Anita
Marcia
Jane
Methods：
Prevent the corrosive environment from getting
at the metal
 Use electrochemical principles to prevent
corrosion

A.Method depend on isolating a metal from its
environment
1.Apply a protective layer
Paint
 coating
 Plastic

Apply a protective layer
 If oxygen and water can’t get to the metal，it
won’t corrode.
 Cheapest and most useful way of preventing
from corrosion.

2.Apply a metal which is corrosion resistant to
the surface of original metal.
Steel
 Alloy of iron

Steel contains a small amounts of carbon and
various metals.
 Unprotected steel cans are unsuitable use of
food, the steel is plated with a thin layer of tin
 Outermost layers of tin atoms oxidize quickly,
producing a thin tin oxide layer.
 Protective oxide coating adheres strongly to the
underlying tin metal to prevent further
corrosion.

The process of protecting a substance from
unwanted oxidation by connecting it to a
substance having a higher tendency to oxidize.
 (making it the cathode of an electrochemical
cell.)


if the two metals are put together, the corrosion
of the Mg will oxidize first which prevents
corrosion of the iron.
O2
Fe

O2
Fe
Mg
In Cathotic Protection, the metal is surrounded
by another material in order to insure that the
metal will not be oxidized.
Any of these
metals would
work to protect
Iron.
1. Ships
aluminum hulls with steel fixtures
2. Galvanized steel
Zinc coating on steel
Definition
 A voltage is applied with an external power
supply to keep the Fe slightly negative. Thus,
the Fe surface has excess e- s so it doesn’t
have to oxidize in order to supply e-s to O2
Fe
Metal oxide lose electrons
and become cations,
For example, Fe2+ iron after
the first change into rust.
Plus the current through the
body to be protected (such as
steel) a cathode current to
compensate for the loss of eFe, so that protected the body
(Fe) from corrosion.
HOW IT WORK
For larger structures, galvanic anodes cannot
deliver economically enough current to provide
complete protection. Impressed current cathodic
protection (ICCP) systems use anodes connected
to a DC power source. Usually this will be a
cathodic protection rectifier, which converts an AC
power supply to a DC output. In the absence of an
AC supply, alternative power sources may be used,
such as solar panels, wind power or gas powered
thermoelectric generators
CHANGE THE CONDITIONS IN THE
CHEMICAL SURROUNDINGS SO AS TO
LOWER THE TENDENCY OF THE
SURROUNDINGS TO REDUCE

When iron is placed in contact with water
containing oxygen, it will oxidize the iron.

If oxygen is removed from the solution, the
reduction tendency will drop.

And in order to lower [H+],[OH] should be added.

So for the iron which placed in NaOH solution
will not rust.
REFENRENCES
http://en.wikipedia.org/wiki/Cathodic_protecti
on
 http://www.corrosionist.com/Cathodic_Protecti
on_Sacrificial_Anodes.htm
 http://www.npl.co.uk/upload/pdf/basics_of_co
rrosion_control.pdf
