Cathodic charge

Later work on aluminium alloys has also focused more closely upon the role of hydrogen which had not previously been widely considered as an embrittling species in the stress-corrosion cracking process for these alloys. The idea was not new, however. Reports of intergranular failure under cathodic charging conditions had been made at a much earlier time . A reduction in stress-corrosion life and alloy ductility in a high purity Al-5Zn-3Mg alloy had been found in specimens pre-exposed to a 2% NaCI solution" , an effect that was accentuated if specimens were stressed". ... 

Cathode (charged state) Anode (charged state)... 

Here ia is the exchange current density of the electrode reaction based on the bulk concentration aa and ac are the anodic and cathodic charge transfer coefficients, respectively and y is a dimensionless kinetic parameter. 

P Cathodic charge-transfer coefficient 0(A) Quantity of the order of magnitude... 

The cracking susceptibility of a micro-alloyed HSLA-100 steel was examined and compared to that of a HY-100 steel in the as-received condition and after heat treatment to simulate the thermal history of a single pass weld. Slow strain rate tensile tests were conducted on samples of these alloys with these thermal histories in an inert environment and in an aqueous solution during continuous cathodic charging at different potentials with respect to a reference electrode. Both alloys exhibited reduced ductilities at cathodic potentials indicating susceptibility to hydrogen embrittlement. The results of these experiments will be presented and discussed in relation to the observed microstructures and fractography. 

On the mixed electrode of metallic iron immersed in acidic solutions, the anodic and cathodic charge transfer reactions (the anodic transfer of iron ions and the cathodic transfer of electrons) proceed across the electrode interface, at which the anodic ciurent (the positive charge current) is exactly balanced with the cathodic current (the negative charge current) producing thereby zero net current. 

A bare surface of silicon can only exist in fluoride containing solutions. In reality, in these media, the electrode is considered to be passive due to the coverage by Si— terminal bonds. Nevertheless, the interface Si/HF electrolyte constitutes a basic example for the study of electrochemical processes at the Si electrode. In this system, the silicon must be considered both as a charge carrier reservoir in cathodic reactions, and as an electrochemical reactant under anodic polarization. Moreover, one must keep in mind that, according to the standard potential of the element, both anodic and cathodic charge transfers are involved simultaneously (corrosion process) in a wide range of potentials. 

The theoretical model generally used for predicting the overvoltage-current function for metal/metal ion systems is based on the quasi-thermo-dynamic arguments of transition state theory. The anodic charge transfer process is considered to involve the rupture of the bond between an adatom - i.e. a metal atom in a favourable surface site - and the metal, followed by, or coincident with, the formation of electrostatic bonds between the newly formed ion and solvent or other complexing molecules. The cathodic charge transfer follows this mechanism in reverse ... 

Fig. 5.17. Changes in the SH intensity (solid line), phase (broken line), and cathodic charge passed (open circles) as a function of applied bias potential. Ag(110) in 0.25 M Na2S04, 5 mM T12S04, pH = 3.0. Incident wavelength = 1064 nm. From Ref. 146.

Electrokinetic parameters [10] Ideal potential Anodic preexponential coefficient Cathodic preexponential coefficient Anodic activation energy Cathodic activation energy Anode charge transfer coefficient Cathode charge transfer coefficient 0.8961 V 1.6e9 3.9e9 120 J mol-1 120 J mol-1 0a = 2, 0C = 1 ea = 1.4, 0C = 0.6... 

For each monomer and ionic liquid, measurement of the total cathodic charge passed during reduction of the polymers in the final post-polymerization CVs, compared to the peak polymer oxidation currents from the final growth cycles, allows comparison of the film electrochemical activities while taking into account the relative amounts of the polymer. The former value is often used as an indication of the amount of polymer grown, but this assumes that the electrochemical activities of the films are identical. 

Figure 6.61 Delayed fracture times and minimum stress for cracking of 0.4% C steel for various hydrogen concentrations obtained by different baking times at 150°C of cathodically charged specimens (Craig)5...

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