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Problems with silver cyanide bath

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I am a lab supervisor at a barrel electroplating shop currently having problems with a cyanide silver plate bath. The bath is leaving a very dull, white finish on small parts of nearly every metal. The most difficult thing about this is that another silver bath with same potassium cyanide/potassium silver cyanide concentrations is working fine. Temperature in each bath is lower than normal (about 10 degrees F less) but this doesn't explain why only one will not plate. I suspect it may be high carbonate concentrations in the problem bath but I do not know how to test for this or what to do to correct it. Any help would be appreciated.

Dom Sideri
Laboratory supervisor - Lawrence, Massachusetts


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Do you have Hull cell test equipment and have you tried it?

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


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Dear Mr Sideri,

To analyse for Carbonate content: Pipette accurately a 10ml sample of plating solution into a 600ml squat form beaker. Add 300 mls of de-ionised water and heat on a hot-plate with a boiling rod in the beaker.*DO NOT BOIL** Add 10% Barium Chloride solution until no more precipitate forms in the beaker then filter through a Whatman number 40 filter paper. Wash the filter paper and beaker thoroughly with hot de-ionised water until the final washings no longer turn pH indicator paper blue. Transfer the filter paper back to the original beaker, pulp up and add 200ml of de-ionised water and a few drops of Methyl Orange indicator solution. Titrate with 1.0N Hydrochloric Acid while stirring the pulped filter paper with the boiling rod. End-point is; Orange to Red.

Calculation:

Titre mls x 5.3 = g/l Sodium Carbonate
Titre mls x 6.91 = g/l Potassium Carbonate

Nigel Gill, B.Sc. MIMF AIEMA MRSC
- Blantyre, Glasgow, Scotland

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