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Selective etching of iron

My system is Fe-Au, which iron is matrix and gold are nanowires embedded in iron. now I want selective etching of iron and get gold nanowires, I want to know how to do it? use chemical method or electrochemical method? Thanks!

Ying
- Bochum, Germany
2007

One option. Concentrated nitric acid dissolves iron but not gold. Warning! Produces dangerous fumes, heat and regulated waste.

Guillermo Marrufo
Monterrey, NL, Mexico
2007

Actually, 50% nitric dissolves iron faster. Really pure nitric acts as an oxidizer and is slow in the attack. 50% is safer to use and would require the purchase of less. A FEW grains of table salt will speed up the attack on the iron as will a few drops of copper chloride.

James Watts
- Navarre, Florida
2007

Electrolytic etching is much safer then nitric acid (you can use very diluted hydrochloric or sulfuric acid as electrolyte,object=anode). Hope it helps and good luck!

Goran Budija
- Cerovski vrh Croatia
2007

I agree to James about the 50% concentration being better if we are talking about steel. The carbon and other elements always present in it tend to form a passive layer with concentrated nitric. With pure iron, this layer doesn't form, so concentrated works faster. About the addition of chlorides, I must disagree. Chlorides together with nitric may attack the gold and damage those nano wires. Best regards to all,

Guillermo Marrufo
Monterrey, NL, Mexico
2007

Thanks for all your kind answers! But the question is that I have tried many kinds of acids, like HCl, HNO3, H2SO4, but all of them didn't work. The surface of my sample will become black after a while, form something like black layer on the surface. The black layer can be removed by sonification, but that is not what I wanted.

Ying
- Bochum
2007