PASSIVATION
What is the passivation :
Passivation is called in normal terms but it is technically
a chromate conversion coating process which
mostly apply on zinc or cadmium coated surface ,aluminium, etc . That particular metal react with chrome
base chemicals and form the that metal chromate film .
Why we do passivation :
Passivation we do on zinc or cadmium coated surface for
corrosion resistance . On aluminium surface we do chromate
conversion lubricity , or foundation coatings for subsequent coating
like powder coating, painting, oil etc.
Types of
Passivation :
HEXAVALENT
PASSIVATION FOR ZINC & CADMIUM COATED SURFACE
1. Blue passivation – Sodium di chromate base
thin coating , which give approx. 24 hours in salt spray for white rust. Appearance will be bright blue finish .
2. Yellow passivation – chromic acid hexavalent base , which
give approx. 96 hours in salt spray for white rust.Appearance will be bright irridescent finish .
3. Black passivation - chromic acid hexavalent and
silver base , which give approx. 96 hours in salt spray for white rust.
4. Green passivation - chromic acid hexavalent base , which
give approx. 120 hours in salt spray for white rust.
TRI VALENT
PASSIVATION FOR ZINC
1. Blue passivation – Trivalent chromium base
thin coating , Appearance will be bright blue finish .
2. Yellow passivation – Trivalent chromium base , which
give thick coating and approx. 96 hours in salt spray for white rust.
3. Black passivation - Trivalent chromium and Non silver
base , which give approx. 96 hours in salt spray for white rust.
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