# Rh plating solution



## arthur kierski (Aug 29, 2018)

i forgot the h2so4 quantity in a rh plating bath----i remenber,that it is 2grams of RH in in a solution of 100cc----i think it is 20 cc of h2so4-------Can someone elucidate my doubt?

Thanks in advance
Arthur Kierski


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## goldsilverpro (Aug 30, 2018)

arthur kierski said:


> i forgot the h2so4 quantity in a rh plating bath----i remenber,that it is 2grams of RH in in a solution of 100cc----i think it is 20 cc of h2so4-------Can someone elucidate my doubt?
> 
> Thanks in advance
> Arthur Kierski



Hey, Arthur,

Good to have you back. I, for one, missed you.

It's been about 40 years since I've done any rhodium plating, but, I think those numbers you gave are for 1 liter of solution - 2g/l Rh and 20 ml/l conc. H2SO4. Here's a link that has a little info on it. This is the #1 forum on the internet for plating and other types of metal finishing - painting, powder coatings, conversion coatings, metal coloring, etc. And, lately, Ted added a PM refining category. You don't have to register on this forum and anyone can post.

https://www.finishing.com/304/19.shtml

On there, there's a formula by Goran Budija (see below). He posts a lot on there and has a lot of knowledge. He's very abrupt and never gives any details, but I find most everything he writes is technically correct. I don't really care for the aqua regia part, though. We used to sell a concentrate of 2 g of rhodium sulfate in 100ml sealed bottles. The customer would then dilute it to about 950ml with pure water, add the 20ml of reagent grade 98% H2SO4, and then bring it up to 1000ml with pure water.

At Sel-Rex, about 50 years ago, we sold a lo-stress Rh solution called Rhodex. You could plate a lot thicker than with the 2g/l bath. It was more of an engineering bath. I'm thinking it plated less bright than the standard 2 g/l decorative bath. I think it contained 5g/l Rh, as a sulfate, 50ml/l H2SO4, and some quantity of sulfamic acid that I've forgotten. I think there's a Sel-Rex patent on it. I know there are a lot of "I thinks" in this post, but it has been 50 years.

"Simple rhodium plating bath:
2,5-5 gm rhodium(dissolve it in Aqua regia,then evaporate and add to bath)
20-60 ml sulphuric acid(or phosphoric)
1 lit water ,up to 1 A/dm2, 20 °C temp. platinized titanium anode"

Goran Budija
- Zagreb, Croatia


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## arthur kierski (Aug 30, 2018)

Thanks a lot for your reply Goldsilver pro---whem many years ago i decided to make rh plating bath----i did the folowing way : buy Rh sponge from Kitco or Jm----mix the sponge with 3or 4 times of nahso4 and makes a fussion in a closed kiln for 2,3,hours at 600 or more degress centigrates---let it cool and put in a becker with distilled water and boil it------rhsulphate goes to solution and not dissolved rh---- is filtered and weighted---now one knows how much rh was dissolved----supposed 30grams of rh was dissolved---that is15 rh plating bath,adjust to 1,5litres ,add30 cc of h2so4 before adjusting to 1,5litres-----then put the rh bath in 15 100ml bottles
when is used rh wire, and spent rh baths--the procees to make rh plating solution,requires a thorough purification to eliminates impurities------is tottally diferent

thanks for the moment---i remember now,that i used 20cc of h2so4 per litre -----


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