A Rotating Ring-Disc Electrode Study of the Hydrogen Evolution during Zinc Deposition from Zincate Electrolytes

The rotating ring-disc electrode technique offers a simple method for determination of the evolved hydrogen by its detection at the ring during zinc deposition on the disc (steel).

Potentiodynamic investigations have established an increased hydrogen production with shifting of the cathode (disc) potential towards the more negative direction.

The measurements of the ring current versus time at constant disc current show that the hydrogen evolution is intensive mainly in the first 1–2 sec of the zinc deposition. Thereafter it decreases gradually and becomes constant after 3–4 min period from the beginning.

It was found from the cathodic and anodic potentiodynamic curves that the process of hydrogen evolution during zinc deposition was stimulated in the presence of the additives in the electrolyte, particularly by the combinations of basic additives and brighteners.     

Hydrogen entry into steel during atmospheric corrosion process

Hydrogen entry and permeation into iron were measured by an electrochemical method during atmospheric corrosion reaction. The hydrogen permeation was enhanced on passive films because the hydrogen adsorption increased by the hydrogen evolution mechanism which is different from that on a bear iron surface. The permeation rate during a wet and dry corrosion cycle showed a maximum in the drying process depending upon the surface pH and the corrosion potential. The pollutant such as Na₂SO₃ which decreases the pH and the corrosion potential causes an increase in the permeation rate. The mechanism of the change in the permeation rate during the wet and dry cycles is explained by the polarization diagram of the electrode covered by thin water layer.     

镍硫钴析氢电极的制备及性能研究

采用电沉积方法制备Ni-S-Co合金电极,通过正交实验和极化曲线测试研究了CoSO4·7H2O浓度、电流密度、电镀液温度、电沉积时间和电解液温度对Ni-S-Co电极析氢性能的影响.采用SEM,XRD和EDXA对镀层的形貌、结构和组成进行观察和分析.实验结果表明:制备具有最佳析氢活性的Ni-S-Co电极的工艺条件是25 ...     

Electrodeposition, characterization and long term stability of NiW and NiWZn coatings on copper substrate in alkaline solution

This paper describes the electrodeposition of Ni, NiW and NiWZn coatings onto copper surfaces from electrolyte solutions containing Na₃C₆H₅O₇, Na₂WO₄, NiSO₄ and ZnSO₄. The electrocatalytic effects of electrodeposited coatings were investigated for hydrogen evolution reactions in 1 M NaOH solution. Surface characterization studies were carried out by energy dispersive X-ray spectroscopy, scanning electron microscopy, atomic force microscopy and cross-section analysis. The effect of operating conditions on the chemical composition, microstructure and electrocatalytic properties of Ni-W coatings was studied. The Zn ions were used to improve the active surface area and catalytic activity of the electrodeposited surface. The electrocatalytic activity of NiW and NiWZn coated electrodes for the hydrogen evolution reaction in alkaline solution was compared with that of an electrodeposited Ni electrode and copper substrate by using cathodic polarization curves and electrochemical impedance spectroscopy techniques over 96 h of electrolysis. The results proved that the NiWZn coated electrode showed better electrocatalytic activity and durability than bare Cu, Ni and NiW coatings.     

Effect of corrosion medium composition on rate of crack growth in X70 pipeline steel

The growth rates of corrosion cracks in X70 pipeline steel are determined in weakly acidic (pH 5.5) buffer solution with additives of a number of compounds that are a part of the soil electrolyte or are steel corrosion inhibitors. It is shown that the effect of components of electrolyte on the rate of crack growth agrees fairly well with their stimulating or inhibiting effect on the anodic dissolution of iron. The rates of hydrogen permeation into steel are measured and the effect of hydrogen absorbed by the metal on the anodic process in the studied corrosion media is considered.     

添加剂对Zn/KOH/AgO电池性能的影响

本文以电沉积锌为负极,过氧化银为正极,KOH溶液为电解质,组装成Zn/KOH/ AgO模拟电池.研究不同浓度的KOH电解质溶液对Zn/KOH/AgO电池比容量的影响,探索电解质溶液中不同添加剂对电池放电过程中锌电极钝化的影响,并考察了放电倍率对电池性能的影响.结果表明:KOH电解质溶液的最佳浓度为5 mol/L,电解质...     

Diffusion Phenomena of Electrolytic Hydrogen in Pure Iron Membranes

Abstract

The variation of overpotential with time on iron membranes cathodically polarised in M/3 sulphuric acid has been found to be due to the formation of an adsorbed layer of hydrogen. This layer decays with time but it can be removed by the application of an alternating current.

Anomalous time-lag curves, permeation maxima and the formation of ‘barriers’ in the course of diffusion of electrolytic hydrogen reported in the literature can be largely attributed to the surface adsorbed hydrogen.

Hydrogen concentrations determined from diffusivity and permeation values are presented together with an experimental methodfor the determination of hydrogen retained in traps.     

Studies on the Mechanism,Structure and Microhardness of Ni-W Alloy Electrodeposits

The electrodeposition of Ni-W alloy has been studied on the glassy carbon electrode by the cyclic voltammetry and potentiostatic step methods. It has been found that electrodeposition of Ni-W alloy involves an intermediate valence tungsten oxide which inhibits hydrogen evolution. Ni-W alloy electrodeposition occurs by a mechanism involving progressive nucleation followed by three dimensional growth.

The structures of nickel-tungsten alloy deposits were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The XRD results from Ni-W alloy deposits reveal a face-centered cubic solid solution, the microstructure of the deposits exhibit (111) preferred orientation. The lattice constant and microhardness of Ni-W alloy deposit increase as the tungsten content increases, the XPS results of Ni-W alloy deposits indicate that the nickel and tungsten of the deposits exist in the metallic state, but the Ni-W alloy deposit with a tungsten content of 40.7% is an intermetallic compound. The XPS results of the deposit with tungsten content of 40.7% show that the atomic ratio of Ni to W is 4:1, so β-Ni₄ W alloy can be obtained by electrodeposition and its microhardness (Hv) is as high as 672.8.     

Amperometric hydrogen permeation measurement in iron using solid polymer electrolyte fuel cells

Electrolytic hydrogen permeation through iron membranes was measured simultaneously by means of a solid polymer electrolyte fuel cell (SPEFC) and standard aqueous-phase hydrogen oxidation. Two configurations of SPEFC were tested: the first included a separate anode for hydrogen oxidation and the second used the iron membrane surface itself, plated with palladium, as the anode. The results showed a limiting hydrogen permeation flux for the first configuration but not for the second, which yielded about 64% of the correct output.     

A Study on Zinc-Iron Alloy Electrodeposition from a Chloride-Electrolyte

The electrodeposition of zinc-iron alloys from a chloride-based electrolyte has been studied using electrochemical polarisation techniques, Ager Electron Spectroscopy (AES), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDXA) and Computer Assisted Pulse Plating (CAPP).

A change in the electrodeposition mechanism from equilibrium codeposition to anomalous codeposition with a change in cathodic current density has been observed.

Zn-Fe alloys with compositions ranging from less than 5 wt-% to more than 75 wt-% Fe have been electrodeposited from a single electrolyte, making this system ideal for production of compositional modulated alloy (CMA) electrodeposits. Chloride content, pH and agitation of the electrolyte have been observed to have a strong influence on the reaction at the cathode surface, just as the use of pulse reversal current during electrodeposition.

A theory on the electrodeposition mechanism, accounting for the above observations, is presented.     

Effect of Arsenic on Permeation of Hydrogen Through Steel Membranes polarized cathodically in aqueous solution

A sensitive technique is developed for studying the effect of As and its compounds on the permeation of hydrogen through steel membranes electrolytically charged at various pH values. Use of a rotating disc electrode permits to change pH at the cathode over a large range without changing composition of the bulk electrolyte. The results of this study strongly support previous conclusions as to the dominant part played by promoter hydrides as species accelerating the entry of hydrogen into metals. In the case under consideration, AsH₃ has been found to promote the permeation of hydrogen evolved from acid and alkaline media. On the other hand, surface films, deposits, and precipitates of As impede the entry of hydrogen into the steel.     

Deposits formed on iron during cathodic polarization in the presence of arsenic and their effect on hydrogen permeation

Deposits produced on iron and steel during cathodic polarization in the presence and absence of arsenic in acid and alkaline solutions have been studied microscopically, by electron microprobe analysis, and by double layer capacity measurements. The results of these studies are compared with permeation rates of hydrogen through rotating membranes. It is shown that the compactness of the deposits and their effect on the permeation depend on following major factors: surface condition and pre-treatment of the cathode, pH of the electrolyte, As concentration, electrode potential. Elemental arsenic deposited on the cathode does not promote the permeation of hydrogen. On the contrary, adherent and compact films impede the entry of hydrogen into the metal phase. Arsine adsorbed on the metal surface is the main promoting species.     

The Effect of Sorbed Hydrogen on the Dissolution of Iron in a Thiocyanate-Containing Sulfuric Acid

With the cycling of potential step, the dissolution rate of iron is shown to decrease with an increase in the degree of its surface coverage with hydrogen atoms. With a bipolar electrode (a membrane), an increase in the concentration of hydrogen in the metal phase was found to decelerate the anodic dissolution of iron in a base sulfate electrolyte and accelerate it in the presence of thiocyanate ions. The latter phenomenon indicates the possibility of activating the ionization of iron with the hydrogen dissolved in it. The rate constants of individual stages of the cathodic evolution of hydrogen are calculated.     

The effect of additives on the corrosion resistance of Zn electrode in alkaline battery system

Zn electrodes are widely used as an anode material in alkaline battery systems in highly concentrated KOH electrolyte. However, it is well known that their life cycle is significantly shortened due to dendrite growth caused by high dissolution and rapid electrochemical reaction. In this study, additives such as Ca(OH)_￡σ, citrate, tartrate, and gluconate were added to 40% KOH electrolyte solution at 25 and 5 wt.% Pb₃O₄ was mixed with the Zn electrode. The effects of both Pb₃O₄ and the additives on the electrochemical behavior of the Zn electrode were investigated through corrosion potential measurements, potentiodynamic polarization curves, cyclic voltammetry, and SEM photographs. The addition of Pb₃O₄ had a considerable effect on decreasing the corrosion rate of the Zn electrode, and the corrosion potential of the Zn electrode with Pb₃O₄ addition shifted to a more positive potential than that of a pure Zn electrode. However, upon addition of other additives, the corrosion potential was slightly shifted to the negative direction again. The addition of 4 kinds of additives appeared to play an important role in improving the corrosion resistance. Moreover, among the four additives, tartrate displayed a relatively good effect in terms of increasing the corrosion resistance as well as improving the discharging characteristics among.     

Double electrolyte sensor for monitoring hydrogen permeation rate in steels

An amperometric hydrogen sensor with double electrolytes composed of a gelatiniform electrolyte and KOH solution has been developed to determine the permeation rate of hydrogen atoms in steel equipment owing to hydrogen corrosion. The gelatiniform electrolyte was made of sodium polyacrylate (PAAS), carboxyl methyl cellulose (CMC) and 0.2 mol dm⁻³ KOH solution. The results show that the gelatiniform electrolyte containing 50 wt.% polymers has suitable viscosity and high electrical conductivity. The consistent permeation curves were detected by the sensor of the double electrolyte and single liquid KOH electrolyte, respectively. The developed sensor has good stability and reproducibility at room temperature.     

A study on cobalt electrodeposition onto a carbon steel electrode

Abstract

The electrodeposition of cobalt on to a carbon steel working electrode was studied through the comparison between theoretical and experimental polarisation curves. The former was obtained using the Butler–Volmer equation with electrochemical parameters, such as Tafel slope values, exchange current densities, cathodic limit current densities and equilibrium potential values. The following results were obtained: the anodic region refers to the iron oxidation with a Tafel slope of about 0·055 V decade^?1, which is near the theoretical value (0·059 V decade^?1); the experimental cathodic region represents the cobalt and hydrogen ion reduction; the limiting current density (?1 × 10^?3 to ?1 × 10^?2 A cm^?2) obtained was near the calculated value, ?3·7 × 10^?3 A cm^?2.     

Linear sweep voltammetry of the electrodeposition of copper from a methanesulfonic acid bath containing a perfluorinated cationic surfactant

The influence of a perfluorinated, cationic surfactant, DuPont™ ForaFac® 1098, on the electrodeposition of copper from a CH₃SO₃H bath was investigated. The background electrolyte contained 0.005 mol dm^− 3 hydroquinone and 12.5vol.% (1.93 mol dm^− 3) methanesulfonic acid, surfactant (0.002 to 0.12 vol.%) and copper ion (0.02 to 0.5 mol dm^− 3) at 23 °C. The effects of electrode rotation speed, surfactant concentration and copper ion concentration were investigated. Linear sweep voltammetry was used to identify the charge transfer, mixed control and mass transport control regions. Changes in the limiting current density, copper nucleation potential and hydrogen evolution potential are discussed. The shift in copper nucleation potential was also investigated as a function of the surfactant and copper ion concentrations. Copper was electrodeposited, at a constant potential, onto a rotating cylinder electrode and the surface morphology was characterised using scanning electron microscopy.     

Gas absorption in grey cast iron during mould filling

Abstract

The effect of mould filling on the hydrogen and nitrogen concentration in grey cast iron has been investigated. A special mould was designed and the influence of several process and mould parameters, such as degree of turbulence, permeability, core binder and coatings, were studied. The hydrogen concentration increased during mould filling and the absorption was favoured by turbulent filling, low permeability and larger gas evolution from the mould and cores. In some cases, the hydrogen concentration in the iron after mould filling almost reached the solubility limit, which increases the risk that gas precipitates during solidification.

Exact values of the influence of mould filling on the nitrogen concentration could not be obtained, but some observations could still be conducted. The absorption of nitrogen seemed to be favoured by the same parameters as hydrogen.     

Pulsed electrodeposition of hydroxyapatite on titanium substrate in solution containing hydrogen peroxide

Hydroxyapatite（HAP） coatings were prepared on the titanium substrate in the electrolyte containing H2O2 by the pulse electrodeposition. The introduction of H2O2 restrains the evolution of H2 and improves the adhesive strength between coatings and substrate. The results of pulse electrodeposition show that the relaxation time of the pulse is beneficial to growth of HAP because it makes ions diffuse from bulk to the surface of electrode and reduces concentration polarization in the next pulse time. It is beneficial to the increase of the duty circle of the pulse for deposition of HAP, but the result is not good if it is increased excessively. With increasing potential, it is good for the growth of HAP coatings. If the potential is too high, if is easy for HAP coatings to drop off during the process of electrodeposition under too intensive polarization, such as -1.0 V （vs SCE）, and there is not many coatings on the substrate. The combination of pulse electrodeposition and addition of hydrogen peroxide can assuredly improve the physico-chemical properties ofhydroxyapatite coatings.     

Electrochemical behaviour of iron in alkaline sulphide solutions

Abstract

Cyclic voltammograms and galvanostatic polarisation curves were traced for the iron electrode in alkaline solutions containing sulphide species. In sulphide free NaOH solution, the galvanostatic anodic polarisation curves are characterised by two well defined steps before tending finally to values characteristic for the oxygen evolution reaction. However, using cyclic voltammetry technique, three anodic peaks are distinct. On the other hand, the cathodic half cycles using both techniques are characterised by two cathodic reduction steps before hydrogen evolution commences. In the presence of increasing sulphide content the polarisation curves are characterised by the presence of several anodic and cathodic regions. The anodic regions correspond to the simultaneous formation and oxidation of different Fe sulphide and oxide species. A mechanism is thus proposed for the formation and reduction of iron sulphide species.