Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, William Kroyer
<william.kroyer@...> wrote:
> CuCl can be regenerated.  It already has copper in it to begin
> with.  It seems to me that when etching you are actually just
> making more CuCl.  ...  I'm guessing it's "reguvinated" by
> simply adding more HCl or H2O2.

Yeah.  See for instance here:
http://members.optusnet.com.au/~eseychell/PCB/etching_CuCl/index.html#operate_acid
(or our own archives.)

The etch reaction is:
   CuCl2 + Cu --> 2CuCl

Where CuCl2 is supposed to be bright green, and CuCl is brown muddy
stuff.

The "regeneration" reaction is:
    CuCl + HCl + O --> CuCl2 + H2O
In my case the O is provided by bubbling air through the solution.

But the CuCl2 is supposed to be green, and the CuCl2 sorta brown and
borderline insoluble, so I'm at a loss as to how I got blue...

Dilute solution of CuOH, perhaps (this is normally pretty insoluble.)

I was hoping to avoid titration-like measurements, but perhaps this
is going to be impossible, basing replenishment on color, opacity,
and the fact that I though aeration-based replenishment would just
stop when it was done (and some free HCl isn't so bad), but I guess
I can also drive away all the HCl...

BillW