Anodic dissolution definition

There is, however, a definite difference in the electrode potential between the photoexcited rc-type electrode and the p-type electrode of the same semiconductor. The electrode potential of the former is less positive than that of the latter by a magnitude nearly equal to Ae = n P p P, which is the difference between the flat band potential of the n-type and that of the p-type. The anodic dissolution of the photoexcited w-type semiconductor electrode, as a result, will occur in the potential range less positive by about Ae than that for the p-type electrode of the same semiconductor. Figure 22.10 shows schematic polarization curves of the anodic hole emitting dissolution with an n-type electrode and with a p-type electrode of the same semiconductor under the dark and photoexcitation conditions. Such photoexcited dissolution was observed with w-type GaAs electrodes [14,15],... 

It has been found that about 15% of the total anodic dissolution current is consumed locally by hydrogen evolution in A1 pits and crevices [65, 66]. This means that the current measured at an applied potential is only a fraction of the true anodic dissolution current. Finally, the determination of pit growth kinetics at open circuit is a challenge, because by definition, no net current is passed at open circuit. 

The second holds that metals passive by Definition 1 are covered by a chemisorbed film—for example, of oxygen. Such a layer displaces the normally adsorbed H2O molecules and decreases the anodic dissolution rate involving hydration of metal ions. Expressed another way, adsorbed oxygen decreases the exchange current density (increases anodic overvoltage) corresponding to the overall reaction M -1- ze. Even less than a monolayer on the surface is... 

Definition of atomic crystallographic sites of significance in anodic dissolution. Schematic on a square 2D lattice kinks at steps (edges or ledges), corners, and terraces positions. 

The presence of water does not only create conditions for the existence of an electrolyte, but it acts as a solvent for the dissolution of contaminants [10], Oxygen plays an important role as oxidant element in the atmospheric corrosion process. The thickness of the water layer determines the oxygen diffusion toward the metallic surface and also the diffusion of the reaction products to the outside interface limited by the atmosphere. Another aspect of ISO definition is that a metallic surface is covered by adsorptive and/or liquid films of electrolyte . According to new results, the presence of adsorptive or liquid films of electrolyte perhaps could be not in the entire metallic surface, but in places where there is formed a central anodic drop due to the existence of hygroscopic particles or substances surrounded by microdrops where the cathodic process takes place. This phenomenon is particularly possible in indoor conditions [15-18],... 

To test this prediction the surface of CuS membranes, dissolved anodically in the media discussed above, was analyzed for the presence of sulphur by using SEM/EDAX technique with sulphur probe. In 1 M HCl the sulphur presence can clearly be seen already after one anodic half-cycle (Fig. 10). In 1x10 M HCl no sulphur could be detected. In 1x10 M HCl + 1 M KCl the result of the analysis was not definite, the surface analyzed by XRD, however, provided the strong indication of sulphur presence, because of the characteristic low-angle spectrum. Fig.9. To facilitate sulphur formation under these conditions potentiostatic dissolution at +600 mV (SCE) for 72 h was attempted. The presence of sulphur was quite evident (Fig.ll) which is opposite to the observation of CuS membrane surface dissolved under the same conditions in lxlO M HCl, (Fig.5). Finally, the surface of CuS disc left in... 

Although there is no external current, anodic and cathodic processes can still occur at sites on the interface between solid and aqueous solution because of the electrolytic conductance of the corrosive medium. At electrochemical equilibrium, this leads to a definite jump in the electrical potential at the phase boundary. Kinetic barriers to certain partial reaction steps of the electrochemical process can cause the potential to be displaced from its equilibrium value. Thus, for example, instead of a dissolution of metal ... 

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