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

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

Revised Pages

Design Problems • 703

Log current density

Overvoltage

Velocityv 1

v 5 > v 4 > v 3 > v 2 > v 1

v 2 v 3 v 4 v 5

Figure 16.26 Plot of overvoltage versus logarithm of

current density for a solution that experiences combined

activation–concentration polarization at various

solution velocities.

Corrosion Prevention

16.14 (a)What are inhibitors?

(b)What possible mechanisms account for

their effectiveness?

Oxidation

16.15For each of the metals listed in the table, com-

pute the Pilling–Bedworth ratio. Also, on the

basis of this value, specify whether or not you

would expect the oxide scale that forms on

the surface to be protective, and then jus-

tify your decision. Density data for both the

metal and its oxide are also tabulated.

Metal Density Oxide Density

Metal (g/cm^3 ) Metal Oxide (g/cm^3 )

Mg 1.74 MgO 3.58

V 6.11 V 2 O 5 3.36

Zn 7.13 ZnO 5.61

16.16In the table, weight gain–time data for the ox-

idation of nickel at an elevated temperature

are tabulated.

W(mg/cm^2 ) Time(min)

0.527 10

0.857 30

1.526 100

(a)Determine whether the oxidation kinet-

ics obey a linear, parabolic, or logarithmic

rate expression.

(b)Now computeWafter a time of 600 min.

16.17In the table, weight gain–time data for the

oxidation of some metal at an elevated tem-

perature are tabulated.

W(mg/cm^2 ) Time(min)

1.54 10

23.24 150

95.37 620

(a)Determine whether the oxidation kinet-

ics obey a linear, parabolic, or logarithmic

rate expression.

(b)Now computeWafter a time of 1200 min.

DESIGN PROBLEMS

16.D1Suggest an appropriate material for each of

the following applications, and, if necessary,

recommend corrosion prevention measures

that should be taken. Justify your sugges-

tions.

(a)Laboratory bottles to contain relatively

dilute solutions of nitric acid

(b)Barrels to contain benzene

(c)Pipe to transport hot alkaline (basic) so-

lutions