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ABOUT CORROSION

CORROSION




It is defined as the chemical or electrochemical attack of metals by the environment.

the effects of corrosion by these factors;


  • humidity
  • temperature
  • purity of  metal
  • the physical state of metal
  • nature of ions present in it
  • PH
  • position in electrochemical series
  • relative areas of anode and cathode

electrochemical theory of corrosion;


this theory depends on its electrode potential of metal(anode).if a high electrode metal comes in contact with the low electrode(cathode) potential metal causes the galvanic cell setup.

note: the large corrosion occurs at anodic metal.

the galvanic cells are three types:


composition cell;

in this, both the zinc and copper electrodes are dipped in the same electrolysis solution. 
here the zinc is act as anode and the copper is act as like cathode.the electrons are transferred from anode to cathode.here the anode gets corroded.

stress cell;

These types of cells formed by the drawing, rolling, welding, heat treatment of metals.
stressed areas at the metal act as like an anode causes corrosion.

concentration cell;

this type of cells formed the differential oxygen concentration.poor oxygenated parts act like anodes and causes the corrosion.

RUSTING OF IRON:


  • (Fe2O3xH2O)
  • corrosion of iron is called rusting.

prevention methods for avoiding:

  • using metal high purity
  • alloying
  • protective coating by the metallic or non-metallic or organic.

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