On Wed, Mar 9, 2011 at 8:14 PM, Ben L <
bhleavi@...> wrote:
>
>> > I am a "lurker" on this list and am following this
>> > peroxide and HCl with great interest.
>> >
>> > I keep looking for a straightforward answer to
>> > the what to use, in what strengths, and in what
>> > proportions.
>> >
>> > About the time I think I have an answer then
>> > someone comes along and complains about
>> > the subject. Fact of the matter is the subject
>> > seems to have more than one answer, for
>> > reasons I still have not understood.
>>
>
> As for want to use. Hydrochloric Acid sold as Pool and Concrete Cleaner and Drug Store 3% Hydrogen Peroxide.
>
> I believe that the Mix is 1 part Hydrochloric Acid to 2 part Hydrogen Peroxide. This should get you started. If you are to regenerate it using Hydrogen Peroxide then you might want to use higher % so you don't water it down too much as the 3% is mostly water. I regenerate with air pumped into the tank, this takes awhile. As the tank level goes down I add some 3% Hydrogen and Hydrochloric Acid.
>
> Look for Adam Seychell paper in the files section on it if you really want to get into the details of this and the real way to maintain it.
> His paper is the real method if you want to maintain it correctly.
>
> The list is for people to learn by asking questions, and the ones on the list that have been around and have the experience should be willing to answer the questions when they feel that they know the answer to it. but if you don't want to answer a question move on to the next message. Pass over ones that the subject is not of interest to you. Deleting a message takes less time than writing a message of complaint.
>
> Sometimes you might find that you learn something by answering someone questions because it makes you think.
>
>
> Ben
>
(I have been writing this all day a little bit at a time while I was at work.)
Okay, first a gripe about this thread. Completely agree with Ben in
that I think it's great new people are signing up and asking
questions. I've been subscribed here for a long time also so I have
seen plenty of redundancy too but we are here to help new people get
into the hobby of making their own boards not to chastise them.
Doing chemistry by volume is just a bad idea. Weight/mass ratio's are
much easier to work it.
When etching a board with Cupric Chloride it really doesn't matter
what strength we use as long as we have the correct proportions of
H2O2 (hydrogen peroxide) and HCL (hydrochloric acid). We only need
enough volume to cover our board. A stronger solution would be easier
to store as regnerating with weak H2O2 and HCL would increase the
volume greatly. Starting off with weak H2O2 and HCL should be
sufficent for most small runs.
This is how our reaction works:
First we are making Cupric Chloride (CuCl2):
Cu + H2O2 + 2HCl -> 2H2O + CuCl2
The Copper reacts with the CuCl2 from the previous reaction to form
Cuprous Chloride (CuCl):
Cu + CuCl2 -> 2CuCl
The Cuprous Chloride continues to react with the H2O2 and HCL to
continue the reaction.
CuCl + H2O2 + 2HCL -> 2H2O + 2CuCl2
It's a chain reaction and these reactions are all happening
simultaneously but each mole of HCl used dissolves 1 mole of copper.
H2O2 has a molecular mass of 34.0147 grams/mole and HCL is 36.46
grams/mole. With 100 grams of 3% H2O2 we would have 3 grams or 0.088
moles of H2O2 (3 grams divided by 34 grams/mole). We would need 0.176
moles of HCl for the reaction. That would be 0.176 moles x 36.5
grams/mole = 6.42 grams. With 27% HCl that would be 6.42 devided by
27% equals 23.78 grams of 27% HCl Solution. 23.78 grams of HCl per 100
grams of H2O2 would be a 1:4.2 ratio. This would of course would
change with different concentrations.
When regenerating our solution by adding more H2O2 and HCl we are
adding it to a solution of CuCl and water. The reaction above starts
with 114.374 grams of water and generates another 3.178 grams of water
so we have roughly 117.5mL of water when the reaction is complete.
This is why to regenerate the etchant it would be best to use more
concentrated chemicals so it doesn't get too diluted. If the reaction
doesn't use up all of the H2O2 and HCL the H2O2 will break down in the
light to H2O and O2 so regenerating with only H2O2 may work. Add H2O2
to the CuCL and water solution first. If the reaction starts there was
HCL left in the solution. When adding H2O2 causes no results it's time
to add proportionate amounts of both H2O2 and HCl to continue the
reaction.
***************
I've been wanting to do this for a while so I decided to write a
JavaScript calculator this evening to do the math so you guys can play
around with the concentration numbers. It can be found here along
with the complete write up:
http://www.totse2.com/easy-e/cupricchloride.html
All of that should be correct but please let me know if any of my
chemistry is wrong and I will update my page.
***************
--
Erik L. Knise
Seattle, WA