Comparative study of Nb, Nb-10W, and Nb-16Ta-12W corrosion behavior in sodium hydroxide solutions

The electrochemical behavior of niobium, Nb-10W, and Nb-16Ta-12W alloys is investigated in sodium hydroxide solutions at different temperatures, using open-circuit potential (OCP) measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). OCP and polarization measurements show that the three materials are spontaneously active in 10, 15, and 30 wt.% NaOH at 25, 50, and 75 °C. The anodic polarization curves show in all cases a dissolution-passivation peak followed by a current plateau, corresponding to oxides formation. The spontaneous active corrosion of the three materials mainly leads to the formation of sodium niobates, as detected by X-ray diffraction analysis of the corrosion products. The evolution of the corrosion current densities obtained from Tafel extrapolation of polarization curves and the polarization resistance values determined from EIS measurements indicate that the corrosion rates of Nb, Nb-10W, and Nb-16Ta-12W alloys increase with increasing NaOH concentration and temperature. In all cases, the increasing order of corrosion resistance is: Nb<Nb-10W<Nb-16Ta-12W.     

Effects of minor additions of ruthenium on the passivation of duplex stainless-steel corrosion in concentrated hydrochloric acid solutions

The effects of minor additions of ruthenium (0.14%, 0.22%, and 0.28%) on the passivation of duplex stainless-steel (DSS, Fe–22%Cr–9%Ni–3%Mo) corrosion in 2 M HCl solutions have been studied using open-circuit potential (OCP), potentiodynamic cyclic polarization, potentiostatic current–time, electrochemical impedance spectroscopy (EIS), and weight loss measurements. OCP measurements showed an increased shift in the corrosion potential to more positive values with increasing Ru content. Polarization and EIS experiments indicated that the presence of Ru and the increase of its content decrease the corrosion rate, critical and passive current density, and polarization resistance. Moreover, it shifts the corrosion and pitting potentials to more positive values. Current–time measurements at −100, −50, and 50 mV versus Ag/AgCl also confirmed that the severity of pitting corrosion decreases with an increasing Ru content. Weight-loss time data showed good agreement with the electrochemical measurements.     

Sweet aqueous solution for electrochemical synthesis of polypyrrole: Part 1-A. On non-ferrous metals

The electrosynthesis of polypyrrole (PPy) has been achieved on aluminum electrode in aqueous medium of 0.1 M saccharin sodium salt and 0.5 M pyrrole. Scanning electron microscopy shows that the PPy coating obtained in galvanostatic and potentiostatic modes starts with small islands at weak applied potentials or current densities. Moreover, energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) reveal a good homogeneity of the film achieved in cyclic voltammetry during 10 cycles. The electrochemical impedance spectroscopy (EIS) results show that the coating decreases the polarization resistance of the aluminum electrode. The open circuit potential (OCP) and dc polarization measurements achieved in HCl and NaCl solutions displayed a large positive displacement of corrosion potential and a reduction of corrosion current in the case of PPy coating electrode in comparison with electrode bare.     

Mica/polypyrrole (doped) composite containing coatings for the corrosion protection of cold rolled steel

Micas/polypyrroles (PPys) doped with molybdate, p-toluene sulfonate, dodecyl benzene sulfonate, and 2-naphthalene sulfonate composite pigments were synthesized by chemical oxidative polymerization and characterized in coatings for corrosion protection on cold rolled steel substrate by various electrochemical techniques. Synthesized composite pigments were characterized for morphology by scanning electron microscopy, which indicated physical formation of PPy on the surface of mica. Chemical composition of the composite pigments was analyzed by X-ray photoelectron spectroscopy which chemically confirmed doped PPy formation on the mica surface. Coatings were formulated at 20% pigment volume concentration (composite pigments or as-received mica pigment) and were applied on cold rolled steel substrate. Coatings were exposed to salt spray test conditions (ASTM B117) for 30 days and were periodically assessed for corrosion with electrochemical impedance spectroscopy (EIS), open circuit potential (OCP), and potentiodynamic polarization. EIS and circuit modeling results demonstrated higher coating resistance (R _c) for mica/PPy (doped) composite coatings as compared to as-received mica pigment containing coating after 30 days of salt spray exposure. Lower current density and more positive corrosion potential values were observed for mica/PPy (doped) composite coatings as compared to mica pigment-based coating in potentiodynamic polarization measurements, indicating improved corrosion protection for cold rolled steel substrate. OCP measurements revealed more positive values for mica/PPy (doped) composite coatings as compared to mica pigment-based coating suggesting superior corrosion protection for mica/PPy (doped) composites.     

Influence of Various Albumin Concentrations on the Corrosion Resistance of Zr-2.5%Nb Alloy

The Zr-2.5% Nb alloy corrosion resistance in four saline solutions with and without albumin was tested through electrochemical measurements of electrochemical impedance spectroscopy (EIS), linear polarization, and cyclic voltammetry at human body temperature.

The EIS measurements were performed at open circuit potential. The impedance spectra were recorded and the equivalent electric circuits were elaborated. From the linear polarization the Tafel slopes were recorded and the corrosion parameters were calculated. From the potentiodynamic polarization curves, the breakdown potential, the protection potential, and the protection domain were observed.

The amount of ions released from the material was quantified using the ICPMS technique and the results concerning the corrosion resistance were compared with those obtained from linear and cyclic polarization.

Before and after potentiodynamic polarization the topographic measurements were performed; the roughness at the samples surface was observed using AFM. The roughness was co-related to the contact angle measurements.     

Corrosion protection of mild steel by polyvinylsilsesquioxanes coatings in 3% NaCl solution

Polyvinylsilsesquioxanes (PVS) coatings were synthesized by the hydrolytic polycondensation of vinyltrimethoxysilane using hydrochloric acid as a catalyst. Their structure was characterized by Fourier transform IR (FTIR) and the viscosity [in centipoise(cP)] of polyvinylsilsesquioxanes was measured at 298 K. The electrochemical behavior of I–IV coated steel electrodes, of polymer concentration as follows: [I(20%), II(40%) of viscosity 50 cP and III(20%), IV(40%) of viscosity 15 cP], was investigated in 3% NaCl solution using various electrochemical techniques, i.e., open-circuit potential (OCP), potentiodynamic polarization, electrochemical impedance measurements (EIS), and surface examination via scanning electron microscope (SEM) technique. The influence of immersion time on the electroctrochemical behavior of polysilsesquioxane-coated electrodes was also studied. The results of polarization measurements showed that corrosion current density (i _corr) decreases in the order IV > III > II > I. Also, the film resistance is the highest for PVS-coated electrode I as evaluated from EIS measurements. OCP, EIS, and polarization results are in good agreement with each other. The obtained results were confirmed by surface examination using scanning electron microscope.     

Effect of sodium molybdate on the corrosion behavior of cold rolled steel in peracetic acid solution

The effect of sodium molybdate (Na₂MoO₄) on the corrosion of cold rolled steel (CRS) in peracetic acid (PAA) solution was investigated by gravimetric measurements, Tafel polarization curves, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). All the data indicate that Na₂MoO₄ acts as a very good inhibitor in PAA solution. The inhibition efficiency increases with increasing concentration of Na₂MoO₄ and immersion time. The inhibition efficiencies, calculated from gravimetric measurements, Tafel polarization curves and electrochemical impedance spectroscopy, are in reasonably good agreement and are very similar in the three cases. Furthermore, polarization data show that Na₂MoO₄ behaves as an anodic passive type inhibitor. Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) were used to characterize the corrosion surface. A probable mechanism is presented to explain the experimental results.     

Corrosion behavior of DLC-coated NiTi alloy in the presence of serum proteins

Uniform and adherent diamond-like carbon (DLC) coatings are deposited on NiTi alloy by arc enhanced magnetron sputtering (AEMS). The effects of serum proteins, bovine serum albumin (BSA) and fibrinogen (Fib) on the corrosion behavior of DLC-coated NiTi alloy in phosphate buffer saline (PBS) solution are investigated at 37 °C using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. The results show that DLC coatings, which enhance the corrosion resistance of the NiTi alloy especially in the presence of BSA, move the OCP to the positive direction, increase the polarization resistance, lower the corrosion current density, and enhance the breakdown potential. The presence of fibrinogen shows the similar effect but less notable than BSA. The associated mechanism is also discussed.     

Localized corrosion of carbon steel in a CO2-saturated oilfield formation water

In this work, corrosion and localized corrosion behavior of X65 pipeline steel were studied in a simulated, CO₂-saturated oilfield formation water by various electrochemical measurement techniques, including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, galvanic current and localized EIS (LEIS). The morphology and composition of the formed corrosion scale were characterized by scanning electron microscopy and energy-dispersive X-ray analysis. A conceptual model was developed to illustrate the occurrence of localized corrosion of the steel under scale. Both galvanic current and LEIS measurements showed that a galvanic effect existed between the bare steel and the scale-covered region. The scale-covered region served as cathode and the bare steel site as the anode. The big cathode vs. small anode geometry accelerated the local corrosion reaction. At an elevated temperature, a compact, crystalline scale was formed on the steel surface, enhancing the galvanic effect. Moreover, the stability of the scale was increased with time, and localized corrosion of the steel under scale experienced mechanistic changes with time.     

Electrochemical behavior and anticorrosion properties of modified polyaniline dispersed in polyvinylacetate coating on carbon steel

Conducting polyaniline (Pani) was prepared in the presence of methane sulfonic acid (MeSA) as dopant by chemical oxidative polymerization. The Pani-MeSA polymer was characterized by FT-IR, UV-vis, X-ray diffraction (XRD) and impedance spectroscopy. The polymer was dispersed in polyvinylacetate and coated on carbon steel samples by a dipping method. The electrochemical behavior and anticorrosion properties of the coating on carbon steel in 3% NaCl were investigated using open-circuit potential (OCP) versus time of exposure, and electrochemical techniques including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and cyclic voltammetry (CV). During initial exposure, the OCP dropped about 0.35 V and the interfacial resistance increased several times, indicating a certain reduction of the polymer and oxidation of the steel surface. Later the OCP shifted to the noble direction and remained at a stable value during the exposure up to 60 days. The EIS monitoring also revealed the initial change and later stabilization of the coating. The stable high OCP and low coating impedance suggest that the conducting polymer maintains its oxidative state and provides corrosion protection for carbon steel throughout the investigated period. The polarization curves and CV show that the conducting polymer coating induces a passive-like behavior and greatly reduces the corrosion of carbon steel.     

Effect of physico-chemical properties of simulated body fluids on the electrochemical behaviour of CoCrMo alloy

The behaviour of the CoCrMo alloy was studied under different experimental conditions of solution pH, chemical composition (phosphate buffer solution with and without addition of bovine serum albumin) and aeration (presence and absence of oxygen in the solution). With this purpose, electrochemical techniques such as open circuit measurements (OCP), potentiodynamic curves, potentiostatic tests and electrochemical impedance spectroscopy (EIS) were employed.The results show that the general corrosion behaviour of CoCrMo alloy depends on the solution pH. Thus, the effect of BSA and the aeration conditions are related to the solution pH. At pH 3 no influence of BSA was observed in deoxygenated solutions which imply that BSA acts over the oxygen reduction reaction in acidic media. On the contrary, a noticeable influence of BSA addition was observed at pH 7.4 (independently on the gas content). Finally, at pH 10, the influence of BSA was only significant in oxygenated solution. It was found that H₂PO₄⁻ favours the formation of passivating compounds which improves the resistance of the CoCrMo alloy to passive dissolution. Therefore, when the concentration of the H₂PO₄⁻ increases (when pH decreases) the polarization resistance of the alloy also increases. On the other hand, the oxygen (aerated conditions) decreases the polarization resistance of the alloy in all the studied conditions.     

Inhibition of CuNi10Fe corrosion in seawater by sodium-diethyl-dithiocarbamate: an electrochemical and analytical study

The efficiency of sodium-diethyl-dithiocarbamate (NaDDTC) as corrosion inhibitor for CuNi10Fe alloy was studied in natural seawater by means of immersion tests, polarization measurements, electrochemical impedance spectroscopy (EIS) and Auger electron spectroscopy (AES). After immersion of the alloy for 24 h in various concentrations of NaDDTC, layers were formed which act as a physical barrier to the corrosion attack. The polarization curves obtained with electrodes in seawater indicate retardation of both the anodic and cathodic processes. From EIS measurements equivalent circuits, which illustrate the behaviour of the reaction product film, were proposed and individual circuit elements at the open circuit potential and anodic polarization were defined. The results obtained for inhibitor efficiency from weight losses, corrosion currents and from impedance measurements are in fair agreement. The inhibition film does not lose efficiency even at anodic polarization, although the AES measurements indicate a change in the organic molecule structure. The hypothesis proposed is that a possible reconstruction of the organic molecule takes place, with release of CS₂.     

Corrosion behavior of carbon steel coated with magnesium electrodeposited from methyl magnesium chloride solution

Magnesium coating was electroplated on carbon steel to improve its corrosion protection. The analytical characterization of the magnesium coating was performed by scanning electron spectroscopy and energy dispersive X-ray spectroscopy. The electrochemical behavior of Mg-coated carbon steel was assessed by electrochemical impedance spectroscopy, open-circuit potential measurements and potentiodynamic polarization curves in 0.03% sodium chloride solution. The electrochemical results showed that the self-corrosion current density (i _corr) of magnesium-coated steel was 0.32 mA cm^?2 (about 1.8% of that of uncoated steel). Impedance results showed an increase of the total impedance when magnesium coating was applied on steel substrate. The corrosion protection was ensured by a two-step mechanism. The first step was cathodic polarization; the second step was the formation of a barrier due to magnesium oxides composed of MgO, Mg(OH₂) and Mg(OH₃)Cl.     

Corrosion behaviour of tantalum in sodium hydroxide solutions

The corrosion behaviour of tantalum has been investigated in sodium hydroxide solutions at different temperatures, using open-circuit potential measurements, potentiodynamic polarization, polarization resistance method and electrochemical impedance spectroscopy. Tantalum showed a passive behaviour in 5 and 10 wt % NaOH at 25, 50 and 75 °C, and in 15 wt % NaOH at 25 and 50 °C. In 15 wt % NaOH at 75 °C and in 30 wt % NaOH at all temperatures, tantalum presented a passive–active transition (self-activation) due to the spontaneous dissolution of its superficial air-formed oxide, and afterwards remained in the active state for long times, forming a polytantalate compound. In all cases, the corrosion rates increase with increasing NaOH concentration and temperature.     

Electrochemical study of the corrosion behaviour of copper surfaces modified by nitrogen ion implantation

Electrochemical impedance spectroscopy (EIS) and d.c polarization resistance measurements (Rp) were used to study the corrosion resistance of surface layers produced by nitrogen ion implantation into copper substrates. Ion implantation was carried out using a Wickham ion beam generator, applying an acceleration voltage of 100keV, a mean current of 0.40 mA and a nitrogen dosage of 4 × 1017 ions cm–2. Surface analyses were made by Auger electron spectroscopy (AES). Electrochemical measurements (EIS and Rp) performed in a 0.6m sodium chloride solution show nitrogen-implanted specimens have greater a.c. and d.c. apparent polarization resistance than nonimplanted specimens. The results obtained with electrochemical measurements indicate that nitrogen ion implantation in copper forms a protective surface layer which improves the corrosion resistance of the pristine material, a feature of great interest for the design of new contact materials for the electricity and electronic industries.     

THE ROLE OF PHOSPHONATE DERIVATIVES ON THE CORROSION INHIBITION OF STEEL IN HCL MEDIA

The inhibition of corrosion of steel by two P-containing compounds, sodium methyldodecyl phosphonate and sodium methyl (11-smethacryloyloxyundecyl) phosphonate, in hydrochloric acid has been investigated at various temperatures using electrochemical techniques (impedance spectroscopy (EIS), potentiodynamic polarization) and weight loss measurements. Inhibition efficiency (E%) increased with phosphonate concentration. Adsorption of inhibitors on the steel surface in 1 M HCl follows the Langmuir isotherm model. EIS measurements showed that the dissolution process of steel occurred under activation control. Polarization curves indicated that inhibitors tested acted as cathodic inhibitors. The temperature effect on the corrosion behavior of steel in 1 M HCl without and with the inhibitor was studied in the temperature range from 313 to 353 K. The adsorption free energy and activation parameters for the steel dissolution reaction in the presence of phosphonates were determined.     

THE ROLE OF PHOSPHONATE DERIVATIVES ON THE CORROSION INHIBITION OF STEEL IN HCL MEDIA

The inhibition of corrosion of steel by two P-containing compounds, sodium methyldodecyl phosphonate and sodium methyl (11-smethacryloyloxyundecyl) phosphonate, in hydrochloric acid has been investigated at various temperatures using electrochemical techniques (impedance spectroscopy (EIS), potentiodynamic polarization) and weight loss measurements. Inhibition efficiency (E%) increased with phosphonate concentration. Adsorption of inhibitors on the steel surface in 1 M HCl follows the Langmuir isotherm model. EIS measurements showed that the dissolution process of steel occurred under activation control. Polarization curves indicated that inhibitors tested acted as cathodic inhibitors. The temperature effect on the corrosion behavior of steel in 1 M HCl without and with the inhibitor was studied in the temperature range from 313 to 353 K. The adsorption free energy and activation parameters for the steel dissolution reaction in the presence of phosphonates were determined.     

In situ Raman spectroscopy and electrochemical techniques for studying corrosion and corrosion inhibition of iron in sodium chloride solutions

The corrosion of single crystal pure iron in 3.5% NaCl solutions and its inhibition by 3-amino-5-mercapto-1,2,4-triazole (AMTA) have been studied using in situ and ex situ Raman spectroscopy, cyclic voltammetry (CV), open-circuit potential (OCP), potentiodynamic polarization (PDP), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. CV experiments indicated that the iron electrode in the chloride solution alone showed an anodic peak at ∼−650 mV after the 5th cycle shifted to ∼−610 mV after the 20th cycle; another cathodic peak appeared at ∼−990 mV. In the presence of 1.0 mM AMTA, these two peaks shifted to ∼550 and −1050 mV, respectively. OCP, PDP, CA and EIS revealed that the presence of AMTA and the increase of its concentration move the corrosion potential to more positive values and decrease both the corrosion current and corrosion rate. This effect also increases with increasing the immersion time of iron electrode to 24 h in the test electrolyte. In situ and ex situ Raman investigations confirmed that the addition of AMTA molecules to the chloride solution strongly inhibits the iron corrosion through their adsorption onto the surface blocking its active sites and preventing its corrosion.     

The influence of nanocrystalline state of iron on the corrosion inhibitor behavior in aqueous solution

Effect of grain size reduction on the electrochemical and corrosion behavior of iron of different grain sizes (32–320 nm) produced by direct and pulsed current electrodeposition was characterized using Tafel polarization curves and electrochemical impedance spectroscopy (EIS). The grain size of deposits was determined by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The most intensive first-order peak (110) of the XRD patterns was taken for detailed analysis using a Gaussian fitting curve. The electrochemical tests were carried out in electrolyte 30 mg L⁻¹ NaCl + 70 mg L⁻¹ Na₂SO₄ + 250 mg L⁻¹ NaNO₂ aqueous solution. It was found that the corrosion potential and corrosion current density significantly changed as the microstructure morphology was changed. Results obtained from electrochemical tests suggested that the inhibition effect and corrosion protection of sodium nitrite inhibitor in near-neutral aqueous solutions increased as the grain size decreased from submicrocrystalline to nanocrystalline. This was attributed to the excess free energy, and concomitantly the increased number of the active sites caused by higher grain boundary and triple junction content in the nanocrystalline surface, which provides sites for electrochemical activity, and effect of sodium nitrite, was more pronounced.     

Theoretical and Experimental Studies for Corrosion Inhibition Performance of Q235 Steel by Imidazoline Inhibitors against CO2 Corrosion

The inhibition performance of two imidazoline inhibitors, 1-(2-thioureaethyl)-2-alkyl-imidazoline (TAI) and chloride-1-(2,3-dihydroxylpropyl)-1-(2-thioureaethyl)-2-alkyl-imidazoline sodium phosphate (TAIP), for Q235 steel in saltwater saturated with CO₂ was studied by using molecular dynamics simulations and quantum chemistry calculations. The conclusions were experimentally verified by weight loss, polarization curves, electrochemical impedance spectroscopy (EIS) and surface analysis techniques. The theoretical results suggest that imidazoline ring and heteroatoms are the active site and the adsorption stability weakens gradually in the order of TAIP, TAI. Experimental results show that the two inhibitors act as mixed type inhibitors and can inhibit the corrosion of Q235 in CO₂ saturated saltwater solution.