I'm glad to see its finally working.
As I learned on the weekend, the bubbles is what makes the
process move forward. It was a bad idea to initially let the
copper stay in a stagnant solution. The correct method is to add
all the acid and copper together in one hit and bubble it like
crazy. Then wait until it turns to a transparent deep green. At
150g/L of copper (SG 1.3) you won't see through more than 1cm
without a bright backlight. A drop on white surface shows up nice
bright green.
Thanks for this link,
http://www.pacificsun.ca/~robert/pcb/cucl.htmI like his idea of HCl titrations using a eyedropper and counting
the drops. Just look for the formation of insoluble Cu hydroxide,
which will turn the solution cloudy. The eye dropper method is
good enough for determining the acid content of this etchant. An
indicator will make it easier. I'll post more analysis details
another time.
The HCl can be very low 0.1M and still etch perfectly ok. At very
high say 3M then it will create more fuming. The HCl should never
be zero because air regeneration cannot happen and your solution
will quickly build up insoluble copper(I) film over the copper
and inhibit etching.
One thing I noticed in the article is that he uses much lower
copper content (100g/L of CuO) or 80g/L of copper. I'm sure at
140g/l copper you get over double the speed, I'll have to check
that again.
Grant, you mention 5.0 pounds of copper (2.3kg). if you desire
140g/L of dissolved copper then you looking at 16 liters of
etchant !. Thats a lot of etchant :) Worry about disposal another
day.
The HCl will needed to react with all this copper and have some
left over for about a 1M of free HCl then you'll need;
Moles of copper = 2300grams / 63.5 = 36 moles
Cu + 2HCl -> CuCl2
So you need twice as many moles of HCl than moles of Cu, or 72
moles. You also need another 16 liters ∗ 1 Mole/liter = 16 moles
of HCl. Total moles of HCl = 72+16 = 88.
according to.
http://www.starch.dk/isi/tables/hcl.htmand the fact that molecular weight of HCl = 36.g grams/mole
then
30%wt HCl = 345g/l = 345/36.5 = 9.5 Moles/Liter.
then to calculate the volume HCl needed to get 88 moles
Total volume of 30% HCl = 88/9.5 = 9.3 liters.
I hope I'm making some sense here.
Adam
grantfair2001 wrote:
> I am happy to say that I can now see unmistakeable signs of progress
> with my etchant. I now have about 17 litres of it, in a 34 litre
> Coleman cooler, gugrgling away on the floor next to my laundry tubs.
>
> The air bubbler I made is the type described at Think & Tinker:
>
> http://www.thinktink.com/stack/volumes/voliii/equipmnt/bubltank/bubltank.htm
>
> I am using air from the exhaust output of a small vacuum pump.
> Sometime recently, the bubbler started putting out more air, so almost
> all the surface of the etchant is constantly bubbling vigorously. I
> don't know whether the sparger moved, or the pump, which has carbon
> vanes, suddenly decided to put more air out. The pump has been running
> continuously for several days with only slight heat to the touch for
> the motor case. The pump casing seems even less warm than the motor
> casing.
>
> Anyway, I can see two changes tonight (in addition to the more
> vigorous air bubbling).
>
> The etchant is an even deeper brown color than it has been for a few
> days. It is so dark I can hardly see the wire under the etchant
> surface. And all the remaining wire is clearly decreasing in diameter.
> (I hung one piece of copper wire over the edge of the tank about 4
> days ago. The etched part is 1/2 the diameter or less than the
> unetched end). Also, at the start, the whole mass of copper wire was a
> large jumble, with some wire under etchant and some above it. Clearly
> the etchant is working, because the level of wire above the surface
> has substantially decreased.
>
> It is great to see this working, after the slow start I had, and all
> my worrying and wondering. I hope I will be able to start etching
> boards within a week or so. Yahoo!
>
> I do like this process because:
>
> 1) it is non-polluting
>
> 2) replenishing HCl is cheap and easy to do
>
> 3) a Coleman cooler, 8 litres of HCl, and 5 pounds of copper wire,
> along with a bubbler are all it took me to get started, (along with a
> hell of a lot of advice)
>
> 4) this list is a great source of information and encouragement
> (thanks Adam, and everyone else who helped!)
>
> 5) cheap and dirty chemical analysis is possible - see:
>
> http://www.pacificsun.ca/~robert/pcb/pcb.htm
>
> for related work by Donald Aitken and Robert Grauman
>
> Grant
>
>
>
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