Chemical Piranha and Aqua Regia Solution
Monday July 21, 2008
Many common acids will dissolve common metals, but it can be challenging to remove noble metals and organic residues. This is where aqua regia and piranha solution come in handy. Aqua regia is useful for dissolving gold or platinum. Piranha solution is used to remove organics from the surface of gold or silicon. Both solutions are powerful and should be used with extreme care.
Aqua Regia
3 parts HCl (hydrochloric acid) to 1 part HNO3 (nitric acid)
Mix aqua regia under a fume hood since the reaction of HCl and HNO3 produces NOCl (nitrosyl chloride), Cl2 (chlorine gas), and H2O (water) .
Piranha Solution
5 parts H2SO4 (sulfuric acid) to 1 part H2O2 (hydrogen peroxide)
Add the peroxide to the acid, not the other way around. The reaction to produce piranha solution evolves heat, possibly boiling when the reactants are mixed.
Aqua Regia
3 parts HCl (hydrochloric acid) to 1 part HNO3 (nitric acid)
Mix aqua regia under a fume hood since the reaction of HCl and HNO3 produces NOCl (nitrosyl chloride), Cl2 (chlorine gas), and H2O (water) .
Piranha Solution
5 parts H2SO4 (sulfuric acid) to 1 part H2O2 (hydrogen peroxide)
Add the peroxide to the acid, not the other way around. The reaction to produce piranha solution evolves heat, possibly boiling when the reactants are mixed.
Comments
Piranha can be extremely dangerous. It is difficult to buy chemicals pure enough for this solution to be stable, and difficult to keep it clean enough to use. Common lab grade chemicals will result in temperature spikes to about 150C.
Piranha is well named, it will AGGRESSIVELY eat your flesh if it touches you. An unstable powerful oxidant is formed which is approximately H2SO5. Piranha is essentially dissolved oxygen atoms ready to burn any fuel.
I recommend that nobody make this.
I am a chemist by education and have 40 yrs of lab experience. What should be the peroxide concentration for the piranha solution?
Plenty of piranha around here in Brazil, but won’t do this job.
Thank you.
Never use 50% peroxide sol’n, as explosion is a very real possibility. 30% H2O2 is more than enough.
Can anybody tell me will the excess use of piranha solution (H2SO4: Peroxide; 2:1) on gold surface to remove the organics can also etch the gold surface and make it rough with time.
Thanks