Metal finishing Q&As since 1989

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citric acid deoxidizing of aluminum?

We produce aluminum hydroxide coagulents by an electrochemical process which oxidizes
aluminum plates in an aqueous environment. The plates develop a non-conductive oxide layer which must be removed. We employ ultrasonic agitation of the cleaning,deoxidizing and rinse baths. My question is do you know if citric acid [on eBay or Amazon] could be employed as a substitute for the hydrofluoric acid now in use. Residual acids have caused aluminum fluoride to form on the plates in the past as well as all the toxicity and handling problems that accompany hf use.

Gary Levesque
Waste Water Recycling Research - Hyannis, Mass. 02601
2005

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citric acid may work. I have not tried it. I have used sulfamic acid 30-40 g/L. Note: no matter what acid you use, and oxide film will form immediately after deoxidizing. It starts to form in the rinse, and exposure to air completes the film.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
2005

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I think that you can use citric acid (up to 100 gm /lit. water),or you can use 5 % ammonium citrate solution(mixture of 5o gm citric acid / 1 lit . water/+ some ammonia [on eBay or Amazon],pH must be 9!).

Good luck!

Goran Budija
- Cerovski vrh Croatia
2005