1. Pewter, which is mainly tin, was commonly used for tableware on old sailing s

Question

1. Pewter, which is mainly tin, was commonly used for tableware on old sailing ships. However, divers rarely find pewter objects in sunken ships unless an iron object is nearby. Please explain. The galvanic series in sea water (shown below) may be helpful.
Galvanic Series in Seawater

        
Increasingly
     cathodic
    (protected)


Increasingly
       anodic
      (corroded)
        Gold
Graphite
Titanium
Silver
18 Cr-8Ni stainless steel (passive)
11-30 wt% Cr stainless steel (passive)
Silver solder
Monel (70 wt% Ni, 30 wt% Cu)
Bronzes (Cu-Sn)
Copper
Brasses (Cu-Zn)
Nickel
Tin
Lead
18Cr-8Ni stainless steel (active)
Steel or iron
Cast iron
2024 aluminum
Cadmium
Aluminum
Zinc
Magnesium

Explanation / Answer

Corrosion is an electro chemical process where corroding metals acts as anode. oxidation occus at anode and the metal corrodes. In presence of iron , a galvanic cell will be generated. As iron is more anodic than Tin, iron will act as anode and as a result corrosion occurs from iron and Pewter (made of Tin) will be saved.

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