Metal Dissolution Reaction Research Articles

Determination of the diffusion coefficients of ligands in metal complex systems

A model for the anodic dissolution of metal ions in solutions containing completing agents is presented. Together with experimental results from a rotation rate step technique on a rotating-disc electrode, it is used to determine the diffusion coefficients of ligand ions. Supplementary information on the metal dissolution reaction and the association kinetics of the metal complexes is obtained by fitting the calculated to the experimental current transients for the dissolution of silver in various complexing media.

Reaction distribution in a corroding pit

An analysis of the reaction distribution over a corroding pit is presented. If the liquid-phase conductivity and the interfacial rate constants for the metal-dissolution reaction are known, the results of this secondary current distribution problem can be used to estimate the maximum rate of pit growth. The approach taken involves the conformal mapping of the pit geometry onto a new coordinate system; the finished transformation is shown to remove the singularity at the pit edge and provide a bounded region over which only a limited number of mesh points are required to perform accurate numerical analysis. Numerical calculations for the pit dissolution rate subject to linear and Tafel polarization are fitted to simple expressions; as a consequence, the results of this work can be used without having to resort to numerical methods. For the linear polarization analysis, the results are generalized in a manner that allows one to consider an arbitrary number of reactions on the pit surface.

Metal deposition and dissolution monitored by In situ scanning tunneling microscopy

The possibilities of scanning tunnelling microscopy (STM) for the study of metal deposition and dissolution reactions under in situ electrochemical conditions will be described and illustrated by examples. The metal reaction being studied is copper deposition and dissolution on foreign substrates such as Au(111), or polycrystalline copper. Data on atomically-resolved copper adlayers and on bulk copper deposition on gold will be presented. In addition, time resolved in situ STM for the study of copper deposition and dissolution on polycrystalline copper will be shown as well. From the latter local reaction rates can be estimated. The necessity to consider a possible influence of the tip on the results will be emphasized and the reasons for such an interference of the tip will be briefly discussed.

Simulating Impedance Spectra from a Mechanistic Point of View: Diffusion Effects in Metal Dissolution Reactions.

Simulating Impedance Spectra from a Mechanistic Point of View: Diffusion Effects in Metal Dissolution Reactions.

Electrochemistry of Chromium‐Metalloid Alloys in Sulfuric Acid— II

The electrochemistry of glassy , , , and mixed‐phase glassy ∼A‐15, nanocrystalline were examined in comparison to chromium. For oxidizing conditions these materials are passive and exhibit similar film formation kinetics. In reducing environments, chromium is in the active state. The excellent corrosion behavior of and is attributed to the fact that, unlike chromium, these materials cannot be stably activated. The characteristics of chromium‐metalloid materials resemble that of chromium‐noble metal alloys. By analogy to the noble metals, alloying with phosphorus and boron accelerates the kinetics of proton reduction such that the steady‐state electrochemical potential of the system is set in a domain consistent with the passive state of chromium. The metalloids also block the metal dissolution reaction at active potentials. For the degree of anodic inhibition increases significantly with phosphorus concentration. The remarkable effect of the metalloids on corrosion resistance may be partially attributed to the metalloid‐hydride and proton reduction equilibria being positive of the active‐passive transition of chromium. This correlation helps rationalize the varying effects of alloying boron and phosphorus with different transition metals, e.g., reactive vs. passive .

Jet and Laser‐Jet Electrochemical Micromachining of Nickel and Steel

Experimental results on jet and laser‐jet electrochemical micromachining of nickel and steel in neutral solutions of sodium chloride and sodium nitrate are reported. In the absence of a laser beam, a nitrate solution is better suited for micromachining at high current densities, since it yields high machining rates and relatively low overcutting. In the presence of a laser beam, however, nitrate solution is found to be unsuitable for micromachining, since oxygen evolution is the dominant anodic reaction even at high current densities. In chloride solution, on the other hand, metal dissolution reaction is independent of laser power, but the laser beam helps in focusing the applied current into the machining area thereby increasing the effective machining rate and precision.

Influence of electrochemical potential on the wear of metals, particularly nickel

The wear of nickel and of alloy steels under the influence of an impressed potential is discussed in terms of a model which considers both the kinetic and thermodynamic properties of the metal/electrolyte reactions and of the electrochemical reactions of oxygen, hydrogen and water. The experimental data can be interpreted in terms of the electrochemical formation of an oxide film within the wear scar and its subsequent removal by mechanical action. The voltage range over which transitions to an increased wear rate occur are related to the Tafel slopes associated with metal dissolution reactions.

The influence of acid soluble sulfide inclusions on the passivation behaviour of austenitic CrNi stainless steels

The cathodic and anodic effects of acid soluble sulfide inclusions on the passivation behaviour of unstabilized austenitic CrNi(Mo) stainless steels were studied by means of potentiodynamic polarization measurements in 0.1 NH 2SO 4 acid solutions. The effects are due to alterations of the kinetics of both the anodic and cathodic partial processes of corrosion through H 2S or HS − ions resulting from the chemical dissolution of sulfide inclusions. Increasing amounts of H 2S or HS − ions in the electrolyte result in an increase in the hydrogen overvoltage with a coincidental decrease in the cathodic Tafel slope and an increasing stimulation of the anodic metal dissolution reaction.

The Effect of Ammonium Chloride and Fluid Velocity on the Corrosion Behavior of Copper in Sodium Bicarbonate Solutions

Abstract The effect of ammonium chloride additions on the corrosion behavior of copper in 1 N sodium bicarbonate solutions has been characterized using a rotating ring-ring linear cyclic voltammetry technique. The experimentation and solution compositions used were selected to account for an unusually high incidence of pitting found to occur on interior surfaces of copper cold-water plumbing fixtures in the vicinity of neutral soldering flux residues. Although concentrations of ammonium chloride above 0.05 N were found to result in an increase of corrosion rate often attributed to the stabilization of a cuprous ion complex metal dissolution reaction product, under freely corroding conditions in an air-saturated solution, corrosion of copper metal would occur by an anodic process in which current was distributed between both soluble metal ions (cuprous and cupric ions) and insoluble corrosion product deposits. Although increases in applied potential or relative fluid velocity produced increases in the total corrosion rate, there was also a change in current distribution between the various components of the overall anodic process. Results from this study suggest that soluble and insoluble corrosion products (cathodically or anodically generated during a single linear polarization cycle) affect corrosion behavior during either successive cycles or extended exposure periods to such an extent that sole reliance on single-cycle anodic polarization behavior for the prediction of long-term corrosion resistance for copper and its alloys should be avoided.

Aspects of the electrochemistry of lead in acid media Part II. Active dissolution in oxygenated and deoxygenated perchloric acid solutions

Steady-state current-potential, double-layer capacity and impedance measurements have been made on lead in 0.1 M and 5 M perchloric acid solutions under nitrogen and oxygen saturated conditions. It is shown that the metal dissolution reaction is a quasi-reversible process. Evidence for a charge-transfer mechanism involving two consecutive one-electron transfers is given with Pb [1] as an intermediate. A large enhancement in the rate of dissolution in the presence of oxygen is confirmed, although there is no evidence for a change in the reaction mechanism. It is suggested that these results will have consequences with regard to the operation of lead-acid batteries since, in particular, passivation processes at the negative are likely to affected.

Aspects of the electrochemistry of lead in acid media: Part II. Active dissolution in oxygenated and deoxygenated perchloric acid solutions

Steady-state current-potential, double-layer capacity and impedance measurements have been made on lead in 0.1 M and 5 M perchloric acid solutions under nitrogen and oxygen saturated conditions. It is shown that the metal dissolution reaction is a quasi-reversible process. Evidence for a charge-transfer mechanism involving two consecutive one-electron transfers is given with Pb [1] as an intermediate. A large enhancement in the rate of dissolution in the presence of oxygen is confirmed, although there is no evidence for a change in the reaction mechanism. It is suggested that these results will have consequences with regard to the operation of lead-acid batteries since, in particular, passivation processes at the negative are likely to affected.

Effect of Chloride Ions on the corrosion behaviour of iron‐nickel alloys in sulphuric acid solutions

AbstractThe effect of chloride ions on the corrosion behaviour of binary iron‐nickel alloys in sulphuric acid solutions has been investigated using polarization resistance and potentiodynamic polarization measurements. A moderate inhibition effect of the chloride ions on the corrosion of these alloys has been found, which depends on the pH of the medium, as well as on the composition and the structure of the alloys investigated. It has been shown that the action of the chloride ions on the partial corrosion reactions is reflected by an inhibition of the cathodic hydrogen evolution reaction and by an activation of the anodic metal dissolution reaction, the first effect being stronger. Using atomic absorption analysis it has been established that no preferentional dissolution of the alloy components in the presence and in the absence of chloride ions occurs during the corrosion of the iron‐nickel alloys.

Effect of Alternating Current on Corrosion of Low Alloy and Carbon Steels

Abstract The corrosion rates of low alloy steel and carbon steel in 0.1 N NaCI were accelerated by factors of 4 to 6 when an alternating current density of 30 mA/cm2 (60 cps) was applied in dilute salt solutions purged with nitrogen. Tests with low frequency alternating anodic and cathodic current showed that both steels polarized more rapidly in the cathodic direction than in the anodic. Thus, the anodic half-cycle of AC did not have time to restore the potential to its original value after the preceding cathodic half-cycle. The result is a net cathodic polarization which accelerates or “depolarizes” the anodic metal-dissolution reaction by lowering the anodic Tafel slope. Depolarization of the anodic reaction was confirmed by polarization measurements in the presence of AC. Depolarization of the anodic reaction by AC was also observed in aerated solutions, but the corrosion rate was controlled by diffusion of dissolved oxygen, and no increase in corrosion rate was measured. Possible mechanisms of anodic depolarization are discussed.

The corrosion behaviour of Al‐cast iron in sulfuric acid

AbstractThe polarisation behaviour of Al‐cast iron has been determined in sulfuric acid at 25°C and has been compared to the behaviour of classical cast iron and commercial steel in the same environment.It was concluded from indirect electrochemical measurements (δEcorr/δpH and δlog icorr/δpH) that the metal dissolution reaction was independent of pH under the given experimental conditions, and that bA = 0,05 V for the three alloys. bC changes from 0,116 V on steel to 0,305 V on classical cast iron and ∞ on Al‐cast iron. The B values are respectively 0,015 V; 0,019 V and 0,024 V 0,024 V.

The Röschenbleck equation

Several authors have proposed the use of the Röschenbleck equation δ E corr 2.3 δ pH = B as an alternative method for the determination of B. This latter value must be known when the linear polarization technique for the evaluation of the corrosion current density is used. This equation has however to be corrected, because it doesn't take the pH dependence of the partial metal dissolution reaction into account. The following equation is proposed: δ E corr 2.3 (p+q) δ pH = B with p and q respectively the reaction order of the partial current densities with respect to the hydroxyl and hydrogen ions.

Temperatur- und konzentrationsabhängigkeit der stromausbeute bei der transpassiven auflösung des eisens unter stationären bedingungen

It is possible, to write an expression for the current efficiency of transpassive metal-dissolution reactions, connected with an oxygen evolution, as a function of reaction cd. It can be shown, which parameter of this function is affected by temperature and the concentration of the reactants. The variation of this parameter allows the calculation of the order of the reactions and the activation energies. This introduces a new method for the estimation of kinetic parameters of electrode reactions at high cd, avoiding potential measurements. With respect to the practical importance of a mathematical expression for the current efficiency as a function of cd, concentration of electrolyte and temperature, for instance for the electrochemical machining, the validity of the deduced equations is demonstrated by experimental investigations concerned with the dissolution of steels in nitrate solutions.

Kinetics of electrode reactions in liquid ammonia. Part 3.—The silver electrode in acid solution

The behaviour of the silver electrode in acid solutions of liquid ammonia has been studied by steady and non-steady state electrochemical measurements and electron microscopy. The apparent rate constant and standard potential have been determined. The rate-determining step in silver deposition and dissolution is the charge transfer reaction which is probably coupled with an adatom diffusion mechanism. Oxidised species originating from the solvent are adsorbed on silver except at cathodic values of electrode potential. The anodic behaviour of silver is complicated by the formation of anodic deposits, probably silver nitride, in parallel with the metal dissolution reaction. By making comparisons with silver electro-deposition from simple and cyanide aqueous baths it is concluded that the adsorbed solvent decomposition products are responsible for the poor quality of deposits from ammoniacal electrolytes.

Oxygen Reduction and Corrosion Kinetics on Phase‐Oxide‐Free Palladium and Silver Electrodes as a Function of Temperature in 85% Orthophosphoric Acid

Oxygen reduction on oxide‐free palladium and silver surfaces has been studied as a function of temperature in purified 85% orthophosphoric acid. In each case, oxygen reduction is first order, and available evidence suggests that on both metals the reaction is the rate‐determining step. Experimental activation energies, extrapolated to the reversible oxygen electrode potential, are on palladium and about 26 kcal on silver. Activity of the palladium electrode is only slightly (< one decade) less than on platinum under the same conditions, whereas silver is even less active than gold. On palladium, as with platinum, the extrapolated activation energy includes a heat of adsorption term corresponding to the effect of Temkin‐type equilibrium adsorption of ‒O species derived from water oxidation, which are present on the electrode under the experimental conditions. This term may be eliminated by considering activation energies extrapolated to potentials at which ‒O adsorption is small, where an activation energy difference between silver and palladium on the order of 9.8 kcal occurs. This suggests that the intermediate is relatively strongly adsorbed on palladium and only weakly on silver, and accounts for the rate difference on the two metals.Rest potentials of the metals are corrosion mixed potentials and the metal dissolution reaction is fast in both cases so anodic processes are under Nernstian control. Palladium passivates at potentials greater than 900 mV HRE. No passivation of silver was observed.

Electrodeposition of Gallium on Liquid and Solid Gallium Electrodes in Alkaline Solutions

A galvanostatic short time transient method has been used to examine deposition and dissolution on gallium electrodes in alkaline solutions of gallic chloride. The cathodic metal deposition current was distinguished from the total current by current efficiency determinations in steady state.Behavior on the liquid electrode is consistent with a charge‐transfer controlled mechanism in all current density regions, and the rate‐determining step is probably .On the solid electrode, the rate constants of the transfer reaction are nearly those of the liquid electrode. However, the behavior in the low current density regions is qualitatively different from that on the liquid. Analysis of phenomena in this region suggests that surface diffusion begins to control the rate of the over‐all deposition process on the solid cathode. Rate constants of the surface diffusion process evaluated from the low current density region are semiquantitatively applicable to deviations from the Tafel equation which occur on the solid at high current densities (surface diffusion controlled limiting current). The results provide support for the existence of rate‐controlling surface diffusion in metal deposition and dissolution reactions.