Electrochemical parameters polarization curve constructed

Fig. E4.5 Polarization curve constructed using the electrochemical parameters given in Table E4.3.

The -> polarization curves for irreversible and quasireversible systems are shown in Figure (a). The respective -> Tafel plots are presented in Figure (b). Tafel plots can be constructed only for electrochemically irreversible systems, and kinetic parameters can be determined only when irreversible kinetics prevails. A switching from reversible to irreversible behavior and vice versa may occur. It depends on the relative values of ks and the -> mass transport coefficient, km. If km ks irreversible behavior can be observed. An illustration of the reversibility-irreversibility problem can be found in the entry -> reversibility. 

E4.1. Calctilate and construct, using mixed potential theory, the critical passivation current density (a) potentiostatic and (b) galvanostatic polarization curve for anodic dissolution for active-passive metal that has the following electrochemical parameters Ecorr= 0-5 V vs. SCE, Epp= — 0.4 V vs. SCE, 4orr= 10 A/cm, K = 0.05,. , = 10 A/cm andEtr= + l-0V vs. SCE. 

E4.3. Construct an anodic polarization curve and calculate the critical passivation current density of an active-passive alloy using mixed potential theory with the following electrochemical parameters Econ = 0-b5V vs. SCE /corr= 10 " A/cm fca = 0.1, Epp= —0.3 V vs. SCE and /pass = 10 A/cm, Etr = + 0.9 V. 

Use the following electrochemical parameters to construct polarization curves for Corrosion current of the coupled anode, fcorr.coupie and corrosion current of coupled cathode, Jcorr.C.couple ... 

The polarization curve (Fig. E4.8) for alloys A, B, C, and D is constructed using the electrochemical parameters given in the table. Alloy D does not exhibit passivation. The polarization curve for this alloy is constructed using the Tafel equation by taking Ceq= — 0.2 V vs. SCE. 

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