Unit 2- Class 8- CORROSION (Corrosion Control)

ORGANIC COATING:
Coating of inert organic materials like paints, and lacquers on metallic surface to protect the metal usually thickness of the organic coating is less than 0.4mm thickness.

 The functions of organic coating are:
i)    The organic coating serves as a barrier between the metal surface and corrosive environment.
ii)    The pigment or drying oils present in the paint often exert and inhibitive action by electrochemical and other means.

 There are certain requirements to have a good organic coating they are:
i)    The organic coating should adhere tenaciously to the metal surface and should improve its physical appearance.
ii)    The film formed should be uniform, continuous and act as a barrier to air and water.
iii)    It should chemically increase, so that atmosphere pollution are not there.
iv)    Should have reasonably long life.
v)    Should easily available, low cost and easy and properly applicable.
               
 The performance of paint depends on the technique employed during application method.

The application of organic coating involves following steps
i)    Surface preparation:  It includes degreasing the surface and removing rust and scale from it.
ii)    Priming:  This is the first coat of primer like phosphate coating which must strongly adhere to the surface so that painting can properly done.
iii)    Filling:  Fillers like nitrocellulose epoxides etc. are applied on well-dried surface in order to improve external appeaence.
iv)    Sanding:  The roughness and irregularities on the surface are smoothened by means of emery paper.
v)    Final finishing coat of organic paints of two or three coat.
                
Organic coating usually applied such as brushing, spraying, dipping etc. Break of organic coating causes severe corrosion.