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Gold SG problem

(-----) 2006


We are an electroplating company here in Cebu Philippines. We have rack plating, barrel plating and reel-to-reel plating. We have gold plating on our reel-to-reel process; at present,& we encountered abnormal specific gravity on our gold bath. We set 7-18 baumé as our s.g. standard range but we are maintaining at an optimum of 13.5 baumé. However, we observed that our gold bath s.g. & is keep on increasing even if there's no addition of density adjusting salt. In fact, the s.g. as of this time is already 21.5 baumé. We have read on electroplating books that if gold bath s.g. will show sign of uncontrollable increase, the solution has already aged and needs to be renewed. Because of the anticipated big cost involved, we would like to save the bath and further use it. & We tried & the lab scale & dilution by 50%, & however, the s.g. drop was only 2 baumé.

Please help us to further use our gold bath with its condition of high s.g. This gold bath is already 3 years old. For now, we did not encounter yet any quality problem on our gold, but we are afraid that major problems will arise soon. And also, please give us advise on other gold bath maintenance, for now, our only maintenance are the following:

1. trice a week pH monitoring (if high pH, pH adjusting salt is added; if low, 20% KOH is added)

2. trice a week s.g. monitoring (if low, density adjusting salt is added; if high, no action made)

3. monthly metallic impurity checking (so far, no abnormality has been encountered)

4. organic impurity checking; no frequency has been established, only when the plating engineer will request (so far, no abnormality has been encountered)

5. daily addition of gold

We hope to hear from you soon.

Thank you.

Chandrina S. Pelicano
- Philippines


Hello Chandrina,
This is a common problem in reel to reel gold plating. Unlike rack and barrel plating there is normally very little dragout of the gold solution. This is a good thing as far as economics go, but because of low dragout conditions the SG will rise automatically. Gold salts (PGC) are usually 67.0- 67.5% gold metal content by weight. You plate out the gold metal, but are left with the added salts from the complex. Over time the salts build up, causing the SG to rise. The only thing I could suggest is to contact your gold supplier to see if they can give you straight 67.5% PGC. Some proprietary gold salts contain conducting salts that you obviously don't need. If the gold bath has lasted three years you are doing really well considering it is reel to reel plating! Good Luck!

Mark Baker
Process Engineer - Syracuse, New York

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