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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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More curious electrochemistry
I was unhappy with the depth of my brass etching. Calculations
suggested that I should be getting about 0.020" depth for the given current and time but I was getting about 0.006". I thought that the explanation was that the current was wasted on gas production at the anode (whatever the gas may be). I was not sure what the problem was. I found a pot of my old electrolyte (bought from a commercial vendor) and tried it. I quickly found two things; 1) At current density over 0.1A/cm2 there was gas production on anode and if one went even higher there was gas production on the cathode as well. 2) At the beginning of the process there are some weird things happening. My power source delivers constant current and to do so the voltage fluctuates wildly (up to 20 V) and at one point there was an oscillatory type of effect where the voltage dropped, gradually increased and dropped again at about 1 of these events every two seconds. Anyway I managed to etch a piece of brass and separately a piece of copper with an area of 100mm2 to the depth of 0.009" which was consistent with calculated prediction. Today I tried my new electrolyte (CuSO4, H2SO4 in H2O) on a piece of brass with an area of about 450 mm2 (I had an accident with the resist). At the start of the process I set the current at 0.45A and got it with hardly any voltage at all. At 8 minutes the instability started as above, then it settled with the current steady and voltage of 10V. After 90 minutes the instability reappeared but was less dramatic, the voltage oscillating between 2 and 4 volts keeping the current steady. There was no detectable gas production throughout. I went for total 2 hours. The result is he http://www.flickr.com/photos/2768312...in/photostream I cannot even begin to guess why the current blew a hole where it did while only removing between 0.0065" and 0.0075" elsewhere. The cathode, BTW, showed a pretty even deposit of copper throughout. Michael Koblic, Campbell River, BC |
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