Electrochemistry gold on cathodes

[john1986]

Hello all

I am currently doing gold electroplating. I have gold build up on the cathodes so i have been chipping it off before it gets too much. Chemicals i use during plating process are Auruna 311 and Auruna cap 50. Is the gold that that i am chipping off high karat and how would i go about melting and purifying if needed. The gold seems very hard so dose this mean its low karat or is this just because of the process? The bits that im chipping off are are between 1 and 3 mm thick.

Cheers john

 

[goldsilverpro]

http://www.schloetter.co.uk/plating-processes/gold-process.htm

Some solutions contain base metals, primarily as hardeners, and some don't. These solutions are proprietary and they don't tell you the other ingredients. You'll never really know unless you refine the flake to pure gold. In my opinion, this is best done using aqua regia. The Hoke book and the many discussions of this method on the forum will tell you how to do this.

What is the weight of the flake you've accumulated? How much solution did you process to get that flake?

 

[john1986]

I use £1000-£2000 of gold solution auruna 311 a week half to 1ltr bottle (five day week) bottle contains 50g of au. Around 1mm a day gets deposited on the cathodes if i use the same jig all day. i have been chipping it off every couple of weeks for about 3 months . Most of the time i run 9 jigs through the bath each in for 7 minutes at 13amp so takes a while for gold to build up as im not using same jig constantly. Its weight is 22g i know its not a big amount but i was thinking over time say every 6 months or so i melt or do whatever to purify it.

john

 

[goldsilverpro]

I use £1000-£2000 of gold solution auruna 311 a week half to 1ltr bottle (five day week) bottle contains 50g of au. Around 1mm a day gets deposited on the cathodes if i use the same jig all day. i have been chipping it off every couple of weeks for about 3 months . Most of the time i run 9 jigs through the bath each in for 7 minutes at 13amp so takes a while for gold to build up as im not using same jig constantly. Its weight is 22g i know its not a big amount but i was thinking over time say every 6 months or so i melt or do whatever to purify it.

john

Is this what you're saying? The gold on your jig or rack or fixture or part holder, or whatever you decide to call the fixture that holds the parts that you are plating, builds up, and, every so often, you peel the gold off of the fixture.

Since I don't know the surface area of the parts and the exposed surface area of the jig, the information that you're plating at 13A for 7 minutes isn't that valuable.

According to the link I gave, at the ideal current density for the 311 bath, assumingly, the plating rate is 0.2 microns (.000008") of thickness per minute. Therefore, in plating a jig for one 8 hour day, the thickness should be .00384", or less than 0.1mm. Yet, you say the buildup on the jig is 1mm/day, about 10 times more than theoretical for an 8 hour day.

I can't understand why the jig hasn't been properly coated (except for only the contact points) with a non-conductive plastic coating, such as plastisol, to prevent the metal from plating on the entire jig. I would think that proper plating procedure would demand this. Can you provide a photo of a jig with the part attached?

Back to the original problem. You have collected 22 grams of questionable metal. If you want to know how much gold is there, dissolve everything in aqua regia and precipitate the gold with sodium metabisulfite. The complete method for doing this is found on this forum.

 

[Lino1406]

Seems you need (besides isolating jigs) current thieves
around the plated objects, to get leveled gold where you
want it, otherwise you are throwing gold

 

[goldsilverpro]

Seems you need (besides isolating jigs) current thieves
around the plated objects, to get leveled gold where you
want it, otherwise you are throwing gold

Maybe he already has a thief incorporated on the jig and that's where the gold is building up. Thieves are high current density areas and, during each cycle, the gold plated on them would be thicker (and, more stressed, mainly due to the high current) than that plated on the parts. During each plating cycle, a separate layer of gold deposits on the jig. These layers are not totally adherent to each other and, since they are stressed (especially with alloyed, hardened gold), they tend to peel from each other. Tiny flakes can be broken off and these can be mechanically incorporated into the gold deposit on the part and cause roughness. For this reason, some platers use chemical strippers (usually proprietary) to strip the buildup on the jigs down to the base metal after a few (or, just one) cycles. This is much better policy than trying to peel the build up manually. It's almost impossible to remove it all manually. You leave small pieces and these can get into the bath.

Need a photo of the jig, preferably one with a part mounted to it. Otherwise, this is all guesswork.

 

[4metals]

Any plating I have ever done in racks or jigs always involved an un-derplate. Likely the material he is taking off the rack is layered with copper and nickel.

 

[goldsilverpro]

Any plating I have ever done in racks or jigs always involved an un-derplate. Likely the material he is taking off the rack is layered with copper and nickel.

This is new to me also, but, according to the link I gave above, the 311 bath is used to deposit gold directly on stainless, etc., and, if that's what he's doing, there would be no underplate.

"AURUNA 311

AURUNA 311 has been specifically developed for direct gilding of stainless steel. The process is also well suited for chrome-nickel alloys, molybdenum steels and low activity nickel alloys. Excellent as a strike solution, prior to heavy deposit gold plating.

The bath has a gold content 2 - 4 g/l, according to application and a deposition rate up to 0.2 µm per minute."

 

[4metals]

So it's the Woods Nickel strike of the Gold world?

 

[goldsilverpro]

So it's the Woods Nickel strike of the Gold world?

Sounds like it. I get the idea it's mainly used for plating surgical and other SS medical equipment. Might be HCl based.