Corrosion Protection Flashcards
What is the approximate cost incurred by corrosion on the US economy per year
Around $300 bn - Around 3.5% of the GDP
What are the two ways in which corrosion incurs direct costs
components that are corroding need to be replaced and spending money to develop means to prevent corrosion
What are the ways in which corrosion incurs indirect costs
Shutdown of facilities, disrepair causing loss of product (such as leaking pipes), loss of efficiency, contamination of products
Does oxidation occur at the anode or the cathode
The anode
What are the products and intermediate products formed in the oxidation of iron by water
Fe turns into Fe2+ and 2e- (oxidation)
The 2e- is donated to O2 and 2H2O to form 4OH- (reduction)
The Fe2+ reacts with the OH- to form Fe(OH)2 precipitation
Fe(OH)2 reacts with O2 to form Fe2O3.H20 (rust formation)
Due to the nature of corrosion as a redox reaction, what can be visibly seen on the location of the rusting
A corrosion pit adjacent to a corrosion product “hill”
What are the four ways to prevent/ reduce corrosion
Using corrosion inert materials (usually not possible due to scarcity or poor mechanical properties)
Using paint/ coating
Connecting the iron to a more reactive sacrificial metal such as zinc or magnesium which will donate electrons to the iron. (galvanic protection)
Supplying electrons to the iron (cathodic protection)
How does galvanised steel repair itself from corrosion
If the zinc coating around the steel is scratched, the steel underneath is exposed, but the corrosion products of the zinc seal the hole. Any steel beneath is protected as zinc donates electrons to iron.
What is the difference between cathodic and galvanic protection despite both needing an anode metal
The anode metal in cathodic protection does not need to lose any electrons
