The electrochemical behavior of brass in natural seawater in the absence and presence of thiadiazole derivatives, namely, 2-amino-5-(4-methoxyphenyl)-1,3,4-thiadiazole (AMOPTD), 2-amino-5-(4-methylphenyl)-1,3,4-thiadiazole (AMPTD), 2-amino-5-(4-pyridinyl)-1,3,4-thiadiazole (APTD), and 2-amino-5-(4-nitrophenyl)-1,3,4-thiadiazole (ANPTD), has been investigated by electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The optimum concentration of the studied inhibitors showing the highest inhibition efficiency was also evaluated at five different temperatures in the range between 303 and 343 K. The inhibition efficiency was found to increase with increase in concentration of the inhibitors but decrease with rise in temperature for all the studied inhibitors except ANPTD. Thermodynamic and kinetic parameters for the adsorption process were determined. Quantum chemical approach was further used to calculate some electronic properties of the molecule in order to confirm any correlation between the inhibitive effect and molecular structure of the studied inhibitors. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis confirms that dezincification was minimized to a greater extent in the presence of the investigated inhibitors. Scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), and Fourier transform infrared spectroscopy (FT-IR) observations of the brass surface confirmed the existence of such an adsorbed film.
The effect of introducing WO 3 (tungsten oxide) nanoparticle in the epoxy coating was analyzed by electrochemical impedance spectroscopy and scanning electrochemical microscopy (SECM) methods in 3.5% NaCl. The (3-glycidyloxypropyl)trimethoxysilane was treated with the nanoparticle for the proper dispersion and chemical interaction of nanoparticle with the epoxy resin. The introduction of WO 3 nanoparticle in the epoxy coating enhances the charge transfer resistance (R ct ) as well as the film resistance (R f ). The observation of iron dissolution and oxygen consumption was done by applying the appropriate SECM tip potential in the WO 3 -modified nanocomposite coated steel. The epoxy and epoxy-WO 3 nanocomposite-coated samples were used to study the adhesion and anticorrosion properties. The analysis by SEM/EDX displayed that the enriched W was detected in the nanocomposite coating of steel. The presence of the nano level corrosion product containing W was confirmed by focused ion beam-transmission electron microscope analysis. The high corrosion protection properties of the epoxy-based nanocomposite coating was due to the complex nanoscale layer formed and chemical interactions of epoxy resin with surface-modified nanoparticle in nanocomposites.
Preparation of the MaterialsMid steel with composition in mass % is 0.1C, 0.2Si, 0.5Mn, 0.025P, 0.002S, 0.045Al, 0.005N, 0.004O, and rest is Fe. Silicon carbide papers with 800, 1000, and 1200 grit were used for abrading the metal sample. Then, the sample was coated after rinsing with distilled water and acetone. Bisphenol A and the aliphatic amine as hardener were purchased from Sigma-Aldrich. The average particle size of tungsten oxide nanoparticles is 50 nm and was obtained Additional Supporting Information may be found in the online version of this article.
Purpose
This paper aims to investigate the effect of introducing nano-ceria (CeO2) particles to the epoxy coatings on mild steel in natural seawater.
Design/methodology/approach
The epoxy–ceria nanoparticles were coated with mild steel using a wire-wound draw-down bar method. The effects of ceria nanoparticles on the corrosion resistance of epoxy-coated samples were analyzed using scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS).
Findings
Localized measurements such as oxygen consumption and iron dissolution were observed using SECM in natural seawater in the epoxy-coated sample. The increase in film resistance (Rf) and charge transfer resistance (Rct) values by the addition of nano-ceria particles in the epoxy coating was measured from EIS measurements after wet and dry cyclic corrosion test. Scanning electron microscope (SEM)/energy dispersive X-ray spectroscope (EDX) analysis showed that complex oxides of nano-ceria were enriched in corrosion products at a scratched area of the coated mild steel after corrosion testing. Focused ion beam-transmission electron microscope (FIB-TEM) analysis confirmed the presence of the nanoscale oxide layers of ceria in the rust of the steel.
Research limitations/implications
The tip current at −0.70 V for the epoxy–CeO2-coated sample decreased rapidly because of cathodic reduction of the dissolved oxygen. The increase in film resistance (Rf) and charge transfer resistance (Rct) values by the addition of nano-ceria particles in the epoxy coating were measured from EIS measurements after wet and dry cyclic corrosion test.
Practical implications
The presence of complex oxide layers of nano-ceria layers protects the coated steel from rusting.
Social implications
The use of this nano-ceria for corrosion protection is environment-friendly.
Originality/value
The results of this study indicated the significant effect of nano-ceria particles on the protective performance and corrosion resistance of the epoxy coating on mild steel. The dissolution of Fe2+ was lower in the epoxy–ceria nanoparticle-coated mild steel than that of the epoxy-coated mild steel resulting in a lower anodic current of steel. The increase in film resistance and the charge transfer resistance showed that the nano-ceria particles and the formation of complex oxides provide better barrier protection to the coating metal surfaces.
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