The effect of sulfate and nitrate ions on the passivation and activation of silver in alkaline solutions

Based on the concept of a competitive adsorption of hydroxide ions with SO₄²⁻ and NO₃⁻ activating anions, some peculiarities of the anodic behavior of silver in alkaline solutions containing sulfates or nitrates are explained. At the ascending branches of the anodic peaks, a co-adsorption of OH⁻ and SO₄²⁻ or NO₃⁻ results in the formation of mixed adsorption complexes, which are soluble better than hydroxide ones. An increase in the part of the soluble oxidation products of silver is observed if a rotating disc electrode with a ring is used. Passivation of silver is explained by a change in the electronic structure of the adsorption complexes when certain potential values are reached, while a local activation, by the destruction of these complexes at the passive state potentials between the anodic peaks. At the depassivation, pH value of the solution in pits decreases, which results in the formation of Ag₂SO₄ or AgNO₃ salts. The presence of the salts in a deposit on the electrode is confirmed by the appearance of a C ₃ cathodic peak. Original Russian Text ? N.N. Lesnykh, N.M. Tutukina, I.K. Marshakov, 2008, published in Fizikokhimiya Poverkhnosti i Zashchita Materialov, 2008, Vol. 44, No. 5, pp. 472–477.     

Electrochemical synthesis of polypyrrole on aluminium in different anions and corrosion protection of aluminium

In this study, polypyrrole was deposited on the aluminium in different anions (CO₃²⁻, NO₂⁻, CrO₄²⁻, DBS⁻). The contribution of anions to formation of polypyrrole film was investigated by using cyclic voltammetry (CV) technique. The effect of polypyrrole film on the corrosion of aluminium was searched in 0.1 M HCI solution by using potentiostatic method. For this purpose, polarization curves were obtained, corrosion current density (icorr), corrosion potential (Ecorr), polarization resistance (Rp) were determined from the polarization curves. Moreover, the percent efficiency of coating was calculated. The complexes of pyrrole pentamers and different anions (CO₃²⁻, NO₂⁻, CrO₄²⁻, DBS⁻) were studied using ab initio quantum chemical at the Hartree-Fock (HF) levels with STO-3G, 3-21G, 6-31G(d,p) [13] basis sets and HOMO-LUMO energy gap is calculated by B3LYP method with 3-21G* and 6-31G(d,p) basis sets. The polypyrrole film obtained in CrO₄²⁻ anion is determined to be the most effective in prevention to pitting corrosion of aluminium as experimental and theoretical.     

Gold anion catalysis of methane to methanol

The oxidation of CH₄ has been investigated in the presence and absence of the atomic Au⁻ ion catalyst. We have employed the first principles density functional theory (DFT) and dispersion-corrected DFT calculations for the transition state on the Au⁻ ion and analyzed the thermodynamics properties of the reactions as well. Our results demonstrate that atomic gold anions could be used to catalyze CH₄ into valuable industrial products without the emission of CO₂, thereby making gold extremely valuable. The fundamental mechanism involves breaking the C–H bond through the formation of the anionic Au⁻(CH₄) molecular complex permitting the oxidation of CH₄ to methanol at the temperature of 325 K which is below that of CO₂ emission. Potentially, this could significantly impact the quality of our environment.     

Electrodeposition of platinum metal and platinum-rhodium alloy on titanium substrates

A method for application of an adherent platinum (Pt) and platinum-rhodium (Pt-Rh) alloy plate to a titanium (Ti) substrate includes steps of surface pretreatment, anodization, and electrodeposition of Pt and Pt-Rh alloy from their electrolytic baths consisting of H₂Pt₂Cl₆·6H₂O (20 gL⁻¹), and HCl (300 gL⁻¹) for a Pt bath. The Pt-Rh bath consists of H₂Pt₂Cl₆·6H₂O (20 gL⁻¹), and HCl (300 gL⁻¹) and Rh₂ (SO₄)₃ (2 gL⁻¹). At the optimum conditions of electroplating, the Pt and Pt-Rh deposits were formed over the anodized Ti substrates with high adhesion, brightness, and high current efficiency (35.33% for Pt and 70.38% for the Pt-Rh alloy).     

Nickel electrodeposition from novel lactate bath

Abstract

A new electroplating bath for nickel deposition has been developed. Lactic acid was used as a complexing agent in the bath replacing boric acid. The effect of bath composition, current density, pH and temperature on the cathodic polarisation, cathodic current efficiency, morphology and structure of the deposit was carried out. Optimum conditions for producing sound and satisfactory nickel deposits were: 0·30M NiSO₄.7H₂O, 0·50–1·0M lactic acid and 0·3M Na₂SO₄ at pH=10, c.d.=0·98 to 9·80 mA cm^?2 and 25°C. The surface morphology of the deposited nickel was investigated using SEM. The crystal structure was examined by X-ray diffraction analysis. The results showed that the nickel deposits have a face centred cubic structure.     

An application of electrochemical method for studying nano-composite plating

Nickel plating is investigated using an electrochemical method in this study. Cathodic polarization indicated that electrode polarization at a current density of 10⁻¹ A/cm² increased by approximately 100 mV in a pH range 3–5, and by nearly 150 mV with 1 g/L of carbon powder in a Watts solution, as compared to bare nickel. The influence of inert particles such as carbon powder, silicon carbide and rice husk ash included in the nickel deposit was studied further using a potentiodynamic technique. Results showed that a co-deposit of nano-particles increased cathodic polarization. With a three-fold increase of the carbon powder in the plating solution, the polarization potential of the nickel deposit was doubled at a current density of 10⁻² A/cm². Passivation of the nickel deposit in the presence of all of the inert particles studied was improved in the area of hundreds of times higher compared to a bare nickel deposit. By increasing the amount of inert particles to twenty times the original amount, the passive current density was decreased by 85–95%. A co-deposit of rice husk ash in the nickel deposit decreased the passive current density by 98%, compared to a carbon and silicon carbide powder. Thus, rice husk ash has the potential to improve the pitting corrosion resistance of nickel composite plating.     

Effect of cyclic benzo-12-crown-4 polyether on copper electrodepsosition from sulfate aqueous ethanol baths

It is found that the effectiveness of crown ether (with benzo-12-crown-4 as an example) is a function of the composition of the water-ethanol solvent and the bulk and surface concentration of sulfate anions. An increase in the adsorbability of sulfate anions at Cu in the presence of the crown ether (Ψ’-effect) enhances its inhibitive effect on copper electrodeposition. The electrode reaction is best inhibited, and electroplates with enhanced tribotechnical characteristics are obtained, in the zone of ethanol structure stabilization, in which the adsorption of SO₄ ²⁻ anions by copper is the highest because of the “desalting” effect. Original Russian Text ? V.V. Kuznetsov, L.M. Skibina, S.V. Geshel’, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 3, pp. 272–278.     

Effect of the composition of water-acetone solvent and benzhydrazine structure on their efficiency during cadmium electrodeposition from perchlorate media

The feasibility of controlling the degree of retardation of a cathodic process by changing the ratio of the components in the liquid phase and nature of electron shifts in additive molecule (benzhydrazine) is discussed. The minimum electrode reaction rate is observed in a range of water structure stabilization under conditions of the predominant adsorption of organic molecules. The highest efficiency are achieved using an additive with an electron-donating substituent in the molecule. The highest rate of the electroreduction of Cd²⁺ and the lowest efficiency of the additives are registered in the region of the loosening of the structure of the mixed solvent, causing selective ion solvation to become possible, which results in an abrupt increase in the adsorption activity of ClO₄⁻ anions on the cathode and is the main reason for the ψ’ effect during the electroreduction of metal ions.     

Characterization of Hydrogen Permeation in Armco-Fe during Cathodic Polarization in Aqueous Electrolytic Media

The study of hydrogen permeation behavior in Armco-Fe showed that 0.1 M H₂SO₄ was a more effective medium for cathodic polarization compared to 0.1 M NaOH. When both electrolytes were “poisoned” with 1.00 g/L Na₂HAsO₄ · 7H₂O, as hydrogen recombination inhibitor, the corresponding hydrogen permeation levels were 3.5 × 10⁻⁵ A/cm² in 0.1 M H₂SO₄ while 0.75 × 10⁻⁵ A/cm² in 0.1 M NaOH. The breakthrough times were less than 30 s in 0.1 M H₂SO₄, while about 100 s in the NaOH. With varying amounts of “poisons”, peak permeation of hydrogen (1.75 × 10⁻⁵ A/cm²) was achieved with 10 g/L Na₂HAsO₄ · 7H₂O in 0.1 M H₂SO₄, while the least permeation resulted with 10 g/L (NH₂CSH₂) Thiourea addition for same level of 1.00 mA/cm² cathodic polarization.     

Electroplating of nickel from acetate based bath – Hull Cell studies

Abstract

Electroplating of nickel onto steel substrates from an electroplating bath containing nickel acetate, nickel chloride, boric acid and acetic acid has been investigated under different levels of operating conditions such as bath composition, current density and temperature. A detailed study has been made on the influence of these variables by measuring cathodic current efficiency and throwing power for various baths. Deposition parameters have been optimised using Hull Cell experiments. From potentiodynamic polarisation studies on Ni deposits it was revealed that E _corr moved towards the more negative direction. It is inferred from this fact that there is cathodic control of the corrosion reaction. The R _t value increases with increasing deposit thickness and the corresponding C _dl value is decreased.     

Specific effects of propargyl alcohol and propargyl chloride on an iron electrode in inorganic acids

The effect of acetylenic compounds, namely, propargyl alcohol (PA) and propargyl chloride (PC), on electrode processes occurring on Armco iron in hydrochloric, sulfuric, phosphoric, and perchloric acids was studied with the use of potentiostatic polarization. In oxygen-containing acids with hydrophilic anions, PA and PC are hydrogenated, thus decreasing the cathodic overpotential and significantly retarding iron ionization, which causes pitting at a free corrosion potential. More hydrophobic Cl⁻ anions increase the cathodic overpotential and hinder the hydrogenation process. Propargyl chloride inhibits electrode reactions and iron corrosion more effectively than does less hydrophobic PA.     

Characterization of Zinc-Cobalt Electrodeposits

The structure and morphology of electrodeposits depend on many factors including temperature, current density, time of deposition and composition of the bath. The properties of an electrodeposit depend on its micro structure. For example corrosion and wear resistance, hardness, internal stress, strength, brightness, electrical conductivity, magnetic properties and leveling are all affected by structure.

The relationships between electroplating parameters such as current density, temperature, bath agitation and electrolyte composition have been investigated for the zinc-cobalt system. It was found that electrolyte composition and temperature affect both deposit composition and morphology. The cathodic current efficiency decreased with current density and hardness was raised with increasing cobalt content in the deposit.

Three powerful techniques were used to access the microstructure of zinc-cobalt deposits: scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The results show that the alloy is constituted of a single phase of a solid solution of cobalt dissolved in zinc within an hexagonal crystal system. The deposit is porous and changes from dendritic to nodular with increasing cobalt content.     

Sensing behavior of silica-coated Au nanoparticles towards nitrobenzene

In the present work, we report silica-stabilized gold nanoparticles (SiO₂/Au NPs) as a wide-range sensitive sensing material towards nitrobenzene (NB). Surface hydroxyl groups of silica selectively form Meisenheimer complex with electron-deficient aromatic ring of NB and facilitate its immobilization and subsequent catalytic reduction by Au cores. Silica-coated Au NPs were synthesized and characterized for their chemical, morphological, structural, and optical properties. SiO₂/Au NPs-modified electrodes were characterized with impedometric and cyclic voltammetric electrochemical techniques. SiO₂/Au NPs are found to have a higher optical detection window of range, 0.1 M to 1 μM and a lower electrochemical detection window of range, 10⁻⁴ to 2.5 × 10⁻² mM with a detection limit of 12.3 ppb. A significant enhancement in cathodic peak current, C ₁, and sensitivity (102 μA/mM) was observed with modified electrode relative to bare and silica-modified electrodes. The I _P was found to be linearly co-related to NB concentration (R ² = 0.985). The interference of cationic and anionic species on sensor sensitivity was also studied. Selectivity in the present sensing system may be further improved by modifying silica with specific functional moieties.     

Influence of corrosion properties on electrochemical migration susceptibility of SnPb solders for PCBs

Electrochemical migration is caused by the adsorption of water and the bias voltages between the electrodes or pads which form an electric circuit or in the solders used to connect the parts. This work focused on the elucidation of the mechanisms of electrochemical migration of pure Sn, Sn37Pb, and Sn55Pb solders in electronics. The electrochemical migration behavior was discussed on the basis of the polarization behavior of SnPb solders. After the water drop test, the time to failure decreased with increasing Pb content in Cl⁻ solution and increased with increasing Pb content in SO₄ ²⁻ solution. In the case of the SnPb solder alloys, the pitting potential, the passive current density, the cathodic current density and the efficiency of cathodic deposition of the alloying elements were closely related to the resistance of the electrochemical migration.     

Influence of Bath Compositions and Some Operating Conditions on the Electroplating of Cobalt from Aqueous Sulphate Baths

A systematic study has been made of the influence of aqueous sulphate bath constituents on the cathodic polarization curves during cobalt electrodeposition. The optimum bath composition has been established and it contains: 0.30 mol l^?1 CoSO₄.7 H₃0, 0.30 mol^?1 H₃BO₃. 0.05 mol l^?1 (NH₄)₂SO₄ and 0.10 mole l^?1 Na₂SO₄.10 H₂o. Cobalt electroplating from the optimized bath has been performed under a variety of conditions viz: pH, 1.5 to 5.3; current density, 0.2 to 2.0 A dm^?2 and temperature 25 to 53°C. Under the most suitable conditions, the optimum bath is characterized by a high cathodic efficiency (~ 99%), moderate throwing power (21.6%) and throwing index (1.47). The bath produced smooth, adherent and semibright plates characterized by a high microhardness (411.4 kgf mm^?2) and their morphologies, as revealed by scanning electron microscopy, showed a dependence on the plating variables.     

Embrittlement of a Duplex Stainless Steel in Acidic Environment Under Applied Cathodic Potentials

Hydrogen-induced degradation of mechanical properties of a duplex stainless steel in 0.1N H₂SO₄ solution has been studied under in situ cathodic charging conditions. Significant reductions in percentage of elongation, toughness, and time to failure were noticed due to the ingress of hydrogen into the material at various applied cathodic potentials in the range of −200 to −800 mV (SCE). Cleavage fractures were identified mainly in the ferritic phases. Crack growth was observed to be inhibited by the austenite phase. However, depending on the severity of the environment, both the ferrite and austenite phases could be embrittled. At less negative potentials, presence of surface film and low hydrogen fugacity seemed to control hydrogen ingress in the metal. Addition of thiosulfate to the acidic solution further degraded the mechanical properties of the steel at the applied cathodic potential.     

Electrodeposition of alloys XIX: Electrodeposition of lead-tin alloys

Pb-Sn alloys containing from 1.2 to 94.3 wt.% Sn were electrodeposited from aqueous solutions prepared from diethylenetriaminepentaacetates of the two metals. The effects of current density and the solution composition on the composition of deposits and cathodic current efficiencies were investigated. Pb-Sn alloy deposition was of irregular type. At current densities equal to or less than 2.0 A dm^-2, lead deposited preferentially. At current densities of more than 2.0 A dm^-2 and in solutions containing more than 50.0 met.% Sn (the percentage weight of the total metal content), preferential deposition of tin occured. An increased in the tin content of the bath increased the percentage of tin in the deposit. The presence of chloride ions in the bath did not seem to affect the composition of the deposit.     

The corrosion inhibition of Ti-alloy (VT-9) in mixture of H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-NaF by organic compounds

This investigation deals with corrosion behavior of high strength titanium alloy in concentrated sulphuric acid solution containing different concentrations (500, 1000, 1500 ppm) of fluoride ion (F⁻) using various organic compounds (MPA, L-OH, NFP) as inhibitor, potentiodynamically. The open circuit potential values noted before and after each experiment, varied appreciably. These values were negative before polarization but after completion of the experiment turned positive and remained stable over long period of time. It is observed that cathodic current density values increase with increasing cathodic potential (more negative) and fluoride ion. The values of cathodic Tafel slopes derived from the curves (∼110 − 140 mV/dec I) indicate hydrogen evolution reaction (h.e.r). The corrosion potential (E _corr) varied slightly with addition of inhibitors. The corrosion current densities (I _corr) increased with increasing fluoride ion concentration, but these values decreased appreciably when inhibitor (MPA) was used. SEM micrograph reveals reduction of pits in the presence of inhibitor (MPA). So this concludes that organic compound was used in this case acts as a good inhibitor. The article is published in the original.     

CO<Subscript>2</Subscript> electrochemical reduction via adsorbed halide anions

The electrochemical reduction of CO₂ was studied utilizing halide ions as electrolytes, specifically, aqueous solutions of KCl, KBr, KI. Electrochemical experiments were carried out in a laboratory-made, divided H-type cell. The working electrode was a copper mesh, while the counter and reference electrodes were a Pt wire and an Ag/AgCl electrode, respectively. The results of our work suggest a reaction mechanism for the electrochemical reduction of CO₂ where the presence of Cu-X as the catalytic layer facilitates the electron transfer from the electrode to CO₂. Electron-transfer to CO₂ may occur via the X⁻ _ad(Br⁻, Cl⁻, I⁻)-C bond, which is formed by the electron flow from the specifically adsorbed halide anion to the vacant orbital of CO₂. The stronger the adsorption of the halide anion to the electrode, the more strongly CO₂ is restrained, resulting in higher CO₂ reduction current. Furthermore, it is suggested that specifically adsorbed halide anions could suppress the adsorption of protons; leading to a higher hydrogen overvoltage. These effects may synergistically mitigate the over potential necessary for CO₂ reduction, and thus increase the rate of electrochemical CO₂ reduction.