Investigation of the specific adsorption of HSO4(SO4) and Cl ions on Co and Fe by radiotracer technique in the course of corrosion of the metals in perchlorate media

The adsorption of sulphate and chloride ions on Co and Fe was studied in 0.5 mol dm⁻³ NaClO₄ supporting electrolyte at various pH values by radiotracer technique in the course of the corrosion (dissolution) of the metals. The effect of the reduction of ClO₄⁻ ions (leading to the formation of Cl⁻ ions) on the radiotracer measurements was investigated. It was found that the adsorption of chloride and sulphate ions occurs in different pH ranges. This phenomenon was explained by the assumption that the adsorption strength of the two species is very different on oxide covered and “pure” metal surfaces.     

A SERS investigation of the electrodeposition of Au in a phosphate solution

The spectroelectrochemical behaviour of cyanide and phosphate ions adsorbed on a Au electrode during electrodeposition and corrosion in a KAu(CN)₂ phosphate bath was studied by in situ SERS (Surface Enhanced Raman Spectroscopy) and cyclic voltammetry. SERS spectra exhibiting features corresponding to CN⁻ and PO₄⁻ vibrations were recorded under potentiostatic control in an interval from − 1600 to + 1500 mV vs. Ag/AgCl. Surface CN⁻ species are the dominating ones under both cathodic and anodic polarisations. As far as the phosphate vibrations are concerned, bands related to PO₄⁻ are visible in both cathodic and anodic conditions. A fluorescence background was evident in the potential range − 1300 ÷ + 1300 mV. At cathodic potentials phosphate ion adsorption on electrode surface prevails over cyanide for potentials more cathodic than − 1000 mV. At − 700 mV a discontinuity is noticed in the Stark tuning of CN⁻, probably due to a change of Au(CN)₂⁻ adsorption mechanism. At anodic potentials bands due to cyanide oxidation could be observed.     

Organic additive-copper(II) complexes as plating precursors

Cu(II) ions previously coordinated with typical electroplating organic additives were investigated as an alternative source of metal for plating bath. The coordination complexes were isolated from reaction between CuSO₄ and organic additives as ligands (oxalate ion, ethylenediamine or imidazole). Deposits over 1010 steel were successfully obtained from electroplated baths using the complexes without any addition of free additives, at pH = 4.5 (H₂SO₄/Na₂SO₄). These deposits showed better morphologies than deposits obtained from CuSO₄ solution either in the absence or presence of oxalate ion as additive (40 mmol L^− 1), at pH = 4.5 (H₂SO₄/Na₂SO₄). It is suggestive that the starting metal plating coordinated with additives influences the electrodeposition processes, providing deposits with corrosion potentials shifted over + 200 mV in 0.5 mol L^− 1 NaCl (1 mV s^− 1). The resistance against corrosion is sensitive to the type of additive-complex used as precursor. The complex with ethylenediamine presented the best deposit results with the lowest pitting potential (− 0.27 V vs 3.0 mol L^− 1 CE). It was concluded that the addition of free additives to the electrodeposition baths is not necessary when working with previously coordinated additives. Thus, the complexes generated in ex-situ are good alternatives as plating precursors for electrodeposition bath.     

Electrochemical pitting corrosion behaviour of α-brass in LiBr containing solutions

The potentiodynamic anodic polarization curve of α-brass (70% Cu-30% Zn) in 1 M LiBr solution showed an initial active region of the alloy dissolution followed by two well defined anodic current peaks then a narrow passivation region before the pitting potential (E_pit) is reached. The initial active anodic region exhibited Tafel slope with 90 mV dec⁻¹ attributed to the formation of CuBr₂⁻ complexes. The anodic current peaks were attributed to the formation of CuBr and Cu²⁺ ions, respectively. The change of pH values of LiBr solution did not affect the anodic polarization curves of α-brass. Increasing the solution temperature from 30 to 90 °C changed the corrosion type from pitting to general one. The addition of 10⁻² M benzotriazole (BTAH) to 1 M LiBr solution is completely inhibited the pitting corrosion at 30 °C while it did not inhibit the pitting at 90 °C. The inhibition effect was attributed to the adsorption of BTAH molecules on the alloy surface, which obeys Langmuir isotherm. The presence or absence of pitting corrosion was confirmed by using SEM.     

EQCN study of anodic dissolution and surface oxide film formation at Au in the presence of Cl or Br ions: A model process for corrosion studies

The anodic dissolution of an Au electrode and associated thin-layer oxide film formation in aq. H₂SO₄ in the presence of Cl⁻ or Br⁻ ions at various concentrations provides a model process for metal corrosion. In the present work such processes were investigated using cyclic voltammetry and chronoamperometry, with complementary nanogravimetry measurements using the EQCN. The results clearly indicate that in 0.5 M H₂SO₄ electrolyte, containing 1 mM Br⁻ or Cl⁻, Au dissolves over the potential range 1.0 - 1.45 V(RHE) through a 3e oxidation process involving Au complex-ion formation that can be followed in situ by means of UV spectroscopy. The linear relationship between mass changes and reciprocal square-root of sweep-rate and between anodic currents in cyclic voltammetry at ca. 1.20 V for Br⁻ (1.39 V for Cl⁻) and square-root of sweep-rate/or electrode rotation rate indicated quantitatively that the dissolution process is diffusion-controlled. It was interesting to find that electrode rotation in the presence of Cl⁻ ions has little effect on the anodic formation of surface oxide, while, on the contrary, with Br⁻ ions present, currents for oxide film reduction are not observed at rotation rates > ca. 400 rpm.     

Hydrogen embrittlement of duplex stainless steel under cathodic protection in acidic artificial sea water in the presence of sulphide ions

By slow strain rate technique, hydrogen embrittlement (HE) of a 2205 duplex stainless steel was studied in deaerated acidic (pH 6.5) artificial sea water, in the absence and in presence of sulphide ions (1-30 ppm). Strain rate tests (1 × 10⁻⁶ s⁻¹) were performed on specimens polarized at −0.9; −1.0 and −1.2 V_SCE at 25 ± 0.1 °C. HE was evaluated by R, the ratio between the % elongation to fracture in the aggressive solution and in air.Duplex stainless steel were subjected to HE in acidic artificial sea water at −0.9 V_SCE. HE increased at −1.0 V_SCE but it was reduced at −1.2 V_SCE. This decrease was attributed to the influence of a calcareous deposit.Sulphide ions at 1 ppm were sufficient to stimulate HE of duplex stainless steel. The higher the sulphide amount and the more negative the cathodic potential, the higher HE was. In the presence of S²⁻, the shielding effect of the calcareous deposit was not evident.     

Synthesis of tertiary amines and their inhibitive performance on carbon steel corrosion

Some tertiary amines in the series of 1,3-di-amino-propan-2-ol, referred as 1,3-di-morpholin-4-yl-propan-2-ol (DMP) and 1,3-bis-diethylamino-propan-2-ol (DEAP), had been synthesized by alkylation reaction. These compounds were checked by MS, IR, ¹H NMR and ¹³C NMR. The electrochemical performance of these products was investigated through potentiodynamic polarization measurement and electrochemical impedance spectroscopy (EIS) under thin electrolyte layer with thickness of 100 μm, and their inhibition efficiencies were measured using gravimetric method. These compounds, retarding the anodic dissolution of iron by the protective layer bonding on the metal surface, were anodic inhibitors under thin electrolyte layer. Polarization data indicated that the inhibitive performance of DMP for carbon steel was improved with the increasing of concentration, whereas DEAP showed a maximum inhibiting power at 2.5 × 10⁻² M. The values of the charge transfer resistance, obtained from impedance plots of carbon steel, showed that DEAP was a promising inhibitor. The gravimetric results showed that the inhibition efficiency of DEAP at 2.5 × 10⁻² M was 95%. The adsorption on the carbon steel surface followed Langmuir isotherm model. The Fourier transform spectroscopy (FTIR) was used to analyze the surface adsorbed film.     

Effects of pH and chloride concentration on pitting corrosion of AA6061 aluminum alloy

Effects of pH solution and chloride (Cl⁻) ion concentration on the corrosion behaviour of alloy AA6061 immersed in aqueous solutions of NaCl have been investigated using measurements of weight loss, potentiodynamic polarisation, linear polarisation, cyclic polarisation experiment combined with open circuit potential transient technique and optical or scanning electron microscopy.The corrosion behaviour of the AA6061 aluminum alloy was found to be dependant on the pH and chloride concentration [NaCl] of solution. In acidic or slightly neutral solutions, general and pitting corrosion occurred simultaneously. In contrast, exposure to alkaline solutions results in general corrosion. Experience revealed that the alloy AA6061 was susceptible to pitting corrosion in all chloride solution of concentration ranging between 0.003 wt% and 5.5 wt% NaCl and an increase in the chloride concentration slightly shifted both the pitting E_pit and corrosion E_cor potentials to more active values. In function of the conditions of treatment, the sheets of the alloy AA6061 undergo two types of localised corrosion process, leading to the formation of hemispherical and crystallographic pits.Polarisation resistance measurements in acidic (pH = 2) and alkaline chloride solutions (pH = 12) which are in good agreement with those of weight loss, show that the corrosion kinetic is minimised in slightly neutral solutions (pH = 6).     

The initial stage of pitting corrosion on coated steels investigated by photon rupture in chloride containing solutions

A photon rupture method, film removal by a focused pulse of pulsed Nd-YAG laser beam irradiation, has been developed to enable oxide film stripping at extremely high rates without contamination from the film removal tools. In the present study, Zn-55mass%Al alloy and Al-9mass%Si alloy-coated steel specimens covered with protective nitrocellulose film were irradiated with a focused pulse of a pulsed Nd-YAG laser beam at a constant potential in 0.5 kmol m⁻³ H₃BO₃-0.05 kmol m⁻³ Na₂B₄O₇ (pH = 7.4) with 0.01 kmol m⁻³ of chloride ions to investigate the initial stage of localized corrosion. At low potentials, oxide films on both coated alloys were reformed after the nitrocellulose films were removed by this method. The oxide film formation kinetics follows an inverse logarithmic law, in agreement with Cabrera-Mott theory. However, at high potentials, localized corrosion producing corrosion products occurs at the area where nitrocellulose film was removed. Nevertheless, when the applied potential is less noble, the dissolution current of the Zn-55mass%Al-coated steel samples is higher than that of Al-9mass%Si-coated samples.     

Electrochemical behaviour of Cu-40Zn in 3% NaCl solution polluted by sulphides: Effect of aminotriazole

The electrochemical behaviour of Cu-40Zn alloy, in 3% NaCl medium pure and polluted by 2 ppm of S²⁻ ions, has been studied in the absence and presence of the 3-amino-1,2,4 triazole (ATA) as corrosion inhibitor. Electrochemical measurements (polarisation curves and electrochemical impedance spectroscopy) showed that sulphides accelerate the alloy corrosion. The studies revealed that ATA inhibits both cathodic and anodic reactions, indicating a mixed type of inhibition. The inhibiting effect was higher in presence of S²⁻ ions than in its absence. Scanning electron microscopy analysis showed that the inhibitor acts by preventing the adsorption of S²⁻ ions, and formation of Cu₂S at the alloy surface. The inhibition efficiency reaches 98% at a concentration of 5 × 10⁻³ M.     

Inhibiting effects of butyl triphenyl phosphonium bromide on corrosion of mild steel in 0.5 M sulphuric acid solution and its adsorption characteristics

Butyl triphenyl phosphonium bromide (BuTPPB) has been evaluated as a corrosion inhibitor for mild steel in 0.5 M H₂SO₄ solutions using galvanostatic polarisation and potentiostatic polarisation measurements. The study was also complemented by infra red (IR) spectroscopy, scanning electron microscopy (SEM) and quantum chemical calculations. Galvanostatic polarisation measurements showed that the presence of BuTPPB in aerated 0.5 M H₂SO₄ solutions decreases corrosion currents to a great extent and the corrosion rate decreases with increasing inhibitor concentration at a constant temperature. At 298K, inhibition efficiency was found to be 94.5% for 10⁻⁷ M BuTPPB which increased to about 99% for the BuTPPB concentration of 10⁻² M. The effect of temperature on the corrosion behaviour of mild steel was studied at five different temperatures ranging from 298 to 338K. The polarisation curves clearly indicate that BuTPPB acts as a mixed type inhibitor. Adsorption of BuTPPB on the mild steel surface follows the Langmuir isotherm.Potentiostatic polarisation measurements showed that passivation was observed only for lower BuTPPB concentrations (10⁻⁵ and 10⁻⁷ mol l⁻¹) for the mild steel in 0.5 M H₂SO₄. IR and SEM investigations also confirmed the adsorption of BuTPPB on the mild steel surface in 0.5 M H₂SO₄ solutions. The molecular parameters obtained using PM3 semi-empirical method, were correlated with the experimentally measured inhibitor efficiencies.     

High resistivity magnesium-rich layers and current instability in anodizing a Mg/Ta alloy

Strikingly different morphologies of amorphous anodic films on a Mg/40 at.%Ta alloy are shown to result from single-stage and sequential anodizing procedures. The alloy, prepared by magnetron sputtering, was anodized galvanostatically in ammonium pentaborate (pH 8.3) and sodium silicate (pH 12.6) electrolytes at 293 K and studied by transmission electron microscopy, Rutherford backscattering spectroscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy. For one-step anodizing in the pentaborate electrolyte, a single-layered film, of approximate composition Ta₂O₅ · MgO, forms at a ratio of ∼1.8 nm V⁻¹. In the silicate electrolyte, an outer, magnesium-rich layer, containing silicon species, also forms, with a ratio of 0.8 nm V⁻¹. The outer layer can develop due to relatively fast migration of magnesium ions in the inner layer and the stabilization of the pH at the film surface, probably linked to generation of a silica gel that also limits loss of magnesium species to the electrolyte. Further thickening of the anodic film, in ammonium pentaborate electrolyte, produces fingers of low resistivity, inner oxide that penetrate the pre-existing, high resistivity outer layer, with a bi-modal distribution of finger sizes. When fingers reach the film surface, magnesium ions are ejected to the electrolyte. The absence of fingers in films grown in sodium silicate electrolyte is possibly due to prevention, by the silica gel, of their initiation.     

Influence of fluoride ions on the amorphous phosphating of aluminium alloys

The influence of the F⁻ ions containing compounds: NaF, HBF₄, H₂SiF₆, NH₄F·HF and their concentrations on formation of phosphate coatings on Al in МоО₄²⁻ ions containing solutions, as well as protective properties of the phosphate coatings in a 0.5 M Na₂SO₄ solution have been studied. The studies of film composition by the XPS method have shown, that the phosphate coating consists of the metal phosphates from aluminium alloy and the Mo (IV, V) phosphates, which are formed during reduction of МоО₄²⁻ ions. The mass of phosphate layer and that of etched metal depend on the nature of fluoride ions, which can be arranged in the following order according to the decrease in strength of their influence: H₂SiF₆ > NH₄F·HF > HBF₄ > NaF. Polarization measurements in a 0.5 M Na₂SO₄ solution and the calculated electrochemical parameters testify that phosphated Al samples exhibit a lower corrosion rate and a higher corrosion resistance as compared to non-phosphated Al substrate.     

Role of additives in electroless copper plating using hypophosphite as reducing agent

In electroless copper plating baths using hypophosphite as the reducing agent, nickel ions was used to catalyze hypophosphite oxidation. However, the color of the copper deposits was dark or brown and the electrical resistivity was much higher than that obtained from formaldehyde baths. Polyethylene glycol (PEG) and K₄Fe(CN)₆ were used to improve the microstructure and properties of copper deposits obtained from electroless copper plating bath using hypophosphite as the reducing agent. The effects of PEG concentration on the deposition rate, the microstructure, morphology and electrical resistivity of the copper deposits, and the electrochemical reactions of hypophosphite (oxidation) and cupric ion (reduction) were investigated. The traces of hydrogen escaping from the deposits surface disappeared and the color of the copper deposits changed from dark-brown to dark red when the PEG concentration was 1.67 × 10^− 5 M or more. The deposition rate increased and the electrical resistivity of the copper deposits decreased slightly with the addition of PEG to the plating solution. The electrical resistivity of copper deposits decreased to 2.85 μΩ cm with 1.67 × 10^− 5 M PEG and 4.70 × 10^− 6 M K₄Fe(CN)₆ in the bath. Larger grain size and higher (220) plane orientation were obtained with the increase of PEG concentration in the bath. The electrochemical current–voltage results showed that PEG accelerated the catalytic oxidation of hypophosphite at active nickel sites and had little effect on the reduction reaction of cupric ions on the deposit surface by adsorption on the electrode.     

Selective single pulse femtosecond laser removal of alumina (Al2O3) from a bilayered Al2O3/TiAlN/steel coating

We studied surface modification of a double layer protective coating on steel induced by single fs laser pulse irradiation in ambient air. The outer alumina (Al₂O₃) layer, which protects against aggressive environments, was 1.7 μm thick and the titanium aluminum nitride (TiAlN) layer in contact with the steel surface had a thickness of 1.9 μm. The pulses (λ = 775 nm, τ = 200 fs) were generated by a Ti:sapphire laser source. The pulse energy was varied from 0.32 μJ to 50 μJ, corresponding to an incident laser fluence of 0.11 J cm^− 2 to 16.47 J cm^− 2. The surface damage threshold was found to be 0.20 J cm^− 2 and the alumina layer removal was initiated at 0.56 J cm^− 2. This selective ablation of alumina was possible in a wide range of fluences, up to the maximum applied, without ablating the TiAlN layer beneath.     

Synergistic effect between cationic gemini surfactant and chloride ion for the corrosion inhibition of steel in sulphuric acid

Corrosion inhibition of cold rolled steel in 0.5 mol L⁻¹ sulphuric acid by a quaternary ammonium gemini surfactant, l,3-propane-bis(dimethyl dodecylammonium bromide) (designated as 12-3-12), in the absence and presence of chloride ions was investigated at different temperatures. The results revealed significant synergistic effect between gemini 12-3-12 and chloride ions for the corrosion protection of cold rolled steel in sulphuric acid, and that the novel composite inhibitor system containing cationic gemini surfactant and chloride ions was efficient and low-cost for steel corrosion inhibition in sulphuric acid medium, even when concentration of 12-3-12 was as low as 1 × 10⁻⁶ mol L⁻¹. By fitting the obtained experimental data with Langmuir adsorption model and Arrhenius equation, some thermodynamic and kinetic parameters such as adsorption free energy, the apparent activation energy, and the pre-exponential factor were estimated. The adsorption mechanism of the gemini surfactant onto steel surface in acid medium in the absence and presence of chloride ions was also discussed, respectively.     

The characterisation of the protective film formed by benzotriazole on the 90/10 copper-nickel alloy surface in H2SO4 media

The nature of the protective film formed by benzotriazole (BTAH) on the surface of the 90/10 CuNi alloy in deaerated 0.5 mol L⁻¹ H₂SO₄ solution containing Fe(III) ions as oxidant was investigated by weight-loss, calorimetric measurements, and by surface-enhanced Raman spectroscopy (SERS). The SERS measurements show that the protective film is composed by the [Cu(I)BTA]_n polymeric complex and that the BTAH molecules are also adsorbed on the electrode surface. A modification of the BET isotherm for adsorption of gases in solids is proposed to describe the experimental results obtained from weight-loss experiments that suggest an adsorption in multilayers. Electrochemical studies of copper and nickel in 0.5 mol L⁻¹ H₂SO₄ in presence and absence of BTAH have also been made as an aid to interpret the results. The calculated adsorption free energy of the cuprous benzotriazolate on the surface of the alloy is in accordance with the value for pure copper.     

Molybdate/Al(III) composite films on steel and zinc-plated steel by chemical conversion

A molybdate(VI)-Al(III) chemical conversion process was developed as an alternative to the chromate processes. Steel and zinc-plated steel specimens were treated in the solutions of 0.16 mol l⁻¹ ammonium alum (AlNH₄(SO₄)₂ · 12H₂O) with small amounts of ammonium molybdate(VI) (0.002-0.016 mol l⁻¹ (NH₄)₆Mo₇O₂₄ · 4H₂O) at 60 °C for 10-30 min in an ultrasonic rinsing apparatus. The formed films were composed of oxyhydroxides containing Mo(V,VI), Al(III), Fe(II,III), and sulfate ions (and Zn(II) ions in the case of zinc-plated steel), and showed good corrosion resistance in an aerated 0.5 mol l⁻¹ NaCl-0.15 mol l⁻¹ H₃BO₃ solution (pH=7). The films macerated during the corrosion test, but they did not detach and functioned as a protective layer. This process may be useful in forming undercoats for paints and polymer coatings on steel and zinc-plated steel.     

The effect of various halide ions on the passivity of Cu, Zn and Cu-xZn alloys in borate buffer

Cu and Zn metals and four of their alloys, Cu-10Zn, Cu-20Zn, Cu-30Zn and Cu-40Zn, were studied in borate buffer, pH = 9.2, in the presence of the halides, NaF, NaCl, NaBr and NaI. Electrochemical polarization and SEM/EDS methods were used in the study. The mechanism of corrosion of copper and copper alloys induced by iodide ions differed fundamentally from that induced by other halide ions. Iodide ions promote the general type of corrosion during which very slowly soluble CuI is formed. F⁻, Cl⁻ and Br⁻ ions promote localized corrosion attack. All halide ions induce localized corrosion on the passive layer on zinc. The breakdown potentials of Cu, Zn and four Cu-xZn alloys were measured as a function of concentration and type of halide ions.     

On the corrosion inhibition of low carbon steel in concentrated sulphuric acid solutions. Part I: Chemical and electrochemical (AC and DC) studies

The influence of the concentration of adenine (AD), as a safe inhibitor, on the corrosion of low carbon steel (LCS) in aerated 4.0 M H₂SO₄ solutions was studied. The investigations involved weight loss, potentiodynamic polarization, impedance and electrochemical frequency modulation (EFM) methods. Variations of open-circuit potential (OCP) as a function of time till steady-state potentials were also studied. Measurements were conducted under the influence of various experimental conditions complemented with ex situ EDX examinations of the electrode surface. By using EFM measurements, corrosion current density was determined without prior knowledge of Tafel slopes. Results obtained revealed that together with iodide ion, AD is an effective corrosion inhibitor for LCS corrosion in H₂SO₄ solutions. Synergism between iodide ion and AD was proposed. Potentiodynamic polarization studies showed that AD alone and the mixture of AD and iodide ions act as mixed-type inhibitors for the corrosion of LCS in 4.0 M H₂SO₄ solution. The inhibition mechanism involves the electrostatic adsorption of protonated AD molecules on the LCS surface charged with a negative layer of chemisorbed I⁻ ions. An adherent layer of inhibitor is postulated to account for the protective effect. EDX examinations of the electrode surface confirmed the existence of such adherent layer on the electrode surface. The inhibition efficiency increases with increase in the concentration of AD and immersion time. The potential of zero charge (PZC) of the LCS electrode was determined in 4.0 M H₂SO₄ solutions in the absence and presence of 0.001 M KI, and the mechanism of adsorption was discussed. The results obtained from chemical and electrochemical measurements were in good agreement.