Week 3 - Corrosion

Question 1

What is corrosion

Answer 1

chemical or electrochemical reactions between a metal- based material and its environment that produces a deterioration in the material and its properties. Even very small or localized corrosion can cause mechanical failure.

Question 2

What are the 2 main types of corrosion

Answer 2

• Dry chemical corrosion
• Wet redox corrosion

Question 3

What are the 3 types of wet corrosion

Answer 3

• galvanic corrosion
• stress corrosion
• crevice corrosion

Question 4

What is a redox reaction

Answer 4

Reaction where there is a change in oxidation number in components on the LHD and RHS of a reaction

Question 5

What is oxidation

Answer 5

LOSS of electrons

Question 6

What is reduction

Answer 6

GAIN of electrons

Question 7

What is cell potential (Ecell)

Answer 7

the difference between the potentials (electrical potential) of the 2 half cells (due to the separation of charges

Ecell indicates the driving force on the electrons in the wire connecting the 2 electrodes) at the given concentration (- —> +)

Ecell is the measured voltage across the 2 electrodes of the cell

Question 8

What is the equation of Ecell (cell potential)

Answer 8

Question 9

Is the anode more positively or negatively charged in an Ecell

Answer 9

negative

Question 10

is the cathode more positively or negatively charged in an Ecell

Answer 10

Positive

Question 11

What is the standard potentials for half reaction based off

Answer 11

The hydrogen half cell
standard hydrogen electro which equates to 1 volt

Question 12

What is nearnst equation used to calculate

Answer 12

Cell voltage - Ecell

Question 13

What Ecell makes the reaction spontaneous

Answer 13

if it is +ve

Question 14

What Ecell makes a reaction non spontaneous

Answer 14

if its -ve

Question 15

If the Ecell is positive then Gibbs free energy is

Answer 15

negative

Question 16

How does the corrosion (rusting) of iron occur

Answer 16

series of redox reactions that includes the oxidation of
Fe(s) —> Fe2+(aq)
and the
reduction of Fe+2 to Fe3+ aw Fe2O3(s)

Anodic Fe –> Fe2+ –> Fe3+
Cathodic O2 –> OH-

Question 17

Why does a galvanic cell form in the oral cavity

Answer 17

as saliva acts as an electrolyte

Question 18

What is the activity series

Answer 18

a listing of redox half reactions in order of decreasing ease of oxidation

Question 19

A metal at the top of the activity series is

Answer 19

oxidizes readily

Question 20

What is an active metal

Answer 20

A metal which is inclined towards oxidation (higher up on the activity series) e.g. Na, Mg

Question 21

What is dissimilar metal corrosion

Answer 21

Where a galvanic cell is established due to differences in electrode potential between 2 metals in close proximity (+ saliva electrolyte in the oral cavity)

Different metals have different activity or redox potential causes a current to form

Question 22

What is an example of dissimilar metal corrosion in the oral cavity

Answer 22

Au inlay in close proximity to Hg amalgam filling in saliva electrolyte

Question 23

What happens when someone has a Hg filling and bits Alfoil (aluminum)

Answer 23

The aluminum acts as an active anode and the filling acts as an inactive cathode. This reaction causes electrons to form a current which is transferred into the filling, hitting the tooth nerve causing pain.
Al = active anode
Saliva = electrolyte
Filling = inactive cathode

Question 24

What is crevice corrosion

Answer 24

Crevice corrosion is a localized form of corrosion that occurs in confined spaces or crevices, Inside the crevice, the oxygen content is significantly lower compared to the outside environment, leading to an aggressive corrosive environment.

the crevice where a metal implant meets bone provides a low oxygen environment and this allows active ion loss to occur in the crevice

Question 25

What is stress corrosion

Answer 25

Corrosion (crack propagation) which requires a corrosive environment and a local stress (compressive, tensile)
Electrochemical cells can be set up between deformed regions (anode) and unaltered region (cathod3) with saliva acting as electrolyte.

is a type of failure in materials that occurs due to the combined effects of tensile stress and a corrosive environment.