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Callister - An introduction - 8th edition

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714 • Chapter 17 / Corrosion and Degradation of Materials<br />

17.27 h c 2.3RT i<br />

log a 1 b Overvoltage for concentration polarization 686<br />

nf i L<br />

17.32 P-B ratio A Or M<br />

Pilling–Bedworth ratio for divalent metals 704<br />

A M r O<br />

17.33 P-B ratio A Or M<br />

Pilling–Bedworth ratio for other than divalent metals 704<br />

aA M r O<br />

17.34 W 2 K 1 t K 2<br />

Parabolic rate expression for metal oxidation 706<br />

17.35 W K 3 t<br />

Linear rate expression for metal oxidation 706<br />

17.36 W K 4 log 1K 5 t K 6 2 Logarithmic rate expression for metal oxidation 706<br />

List of Symbols<br />

Symbol<br />

Meaning<br />

A<br />

Exposed surface area<br />

A M<br />

Atomic weight of metal M<br />

A O<br />

Formula weight of the oxide of metal M<br />

f<br />

Faraday constant (96,500 C/mol)<br />

i<br />

Current density<br />

i L<br />

Limiting diffusion current density<br />

i 0<br />

Exchange current density<br />

K<br />

CPR constant<br />

K 1 , K 2 , K 3 , K 4 , K 5 , K 6 Time-independent constants<br />

[M n<br />

1 ], [M n<br />

2 ] Molar ion concentrations for metals 1 and 2 (Reaction 17.17)<br />

n<br />

Number of electrons participating in either of the<br />

half-cell reactions<br />

R Gas constant (8.31 J/mol#<br />

K)<br />

T<br />

Temperature (K)<br />

t<br />

Time<br />

V 0 1, V 0 2<br />

Standard half-cell electrode potentials (Table 17.1) for<br />

metals 1 and 2 (Reaction 17.17)<br />

W<br />

Weight loss (Equation 17.23); weight gain per unit area<br />

(Equations 17.34, 17.35, 17.36)<br />

b<br />

Half-cell constant<br />

r<br />

Density<br />

r M Density of metal M<br />

Density of the oxide of metal M<br />

r O<br />

Important Terms and Concepts<br />

activation polarization<br />

anode<br />

cathode<br />

cathodic protection<br />

concentration polarization<br />

corrosion<br />

corrosion penetration rate<br />

crevice corrosion<br />

degradation<br />

electrolyte<br />

electromotive force (emf) series<br />

erosion–corrosion<br />

galvanic corrosion<br />

galvanic series<br />

hydrogen embrittlement<br />

inhibitor<br />

intergranular corrosion<br />

molarity<br />

oxidation<br />

passivity<br />

Pilling–Bedworth ratio<br />

pitting<br />

polarization<br />

reduction<br />

sacrificial anode<br />

scission<br />

selective leaching<br />

standard half-cell<br />

stress corrosion<br />

weld decay

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