Review the use of equilibrium principles in corrosion control or presentation?

Question

Review the use of equilibrium principles in corrosion control or presentation?

Answer 1

Corrosion normally occurs at a rate determined by an equilibrium between opposing electrochemical reactions.

  The first is the anodic reaction, in which a metal is oxidized, releasing electrons into the metal.  

  The other is the cathodic reaction, in which a solution species (often O2 or H+) is reduced, removing electrons from the metal (and making it possible for the metal ion to be liberated into solution).

When these two reactions are in equilibrium, the flow of electrons from each reaction is balanced, and no net electron flow (electrical current) occurs.  The two reactions can take place on one metal or on two dissimilar metals (or metal sites) that are electrically connected.

Why this is important:  if the electrical current can be supressed (an "equilibrium" balance), corrosion will be minimized.

Answer 2

one methods used in corrosion control is the "cathodic protection". cathodic protection works by supplying an external sources of electrons, a current, to metal to be protected, so to move the corrosion reaction in the opposite direction and stop the corrosion.

if u consider the corrosion of a metal:

Metal ----> Metal n+  +  n electrons

for example

Fe ------->  Fe2+ + electrons

you see that if you supply electrons to the iron you will reverse the corrosion reactions and:

Fe2+ + 2electrons ----> Fe

"cathodic protection" works by connecting the metal to be protected with a metal that corrode more easily (galvanic anodes cathodic protection) or to an external current supply (impressed current cathodic protection)

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