Effect Of Cathodic Polarization Research Articles

Special features of hydrogen embrittlement of structural steels in biogenous hydrogen sulfide

We study the effect of cathodic polarization with simultaneous action of biogenous hydrogen sulfide on the susceptibility of AB-2Sh and St3sp structural steels to hydrogen embrittlement in marine biological media of different activities. Uniform and concentrated components of the plastic deformation caused by stretching of smooth cylindrical specimens at the rate of ɛ=10−1 s−1 under hydrogen charging conditions are determined. We suggest a method for identification of processes occurring in the neck of a stretched specimen with respect to those that can take place near crack-type defects in submarine constructions.

Effect of cathodic polarization on the floatability of chalcopyrite in the absence of oxygen

Rest potential, cyclic voltammetry and chronopotentiometry measurements were made to study the effects of cathodic polarization of chalcopyrite, simulating the mineral contacted with grinding media under a nitrogen atmosphere. The reaction products on the chalcopyrite surface were identified by XPS, and the mechanism of the cathodic reaction was proposed. Microflotation tests were performed to investigate the effects of surface changes on the floatability of chalcopyrite.

An electrochemical investigation of dissolution of NdFeB magnets in acid solution under cathodic polarization

The effect of cathodic polarization, pH value of sulphate solution and stirring rate on the kinetics of dissolution of Nd 15Fe 77B 8 magnets in magnetized and demagnetized states have been studied. With the increase of cathodic polarization the rate of dissolution increases. The reason for this abnormal dissolution is hydrogenation and mechanical degradation of the magnet surface. The abnormal dissolution rate increases linearly with the square root of the H 2 evolution current density. NdFeB magnets in the magnetized state, as compared to demagnetized one, undergo lower abnormal dissolution. Independently of magnetization state the surface of the magnets deteriorates strongly after the cathodic exposure.

Ambiguous Effect of cathodic polarization on crack growth as the general regularity of stress‐corrosion cracking of structural materials

AbstractThe present study is concerned with the possibility of using the ambiguous effect of cathodic polarization (AECP) on crack growth as a diagnostic tool for determining the role of local anodic dissolution and hydrogen embrittlement in the mechanism of stress‐corrosion cracking (SCC) of different structural materials, irrespective of their base, microstructure and strength. It is shown that AECP is the general regularity of SCC and that the unambiguous effect of polarization (either the acceleration or retardation of crack growth irrespective of loading conditions) may be viewed as a particular case of this general regularity.

The effect of cathodic polarization on the corrosion fatigue behavior of a precipitation hardened aluminum alloy

Fatigue experiments were conducted on polycrystalline and monocrystalline samples of a high purity Al, 5.5 wt pct Zn, 2.5 wt pct Mg, 1.5 wt pct Cu alloy in the peak-hardened heat treatment condition. These experiments were conducted in dry laboratory air and in 0.5N NaCl solutions at the corrosion potential and at applied potentials cathodic to the corrosion potential. It has been shown that saline solutions severely reduce the fatigue resistance of the alloy, resulting in considerable amounts of intergranular crack initiation and propagation under freely corroding conditions for polycrystalline samples. Applied cathodic potentials resulted in still larger decreases in fatigue resistance and, for poly crystals, increases in the degree of transgranular crack initiation and propagation. Increasing amounts of intergranular cracking were observed when applied cyclic stresses were reduced (longer test times). The characteristics of cracking, combined with results obtained on tensile tests of deformed and hydrogen charged samples, suggest that environmental cracking of these alloys is associated with a form of hydrogen embrittlement of the process zones of growing cracks. Further, it is suggested that stress corrosion cracking and corrosion fatigue of these alloys occurs by essentially the same mechanism, but that the often observed transgranular cracking under cyclic loading conditions occurs due to enhanced hydrogen transport and/or concentrations associated with mobile dislocations at growing crack tips.

Catalytic Activity of Iron, Nickel, and Nickel‐Phosphorus in Electroless Nickel Plating

The catalytic activity for electrooxidation of hypophosphite and electroless nickel plating on iron, nickel, and electrolessly plated nickel (with 2.2–2.9 weight percent (w/o) P) was investigated in an ammoniacal solution of pH 8.8 at 50°C by potential measurements and linear sweep voltammetry from −0.3V to 0.92V vs. SCE. Cathodic polarization of any of the substrates (in ) before testing or permeation of hydrogen through iron foils during testing reduced the incubation time for electroless plating, increased anodic dissolution of the substrates in the passive region, and increased the hypophosphite electrooxidation on nickel and nickel‐phosphorus at potentials of thermodynamic stability for nickel oxides or hydroxides. The nickel‐phosphorus substrate exhibited significantly higher activity than pure nickel, in a similar manner to the effect of cathodic polarization. The effect of cathodic polarization and hydrogen is associated with the electrochemical reduction of surface oxides, whereas the higher activity of nickel‐phosphorus deposits (as compared to that of pure nickel) is explained by the lower protectivity of surface oxides on these deposits.

Effect of Heat Transfer on the Cathodic Polarisation of Steel in Saline Solution

AbstractAn apparatus is described for studying the effect of heat transfer on the cathodic polarisation of steel in flowing saline solutions.The effect of heat transfer on the diffusion-limited current for reduction of oxygen in 3·2% sodium chloride solution could be accounted for in terms of the effect of temperature at the metal/solution interface on the diffusion coefficient of oxygen.In sea water, the combined effect of cathodic polarisation and heat transfer enhanced the deposition of calcareous deposits on steel. Some implications of calcareous deposition on cathodic polarisation of steel are discussed.

The mechanisms of crack growth in stress corrosion cracking of aluminium alloys

AbstractModern understanding of possible mechanisms of crack growth in corrosion cracking of aluminium alloys immersed in various corrosion media such as aqueous solutions, saturated and undersaturated vapour, gaseous hydrogen, etc. is discussed in this review. The experimental data used as a basis to conclusions about the mechanisms of corrosion cracking in aluminium alloys are critically examined. A special emphasis is given to new methods to determining the effect of local anodic dissolution and hydrogen embrittlement in crack growth, i.e. the method of comparative tension and torsion tests deformations of types I and III, and the method based on evaluating ambiguous effect of cathodic polarization on crack growth.

The Effect of Cathodic Polarization on the Creep Rate of Gold

Annealed gold wires were loaded at 0 mV vs. SCE. The specimens were then polarized during 1 min intervals to successively more negative potentials ranging from −200 to −1800 mV in steps of 200 mV. The extra strains measured as a function of the electrode potential had a characteristic distribution depending on the composition, oxygen content, and pH of the test solution. In general there are two peaks. In deaerated alkaline solutions a first peak occurred between −200 and −600 mV. This peak was completely absent in deaerated acid solutions. It is ascribed to dislocation pinning at the metal surface by chemisorbed OH− ions during loading of the specimen. A first peak probably due to adsorbed reappears in oxygenated acid solutions. A second peak was observed in all test solutions. This peak occurs at electrode potentials more negative than −1000 mV vs. SCE.

Investigation of the Kinetics and Mechanism of Subcritical Crack Growth by Delayed Failure of Titanium Alloys In and Out of Corrosive Environments

Abstract The kinetics of crack growth by SCC of titanium alloys in some solutions have been studied by the electrical resistivity method. The effect of cathodic polarization on crack growth rate was used for investigation of the mechanism of SCC of titanium alloys in different conditions. The hydrogen diffusion model is proposed to describe the kinetics of delayed failure of titanium alloys in the absence of a corrosive environment. According to this model, it is possible to determine DH from kinetic data. The subcritical crack growth mechanism in the absence of a corrosive environment is shown to be internal hydrogen embrittlement.

Effect of cathodic polarization on the rate of growth of cracks in corrosion cracking of high-strength steels in deaerated, aerated, and hydrogen-sulfide-saturated solutions of chlorides

Effect of cathodic polarization on the rate of growth of cracks in corrosion cracking of high-strength steels in deaerated, aerated, and hydrogen-sulfide-saturated solutions of chlorides

Investigation of the Mechanism of Stress Corrosion Cracking in High Strength Steels

Abstract An analysis is given of the modern outlook on the mechanism of cracking in high strength steel in the case of stress corrosion cracking (SCC). It is shown that numerous experimental data cannot be interpreted in terms of hydrogen embrittlement when it is considered as the only mechanism of crack growth. A phenomenon is described of multiple effects of cathodic polarization on the rate of crack growth in cracking of high strength steels. A new mechanism of SCC is suggested, whose main feature is found in that it not only allows for, but is in fact based upon the possibility of SCC of high strength steels by several mechanisms: local anodic dissolution, hydrogen embrittlement, and adsorption strength reduction. The mechanism entails alternation of rate-limiting processes, depending on various metallurgical and electrochemical factors, and on crack growth rate, which affect the kinetics of formation of barrier layers at the crack tip. A definition of critical growth rate is introduced, which is then investigated as function of a number of factors.

Ambiguous effect of cathodic polarization on speed of crack growth during stress corrosion cracking of high-strength steels in inhibited sodium chloride solutions

Ambiguous effect of cathodic polarization on speed of crack growth during stress corrosion cracking of high-strength steels in inhibited sodium chloride solutions

Obscure effect of cathodic polarization on rate of crack propagation during stress corrosion cracking of high-strength steels

Obscure effect of cathodic polarization on rate of crack propagation during stress corrosion cracking of high-strength steels

Electrochemical behaviour and stress-corrosion cracking of titanium in alcoholic solutions

The electrochemical behaviour of titanium in neutral methanolic and ethanolic solutions containing chlorides, and corrosion tests performed with U-bend specimens in similar solutions, indicate that stress-corrosion phenomena occur on titanium when particular anodic and cathodic conditions are settled. In neutral aerated ethanolic solutions the oxide film is stable and its electronic properties (ionic and electronic currents) are similar to the ones observed in aqueous solutions. Exception is made only for the breakdown potential. In ethanolic solutions, stress-corrosion occurs only in the presence of depolarizing species which can set mixed potentials more noble than the one characteristic of oxygen (i.e. FeCl 3). Breakdown potential weakly depends on the chloride concentration, but the adsorption of chlorides on the oxide surface, in ethanolic solutions shifts the steady state potential of the metal to more active potentials so that, from the electrochemical point of view the more concentrated NaCl solutions, appear to be less effective in promoting stress-corrosion, the corrosion potentials settled at the higher Cl − concentrations, being less noble than the potentials settled at the lowest Cl − concentrations. In this case the role of Cl − in the dissolution of titanium in ethanolic solution seems to be restricted to the formation of complex ions. The stability of titanium oxide films in methanolic solutions is very weak and, in the anodic sense, is restricted to a very narrow range of potentials. Presence of oxygen can create mixed potentials more noble than the breakdown potentials and thus the stress-corrosion occurrence. The beneficial effect of cathodic polarization in neutral alcoholic environment can be due to the establishment of corrosion potential less noble than breakdown potential of the oxide film.

Influence of the combined effect of cathodic polarization and inhibitors on the corrosion of Al in HCl

The effect of external cathodic polarization on the behaviour of organic inhibitors for Al alloys in HCl has been studied. It was observed that several inhibitors become more effective under the influence of external cathodic polarization, as for instance 2-butanone for Al-2S and Al-65S and cyclohexanone for Al-57S. The protective potential for Al alloys is not altered in the presence of most of the inhibitors studied, only in the case of ethylenediamine is the protective potential lowered.

The stress corrosion cracking mechanism of α-titanium alloys at room temperature

The role of H in causing rapid transgranular s.c.c. in α-Ti alloys is discussed in detail inrelation to the hypothesis that H enters the unfilmed surface at the crack tip and causes slow strain-rate embrittlement. The protective role of cathodic protection in neutral solutions, the relatively slow rate of H diffusion and similar cracking in media that do not contain H are each discussed. The ratio of activating to passivating species in the environment is important in promoting film formation and accounts for the protective effect of cathodic polarization. It is not effective in non-film-forming conditions. Fractographic comparison with hydrided specimens indicates that some form of “long range” effect is possible, i.e. rapid fracture can occur into regions that do not contain large amounts of hydrogen. Results in CCI 4 suggest that the residual H 2O content (200 ppm) is responsible for cracking. In CH 3OH-HCI environments the degree of embrittlement increases as the strain-rate is lowered. Evidence for H embrittlement is provided by (i) pre-exposed unstressed specimens which exhibit cleavage to considerable depths when subsequently broken in air, an effect that can be removed by an intermediate baking treatment, (ii) quantitative fractographic measurements of specimens anodically polarized in CH 2OH-HCI, in which the cleavage markings obtained upon subsequent. fracture in air are not seen if the dissolving front progresses at a rate comparable to H diffusion, and (iii) fractographic comparisons with broken hydrided specimens. Physical, mechanical and chemical aspects of the mechanism are considered.

Effects of external cathodal polarization on classical motor conditioning in dogs

The present study was designed to determine the effects of cathodal polarization on the establishment of motor conditional reflexes (CR's), with faradic shock as reinforcement. Ten dogs were used as controls and another seven as experimental subjects (ES's). In the ES's, stainless-steel electrodes were implanted on the face, infraorbitally, for chronic polarization. Four days later the ES's were trained in a soundproof room with classical conditioning procedures while they were co9nstantly polarized with direct current (1 to 2 ma). Control dogs showed strong (+3 and +4) motor CR's within the first 50reinforced trials, with differentiation after 50 trials. In contrast, the ES's showed poor motor conditioning: six ES's showed poor motor CR's in the first 50 reinforced trials. Only one ES showed prompt, good motor CR's. The fact that cathodal polarization interferes with theestablishment of motor CR's suggests an inhibitory effect on the acquisition of musculoskeletal CR's. It is possible that the inhibitory effects observed are related to the depression produced by cathodal polarization in humans.

Role of hydrogen in the fracture of steel in neutral corrosive media

1. The effect of cathodic polarization upon the endurance of steel fatigued (in the plastic range) in neutral and acid electrolytes is represented by qualitatively similar curves. This is an indirect proof of the possibility of hydrogen embrittlement of metals fatigued in neutral electrolytes. 2. The harmful effect of hydrogen upon the “plastic endurance” at relatively low cathodic current densities is aggravated by the presence of stress concentrators formed as a result of selective corrosion.

PREVENTION OF STRESS‐CORROSION CRACKING BY CATHODIC PROTECTION

Background to tests. Cathodic protection has been used on an industrial scale for the protection of pipelines and underwater structures for many years. It has not, however, been applied to structures in which, although the general corrosion resistance is high, there is likelihood of failure by stress‐corrosion cracking. The purpose of the investigation reported here was to determine the effect of cathodic polarisation in a range of commercial alloys which were liable to this type of failure. The idea of using cathodic protection is especially attractive, as metallic or non‐metallic coatings, though they delay the onset of stress corrosion, are not suitable preventive measures. Pitting in the coatings soon results in earlier failure and some materials, such as stainless steel, are difficult to coat.