KIT 357 Experiment 1: Corrosion of metals

OBJECTIVES
1. To understand the general corrosion principles and determine the corrosion cell within a metal specimen.
2. To determine anode and cathode in a corrosion process.
3. To evaluate the effects of area of the electrodes, oxygen concentration and stress on the corrosion rate.
4. To study some of the methods of corrosion protections.
INTRODUCTION
The corrosion of metals is a problem of great economic importance. Corrosion is the destructive result of chemical reactions between a metal or metal alloys and its surrounding. In this experiment you will carry out a series of investigations concerning the chemical principles involved in corrosion and in some of the methods used for corrosion protection.
INITIAL PREPARATION
1. Clean the following tests specimens with abrasive paper, then rub them with tissue paper soaked in acetone to remove any grease:
• 2 copper specimens of 9 cm x 2 cm and 1 specimen of 9 cm x 5 cm.
• 2 zinc specimens of 9 cm x 2 cm.
• 2 aluminium specimens of 9 cm x 2 cm.
• 3 iron specimens of 9 cm x 2 cm.
2. Prepare the following solutions:
• 1 litre solution of 3 %(w/w) NaCl
• 250 mL solution of 0.5 % (w/w) potassium ferricyanide
• 250 mL solution of 1.0 M copper sulphate
• 100 mL solution 0.5 % (w/v) phenolphthalein ( 1 g in 100 mL ethanol and 100 mL water)
• 250 mL solution of 0.1 M ZnSO4.
• 250 mL solution of 0.1 M Na2CrO4.
• 250 mL solution of 0.1 M NaNO2
3. Prepare ferroxyl indicator solution as follows:
4. Measure out 200 mL 3 % NaCl solution and 100 mL 0.5 % potassium ferricyanide solution and mix them together in a 400 mL beaker. To this mixture add slowly, with continuous stirring, 20 mL phenolphthalein solution.
5. Suspend one of the iron test specimen has a hole bored in one end, by a thread passed through the hole, from a glass rod laid across a tall 250 mL beaker. Pour the concentrated HNO3 into the beaker until test specimen is completely immersed, and set a side in a safe place (fume cupboard) for later use (Experiment D).
The experiments are divided in few parts:
EXPERIMENT A: Determination of Anodic and Cathodic Reactions in the Corrosion of Iron
EXPERIMENT B: Effect of cathode surface area, oxygen concentration and stress on corrosion rate
EXPERIMENT C: Corrosion protection of iron by mean of cathodic protection
EXPERIMENT D: Corrosion protection by passive or oxides layer
EXPERIMENT E: Corrosion inhibitor
REFERENCES
1. A. Jones, Principles and Prevention of Corrosion, Mcmillan, New York, 1992
2. L.L. Shreir, Corrosion, Vol.I, Metal/Environment Reactions, Vol.II, Corrosion Control, 2nd ed., Newnes-Butterworth, London, 1976.
3. M.G. Fontana, Corrosion Engineering, 3rd ed., McGraw-Hill, New York, 1986.