Polarization potentiostatic

Fig. 11. Potentiostatic polarization curve on Co3P, measured in a droplet of DI water. The Tafel region is marked [125]. (Reprinted by permission of The Electrochemical Society).

Cathodic behavior after the prolonged (up to 10 s) potentiostatic polarization in... 

Fig. 8.12 SEM micrographs of electrodeposited Al on gold formed after potentiostatic polarization for 2 h in the upper phase of the mixture AlCl3/[BMP]Tf2N (a) at room temperature, E = —1.7V (b) at 100°C, E = —0.45 V. (c) EDAX profile for the area shown in the SEM micrograph (a) [89].

Janz G.J., Conte A. (1964) Potentiostatic Polarization Studies in Fused Carbonates -1. The Noble Metals, Silver and Nickel. Electrochemica Acta. 9, 1269-1278. 

A second related issue is the asymmetry in the E-i response near Ecelectron transfer reaction that is different from the metal oxidation reaction. Therefore there is no fundamental reason why pa and pc should be equal, and they should be expected to differ. The extent of their difference defines the degree of asymmetry. Asymmetry matters because the extent of the region where Eq. (2) is a good approximation of Eq. (1) then differs for anodic and cathodic polarization (29). The errors in assuming 10 mV linearity using both the tangent to the E-i data at Econ and for +10 or -10 mV potentiostatic polarizations have been defined for different Tafel slopes (30). 

This elevation was attributed to the effect of chromate on metastable pitting. Figure 6b shows plots or current density versus time for high purity A1 wire loop electrodes potentiostatically polarized to -0.500 Wxe in the same solutions as those shown in Fig. 6a. As the chromate concentration is increased from 0 to 25 pM, and then from 25 to 50 pM, the metastable pit nucleation rate (events per unit time) diminishes, as does the magnitude of individual events (event peak current). The presence of chromate appears to decrease the metastable pit growth... 

Artificial crevice electrodes have been used to study the effect of dichromate on active dissolution of aluminum. In these experiments, 50 pm thick commercially pure A1 foils were placed between thin plastic sheets and mounted in epoxy. This assembly was fixed against a square cell that accommodated counter and reference electrodes and a trap that allowed for H2 gas collection. A schematic illustration of this cell and electrode is shown in Fig. 9 (36). Crevice corrosion growth experiments were conducted in aerated 0.1 M NaCl solution with additions of either 0.01 or 0.1 M Na2Cr207. Artificial crevice growth experiments were conducted under potentiostatic polarization at potentials ranging from 0 to... 

Potentiostatic polarization is widely used to determine the steady-state corrosion behavior of metals and alloys as a function of potential in environments of interest. This technique involves holding a specimen s surface at a series of constant potentials versus a reference electrode, and then measuring the current necessary to maintain each of the applied potentials. From this dependence of the current on the applied potential of the sample, a number of parameters important for understanding the corrosion behavior of the material in the environment (such as icon, b3, and bc) can be determined as pointed out in Chapter 2. 

There are two types of potentiostat setups in the laboratory, and each requires a different procedure to perform a potentiostatic polarization. Determine which type of potentiostat (PAR 273 or VersaStat) is at your station and use the appro-... 

The test method ASTM F7464 covers the determination of the resistance to either pitting or crevice corrosion of passive metals and alloys from which surgical implants are produced. The resistance of surgical implants to localized corrosion is carried out in dilute sodium chloride solution under specific conditions of potentiodynamic test method. Typical transient decay curves under potentiostatic polarization should monitor susceptibility to localized corrosion. Alloys are ranked in terms of the critical potential for pitting, the higher (more noble) this potential, the more resistant is to passive film breakdown and to localized corrosion. (Sprowls)14... 

The potentiostatic polarization method has been used to study the inhibitive behavior of 5-nitrobenzothiazoles on the corrosion of pure aluminum in 0.1 M HC1... 

The thickness of the Ti02 layer as well as that of the other quasi-noble metal layers can be determined from the linear dependence of the consumed charge on the electrode potential. The same can be performed under potentiostatic polarization conditions. 

Fig. 5.19 Potentiostatic polarization curve for pure chromium in hydrogen-saturated (deaerated) 1 N H2S04at25 °C. Dashed section is a cathodic "peak" where the hydrogen-ion reduction dominates over the passive chromium oxidation. Redrawn from Ref 9...

---