more info
Letter 16675

Hexavalent Chrome or Trivalent Chrome
++

Please can you tell me the main differences between hexavalent chrome plating and trivalent chrome plating.

Scott Campbell
Havelock Europa - Dalgety Bay, Fife, Scotland



--------------------------------------------------------------------------------
++
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.