Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-16 GTBL042-Callister-v2 September 13, 2007 13:10

Revised Pages

674 • Chapter 16 / Corrosion and Degradation of Materials

H+

H+

H+

H+ H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

Depletion

zone

Cathode Cathode

H+

H+

H+

H+

H+

H+

H+

H+

H+

(a) ( b)

Figure 16.8 For hydrogen reduction, schematic representations of the H+distribution in

the vicinity of the cathode for (a) low reaction rates and/or high concentrations, and (b) high

reaction rates and/or low concentrations wherein a depletion zone is formed that gives rise

to concentration polarization. (Adapted from M. G. Fontana,Corrosion Engineering,3rd

edition. Copyright©c1986 by McGraw-Hill Book Company. Reproduced with permission.)

Log current density, i

iL

(a)

0

+

Overvoltage, –

c

Log current density, i

iL

i 0

(b)

0

+

Overvoltage,



Activation

polarization

Concentration

polarization

Figure 16.9 For reduction reactions,

schematic plots of overvoltage versus

logarithm of current density for

(a) concentration polarization, and

(b) combined activation–concentration

polarization.