Potential passive

See also Corrosion Potential, Electrode Potential, Equilibrium Potential, Flade Potential, Open-circuit Potential, Passivation Potential, Protection Potential, Redox Potential.)... 

The direct electrochemical oxidation of NAD(P)H is possible but for this purpose relatively high oxidation potentials are necessary and potential passivation of the electrodes can occur. Because of the low speed of NADH oxidation and to avoid fouling of the electrodes, mediators like phenanthroline derivates are often used for advanced electron transfer. Those systems can be coupled efficiently with enzyme-catalyzed reactions which require NAD(P)H oxidation. 

This system permits brief descriptions of some key concepts encountered in corrosion phenomena electrode potentials, exchange currents, mixed potentials, corrosion potentials, passive films, as well as leading to thermodynamic descriptions of systems.- ... 

Ucorr = corrosion potential, = passivation potential. Up = pitting potential,... 

Figure 10.10 Current-potential plot of an iron electrode in an acid electrolyte (schematic representation). passivation potential, passivation current density, E-p Flade potential, and passive current density.

Tested alloys in physiological solutions have the ability to repassivation. The repassivation ability of the material determined from the curve back after exceeding pits nucleation potential. Bidirectional potentioki-netic curves for sample I is shown in Fig. 6 (arrows indicated the direction of the potential change). The repassivation potential for sample I (the most resistant in the environment) is about 0.09 V vs. SCE (Fig. 6). Below this potential passive layer is stable, and the material should not undergo the pitting corrosion. 

Metal/Alloy Corrosion Potential Passive Current Density Breakdown Potential ... 

At higher potentials, passivity is observed to break down and the dissolution rate of the metal increases dramatically. This process is commonly due to the oxidative ejection of cations from the barrier layer for example,... 

Figure 15.4 Mapping electrochemical material loss against mechanical erosion rates for a nonpassivating surface carbon steel (AISI1020) along with two potentially passivating surfaces of nickel aluminum bronze (NAB) one that has been thermally sprayed by high-velocity oxy-fuel deposition as a coating on carbon steel ( j and another which has been cast (A.). These results were obtained from jet impingement erosion-corrosion tests. Reprinted from Ref. [7]. Copyright (2007) with permission from Elsevier.

Pourbaix diagram (electrode potential-pH diagram)—a graphic representation showing regions of thermodynamic stability of species in metal-water electrolyte systems, primary passive potential (passivation potential)— the potential corresponding to the maximum active current... 

The treatment conditions are the same as those in Fig. 7. The electrochemical test results for Hybrid-NCT, Nitriding-NT, Carburizing-CT were described in Fig. 12 The NT and CT showing that the current density of treated stainless steel were decreased in the anodic region which indicating positive effect regarding the improvement of corrosion resistance compared to the substrate. After Hybrid-NCT treatment, the anodic pwlarization curved is shifted towards lower current density which explain that the corrosion rate was decreased and the polarization current measurement gave 0.00003 mA/ cm and demonstrate an improvement in corrosion resistance as compared to that untreated and individually nitrided and carburized steel, while passivation current of NCT is the lowest followed by CT, NT and untreated respectively. This trend also similar to the maximum potential passivation behaviour since the... 

The third region is where the rise in potential (passive state) occurs. .. (C D)... 

Porous Geopolymers as Potential Passive Cooling Elements in Buildings... 

Figure 6.32. Fe electrode in water at pH = 7 and [Fe++] = 10 mol/ . The equilibrium potential is — 0.60 volt (A). When an increased potential A-B is imposed on the electrode, the current density is increased until the potential reaches approximately —0.25 volt. At this potential, passivation B-C is obtained and the current density decreases abruptly to almost 0. The passivation is due to precipitation of a dense oxide layer on the electrode (see example 6.2).

Potentiostatic transients show a similar sequence of layer formation as obtained for the variation of potential. Passivation of Fe-22A1 at E = 1.0 V in phthalate buffer pH 5.0 forms first Fe(II) with a maximum at fp = 10 s and a fall to negligible values at tp = 100 s. Fe(in) starts to grow continuously after fp = 1 s up to fp = 1000s. As a very reactive metal, A1 forms already Al(III) at the very beginning of the transient. Its content decreases with time when Fe(III) enters the film between fp = 1 and 10 s. Up to fp = 0.1 s, the film contains large amoimts of OH and water. After this initial time, water disappears completely (after Is) and OH stabilizes at 40%. ARXPS shows that OH is located in the outer part of the passive layer. 

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