How Do I Etch Au-Carbon Deposit on Ceramic?

Is there any way you can put on a making layer before your EFO process to shield the material in the first place instead of etching it off later?

Do you mean "masking" layer?

Why yes, Yes I do.

_{<Grumbles about spell check, among other incomprehensible gibberish>}

Wasn't sure. I thought it might have been jargon specific to the "EFO process". Something like, "You must apply the making layer within twenty minutes of Flame Off."

mercury will remove the gold and allow you to recover the gold by distillation of the amalgam. not so sure about the carbon.

Unfortunately, I can not mask the ceramic as it is actually the holder for the Au that is being cut. The Au get deposited on the the ceramic during the cutting process. At this time masking is out of the question so we are looking for a method to clean the ceramic surface.

Have you heard of aqua regia??

Seems like it might be the ticket, Says it completely dissolves royal metals.

FROM WIKIPEDIA:

"Aqua regia is also used in etching and in specific analytic procedures. It is also used in some laboratories to clean glassware of organic compounds and metal particles."

"The mixture is formed by freshly mixing concentrated^[1]nitric acid and hydrochloric acid, usually in a volume ratio of 1:3, respectively. It was named so because it can dissolve the so-called royal metals, or noble metals, gold and platinum. However, ruthenium,tantalum, iridium, osmium, titanium, rhodium and a few other metals are capable of withstanding its corrosive properties."

Au is relatively innert to aqua regia. We current use it for etching other metals/alloys deposited on Au. Au remains intact after the etching process.

"Au is relatively inert to aqua regia."

I'm sorry, but that's just plain wrong.

From the American Chemical Society:

"Aqua Regia is a mixture of hydrochloric acid and nitric acid. It can (and will) dissolve gold, which single acids alone cannot do. Each of the acids separately have no effect on the gold but a mixture of the two dramatically reacts with the gold."

That's very interesting considering it is specifically used to dissolve gold (Au). That was it's purpose when it was discovered. It is proven to completely dissolve gold and platinum.

I suspect you have another look, If you cannot dissolve the gold with your Aqua Regia, I'm afraid it's not really Aqua Regia.

Don't discount it yet until you're absolutely sure you know what your talking about.

You are correct. When I was looking at processing and refining gold ore, Aqua Regia was one of the methods to remove gold from the surrounding rock and other metals its was mixed with. It must be mixed correctly though otherwise it doesn't really work very well. Although dangerous to the untrained, the cyanide process can separate gold from its surroundings as well, but that is probably not a process you would want to get into in this context. But maybe?

Temp I suspect plays a large role in the reactivity RVZ71, he may be talking about low temps whereas you are thinking higher temps. And of course, the ratio is important too, if one of the etched components were neutralizing one of the two acids preferentially, then the resulting acid might not actually be Aqua Regia after all is said and done.

About 25 years ago we have setup a CNC 3 axis laser to tunnel out impurities in diamond. We cut to the impurity. This makes a very capilar tunnel with a black carbon wall. In fact worse than the impurity itself.

Because of the small diameter we have no means of washing the wall down.

Yhis is what we did: the diamonds are put in a pressure tight teflon container, that also goes in a red copper bigger container.

A solution of "koenigwasser" is applied in the teflon container and then the whole bunch goes in a electric oven for a weekend.

After a few days, the diamonds come out free of carbon traces.

The solution is very corrosive and so are the fumes. The anodized alumium windows are even getting damaged. (koningswater)

The formula must be available on the web I guess.

Interesting. I will look into this. Thanks a lot. Joe

It turns out that koningswater is also aqua regia.

Yes.

"Der Name Königswasser (lat.: aqua regis oder aqua regia, königliches Wasser) leitet sich von der Fähigkeit dieser Lösung ab, die „königlichen" Edelmetalle Gold und Platin zu lösen."

"The name of Königswasser (Latin: aqua regia or aqua regis, royal water) is based on the ability of this solution to dissolve the "royal" Precious metals gold and platinum." (courtesy of Google Translate)

http://de.wikipedia.org/wiki/K%C3%B6nigswasser

You need to make only enough for a single operation. You can't store it. Aqua Regia decomposes over time, losing activity.

http://en.wikipedia.org/wiki/Aqua_regia

A solution of KI and I is a traditional etchant for gold. Both carbon and gold can be removed in a plasma cleaner, but carbon will re-deposit in minutes from the atmosphere. You should also be able to adjust your EFO to minimize gold vaporization and/or provide a nozzle to suck or blow the vapor away from the substrate.