Cyanide-free silver plating solutions

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A. There is more than one available. Technic's Cyless Silver was probably the first. I think that it still requires a cyanide silver strike for some applications. The mfgr. can certainly tell you.

A. One of the producers is EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser] (East Berlin, Wisconsin) too (E 50/50 bath or something similar). Good luck!

And two recipes:
recipe 1: 40 gm AgCl, 200 gm potassium ferrocyanide ⇦this on eBay or Amazon [affil links] , 20 gm K2CO3, stainless steel anodes, 1-5A/dm2, 80 °C
recipe 2: 15-90 silver pyrophosphate K4P2O7 100-350 gm ammonium carbonate 20-145 gm 0,5-12 A/dm2, 18 °C (recipes are from USSR literature)

A. A silver fluoborate bath would be interesting. I don't know if one is possible, but I know that the chemical, "silver fluoborate" exists. At least, here's a data sheet on it. http://www.conncoll.edu/offices/envhealth/MSDS/chemistry/S/Silver-tetrafluoroborate.htm

You could probably make it by combining stoichiometric amounts of Silver Carbonate and Fluoboric Acid. You can make, as a precipitate, the Silver Carbonate with Silver Nitrate soln. and sodium carbonate ⇦this on eBay or Amazon] and agitation. You could even make the Nitric Acid-free Silver Nitrate that's needed by dissolving 99.99% silver in good Nitric Acid. The secret to acid-free is to add only enough acid to dissolve 90% of the silver metal present (hood). One gallon of Nitric Acid will dissolve about 100 troy ounces of Silver. Boil at the end and filter. The solution is reasonable pure Silver Nitrate. The purifying of the silver is another story.

I have used Ni, Sn, and Cu Fluoborate baths, all with great success. They are acid and bond well to most substrates, without a strike, especially if you go in live. Their deposit characteristics are excellent, also. They use soluble anodes and operate near 100% efficiency. Copper is plated from a soln. of Copper Fluoborate only. Nickel has about 4 oz/gal Boric Acid added. Tin has 3.3 oz/gal Boric Acid and 20 oz/gal free Fluoboric Acid, plus some additives. The metal contents of the 3 range from 8-10 oz/gal. The pH's range from .2 to 3.5, depending on the metal used. Temps are from room temp. to 170 F. Current densities are from 25-250 amp/sq.ft. Probably no agitation should be used.

If it were me, I'd play with this bath, in beakers [beakers on eBay or Amazon [affil links] . It might work great. It might not work at all. There may be some factor I'm not aware of.

In the late 60's, we had a customer that was using Silver DMSO baths to precision plate some critical electronic parts. I think they had a patent on the process. I think it worked great. It could be dangerous, though, since DMSO can take itself and other materials through the skin. I don't know the adhesion properties of Silver from DMSO baths.

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Ed. note Sept. 2020: Unfortunately the URL Chris cited is now broken.

A. You can plate directly on SS with ferrocyanide bath (nontoxic cyanide compound)!

A. Hello Todd,
I think you are headed in the right direction by ridding yourselves of Cn. Let's say you buy silver and additives from company A, have been for years. They should value your business if your usage is decent and you pay your bills on time. Do they have a cyanide free process that has been established and proven in the marketplace? If so, have the supplier give you a list of customers that use the process. Call them and ask about the quality and stability of the bath, as well as quirks. Inquire info such as base metal to be plated, type of products they plate, etc. If these inquiries are favorable, ask your current supplier if they would consider an ounce for ounce conversion to switch to the Cn free bath. Most times the supplier will provide you with the same amount of metal that is in the old bath, to make it more affordable to start the new process. You will probably have to buy the electrolyte, which is a lot less than having to buy all the silver, and wait for the refining settlement. I have seen cases where the supplier will also pick up the tab on the refining of the silver.
If the current supplier does not have a viable alternative, go to supplier B. Ask them for bath evaluation terms. They install the bath, get you kicked off, you evaluate it for 30 days. If the bath performs as expected, then you are billed for it. Because you are a new customer, supplier B may also give you an ounce for ounce conversion with a refining deal. As far as doing away of Cn Cu, there are alkaline copper baths out there that work very well. Good Luck to you.

A. This is an abstract from a dissertation on Cyanides, risks and alternatives

A number of non-cyanide processes have been proposed. (for silver)
Fischer and Weimer passim (1964)15 note processes based on:-
Silver Iodide; Schlotter, Korpium and Burmeister. (1933)
Silver sulphite; Yampoulski. (1961)
Silver nitrate/ thiourea ⇦this on eBay or Amazon [affil links] ; Gockel (1934)
Silver Thiosulphate, Kodak Pathe French patent 704,663
Silver Pyrophosphate, US patent 2,504,272
Other processes are reported based on fluoboric acid, lactic acid, sulphamic acid and ferrocyanide. Fisher and Weimer (1964)15 ibid..
Although each author makes claims for a stable process offering good deposits, it is significant that there is no evidence that any of these has been successfully introduced into industry.

You also need to consider things like effluent treatment (cyanide is simple) and importantly - does it work.

A. If we can believe to one ex USSR book(Galvanotehnika blagorodnih I redkih metalov/Electroplating of precious and rare metals/Leningrad 1970), mixed ferrocyanide /sulphite based bath can be used as effective substitute for cyanide based baths (according to that book even production trials confirmed it).
40 gm silver chloride
60 gm potassium ferrocyanide ⇦this on eBay or Amazon [affil links]
25 gm sodium carbonate ⇦this on eBay or Amazon]
100-150 gm sodium sulphite
1 lit water 0.2-0,5 a/dm2
Hope it helps and good luck!

A. Afternoon there is a company in Oxnard: Zinex

A. Todd,
If you want to rid your company of cyanide, it will take some work and dealing with the right people. I was privileged to install a cyanide free silver in 1993 for a company in New York. It was used for barrel plating. The customer used it for years. Was it as trouble free as the cyanide process? No. They had to watch the process a little closer. The customer did have less trouble and headaches with local environmental authorities however. The customer was also commended for the efforts they took to make the change.
Call a reputable precious metal supplier such as Technic, Inc. You will want a supplier behind you that has experience and know-how. Good luck in your efforts!

A. Hi Prasad,

There are at least three suppliers who offer cyanide-free silver that we know of: EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser], Technic, and Zinex. My own understanding is that the color of cyanide-free silver is considered a little "off" for decorative use, but fine for electronic use. Talk to somebody and get started; good luck.