Pulse plating effect on microstructure and corrosion properties of Zn–Ni alloy coatings

The influence of pulse plating parameters on the surface morphology, grain size, lattice imperfection and corrosion properties of Zn–Ni alloy has been studied. The coatings were electrodeposited in an alkaline cyanide-free solution. AFM was applied for surface morphology examination, XRD measurements were carried out for phase composition and texture analysis, electron probe microanalysis was used for alloy chemical composition studies, while electrochemical techniques were applied for corrosion performance evaluation. The pulse plated Zn–Ni coatings appeared to consist of the γ-Zn₂₁Ni₅ phase and the composition of the alloy depended on the plating parameters. The grain size, lattice imperfection and homogeneity of grain distribution were established to be the main factors determining corrosion behaviour of the coating. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005     

Variable Mott-Schottky plots acquisition by potentiodynamic electrochemical impedance spectroscopy

Potentiodynamic electrochemical impedance spectroscopy provides extraction of potential-dependent space charge layer capacitance from potentiodynamic impedance spectra of non-stationary semiconductor–electrolyte interface. The new technique has been applied for acquisition of Mott-Schottky plots of cathodically treated TiO₂ anodic films. Cathodic treatment in 1 M H₂SO₄ increases donor density and flat band potential of TiO₂. Freshly doped films show hysteresis in the space charge layer capacitance in cyclic potential scans. The subsequent cycling eliminates the hysteresis but preserves the greater part of the doping effect. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, 13–16 March 2005     

Impedance-based sensing of the interlayer adhesion loss in organic coating systems

The detrimental effects of environmental conditions on the protective organic systems on the metals are well known. Variable parameters like temperature, humidity and UV radiation influence the protective properties of coatings on metals. Adhesion of coatings to the substrate and the interlayer adhesion between separate coating layers are main parameters describing the protective properties of coating systems. Traditional methods of evaluation are destructive and do not allow the monitoring of such influences. By using conductive electrodes between the layers of protective coating system and electrochemical impedance spectroscopy (EIS) method, it is possible to detect the changes caused by adhesive debonding and accumulation of water at the interface. Large changes in the impedance values were observed when humidity and temperature conditions were changed. A new approach to continuous monitoring and quantification of adhesion changes at real conditions using EIS was proposed. Examples of monitoring data during laboratory temperature cycling and during real outdoor exposure were shown. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005     

Electrochemical materials science: tailoring intrinsically conducting polymers. The example: substituted thiophenes

A series of 3-(p-X-phenyl) thiophene monomers (X= –H, –CH₃, –OCH₃, –COCH₃, –COOC₂H₅, –NO₂) was electrochemically polymerized to furnish polymer films that could be reversibly reduced and oxidized (n- and p-doped). The oxidation potentials of the monomers and formal potentials of the n- and p-doping processes of polymers were correlated with resonance and inductive effects of the substituents on the phenyl ring as well as the semiempirically calculated heat of formation of the monomer radical cations. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13-16, 2005     

Effects of carbon nanofiber composites on electrode processes involving liquid|liquid ion transfer

Composite electrodes were prepared from chemical vapor deposition grown carbon nanofibers consisting predominantly of ca. 100 nm diameter fibers. A hydrophobic sol–gel matrix based on a methyl-trimethoxysilane precursor was employed and composites formed with carbon nanofiber or carbon nanofiber—carbon particle mixtures (carbon ceramic electrode). Scanning electron microscopy images and electrochemical measurements show that the composite materials exhibit high surface area with some degree of electrolyte solution penetration into the electrode. These electrodes were modified with redox probe solution in 2-nitrophenyloctylether. A second type of composite electrode was prepared by simple pasting of carbon nanofibers and the same solution (carbon paste electrode). For both types of electrodes it is shown that high surface area carbon nanofibers dominate the electrode process and enhance voltammetric currents for the transfer of anions at liquid|liquid phase boundaries presumably by extending the triple-phase boundary. Both anion insertion and cation expulsion processes were observed driven by the electro-oxidation of decamethylferrocene within the organic phase. A stronger current response is observed for the more hydrophobic anions like ClO₄⁻ or PF₆⁻ when compared to that for the more hydrophilic anions like F⁻ and SO₄²⁻. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005     

Improved electrooxidation of phenol at exfoliated graphite electrodes

In the presented paper, we report on electrochemical oxidation of phenol occurring at exfoliated graphite (EG) in alkaline solution. The mechanism of the electrocatalytic reaction of phenol oxidation was modified on adding methanol to the phenol-containing electrolyte. Using the voltammetry method, the influence of methanol additive on cyclic behavior of EG electrode was examined. A particular attention has been paid to the first two cycles when an abrupt decrease in electrocatalytic activity of various electrode materials has been observed. The results obtained showed that in the presence of methanol EG, electrode preserves its electrocatalytic activity for a longer time of phenol oxidation. In the absence of methanol in a phenol/KOH electrolyte, the charge of phenol oxidation peaks decreases sharply on cycling, whereas in the presence of methanol, the observed drop is considerably inhibited. The anodic charge attained for the 15th cycle of phenol oxidation in methanol-admixed electrolyte is the same as that for the third cycle recorded in methanol-free electrolyte. The thermogravimetric analysis (TG), Fourier-transformed infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) data showed that an improved electrocatalytic activity of EG can be accounted for by new chemical composition of oligomer film built on the EG surface with the participation of methanol and/or the products of its oxidation.Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005.     

Electrodeposition of Au/nanosized diamond composite coatings

Ultra-dispersed diamond UDD particles were codeposited in gold matrix coatings from a sulphite electrolyte, changing bath load and key operating parameters. The influence of electrolyte pH, current density and bath load on current efficiency, particle co-deposition, surface morphology and microhardness of composite coatings was investigated. UDD incorporation is mainly affected by bath load; however, particle embedding is specifically sensitive to electrolyte pH and deposition current density. The maximum mass fraction of carbon in the coating, about 0.55%, is obtained by depositing from ultrasonically pre-treated electrolytes with UDD concentration 20 g l⁻¹, pH 9.5 and 3 mA cm⁻² . Au/UDD composites are characterised by an increased microhardness and improved wear resistance. When compared to pure gold coatings which are notoriously weak, Au/UDD electrodeposits from sulphite electrolytes represent a significant improvement. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, 13–16, 2005     

Nickel foam-based composite electrodes for electrooxidation of methanol

Nickel foam and five nickel foam-based composite electrodes were prepared for being used as anode materials for the electrooxidation of methanol in KOH solution containing 0.1 and 1.0 M of methanol. The layered electrodes composed of nickel foam, platinum nanoparticles, polyaniline (PANI) and/or porous carbon (C) prepared in various assemblies. As shown by SEM analysis, depending on the preparation conditions, the electrodes of different morphologies were obtained. Using the cyclic voltammetry method, the oxidation of methanol on nickel foam electrode was observed in the potential range 0.4 V ↔ 0.7 V, where the Ni(OH)₂/NiOOH transformation occurred. The presence of Pt particles in electrode gave rise to the increase in electrocatalytic activity in this potential range. For electrodes containing dispersed platinum catalyst (Ni/Pt, Ni/PANI/Pt and Ni/C/Pt), the oxidation of methanol was noted also in the potential range −0.5 V ↔ 0.1 V. The electrocatalytic activities of the examined electrodes toward methanol oxidation at low potentials were in order Ni/Pt > Ni/C/Pt > Ni/PANI/Pt, whereas at high potentials in order Ni/PANI/Pt > Ni/Pt> Ni/C/Pt > Ni. Among the examined electrodes, the most resistant to cyclic poisoning appeared to be the Ni/C/Pt electrode. Presented at the 4Th Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005     

Potentiometric sensors for Ag+ based on poly(3-octylthiophene) (POT)

Potentiometric ion sensors were prepared from the conjugated polymer poly(3-octylthiopene) (POT). The influence of additional membrane components, including silver 7,8,9,10,11,12-hexabromocarborane (AgCB₁₁H₆Br₆) and potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (KTpFPB) as lipophilic salts, and [2.2.2]p,p,p-cyclophane as silver ionophore, was studied. The membrane components were dissolved in chloroform and membranes were prepared by solution casting on glassy carbon disk electrodes. For comparison, POT-based potentiometric sensors were also prepared by galvanostatic electrosynthesis of POT from the 3-octylthiophene monomer. All the POT-based ion sensors fabricated by solution casting show Nernstian or slightly sub-Nernstian response to Ag⁺, even those based only on POT without any additional membrane components. The potentiometric response of electrochemically polymerized POT depends on the film thickness and the doping anion incorporated in the conducting polymer during polymerization. It is of particular importance that chemically synthesized undoped POT (without any additives) shows a sensitive and selective potentiometric response to Ag⁺ ions although UV-vis results show that POT remains in its undoped form, i.e., POT is not oxidized by Ag⁺. This indicates that undoped POT can exhibit good sensitivity and selectivity to Ag⁺ also in the absence of metallic silver in the polymer film. In this case, the potentiometric response is related to interactions between Ag⁺ and the conjugated polymer backbone. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, 13–16, 2005     

The Markov chain model of alloy electrodeposition: application to NiCo and NiMo

The Markov chain model of alloy deposition was applied to cobalt–nickel. The characteristic parameters of the model are the g _i values describing the selectivity of the deposition process for its components. The values recently determined for Co and Ni (g _Co and g _Ni) depend on the current density. This could be quantitatively described by the mass transport limitation for Co. The model was also applied to the nickel–molybdenum system, an example for induced co-deposition. Data published by Podlaha and Landolt [4, 5] could be described by the equation

Dynamic electrochemical impedance spectroscopy measurements of passive layer cracking under static tensile stresses

Electrochemical impedance spectroscopy allows the examination of corrosion susceptibility and resistance for different construction materials, in particular the determination of the properties of their passive films. This technique makes possible the analysis of electrochemical processes in time domain, including rapid phenomena such as changes in the properties of passive films, but it has never been used for passive layer cracking examination. In many cases, fracture of the passive film under tensile stresses leads to stress corrosion cracking. Therefore, investigations of passive layer cracking on austenitic stainless steels under tensile stresses facilitate the understanding of the mechanism of stress corrosion cracking in these common engineering materials. The effect of static tensile stresses on the passive film cracking behaviour of type 304L stainless steel immersed in 0.5 M NaCl solution at room temperature has been investigated. This paper presents the impedance spectra obtained for 304L stainless steel samples at different potential values.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003)     

Electrochemical characteristics of La0.6Sr0.4CoO3-δ, Pr0.6Sr0.4CoO3-δ and Gd0.6Sr0.4CoO3-δ on Ce0.85Sm0.15O1.925 electrolyte

Cyclic voltammetry, chronoamperometry and electro-chemical impedance have been used for the analysis of the following medium temperature half-cells: Ce_0.85Sm_0.15O_1.925| La_0.6Sr_0.4CoO_3-δ, Ce_0.85Sm_0.15O_1.925| Pr_0.6Sr_0.4CoO_3-δ and Ce_0.85Sm_0.15O_1.925| Gd_0.6Sr_0.4CoO_3-δ. The influence of the atomic mass of the A–site cation in the perovskite cathode on the oxygen reduction kinetics has been discussed. The total polarisation resistance, obtained from the Z′′, Z′-plots, increases with the rise of atomic mass of the cation in the A-site position. Two different time constants have been obtained for the oxygen electroreduction process, and the replacement of La³⁺ by Gd³⁺ in the cathode material decreases somewhat the surface catalytic activity, but the noticeably higher low-frequency series resistance, i.e. mainly diffusion-like mass transfer resistance, values have been obtained. However, the mainly diffusion-limited process at T≤773 K for Gd_0.6Sr_0.4CoO_3-δ and the kinetically mixed process (diffusion + charge transfer) for Pr_0.6Sr_0.4CoO_3-δ and La_0.6Sr_0.4CoO_3-δ have been established. At higher temperature (T≥993 K) and more negative potentials, the O₂ reduction process is limited mainly by the heterogeneous charge transfer step. Presented at the fourth Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005.     

Electrochemically induced transformations of ruthenium(III) trichloride microcrystals in salt solutions

Ruthenium (III) trichlorid solid crystals have been mechanically attached to gold surfaces and studied by cyclic electrochemical quartz crystal microbalance measurements in the presence of aqueous solutions of different concentrations containing M⁺Cl⁻, where M⁺=H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺. The RuCl₃ and the complexes formed during the electrochemical transformations show two or more reduction and reoxidation pairs of waves, depending on the experimental conditions (concentration, scan rate, and potential range). The voltammetric peaks are shifted into the direction of higher potentials with increasing electrolyte concentrations except at very high concentrations when the peaks belong to the first reduction/reoxidation processes move oppositely. The mass change was reversible, during reduction mass increase, while during oxidation mass decrease occurred at medium electrolyte concentrations in two, more or less distinct steps. At high or low concentrations the mass excursions are more complex involving different mass increase/decrease regions as a function of potential which vary with the potential range of the measurements. The peak potentials and the electrochemical activity strongly depend on the nature of the cations and pH. It is related to the formation of complexes in different compositions. The mass change decreases with increasing electrolyte concentrations attesting the important role of the water activity and the transport of solvent molecules. It was concluded that in dilute solutions during the first reduction step M⁺ ions enter the surface layer. The strongly hydrated Li⁺ ions transfer water molecules into the microcrystals, while simultaneously with the incorporation of K⁺, Rb⁺, and Cs⁺ ions H₂O molecules leave the surface layer. The opposite transport of ions and solvent molecules occur during oxidation. In the course of further reduction the incorporation of all ions studied except that of Cs⁺ ions is accompanied with water sorption. The number of sorbed water molecules is proportional to the hydration number of these ions. A reaction scheme is proposed in which M⁺ _m-3[Ru^IIICl _m (H₂O) _n ]^3-m · xH₂O (m≥3) and [Ru^IIICl _m (H₂O) _n ]^3-m (Cl⁻)_3-m · xH₂O (m≤3) type complexes are reduced to the respective – or depending on the electrolyte concentration higher or lower – Ru(II)chloro complexes resulting in mixed valence compounds (phases). Taking into account the layered structure of RuCl₃ the electrochemical reduction can be explained as an intercalation reaction in that mixed valence intercalation phases with a general formula M _x ⁺(H₂O) _y [RuCl₃] ^x− are formed from RuCl₃·x H₂O. The reduction/reoxidation waves are related to the redox transformations of Ru(III) to Ru(II) sites, while the composition of the polynuclear complexes and the structure of microcrystals change. Presented at the 4th Baltic Conference on Electrochemistry, Greifswald, March 13.−16., 2005.     

Microscopic observation of the crystalline form of poly(<Emphasis Type="Italic">o</Emphasis>-methoxyaniline) on a membrane electrode

We describe electrochemical and microscopic (SEM) studies on the electrochemical polymerization of poly(o-methoxyaniline). The crystalline form of the polymer was obtained. The poly(o-methoxyaniline) crystals are formed on a membrane electrode from an acidic solution of the monomer. It is suggested that the pores of the membrane work as nuclear crystallization points.Contribution to the 3rd Baltic Conference on Electrochemistry, Gdansk-Sobieszewo, Poland, 23–26 April 2003Dedicated to the memory of Harry B. Mark, Jr. (28 February 1934–3 March 2003)     

Study of the electrochemical behaviour of a carbon steel electrode in sodium sulfate aqueous solutions using electrochemical impedance spectroscopy

The study of a plain carbon steel (AISI 1020) in Na₂SO₄ aqueous solutions at different concentrations was carried out by electrochemical impedance spectroscopy (EIS) in order to determine the corrosion mechanism and to obtain representative corrosion rates of the system. EIS was used to measure corrosion current densities at high concentrations in the range 0.1–1 wt% Na₂SO₄, but in the low concentration range, from 0.001 to 0.01 wt%, a scattered Nyquist plot was obtained. Other electrochemical techniques, such as polarization resistance (PR), Tafel plots and electrochemical noise (EN), were also used in this analysis. The charge transfer resistance was determined and compared with the PR and noise resistance. Electronic Publication     

Synthetic diamond, a new electrode material for electroanalysis

Depending on the doping level, diamond exhibits properties of either a semiconductor or a semimetal. Heavily doped “metallic” diamond was found to be a corrosion-resistant electrode, suitable for electrochemical syntheses and analyses. The advantages of synthetic diamond in electroanalytical chemistry are its corrosion resistance, good reproducibility of electrochemical properties, low background currents, and selectivity to a number of reactions used to develop electroanalytical methods. Presented at the V All-Russian Conference with the Participation of CIS Countries on Electrochemical Methods of Analysis (EMA-99), Moscow, December 6–8, 1999.     

Evaluation of corrosion behaviour of selected metallic samples by electrochemical noise measurements

Electrochemical noise (EN) denotes spontaneous fluctuations in potential and current originating from the corrosion processes. In this work, EN was measured for three model metallic materials of known corrosion properties: Al, Fe and Fe30Al. Corrosion behaviour was assessed in neutral, acidic or alkaline solutions containing 4 wt% NaCl. Correlation between the electrochemical noise and corrosion intensity was established on the basis of appropriate treatment of the recorded numerical data and ex situ examination of the specimen surface. The parameter, referred to as EN resistance, allowed relatively simple and rapid evaluation of the corrosion behaviour of the investigated metallic materials.     

Online Monitoring of the Atmospheric Corrosion of Aluminium Alloys Using Electrochemical Noise Technique

In this work, an electrochemical system based on electrochemical noise (EN) technique for online detection and monitoring of atmospheric corrosion of LY12CZ aluminium alloys has been established. A detecting probe and a monitoring instrument with a software have been developed to perform the electrochemical noise measurements with zero resistance ammeter (ZRA) mode. Experimental results show that the atmospheric corrosion behaviour of aluminium could be effectively detected and monitored by the analysis of the electrochemical potential and current noise, also by the noise resistance variation.     

Corrosion monitoring using electrochemical noise and linear polarization resistance in fuel oil combustion gas environment

Corrosion monitoring of different steels is carried out online in a combustion rig firing 32 kg/h of fuel oil. Two temperature-controlled probes are designed to allow control of the specimens temperature and the use of electrochemical noise (EN) and linear polarization resistance (LPR) techniques for corrosion monitoring. Two probes are placed where the combustion gas reached a temperature of 850–900°C, and another one at the combustion gas exit where the rig was at 200–240°C. Corrosion rates of an austenitic and a ferritic steel are obtained where the temperature of the combustion gas is 850–900°C, firing fuel oils with different content of Na-V-S. Corrosion monitoring of mild steel is carried out in the test burning a fuel oil with the higher content of Na-V-S by placing a corrosion probe in the low combustion gas temperature zone. The EN results show that this technique is able to assess the corrosion rate in an environment at high temperature where fuel oil ashes deposited and at a temperature high enough where they start to melt and a corrosion process proceeds. Results show that this technique is able to assess the corrosivity of fuel oil ashes originated from fuel oil containing different amounts of sodium, vanadium, and sulfur as corrosion causing impurities. Results of the low-temperature probe show that EN and LPR are able to detect the onset of corrosion on mild steel as a result of sulfuric acid condensation on the probe. However, the corrosion rates are not the same, because localized corrosion is taking place as detected by the EN technique. It is demonstrated that the use of two techniques for corrosion monitoring can give a better understanding of the corrosion process. Electrochemical techniques used to assess the corrosion resistance of alloys at high and low temperatures prove to be a valuable tool for the purposes of materials selection or controlling the main process variables that affect the corrosion resistance of materials in industrial equipment. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 5, pp. 627–632. The text was submitted by the authors in English.     

Ergodic Analysis of Three-Dimensional Chebyshev Spectrum of Electrochemical Noise

Russian Journal of Electrochemistry - The ergodicity of electrochemical noise of corrosion process with respect to the three-dimensional Chebyshev spectrum is studied. The electrochemical noise of...