Home /
Search 🔍
the Site

Chime right in! (no registration req'd)


"Tri and Hexavalent Chrome Plate"


Please forgive my ignorance but I am new to electroplating. I have been reading in these letters about tri and hexavalent chrome plate. We are talking about the valency of the chrome species in the bath are we not? The last I knew chrome plated onto a substrate as metallic chrome with a valence state of zero.

Pat Reid
Consultant - Costa Mesa, California, USA


Hello Pat. You are correct, as far as you take it, but the situation you are describing does not cover all of the possible applications of trivalent and hexavalent chromium in the metal finishing field.

You are right that electroplated chromium, whether used as a "hard chromium" wear surface or as a "decorative" nickel plus chrome plating, is deposited as a metal at a valence state of zero such that it is somewhat irrelevant from an environmental standpoint whether that item was chrome plated in a trivalent plating bath or a hexavalent plating bath.

But there is another application for chrome in the metal finishing industry that is NOT chrome plating but is even more common that chrome plating, and where the valence of the solution in the process does matter. After parts are zinc plated, the zinc is virtually always subsequently 'chromated' to prevent white rust from occurring. This involves a dip in a bath of trivalent or hexavalent chromium as a "chromate conversion process"; in this case the chrome creates a corrosion fighting gel which is largely comprised of what was in the bath, and which ships with the part and remains on the part in service. This gel will have a lot of hexavalent chromium in it if the bath was hexavalent chromium. Some other plated surfaces besides zinc are often also chromate conversion coated, and chromate conversion coating is a very common corrosion protection process for aluminum as well.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

finishing.com is made possible by ...
this text gets replaced with bannerText
spacer gets replaced with bannerImages

Q, A, or Comment on THIS thread SEARCH for Threads about ... My Topic Not Found: Start NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

Chemicals &
Consult'g, Train'g
& Software

About/Contact    -    Privacy Policy    -    ©1995-2021 finishing.com, Pine Beach, New Jersey, USA