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Topic: HCl + H2O2 as a metal etchant?  (Read 10443 times)

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Offline aaronsilber

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HCl + H2O2 as a metal etchant?
« on: April 05, 2010, 07:13:33 PM »
Hey um.... smarter peoples :)

Anyways, I've been doing some experimentation with different copper etchants and such. I've tried two more "commercial" solutions - ammonium persulfate - (NH4)2S2O8 - and ferric chloride - FeCl3. Now I have practically no experience in chemistry at all - I tend to be the one programming web backends and such. I've heard some things about a mystical "Cupric Chloride" as a third etchant - using just hardware store muriatic (hydrochloric) acid and drugstore peroxide. So I tried a 1:2 30.45% hydrochloric acid to ~3% hydrogen peroxide solution. And it does dissolve copper - but so do ammonium persulfate and ferric chloride. I've thought it out a bit and realized that the gas building up in the etchant bottles was hydrogen - when the Cu atoms bind with the Cl in HCl and H2O2 you get CuCl H2O2. But for each HCl molecule that gets changed into CuCl, it reduces the effectiveness of the etchant and also gives it a green tint. My main questions are as follows: a) What is H2O2 there for? I know HCl alone doesn't etch the copper at all. b) How do I restore CuCl to HCl? Is it possible without started a completely new batch? and finally, c) Precisely how much H2O2 do I need for this reaction to occur?

I'm thinking the peroxide has something to do with oxidizing the copper before it binds with the chlorine atom. But anyways, hope you guys know what I'm talking about!

Thanks in advance.

Offline skyjumper

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Re: HCl + H2O2 as a metal etchant?
« Reply #1 on: April 05, 2010, 10:07:09 PM »
It sounds like similar properties to this. http://en.wikipedia.org/wiki/Piranha_solution

Offline Borek

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Re: HCl + H2O2 as a metal etchant?
« Reply #2 on: April 06, 2010, 03:58:00 AM »
I've thought it out a bit and realized that the gas building up in the etchant bottles was hydrogen

Not necesarilly, hydrogen peroxide decomposes to water and oxygen.

HCl alone is not enough to dissolve copper, as copper is too noble to be dissolved just in acid (no matter how strong). You need some additional oxidizing agent. It can be an acid itself (that's the case of nitric acid), it can be something else, like Fe3+ or persulfate, or hydrogen peroxide.

Search forums, I think chemistry behind copper etching was already discussed before.
« Last Edit: April 06, 2010, 04:24:41 AM by Borek »
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Offline aaronsilber

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Re: HCl + H2O2 as a metal etchant?
« Reply #3 on: April 06, 2010, 01:34:35 PM »
Thanks for the help. I'm pretty sure it does, for one reason or another, give off hydrogen -- I was able to light a balloon full of the etchant's offgassing on fire, and it gave that characteristic "pop" from way back when with all those classroom water electrolysis experiments. I'll search around and see if this has already been asked.

EDIT:
H202 + 2Cu --> 2CuO + H2
CuO + 2HCl --> CuCl2 + H2O

I dug this up and it seems about right. Oxygen would also ignite in a similar fashion to what I believed to be hydrogen.

Offline Borek

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Re: HCl + H2O2 as a metal etchant?
« Reply #4 on: April 06, 2010, 03:11:33 PM »
You have selected reactions that I ignored - not without a reason. I strongly doubt hydrogen presence.
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Offline skyjumper

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Re: HCl + H2O2 as a metal etchant?
« Reply #5 on: April 06, 2010, 07:31:06 PM »
The oxygen wouldn't burn with a pop. Its more of an accelerator H2O2 gives off O2 normally as it decomposes (on light exposure)

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