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topic 49143

pH of gold plating bath

A discussion started in 2008 but continuing through 2018

June 26, 2008

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). 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

Diana Fe Espinosa
plating shop employee - Cebu City, Philippines

simultaneous June 29, 2008

? Hi Diana Fe Espinosa,
Can you tell us what is the volume of your bath.
There is something wrong somewhere and I feel it will relate to bath volume.
Then I will be able to help you.

t k mohan
T.K. Mohan
    plating process supplier 
Mumbai, India

June 30, 2008

A. Diana Fe,

As a formulation chemist, my experience has been:

At a constant solution Temperature, solution agitation, metal concentration, specific gravity, additives (brighteners with organic or chelated metals), current density, linear velocity of reel material;

The increase in pH means increase in deposition efficiency.
If no adjustment made to the other parameters, the gold deposit properties changes too, such as hardness, grain structure, solderability etc.

Good luck,

Hamilton Solidum
- Mays Landing, New Jersey

July 1, 2008

Q. Hi!

The volume of our baths are 50 L & 100 L.

Thanks ahead.

Diana Fe Espinosa [returning]
electroplating - Cebu City, Philippines

July 6, 2008

Rose Gold Plating Solution

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 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 Baker
process engineer - Malone, New York

July 9, 2008

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.

t k mohan
T.K. Mohan
    plating process supplier 
Mumbai, India

July 12, 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 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.


Diana Fe Espinosa [returning]
electroplating - Cebu City, Philippines

simultaneous July 18, 2008

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.

with increased efficiency, you will have less stray current therefore less decomposition product.

Check your insoluble anode, make sure it is not corroding.

The other alternative is to replace your plating bath more frequently.

Good Luck,

Hamilton M. Solidum
- Mays Landing NJ

July 18, 2008

A. Hi Diana,
Stop adding citric acid or tripotassium citrate, just use a dilute sulphuric acid to reduce the pH, if required you can raise the pH by sodium hydroxide.
good luck

Panjala Mukesh Panjala Mukesh
     fashion jewelry mfgr.
Hyderabad, India

July 18, 2008

A. Hi Diana,
I do not think your company will let down your suggestion if your Boss is practical!
your company is not going to loose any thing. Initially have a sump (extension tank as you said) of double the capacity i.e. 80 liters = 80 x 3 = 240 grams gold.This is going to be a capital investment for the company. You can show the saving by the smooth working of the tank.Have a pump running to displace the solution from the plating cell. I am quoting your line ... if we add tripotassium citrate to let SG down, the pH would also rise. Please advise. Pot.citrate will reduce the pH and increase the SG ... I know it may be an error!

t k mohan
T.K. Mohan
    plating process supplier 
Mumbai, India

"Gold Plating Technology"
by Reid & Goldie
from Abe Books

July 21, 2008

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.

Diana Fe Espinosa [returning]
electroplating - Cebu City, Philippines

July 23, 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,,

Hamilton M.Solidum
- Mays Landing, New Jersey

July 24, 2008

A. Hi Diana,
Citric acid is not conducting salt. Usually it is a proprietary formulation,supplied by manufacturers.

t k mohan
T.K. Mohan
    plating process supplier 
Mumbai, India

simultaneous July 26, 2008

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.

- Warsaw, Poland

July 26, 2008

Q. Good day!

Thank you very much. As of now, we're in the process of planning for the increase of our tank volume.

On the other hand, I'm posting a new inquiry with topic 49450 ... maybe you could be of help again, please.

Thanks ahead.


Diana Fe Espinosa [returning]
electroplating - Cebu City, Philippines

October 8, 2018

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.

maulik soni
mangalmurti gold forming - ahmedabad, gujarat, india

October 10, 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
Geoff Smith
Hampshire, England

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