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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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pH of gold plating bath
Q. Hi!
I'm working in an electroplating company as Laboratory personnel here in the Philippines. We have Gold plating on our reel-to-reel process. Right now, we have a problem on our Au plating deposition. We are maintaining its concentration to 3g/L but still we encountered NO GOOD thickness in the early hour of operation. Upon investigation and monitoring of its parameters, we found out that its SG is increasing even if there's no addition of density adjusting salt. In fact, its SG reaches to 23.5 °Baumé wherein our requirement is 13.5 °Baumé only. As we consulted this problem to one of our consultant, she said that aside from low drag-out, one factor why it keeps on going up is caused by our addition of pH adjusting salt (citric acid
⇦this on
eBay
or
Amazon [affil links] ). We have a daily pH checking of our Au bath and its standard requirement is 4.0 - 4.4 with an optimum of 4.2. Her suggestion is to stop adding citric acid not until the SG goes down. My concern is how about our pH control?Is it possible to operate the Gold bath @ pH of 5.0 or more?Does high pH have great effect on our plating quality?If so, then what possible plating defects it would be?
Hoping to hear from you soon.
Thank you
plating shop employee - Cebu City, Philippines
June 26, 2008
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June 29, 2008 ? Hi Diana Fe Espinosa,  T.K. Mohan plating process supplier - Mumbai, India A. Diana Fe, - Mays Landing, New Jersey June 30, 2008 |
Q. Hi!
The volume of our baths are 50 L & 100 L.
Thanks ahead.
electroplating - Cebu City, Philippines
July 1, 2008
A. I agree with Hamilton. At a higher ph you will plate a higher percentage of gold from the Ni-Au or Co-Au alloy (whichever applies). So yes, it will effect your hardness and cost you more money because more gold and less alloy (preferentially) is being plated on the part. Color will change as well. The 50 liter bath seems a little small for what you are doing. With acid hard golds you can use 5% sulfuric acid if you are very careful. Add it very slowly while mixing. You can get a good idea on how much of the diluted acid to add by titrating in a 1L beaker [beakers on eBay or Amazon [affil links] with use of a magnetic stirrer. Then do the math for bath addition. This way you won't overshoot your 4.0 low limit, and your baumé won't rise as fast. Good Luck.
Mark Bakerprocess engineer - Malone, New York
A. Hi Diana,
I know the volume is the problem. Yo can see that Mark also pointed this. In a reel-to-reel the preferred volume is more, because,the high current density used to plate does very complicated reactions in the plating bath. Please remember it would be ideal to pass 0.2 amps/liter of plating bath. I am sure you are passing more current. Try to bring up volume of the bath relating to amp. passed, i.e., 0.2 amp/liter.
Your problem will be solved for sure.
Regards
T.K. Mohan
plating process supplier - Mumbai, India
July 9, 2008
Q. Sir,
Is there any other countermeasures aside from increasing our bath since our machine is design only for that volumes and if there's gonna be an extension tank then I don't think the company would allow us to do so because that means an increase in Au consumption i.e gold make-up...how about pH and SG relationship of replenishment strategy. Because right now, as we added citric acid for pH adjustment, the SG would also rise...if we add tripotassium citrate to let SG down, the pH would also rise. Please advise.
Thanks.
electroplating - Cebu City, Philippines
July 12, 2008
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A. Increase gold concentration to at least 6 gm per liter. these will increase your plating efficiency. You increase your line speed, will increase drag-out. - Mays Landing NJ July 18, 2008 A. Hi Diana,  Panjala Mukesh fashion jewelry mfgr. Hyderabad, India July 18, 2008 A. Hi Diana, T.K. Mohan plating process supplier - Mumbai, India July 18, 2008 |
by Reid & Goldie
(hard to find & expensive; if you
see a copy cheap, act fast)
on eBay or
AbeBooks
or Amazon
(affil links)
Q. Good day!
Thank you very much for the responses. I'll open this up to my superior.
For the meantime, I'm confused if citric acid is also a conductive salt. Any idea?
Thanks ahead.
electroplating - Cebu City, Philippines
July 21, 2008
A. It is very common to use a mixture of Potassium or Sodium Citrate(mono, di, tri) with citric acid at a weight ratio of the desired operating pH as conducting salts.
During electrolysis, your citrates, gold salts breaks down leaving a lot of K+ or Na+ ions making your ph to go up. You add citric acid to make Potassium or Sodium citrate.
Good Luck,,
- Mays Landing, New Jersey
July 23, 2008
A. Hi Diana,
citric acid is not conducting salt. Usually it is a proprietary formulation,supplied by manufacturers.
Regards
T.K. Mohan
plating process supplier - Mumbai, India
July 24, 2008
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A. If you meet a problem of current efficiency in acid gold plating never forget the temperature and gold concentration. If you change pH only you change also alloy properties. In that case you should keep the temperature at 40 or more and gold at 4 g/L. Good luck. Janusz LABEDZ- Warsaw, Poland July 26, 2008 Q. Good day! electroplating - Cebu City, Philippines July 26, 2008 |
Q. Hello sir ...
I have gold plating bath. I want to know about pH level and density. I have managed 5 gm/liter gold deposit. I have gold forming plating bath, guaranteed jewellery plating, plating 200-300 ml gold in 1 jeweller item.
mangalmurti gold forming - ahmedabad, gujarat, India
October 8, 2018
A. Hi Maulik
There are many types of gold plating solution and each has its best range of pH and supporting salts.
If you are using a proprietary bath the supplier will have a data sheet with all the information to operate it and will usually offer technical support if it goes wrong.
If you are using your own formulation you are on your own and will learn how much research suppliers put into determining these variables.
Geoff Smith
Hampshire, England
October 10, 2018
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