sacrificial protection and galvanising Flashcards
what is galvanising
the coating of a metal with zinc protects the underlying iron in two ways
how does galvanising protect iron
- it prevents oxygen and air getting into contact with the iron
- it protects by sacrificial protection
what is sacrificial protection
when a more reactive metal is placed in contact with a less reactive metal, the more reactive corrodes the other metal first, preventing the corrosion of the less reactive metal
sacrificial protection of iron by zinc
if some galvanised iron is scratched, some of the iron surface is exposed and in the presence of water, an electrochemical cell is set up
zinc is more reactive than iron, so it loses electrons more rapidly than iron
the zinc corrodes faster than iron. we say that it is a sacrificial metal
the iron remains protected because the electrons are accepted on the surface keeping it in a reduced state rather than oxidising
the electrons donated by the zinc react with hydrogen in the water to release hydrogen gas