Metal Corrosion

Question 1

Explain Redox Chemistry?

Answer 1

• OILRIG
  oxidation is loss of electrons and reduction is gain of
  elections

Question 2

What happens at the cathode?

Answer 2

Reduction, which means that electrons are added

Question 3

What happens at the anode?

Answer 3

Oxidation, which means that electrons are lost

Question 4

What is corrosion?

Answer 4

corrosion is the oxidation of metal oxides

Question 5

Why does corrosion happen within the body?

Answer 5

There is lots of water present in the body

water is H2O so therefore there is oxygen

Question 6

What is Ionisation?

Answer 6

The direct formation of metallic cations under acidic or reducing (oxygen-poor) conditions

Question 7

What is Hydroxylation?

Answer 7

The reaction of water under alkaline or oxidising conditions to form a hydroxide

Question 8

Why are all metals found in nature in their ore?

Answer 8

Because metals want to be in their lowest energy state, a corroded state is a low energy state

Question 9

What is Galvanic Corrosion?

Answer 9

Two different metals in contact act as an anode and a cathode, the less noble metal acts as an anode and corrodes.
This only happens when two metals with different electrochemical potentials are in electrical contact and exposed to an electrolyte

Question 10

What is Crevice Corrosion?

Answer 10

• It begins with a crevice between two metals that is large enough for an electrolyte to get in but small enough to become stagnant
• Uniform corrosion occurs initially until all the oxygen in the stagnant zone is used up, the reduction of oxygen stops but the dissolution of the metal continues
• There is an excess of positive charge due to the metal ions which is balanced by the migration of Cl-/OH- ions into the crevice
• The metal ions and hydroxide ions react with water to form an insoluble metal hydroxide and hydrochloric acid
• The chloride and Hydrogen ions accelerate the dissolution rates of most metals and alloys so the process becomes autocatalytic

Question 11

What is Cathodic Protection?

Answer 11

protection of a metal structure by making it act as a cathode

Question 12

What is an example of cathodic protection?

Answer 12

steel with a protective layer of zinc, the zinc preferentially oxidises, when scratched zinc still protects steel because steel is cathodic to zinc in most aqueous solutions and corrodes preferentially

Question 13

What is a Protective Coating?

Answer 13

When an oxide layer forms over a metal which stops corrosion

Question 14

What are the pros and cons of using titanium with an oxide protective coating?

Answer 14

Pro - titanium oxide is bioactive and integrates with tissue
Con - Titanium oxide breaks down easily under stress and produces wear particles

Question 15

What is fatigue?

Answer 15

Progressive and localised structural damage that occurs when a material is subjected to cyclic loading?

Question 16

What is Fretting?

Answer 16

A special wear process that occurs at the contact area between two materials under load and subject to minute relative motion by vibration or some other force.