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topic 17961

Chromium solution electrodeposits


I'm trying to electrodeposit Chromium from a solution of dichromate + sulphuric acid (used cleaning solution). I had no success in using graphite anode and cathode, lead anode, low alloy steel, copper, mercury layered copper. Sulphate and pH were adjusted to recommended values (1% and 1-2, respectively). I read in a book that "chromium solution" does not work in electrodepositing process. What's wrong ?

Helio Akira Furusawa
- São Paulo, SP, Brazil

First of two simultaneous responses -- 2002

Chromium deposition from hexavalent chromium is not as easy as you may have thought. The solution needs a ratio of 100:1 CrO3: H2SO4 and needs to be at a relatively high temperature (40-60C). Typically you need 250g/l CrO3 in the bath.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

Second of two simultaneous responses -- 2002

Chromium is difficult to plate: the catalyst ratio must be exactly right [one pound of sulfuric acid for each one hundred pounds of chromic acid], and the current must be high enough [you won't just plate slow at 20-40 ASF, you will not plate at all]. Are you trying to plate at a minimum of one amp per square inch? I'm not a chemist so I may be just muddying the waters rather than clarifying them by mentioning that chrome plating solution contains chromic acid [H2CrO4] rather than dichromate [H2Cr2O7]. The pH of the solution you are trying to plate from sounds high to me, and may be representative of the dichromate form.

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

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