(Note: I am an economist, not a chemist. Please depart a remark for those who’ve received any corrections and/or additions to these things!)
I came upon this concept after I noticed this web site: Etching with Air Regenerated Acid Cupric Chloride by Adam Sechelle. Cupric chloride could be re-used indefinately by topping up the acid ranges and including oxygen (bubbled in from the ambiance). Sounds low-cost and environmentally pleasant besides.
The web site’s received a number of good chemistry data on cupric chloride etching. His knowledge on etching speeds is nice, and his simple titration procedure for sustaining the acidity of the answer is fairly good.
To make the cupric chloride answer, he dissolves a bunch of copper wire in hydrochloric acid, and mentions possibly utilizing hydrogen peroxide to hurry up the oxidation, however would not go into element.
Which received me pondering. You did not have any cupric chloride but, however you can also make it by dissolving copper. Dissolving copper is the identify of the etching recreation. So we are able to make one etchant that makes one other etchant that is infinitely re-chargeable. Elegant.
Turns out that hydrochloric/peroxide is a typical home-brew etchant (and I’ve re-re-invented the wheel, once more) however I assume that individuals received so used to throwing away their “spent” etchant that they do not take into consideration re-using it. The complete level of this instructable is that you do not throw it away, however use the dissolved copper forevermore as your long-run etchant.
Here’s what is going on on chemically:
Before there’s a lot copper dissolved within the answer, Cu + 2 HCl + H2O2 -> CuCl2+ 2H2O is the dominant internet response. That is, the additional oxygen in answer from the peroxide is oxidizing the copper steel, in presence of the acid, to make copper (II) chloride. That’s our starter etchant. The ensuing CuCl2 shoud be a pleasant emerald inexperienced shade.
After you’ve got dissolved a number of copper into the answer, and used up all of the peroxide, the copper chloride does a lot of the etching for you: CuCl2 + Cu -> 2 CuCl. That’s the tip etchant.
Eventually you etch a lot that you simply convert all of the CuCl2 into CuCl, which does not dissolve copper (and is a yucky brown shade). As lengthy as you’ve got received sufficient acid within the answer, you possibly can merely add extra oxygen to re-oxidize the copper(I), making extra copper(II) chloride and water: 2 CuCl + 2 HCl + O -> 2 CuCl2 + H2O. And then you possibly can etch once more.
Two issues to take care of: CuCl2 ranges and acid ranges.
CuCl2: After all of the peroxide is used up, and the answer begins turning brownish, you may have so as to add oxygen to regenerate the answer once more: toss in a number of extra capfuls of peroxide or bubble air by the answer or swirl it round vigorously, or simply pour it into an open container and wait. It’s simple to inform once you’re able to etch once more, as a result of the answer turns inexperienced.
It’s additionally unimaginable so as to add an excessive amount of oxygen by including air, so bubble/swirl to your coronary heart’s content material. If you are utilizing peroxide so as to add oxygen, be sparing — a little bit goes a great distance, and it is largely water so that you’re diluting your etchant by including it.
Acid: Note that HCl is being consumed within the starter etchant and the regeneration reactions. So we will have so as to add a bit extra acid as time goes by. If you discover that it is more durable to re-green your brown etchant, it is most likely time to start out pondering acid.
I’ve tried the titration described on Adam’s website a pair occasions, and it is fairly simple however requires an correct scale and pure lye (again to the ironmongery shop…). It’s simpler to only toss in a capful of acid each few batches of boards, which appears to do the trick for me.