Hi,
It is definitely add the acid to H2O2.
In Portuguese there is an easy way to remember: H2O2 and water are
feminine nouns in Portuguese, so we always have to remember: ladies
first :)

Virginia Soares
INESC-MN
Rua Alves Redol,9
1000-029 LISBOA
PORTUGAL
www.inesc-mn.pt

-----Original Message-----
From: Zhiwei Zou [mailto:zouz@email.uc.edu]
Subject: RE: [mems-talk] About the Piranha cleaning

I am confused about the sequence of mixing these two chemicals. Some
materials said add H2O2 to H2SO4 but others do it reversely.
Who can help me to confirm it?