Cmt 555 Expt 6

EXPERIMENT 6: CORROSION OF IRON

OBJECTIVES:

1. To study the influence of environment (moisture/water and O2) on corrosion

2. To study the effect of ionic/electrolyte on corrosion

3. The effect of a second metal (copper and aluminum) in contact with the iron in an electrolyte solution

INTRODUCTION

Corrosion is the formation of undesirable metallic compounds at the surface of pure metals or alloys. Most metals are very reactive and will react with other substances they come in contact with in their environment especially the atmosphere, water and moist solids. Oxygen, water, carbon dioxide, ions in solution and hydrogen sulfide are the main substances involved in corrosion. Rusting is the corrosion of iron. Rusting of metals is a special case of metal oxidation. Iron will oxidize to form rust. Water will cause metals to rust; this reaction can be accelerated by adding salts. In the corrosion process, metals get oxidized. For example in mild steel (which is greater than 99% iron) the metal corrodes according to the following:

Fe(s) Fe2+ (aq) + 2e

These electrons are consumed by reacting with another substance (usually oxygen but it can be H+ in acids) in reduction as in

O2(g) + 2H2O(l) +4e 4OH-

These two half reactions together give the overall reaction:

2Fe + O2 + 2H2O 2Fe2+ + 4OH-

PROCEDURE

A: THE INFLUENCED OF ENVIRONMENT ON CORROSION OF IRON

Method:

Each of the nails was cleaned with fine sandpaper. Three of the test tubes were filled with tap water (enough to cover the nail) and one test tube was left dry. A nail was added to each test tube (1 test tube without water and 3 test tubes with water) and then a layer of oil was poured over the water in one of the test tubes. The oil was floated to the top of the water and a separate layer was formed.

Another test tube containing iron nail was immersed in water was degassed by flowing N2 gas in the solution for 5 minutes. The test tube was covered with a rubber...