Homebrew PCBs

I did another test. This time I simply put clean copper 
metal in the 20% acid and bubbled lots of air through it. It 
took just over 3 hours to completely dissolve the copper and 
produce a deep green colored cupric chloride etching solution.

makeup data:

40 ml of  26%wt HCl acid
20 ml of water
8.7 grams of copper.


Here are some pictures of the test.
First pic is after 5~10 minutes, the second is after 2 hours.
http://www.alphalink.com.au/~seychell/CuCl2_prep03_5minutes.jpg
http://www.alphalink.com.au/~seychell/CuCl2_prep03_2hours.jpg

I haven't got a picture of the final solution, the camera 
got taken away.

Some notes:
* Its clear that atmospheric oxygen feeds the reaction, so 
more air that comes into contact with the solution the 
faster the copper dissolves. Fine bubbles are a *BIG* 
advantage here. A previous test showed it takes about 48 
hours when bubbling large bubbles from the end of a hose.

* The reaction accelerates as copper is dissolved. Initially 
the solution goes from clear to slightly green, then slowly 
becomes an olive brown in 1 hour, then to a dark brown in 
rather quickly there after. After 2 hours the reaction rate 
is enough to generate a significant amount of heat. This 
heat further accelerates the reaction. I thermally insulated 
the vessel and measured the temperature stabilized to about 
20\ufffd above ambient (38\ufffdC). Heat loss would of occurred from 
the air passing through the solution.

* For some strange reason the bubbles produce an increasing 
amount of foam as more of the copper dissolves, until at the 
very end when the solution is green (i.e. no copper(I) 
remaining) the foam gets to a stage that its difficult to 
control. You may need up to 100 mm of head room for the 
foam. All of the experiments I've done had this exact same 
effect.
I suspect the foam has an advantage because it would 
increase the air contact area to the solution.


Adam