Electrochemical Polarization Measurements Research Articles

The effect of the ultrasound agitation and source of ceria particles on the morphology and structure of the Zn–Co–CeO2 composite coatings

The goal of this research was to develop and analyse novel Zn–Co–CeO 2 protective coatings on steel. Two different sources of ceria (CeO 2 ) particles were employed: commercial powder and synthesized stable colloidal dispersion-sol. The plating solution was agitated by ultrasounds (20 and 30 W cm −2 ) or by magnetic stirrer (300 rpm) during electrodeposition. The CeO 2 particles used were characterized by different methods, namely scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) to compare the morphology, crystallinity and particle size. The morphology of developed composite coatings was analysed by SEM, the preferred texture was calculated based on XRD results and corrosion behaviour was evaluated by electrochemical impedance spectroscopy (EIS) and polarization measurements. Utilizing ultrasounds during electrodeposition resulted in advanced properties of the nanocomposite coatings compared to magnetic stirring. The particle content in the coatings increased to ~5 wt% when ultrasounds were applied and ceria sol used as a source of particles. Presence of ceria in composite coatings offered favourable action in corrosion behaviour increasing barrier properties of composite coatings, thereby providing a prolonged lifetime of Zn–Co alloy coatings. The benefit was more pronounced in the case of ceria sol, and deposition at 20 W cm −2 , when values of impedance modulus at low frequencies reached four times higher values after 4 days exposure to 3 wt% NaCl solution than for coatings deposited with magnetic stirring for both ceria source. The lowest value of corrosion current density (2.15 μA cm −2 ) was determined for Zn–Co–CeO 2 (CeO 2 sol) composite coatings deposited under 20 W cm −2 US power.

Acidic surface treatment of mild steel with enhanced corrosion protection for silane coatings application: The effect of zinc cations

Surface pretreatment is a key influential parameter on the protective function of silane coatings. The present study considers examining the effect of zinc cations addition to acid pretreatment solution on subsequent silane coating corrosion protection on mild steel. The electrochemical properties of subsequent silane coating on pretreated plates were assessed by electrochemical impedance spectroscopy and polarization measurements. The polarization resistance increased approximately two times in the presence of 3 g·L−1 zinc cations, which agreed with electrochemical impedance spectroscopy data. Energy-dispersive X-ray spectroscopy (EDS) detected 3.13 wt% Zn on the zinc cation-pretreated substrate. Field emission scanning electron microscopy revealed surface morphological changes of pretreated samples in the presence of zinc cations. Contact angle, atomic force microscopy, grazing incidence X-ray diffraction, and EDS tests on the surface of pretreated samples evidenced that zinc cations reduced the oxidation and corrosion attacks on the steel surface. Raman spectroscopy revealed formation of a complex between Zn2+ cations and the organic inhibitor.

Nano-TiO2 Coating Layers with Improved Anticorrosive Properties by Aerosol Flame Synthesis and Thermophoretic Deposition on Aluminium Surfaces.

TiO2 in the form of nanoparticles is characterized by high photocatalytic activity and high resistance to oxidation, making it an excellent candidate to realize coatings for improving the corrosion resistance of aluminium surfaces. Different coating technologies have been proposed over the years, which often involve the use of toxic compounds and very high temperatures. In this work, an alternative and novel one-step method for the coating of aluminium alloy surfaces with titania nanoparticles is presented. The method is based on the combination of aerosol flame synthesis and direct thermophoretic deposition and allows to produce nanostructured thin coating layers of titania with different features. Specifically, 3.5 nm anatase nanoparticles were synthesized and deposited onto aluminium alloy AA2024 samples. The thickness of the coating was changed by modifying the total deposition time. A thermal annealing treatment was developed to improve the adhesion of nano-titania on the substrates, and the morphology and structures of the coatings were characterized using (ultra violet) UV-vis absorption, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The corrosion resistance behavior of the coatings was evaluated by means of electrochemical polarization measurements, coupled with a numerical analysis using COMSOL software. Both the experimental and numerical electrochemical polarization curves showed a significant increase in the corrosion potential of coated substrates with respect to the bare aluminium and a decrease in the current density. The coatings obtained with higher deposition time and greater thickness showed the best performances in terms of the resistance of the aluminium surfaces to corrosion.

Evaluation of the Wear Resistance and Corrosion Behavior of Laser Cladding Al/SiC Metal Matrix Composite Coatings on ZE41 Magnesium Alloy

Aluminum matrix composites reinforced with SiC particles (SiCp) were deposited on ZE41 magnesium substrates by laser cladding in order to improve their tribological performance. Silicon and titanium were added to the matrix in order to avoid Al-SiC reactivity. The addition of these elements to avoid Al4C3 formation during the laser cladding fabrication was successfully explored in previous research, but the effect of these elements on the wear behavior and the corrosion resistance of these coatings has not been studied. During the fabrication process, there is dilution with the substrate that forms an Al-Mg matrix, which has an influence on the wear and corrosion behavior. Electrochemical polarization and impedance measurements in a 3.5% NaCl solution and the dry sliding conditions on a pin-on-disc tribometer were used to evaluate the different compositions of Al/SiCp coatings on the ZE41 magnesium alloy and uncoated ZE41. All of the composite coatings had lower wear rates than the substrate. However, the coatings showed worse corrosion behavior than the ZE41 substrate, although the addition of Si or Ti improves the corrosion behavior and the wear resistance.

Effect of pH and Immersion Time on the Corrosion Protection of SDBS:ZnSO<sub>4 </sub>Pretreated Mild Steel in Sodium Chloride Solution

In this study, mild steel was treated with SDBS:ZnSO4 compound by immersing the mild steel substrates in a SDBS:ZnSO4 bath of varying pH. The effect of bath solution pH and immersion time on the corrosion protection properties of SDBS:ZnSO4 pre-treated mild steel in sodium chloride solution was investigated using electrochemical impedance spectroscopy (EIS) and polarization measurements. From the EIS results, it was found that the inhibition efficiency provided by the pre-treatment was significantly affected by the pH of the bath solution, where inhibition was highest at pH 6. This is due to the formation of a good protective layer on mild steel substrate caused by the deposition of zinc hydroxide/oxide and SDBS compound. Increasing the immersion time from 1 h to 24 h increased the inhibition efficiency. From the polarization measurements, the current density was significantly reduced, and the shift to a more positive corrosion potential value indicated a higher protection layer was formed on the metal surface during more prolonged immersion. It has been found that longer pre-treatment immersion time allows a denser protective layer formed, which prevented the diffusion of water towards the mild steel substrate that can lead to corrosion.

Anti-Corrosive Substance as Green Inhibitor for Carbon Steel in Saline and Acidic Media

Ficus (FIC) leaf extract used as corrosion inhibitor for carbon steel alloy (C.S) in two corrosive environments (saline and acidic) with four concentrations (1, 2, 3 and 4 ppm) at varied temperature range between (298-328 K) using electrochemical polarization measurements. The importance of this work focused on the use the green chemistry that is far from the chemical materials effect. The results of polarization presented the FIC inhibitor consider a mixed type (anodic and cathodic) inhibitor. Tafel curve used to evaluate the corrosion inhibition activity. In a saline medium, the best inhibitor efficiency reaches to (87%) in 2 ppm and IE% reach to (99%) for HCl medium inhibited by 1ppm. Langmuir isotherm obeys the study by thermodynamic parameters and confirms the physical adsorption.

Electrochemical Deposition and Spectroscopy Investigation of Zn Coatings on Steel

A three-electrode electrochemical cell was used for the optimization of bath constituents and parameters. Galvanostatic electrodeposition from a free additives bath, combining sulfate and chloride compounds results in bright Zn deposits with high corrosion resistance. Surface morphology was observed by scanning electron microscopy, chemical and phase composition were determined by X-ray diffraction, and corrosion investigations by electrochemical techniques. Electrochemical impedance spectroscopy (EIS) and polarization measurements revealed that the electrodeposited Zn coating with the higher current density and pH value had the best corrosion resistance. Bright and uniform surface appearance, of Zn deposits, with a platelet structure, moderate current efficiency and a high corrosion resistance was obtained at a pH of 4.5 and a current density of 16 mA cm−2.

Corrosion Behavior of Cold-Formed AA5754 Alloy Sheets.

In this work, the influence of bending an AA5457 alloy sheet and the resulting microstructural changes on its corrosion behavior was investigated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to perform detailed microstructural analyses of the alloy in its original form and after bending. After immersion in naturally-aged NaCl under open-circuit conditions (0.5 M, adjusted to 3 by HCl), post-corrosion observations were made, and electrochemical polarization measurements were performed to investigate the corrosion mechanisms occurring on both surfaces. The results showed that the corrosion of AA5457 is a complex process that mainly involves trenching around coarse Si-rich particles, crystallographically-grown large pits, and the formation of multiple tiny pits around Si-rich nanoparticles. The experimental data showed that bending AA5457 changed the shape and distribution of Si-rich coarse particles, cumulated a higher dislocation density in the material, especially around Si-rich nanoparticles, and all of these factors caused that corrosion behavior of the AA5754 in the bending area was lowered.

Corrosion inhibition of mild steel by N, N’-(5,5- dimethylcyclohexane-1,3-diylidene)dianiline in acid media: Gravimetric and electrochemical evaluations

The corrosion inhibition efficiency of the Schiff base N,N’-(5,5-dimethylcyclohexane-1,3-diylidene)dianiline (DmChDa) on mild steel in 1M HCl and 0.5M H2SO4 was evaluated using gravimetric, electrochemical impedance spectroscopy, potentiodynamic polarization and electrochemical noise measurement. Experimental results established that DmChDa possess relatively high corrosion inhibition capacity. Langmuir and El-Awady adsorption isotherms were obeyed by the Schiff base in 1M HCl and 0.5M H2SO4 respectively. SEM analysis showed that DmChDa was adsorbed on the steel surface during corrosion inhibition. The variation of metal dissolution with temperature was also examined using gravimetric study.

Chamber Protection of Copper from Atmospheric Corrosion by Compounds of the Triazole Class

Using a set of physicochemical (ellipsometry and contact angle measurements), electrochemical (electrochemical impedance spectroscopy and polarization measurements), and corrosion (periodic moisture condensation and salt fog tests) methods, the properties of adsorption films formed on copper by the chamber method from vapors of benzotriazol (BTA), 1H-1,2,4-triazole, tolyltriazole (TTA), 5-chloro-1,2,3-benzotriazole (CBTA), 3-amino-1H-1,2,4-triazole, and 4-amino-1H-1,2,4-triazole at a temperature of 100°C are studied. It is shown that 1-h chamber treatment of copper with vapors of these compounds leads to the formation of nanoscale hydrophobic adsorption films on it, which inhibits the thermal growth of oxides, but stabilizes the passive state of the metal and increases its corrosion resistance. Among these different triazole compounds tested as chamber corrosion inhibitors, BTA and its substituted derivatives are distinguished. After a 1-h chamber treatment of copper, the protective aftereffect of the adsorption films of triazole derivatives grows symbatically with their saturated vapor pressure at the chamber treatment temperature, i.e., in the following increasing order: CBTA < TTA < BTA. This may indicate that the equilibrium adsorption films do not have time to form at 100°С on the metal within this time period. After a prolonged (24 h or more) chamber treatment of copper with vapors of substituted benzotriazoles, equilibrium adsorption films of inhibitors are formed on it. In this case, the influence of the chamber inhibitor properties on their protective aftereffect alternates. Under such conditions, the least volatile and most hydrophobic substituted benzotriazole, i.e., CBTA, provide the best metal protection.

Correlation between Microstructural Characteristics and Corrosion Properties of Mg-RE Alloys in Ringer’s Solution

The effects of aging heat-treatment and cooling rate from annealing temperature on the microstructure and corrosion properties of a cast Mg-5Gd-2.5Nd-0.5Zn-0.5Zr alloy were studied. The as-cast structure comprised Gd/Nd-rich eutectic phases in α-Mg grain boundaries. In water-quenched and aged specimens, fine Zn/Zr-rich precipitates were developed in the matrix. Furnace cooling caused a significant increase in the volume fraction of both fine and coarse precipitates because of the large difference between the solubility of alloying elements at elevated and room temperatures. Immersion tests for up to 240 h in Ringer’s solution showed a respective corrosion rate of 0.84, 0.73, 0.41, and 0.39 mm y−1 for the furnace-cooled, as-cast, water-quenched, and aged samples. The corrosion behavior was further studied by electrochemical impedance spectroscopy and polarization measurements after 1 and 24 h of immersion in the solution. An increase in the volume fraction of Gd/Nd-rich phases led to a decrease in the corrosion resistance. Large second phases acted as cathodic sites for galvanic corrosion and also locally disturbed the protectiveness of the Mg(OH)2 passive film. Rare earth elements in solid-solution were less detrimental to the corrosion resistance. Less severe corrosion resulted according to SEM observations in the aged and water-quenched samples.

Soft magnetic properties and corrosion resistance of the annealed (Fe0.7Co0.15Ni0.15)75B21Nb4 metallic glasses

The phase structure, magnetic properties and corrosion resistance in the as-spun and annealed (Fe0.7Co0.15Ni0.15)75B21Nb4 metallic glasses (MGs) were investigated. Annealing below glass transition temperature at 693 K causes a reduction in coercivity and ameliorates the soft magnetic properties, originating from the formation of a homogeneous glassy structure. The hysteresis loops of the as-annealed ribbons, especially the 888 K-annealed one, appear to be more rectangular in their geometry, showing that the approach to saturation becomes more expeditious. The synergy of amorphous phase and nano-size magnetic α-Fe(Co) phase in the 753 K-annealed ribbon leads the improvement of saturation magnetization. The corrosion behaviors in seawater solution have been investigated by electrochemical polarization measurement. By evaluating the corrosion potential and current density, annealing treatment induces the detrimental influence in the general corrosion resistance of MG ribbons. However, compared with as-spun amorphous state, the 693 K-annealed relaxation ribbon exhibits superior passivity with lower passive current density and higher pitting resistance as revealed by wider passive region.

Molecular structure and mild steel/HCl corrosion inhibition of 4,5-Dicyanoimidazole: Vibrational, electrochemical and quantum mechanical calculations

Raman (3500-50 cm−1) and FT-ATR/FT-infrared (3500-500/4000-200 cm−1) spectrum of 4,5-Dicyanoimidazole (DCI) were recorded and analyzed by normal coordinate analysis calculations. In addition, we have studied the molecular structure of DCI by means of B3LYP Density Functional Theory (DFT) using 6-31g(d) basis set. Aided by computational outcomes, all vibrational bands were assigned quantitatively to their corresponding fundamentals. The corrosion inhibition efficiency of DCI towards mild steel in 1.0 M HCl has been investigated experimentally and theoretically. Electrochemical impedance spectroscopy, electrochemical frequency modulation and polarization measurements along with thermodynamic predictions were assigned to both the anodic and cathodic inhibition. DCI-metal interactions and charge reallocation were analyzed in terms of Frontier molecular orbital (FMO) and Natural bond orbital (NBO) analysis. Global reactivity descriptors; ionization potential (IP), electron affinity (A), electronegativity (χ), chemical potential (µ), chemical hardness (η), and electrophilicity index have been calculated and assigned to the inhibition efficiency. Good correlation between the theoretical calculations and experimental measurments has been achieved. The results are compared with similar molecular systems whenever appropriate.

Effect of Nd addition on the microstructure, mechanical properties, shape memory effect and corrosion behaviour of Cu–Al–Ni high-temperature shape memory alloys

The effects of rare earth element Nd on the microstructure, mechanical, shape memory properties and corrosion behaviour of Cu-13.0Al-4.0Ni-xNd (wt.%) high-temperature shape memory alloys were investigated in this paper. It was observed that the grains in Cu-13.0Al-4.0Ni-xNd alloys can be refined by adding Nd, and the grain size decreased from the millimeter scale to several hundred microns. The matrix of the Cu-13.0Al-4.0Ni-xNd alloys, composed of 18R and 2H martensite, was not changed by Nd doping. However, the hexagonal (Al,Ni)Cu4Nd phase was formed as the Nd content increased. The grain refinement led to an improvement in the mechanical properties of the Cu-13.0Al-4.0Ni-xNd alloys. When x = 0.5, the compressive fracture stress and strain increased from 580 MPa to 10.5% to 940 MPa and 18.3%, respectively. The Nd addition also enhanced the shape memory effect of the Cu-13.0Al-4.0Ni-xNd alloys, and a reversible strain of 6.8% was obtained for x = 0.2 under a prestrain of 10% after heating. In addition, the results of electrochemical impedance measurement and polarization measurement showed that the corrosion resistance of Cu–Al–Ni alloy were slightly reduced by Nd addition, and the corrosion behaviour of Cu–Al–Ni alloy was mainly controlled by Cu element.

Corrosion Inhibitive Capacity of Vanillin-Based Schiff Base for Steel in 1 M HCl

The inhibitive action of novel vanillin-based Schiff base for corrosion of steel in 1 M hydrochloric acid solution was evaluated by experimentally at the temperature range of 301–331 K. The computed inhibition efficiency of the inhibitor increases with the increasing its concentration as on 10 to 50 ppm. At the same time, inhibition efficiency decreases with the increasing temperature as on 301 to 331 K. Therefore, the increasing inhibition efficiency was attributed to the adsorption of inhibitor molecules onto the steel surfaces, and decreasing inhibition efficiency is because of desorption of inhibitor molecules from steel surfaces to the solution. The electrochemical polarization measurements proposed that the examined vanillin-based Schiff base as an inhibitor in nature, which reduces the corrosion of steel, decreases both anodic and cathodic reactions. In this study, the adsorption of the inhibitor complies with the Freundlich adsorption isotherm and depending on that, they chose compound as a corrosion inhibitor for steel in 1 M HCl through the mixture of physisorption and chemisorption. At long last SEM pictures show the visual thought of the development of the defensive layer onto the steel surfaces, which hinders the corrosion.

Organic-inorganic hybrid anticorrosion coatings with aniline substituted group

Sol-gel method is the most popular way for the preparation of organic-inorganic hybrid anticorrosion coatings. Such sol-gel coatings is environmental friendly and chemical stable, showing enhanced corrosion resistance for metal substrates. Here, a saline with aniline substituted group N-(3-(trimethoxysilyl)propyl)aniline (TMPA) has been used together with tetraethyl orthosilicate (TEOS) for the preparation of organic-inorganic hybrid coating (OIHC) materials by sol-gel approach. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) measurements show that the hybrid coatings exhibit high corrosion resistance on aluminum substrates.

Corrosion Behaviors of the Eutectic Structure in Zn-Al-Mg Alloy Coated Steel in Chloride Containing Aqueous Environment

To clearly understand the effect of the eutectic structure in the Zn-Al-Mg alloy coating on the corrosion behaviors in chloride containing aqueous environments, a bulk Zn-MgZn&lt;sub&gt;2&lt;/sub&gt; sample was fabricated by diffusion bonding process, and a variety of experiments, such as electrochemical polarization and galvanic corrosion measurements, salt spray tests, and cyclic corrosion tests, were carried out. This study revealed that the corrosion potential values of MgZn&lt;sub&gt;2&lt;/sub&gt; and Zn samples exposed to a 5 wt.% of NaCl solution were approximately -1.5 and -1 VSCE, respectively, and the MgZn&lt;sub&gt;2&lt;/sub&gt; showed a higher corrosion current density than Zn at the early stage of corrosion. The continued dissolution of MgZn&lt;sub&gt;2&lt;/sub&gt; phase from the eutectic structure in the coating layer provides not only sacrificial protection, but also environmental conditions for the co-formation of two types of corrosion products (simonkoleite (Zn&lt;sub&gt;5&lt;/sub&gt;(OH)&lt;sub&gt;8&lt;/sub&gt;Cl&lt;sub&gt;2&lt;/sub&gt;·H&lt;sub&gt;2&lt;/sub&gt;O) and hydrotalcite (ZnAl&lt;sub&gt;2&lt;/sub&gt;(OH)&lt;sub&gt;6&lt;/sub&gt;Cl&lt;sub&gt;2&lt;/sub&gt;·H&lt;sub&gt;2&lt;/sub&gt;O)) which have an inhibiting effect on the outer surface. The formation areas and kinetics of the two products on the coating surface were different, and they were greatly dependent upon the types of eutectic structures in the coating layer. Based on the results, a modified anti-corrosion mechanism of Zn-Al-Mg alloy coated steel sheet in chloride containing aqueous environment was proposed.

CORROSION AND WEAR PERFORMANCE OF ZA27/GRAPHENE/B4C HYBRID NANOCOMPOSITES PRODUCED BY POWDER METALLURGY

In this research paper, dry sliding (unlubricated), corrosion and abrasive wear behavior of ZA27/ Graphene/ B4C hybrid nanocomposites were studied. The hybrid nanocomposite samples were fabricated by powder metallurgy technique. Tribological tests were performed by employing a ball-on-disc type in the unlubricated situation and different loads (1, 2, 5 and 10 N). The examination of the worn and corroded surfaces, the powder characterization was performed using scanning electron microscopy (SEM). The findings indicated that the increase in B4C nano-particle content can positively effect on the corrosion and wear behavior of the hybrid nanocomposites. The electrochemical polarization measurements showed that increasing of the nano B4C content causes high corrosion resistance in the hybrid nanocomposites. The corrosion tests showed that the corrosion rate value of the ZA27/Graphene/B4C hybrid nanocomposites decreased from 59.02 mpy to 16.77 mpy with increasing the nano B4C content from 0.25% to 2%.&#x0D;

Isatin thiosemicarbazone derivatives as inhibitors against corrosion of AA6060 aluminium alloy in acidic chloride medium: substituent effects

Five isatin thiosemicarbazone derivatives bearing different substituents (R) at 5-position of the isatin moiety, ISA-R, being R = -H, -CH3, -F, -Cl and -NO2, were synthesized and fully characterized. The corrosion inhibition action of ISA-R on AA6060 aluminium alloy in acidic chloride medium was studied in relation to the substituent effects using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), electrochemical potentiodynamic polarization (PDP) and weight loss measurements. The results showed that the inhibition behaviors of ISA-R were strongly correlated with the substituent modifications. ISA-NO2 was found to possess the highest capability to increase the corrosion resistance of the alloy and ISA-Cl exhibited some inhibition efficacy, whereas the others have little action. ISA-H, ISA-F, ISA-Cl and ISA-NO2 acted as cathodic-type inhibitors, and ISA-CH3 as a mixed-type inhibitor primarily retarding the cathodic processes of the alloy in the corrosion solution. ISA-R can be adsorbed on the alloy surface as evidenced by the results of EDS and XPS. The π-electron density on the isatin ring of ISA-NO2 is more deficient over the other ISA-R, which facilitates the adsorption of ISA-NO2 and formation of a barrier film on the alloy surface, and accordingly enhances its anti-corrosive performance for the alloy.

Impact of Soil Characteristics and Moisture Content on the Corrosion of Underground Steel Pipelines

External corrosion of underground steel structures is a major environmental and economic burden. The severity of such detriment depends on many factors that encompass: soil properties, moisture content, total soluble salts, the presence of microorganism, and method of metal protection. The investigative endeavor put forth bestows prime attention to the effect of soil attributes and moisture loading on the corrosion of submerged steel structures. The exposure to four discrete soil types (saline, clay, calcareous and sand) was explored in this study. Electrochemical linear polarization measurements were deployed as a means of assessing corrosion performance. The results revealed corrosion event severities endured by steel to be strongly underpinned by soil overall characteristics and moisture content in the vicinity. Corrosion potentials were found to possess more negative values with rising soil moisture content. The corrosion rate was rendered consistently peaking in coincidence with 20% (by wt.) moisture contents pertinent to sand, and with a corresponding 25% content in clay, saline and calcareous soils. The corrosivity of soil at the critical soil moisture content increases in the order: calcareous < clay < saline < sand. Scanning electron microscope observations confirmed the existence of corrosion product (loose and porous) with evidence of pitting attack. EDX analysis proved that the corrosion product was mainly composed of iron oxide. Plate counts revealed the absence of bacteria which warrants the exclusion of any microbial detriment as a contributing factor that might underpin corrosion.