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Hexavalent / Trivalent coatings  

March 21, 2008

I would like to know more details about Hexavalent & Trivalent coatings. Also would like to know the merits & demerits of both.

Suryabhan Shinde
Employee - Pune, Maharashtra, India

Hexavalent chrome plating is done out of a chromic acid (H2CrO3) solution in which the chrome is at a +6 oxidation state. This is the traditional approach that has been around for 80 years or so. Some hexavalent plating solutions are generic, some are proprietary.
Trivalent plating is done out of a solution where the chrome is in the +3 oxidation state. This is the newer approach and has been around for 25 years or so. All trivalent chromium plating is based on proprietary baths and usually requires some special equipment features like carbon anodes, or diaphragms to separate the anodes from the plating zone.
Reputedly, trivalent chromium baths involve less dragout, are easier to waste treat, have less stringent ventilation requirements, are not as subject to very low throwing power, etc. On the down side they can plate only very thin layers suitable for decorative plating not hard chrome plating,and the color is a little "off"from the traditional.

Rajesh M B
- Bangalore, Karnataka, India

Rajesh M B, You mentioned that trivalent chrome is slightly "Off" in color from hexivalent chrome. This is something that I have observed and is well known in the industry but no one has been able to explain why the color is "Off".

Can anyone out there explain this color difference?

Tim Hamlett
Decorative Electroplating - North Miami, FL, USA