What is corrosion A The reaction of a metal with oxygen in the air moisture or other substances in the environment is called corrosion B Gold is so unreactive that it does not corrode at all ID: 249847
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Slide1
Corrosion of metals and their protectionSlide2
What is corrosion?
A) The reaction of a metal with oxygen in the air, moisture or other substances in the environment is called
corrosion
.
B) Gold is so
unreactive
that it does not corrode at all.Slide3
Ingredients in hand warmer:
Chemicals:
Iron 3 teaspoon
Salt 1 teaspoon
Activated carbon 2 teaspoon
Water 1ml
Vermiculite 2 teaspoon
Slide4
Corrosion of iron: rusting
A) The corrosion of iron is called
rusting
.
B)
Rust is the powdery reddish brown coating which forms when iron corrodes. C) Its chemical name is hydrated iron(III) oxide, Fe2O3•nH2O.
Chemical formulaSlide5
In the first stage of rusting, some iron atoms lose electrons to form Fe
2+
(
aq
) ions.
Fe(s) Fe2+(aq) + 2e- Then a series of reactions follow. The overall reaction can be represented by an equation:
4Fe(s) + 3O
2
(g) + 2nH
2
O(l)
2Fe
2
O
3
•nH
2
O(s)
《
rust
》 Slide6
Rusting is a
slow
process
. It eventually causes structural weakness and disintegration of the metal
.
E) For rusting to occur, two things must be present: oxygen and water. F) During rusting, iron is oxidized by oxygen in the air.Slide7
What
factors speed up the rusting process
?
Presence
of ionic
substances The rusting process speeds up when water containing ionic substances such as sodium chloride.Slide8
B)
Presence of acidic
pollutants
The emission of
acidic gases from factories to form acids with moisture in air, thus speeding up the rusting process.Slide9
C) Higher
temperature
At
a
higher temperature, reaction becomes faster. The rusting process also becomes faster.
D) Scratching or bending the surface Rusting occurs more quickly where the iron surface is scratched or bent. Slide10
E)
Attachment to a less reactive
metal
The rusting process speeds up if iron is in contact with a
less reactive metal, such as tin and copper. A food can is usually made of mild steel (an iron alloy) coated with a thin layer of tin. When the tin coating of a tin can is damaged, the steel rusts more quickly than when it is alone. KNaCaMgAlZnFeSnPbCuHgAgAuSlide11
How
to prevent rusting
?
A)
Using protective coatings1. Coating with paint, oil, grease or plastic Oil or grease can prevent oxygen and water from reaching the iron. It has a lubricating purpose as well.Slide12
2
.
Tin-plating
Tin-plate
is iron coated with tin. Tin is an unreactive metal. It can protect iron from air and oxygen and hence prevent rusting. Tin-plating is commonly used in making food cans since tin ions are not poisonous. Note: Tin is a less reactive metal than iron. Slide13
3
.
Zinc-plating
Iron coated with a layer of zinc is called galvanized iron and this method is called zinc-plating.KNaCaMgAlZnFeSnPbCuHgAgAuSlide14
4
.
Electroplating
We can plate a very thin layer of metal on iron by an electrical process called
electroplating.Slide15
B)
Using sacrificial
metals
5. Sacrificial
protection
When a lump of a more reactive metal is attached to a piece of iron, the more reactive metal corrodes instead of the piece of iron. The more reactive metal ‘sacrifices’ itself to prevent the piece of iron from rusting. KNaCaMgAlZnFeSnPbCuHgAgAu