[AR] Re: Electroforming Experiment
- From: Peter Fairbrother <peter@xxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sat, 13 Jul 2019 20:38:24 +0100
On 13/07/2019 17:46, Ed LeBouthillier wrote:
On Sat, 2019-07-13 at 16:30 +0100, Peter Fairbrother wrote:
What bath chemistry are you using? "Acid copper" covers a multitude
of sins, from high-speed baths at > 300 g/l copper sulphate to high
throw baths at less than 60 g/l.
I used a basic 8oz Copper Sulfate + 8ml Sulfuric Acid + 1 quart
distilled water with a PEG leveler. Midas Bright was the brightening
agent.
Also: (about 0.04 Amps/sqin)
First impressions: Copper level is ok; not enough acid; current too low;
too many additives.
The copper level is about medium. As you are not using very high
currents or acid concentrations, this is fine.
Did you mean 80 ml of H2SO4? 60ml might be more appropriate, but 8ml is
just too little. Insufficient acid limits the maximum current, and
except at very low currents makes the deposits spongy and occludes
copper salts in the deposit.
Some typical baths, in g/l:
Normal:
CuSO4.5(H2O) 200 - 250
H2SO4 45 - 90
High Throw:
CuSO4.5(H2O) 60 - 100
H2SO4 180 - 270
Too low current causes large grain sizes.
Typical cathode current densities:
Normal - 2-7 A/dm^2
electrotypes (good agitation, continuous filtering): 20 A/dm^2
High current (cooled, very high agitation, PCR) - 50 A/dm^2
Cathode current densities of less than 2A/dm^2 are not often used.
0.04A/sqin is 0.62 A/dm^2 - this is not really enough for a good deposit.
Anode current densities should not exceed the cathode density, or
5A/dm^2, whichever is larger.
PEG in very low doses can just about be used as a leveller, though
high-temperature properties are affected - pentoses are perhaps better.
I have no experience with Midas Bright[*], but most people would not
recommend it for copper which needs good high-temperature properties.
In general, chambers are mostly made from additive-free copper baths -
or maybe one levelling additive at most. Brighteners are for jewellery.
Most additives mess up the high-temperature strength pretty badly, even
in tiny amounts.
HTH
Peter Fairbrother
[*] except it contains carcinogenic benzidines. It also contains cream
of tartar.
Other related posts:
