and simonkolleite were mainly formed on ZnMgAl coating in the absence of CO₂ while hydroxycarbonate and simonkolleite were dominating in ambient air.     

The effect of Sn on autoclave corrosion performance and corrosion mechanisms in Zr–Sn–Nb alloys

The desire to improve the corrosion resistance of Zr cladding material for high burn-up has resulted in a general trend among fuel manufacturers to develop alloys with reduced levels of Sn. While commonly accepted, the reason for the improved corrosion performance observed for low-tin zirconium alloys in high-temperature aqueous environments remains unclear. High-energy synchrotron X-ray diffraction was used to characterize the oxides formed by autoclave exposure on Zr–Sn–Nb alloys with tin concentration ranging from 0.01 to 0.92 wt.%. The alloys studied included the commercial alloy ZIRLO® (ZIRLO® is a registered trademark of Westinghouse Electric Company LLC in the USA and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited.) and two variants of ZIRLO with significantly lower tin levels, referred to here as A-0.6Sn and A-0.0Sn. The nature of the oxide grown on tube samples from each alloy was investigated via cross-sectional scanning electron microscopy. Atom probe analysis of ZIRLO demonstrated that the tin present in the alloy passes into the oxide as it forms, with no significant difference in the Sn/Zr ratio between the two. Synchrotron X-ray diffraction measurements on the oxides formed on each alloy revealed that the monoclinic and tetragonal oxide phases display highly compressive in-plane residual stresses with the magnitudes dependent on the phase and alloy. The amount of tetragonal phase present and, more importantly, the level of tetragonal-to-monoclinic phase transformation both decrease with decreasing tin levels, suggesting that tin is a tetragonal oxide phase stabilizing element. It is proposed that in Zr–Nb–Sn alloys with low Sn, the tetragonal phase is mainly stabilized by very small grain size and therefore remains stable throughout the corrosion process. In contrast, alloys with higher tin levels can in addition grow larger, stress stabilized, tetragonal grains that become unstable as the corrosion front continues to grow further inwards and stresses in the existing oxide relax.     

Investigation of adsorption and corrosion inhibition effect of 1,1’-thiocarbonyldiimidazole on mild steel in hydrochloric acid solution

The adsorption and inhibition effect of 1,1′-thiocarbonyldiimidazole (TCDI) on the corrosion of mild steel (MS) in 0.5 M HCl solution was studied in both short and long immersion time (120 h) with the help of electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR) techniques. For long-time tests, the hydrogen gas evolution (VH₂-t) and the change of open circuit potential with immersion time (E _ocp-t) were also utilized in addition to the former two techniques. The surface morphology of MS after its exposure to 0.5 M HCl solution with and without 1.0 × 10⁻² M TCDI was examined by scanning electron microscopy (SEM). It was demonstrated that the inhibition efficiency of studied inhibitor is concentration depended and increased with TCDI concentration. The higher value of inhibition efficiency was obtained after longer immersion time merely on the basis of strong increase of corrosion rate of mild steel in the blank solution. The high inhibition efficiency was discussed in terms of adsorption of inhibitor molecules and protective film formation on the mild steel surface which was substantiated by SEM micrographs. The adsorption of TCDI on MS was found to obey Langmuir adsorption isotherm.     

Impact toughness of tungsten films deposited on martensite stainless steel

Tungsten films were deposited on stainless steel Charpy specimens by magnetron sputtering followed by electron beam heat treatment. Charpy impact tests and scanning electron microscopy were used to investigate the ductile-brittle transition behavior of the specimens. With decreasing test temperature the fracture mode was transformed from ductile to brittle for both kinds of specimens with and without W films. The data of the crack initiation energy, crack propagation energy, impact absorbing energy, fracture time and deflection as well as the fracture morphologies at test temperature of-70 ℃ show that W films can improve the impact toughness of stainless steel.     

Application of CeH–V/ sol–gel composite coating for corrosion protection of AM60B magnesium alloy

Application of a composite coating on AM60B magnesium alloy consisting of cerium–vanadium conversion coating and a hybrid sol–gel layer was investigated. Scanning electron microscopy and energy dispersive X-ray spectroscopy analyses revealed a cracked nodular structure for the cerium–vanadium conversion coating which was mainly composed of O, Ce, V, and Mg atoms. All the cracks in the conversion coating were completely sealed by a thin, compact and defect-free hybrid sol–gel film. Potentiodynamic polarization and electrochemical impedance spectroscopy experiments in Harrison's solution showed that the cerium–vanadium conversion coating provides minimal protection against corrosion while the composite coating significantly increases the corrosion resistance of the magnesium alloy. Sol–gel film provides protection against corrosion by sealing cracks in the cerium–vanadium conversion coating and acting as a barrier. Scanning electron microscopy analyses after polarization tests confirmed the results obtained by the electrochemical tests.     

Nanodiamond incorporated sol−gel coating for corrosion protection of magnesium alloy

Sol−gel coatings containing various amounts of hydroxylated nanodiamond (HND) particles were applied on the magnesium alloy for corrosion protection. The micrometric defects in the sol−gel coating completely disappeared after adding 0.01, 0.02 and 0.05 wt.% of the HND nanoparticles. The AFM analyses showed that average roughness of the sol−gel film is about 6.7 nm which increases to 16.1 and 20.2 nm after incorporating 0.005 and 0.02 wt.% of the HNDs, respectively. The corrosion resistance of the coatings was tested in Harrison’s solution by means of EIS technique after 15, 30, 60 and 120 min immersion. The corrosion resistance of the sol−gel coating was remarkably enhanced by incorporating different contents of the HNDs and the best result was obtained for 0.01 wt.%. The results of the EIS experiments were confirmed by the potentiodynamic polarization tests. The corrosion resistance enhancement was attributed to the film compactness (due to the chemical interaction with the HNDs), formation of tortuous pathways for diffusion of the corrosive solution, and filling of the defects by the nanoparticles. However, the beneficial effect of the HNDs on the corrosion resistance gradually diminished as the content of nanoparticle was increased. Finally, the micromorphology of the sol−gel nanocomposites was studied after the corrosion tests.     

Corrosion resistance of Al–Cu–Fe alloy powder coated with silica using an ultrasound-assisted sol–gel method

Al–Cu–Fe alloy powder, a high-effective lubrication oil additive, was coated by conventional sol–gel method employing tetraethoxysilane (TEOS) as the precursor for purpose of improving its corrosion resistance. The best condition was obtained according to an orthogonal experiment (L₉(3⁴)). Then, the sol–gel method was modified by employing ultrasound to study the effects of both the ultrasonic power and irradiation time on the coating process. Finally, the coated powder had an high corrosion resistance in the acid media of pH 1. The obtained samples were characterised by FTIR, XRD, SEM and EDS.