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.

In Cathotic Protection, the metal is surrounded by another material in order to insure that the metal will not be oxidized.

O2

Fe Mg

O2

Fe

Any of these metals would work to protect Iron.

1. Ships aluminum hulls with steel fixtures2. 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

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 e-Fe, so that protected the body (Fe) from corrosion.

Fe

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

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.

http://en.wikipedia.org/wiki/Cathodic_protection

http://www.corrosionist.com/Cathodic_Protection_Sacrificial_Anodes.htm

http://www.npl.co.uk/upload/pdf/basics_of_corrosion_control.pdf