46293

Silver anode now turns black during Silver Plating [Pakistan] 

August 24, 2007

We are doing Silver plating process on Nuts and bolts to make them antisieze. Our Tank is Old and solution is checked and additions are made periodically to keep the contents within limits of Standards that we follow. The Tank was working O.K. in the past But recently we are facing a problem that the ANODE which is Pure 99% Silver starts getting a black film during plating. The black layer on Anode slows the deposit rate and we have to take out the Anode from the bath and clean it using an abrasive pad, rinse and again put it back. We have to do this 3 to 4 times in a 15 minutes plating operation. We have checked the bath for KCN and AgCN and their contents are within limit.
Please suggest any troubleshooting/remedial action?.

Muhammad Najeeb
Plasma Shop Employee - Karachi, Pakistan

^-- I want to contact this person and my company is a supporting advertiser of finishing.com

Hi Mohammed,
silver anodes can be available up to 99.97% of purity. Get that.Change the supplier if he cannot.50% of ur problem will be solved.
Now take care in the following areas:
1.Low free cyanide
2.Low pH
3.More current.
Mohemmad why don't u mention the bath composition instead of mentioning "within limit"-what is the limit!!!
There is a ratio of metal and cyanide. But first pl. let us know the "limit" u maintain!Then may be we will help u.
Try to post maximum details rather than leaving things for guessing.
Regards,

T.K. Mohan     plating process supplier  Mumbai, India

Dear Mohan
Thank you for your suggestions. The Bath Make Composition is Four Chemicals are added in De-mineralized water. These are Potassium Silver Cyanide = 13 Oz.wt./gal, Potassium Cyanide = 10 Oz.wt./gal, Potassium Carbonate = 4 Oz.wt./gal, Potassium Hydroxide = 1 Oz. wt./gal.

Gallon is US gallon = 3.785 Liters.

PH value is 12.5 ,

The Solution Control Limits are Silver Metal = 6.0 - 7.5 Oz/gal (Present value 6.1), Potassium Cyanide = 6.0 - 9.0 Oz/gal (Present value 6.5), Potassium Carbonate = 4.0 - 16.0 (not checked recently), Potassium Hydroxide = 0.5 - 2.0 (not checked recently).

We will look for a 99.97 Silver Anode in our local market. Meanwhile, based on the bath details, if you have any other suggestion please let us know.

Regards
Najeeb

Muhammad Najeeb
Plating Shop - Karachi, Pakistan

Najeeb,
Can u convert these conc. into grm/ltr!
I am leaving for a holiday. will be back on 15th
regards,

T.K. Mohan     plating process supplier Mumbai, India

Muhammad,
you would be care full in following areas if your chemical parameters are in range..
1.filtration of solution
2.quality of cyanide
3.current density
4.quality of water
5.pH of solution

regards,

Uroj Shahnawaz
- Karachi, Pakistan

If these anodes were operating OK in this solution until now, then the problem is most likely in the solution. As you indicate that the current is also dropping it sounds like the anodes are polarizing so as your Free cyanide is at the lower end of your range I would try adding a couple of ozs/gal of Potassium Cyanide and see what happens.

Geoff Whitelaw
- Port Melbourne, Vic., Australia

Hi,

Your Anodes are impure, also not annealed and pickled after rolling. It is probably grease that comes out every 15 mins or so since it can be cleaned by an abrasive. Pls also check the operateing voltage at the bus bars.

Deepak Whorra      silver craftwork New Delhi, India