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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
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