Anodic Metal Dissolution Research Articles

Anodic Disintegration of Metals Undergoing Electrolysis in Aqueous Salt Solutions

Abstract Mechanisms of the anodic dissolution of metals in aqueous salt solutions are reviewed and discussed. The review places particular emphasis on metals which have been studied in the author’s...

Zur theorie potentiostatischer ein-und umschaltvorgänge bei der elektrokristallisation

A mathematical treatment of the time-dependence of current-density/overpotential curves for the anodic metal dissolution and the cathodic Deposition processes (Me ⇋ Mez+ + ze−) under special conditions is given. The assumption has been made that the surface diffusion of ad-atoms (D, c0) and the transfer reaction (i0, α, z) are simultaneously rate-determining and that parallel “growth step lines” at a distance 2l (spiral growth on screw dislocations) and a dense concentration of kink sites—for which the equilibrium concentration of ad-atoms c0 always exists—are present. The potentiostatic step η → η* which includes the charging curve 0 → η and the discharge curve η* → 0 is treated through solving the partial differential equation for the surface diffusion with the required initial and boundary values. The theory of Fleischmann and Thirsk has thus been improved upon.An expanded and general definition of crystallization overpotential ηk, is given along with a discussion of the relationship between the total overpotential η and the crystallization overpotential ηk. The experimental determination of crystallization overpotential is further discussed.

The Passivity of Metals

AbstractAfter a survey of the various factors, depending both on the metal and on the attacking substance, that can influence the anodic dissolution of metals, the nature of the passive layer is discussed on the basis of electrochemical and optical studies. Passivation is characterized by a rapid decrease in the anodic current density as the Galvani tension is increased; this is due to the presence of a monomolecular layer, which prevents the metal ions from passing across the phase boundary. The growth of this layer is strongly influenced by transport processes, particularly with in the layer itself. The kinetics of the passivation and activation processes can be explained by the simultaneous occurrence of competing reactions which depend on the potential; exchange adsorption appears to play some part in the passive behavior of metals towards various acids.

The electrochemistry of the stress-corrosion cracking of alpha brass

The stress-corrosion cracking of α-brass has been examined in solutions containing cupric copper, sulphate and ammonia, over the pH range 4·0–9·0, with annealed wires direct-loaded in tension. The very rapid cracking found at pH 7·0–7·3 with loop specimens is confirmed with direct-loaded specimens stressed to about 95 per cent of the yield point. It occurs when the electrode potential reaches 0·25–0·27 V (e H), and is associate) with the formation of a black film of cuprous oxide on the brass surface. It is greatly slowed down by cathodic protection, to nearly zero rate at 1005 V (e H). The results are discussed in terms of the chemistry and the mechanics of the system. Crack initiation is caused by localized preferential dissolution of zinc in locally microstrained stressed metal, and propagation by the preferential anodic dissolution of both zinc and copper at the advancing edge of the crack, where rapid yielding occurs: this yielding disrupts the protective but brittle oxide film there and also stimulates the anodic dissolution of the bared metal.

Anodic dissolution of active metals during plastic flow: Copper

Studies have been made on the effect of continuous plastic flow on the anodic dissolution and cathodic deposition of active copper in acid cupric sulphate solutions. The plastic flow has a stimulating effect on both reactions which increases with the ratio of strain rate to reaction rate. The effect is not lasting, but disappears shortly after the deformation process is stopped. The results are in accordance with a model involving direct dissolution at kinks in crystal steps in the surface.

Anodic dissolution of active metals during plastic flow: iron and nickel

Studies have been made on the effect of plastic flow on the anodic dissolution of active iron and nickel in acid chloride solutions. For both metals, plastic flow has a stimulating effect on the dissolution reaction. The effect increases with the ratio of strain rate to dissolution rate. It is not lasting, but disappears shortly after the deformation process is stopped. The results are in accordance with a model involving direct dissolution at kinks in crystal steps in the surface.

Theory Of Stainless Steel Pitting

Abstract Pit origin and formation in stainless steels are discussed according to results of investigations from the following points of view: 1. Conditions for the Existence of Pitting Corrosion. Pitting potential range and pitting potentials. Functions dependent on the potential which are important for pitting corrosion, effect of inhibitors and results of different methods of investigation are described. 2. Kinetics of Pitting Corrosion. Analysis of the current-time relationship gives information on dependence of potential on the anodic metal dissolution process. Pit growth under potentiostatic, galvanostatic and chemical corrosion conditions can be explained theoretically. 3. Physical Forms of Pitting Corrosion. Shape of pits that can be observed in different potential ranges and under different corrosion conditions are discussed: regular etch pits, hemispherically-shaped pits, under-hollowing and elongated areal pits. 4. Theoretical Explanation of Pitting Corrosion. In connection with the “all-or-none” principle of passivity, which holds that the active and passive states should not coexist at the same potential, it is shown under which circumstances stable pitting corrosion is possible. A concentration effect and a resistance polarization effect are discussed in detail. The origin of pitting corrosion and the pitting potentials are discussed in terms of a chemisorption process and a transport and/or transference theory.

Valency of Ions Formed during Anodic Dissolution of Metals in Acids

The charge of cations of active metals, going anodically into solution in acid or alkaline electrolytes, can be computed from the current applied and the total hydrogen evolution rate after the initial, self‐dissolution rate has been subtracted. However, under such conditions an ionic charge, experimentally not provable, of much higher or lower value than the normal one is calculated. Evidently this charge is apparent and corresponds to the true one only then, if the self‐dissolution rate does not change when the anodic current is applied.It can be shown (by measuring the total hydrogen volume developed) that calculated abnormal valencies result when the change of self‐dissolution rate (difference effect) due to the anodic current is disregarded. In the case of the positive effect, high charges and, in the case of the negative effect, low (apparent) cationic charges are computed. The impossibility of the calculated high cationic charges proves in turn that the positive effect cannot be explained by the expulsion of such cations by the anode. Since it was shown at least in the case of Be (which also might be true with Mg) that the metal partially disintegrated into tiny metal particles under the influence of the anodic current, the need for the assumption of Be+ formation is removed. The appearance of the negative A effect can be explained in a better way.All the phenomena occurring in the anodic compartment in acidic as well as neutral solutions can be explained readily by the consequences of the altered self‐dissolution rates, especially if the activation of the dissolving surface of the anodic metal, the breakdown of the protective films, and the formation of metal fragments by the anodic current are considered.

The Anodic Dissolution and Electrolytic Polishing of Metals

An experimental study has been made, using the potentiostat technique, of the anodic dissolution and electrolytic polishing of nickel in hydrochloric acid. The effect of experimental conditions on the potential/current density curves and the value of the limiting current density has been investigated. Results have been interpreted on the basis of a simple diffusion mechanism, and complications arising from the thick salt films found in the more concentrated solutions have been considered. Some results showing the connection between polishing and passivity have been collected for copper anodes in potassium cyanide solutions containing potassium hydroxide.

Electrochemical Applications for Ultrasonic Waves

Ultrasonic waves at intensities sufficient for cavitation have been found to produce relatively large effects on such electrochemical processes as the corrosion of metals in electrolytic solutions, the anodic dissolution of metals, the formation of gases at electrodes during electrolyses, the electrodeposition of metals, and electrodialysis. A systematic study of several of these effects has been made in order to establish the fundamental nature of the effects. Ranked in order of importance, the basic mechanisms are as follows: (1) the disruption of concentration gradients at the electrode surfaces, (2) the partial destruction or removal of surface layers such as oxides on the electrode surfaces through cavitation, and (3) the partial degassing of the solution immediately adjacent to the electrode surface. The actual and potential practical significance of these various electrochemical effects will be evaluated. [Based in part on research supported by the Office of Naval Research.]

The Rate-Determining Stage in the Anodic Dissolution of Metals

An experimental study has been made, using the potentiostat technique, of the limiting current densities of metal dissolution in electrolytic polishing solutions. The limiting current densities sho...