Potential region

A number of different types of experiment can be designed, in which disc and ring can either be swept to investigate the potential region at which the electron transfer reactions occur, or held at constant potential (under mass-transport control), depending on the infomiation sought. 

Fig. 6. Band edge positions of several semiconductors ia contact with an aqueous electrolyte at pH 1 ia relation to the redox (electrode) potential regions (vs the standard hydrogen electrode) for the oxidation of organic functional groups (26,27).

The switching-off method for 7/ -free potential measurement is, according to the data in Fig. 3-5, subject to error with lead-sheathed cables. For a rough survey, measurements of potential can be used to set up and control the cathodic protection. This means that no information can be gathered on the complete corrosion protection, but only on the protection current entry and the elimination of cell activity from contacts with foreign cathodic structures. The reverse switching method in Section 3.3.1 can be used to obtain an accurate potential measurement. Rest and protection potentials for buried cables are listed in Table 13-1 as an appendix to Section 2.4. The protection potential region lies within U[[Pg.326]

Table 16-2 Protection potential regions for plain carbon and low-alloy steels (YP 800 N mm ) for marine structures...

Pavlov, D. and Rogachev, T. Dependence of the Phase Composition of The Anodic Layer on Oxygen Evolution and Anodic Corrosion of Lead Electrode in Lead Dioxide Potential Region , Electrochim. Acta., 23, 1237 (1978)... 

Carbons exhibiting hysteresis show poor cycling performance, and can be discharged only in a broad potential region of about 1-2 V (Fig. 13) [41, 51, 52, 218-220, 234-236, 244, 277, 278, 287], As a result, the energy efficiency of a lithium-ion cell is reduced. 

A novel nondestructive method for the determination of total charges and hence of EQ=Qy that is based on the CO displacement experiments has been worked out.795,796 This method has been applied to Pt(lll) and Pt(l 10) electrodes in contact with solutions at different pHs. For both Pt faces, the potential-of-zero total charge lies in a potential region similar to that forpc-Pt.8,10,11 It was found that thepztc depends on pH in different ways for Pt(l 11) and Pt(l 10), which demonstrates that not only is the pztc structure sensitive, but also that it varies with pH.795 The value of pztc for Pt(l 11) is more positive than that for Pt(l 10), and df j/dpHis higher for Pt( 111) than for Pt( 110). 

In the polarization curve for anodic dissolution of iron in a phosphoric acid solution without CP ions, as shown in Fig. 3, we can see three different states of metal dissolution. The first is the active state at the potential region of the less noble metal where the metal dissolves actively, and the second is the passive state at the more noble region where metal dissolution barely proceeds. In the passive state, an extremely thin oxide film called a passive film is formed on the metal surface, so that metal dissolution is restricted. In the active state, on the contrary, the absence of the passive film leads to the dissolution from the bare metal surface. The difference of the dissolution current between the active and passive states is quite large for a system of an iron electrode in 1 mol m"3 sulfuric acid, the latter value is about 1/10,000 of the former value.6... 

Once a passive film is formed on a metal surface, as long as the electrode potential remains in the passive potential region, the surface is stable, i.e., scarcely dissolved. However, if there are film-destructive anions like chloride ions in solution, the passive film is locally broken, so that local dissolution of the metal substrate proceeds at the same place. 

At the area between the breakdown potential Eb and the critical pitting potential pit local film breakdown occurs, which leads to the creation of pit nuclei. However, these nuclei are immediately repassivated. Consequently, in this potential region it is concluded that breakdown and repair are continuously repeated without creating pit growth. 

From these treatments, it can be said that there is a potential region from the passivation potential to the lowest film-breakdown potential within which the passive film is stable against electrocapillary breakdown. At the potential beyond the critical pitting potential, not only passive film... 

In this case, if the electrode potential inside the pit remains in the passive potential region, repassivation occurs immediately. 

In the potential region where nonequilibrium fluctuations are kept stable, subsequent pitting dissolution of the metal is kept to a minimum. In this case, the passive metal apparently can be treated as an ideally polarized electrode. Then, the passive film is thought to repeat more or less stochastically, rupturing and repairing all over the surface. So it can be assumed that the passive film itself (at least at the initial stage of dissolution) behaves just like an adsorption film dynamically formed by adsorbants. This assumption allows us to employ the usual double-layer theory including a diffuse layer and a Helmholtz layer. 

Other ways to determine the sensitivity factor S are possible, for example, by comparing microwave reflectance and admittance responses in a potential region with ideal junction behavior.31... 

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