My muriatic+peroxide doesn't seem to renew itself...

[Taylor]

I decided to go with this chemistry instead of ferric because I liked the idea of "self-renewing" etchant. But I don't find that it really does that. Newly-mixed etchant works great, then it becomes relatively useless.

I have been trying to figure out how to manipulate the mixture to get it to keep going. So far I have figured out the following:

-The ideal etchant is an emerald green with lots of little bubbles.
-If it starts getting brown, it needs more hydrogen peroxide
-If it gets really blue, there is too much copper and not enough acid (this happened to me when I was etching one entire side off of double-sided boards)

But what about when it just is really weak?

[John Lyons]

I recharge mine each time I etch with a little of both chemicals.
I use about a pint or more in my etching tray. I probably ad less that half a cup
of the new stuff (both parts ad up to this amount) when I recharge it.

The theory that it recharges itself does not work. I've used a fish tank
bubbler to airate the solution but it doesn't do that much.

John

[The French connection]

Conservation of mass (Lavoisier)!

The overall reaction for etching consumes copper metal and hydrochloric acid, resulting in more Cu2+ and water;

   2HCl(aq) + 2CuCl(aq) + [Ox] → 2CuCl2(aq) + H2O(aq)

As hydrochloric acid (the ingredient of muriatic acid) is consumed and water produced, over time with etching the solution becomes dilute in acid and concentrated in cupric chloride, eventual adjustment using concentrated acid may be required. Eventually as the copper(II) concentration increases, cupric chloride precipitates as a green-blue solid in solution. So, once all the H+ have been consumed, you have to add some more...All this depending on the equilibrium constant of the reaction. Hence, mass conservation! There's no renewing reaction. Maybe oscillating reaction like Belousov–Zhabotinsky reaction, but even tough, it become tired at some point...Perpetual movement is inpossible.

Sorry for the pompous explanation!

Dan

[ItZaLLgOOd]

You lost me after 2HCl

[The French connection]

You lost me after 2HCl

You have pretty much nails it, don't go further!

[Ibanezfoo]

I read some huge explanation on instructibles.com about how you can keep reusing this stuff over and over with all the chemistry behind it.... But I, like you, have discovered this must be BS because mine also doesn't "refresh" no matter what color it is.  It works, but it takes all day (or longer) to etch something.  Fresh stuff etches in ~30 mins or so.

[sean k]

I just keep adding the hydrogen peroxide.

[robmdall]

Try pumping a little air in the bath. Aeration helps a bit.

[Minion]

I use so little of the stuff to etch that I just use new stuff with every new board ..... In all i use less than 1/4 cup total to etch a board or two , just enough to cover the board ........


Cheers

[SonicVI]

Fresh stuff etches in ~30 mins or so.

30 minutes?      Heat it up a little and it will take about 5 minutes.

[Minion]

Even without heating 5 min is a long etch , I did two 3.5 x 2.5 in boards for my stereo eq project last nite and each board took maybe 3-4 minutes .... it is definately the fastests etchant I have used and the cheapest which makes it the best in my books ....


Cheers

[Ibanezfoo]

Fresh stuff etches in ~30 mins or so.

30 minutes?      Heat it up a little and it will take about 5 minutes.

Is it microwave safe?  (minus the copper board obviously )

[John Lyons]

DO NOT HEAT MURATIC and H20o2!!!!!!!!!!!
It does not matter how warm it is it works fine cold.
Plus it will possibly react to heat and explode!

John