(C) Daily Kos This story was originally published by Daily Kos and is unaltered. . . . . . . . . . . WAYWO : Etching, Recycling, and Electrochemistry [1] ['This Content Is Not Subject To Review Daily Kos Staff Prior To Publication.'] Date: 2024-06-09 I’ve previously showed off the stand I 3D printed to go in my etching tank that didn’t come with one. Etching stand 2.0 Carbon fiber arrow shafts held together with beefed up epoxy coated 3D printed parts. Then I showed off the second after the first started falling apart. Apparently acid does that to things. The second one is coated in epoxy and it’s holding up fine. I use ferric chloride to etch copper and brass, an alloy of copper and zinc. Ferric chloride -- (FeCl3), one iron atom (Fe) with three chlorine atoms (Cl) huddled around it is an orangey reddish black brown in solution and it stains everything. If you get it on your clothes your best bet is take the item and submerge it in the tank because that stain ain’t never coming out. Ferric chloride etches by way of a redox (reduction-oxidation) reaction. Chlorine in the etchant attaches to the copper, forming water soluble copper chloride which dissolves. In turn the ferric chloride becomes ferrous chloride (FeCl2).1 2FeCl3​+Cu → 2FeCl2​+CuCl2​ Ferric Chloride FeCl3 Where a copper substraight is exposed to the ferric chloride etching occurs. Metal protected by a “resist” is unaffected. There are many resists. Rembrandt used asphaltum also called “ground.” It’s dissolved in a solvent and poured over a copper plate, the excess allowed to drip off a corner, leaving a thin brown coating that when dry is easily scratched through to expose metal. In college I worked as an engraver and this is what we did but on steel. The solvent was chloroform. These days I use turpentine. Other resists including paint, lacquer, wax, some types of fingernail polish, Sharpie, plastic tape and what I most often use -- photo-transfer film. Pulled from the net, scaled and reverted this pattern has been etched several time. I draw a pattern (generally on a computer) and laser print or photocopy it onto the transfer film. The carbon from the laser printer is then transferred to a piece of copper or brass by ironing the printed surface against the metal. That then is soaked in water and the film is peeled back like a decal, leaving the carbon image attached to the metal. Where the carbon is, the metal will not etch. Where it isn’t, it does. The copper cleaning bucket. Note how long the anode once was. Copper plated on the graphite cathode. Stepping on the accelerator to pick up the pace on copper removal. LWIR image There are many other enchants, however, I know ferric chloride and just dropping it in the tank and walking away for ten or twenty minutes is easy. Eventually the etchant gets used up and all that’s left is cupric chloride (CuCl2) and ferrous chloride which won’t attack copper. Spent iron chloride etchant needs to be sent for hazardous waste disposal. That’s expensive and it then needs to be replaced, also expensive. Hobbyists often pour it down the drain. If not for the copper, that wouldn’t be a big deal. Not legal but also not any more damaging to the environment than all the other things that we’re allowed to pour down the drain. The presence of copper however makes it an environmental toxin. I recycle it which is where the electrochemistry comes in. First the copper is removed using electricity. Spent etchant is put in a bucket with two electrodes opposite one another. The negative terminal of a power supply is connected with a wire to a piece of graphite to make a cathode. The positive terminal is connected to a piece of iron or steel to make an anode. The copper plates out on the graphite, freeing chlorine, which (if the voltage is correct) mostly remains in solution. In turn the iron anode dissolves into the soup reacting with the free chlorine making more ferrous chloride. Eventually all the copper is removed, leaving a solution of only ferrous chloride. All that can take a good deal of time. Alternatively, turning up the voltage to drive off chlorine while pumping in iron quickly leads to a warm if not hot saturated solution. Ferrous chloride needs to be converted back into ferric chloride to be used again. There are a couple ways to do that. The easy fast way is to add hydrogen peroxide, slowly. An energetic reaction follows which can easily make a huge mess. Yes, experience. It also dilutes the solution which means it must be dehydrate. And of course, I have to buy hydrogen peroxide. There’s another much slower way that costs me basically nothing. Namely, bubble air through it. I do that with a battery-backed-up aquarium pump powered through a USB cable connected to a small solar panel. During the day the panel runs the pump and charges the battery, and at night the battery runs the pump. It takes about a month of bubbling to convert a gallon of ferrous chloride back into ferric chloride. Although there is a drastic color change from light green to dark orange-brown there’s a more definitive way to tell when it’s done. Bubbling air through ferrous chloride creates a substantial amount of surface foam. Bubbling air through ferric chloride doesn’t. When there’s nearly no foam, it’s done. The aquarium pump in the shade and solar panel not in the shade. An old apple juice bottle filled with recently converted ferric chloride. As I added iron to the mix there is no longer enough chlorine to change all the ferrous chloride (FeCl2) into ferric chloride (FeCl3). I can add chlorine by adding hydrochloric acid (HCl). Unfortunately this dilutes the solution. 4FeCl2 + 4HCl + O2 → 4FeCl3 + 2H2O If I don’t add hydrochloric acid I still get ferric chloride. The molecules cannibalize each other. Some ferrous molecules are stripped of their chlorine and the loose iron takes up the oxygen. 12FeCl2 + 3O2 → 8FeCl3 + 2Fe2O3 The result is ferric chloride and iron oxide (Fe2O3) also known as rust or rouge or makeup. Iron oxide isn’t soluble in water so it falls out of solution and could be filtered off. Interestingly mixing hydrochloric acid and rouge makes ferric chloride and water directly. Fe2O3 + 6HCl → 2FeCl3 + 3H2O Currently I have about 5 gallons of etchant. A gallon in the etching tank, a couple of gallons being cleaned and a couple of gallons that were mostly ferrous six weeks ago and mostly ferric now. They’re dilute however. I’ll let them sit in the Sun for a couple of weeks to dehydrate before I squirrel them away. I only do this every few years. Pulling the copper out is tedious and messy, so I put it off. Hey kids, have fun at home forcing crystals to grow with electricity. That’s the pile of copper I melted down. The anode on its way to nonexistence. Done!!! Notice how short the anode is. Since I started writing this, I finished cleaning 2 gallons of spent etchant. I electrically drove off so much chlorine and pushed so much iron into solution there was no chlorine left for the copper. A few mornings ago when I checked, green crystals of ferrous chloride had plated out and grown on the graphite. There were more at the bottom of the bucket mixed in with metallic copper. I poured off the fully saturated ferrous chloride and then added water to the sludge at the bottom of the bucket. The crystalized ferrous chloride dissolved and I poured it off too. Then I collected the copper that had settled out. Ferrous chloride being filtered. I’ve also since melted down, rolled out and trimmed some of the metal I pulled out of the etchant. As I did last time I’ll leave a couple of gallons ferrous and when I’ve collected two or three gallons of used etchant I start the whole process over. Every time I do this I reinvent in my head a solar powered semi-self maintaining machine that automates this whole process one drop at a time, a reservoir for spent etchant at the top and one for renew etchant at the bottom. Then when I’m finally done, I promptly forget all about it. Some recovered copper melted and rolled out into 18 gauge metal. 1) It’s actually immensely more complicated. [END] --- [1] Url: https://www.dailykos.com/stories/2024/6/9/2240398/-WAYWO-Etching-Recycling-and-Electrochemistry?pm_campaign=front_page&pm_source=latest_community&pm_medium=web Published and (C) by Daily Kos Content appears here under this condition or license: Site content may be used for any purpose without permission unless otherwise specified. via Magical.Fish Gopher News Feeds: gopher://magical.fish/1/feeds/news/dailykos/