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• Corrosion: -- the destructive electrochemical attack of a material. -- Ex: Rusting of automobiles and other equipment
• Cost: -- 4 to 5% of the Gross National Product (GNP)*

• H.H. Uhlig and W.R. Revie, Corrosion and Corrosion Control: An Introduction to Corrosion Science and Engineering , 3rd ed., John Wiley and Sons, Inc.,

THE COST OF CORROSION

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STANDARD HYDROGEN ELECTRODE

• Two outcomes:

o metal

V < (relative to Pt)

Standard Electrode Potential Adapted from Fig. 18.2, Callister & Rethwisch 9e. -- Corrosion -- Metal is the anode (-) metal, M Platinum M n+ ions ne

• H 2 (gas) 25°C 1M Mn+^ sol’n 1M H+^ sol’n 2e

e- e- H

H

-- Electrodeposition -- Metal is the cathode (+) M n+ ions ne

e-^ e- 25°C 1M Mn+^ sol’n 1M H+^ sol’n metal, M Platinum H

H+^ 2e

o metal

V > (relative to Pt)

H 2 (gas)

The Standard emf Series

The electromotive force (emf) series is generated by coupling to the standard hydrogen electrode, standard half-cells for various metals and ranking them according to measured voltage.

STANDARD EMF SERIES

metal o

• Metal with smaller V corrodes.
• EMF series Au Cu Pb Sn Ni Co Cd Fe Cr Zn Al Mg Na K +1.420 V +0.

metal V metal o Data based on Table 18.1, Callister 9e. more anodic more cathodic  V = 0.153V o Adapted from Fig. 18.2, Callister & Rethwisch 9e.

1.0 M Ni 2+^ solution 1.0 M Cd 2 +^ solution

Cd 25°C Ni Cd o Ni o

• Ex: Cd-Ni cell V < V  Cd corrodes

EFFECT OF SOLUTION CONCENTRATION AND

TEMPERATURE

• Ex: Cd-Ni cell with standard 1 M solutions - Ni 1.0 M Ni 2+^ solution 1.0 M Cd^2 +^ solution

Cd 25°C

• Ex: Cd-Ni cell with non-standard solutions n = #e- per unit oxid/red reaction (= 2 here) F = Faraday's constant = 96, C/mol.
• Reduce V Ni - V Cd by -- increasing X -- decreasing Y -- increasing T
• (^) + Ni Y M Ni 2+^ solution X M Cd^2 +^ solution Cd (^) T RT/F = 0.

Degradation of Materials

• (^) Physical and Mechanical effects of degradation in wood
• (^) Change in cross-sectional dimensions, swelling and shrinkage
• (^) Strength and stiffness decrease as moisture content increases
• (^) Durability is affected

• (^) Coatings can be compromised

Degradation of Materials

• (^) Plastics
• (^) It is widely accepted that plastics do not corrode however micro organisms which can decompose low density polyethylene do exist

Degradation of Materials

• (^) Plastics
• (^) UV light will weaken certain plastics and produce a chalky faded appearance on the exposed surface

Degradation of Materials

• (^) Plastics
• (^) Heat will weaken or melt certain plastics even at relatively low temperatures

Degradation of Materials

• (^) Plastics
• (^) Mould can grow on plastics in moist humid conditions

Degradation of Materials

• (^) Plastics
• (^) Bio-degradation – the chemical breakdown in the body of synthetic solid phase polymers