Materials A: Lecture 14- Corrosion

What is corrosion and how does it occur?

Corrosion is a process in which the composition and physical integrity of a solid material are altered in a corrosive environment. In chemical corrosion, a corrosive liquid dissolves the material, while in electrochemical corrosion, metal atoms are removed due to an electric circuit. Metals, ceramics, polymers, and even materials exposed to radiation or bacteria can undergo corrosion.

Are there instances where corrosion is desirable?

Yes, in some applications, corrosion or oxidation is useful. For example, chemical corrosion and erosion processes are used to create ultra-flat surfaces of silicon wafers for computer chips. Additionally, the degradation of certain biopolymers is beneficial in medical applications, such as dissolvable sutures. Electroplating of metals is another positive application of corrosion.

How does concentration affect electrode potential?

The electrode potential depends on the concentration of the electrolyte. The Nernst equation expresses the electrode potential in nonstandard solutions

What is the Nernst equation?

E = E0 + 0.0592 n log(Cion).

What is Faraday’s equation, and how is it used in electroplating?

The amount of metal plated on the cathode in electroplating, or removed from the anode by corrosion, can be determined from Faraday’s equation: w=ItM/nF. This equation states that one gram equivalent of a metal will be deposited by 96,500 C of charge

How can materials be protected against electrochemical corrosion?

Design measures, Coatings, Inhibitors, Cathodic Protection, Passivation or Anodic Protection, and proper Materials Selection and Treatment