Brass Plating Q&A's, Problems & Issues

A. Hi SAMUEL. Nickel passivates quite quickly. Get some test parts from the nickel tank to the brass tank as quickly as you can consistent with proper rinsing and see if the adhesion problem goes away on that batch.

Luck & Regards,

A. Is there a possibility that you are dragging in acid (which kills the cyanide) from your pretreatment?

Thanks Joel for taking interest in my query. But we have several Pure water rinses after the acid dip prior to Brass Plating.

A. Ferdinand,

I have been servicing and analyzing brass plating solutions for over 30 years. There are many possible reasons for high use of cyanide salts. Firstly, is the cyanide being broken down into sodium carbonate (analytical procedure available in many reference books)? If so, check the solution temperature and agitation. Either can accelerate the breakdown of the free sodium cyanide to form sodium carbonate and hydrogen gas. Another source of this problem is operation at high current densities where large amounts of hydrogen are evolved at the anode.

Gene,

I think you have some points. First, we circulate the 9.5 cu. meter brass solution constantly even without operation. We also maintain the solution temperature at 77 °C. We also use high current at 7.7 A/dm2 because of the continuous plating nature of Copper Foil. Thanks a lot, and we will consider your inputs in our discussions.

A. The temperature seems a bit high on the tank this would cause the cyanide to break down quicker than may be expected.

Is it possible to turn off the heating when not in use and then turn on in time for the tank to be ready for production?

A. Hi Sara,

Langford and Parker, Analysis of Electroplating and Related Solutions [affil link on Amazon, ... on AbeBooks], says 10 ml sample, 150 ml water and 2 ml of 10% KI. Titrate slowly to prevent premature end point. I believe that I used to titrate without the KI until the first turbidity, only then adding the KI. I don't remember if it was for cyanide analysis, but maybe it will improve reproducibility.

I don't remember having trouble with the analysis. What problems are you having?

Regards,

Hi Tom,

Thanks for your reply.

My problem with the cyanide is not with the end point (which is clear), the point is that when you add a known amount of cyanide to the tested solution and you titrate it again, you find out that the result is not accurate.

A. Sara,

I think cyanide analysis is always free cyanide, so if you add cyanide and make a analysis I expect that the results are lower than the value you added. This is because of the cyanide forming complexes. If you use always the exact same analysis method you should get values that are usable in the control of your baths.

Regards,

A. REF a book-not tried:
CuSO₄-40-55 G/L
ZnSO₄-35-55 G/L
ROCHELLE SALT 380-420 G/G
NaOH 80-100 G/L
T=45-50 °C,1-1.5 A/sqdm, good air agitation

OR
Na₆Cu(P₂0₇)-4G/L
Na₆Zn(P₂0₇)-12G/L
NaP₂O₇-11G/L
Na₂HPO₄-18G/L
T=40 °C/1.25-2A/sqdm

Good luck

A. Yes, but then you cannot freeze out the carbonates.

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Ed. note: For a detailed discussion of freezing, and carbonate removal from cyanide plating solutions, etc., please see letter 0473.

A. Dear Amish Gala,
Hi.
Firstly, for bright Brass, we usually use bright nickel as base coat and then a thin film of brass. This thin film can be achieved by low cyanide baths or Medium cyanide in short time, but the low cyanide is much better. As the thin film is too sensitive and active in electroplating polluted air and oxidizes soon, so you can seal it by using 20-30 gr/lit sodium or potassium dichromate in DIW with pH between 6 to 7. (I mean the pH of water). Deep in this solution for 5-10 seconds, rinse twice and let it dry. You won't see the blue parts at edges.
Good Luck

A. Hi John. You've posted here over the years, and you are apparently an experienced brass plater who has been plating satisfactorily, rather than someone who has never done it before. As Durney notes, that means something has changed that you haven't accounted for yet. One possibility that occurs to me (why it's a problem is explained by Fred Mueller in thread 4620), is that maybe you started plating larger parts such that your anode to cathode ratio decreased and the anodes are therefore oxidizing?

Regards,

A. Try what Ted said first, of no help, then go into the Hull Cell and start adding cyanide.

A. Hi John,

What worked for me years ago, was mixing up the brass anodes with equal area of graphite anodes.

By physical observation I could see the evolution of O2 reduce and the anodes worked fine and didn't go passive. The metal content stayed level where I wanted.

All the best :)

 I went into the hull cell and added more cyanide. Thanks to your help! This eliminated the polarized anode problem.
The bath has been performing well.. Thanks!

John

 "I understand that the redness is caused by a lack of ammonia and I have to control the pH between 10.10 to 10.30. Any suggestion?"

You already have the answer. Add a little ammonia and control the pH.

A. Hi Syed. It seems to me that the most important clue in your description is that you say you are adding zinc salt and having no increase in zinc content. Perhaps I'm misunderstanding you because that is simply not possible :-)

Either your analysis procedure does not work, or the salt which you are adding is not zinc salt. Has your supplier analyzed the bath? Have you plated any Hull Cell panels? Is it remotely possible that you are adding a nickel salt or some other salt when you think you are adding zinc?

Luck & Regards,