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Detailed rhodium plating process

 

++++++

Q. I have been trying to do rhodium plating with steps suggested by my supplier:
Preparation
-grinding
-ultrasonic cleaning
Plating
-degreasing at 50 °C
-acid wash with H2SO4
-rinse with distilled water
-plating with rhodium using 4 volts at room temperature

The result has been disappointing; gold I've plated doesn't have the brightness I expected.
Can anyone share their expertise on this matter?
Thank you in advance

Congo Khong
jeweller - Surabaya, Indonesia


++++++

A. Hi Khong,
Though you did not give much about what you do, I would give you some points you may consider.
1. You may go for Rh plating straight after Sulphuric Acid dip without water swill (2-5% H2SO4)
2. Though lately room temp. process is available, it is better to warm the bath.
3. No direct heating but use a water bath.
4. Try plating at 5-6 Volts
5. Live load! (Rectifier should be 'ON' before plating
6. Check your anode (if Pt mesh is used)
7. The surface should be bright.
8. Finally, if the problem still persists, try to give activated carbon treatment (1 g/l)
Regards

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



++++++

A. Hi Khong,

If you are using 1 or 2 liters bath, use in glass beaker and warm the solution ... carbon filtration is done if you have larger bath starting from 10 liters. for 1 or 2 liters you'll need filter paper.

Use Platinum plated anodes. After Sulphuric Acid dip, spray Di water the items, set up voltage 3.5 to 4 if it is ring for 120 second to 200 seconds I'm 100% sure it'll be bright white color.

I do have Rh bath of 5 liters mostly I don't get problem; if I do, I use in tank filtering (that's best for small bath), same as I wrote above I use that way in my bath. Use gold or nickel plated wires.

Good luck


Dipen Pattni
jeweler/goldsmith - Dar-Es-Salaam, Tanzania


May 19, 2011 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. WHAT TEMPERATURE SHOULD A RHODIUM BATH BE SET AT? ROOM TEMPERATURE OR 110 DEGREES?

BILLY CARTHEN
FORMER PLATER - OAKLAND, CALIFORNIA


A. Hi Billy. We appended your question to an existing thread where T.K. Mohan has already answered it. Good luck.

Regards,

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



July 22, 2011

Q. Hi guys and t.k.mohan, sir
My name is pavan Soni and I'm from Pune Maharashtra.
I have purchased the CCCV rectifier and rhodium pen plating solution as well as ultrasonic cleaner of 1.2 l for rhodium finishing but the results are still not up to the mark. I have read every thread over google as well as on finishing.com to overcome the problem but of no use. The procedure which I'm following is as follows:
1. Buffing the 22k gold jewelry to high polish for shine.
2. Then ultrasonic cleaning with solution.
3. Then wash with the dm water, then 5% sulfuric bath, then again with dm water.
4. Electrocleaning at 4 to 6 v for two minutes.
5. Repeat step 3.
6. Afterwards, drying the jewelry with hair dryer.
7. Then finally plating without touching my hand over the place where Rh plating is done. With pen plating at 6-8 volts and normal speed.

Could you guys please help me out? I have gone beyond my budget for this but to no avail.
It would be a pleasure if guys can send me a reply please.

Pavan Soni
Student - Pune, Maharashtra, India


July 25, 2011

A. Pen plating is extremely operator sensitive and jewelry would seem to be extremely difficult.
I would eliminate the drying step.

Finally, no one can really help you until they know what the time, temperature voltage and material/concentration is being used for each step.
Normally the company that you bought the equipment and chemicals from would have a technical services group to help you. If their stuff does not work there is a probability that you will go to another company that will help. Lost customer that will bad mouth their product. Bad business.

James Watts
- Navarre, Florida


July 28, 2011

Q. Hello sir,
I tried eliminating the drying step and detail about temperature voltage and concentration is given below:
I use the pen plating solution @ ROOM temperature and the voltage of the rectifier is 6-8 V for plating and the conc. for H2SO4 is 5% but I don't know the concentration of liquid Rhodium, but I use the liquid as it is sold to me.

Pavan Soni [returning]
- Shahada, Maharashtra, India


August 2, 2011

Q. Hi guys.
Do reply to my query fast ... I'm waiting for your help because I know this is the only place where I can get the desired help.
Hope you guys reply soon.
Regards
Pavan

pavan soni [returning]
- shahada,maharashtra india



September 20, 2012

Q. Sir/Madam:

Recently I have been having a problem with rhodium plating. I have a 5 lt bath and I do white rhodium plating on 18K diamond studded jewelry. Lately after plating the metal has the white color but the diamonds tend to turn black as if some coating is done on it after plating. I removed some diamonds from the jewelry and cleaned them and the diamonds returned to their original color. But when I do plating the diamonds again turn black. I am really confused as to what is happening. I have changed the bath the cleaner solution etc but to no avail. Only after putting the jewelry in a boiling hot sulfuric acid and repeating the rhodium did the diamonds did not turn black. Please advise as to what could be the problem. Thanks.

Gaurav Vij
- New Delhi, India


October 20, 2012

A. Dear sir, I have an answer to your question. First, in diamonds there is a groove in which you rhodium plated, so it shades up black because of channels of metals in between. You first dip rhodium plated studied piece in boric acid and acetone solution. Dry that piece due to volatilization of acetone. Then heat the piece in oxidising flame of lighter up to red hot condition, taking care that channels must not melt while heating. Then quickly dip this piece into slightly hot H2SO4 acid -- and see the effects.

bhupesh mulik
- mumbai,india



December 16, 2014

Q. Hi dear all,
hope you to be fine.
I want to electroplate white rhodium on gold jewelry.
I found that there are various rhodium baths such as RhCl3, Rh2(SO4)3, ... My question is which of these bathes is best to electroplate on gold -- chloride or sulfate salts of rhodium? Which electrolyte will produce a deposit with best quality in brightening, and adherence?
And what about Ruthenium:
RuCl3 or (NH3)4[{RuCl4(H2O)}2(µ-N)]?
Would you please help me? Do you have any suggestions?
It's so vital.
Thanks.

Neda Shirvani
- Isfahan, Iran


December 16, 2014

A. Hello Neda,
When I worked for a world leading supplier of precious metals for electroplating, all of my customers used the Rh Sulfate based baths. Our competitors at that time also supplied the same sulfate based baths. These particular customers were in the diamond district in New York City. The sulfate baths are very stable and as long as you keep them clean and make the necessary additions, you won't have problems. Ruthenium baths are not as user friendly, and are not very common in the industry. I did have a few customers that used ruthenium for electronic plating. If it were me starting out, I would use the Rh Sulfate type bath.

Mark Baker
Process Engineer - Phoenix, Arizona USA


December 17, 2014

A. Good day Neda.

I have worked in the jewellery industry in the past for Avon, and we used a phosphate/phosphoric component. It produces a whiter deposit.
See Patent US1981820 - Process of electrodepositing rhodium.
..." have a solution containing about 2 to 3 grams of rhodium per liter.Then sulphuric acid is added, so that ranging from about 1 to 10% by volume. Then 3cc. of 85% C. P. of phosphoric acid per gram of rhodium is added to the solution".....
Hope this helps.
Regards,

Eric Bogner - Lab Tech.
- Whitby, Ontario, Canada.


December 22, 2014

Q. Hi.
Dear Eric and dear Mark, Thanks a lot for your help. I got that patent :).
Another question: I have two excess rhodium bath replenisher (base rhodium sulphate)(50 g/L Rh).
I want to reform these replenisher solutions to rhodium bath (2 g/L) and then use to electroplate on gold.
Is it possible to make this change? By diluting with deionized water and adjusting pH using H3PO4?
Or it needs special process?
Thanks in advance.

Neda Shirvani [returning]
- Isfahan, Iran


December 23, 2014

A. Hello Neda,
Yes, dilution is possible. The problem I see in diluting the concentration to 2 gr/l is that you will be increasing the solution level in the tank too quickly while making additions to the bath. If memory serves me correct, the common replenishment concentration (as supplied) is 1 gr rhodium sulfate per 100 ml of replenisher. So if you dilute your concentration down to 5 gr per 500 ml you will be fine. I find it odd that you are getting a Rh concentration at 50 g/l. I would hate to spill a 50 gr bottle of Rh on the floor! If it is easier, you could also dilute your replenisher concentration to 10 g/l. Check the ph of your current replenisher, which should be less than 1.0. After your dilution, match that same ph with very small additions of H2S04 if needed. Be sure to use DI water when diluting. Your tech data sheet for the bath will give you the gr/amp min addition rate for proper bath operation. A minimum of one bath analysis per month is recommended. I also agree that a small amount of phosphoric acid should be added to the bath for a whiter deposit. Good Luck.

Mark Baker
Process Engineer - Phoenix, Arizona USA


December 25, 2014-- apologies, finishing.com misfiled this reply, and didn't post it until January 31

Q. Thanks dear Mark.
I'm so sorry. I made a mistake. This rhodium replenisher is 20 g/L. And in your opinion if I diluted this and adjusted the pH, would I get a bright and white deposit of rhodium? I mean maybe it's additive and brightening agent also being diluted? Doesn't it need any other additive?

My customer has 12 bottle of ruthenium replenishers 50 g/L that are excess. could I reform these to ruthenium electroplating bath 5 g/L, too? it's based on (NH34[{RuCl4(H2O)}2(µ-N)] and H2SO4.
Thanks in advance :)

Neda Shirvani [returning]
- Isfahan, Iran



How to replenish rhodium plating bath for long-term quality plating

January 31, 2016

Q. Dear All,
Hope you are fine.

We have a 30 liter rhodium bath. as the bath is new we have a good brightness and white color, after some replenishment, we don't have the same color. How much we must add rhodium per A-Min?

What kind of suggestions you have to keep the first quality?

Many Thanks,

Jalal Jafari
- Isfahan, Iran


January 2016

mfgthumb
Metal Finishing Guidebook

A. Hello Jalal. It is good to hear that you are tracking Amp-Minutes, and it will help you track the rhodium. Rhodium plates from valence state +3, its atomic weight is 102.91, and its S.G. is 12.4. At 100% efficiency, 1.28 grams is deposited per amp-hour and it takes 22.9 amp-hours per square foot to deposit 0.001" thickness.

In the Metal Finishing Guidebook =>
Al Weisberg estimates that -- between metal plated out and dragged out -- you will probably have to replenish 5 g of Rh per 18-20 amp-hours. I don't quite understand why that number is so low unless the efficiency of rhodium plating is only 20%, but hopefully another reader will sort it out for us.

If you are using proprietaries, you'll want to follow the technical data sheet, but if that is not applicable, try to find the Weisberg article in early editions of the Guidebook. It's in my 1998 through 2005 copies, but was gone by the 2012/2013 edition.

Regards,

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


February 8, 2016

A. Hello, just a quick add to Ted's comment. The current efficiency for Rh plating is directly proportionate to the Rh metal concentration of the bath, voltage used and temperature of the bath. It is highly unlikely that your bath is 100% current efficient if you are doing decorative plating. So as Ted mentioned you will want to check your tech data sheet or contact your supplier. You will also want to verify how your Rh replenisher is supplied. You may be adding concentrate instead of replenisher. This difference of add methods rates would depend on the Rh supplier.

Mark Baker
Process Engineering - Phoenix, Arizona USA


February 7, 2016

Q. Hello,
Thank you for your reply.

Here in country, after finishing our jewelry we put them inside boiling sulfuric acid to make the yellow part brighter and more yellow. In this process if we use ultra white rhodium such as K3 from IWG company, it is removed in the boiling sulfuric acid.
If we use normal rhodium, there is no problem. But I need an ultra white rhodium color.

How we can solve this problem? Do you have any ideas?
Thank you in advance.

Jalal Jafari [returning]
- Isfahan, Iran


February 10, 2016

A. Hello, why are you using hot H2S04 after Rh plate? Most platers use a drag out rinse, final hot DI rinse then a steam blast and dry. I have never heard of using a bombing step after Rh. If your Au is bright and shiny enough the Rh should look nice and bright as well.

Mark Baker
Process Engineering - Phoenix, Arizona USA


February 12, 2016

Q. Dear Mark,
Thank you for your reply.
We don't have Rh plating on some parts, so we put them inside the Hot H2SO4 to make a better yellow color for our 18ct golds. In this process sometimes Rh layer is damaged.

Thank you again.

Jalal Jafari [returning]
- Isfahan, Iran


simultaneous February 12, 2016

A. Good day Jalal.

I am not understanding making the yellow parts brighter and more yellow.
Is your jewellery two toned with gold/brass?
Mark has stated the efficiency is directly proportional to Rh metal concentration.Efficiency is also a function of the sulfuric/phosphoric acid as it does affect conductivity/throw.
What is the g/l concentration of the acid? In my experience,phosphoric based baths produce deposits that are much brighter/whiter than sulfuric acid based.
What is the condition of the anode material? As I am sure you are aware, platinized titanium is required to produce white/bright deposits. There is a flame test you can do to verify the presence of platinum. Use a propane torch and heat the anode until it starts to glow. After cooling, if the heated area has darkened, it is indicating the presence of titanium. You cannot plate rhodium with titanium anode material. Platinum will not discolour in this test.
Hope this helps your situation.

Regards,

Eric Bogner, Lab. Tech
Aerotek Mfg. Ltd. - Whitby, Ontario, Canada


February 12, 2016

A. Hello Jalal, your question stated the Rh comes off in the boiling acid, so I commented accordingly. Anyway the new Rh solution you are using may be a sulfate/phosphate base. This type of bath will give you whiter deposits. You want to make certain that the hot H2SO4 solution is well rinsed before going into the Rh. It sounds to me that there is a film left on your pieces. For additional info you can contact your supplier to see if any of their customers have had the same problem. Good Luck!

Mark Baler
Process Engineering - Phoenix, Arizona USA


February 13, 2016

Q. Hello Mark,
Thank you for your information.
There is a miss understanding.
We have bi color plating. that means on our 18ct gold we must plate some area white rhodium and some area must be keep yellow. we use covering varnish for this process.

After rhodium plating we will put plated objects inside hot sulfuric acid then with our new rhodium that create a brighter rhodium, we have problem and in boiling sulfuric acid it removes. we do this process after finishing plating to make yellow area more bright and more yellow.
Our hot acid dip is just 2 seconds.
Hope to hear from you soon.
Thanks,
Jalal

Jalal Jafari [returning]
- Isfahan, Iran


February 17, 2016

A. Hello again Jalal, I wasn't aware you are plating 2 tone pcs. Please be specific when posting a question. The only thing that comes to mind is that you have an adhesion problem. You could do a tape pull test on the plated Rh before the hot acid dip. I have never seen Rh plating subjected to a a boiling acid dip, but it shouldn't come off unless there was an adhesion problem or the Rh deposit is too thin. You will want to make sure the bath is analyzed and up to par.

Mark Baler
Process Engineering - Phoenix, Arizona USA

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