Corrosion

• Deterioration of materials through chemical or electro-chemical interaction with environment
• Attack on metals by agents such as polluted air; sea water (sodium chloride), leading to formation of rust
• Most corrosion ‘wet’
• Lecture approach mainly not via chemical reactions
1. Not a unifying theme for explanations of different corrosion modes
2. Personal sensitivities



• Two different metals electrically in contact immersed in electrolyte
1. Creates galvanic couple where more active metal corrodes (anode) at accelerated rate and more noble metal (cathode) corrodes at a retarded rate (or zero)
• Electrical cells also created by eg:
1. Air bubbles / water droplets
2. Differential stresses in same metal causing local galvanic couple (stress corrosion cracking)