Hey Randy-
I will preface this with - I am not a chemistry major, but I do know a bit of chemistry (more organic than inorganic).
To answer the original question: what the bubbles are that come off of the board from peroxide + HCl etch, it is actually brings up an interesting bit of chemistry. If you look at a oxidation-reduction table you will see that hydrogen is below copper, so as a rule of thumb most Brønsted-Lowry acids such as HCl cannot oxidize copper by themselves (nitric acid not included). Peroxides are a little special; they are very unhappy molecules and easily decompose into hydroxyl radicals on their way to becoming water. These hydroxyl radicals have an oxidation potential close to fluorine and can easily attack copper metal which has a full outer electron shell. The bottom line is that the gas given off on the copper clad is oxygen (O2) and hydrogen (the final electron receptor in the reaction), and I am sure that a bit of HCl off gassing since this is an exothermic reaction. You end up with copper chloride as a final product. If you want to practically speed up the reaction electrolysis is not going to help you by very much, I would suggest either starting with a higher % of peroxide, agitate your solution (with air bubbles or shaking) or warm you solution up a bit.
For those that are interested, Iron choride acts as a Lewis acid since Fe(III) has a higher reduction potential then copper with will act as an electron acceptor. The iron is reduce to Fe(II) and you end up with copper in solution. Ammonium persulfate works on a similar free radical principle as the peroxide + HCl principle, the only downsides are that it tends to be slower, you end up with ammonia gas given off, and the persulfate decomposes rather quickly after you add it to water meaning it is not very reusable (a day or two at the most depending on how contaminated your starting water was).
You can reuse your etchant many times before tossing it (I recharge mine by adding a bit more 30% peroxide). When you do toss it you can easily reclaim your copper before dumping it down the sink since copper ions do very terrible things to the environment (and your septic system's bacteria). You can neutralize the acid by throwing some baking soda (Sodium bicarbonate) into the solution and the peroxide by dumping some bread yeast which contains an enzyme called peroxidase into the solution. You end up with a solution containing copper chloride and sodium chloride in solution. Then you can run an electrolytic cell with copper as the cathode (hooked up to the (-) terminal) and an inert carbon anode. Chlorine will be given off at your anode and your cathode will grow some more copper until the solution becomes depleted (then hydrogen bubbles will start forming on it). Otherwise you may want to consider disposing of it as hazmat when your county does one of those household hazardous material drop-off days. My township does one every 6 months or so good for dropping off unused paint etc.
-JRod
BTW - Hydrogen and oxygen are a bad combination. All they need is a little heat or a catalyst to get over the activation energy and you have fire.
--- In Homebrew_PCBs@yahoogroups.com, "Randy S." <rj3819@...> wrote:
>
> I'm not talking about Chemistry.com here either ..lol
>
> Ok .. using muriatic acid .. with the hydrochloric acid in it mixed with
> peroxide.
>
> I looked a chemelec's website where he uses sulfuric acid and electrodes
> to remove over 90% of the copper, then finishes the board off in ferric
> chloride.
>
> So .. I thought if should work with other acids ..
> I put a electrode in on the negative lead and a scrape piece of board on the
> positive lead, started cranking up the voltage .. and it did indeed start
> drawing
> current and bubbling .. no ventilation so I shut it off right away ..
>
> The questions are :
> He mentioned gases from the electro-etch process, which makes sense as
> there are bubbles .. which are toxic .. I assume the gases from his acid would
> be different then the gases from mine. Chemistry majors ?? What is the gas
> being released from my H2O2 and HCL LOL
> Some kind of a hydrogen chloride gas ?? sounds toxic and flammable .. lol
>
> I was thinking I would make a setup to use my solution, aearate the tank and
> use some electro-etching, if that what it is , to help the process along ...
>
> Sound ok ? Would there be problems with that ?
>
> thanks all
>
> Randy - N2CUA
>