plating, anodizing, & finishing Q&As since 1989
Trivalent chromate compounds and international standards
We are a supplier of parts to the telecommunications industry and use sub-suppliers for all of our surface treatment needs, meaning zinc plating of mild steel and passivation treatment of aluminium. In advance of the change in EU legislation which will result in the banning of hexavalent chromate compounds, will existing technical codes & standards (ASTM, ISO etc.) also cover for the replacement trivalent chromate compounds, or will different standards apply?John Gordon Stewart
enclosure systems - Kirkcaldy, Fife, Scotland
The issue with chromium compounds is the high level of health risk associated with hexavalent chromium compounds. That is, compounds where the chromium has an oxidation state (or valence) of six. Trivalent chromium, by definition, has an oxidation state ( or valence) of three. Furthermore, to be technical, the chromate ion is CrO4(2-), where the chromium has a valency of six, so a trivalent chromate ion is not possible. Trivalent chromium systems are in current use and are being developed to replace their more harmful hexavalent brothers. The HSE in the UK and their counterparts in many other countries are promoting the use of trivalent chromium plating baths as a safe replacement for the more common hexavalent systems.
R&D practical scientist
Chesham, Bucks, UK
Mr John Gordon Stewart
It is correct to say Trivalent Chromate coatings are the immediate replacement of Hexavalent coatings.
However there is worldwide acceptance of two negative characteristics.
1) The extremely thin layer of Trivalent coatings , compared to the Hexavalent coats.
2) The inability of Trivalent coats to " Self Heal " when scratched, unlike the Hexavalent coats.
If the European Union End of Life Vehicle directive is an indicator of things to come, it will be very little to NO Chromates in use in future or by 2007 -8
Different Industry groups maintain their own approach to standardising the removal of Hex chrome to follow the ELV directive by the European Union which is a step in the chosen direction.
Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016
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