Corrosion The iron in steel corrodes easily to form iron II oxide Sodium metal reacts quickly to form sodium oxide The copper roof of the parliament building corrodes to form copper carbonate Tarnished silverware forms silver sulfide ID: 469152
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Slide1
Unit 2: Electrochemistry
CorrosionSlide2
The iron in steel corrodes easily to form iron (II) oxide
Sodium metal reacts quickly to form sodium oxide
The copper roof of the parliament building corrodes to form copper carbonate
Tarnished silverware forms silver sulfideSlide3
Oxygen has a higher standard reduction potential than metals.
This means that oxygen will react with metals to form metal oxides
spontaneously
. Slide4
Airplanes are traditionally made out of aluminum.
Why do they not crumble in a rainstorm (Given the reduction potential of Al is -1.66V?
Aluminum oxide
forms across the surface.
This layer protects the atoms below from oxidation.
The same effect is not seen with iron (rust). In this case the oxide flakes off and allows atoms below to oxidize.Slide5
Composition of Steel: Mixture of elements, primarily iron
Since steel is used to build structural items (buildings, bridges) and is primarily made of iron, a lot of work is done to prevent corrosionSlide6Slide7Slide8Slide9
Corrosion requires water! This is why cars do not rust in dry environments.
Salt is not required, but accelerates the process by providing ions. This is why rusting is more severe in the winter (salted roads).Slide10
Prevent Corrosion
Paint the metal – problematic when scratched
Plate steel with other metals that oxidize to form durable oxides (chromium or tin) – used with stainless steel appliances
Galvanizing
with zinc
Coat steel in zinc ions zinc forms a durable carbonateThe zinc can still be oxidized but when it does it will release the electrons onto the iron, preventing the iron from oxidizing
https://www.youtube.com/watch?v=jimPImGKPy8
https://www.youtube.com/watch?v=Wy6u2kikAA4Slide11
Cathodic
Protection
used to protect buried steel fuel tanks
Loads the metal with electrons so that it becomes a cathode (cannot be oxidized)
there are two methods
Sacrificial anode
- A stronger oxidizing agent (in this magnesium) is used
- The magnesium is continually reduced and sends electrons to the buried steel pipe
Impressed current
The negative terminal of a power supply is attached to the buried steel pipe
The positive terminal is attached to an inert electrode (graphite)
Continuous flow of electrons to the pipe
Used in larger structures where sacrificial anodes with be financial unreasonable (pipeline)