Study on the corrosion behavior of reinforcing steel in simulated concrete pore solutions using in situ Raman spectroscopy assisted by electrochemical techniques

In situ Raman spectroscopy, electrochemical impedance spectroscopy (EIS) and polarization curves were used to study the corrosion behavior of reinforcing steel in simulated concrete pore (SCP) solutions (saturated Ca(OH)₂ solutions). Results indicated that the reinforcing steel remained passive in chloride-free SCP solutions. However, the anodic polarization curve of the steel did not exhibit a stable passive region in the SCP solution with 0.5 M NaCl, the corrosion current density exceeded 0.1 μA cm⁻², the steel surface was unstable with chloride attack and localized corrosion appeared on it with FeCO₃ and Fe₂O₃ as the main corrosion products.     

Investigation on the inhibition effect of aspartic acid and Zn2+ ions on carbon steel surface in aqueous solution

A protective film has been formed on the surface of carbon steel in aqueous environment using a synergistic mixture of an environment-friendly inhibitor, aspartic acid, and Zn²⁺. The synergistic effect of aspartic acid (AS) in controlling corrosion of carbon steel has been investigated by gravimetric studies in the presence of Zn²⁺. The formulation consisting of AS and Zn²⁺ has an excellent inhibition efficiency. The results of potentiodynamic polarization revealed that the formulations are of mixed-type inhibitor. Impedance studies of the metal/solution interface indicated that the surface film is highly protective against the corrosion of carbon steel in the aqueous environment. X-ray photoelectron spectroscopic analysis of the protective film showed the presence of the elements iron, nitrogen, oxygen, carbon, and zinc. The spectra of these elements in the surface film showed the presence of oxides/hydroxides of iron(III), Zn(OH)₂, and [Fe(III)/Fe(II)–Zn(II)-AS] complex. Further, surface characterization techniques such as Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy are used to ascertain the nature of the protective film formed on the carbon steel surface.     

Enhanced corrosion inhibition behavior of carbon steel in aqueous solution by Phosphoserine-Zn2+ system

The corrosion inhibition effect of carbon steel in aqueous solution was using a synergistic mixture of an environmentally friendly inhibitor system phosphoserine (PS) and Zn²⁺ using gravimetric studies, potentiodynamic polarization, and electrochemical impedance studies. Potentiodynamic polarization studies showed that the inhibitor system is a mixed type inhibitor. Electrochemical impedance studies of the metal/solution interface indicated that the surface film is highly protective against the corrosion of carbon steel in the aqueous solution. X-ray photoelectron spectroscopic analysis of the protective film exhibited the presence of the elements viz., iron, phosphorus, nitrogen, oxygen, carbon, and zinc. The chemical shifts in the binding energies of these elements inferred that the surface film is composed of oxides/hydroxides of iron, Zn(OH)₂, and [Fe(II)/(III)-Zn(II)-PS] complex. Further, the surface examination techniques viz., FTIR, SEM, and AFM studies confirm the formation of an adsorbed protective film on the carbon steel surface. Based on the results obtained, a suitable mechanism of corrosion inhibition is presented.     

Zinc dissolution in ammonium chloride electrolytes

The anodic dissolution of zinc RDE in NH₄Cl and NH₄Cl + ZnCl₂ electrolytes at pH 5.5 was studied. XPS and SEM data indicate that the zinc electrode is covered by a porous film composed of a mixture of metallic zinc and zinc hydroxide. The thickness of the film and the zinc hydroxide content is much higher in zinc-containing electrolytes than in NH₄Cl and, although the thickness and Zn(OH)₂ amount decrease with anodic polarization, the electrode is never free from oxidized compounds. Electrochemical results indicate that at low overpotentials the rate of zinc dissolution is determined by the removal of the oxidized blocking particles, while at high overpotentials Zn dissolution takes place through the porous layer.     

Impedance study of hydrogen evolution on Ni/Zn and Ni–Co/Zn stainless steel based electrodeposits

A study on the electrocatalytic performance of Ni/Zn and Ni–Co/Zn alloys for hydrogen evolution reaction (HER) in alkaline media (30 wt.% KOH solution) has been carried out. After preparing by electrodeposition on stainless steel supports, the alloys were leached of to remove part of the zinc and generate a porous layer. For the developed electrodes, the surface roughness factor, R_f, was evaluated by electrochemical impedance spectroscopy (EIS). The HER on these electrodes was evaluated by means of steady-state polarization curves and EIS. The obtained electrodes were characterized by large R_f for HER, and very low overpotentials at the current density of 250 mA cm⁻², η₂₅₀ ∼ 0.138 V at 30 °C. The high electrode activity was mainly attributed to the high surface area of the developed electrodes.     

The spatial distribution of Zn during galvanic corrosion of a Zn/steel couple

The spatial distribution of Zn²⁺ during galvanic corrosion of a model Zn/steel couple in 0.01 M NaCl was investigated using a scanning zinc disk electrode. The couple had a coplanar arrangement of a steel substrate with an electroplated zinc layer at the center. During galvanic corrosion, the marked changes in the Zn²⁺ concentration were confined to a thin solution layer ca. 1.0 mm thick above the couple surface. In this thin solution layer above the zinc layer, a higher concentration region of Zn²⁺ in the range of 5-18 mM extended around the zinc layer in the solution during galvanic corrosion. Conversely, above the steel surface distant from the zinc layer, the surface concentration of Zn²⁺ was almost zero during galvanic corrosion. On this surface, the precipitation of zinc corrosion products due to the hydrolysis reaction of Zn²⁺ was observed. The distribution of the Zn²⁺ concentration supported that Zn²⁺ acted as a buffer that suppressed the increased pH due to the cathodic reaction on the steel surface near the zinc layer and almost no corrosion products formed there. The spatial distribution of Zn²⁺ is discussed in relation to the distributions of potential and pH and the surface morphology of the galvanic couple.     

SYNERGISTIC EFFECT OF N,N-BIS(PHOSPHONOMETHYL) GLYCINE AND ZINC IONS IN CORROSION CONTROL OF CARBON STEEL IN COOLING WATER SYSTEMS

A protective film has been developed on the surface of carbon steel in low chloride aqueous environment using a synergistic mixture of an environmentally friendly phosphonic acid, N,N-bis(phosphonomethyl) glycine (BPMG), and zinc ions. Impedance studies of the metal/solution interface indicated that the surface film is highly protective against the corrosion of carbon steel in the chosen environment. Potentiodynamic polarization studies showed that the inhibitor is a mixed inhibitor. X-ray photoelectron spectroscopic analysis (XPS) of the film showed the presence of the elements iron, phosphorus, nitrogen, oxygen, carbon, and zinc. Deconvolution spectra of these elements in the surface film showed the presence of oxides/hydroxides of iron(III), Zn(OH)₂, and [Zn(II)-BPMG] complex. This inference is further supported by the reflection absorption Fourier transform infrared spectrum of the surface film. Analysis by SEM is presented for both the corroded and protected metal surfaces. Based on all these results, a plausible mechanism of corrosion inhibition is proposed.     

The investigation of the passive behaviour of copper in weakly acid and alkaline solutions and the examination of the passive film by esca and ISS

The passive behaviour of copper is examined in weakly acid and alkaline solutions. The current peaks of the potentiodynamic polarization curves are related to the formation and reduction of passivating oxide layers. These layers have been examined by ESCA and ISS. A duplex structure of the oxide is found with copper I oxide at the metal surface covered by copper II hydroxide for sufficiently positive potentials. The thickness of the anodically formed oxide is deduced from the charges of cathodic reduction in phosphate buffer pH = 7.0 and 8.0 and borax buffer pH = 9.2. 10 to 14 Å of Cu₂O are found for the three buffer solutions not changing decisively with the potential of passivation. The thickness of the covering Cu(OH)₂ is increasing with the potential in the range of 0.30 V_H to 1.20 V_H up to 33, 23, and 19Å in the buffer solutions pH = 7.0, 8.0, and 9.2, respectively. From the increase of the thickness of the Cu(OH)₂ layer with the potential an electrical field strength of ～ 5<d10⁶ V cm^?1 is deduced for the outer part of the passive layer.     

Development of long-lived high-performance zinc-calcium/nickel oxide cells

The addition of Ca(OH)₂ to the zinc electrode of Zn/KOH/NiOOH cells was investigated in order to determine its effect on the rate of zinc active material redistribution (shape change) and cell cycle-life performance. Cells of equal mass and capacity, and therefore the same specific energy, containing 0, 10, 25, and 40 mol% Ca(OH)₂ in their zinc electrodes were constructed and tested. The Ca(OH)₂ and Zn(OH) ₄ ^2– -supersaturated KOH solution formed a calcium-zincate complex during the discharge half-cycle. The solubility of this complex is less than that of ZnO, and the lower zinc species solubility leads to a slower rate of Zn redistribution, thereby extending the cell cycle life. The best cells tested were those with 25%-Ca(OH)₂ electrodes, which lost capacity at a rate of 0.13%/cycle, compared to 0.47%/cycle in calcium-free control cells constructed in the same manner. Also, zinc active material utilization in the calcium-containing electrodes showed a dramatic improvement, compared to the calcium-free zinc electrodes.     

Cathodic reduction of the anodically formed zinc species as a contribution to the study of the potentiodynamic passivation of zinc in alkaline media

The cathodic part of the potentiodynamic curves obtained for upward-facing horizontal 99.9% zinc electrodes in KOH solutions 0.4, 1.0, 2.0 and 3.0 M and sweep rates in the range 1–100 mV s⁻¹ have been systematically analyzed in order to assign the possible species formed and contribute to the study of the potentiodynamic passivation of Zn in alkaline media. The anodic limit of the potentiodynamic cycles was changed and set for significant points of the total curve (between hydrogen and oxygen evolution). Also, the anodic sweep was interrupted at the potentials corresponding to the anodic limit and the cathodic sweep applied immediately from a potential near that of zero current of the cathodic half-cycle. Only two cathodic peaks have been found for the non-interrupted cycles. The assignation of peaks according to the equilibrium potentials of the reduction of the possible species implied, ie Zn(OH)²⁻₄, Zn(OH)₂ and ZnO, is not possible because local pH changes are expected and the zincate concentration near the electrode is unknown. The peak placed at more positive potentials for KOH concentrations 0.4 and 1.0 M is assigned to zincate and that at more negative potentials, to the reduction of the film. Just the opposite assignation has been found for 2.0 and 3.0 M KOH solutions. The experimental results can be interpreted assuming that the product formed at the passivation potential consists of the same chemical species as those corresponding to the first anodic peak, probably Zn(OH)₂ or hydrated ZnO. From calculating the maximum film thickness according to the charge passed and taking into account the recent theoretical analysis made by Chang and Prentice, it is concluded that the direct formation of ZnO on the electrode at the passivation potential as a consequence of local pH changes is not probable.     

Kinetics and mechanism of deposition of zinc from zincate in concentrated alkali hydroxide solutions

Galvanostatic investigation has been carried out of the kinetics of the reaction on zinc amalgam hanging mercury drop immersed in alkaline zincate solutions at KOH concentrations ranging from 1 to 14 normal. Three kinds of data have been extracted: (i) the pseudo-capacitance as a function of overpotential from the portion of the charging curves prior to plateaux, (ii) the Tafel plots from quasi-steady state values at the plateaux and (iii) the Sand's products as function of current density from transition times. In (i), the pseudo-capacitance was found to increase with overpotential, in (ii), two slopes (60 mV dec^?1 and 120 mV dec^?1) have been found in the cathodic direction and a limiting current in the anodic one; in (iii), the Sand's product was found to decrease with increasing (i). On the basis of the above findings the reaction mechanism has been suggested to be of the cece type, with the chemical dissociation of the intermediate univalent zinc complex in between the two elctrochemical steps as rate-determining. A modification of the method of evaluating the reaction orders was introduced to account for a simultaneous change of more than one activity of reactants in concentrated solutions. Using this, reaction order was found to be 2 with respect to both OH^? ions and water, suggesting that the electroactive species is not only reduced in the number of ligands but also dehydrated with respect to the prevailing species. The anodic limiting current appears to be due to the accumulation of Zn(OH) species to cover all the surface free of adsorbed Zn(OH)₂. Exchange cd and rate constants of all the four steps of the reaction have been estimated.     

Effect of sulfur-containing amino acids on the corrosion of mild steel in sulfide-polluted sulfuric acid solutions

The influence of cysteine (RSH) and cystine (RSSR) on the corrosion behavior of mild steel in sulfide-polluted H₂SO₄ solutions was studied by potentiodynamic polarization methods and AC impedance technique. The results show that S²⁻ accelerates the corrosion process markedly, especially the anodic dissolution of iron. Tafel polarization curves show that RSH and RSSR act mainly as anodic-type inhibitors without affecting the mechanism of the hydrogen evolution reaction or iron dissolution. Adsorption of RSH and RSSR in most sulfide-polluted H₂SO₄ solutions obeys Temkin’s isotherm. Impedance studies indicate that in the inhibited and uninhibited solutions, charge transfer controls the corrosion process either at E_corr or at 30 mV vs E_corr. Potentiodynamic anodic polarization curves show that RSSR effectively inhibits the steel dissolution both in the active and passive states and greatly reduces the current oscillations observed in the passive region.     

Dissolution du nickel en transpassivite 2eme partie: etude du degagement d'oxygene simultane et influence du pH

The oxygen discharge was studied in the transpassive range of nickel on 0·5M H₂SO₄. The potential range is separated into two parts, the experimental data indicating that, above 1650 mV/sce the oxygen discharge occurs alone and between 1360 and 1650 mV/sce two reactions namely nickel dissolution and oxygen discharge occur simultaneously. A model is proposed where two OH^? ions are simultaneous adsorbed on the first formed layer of Ni(OH), a fraction of the surface is covered by Ni(OH)₃. The oxygen discharge is also a multistep reaction. Between 1360 and 1650 mV/sce, the dissolution of metal and the oxygen discharge are in competition at all times, the surface is covered simultaneously by Ni(OH)₂ and Ni(OH)₃.The calculated curves are in good accord with the potentiostatic curves, the influence of pH is correlated with the experimental data.     

Protection of stainless steel by polyaniline films against corrosion in aqueous environments

Polyaniline (PANI) thin films were electrochemically deposited by cyclic voltammetry on stainless steel electrode previously covered by a thin film of polyvinyl acetate (PVAc). The corrosion resistance of PANI covered stainless steel substrates was estimated by using potentiodynamic polarization curves and its linear polarization resistance (LPR) was measured in 0.5 M H₂SO₄, 0.5 M NaCl and 0.5 M NaOH aqueous solutions at room temperature. The results indicate that the PANI-PVAc films did improve the corrosion resistance of the stainless steel in NaOH, behaving even worst, in the case of PANI film, than the uncoated substrate. In H₂SO₄ both PANI and PANI-PVAc coatings gave good protection for the stainless steel electrode, with a slightly better performance of PANI-PVAc than PANI. In NaCl solution both PANI and PANI-PVAc films provided a good protection against corrosion. The better performance of PANI-PVAc coatings for corrosion protection in basic media may be due to its major chemical stability compared to simple PANI films, which lose their conductivity in high pH solutions. The E _corr (free corrosion potential) value of the coated substrate was in the passive region of the uncoated substrate in acidic environment but in the active region in neutral or basic environment.     

Evaluation of citric acid added cleaning solution for removal of metallic contaminants on Si wafer surface

We have investigated cleaning solutions based on citric acid (CA) to remove metallic contaminants from the silicon wafer surface. Silicon wafers were intentionally contaminated with Fe, Ca, Zn, Na, Al and Cu standard solution by spin coating method and cleaned in various CA-added cleaning solutions. The concentration of metallic contaminants on the silicon wafer surface before and after cleaning was analyzed by vapor phase decomposition/inductively coupled plasma-mass spectrometry (VPD/ICP-MS). And the surface micro-roughness was also measured by atomic force microscopy (AFM) to evaluate the effect of cleaning solutions. It was found that acidic CA/H₂O solution has the ability to remove metallic contaminants from silicon surfaces. Fe, Ca, Zn and Na on silicon surface were decreased from the order of 10¹² atoms/cm² to the order of 10⁹ atoms/cm² even at low CA concentration, low temperature of CA solution and with short immersion time. CA was also effective in alkali cleaning solution. Fe, Ca, Zn, Na and Cu were reduced down to the order of 10⁹ atoms/cm² in CA added with NH₄OH/H₂O₂/H₂O solution without degradation of surface micro-roughness.     

Effect of pH and impurities on the surface charge of zinc oxide in aqueous solution

The surface charge on some commercially available zinc oxide powders in aqueous solution has been studied. Aqueous suspensions of zinc oxide could not be stabilized electrostatically because of the decreasing pH of suspensions in the region between 7.2 and 12 as a result the transformation of colloidal Zn(OH)_2(S) particles to Zn(OH)_2(aq) ions. The major cationic impurity in the zinc oxide powders is lead, whereas in the aged suspensions of the same powders, zinc and sulphate ions dominate. These ions have the the most significant effect in creating an electrical double layer shell around the zinc oxide particles. The effect of these ions on the surface potential of zinc oxide was studied and the point of zero charge and charge reversal were found to be a direct function of the zinc and sulphate ions' concentration in the supernatant.     

Effect of Al on the galvanic ability of Zn-Al coating under thin layer of electrolyte

The effect of Al on the galvanic ability of Zn-Al coating has been studied under thin electrolyte layers by measuring surface potential and surface pH. The changes of surface potential and surface pH over Zn-Al/steel galvanic couple corroding in artificial sea water (ASW) were measured at 60% and 90% RH at 298 K. In the initial stage of corrosion, Zn-55Al coating has shown better galvanic protection ability than Zn-5Al coating in both 60% and 90% RH. However, Zn-5Al coating was better in long term corrosion. The better galvanic ability of Zn-55Al coating in the initial stage of corrosion was related to the observation of pH as low as low as 2 on its surface. The low pH value was due to hydrolysis of Zn²⁺ and Al³⁺ ions. The low pH value was further confirmed by observing evolution of gas due to H⁺ reduction on the Zn-55Al coating. With the progress of corrosion, the low pH region of coating layer extended towards the base steel. This helped expand the deposition of zinc corrosion products on the steel surface. The enhanced dissolution of zinc in Zn-55Al coating led to the formation of a barrier layer which limited the galvanic protection of remaining steel. This was not the case in Zn and Zn-5Al coating. The X-ray analyses of the corroded samples have shown the deposition of zinc corrosion products on the steel surface, which greatly depended on the RH value. The part of the steel surface covered with zinc corrosion products has shown relatively less noble potential than other part indicating that zinc corrosion products took a role to protect the base steel against corrosion. The results from surface potential and surface pH measurements were substantiated by the surface observation of the corroded sample during and after the corrosion test.     

Methanol Synthesis from CO2 Using Skeletal Copper Catalysts Containing Co-precipitated Cr2O3 and ZnO

Skeletal Cu-Cr₂O₃-ZnO catalysts have been prepared by leaching CuAl₂ alloy particles at 273 K using 6.1 M aqueous NaOH solutions containing sodium chromate (Na₂CrO₄) and sodium zincate (Na₂Zn(OH)₄). The presence of sodium chromate and sodium zincate in the caustic solution was found to affect the pore structure and surface areas of the resulting catalysts. Both BET and Cu surface areas were increased by increasing the concentration of Na₂CrO₄ and of Na₂Zn(OH)₄.Increasing the Na₂CrO₄ level from 0 to 0.06 M in a 6.1M NaOH solution containing 0.2M Na₂Zn(OH)₄ caused the content of ZnO in the catalyst to decrease from 8.8 to 3.0 wt% whilst increasing the Cr₂ O₃ content from 0 to 1.7 wt%, indicating that the presence of Na₂CrO₄ in the leach liquor not only resulted in deposition of a Cr compound but also inhibited precipitation of zinc hydroxide onto skeletal Cu catalysts. On the other hand, increasing the concentration of Na₂Zn(OH)₄ from 0 to 0.6 M in a 6.1 M NaOH solution containing 0.008 M Na₂ CrO₄ resulted in increasing the ZnO loading from 0 to 8.9wt% with an almost constant content of Cr₂ O₃ (1.3 ± 0.2%) in the catalysts, revealing that sodium zincate only led to precipitation of zinc hydroxide and did not suppress Cr₂O₃ formation.Hydrogenation of CO₂ was studied using a gas mixture of 24% CO₂ in H₂ at a total pressure of 4MPa, space velocities up to 210000L kg^-1h^-1 and temperatures in the range 493-533K. The catalysts were found to be both highly active and selective for methanol synthesis. This study confirms the role of ZnO in promoting the activity of copper for methanol synthesis from CO₂ and improving the selectivity by inhibiting the reverse water-gas shift reaction. The role of Cr₂O₃ is to improve the structural development of high surface area skeletal copper.     

The performance of a surface-applied corrosion inhibitor for the carbon steel in saturated Ca(OH)2 solutions

In the present work, the performance of an amino alcohol based surface applied inhibitor was studied by the electrochemical techniques in saturated Ca(OH)₂ solutions. The surface morphology of the carbon steel was observed by scanning electron microscope, and the energy diffraction spectrum was also tested. Results showed that the inhibitor used in this work demonstrated obvious inhibition efficiency on the carbon steel in saturated Ca(OH)₂ solutions. The inhibition mechanism of the inhibitor lies in the quick adsorption of the active component on carbon steel surface.     

Effects of antimony(III) on zinc electrodeposition from acidic sulfate electrolyte containing [BMIM]HSO<Subscript>4</Subscript>

The effect of antimony(III) on the cathodic current efficiency (CE), power consumption (PC), deposit morphology, and polarization behavior during electrodeposition of zinc from acidic sulfate solutions containing 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO₄ was investigated. The results indicated that the addition of Sb(III) alone decreased the CE, increased the PC, and deteriorated the quality of the zinc electrodeposits. However, the combined addition of Sb(III) and [BMIM]HSO₄ was found to be beneficial for zinc deposition and improved the surface morphology of the zinc electrodeposits. Maximum CE and minimum PC were obtained at the combined addition of 0.02 mg dm⁻³ Sb(III) and 5 mg dm⁻³ [BMIM]HSO₄. Depolarization of the cathode was noted in the presence of Sb(III) alone in the electrolyte whereas this effect was partly counteracted by the addition of [BMIM]HSO₄. Cathodic polarization curves were traced and analyzed to determine the electrokinetic parameters such as Tafel slope, transfer coefficient, and exchange current density so as to elucidate the nature of the electrode reactions. The data obtained from X-ray diffractogram revealed that the presence of Sb(III) did not change the structure of the electrodeposited zinc but affected the crystallographic orientation of the crystal planes.