Chemical Etching of Iron and Gold

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G01
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Hello All,

I have a sample which has been covered in a layer of iron and gold for protection. So, in order to work with the sample, we need to etch away the metallic layers. I hear there is a specific chemical recipe for chemically etching away iron and gold from a sample. If anyone can link me to a list of instructions for doing chemical etching of Fe and Au that would be great. Any help at all is appreciated! Thanks.
 
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  • #2
Borek
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I wonder if both will be not dissolved in the aerated cyanide bath, but that's not a recipe, that's a chemical instinct.

Gold is so strongly complexed by cyanides that oxygen from the air is strong anough oxidizer. Iron doesn't need strong oxidizer, in fact any acid will do, but it is complexed by cyanides as well so it will most likely follow the same path as gold. The only problem is what pH will be the best, as low pH will be deadly (evolving HCN) while high can precipitate iron hydroxide (unless complex is strong enough; that can be easily calculated).
 
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Mapes
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Aqua regia will etch both; its recipe is readily available online. You MUST wear personal protective equipment (goggles, face shield, apron, gloves) and use proper ventilation equipment, preferably a chemical fume hood.
 
  • #4
Borek
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Yes, I didn't mentioned it as it will eat through gold, iron and everything else :wink: Cyanide bath - while dangerous too - will be probably more specific.
 
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Mapes
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Yes, I didn't mentioned it as it will eat through gold, iron and everything else :wink: Cyanide bath - while dangerous too - will be probably more specific.
Good point. G01, what is the underlying sample made of?

Potassium iodide is another good selective etchant for gold.
 
  • #6
G01
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Good point. G01, what is the underlying sample made of?

Potassium iodide is another good selective etchant for gold.
Yes. In the mean time I have done some research and decided that a 1:2:10 mix of I2, KI, and H2O are best for my purposes. I here it's very selective and wont attack the material underneath.

Thanks for the advice!
 
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Mapes
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That's good. Silicon won't be affected by any of the etchants we've discussed. Good luck!
 
  • #8
Borek
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Just for the record: I am reading August issue of Journal of Chemical Education and there is a paper that lists several etching baths based on potassium ferricyanide.
 

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