NaCN Abnormality in Brass Plating Solution 

Letter 10051

I have a problem with our Brass Plating Solution. There is abnormal consumption of NaCN even without production (i.e. 12 g/l to 10.5 g/l). At first, I thought we had wrong chemical analysis but I was proven wrong since analyses of the other components are correct. Some say that the NaCN reacts with the Brass Anode; some say formation of oxides on the Anode. I would like to solicit technical help from everyone. By the way, the Brass solution is used to plate copper foils running at 26.5 m/min.

Ferdinand U. Collado
- Sta. Rosa, Laguna, Philippines

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

Joel Tomasetti
- Petersburg, Virginia

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

Ferdinand U. Collado
- Sta. Rosa , Laguna, Philippines

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 Packman
process supplier - Great Neck, New York

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 degrees 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.

Ferdinand U. Collado
- Sta. Rosa , Laguna, Philippines

Gene,

I understand that you have a lot of experience with brass. I have difficulties analysing the free cyanide in brass. Do you have an analysis process that is really working? If positive I will appreciate of you could publish it. (the method mentioned in the Metal Finishing guide works only for new solution).

Sara Michaeli     chemical process supplier Israel

Hi Sara,

Langford and Parker, Analysis of Electroplating and Related Solutions , say 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,

Tom Pullizzi Platronica.com Falls Township, PA

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?

Martin Trigg
surface treatment shop - Stroud, Glos, England

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.

Sara Michaeli     chemical process supplier Israel

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 bathes.

Regards,

Marcus Hahn
- Sachseln, Switzerland