Ch 10 Flashcards
Define corrosion
Destructive attack of a metal by electro chemical interaction or chemical reaction with its environment
List the three conditions for corrosion
Oxidizing agent and Reducing agent
Must be thermodynamically favourable
Reaction occurs at surfaces of the material
What happens at the anode?
Oxidization
Loss of electrons
What happens at the cathode?
Reduction
Gain of electrons
What happens to oxidizing agents?
They’re reduced
What happens to reducing agents?
They’re oxidized
What is not typically involved in the cathode reaction for corrosion?
Metal ions
List the four components to an electrochemical cell, which all must be present for corrosion to occur
Anode
Cathode
Electrical connection
Electrolyte
What does the electrolyte do?
Conducts current via ions
Must be in contact with anode and cathode
How to stop corrosion
Remove one or more of the components from the electrochemical cell
Corrosion: what does passive mean?
Alloy forms, a protective layer
Corrosion: what does active mean?
When the alloy does not produce a protective layer
Why doesn’t stainless steel corrode
Because it corrodes very rapidly than forms, a protective layer, a very thin, inert metal oxide that prevents further reaction
For stainless steel the passive Cr2O3 layer forms
What does the galvanic series show
Inert and active
Define galvanic cell/composition cell
Galvanic corrosion occurs when dissimilar metals are connected and exposed to an electrolyte
Define stress cell
Stress area has a higher free energy and becomes the anode
Define concentration cell
When it dissolves species involved in either the anode or cathode reaction varies in concentration at different locations in the electrolyte
Example: oxygen concentration cell
Large cathode with small anode is what
And why
BAD
The surface area of the cathode is rather large compared to the anode so corrosion happens very fast
List the three main types of electrochemical cells found in corrosion
Galvanic cell
Stress cell
Concentration cell
List 5 methods for corrosion control
Coating
Inhibitors
Reduce dissolved oxygen
Galvanic protection
Reducing temperature
Corrosion control: describe coating
Coating the surface to isolate it from the electrical light with paint or an electroplated layer of a noble metal
Corrosion control: define inhibitors
Make adherent ions that coat the surface and isolated from the electro chemical reaction
Corrosion control: define, reduce dissolved oxygen
Do this by either adding hydrazine to the water, or treating the water, using a hydrogen protection cell that replaces the oxygen in the water with hydrogen
Corrosion control: define galvanic protection
Where are more and noticed metal is hooked up to the metal to be protected and dipped in the electrolyte
Corrosion control: define reducing temperature
Higher temperatures increase the rate of chemical reactions
