Corrosion Flashcards
Requirements for corrosion to occur
Two electrodes (anode and cathode) with different electromechanical potentials
Electrical/physical connection between anode and cathode
Electrolytic connection between anode and cathode
Anode
Electrode from which electrons flow into the electric circuit
Cathode
Electrode into which electrons flow from the electric circuit
In corrosion cells
The anode gets eaten while the cathode is protected from corrosion
Corrosion resistant materials
May be corrosion resistant either because they are naturally noble/cathodic or they are reactive/anodic but have a protective passive layer
Way of creating a difference of electrochemical potential between two electrodes
Two different materials (this is the most common corrosion cell)
Same material, one in oxygen rich environment, one oxygen deprived (oxygen deprived part becomes anode)
Same material, one under applied or residual stress, the other unstresses (stressed part becomes anode)
Same material, one in more aggressive solution, one in less aggressive solution (one in more aggressive solution becomes the anode)
Same material, but connected to a DC electric source, e.g. a battery. (Part connected to + terminal of DC source becomes the anode)
Design against corrosion
Avoid using mixed materials where possible
Better to have a large anode and small cathode
Break the electric circuit by inserting an electric insulator between electrodes
Avoid oxygen deprivation cells
Use annealing heat treatments to remove unnecessary residual stresses
Coatings that provide a barrier between corrosion env and part
Cathodic protection
Anodic protection