Calculations for PCB etching solution.

[juma]

Hi
I'm building GRollins' Aleph X and I want to use regulated power supply (got some LT1083s left from other project).
Did anyone tried that ?
I would like to know how does that affect the sound ?

Here is the PCB I made - one sided, old DIY method - water-resistant marker, HCl (15-30%) + H2O2 (10-15%)

bottom view:

[juma]

top view:

[Nixie]

Originally posted by juma
HCl (15-30%) + H2O2 (10-15%)

I hope these are not in a 1:1 ratio, even at these concentrations, or else you are wasting peroxide -- it's only a catalyst and not used up in the reaction, and a smaller amount will speed up the reaction since you're diluting the acid less.

[carpenter]

Excellent effort on the pcbs, juma. Hope it works well for you. How does that process work? I'd like to give it a shot.

John

[juma]

Hi guys,
it's an old DIY method (I used it for prototyping when I was more in electronics - back in '80s).
You prepare a drawing of PCB on the paper, scotch-tape it over the CLEANED and dried virgin board, drill the holes, use the waterresistant marker to draw the connections.
Then you mix the small quantities of chemicals (muriadic acid and hydrogen peroxyde) in plastic or glass container as Nixie said and dip the board in. After a few minutes (depends of concentration of chemicals) the copper will be eaten and the areas protected by marker will be untouched by acid. Now you clean the board with aceton, wash it, dry it, smear it with soldering cream, use the small amount of solder to cover the copper, clean it again and that's it.
Take care, there will be some heat and fumes in the procces.
I personally prefer the P2P building, but this design will need a lot of tinkering, so I went for the PCB.

But my question was about regulated power supply for Aleph X - did someone try it ? How did it affect the sound ?

[metalman]

Originally posted by Nixie
I hope these are not in a 1:1 ratio, even at these concentrations, or else you are wasting peroxide -- it's only a catalyst and not used up in the reaction, and a smaller amount will speed up the reaction since you're diluting the acid less.

Ever seen the experiment where someone has taken a jar, filled it with a 50% HCl acid solution, put a piece of copper in it, sealed the jar gas tight and left it to sit for a few decades. Absolutely nothing happens to the copper because the corrosion reaction is driven by the presence of dissolved oxygen, and with the jar sealed tight, the small quantity of dissolved oxygen in the solution isn't enough to generate even a superficial amount of copper dissolution.

For etching board, oven the period of minutes to a few hours, the amount of oxygen that is absorbed by the solution in that time is nearly negligible. Add peroxide, and as the corrosion reaction consumes the dissolved oxygen, the peroxide breaks down generating more dissolved oxygen to keep the corrosion reaction going.

Long story short: Peroxide is not acting as a catalyst, it is most definitely a consummable.

Now for those who would argue that Ferric Chloride solutions don't need peroxide, that's because the reaction of ferric (Fe3+) ions to ferrous ions replaces dissolved oxygen reaction.

Don't make me derive the Butler-Volmer equation for all of this.

Cheers, Terry

[Nixie]

Peroxide is only consumed a little in the very beginning of the reaction. Once there is some CuCl4(2-) in the solution as the copper begins to dissolve, no more peroxide is needed as the solution will begin taking oxygen from the air. The solution can be refreshed many times by simply adding more acid and exposing it to the air; no further addition of peroxide is needed.
Thanks to woelen for the formulas:
H2O2 --> H2O + O.
O. + 2 H(+) + Cu + 4 Cl(-) --> H2O + CuCl4(2-)
At this point the reaction has started and peroxide is no longer necessary.
The CuCl4(2-) dissolves more copper:
CuCl4(2-) + Cu --> 2 CuCl2(-)
The CuCl2(-) can be oxidized by air alone:
O2 + 2 CuCl2(-) + 4 H(+) + 4 Cl(-) --> 2 H2O + 2 CuCl4(2-)
The latter two reactions continue while there's enough copper, acid concentration, and air.

Alternatively, you can just put some CuCl4(2-) into the acid instead of peroxide, say by saving a bit from a previously used up solution.

[carpenter]

Don't make me derive the Butler-Volmer equation for all of this.

Oh my god--you wouldn't!

John

[metalman]

Nixie,

Glad to see someone do their homework!

There is only one catch to the scenario you present.
O. + 2 H(+) + Cu + 4 Cl(-) --> H2O + CuCl4(2-)
In order for the gibbs free energy of the above reaction to be negative, the dissolved oxygen concentration must be well above the saturation limit of oxygen in water. Further, the following reaction has a much more negative free energy than that of the above reaction, meaning that it will take place preferentially.
O. + 2H(+) + Cu --> H2O +Cu(2+).

I've attached the Pourbaix diagram for the Cu - H2O - Cl system for your reference. Note that CuCl4(2-) is not present as a stable specie. (Reference: D. Tromans & R. Sun, Journal of the Electrochemical Society, Vol. 138, pg. 3235 (1991)). Note that the area notated by the "*" in the diagram represents the area of stability for CuCl2-3Cu(OH)2.

Carpenter,

Yeah, the first of two graduate level electrochemical engineering courses I took during my masters degree consisted solely of deriving, from first principles, the full Butler-Volmer equation, including the extensions for mass transport and fluid dynamics (including turbulent mixing). That was one course I thought would never end.

Cheers, Terry

[carpenter]

You're one smart guy, Terry.

John