Gold electrolyte for electroforming dental components

[Jwdds]

Hello, Im in the process of research and came across this wonderful forum. I have been reading a lot of posts from this forum as well as general research on the internet youtube etc.

Im trying to recreate a cyanide free electrolyte resulting in a 10 gram Au per 500ml solution which i believe is amonia or ammonium hydroxide with a final pH of 9. So that i can hasten the learning curve I decided to post this algorhythm here in hopes of getting input from you with a experience in refining. Any help would be greatly appreciated. Im not tied to this approach and if anyone can offer something completely different then Im open to that too. I acknowledge that this post is a bit antithical to refining gold since Im asking about deconstructing it instead

I found this patent which appears to be a good start for the formula. I am hoping some of you with more experience can point me down the right path. Here are some general questions I have about the process below?

1) Since Im starting with .9999 gold and I dont mind the extra time vs toxicology of the process I was thinking about using 45ml HCl with 3% peroxide instead of Nitric acid any thoughts on that?

2) After evaporaing in step one it appears they are rehydrating with salt water before adding the barium hydroxide. If im eliminating nitric acid is the NaCl still uselful or just enough distilled water to rehydrate?

3) b-d below; Do you interpret this as adding NaOH till i get the suspension boiling then add additional NaOH till a precipitate forms? is adjusting the pH to raise the pH with NaOH or the pH lowers as the NaOH boils off?

4) I assume I should test my solutions as I go to be sure Im not leaving gold behind in any of the steps, making adjustments as necessary?

After achieving the final solution after Na2S03 I was planning on adding first ammonium hydroxide till i get a pH of 9 then using distilled water to make up the balance of 500ml.

5) does the above alogrythm seem reasonable to you or do you have any suggestions where I can improve this process? I really appreciate your input.



from patent - US6126807A - Process for making sodium gold sulfite solution - Google Patents

1. A process for producing a sodium gold sulfite solution, comprising:
(a) dissolving Ba(OH)2 in an aqueous solution of Na(AuCl4) to produce a mixture;
(b) mixing NaOH with said mixture to produce a suspension;
(c) boiling the resulting suspension;
(d) adjusting the pH of the suspension from step (c) to produce a precipitate and a filtrate;
(e) dissolving Na2 SO3 in a slurry of the precipitate from step (d) to produce a suspension;
(f) heating the suspension from step (e);
(g) filtering the suspension from step (f) to produce a filter cake and a filtrate; and
(h) recovering filtrate as sodium gold sulfite in solution.

 

[Jwdds]

Question 2) solved yes I’ll need Nacl. Sodium for Na(AuCl4) has to come from that addition.

 

[Lou]

Why can't you just buy gold sulfite from Technic and call it a day?

 

[Jwdds]

Why can't you just buy gold sulfite from Technic and call it a day?

Hi Lou I don’t believe they sell gold sulfite, but they do sell a low ph formula for electroplating. Unfortunately it’s not applicable for my processes where I’m growing layers 200-300 microns in a basic solution for finer grain structure . Also The coping that is electroforming is removable from the surface it’s forming on. The necessity for home brew is that resellers are charging 2-3x the cost of gold for their solutions so it’s becoming cost prohibitive to offer theses services as parts move through the food chain. So producing a home brew, if possible, resets the cost of production so these processes and services can be preserved.

 

[Lou]

https://lp.technic.com/semiconducto...IJAE-SqXZFy1hqX5P8u7clIVXYVAVrwBoCEgAQAvD_BwE
It's ammonium gold sulfite if I recall correctly and that is what they are selling. Sodium gold sulfite is what's used for the alkaline baths, usually with the addition of some organic amines and is best used about 7.5-8.5. Either way, it's not three times spot price by any stretch. Probably metal cost + <$10/g fabrication. Hell if you needed a lot, I'd make it for you.
Look at the electron micrographs and tell me if that's not fine enough. Looks like awesome plating to me.

Of course these baths are pH sensitive. Adding sulfuric acid, out comes your gold along with SO2.

 

[Jwdds]

I think for plating this would work well but the solution is optimized for plating up to 100 microns. Also it’s not clear what the concentration of gold is in the solution. See below.

But Lou if you’re interested in creating a solution that works I’m happy to buy it from you.

The solution used now is a version of ammonium gold sulfite, at ph 9, 10 gram per 500ml

I’ve read another patent which is easy to find that discusses additives and stabilizers. But my initial goal is to create the solution then try it out with voltage amperage recommendations I’ve already established then test thickness over time of reaction. There’s a lot of variables but I think it will be a steep learning curve.


From their website

t compatible with almost all photoresists. Elevate®Gold 7990 NBV produces a bright deposit without the use of harmful grain refiners like thallium and arsenic. Provides excellent coplanarity and step coverage. Can be used for plating several different applications (thicknesses ranging from 0.5 - 100 microns) without major modifications to the solution and can be used on a variety of tool sets.

 

[Lou]

Optimized to 100 um. Why don't you just add more ammonia to it and see if it does the exact same thing?
I'd just reach out to them. I still maintain it's not advantageous to setup to do it home-brew style. It's an expensive thing to have to get involved with at home.

 

[Jwdds]

I requested more info, if it’s just gold sulfite that should work. Yes I can add ammonium hydroxide to that to get to ph 9 with a concentration of 10 grams per 500 ml. Thanks for the lead