Cathode

Cu++ copper ions

electrons

electrons

Cu copper s

Fig. 5.31 Daniell cell
Fig. 5.32 Dry Leclanche cell

Fig. 5.33 Corrosion of iron

Fig. 5.34 Bimetallic corrosion between pairs of metals in building applications

An equivalent process takes place in the dry Leclanche cell - the standard torch battery (Fig. 5.32). However, in this case the central carbon rod replaces the copper and the liquid is replaced by an aqueous paste. The anode process is the same as in the Daniell cell with the gradual dissolution of the zinc container.

Anode

Zn zinc

electrons

Fig. 5.33 Corrosion of iron

At the cathode the carbon rod is surrounded by manganese dioxide which oxidises the hydrogen gas, which otherwise would have been produced there by the reaction between water and the electrons.

Fig. 5.35 Bimetallic corrosion between aluminium and steel

Cathode

0 0

Post a comment