Chemical polishing / bright dipping of copper

A. Hi Ian Larcher,

Try soaking you parts on 5% sodium cyanide solution for 2 to 5 minutes depending on the intensity. If this doesn't work you can go for the below given bright solution for copper alloys:

hydrochloric acid-1.5 fl.oz. Room temperature.

You can gradually increase the quantity of HCl for better luster.But excess HCl may lead to spotty surfaces.

A. Hi. Venkat's approaches may do the necessary cleanup. But if you are looking for an actual bright finish, you'll need an oxidizing acid -- I think the generally safest and best is sulfuric acid plus hydrogen peroxide. I'd suggest that you buy it as a proprietary rather than trying to learn chemical formulation

EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser] offers this product.
Luck & Regards,


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

A. Copper will not get bright just from cleaning and a dip in mineral acid. It requires an oxidizing acid process such as nitric acid or sulfuric acid and hydrogen peroxide. Tell your plating process supplier that you need a "copper bright dip" process and they can help you with the details.

A. Gabriel,

I have experience of bright-dipping Beryllium Copper components that may help you. I used a solution of 9% sulfuric Acid (by volume) and 3% Hydrogen Peroxide. To achieve the best results I ran the solution at these concentrations, at 60 °C (140 °F) and with 50 grams per litre of dissolved copper in solution as copper sulphate ⇦ this on eBay or Amazon [affil links] which we subsequently removed via a chiller unit. Analysis for both constituents can be supplied to you later if you wish them.

A. I could be wrong, but I believe you'd be better off with a proprietary formulation because without the proprietary stabilizer the decomposition rate of peroxide will make the process less unaffordable.

Any Suggestions? I am trying to produce a brilliant finish on copper and brass parts. What bright dip methods do you recommend? Toby Edwards - Cedar Park, Texas Your question is difficult to answer without actually seeing your items. Why don't you ask a supply company like Henkel. They sell stabilized hydrogen peroxide and have all necessary know-how about the process. Bo Kønig - Odense, Denmark

A. Hi, Hatem. It's not good to switch away from an accepted approach which works for other people just because you are having difficulty getting it to work -- so I'm not eager to suggest that you give up on that chemistry.

Still, considering safety and environment, I think you might be happier with a sulfuric acid + hydrogen peroxide bright dip than the nitric and/or chromic acid. Good luck.

Regards,

A. Dear Hatem
if you want polish yellow copper allow
I think you can make the following sequence
mix. hydrochloric acid + nitric acid + chromic acid
rinsing water
hydrochloric aid
rinsing water
chromic acid
good rinsing water
with best regards,

A. Hatem,
I whole-heartedly agree with Ted on this -- that for environmental laws, etc., that Hydrogen Peroxide and sulfuric Acid is the best option. From my experience of etching beryllium-copper I suggest the following that worked very well for myself.

Maintain bath at 9% free sulfuric acid by concentration and 3% hydrogen peroxide by concentration at a temperature of 55 °C. Analysis is as follows ...

For hydrogen peroxide:
1 ml sample add about 80 mls of de-ionised water and 1 droplet of Ferroin indicator. Titrate to an orange end-point with 0.1N Ceric Sulphate solution then calculate % free peroxide as Titre mls of 0.1 N Ceric Sulphate x 0.29

For free sulfuric acid:
1 ml sample add about 70 mls of de-ionised water and 3-5 droplets of methyl orange ⇦ this on eBay or Amazon [affil links] indicator. Titrate to a pale-blue end-point with 1.0 N Sodium Hydroxide solution then calculate free %sulfuric Acid as Titre mls of 1.0 N Sodium Hydroxide x 1.4

After etching give a good rinse then a dilute alkaline rinse followed by copper anti-tarnish, rinse in de-ionised water and dry.

Hope this helps!

A. Hi Hatem.
We're having a bit of a language problem, but I think you telling us that you want a bright finish and your nitric acid dip followed by chromating isn't offering it because it doesn't stay bright for long.

If I am understanding, then after you dip in nitric acid, which I assume produces brightness, follow Nigel's sequence: quickly neutralize, rinse, dip in sodium benzotriazole, D.I. rinse, and dry. Luck & Regards,


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