Nace CP 1, Course Manual

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Basic Chemistry and Basic Corrosion Theory 2:24
CP 1 – Cathodic Protection Tester Course Manual
©
NACE International, 2000
02/01/05
Table 2.2. Practical Galvanic Series
Metal Volts vs Cu-CuSO
4
Active or Anodic End
Magnesium –1.60 to –1.75
Zinc –1.10
Aluminum –1.05
Clean Carbon Steel –0.50 to –0.80
Rusted Carbon
Steel
–0.20 to –0.50
Cast/Ductile Iron –0.50
Lead –0.50
Steel in Concrete
–0.20
Copper –0.20
High Silicon Iron
–0.20
Carbon, Graphite +0.30
Noble or Cathodic End
When two different metals are connected, a voltage is generated between
them. The more active metal (toward the anodic end) becomes the anode of
the cell.
A classic example of a galvanic cell is the flashlight battery, shown in Figure
2.17. This consists of a zinc case enclosing an electrolyte and a carbon rod.
From Table 2.2 you can see that the voltage difference between the two
metals is about 1.4V (actually 1.5V in a battery) and that the zinc is the anode
and the carbon is the cathode. This is a useful corrosion cell since the current
produced can do work for us. Eventually the case will corrode through—we
have all seen batteries in that condition.