The surface layer pH in the electroless copper plating process

The pH at the surface of the coating (pH_s) was measured using an ordinary glass electrode, the surface of which was in the zone of the reaction during the autocatalytic reduction of copper(II) ions by formaldehyde. The pH_s value is significantly lower (by up to 1.3 units) than the pH bulk value in most tartrate and ethylenediamine tetraacetate (EDTA) solutions. The pH_s value changes the dependence of the electroless copper plating rate on the alkalinity of the solution (the rate maximum shifts from 12.6 - 12.7 to 11.7 - 12.0). The pH changes at the surface depend mainly on the catalytic process rate and the buffering capacity of the solution; the evolution of H₂ also has a great influence at the medium rate of copper plating (1 - 3 μm h^-1).     

Direct modification of a passivated iron electrode with alkyltriethoxysilanes for preventing passive film breakdown in a borate buffer containing 0.1 M of chloride ion

A passive film on an iron electrode was modified with alkyltriethoxysilanes directly. In order to examine the protective ability of the modified passive film against breakdown, the pitting potential, E_pit was measured by anodic polarization of the modified electrode in a borate buffer solution (pH 8.49) containing 0.1 M of Cl⁻. The value of E_pit for the modified electrode shifted in the positive direction from that of the unmodified electrode, indicating prevention of passive film breakdown. The modified passive film was not broken down in the passive and transpassive regions of polarization curve in some cases. However, many current spikes appeared in the all curves of the modified electrodes. The modified surface of passivated electrode was characterized by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement. There were defects and clusters of associated water within the modified film and hence, Cl⁻ could permeate through the defects, leading to appearance of current spikes and occurrence of breakdown.     

Prevention of passive film breakdown on iron in a borate buffer solution containing chloride ion by coverage with a self-assembled monolayer of hexadecanoate ion

Breakdown of a passive film on iron in a borate buffer solution (pH 8.49) containing 0.1 M of Cl⁻ was suppressed by coverage of the passive film surface with a self-assembled monolayer (SAM) of hexadecanoate ion C₁₅H₃₁CO₂⁻ (C₁₆A⁻). The pitting potential of an iron electrode previously passivated in the borate buffer at 0.50 V/SCE increased by treatment in an aqueous solution of sodium hexadecanoate for many hours, indicating protection of the passive film from breakdown caused by an attack on defects of the film with Cl⁻. No breakdown occurred over the potential range of the passive region by coverage with the SAM of C₁₆A⁻ in some cases. Structures of the passive film and the monolayer were characterized by X-ray photoelectron and Fourier transform infrared reflection spectroscopies and contact angle measurement with a drop of water.     

Streaming potential measurements on stainless steels surfaces: evidence of a gel-like layer at the steel/electrolyte interface

Electric charges at the surface of a passive stainless steel are generally considered as concentrated either in the passive film itself, or at the metal/passive film interface, or in the electrical double layer at the film solution interface. Rest potential time dependence after immersion of a passive surface in aqueous electrolytes suggests however that slow processes occur in the onset of the surface charge. Specific experiments, such as streaming potential measurements and electrochemical impedance spectroscopy in a thin electrolyte cell, were carried out for understanding better this phenomenon. An AISI 304 type austenitic stainless steel with polished or bright annealed surface finishes was immersed in NaCl aqueous solutions with various pH and chloride concentrations. The streaming potential time evolution shows two steps: a first rapid one (∼2 min) is attributed to the onset of the surface charge. The second step is much slower (approximately several hours) and possibly due to an interphase layer between the passive film and the solution. Following this idea, the whole kinetics is controlled by cation migration across the interphase when the pH is larger than the isoelectric pH (pH_iep), while chloride ions are incorporated in the interphase when pH < pH_iep. Impedance measurements allow determining both the kinetics of charge transport and the thin cell conductivity. When glass is used as reference material for the cell walls instead of stainless steel, the Nyquist plots show a high-frequency response. For stainless steel cell walls, a low-frequency response is observed, attributed to a slow charge reorganisation inside the interphase layer. The charge distribution at metal/electrolyte interface is discussed in terms of a gel-like layer which possibly takes place at the passive film/electrolyte interface.     

Pitting and pitting inhibition of iron in sodium sulphate solutions

The anodic behaviour of high purity iron in 0.5 M sodium sulphate solutions was studied. Experiments were made in both acid and alkaline solutions (pH 2.7, pH 9.0, pH 10.0 without buffers; and pH 9.2 with borate buffer). Anodic polarization curves, and surface scratching experiments, showed pitting potentials in 0.5 M Na₂SO₄ pH 9.0 and pH 10.0 solutions. Their values were very close to the corrosion potential obtained in a 0.5 M Na₂SO₄, pH 2.7, pit-like solution. The pitting potential in a borate buffered 0.5 M Na₂SO₄ solution was 50 mV higher than that in the unbuffered solutions. The pitting inhibition potential measured in a 0.5 M Na₂SO₄ solution, pH 10.0, was very close to the passivation potential found in the pit-like solution. All these facts can be explained by the localized acidification mechanism for pitting. The pitting potential is the minimum potential at which an acidified solution can be produced and maintained in contact with the dissolving metal. Similarly the pitting inhibition potential is the electrode potential at which the metal becomes passive in the pit-like solution.     

Effect of solution temperature and ph on adsorption and density of surface charge at aluminum oxyhydroxide /NaF aqueous solution interface

The effect of temperature, pH, and adsorbed fluorine on the density of a surface charge at the aluminum oxyhydroxide /NaF aqueous solution interface is investigated using the method of potentiometric titration. The equilibrium of fluorine ion adsorption in analyzed. Products of electrochemical dimensional machining (ECDM) of an AMG-6 aluminum alloy thermally treated at 200°C are used as an adsorbent. The experiments on the adsorption have been carried out from an acetated buffer with the initial fluorine solution concentrations from 1.0 × 10⁻³ to 1.5 × 10⁻¹ M/l. The adsorption isotherms were plotted for solution temperatures of 20, 30, and 40°C. Adsorption is shown to obey the Langmuir adsorption model. It is demonstrated that, at all solution temperatures, the pH is 5 for the maximal fluorine adsorption on aluminum oxyhydroxide. It has been revealed that the surface charge at the aluminum oxyhydroxide /NaF aqueous solution interface depends on the solution temperature; i.e., the pH of a point of a zero charge point (pH_PZC) of the aluminum oxyhydroxide surface decreases with an increase in temperature. As is the case with temperature, adsorbed fluorine shifts pH_PZC toward smaller values, which is typical for specific adsorption. The temperature dependence of pH_PZC has made it possible to determine the standard mole enthalpy and entropy of surface-charge formation. The interaction of fluorine with aluminum oxyhydroxide is shown to be the result of the chemical affinity of F with surface centers of AlOH₂ ⁺ and AlOH and electrostatic attraction.     

Prevention of zinc corrosion in oxygenated 0.5 M NaCl by treatment in a cerium(III) nitrate solution and modification with sodium hexadecanoate

A self-assembled monolayer (SAM) of hexadecanoate ion (C₁₆A⁻) was prepared on a zinc electrode covered with a layer of hydrated cerium(III) oxide Ce₂O₃. The protection of zinc against corrosion was examined for the electrode coated with the Ce₂O₃ layer and the C₁₆A⁻ SAM in an oxygenated 0.5 M NaCl solution. A more positive open-circuit potential of the coated electrode was maintained during immersion in the solution for 4 h than that of the uncoated one and polarization curves showed marked suppression of the anodic process, implying that the layer modified with the SAM acted as a passive film. The protective efficiency of the modified layer was extremely high, more than 99%. The zinc surface coated with the Ce₂O₃ layer and the C₁₆A⁻ SAM was characterized by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement with a drop of water.     

Preparation of a one-dimensional polymer film on passivated iron by modification of a carboxylate ion self-assembled monolayer with octyltriethoxysilane for preventing passive film breakdown

A self-assembled monolayer (SAM) of 16-hydroxyhexadecanoate ion HO(CH₂)₁₅CO₂⁻(HOC₁₆A⁻) has been prepared on an iron electrode passivated in a borate buffer solution (pH 8.49) in the preceding paper. In this work, the HOC₁₆A⁻ SAM on the passivated electrode was modified with octyltriethoxysilane C₈H₁₇Si(OC₂H₅)₃ to form a film composed of one-dimensional polymer. Prevention of passive film breakdown was examined by anodic polarization measurements of the electrodes uncoated and coated with the modified SAM in the borate buffer containing 0.1 M of Cl⁻. The pitting potential, E_pit of the coated electrode shifted from that of the uncoated electrode in the positive direction, indicating prevention of passive film breakdown. The anodic current density was decreased in the passive and transpassive regions by coverage with the modified SAM. Neither current spikes nor E_pit was observed in the curve of the passive region in some cases, demonstrating complete protection of the passive film against breakdown in the Cl⁻ solution. The modified SAM on the electrode was characterized by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement.     

Complete protection of a passive film on iron from breakdown in a borate buffer containing 0.1 M of Cl by coverage with an ultrathin film of two-dimensional polymer

An ultrathin film of two-dimensional polymer was prepared on a passivated iron electrode by modification of a 16-hydroxyhexadecanoate ion self-assembled monolayer with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃. This film prevented passive film breakdown examined by potentiodynamic anodic polarization of the coated electrode in the borate buffer solution containing 0.1 M of Cl⁻. Neither current spikes nor the pitting potential was observed in the passive and transpassive regions of polarization curve. The anodic current density was decreased in these regions markedly, implying hindrance to permeation of Cl⁻ and water through the film. Structure of the film was clarified by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement with a drop of water. Electron-probe microanalysis of the passivated surface coated with the film after anodic polarization scanning up to the transpassive region revealed that the polymer film prevents pit initiation by an attack on the passive film with Cl⁻.     

Effect of the applied potential on the potential and current distributions within crevices in pure nickel

The electrode potential profile within a crevice was measured in situ during crevice corrosion of nickel in 1N H₂SO₄ under conditions of effective convective mixing of the crevice and bulk electrolytes. Oxidizing power was investigated by applying potentials in the passive region. A steep potential gradient and constant pH were always measured during crevice corrosion. The magnitude of the potential drop and the distance into the crevice of the passive-to-active transition, X_pass,both increased linearly with increasing applied potential, in accordance with the IR>ΔΦ1 criterion. The in situ measured potential E_passatX_pass was, at all times, constant and in the range of the passive-to-active transition for the polarization curve of the bulk solution.     

A study of the passive films on chromium by capacitance measurement

Using capacitance measurement and Mott-Schottky analysis, the semiconducting properties of passive films formed on chromium within the passive potential range under different conditions were investigated. The study reveals a p-type behavior of the passive layers. Two semiconductive parameters, i.e., the acceptor density (N_A) and the flatband potential (E_FB), which are mainly related to composition and surface charges of the passive films, have been measured. The effect of film formation potential, passivation time, pH and composition of solutions on the parameters are discussed. N_A increases either with lowering film formation potentials or with prolonging passivation times. This is attributed to the transformation of a less hydrated oxide film into a more hydrated form. The changes of E_FB are discussed as a function of adsorptive anions and pH values of electrolyte solution.     

Prevention of passive film breakdown on iron by coverage with one-dimensional polymer films of a carboxylate ion self-assembled monolayer modified with alkyltriethoxysilanes

A film composed of a one-dimensional polymer was fabricated by modification of a 16-hydroxyhexadecanoate ion HO(CH₂)₁₅CO₂⁻ self-assembled monolayer (SAM) adsorbed on a passivated iron electrode with octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃. The pitting potential, E_pit of the passivated electrode coated with this film was measured by anodic polarization in a borate buffer solution containing 0.1 M of Cl⁻. The E_pit value of the electrode coated with the film was markedly shifted from the value of the bare electrode in the positive direction, indicating prevention of passive film breakdown. No breakdown occurred over the potential range of passive region in some cases. Structure of the modified SAM was discussed by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement of the electrode surface covered with the film. Suppression of Cl⁻ accumulation at a defect of the passive film was revealed by electron-probe microanalyses of the surfaces uncoated and coated with the SAM modified with octyltriethoxysilane C₈H₁₇Si(OC₂H₅)₃ after anodic polarization in the borate buffer containing Cl⁻.     

Gamma-radiation-induced corrosion of carbon steel in neutral and mildly basic water at 150 °C

The effect of γ-radiation on the kinetics of carbon steel corrosion has been investigated by characterizing the oxide films formed on steel coupons at 150 °C and at two pH values. Results show that continuous irradiation enhances surface oxide formation with the type of oxide formed dependant on the solution pH. For experiments at 150 °C and a [OH⁻] equivalent to that for pH_{25 °C} = 10.6, the surface oxide on carbon steel after γ-irradiation was non-porous and uniform, and no localized corrosion was observed. This oxide, however, appears to be susceptible to brittle fracture during cooling. Raman spectroscopy of the surface film indicates that it is a mixture of the phases of Fe₃O₄ and γ-Fe₂O₃. In contrast, at 150 °C with [OH⁻] equivalent to neutral pH_{25 °C}, metal dissolution is significant and the surface oxide film is very porous. Raman spectra show that this oxide film is also composed of a mixture of Fe₃O₄ and γ-Fe₂O_3. The results from this work combined with previously reported electrochemical studies of the same system as a function of pH and temperature can be used to deconvolute the effects of radiation, pH and temperature on the nature of the corrosion process.     

Preparation of a two-dimensional polymer film on passivated iron by modification of a carboxylate ion self-assembled monolayer with alkyltriethoxysilanes for preventing passive film breakdown

The effect of an ultrathin, regularly arranged polymer film on prevention of passive film breakdown on iron in the presence of chloride ion was investigated. The film of two-dimensional polymer was prepared by modification of a 16-hydroxyhexadecanoate ion self-assembled monolayer adsorbed on a passivated iron electrode with 1,2-bis(triethoxysilyl)ethane(C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octyltriethoxysilane C₈H₁₇Si(OC₂H₅)₃. The pitting potentials of the passivated electrodes bare and covered with the polymer film were determined by anodic polarization measurements in a borate buffer solution containing 0.1 M of Cl⁻. The pitting potential of the coated electrode was higher than that of the uncoated one, indicating prevention of passive film breakdown. No breakdown was observed over the potential range in the passive and transpassive regions by covering the passive film with the well-arranged two-dimensional polymer film. The film was characterized by X-ray photoelectron and FTIR reflection spectroscopies and measurement of the contact angle with a drop of water.     

Kinetic Regularities of Zinc Corrosion in Chromating Baths

Electrochemical modeling of zinc corrosion in chromate solutions showed that its rate (which is controlled by the limiting current density of Cr(VI) reduction to Cr(III)) is determined by the limiting diffusion current of hydrogen ions to the zinc electrode surface partially covered with the chromate coating. The sizes of active and passive surface sites are comparable with the thickness of the diffusion layer of the solution, which means that the zinc surface corroding in a chromate solution is macroscopically heterogeneous. Investigating the kinetics of the electrode reactions showed that, in the absence of a noticeable film formation, the steady-state cathodic polarization curve of zinc in sulfate–chromate solutions can be described by a kinetic equation that takes into account the pH _s dependence on the dissolution rate of zinc.     

In situ gravimetry of nickel thin film during potentiodynamic polarization in acidic and alkaline sulfate solutions

The passivation process of nickel thin films during potentiodynamic polarization in acidic and alkaline sulfate solutions was analyzed by an electrochemical quartz crystal microbalance (EQCM) to separate the partial current density of nickel dissolution through the passive film, i_Ni²⁺, and the partial current density of film growth, i_O^2-. The values of i_Ni²⁺ and i_O^2- during potentiodynamic polarization (20 mV s⁻¹) in the passive potential region could be separated by comparing the mass change rate and net polarization current as a function of electrode potential. It is found that i_Ni²⁺ is larger than i_O^2- in pH 3.0, 0.5 M sulfate solution, while the situation reverses in pH 12, 0.5 M sulfate solution. The sulfate concentration dependences of i_Ni²⁺ and i_O^2- in pH 3.0, sulfate solution were significant as compared to those in pH 12, sulfate solution.     

The corrosion behavior of carbon steel in CO2‐saturated NaCl crevice solution containing acetic acid

The corrosion behavior of X52 carbon steel electrodes in CO₂‐saturated NaCl crevice solution containing HAc was investigated by electrochemical measurements. Chemical environment measurements by Cl^? and pH microprobes show an enrichment of Cl^? ions and an increase of pH values inside the crevice. Moreover, both increments could accelerate with the decreasing dimension of the crevice mouth due to the high diffusive resistance. When the electrode in the crevice solution is coupled with the electrode in bulk solution, the alkalization and the enrichment of Cl^? ions in the crevice solution can result in a negative shift of potential of the electrode in crevice solution, while the potential of the electrode in bulk solution shifts positively during the corrosion process. Thus, a galvanic corrosion is established with the electrode in the crevice solution acting as anode while another in the bulk solution as cathode, i.e., the corrosion in the crevice solution was enhanced while the corrosion in the bulk solution was retarded. The anodic dissolution and the cathodic reduction processes dominate in the crevice solution and in the bulk solution, respectively.     

The role of electrolyte concentration on crevice corrosion of pure nickel

In this work an artificial crevice electrode was used in conjunction with a fine microprobe assembly to measure the potential inside the crevice. Using this setup crevice corrosion of commercially pure nickel was investigated in sulfuric acid with concentrations: 0.5, 1 and 2N. The outer surface of the Ni was held at a passive potential of 530 mV(SCE) while the experiment was running. The results showed a steep potential decay observed in all concentrations. For 0.5, 1 and 2N H₂SO₄, the total potential drop inside the crevice was: 681, 619 and 593 mV, respectively. This indicates the higher the acid concentration is the lower the potential drop will be. On the other hand, the measured current was highest (4.09 mA) for 2N and lowest (1 mA) for 0.5N. On the crevice wall a boundary was found to exist between the passive and the active regions. These findings point toward the IR voltage drop mechanism operating for this system.     

Galvanic cells encountered in the corrosion of steel reinforcement — III. Differential surface condition cells

Galvanic cells resulting from coupling passive/active or rusted/bright electrodes have been investigated in alkaline solutions, in absence or presence of Cl^? ions. The results indicated that in absence of Cl^? ions, the pre-passivated electrodes were protected from corrosion in solutions of pH 10 and 10·5 when coupled with normal steel electrodes. The steady-state galvanic current density increased with the decrease of pH, accompanied by a slight increase of cell e.m.f., a negative shift in the mixed potential and depolarization of the cathodic process. In presence of Cl^? ions, the corrosion rate was determined by the kinetic retardation of the corrosion system and the cell e.m.f. Computation of the ohmic drop was found to be highest in NaOH of pH 10 (ohmic control ? 19·4%). The passive film formed on a bright electrode had better passivating properties than that formed on an electrode having originally mill-scale on its surface. Breakdown of passivity of the non-rusted electrode occurred when coupled with rusted steel in just inhibiting solutions. In corrosive solutions, there was an initial enhancement of corrosion of the bright electrode which decreased greatly with time accompanied by activation of the rusted electrode.