Homebrew PCBs

On Mon, 28 Feb 2011 09:34:35 -0800 (PST), you wrote:

>Was looking at the MSDS for the 30% h2o2 .. yikes .. 
>This etching boards can be dangerous stuff .. lol

It won't be as dangerous as you think.  Use 30 VOL (produces 30 times
more oxygen) H202, That's 3% Hydrogen Peroxide.  You get it at
drugstores and the like.  NOT 30%.

Harvey

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>Randy
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>________________________________
>From: jurod81 <jurod81@...>
>To: Homebrew_PCBs@yahoogroups.com
>Sent: Mon, February 28, 2011 11:03:38 AM
>Subject: [Homebrew_PCBs] Re: Question for the chemistry majors !!
>
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>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 Br\ufffdnsted-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 \ufffd 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
>>
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