Detailed rhodium plating process

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 sulfuric 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

A. Hi Khong,

If you are using 1 or 2 liters bath, use in glass beaker [beakers on eBay or Amazon [affil links] 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 sulfuric 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

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

Regards,

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.

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.

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

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 andacetone ⇦ this on eBay or Amazon [affil links] Warning! highly Flammable! solution. Dry that piece due to volatilization of acetone ⇦ this on eBay or Amazon [affil links] Warning! highly Flammable! . 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.

A. Hello Neda,
When I worked for a world leading supplier of precious metals for electroplating, all of my customers used the Rh sulphate based baths. Our competitors at that time also supplied the same sulphate based baths. These particular customers were in the diamond district in New York City. The sulphate 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 sulphate type bath.

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 sulfuric 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,

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 sulphate 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.

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,

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.

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.

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.

A. Hi Arthur. I haven't filtered rhodium plating solution but I don't think a vacuum system will hurt it. There are different grades of carbon, some is even attached to resin particles which look like ion-exchange resin to keep the process less dusty and messy, so it might be hard for others to suggest the right filter mesh for you. Why not put a bit of your carbon into some tap water and just try a few filter disks to see how big a mesh will still catch it all? Good luck.

Regards,