Copper etching using HCl and H202
OBones
I regularly etch copper plates using a mix of hydrochloric acid (23%
concentration), hydrogen peroxide (35% concentration) and some tap water.
When the copper plate is dipped into the mix, gassing occurs and the mix
gets a blue/green color which intensity depends on the quantities of the
various components of the mix.
I don't know the exact nature of the gas that gets out and the various
websites that describe this method do not agree on what it is. Some say
it's pure oxygen (02), some others say it's pure chlorine, some just say
it's "toxic gas".
I had some chemistry lessons back in high school but this seems out of
my reach without further assistance. Here is what I got so far:
H202 + H+ + Cl- + H20 + Cu ---> Cu2+ + H20 + ???
Could you tell me which equation is right and which gas gets out of this?
Thanks in advance
Regards
Olivier
Bill Penrose
> Hi all,
>
> I regularly etch copper plates using a mix of hydrochloric acid (23%
> concentration), hydrogen peroxide (35% concentration) and some tap water.
> When the copper plate is dipped into the mix, gassing occurs and the mix
> gets a blue/green color which intensity depends on the quantities of the
> various components of the mix.
> I don't know the exact nature of the gas that gets out and the various
> websites that describe this method do not agree on what it is. Some say
> it's pure oxygen (02), some others say it's pure chlorine, some just say
> it's "toxic gas".
Even if it's not toxic, there will likely be spray in it that you
should avoid. Ventilation or a powered vented hood should be used
regardless. Also, the HCl will damage metal things in the vicinity
sooner or later.
If it's chlorine, you'd detect the odor of bleach pretty quick.
Isn't 35% peroxide hard to get these days, what with terrorists and
shoe bombs and all? Ammonium persulfate is easier to use and control
and stores better.
DB
OBones
> On Apr 27, 9:20 am, OBones <obones_gfd_@_gfd_altern.org> wrote:
>> Hi all,
>>
>> I regularly etch copper plates using a mix of hydrochloric acid (23%
>> concentration), hydrogen peroxide (35% concentration) and some tap water.
>> When the copper plate is dipped into the mix, gassing occurs and the mix
>> gets a blue/green color which intensity depends on the quantities of the
>> various components of the mix.
>> I don't know the exact nature of the gas that gets out and the various
>> websites that describe this method do not agree on what it is. Some say
>> it's pure oxygen (02), some others say it's pure chlorine, some just say
>> it's "toxic gas".
>
> Even if it's not toxic, there will likely be spray in it that you
> should avoid. Ventilation or a powered vented hood should be used
> regardless. Also, the HCl will damage metal things in the vicinity
> sooner or later.
Ventilation is part of the process, no doubt about that.
> If it's chlorine, you'd detect the odor of bleach pretty quick.
Fair enough.
> Isn't 35% peroxide hard to get these days, what with terrorists and
> shoe bombs and all? Ammonium persulfate is easier to use and control
> and stores better.
It's not that hard, but yes, it's not available at any DIY store.
Ammonium persulfate must be heated which makes not as convenient as the
above mix that works at ambient temperature.
Thanks
Olivier
Madalch
>
> I regularly etch copper plates using a mix of hydrochloric acid (23%
> concentration), hydrogen peroxide (35% concentration) and some tap water.
> When the copper plate is dipped into the mix, gassing occurs and the mix
> gets a blue/green color which intensity depends on the quantities of the
> various components of the mix.
> I don't know the exact nature of the gas that gets out and the various
> websites that describe this method do not agree on what it is. Some say
> it's pure oxygen (02), some others say it's pure chlorine, some just say
> it's "toxic gas".
The gas is surely oxygen, since the hydrogen peroxide will decompose
with nearly anything as a catalyst.
The simplest form of the reation is question is likely:
Cu + H2O2 + 2H+ --> 2 H2O + Cu(2+) or
Cu + H2O2 + 2HCl --> 2 H2O + CuCl2
(This isn't exactly correct, since the chloride ions will form a
complex ion with copper(II), but it's close enough for government
work. If you've got a high concentration of chloride, you'll be
getting a greener solution; less chloride and you'll get blue.)
The formation of oxygen is from 2 H2O2 --> 2 H2O + O2, a side
reaction. But HCl will also evaporate and contaminate the oxygen, so
don't consider it safe to breathe.
OBones
> On Apr 27, 9:20 am, OBones <obones_gfd_@_gfd_altern.org> wrote:
>> Hi all,
>>
>> I regularly etch copper plates using a mix of hydrochloric acid (23%
>> concentration), hydrogen peroxide (35% concentration) and some tap water.
>> When the copper plate is dipped into the mix, gassing occurs and the mix
>> gets a blue/green color which intensity depends on the quantities of the
>> various components of the mix.
>> I don't know the exact nature of the gas that gets out and the various
>> websites that describe this method do not agree on what it is. Some say
>> it's pure oxygen (02), some others say it's pure chlorine, some just say
>> it's "toxic gas".
>
> The gas is surely oxygen, since the hydrogen peroxide will decompose
> with nearly anything as a catalyst.
>
> The simplest form of the reation is question is likely:
> Cu + H2O2 + 2H+ --> 2 H2O + Cu(2+) or
> Cu + H2O2 + 2HCl --> 2 H2O + CuCl2
>
> (This isn't exactly correct, since the chloride ions will form a
> complex ion with copper(II), but it's close enough for government
> work. If you've got a high concentration of chloride, you'll be
> getting a greener solution; less chloride and you'll get blue.)
That's what I observed. If I put one part H202 and one part HCl, the
solution reacts very fast and turns very green. If add one or two parts
of water, it reacts much slower and only turns slightly blue.
> The formation of oxygen is from 2 H2O2 --> 2 H2O + O2, a side
> reaction. But HCl will also evaporate and contaminate the oxygen, so
> don't consider it safe to breathe.
Fair enough. So in summary, H202 is not strictly necessary but it helps
accelerate the process as it oxidises the copper and as such makes it
easier to transform the copper into the final copper chloride. Am I right?
Craig
Not quite. The H2O2 really is necessary. To prove it to yourself,
try adding only the HCl to your copper. Nothing will happen. Then
add the H2O2 and it should work like always.
Most other metals (iron, etc.) can be etched just with acid. Copper
is less active and needs a stronger oxidizer, like H2O2. So, it won't
work if you leave it out, even if you let it sit for a long time.
The oxygen gas is from H2O2 that *didn't* do what you want. The H2O2
either oxidizes itself to make O2, or it oxidizes your copper. Some
amount of this side reaction is unavoidable, no matter what you do - I
wouldn't lose sleep over it. :)
- Craig
Madalch
> accelerate the process as it oxidises the copper and as such makes it
> easier to transform the copper into the final copper chloride. Am I right?
As Craig said, it is necessary, because it is the oxidizing agent.
Copper will not dissolve in pure hydrochloric acid.
It will dissolve slowly in hydrochloric acid that contains a
significant amount of copper(II) chloride, though. The copper(II)
chloride reacts with the copper to form copper(I) chloride (which is
only soluble in the presence of a high concentration of chloride ions
from the acid). Copper(I) chloride in solution reacts relatively
slowly with the oxygen in the air to give copper(II) chloride.
This reaction might be too slow for your purposes, but you might be
able to use a lower concetration of hydrogen peroxide, and thus make
things easier for yourself.
OBones
Ah yes, makes more sense this way. But then couldn't it be a two part
process, leading to this:
H202 + 2Cu --> 2CuO + H2
CuO + 2HCl --> CuCl2 + H20
thus leading to hydrogen generation. This might be completely wrong
though... Any opinion very much appreciated
Madalch
> But then couldn't it be a two part
> process, leading to this:
>
> H202 + 2Cu --> 2CuO + H2
> CuO + 2HCl --> CuCl2 + H20
>
> thus leading to hydrogen generation. This might be completely wrong
> though... Any opinion very much appreciated
No- hydrogen is not evolved in this reaction. Your first reaction
could be H2O2 + Cu --> CuO + H2O, but this would not be an accurate
representation of the mechanism.
OBones
So the gas is just a side effect? That's what I have a hard time
figuring out as there is a quite lot of it coming out of the reaction,
right from the surface of the copper.
Madalch
> So the gas is just a side effect? That's what I have a hard time
> figuring out as there is a quite lot of it coming out of the reaction,
> right from the surface of the copper.
Yes- the copper surface catalyzes the decomposition of hydrogen
peroxide. So will iodides, manganese dioxide, blood, and a whole host
of other things.
If you want to test this gas, you can fill a test tube, jar or bottle
with water, and invert it over the copper surface to collect the gas.
If it's chlorine, it will be green.
If it's hydrogen, it will "pop" when you hold a lit match to it.
If it's oxygen, it will reignite a glowing splinter (take a toothpick,
light it on fire, blow it out, and immediately put it in the test
tube).
Martin Brown
> Madalch wrote:
>> On Apr 27, 1:29 pm, OBones <obones_gfd_@_gfd_altern.org> wrote:
>>> Fair enough. So in summary, H202 is not strictly necessary but it helps
>>> accelerate the process as it oxidises the copper and as such makes it
>>> easier to transform the copper into the final copper chloride. Am I
>>> right?
>>
>> As Craig said, it is necessary, because it is the oxidizing agent.
>> Copper will not dissolve in pure hydrochloric acid.
You could use air as the source of oxygen if you wanted, but it would be
slower. There are recipes for this online using just CuCl2 & HCl.
The peroxide is essential to the HCl based etch system.
>>
>> It will dissolve slowly in hydrochloric acid that contains a
>> significant amount of copper(II) chloride, though. The copper(II)
>> chloride reacts with the copper to form copper(I) chloride (which is
>> only soluble in the presence of a high concentration of chloride ions
>> from the acid). Copper(I) chloride in solution reacts relatively
>> slowly with the oxygen in the air to give copper(II) chloride.
>>
>> This reaction might be too slow for your purposes, but you might be
>> able to use a lower concetration of hydrogen peroxide, and thus make
>> things easier for yourself.
>
> Ah yes, makes more sense this way. But then couldn't it be a two part
> process, leading to this:
>
> H202 + 2Cu --> 2CuO + H2
> CuO + 2HCl --> CuCl2 + H20
>
> thus leading to hydrogen generation. This might be completely wrong
> though... Any opinion very much appreciated
You will never get hydrogen evolved from an oxidising medium like this.
You may get some oxygen from decomposition of the H2O2 and also traces
of chlorine oxides from side reactions - the latter are very water
soluble and may play a part in speeding up the attack on the copper.
Copper is quite resistant to pure HCl attack without something like Fe3+
or Cu2+ ions to help and an oxidising environment to drive the reaction.
Regards,
Martin Brown
** Posted from http://www.teranews.com **
number6
Etching Copper with HCl requires a source of Chlorine ... Some etches
use Chlorine directly .... others generate it in situ with Sodium
Chlorate ... or Peroxide as you are doing ...
It is hard to tell what green blue gas is ... but I feel from how you
describe things that it is due to copper oxychloride solution or
particulates being carry along with the gas ... You will have the
potential to release a lot more O2 than Cl2 ... and although Cl2 has
color ... its intensity is rather light ...
Madalch
> It is hard to tell what green blue gas is ... but I feel from how you
> describe things that it is due to copper oxychloride solution or
> particulates being carry along with the gas ...
The solution is green-blue; the colour of the gas was not mentioned.
OBones
That's right. I cannot see any colour when I let the gas vent freely.
However, I have not yet tried to capture it as you suggested. I'll do
this as soon as I can and will keep you posted.
Aaron Hicks
Last I checked, I could purchase 30% (or 35%- I forget) hydrogen
peroxide at a local hydroponics store. Very pricey on a per quart basis,
but they stocked it on the shelf. I also noted our local vitamin store
stocked hydrogen peroxide- even kept it refrigerated. That was just a
couple of weeks ago. Haven't checked hydroponics stores in the past year
or so, so that may have changed.
I used to make the evil peroxides (under gov'munt contract), years
before 9/11. Nasty stuff.
The address in the header isn't valid. Send no email there.
-AJHicks
Chandler, AZ
OBones
I just did that but it's not conclusive. I filmed the whole process,
it's visible here:
http://www.dailymotion.com/video/x5f2vk_gravure-eau-oxygenee-acide-chlorhyd_tech
The first bit of copper is put inside the solution at 2:39 and one can
see fumes going out of the solution.
At the end, I tried to identify the gas, but to me it's not conclusive.
Any opinions welcome.
Cheers
Olivier
Bill Penrose
> The first bit of copper is put inside the solution at 2:39 and one can
> see fumes going out of the solution.
> At the end, I tried to identify the gas, but to me it's not conclusive.
The classical oxygen test involves a smoldering wooden match or splint
inserted into the test tube. A bunsen burner inducts air at the bottom
of the barrel. It's uncertain whether oxygen applied directly to the
flame like that would have any visible effect.
Good technique. You wear gloves and measure stuff. Safety glasses,
too, I bet?
Dangerous Bill
OBones
> On May 14, 3:17 am, OBones <obones_gfd_@_gfd_altern.org> wrote:
>> The first bit of copper is put inside the solution at 2:39 and one can
>> see fumes going out of the solution.
>> At the end, I tried to identify the gas, but to me it's not conclusive.
>
> The classical oxygen test involves a smoldering wooden match or splint
> inserted into the test tube. A bunsen burner inducts air at the bottom
> of the barrel. It's uncertain whether oxygen applied directly to the
> flame like that would have any visible effect.
I tried with a match that I lit and then just blew, but it did not do
anything visible. I tried with a lit match and it turned it off, just
fumes inside the tube. I did not film this though, but I could if you
think it could help.
> Good technique. You wear gloves and measure stuff. Safety glasses,
> too, I bet?
Just my regular viewing glasses, I did not feel the need for any more
specialized glasses as I do not look directly over the recipient.
Madalch
OBones
> It's oxygen.
I'm very well inclined to believe you, but I did not see the "rebirth"
of the flame. Could you elaborate a bit more?
Madalch
You would need to use a larger sample to see the effective "rebirth"
of the flame- that little test tube you collected wouldn't do much.
Hydrogen peroxide will decompose to give oxygen, and is readily
catalyzed by a lot. In your video, you can see bubbles of it forming
on the glass when there's no copper present. That's exactly what you
expect to see with concentrated hydrogen peroxide decomposing.
OBones
> On May 14, 1:51 pm, OBones <obones_gfd_@_gfd_altern.org> wrote:
>> Madalch wrote:
>>> It's oxygen.
>> I'm very well inclined to believe you, but I did not see the "rebirth"
>> of the flame. Could you elaborate a bit more?
>
> You would need to use a larger sample to see the effective "rebirth"
> of the flame- that little test tube you collected wouldn't do much.
That's what I suspected. This one is 3ml. What minimal volume would be
enough in your opinion?
> Hydrogen peroxide will decompose to give oxygen, and is readily
> catalyzed by a lot. In your video, you can see bubbles of it forming
> on the glass when there's no copper present. That's exactly what you
> expect to see with concentrated hydrogen peroxide decomposing.
Fair enough, that makes sense.
Thanks for your input.
Regards
Olivier