BigFoot - 15-8-2016 at 10:30
Hi all,
I've 8 PCB's covered with gold (total weight: 703gr) and i dont know how much to use from HCI and how much from Hydrogen peroxide.
There is some formula to calculate this ratio?
Usually i use 200ml from Hydrochloric acid 32% and 150ml from Hydrogen peroxide 3%
Metacelsus - 15-8-2016 at 14:21
The half-reaction for hydrogen peroxide will be:
H2O2 + 2 H+ + 2 e- -> 2 H2O
Therefore, you should use at least twice as many moles of hydrochloric acid as hydrogen peroxide. 3% hydrogen peroxide is roughly 0.88 M, and 32%
hydrochloric acid is roughly 10.2 M. As you can see, you are now using a large excess of hydrochloric acid.
The half-reaction for gold will likely be:
Au -> Au3+ + 3 e-
This implies you should use 3 moles hydrogen peroxide per 2 moles gold. However, other metals will be present, so it's hard to calculate the amount
you'll need.
BigFoot - 16-8-2016 at 08:03
Thanks for your answer,
right now i use 200ml HCI and 50ml H2O2
and after 24h, it's kind of working, the gold start to fall from the board.
