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Anne Marie Helmenstine, Ph.D.

Chemical Piranha and Aqua Regia Solution

By July 21, 2008

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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.

Comments

July 21, 2008 at 5:09 pm
(1) Sean OBrien says:

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.

July 28, 2008 at 6:57 am
(2) Josť Silva says:

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.

September 22, 2008 at 3:01 pm
(3) Seth says:

Never use 50% peroxide sol’n, as explosion is a very real possibility. 30% H2O2 is more than enough.

February 20, 2009 at 8:46 am
(4) Nitin says:

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

June 23, 2010 at 1:32 pm
(5) Scott Reese says:

I am the project manager for the manufacture of 156mm wafer carriers. The primary material selected is PFA or PTFE. On a secondary level, I can manufacture (at less capitol outlay) from aluminum, but suspect about the compatibility with piranha solution. Any advice would be appreciated.

January 31, 2011 at 10:47 pm
(6) bonn says:

Hi Im new here.
Can anyone please help me regarding my inquiry?
Can I use Stainless steel 316/316L in a piranha solution environment?

thank you.

June 8, 2011 at 1:50 am
(7) gil says:

Isn’t it the other way around? Add the sulfuric acid to hydrogen peroxide? Like “Never add water to acid.”

May 16, 2012 at 7:12 pm
(8) Jason says:

Most sources recommend adding peroxide to acid (as in, “always add acid”), although a minority argue that with H2SO4 being denser than H2O2, it’s better to add the denser substance to the less dense substance, as the denser substance will sink and thus be less likely to boil out.

My experience is that stainless steel can be used for brief periods (~1 minute) with 70:30 piranha at temperatures below ~60 C. It is not recommended to use steel vessels for piranha cleaning.

May 28, 2012 at 4:08 am
(9) Pio says:

Does piranha solution attacks ceramic (Ba2TiO3) and Alumina (Al2O3) materials?

October 15, 2013 at 5:18 am
(10) Shadi says:

Hi. I use Piranha for washing the glassware that I use. Does anybody know of Piranha can get Al or any Al compositions as residual away from Pt wire that I have used as counter electrode? If Piranha is not enough, will Aque Regia help?

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