Linear Polarization Techniques Research Articles

Efficiency of Amino Alcohols as Corrosion Inhibitors in Reinforced Concrete

The objective of this paper is to investigate the behaviour of amino alcohol corrosion inhibitors when they are used in reinforced cement mortars either as admixtures in the cement paste or as coating applications on the surface of the rebars. The reinforced cement mortars were exposed to both partial and full immersion in 3.5 wt% NaCl solution. Electrochemical measurements such as half-cell potential and linear polarization technique, as well as weight loss of the embedded rebars were performed in order to obtain information on the corrosion behaviour of the reinforcing steel in cement mortar. Results demonstrate that the amino alcohol corrosion inhibitors offer protection against rebar corrosion in cement mortars.

Microstructural, corrosion and nanomechanical behaviour of ceramic coatings developed on magnesium AZ31 alloy by micro arc oxidation

Microstructural, corrosion and nanomechanical behaviour of micro arc oxidised (MAO) coating grown on magnesium AZ31B alloy was evaluated. Microstructural characterization of the coating was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) followed by image analysis and energy dispersive spectroscopy (EDX). Linear polarization technique was used to evaluate the corrosion behaviour of the MAO coating. Further, nanoindentation was employed to evaluate nanohardness and Young’s modulus of the MAO coating. The characteristic values of both the nanohardness and the Young’s modulus were calculated through the application of the Weibull statistics.

Corrosion behavior of reinforcing steel embedded in chloride contaminated concretes with and without metakaolin

One of the most remarkable drawbacks of the reinforced concrete structural elements is the corrosion of reinforcement. Especially, in marine structures or in such environments where chloride contamination risk exist this issue gains much importance. In this study, chloride contamination of the concrete was implemented by adding 0%, 1.5%, 3%, and 5% NaCl by weight of the total binder content, into concrete. To assess the influence of high reactivity metakaolin (MK) incorporation on the corrosion resistance of the chloride contaminated concrete, 5% and 15% MK replacement levels by the total weight of the binder were assigned in concrete production. The corrosion behaviors of reinforcing bars embedded in concretes were monitored through accelerated corrosion test, corrosion current density and the corresponding corrosion rate by linear polarization technique (LPR). Moreover, the electrical resistivity of concrete was measured. Analysis of the test results indicated that MK was proved to be effective in inhibiting the active corrosion of concrete even at severe chloride contamination levels.

Electrosynthesis and performances of cobalt–ceria nanocomposite biocoatings

Co–CeO2 nanocomposite coatings were obtained by electrocodeposition of nanoparticulate cerium oxide bioceramic (25 nm mean diameter) into cobalt matrix on stainless steel support and the resulting properties were evaluated comparatively with pure cobalt layers. The surface and anticorrosion properties in the simulating body fluid (SBF) solution of the obtained Co–CeO2 nanocomposite layers are characterised using scanning electron microscopy with energy dispersive spectroscopy system, ultrahigh microtopography, Vickers surface microhardness, linear polarisation and electrochemical impedance spectroscopy techniques. The results indicate that CeO2 nanoparticles are uniformly dispersed into cobalt matrix and influence the surface morphology, microtopography, and microhardness and corrosion behaviour of nanocomposite coatings obtained. Coating thickness increases with increased current density as well as the surface roughness and microhardness. At the same time, the results obtained by corrosion tests show that when compared with the traditional polycrystalline cobalt films, the obtained Co–CeO2 nanocomposite layers exhibit the enhanced corrosion resistance in the SBF solution.

Vanadia-based coatings of self-repairing functionality for advanced magnesium Elektron ZE41 Mg–Zn–rare earth alloy

A smart vanadia protective coating of self-repairing functionality that has proven to provide superior corrosion resistance for several magnesium and aluminum alloys has successfully been designed by our group. A newly developed series of magnesium alloys, namely ZE41 alloy, has recently been proposed for automotive, electronics and aerospace applications. The advanced ZE41 alloy possesses very low density, high specific strength, and good castability and weldability characteristics compared to aluminum and steel based alloys. However, the corrosion resistance of ZE41 alloy in the presence of corrosive chloride environment is relatively low. The possibility of utilizing such coatings to add self-repairing functionalities to ZE41 alloy was discussed in this paper. The electrochemical corrosion behavior of the vanadia coatings over ZE41 alloy was investigated in 3.5% NaCl solution using EIS, linear polarization and cyclic voltammetry techniques. The optimum conditions for obtaining protective vanadia coatings of self-repairing abilities and improved localized corrosion resistance were determined. Surface examination of the coatings was investigated using SEM-EDS and macroscopic imaging.

Flat Absorber Phosphorous Black Nickel Coatings for Space Applications

A new process of flat absorber black nickel alloy coating was developed on stainless steel by electrodeposition from a bath containing nickel, zinc and ammonium sulphates; thiocyanate and sodium hypophosphite for space applications. Coating process was optimized by investigating the effects of plating parameters, viz concentration of bath constituents, current density, temperature, pH and plating time on the optical properties of the black deposits. Energy dispersive X-ray spectroscopy showed the inclusion of about 6% phosphorous in the coating. The scanning electron microscopy studies revealed the amorphous nature of the coating. The corrosion resistance of the coatings was evaluated by the electrochemical impedance spectroscopy (EIS) and linear polarization (LP) techniques. The results revealed that, phosphorous addition confers better corrosion resistance in comparison to conventional black nickel coatings. The black nickel coating obtained from hypophosphite bath provides high solar absorptance (αs) and infrared emittance (ɛIR) of the order of 0.93. Environmental stability to space applications was established by the humidity and thermal cycling tests.

Effect of Chromium on the Corrosion Behavior of Powder-Processed Fe-0.6 wt % P Alloys

Phosphoric irons (i.e. Fe-P alloys containing low phosphorous in the range 0.1 to 0.7 wt. %) with/without addition of chromium were prepared by powder forging route. The corrosion behaviour of these alloys was studied in different environments. The various environments chosen were acidic (0.25 M H2SO4 solution of pH 0.6), neutral/marine (3.5 % NaCl solution of pH 6.8) and alkaline (0.5 M Na2CO3 + 1.0 M NaHCO3 solution of pH 9.4). The corrosion studies were conducted using Tafel Extrapolation and Linear Polarization techniques. The results were compared with the corrosion resistance of electrolytic Armco iron. It was observed that, chromium improved the resistance to corrosion in marine conditions only. Corrosion rates were higher in acid medium due to the enhanced hydrogen evolution and hence, the cathodic reaction. The corrosion rates were minimal in alkaline medium and low in neutral solution.

Electrochemical behavior of NixW1−x materials as catalyst for hydrogen evolution reaction in alkaline media

In the present work, results of electrochemical evaluation, as well as morphological and structural characterization of NixW1−x materials with x=0.77, 0.64, 0.4, 0.19 and 0.07 processed by means of high energy ball milling from high purity powders are presented. Also, the electrocatalytic performance on the hydrogen evolution reaction (HER) of the NixW1−x materials evaluated by linear polarization and cyclic voltammetry techniques in alkaline media at room temperature is discussed. The structural and morphological characterization of the as-prepared materials was carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results indicated a small-particle clusters and solid solution formation. According to the kinetics parameters the best electrocatalytic activity was observed at Ni64W36.

THE EFFECT OF ENVIRONMENTALLY BENIGN FRUIT EXTRACT OF SHAHJAN (MORINGA OLEIFERA) ON THE CORROSION OF MILD STEEL IN HYDROCHLORIC ACID SOLUTION

The inhibition of the corrosion of mild steel in hydrochloric acid solution by the fruit extract of shahjan (Moringa oleifera) was studied using weight loss, electrochemical impedance spectroscopy (EIS), linear polarization, and potentiodynamic polarization techniques (Tafel). Inhibition was found to increase with increasing concentration of the extract. The effect of temperature, immersion time, and acid concentration on the corrosion behavior of mild steel in hydrochloric acid solutions with addition of extract was also studied. The inhibition occurred via adsorption of the inhibitor molecules on the mild steel surface obeying the Langmuir adsorption isotherm. Thermodynamic activation parameters such as activation energy, enthalpy (ΔH*), and entropy (ΔS*) of activation for corrosion process were calculated and discussed. The results obtained show that both chemical and physical adsorption of inhibitor molecules occur simultaneously and the fruit extract of shahjan (Moringa oleifera) could serve as an effective inhibitor of the corrosion of mild steel in hydrochloric acid media.

Effects of Annealing on Electrochemical Corrosion of Fe<sub>73.5</sub>Si<sub>13.5</sub>B<sub>9</sub>Nb<sub>3</sub>Cu<sub>1</sub> Alloys

The electrochemical corrosion affects soft-magnetic properties and service life of amorphous or nanocrystalline Fe73.5Si13.5B9Nb3Cu1 alloys. Therefore it is important to characterize the corrosion characteristic of the alloys for their potential application to engineering fields and further alloy development. In this study, the corrosion behavior of nanocrystalline Fe73.5Si13.5B9Nb3Cu1 alloys prepared by crystallization from the amorphous state was studied and compared with that of their amorphous counterparts by linear polarization (PLZ) and electrochemical impedance spectroscopy (EIS) technique. In electrolyte of 0.01 M NaCl, annealing at 550 °C leads to the decreased corrosion rate, while crystallization at 650 °C gives rise to the increase of corrosion rate. In the blend solution of 0.1 M NaCl and 0.1 M NaOH, heat-treatment at 550 °C or 650 °C improves the corrosion resistance for the alloys.

Corrosion of Amorphous Fe<sub>73.5</sub>Si<sub>13.5</sub>B<sub>9</sub>Nb<sub>3</sub>Cu<sub>1</sub> Alloys on the Synergistic Effect of Chloride and Hydroxyl Ions

The soft-magnetic properties and service life of amorphous or nanocrystalline Fe73.5Si13.5B9Nb3Cu1 have been influenced by the corrosion of the alloy. In this study, the electrochemical corrosions of amorphous Fe73.5Si13.5B9Nb3Cu1 in the blend solutions of sodium chloride and sodium hydroxide were investigated by linear polarization (PLZ) and electrochemical impedance spectroscopy (EIS) technique. The presence of OH- in the blend solution gave rise to typical passivation of the alloy. A suitable concentration of OH- was required for the low corrosion rate. And the higher concentration of OH- led to a faster corrosion. Increase of concentration of Cl- aroused more obvious corrosion. These results were ascribed to the deteriorating effect of Cl- and high-concentration OH- on the passive film formed on the surface of amorphous Fe73.5Si13.5B9Nb3Cu1.

Intelligent self-healing corrosion resistant vanadia coating for AA2024

This paper is a continuation of our investigation into the designing of chromate-free anti-corrosion coatings for aluminum and magnesium based materials for marine, automotive and aerospace applications. In this paper, a simple vanadia based chemical conversion coating was applied for improving the corrosion resistance of high strength AA2024 alloy. The effect of vanadia solution concentrations (10, 30 and 50 g/l) on the corrosion behavior was investigated. EIS, linear polarization and cyclic voltammetry techniques were used to evaluate the electrochemical behavior in 3.5% NaCl. Vanadia coatings prepared by dissolving 10 g of vanadate salt per liter showed the best localized corrosion resistance as measured by EIS and polarization techniques. The optimum conditions to obtain corrosion protective coatings for AA2024 were determined. Surface examination of the samples was investigated using AFM, SEM-EDS and macroscopic images.

Smart self-healing anti-corrosion vanadia coating for magnesium alloys

Eco-friendly vanadia based chemical conversion coating was applied for improving the corrosion resistance of a newly developed magnesium AZ31 HP–O alloy. The effect of vanadia solution concentrations (10, 30 and 50 g/l) and pH (neutral pH 7 and pH 9) on the corrosion protection performance of a magnesium substrate were investigated. EIS and linear polarization techniques were used to evaluate the electrochemical behavior in 3.5% NaCl. The results showed a marked increase in the localized corrosion resistance after applying vanadia surface treatment of 50 g/l due to self-healing effect. The optimum conditions to obtain protective coatings for AZ31 HP–O with a self-healing ability were determined. Changes in surface morphology, composition and microstructure of the conversion coatings were followed by SEM-EDS and macroscopic imaging techniques.

Co-ZrO 2 electrodeposited composite coatings exhibiting improved micro hardness and corrosion behavior in simulating body fluid solution

The aim of this work was the deposition of zirconium oxide bioceramic particles in cobalt matrix within the research work aimed at obtaining metal matrix composite coatings (MMC) under direct current and the evaluation of their protective properties. The cobalt/zirconia micro structured composite coating containing bioceramic of ZrO 2 dispersed phase was prepared using direct current (DC) electrodeposition method. The surface morphology, cross section and anti-corrosion property in SBF solution of the obtained Co/ZrO 2 composite films, are characterized using optical microscopy, scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS) system, atomic force microscopy (AFM), ultrahigh-micro-topography, linear polarization and electrochemical impedance spectroscopy (EIS) techniques. The results indicate that, ZrO 2 particles are uniformly dispersed into Co matrix and influence the surface microtopography, microhardness and corrosion behavior of composite coatings obtained. Coating thickness increases with increased current density as well as the surface roughness and microhardness. At the same time, the results obtained by polarization curves and EIS methods show that, when compared with the traditional polycrystalline Co film, the obtained Co/ZrO 2 composite film exhibits the enhanced corrosion resistance in SBF solution.

Alternative blended cement with ceramic residues: Corrosion resistance investigation on reinforced mortar

Blended cements are largely used for concrete: they are usually considered cements with a low environmental impact, as they require less clinker than ordinary Portland cement (OPC). Different constituents can be used as supplementary clinker component usually leading to cement with high resistance to outdoor environment. Polishing residue (PR), coming from porcelain stoneware tiles production, can be successfully used as new constituent for blended cement, however its action for enhancing the durability of cement matrix must be assessed. With this purpose, electrochemical tests (half cell potential, impressed voltage and linear polarization techniques) have been carried out on steel reinforced mortar samples, prepared using a 25% PR based cement and 100% OPC as binder and exposed to a 3.5% NaCl solution. The corrosion resistance results and microstructure analysis highlight better durability performances for PR based cement than those exhibited by OPC, mainly for curing time > 28 days.

Performance evaluation of organic coatings against corrosion in reinforced cement mortars

Protection against corrosion in reinforced concrete structures is commonly accomplished by the usage of organic coatings which are applied on the surface of the mortars. Nine coatings from five major categories produced in Greek industry were studied in order to evaluate their performance when applied on cement mortars and exposed to highly corrosive environment under the presence of chloride ions or carbon dioxide. An appropriate series of tests was conducted in order to examine and verify the protection of the coatings against corrosion. The implemented evaluation methods included: (a) half-cell potential measurements and linear polarization technique to determine the protection provided by coatings against chloride ions corrosion, (b) carbonation depth measurements, (c) estimation of the mass loss that steel rebars exhibit after the end of the experiment and (d) determination of liquid water and water vapour transmission rate for the coatings tested. The results suggest that acrylic coatings can offer a satisfying protection level against carbonation and elastomeric coatings can protect rebars from chloride ions corrosion.

Corrosion behavior of mild steel in the presence of scale inhibitor in sulfuric acid solution

Surfactants such as non-ionic polyethylene glycol tert-octylphenyl ether (Triton X-114) have been studied as efficient corrosion inhibitors in acid medium. In this study inhibition performance of Triton X-114 has been evaluated as corrosion inhibitor for mild steel in 0.5 mol l−1 H2SO4. The electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and linear polarization (LPR) techniques has been applied to determine the electrochemical behaviour of Triton X-114. The maximum efficiency of Triton X-114 was found as 96% at the concentration 5.0 × 10−5 mol l−1. The adsorption isotherm of inhibitor on the mild steel surface was found to be in a good agreement with the Langmuir and the standard free energy value (ΔGads°) was calculated as −50.1 kJ mol−1, which shows that adsorption of Triton X-114 on the mild steel surface improves the inhibition characteristics in 0.5 M H2SO4.

Structure and electrochemical properties of ball-milled Co-carbon nanotube composites as negative electrode material of alkaline rechargeable batteries

A series of cobalt-carbon nanotube (CNT) composites is synthesized by direct ball-milling of Co and CNT powders with different Co/CNT weight ratios. The microstructure, morphology and chemical state of the ball-milled Co-CNT composites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It is found that metallic Co nanoparticles of 50–100 nm in size are highly dispersed on the inactive CNT matrix after ball-milling. The electrochemical performance of Co-CNT composites as negative electrode material of alkaline rechargeable batteries is investigated by galvanostatic charge–discharge, linear polarization and cyclic voltammetry (CV) techniques. The results show that the Co-CNT composite (weight ratio 5/1, BM 10 h) displays the optimized electrochemical performance, including discharge capacity and cycle stability. The reversible faradaic reaction between Co and Co(OH) 2 is dominant for ball-milled Co-CNT composites.

The Influence of HSO<sub>3</sub><sup>-</sup> Activity on Electrochemical Characteristics of Copper

The electrochemical behavior of copper in various concentrations of NaHSO3 solution was investigated with linear polarization and cyclic voltametry technique at room temperature. The results showed that the concentration of bisulfite ions has noticeable effects on the behavior of copper. With HSO3 -concentration increasing, the passivity region, ascribed to the formation of absorption layer Cu (HSO3) ads - or Cu (SO4) ads 2-, appearing at the lower potential range in the polarization curve inclined to transform into an active region; whereas another passivity region, due to the appearance of CuO or Cu2O layer on the surface, took place at a higher potential region. The formation and the reduction of CuO or Cu2O were irreversible.

Inhibition effect of environmentally benign Karanj (Pongamia pinnata) seed extract on corrosion of mild steel in hydrochloric acid solution

The inhibition of the corrosion of mild steel in hydrochloric acid solution by the seed extract of Karanj (Pongamia pinnata) has been studied using weight loss, electrochemical impedance spectroscopy, potentiodynamic polarization, and linear polarization techniques. Inhibition was found to increase with increasing concentration of the extract. The effect of temperature, immersion time, and acid concentration on the corrosion behavior of mild steel in 1 M HCl with addition of extract was also studied. The adsorption of the extract on the mild steel surface obeyed the Langmuir adsorption isotherm. Values of inhibition efficiency calculated from weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy are in good agreement. Polarization curves showed that Karanj (P. pinnata) seed extract behaves as a mixed-type inhibitor in hydrochloric acid. The activation energy as well as other thermodynamic parameters for the inhibition process was calculated. The adsorbed film on mild steel surface containing Karanj (P. pinnata) seed extract inhibitor was also measured by Fourier transform infrared spectroscopy. The results obtained showed that the seed extract of Karanj (P. pinnata) could serve as an effective inhibitor of the corrosion of mild steel in hydrochloric acid media.