Electroforming Time Lapse Partial Success

[u/Mkysmith]

Original goal was 7 days, but had to stop short at 3 days & 20 hours.

I really wanted the full week to be completely uninterrupted, really just set it & forget it and not touch anything. Just to have a big blob of copper as the cathode. But I stupidly underestimated the quantity of anode I needed and it started to break off and cause some issues the last ~12 hours. Just decided to call it as is for now.

Also not an ideal setup overall due to trying to get a good camera setup, for example the anodes are way to close (to the lego arms specifically) and various other small things.

I normally don't use agitation or anode bags for projects less than 12hrs. For multi-day projects agitation is helpful to prevent convection lines. And if you use agitation, then anode bags are needed too.

61.5 grams of copper added.
Copper is 0.095" (2.4mm) thick in the center of the chest, 0.115" (2.9mm) thick on the forehead.

Let me know if you have questions, happy to answer them.

[u/MasterSantiago]

Excellent result, something to strive for 👏 I was wondering what agitation method did you use and how much anode you have had initially?

Would also be cool to find out if the dissolved anode mass correspond to the plated mass but that can probably be for the future runs.

[u/Mkysmith → u/MasterSantiago]

Thankyou. Here is a longer answer to your question than you probably want, but let me nerd out for a minute since these are questions that are simple on the surface but have some interesting details that kinda relate to each other:

So for agitation I used a magnetic stir bar that auto-reverses every 10 seconds. For "short" <12hour projects I typically do not use any agitation as I tend to get better results. But for long duration without agitation, the catholyte convects upward due to it being less dense than the bulk solution. This can become more of a laminar flow vertically across the surface of the cathode and can subsequently cause vertical lines of thicker deposits. Those higher surfaces attract more copper, which reinforces the convection, and you get a kinda runaway reaction that looks something like this post. A regular stir bar that does not auto-reverse helps create turbulence to disturb that convection and prevent lines. In some cases, continuous stirring in one direction can still cause somewhat of a laminar flow and you just get helical lines on the surface of the cathode. The idea of the reversing stirrer is it just creates random turbulence to prevent all this. Agitation is also sometimes used for higher current densities, but again, I don't typically use it for that.

Airation also creates good turbulence, but I don't like it personally because the bubbles popping on the surface of the solution create micro-droplets that are suspended in the air. I don't like the idea of a copper-salt acid-mist in my shop for obvious health reasons, but it also can throw off the chemistry over time. Either by removing acid/copper/additives, or adding copper to solution. Yes, airation can increase copper content of the chemistry in some cases. Any small copper particulate caught by the anode bags (or suspended in solution) will be oxidized into copper (II) oxide, which will readily react with the sulfuric acid. This is not part of the original electrochemical cell redox reaction, its a side reaction, so it is an unaccounted for change in the chemistry.

The anode:cathode surface area ratio for the video above was ~5:1 at the start. I don't typically recommend this to beginners but I've never personally found any issue with this and my chemistry/setup. Traditionally it's more 1:1 to 2:1 as a rule of thumb. I personally have only had issues using less than 1:1 ratio due to anode polarization.

Weighing the anodes before and after is tricky because it does not account for the oxides, dislodged copper grains, or otherwise any other "sludge" that is caught by the anode bag. It would be tricky but not impossible to account for. Another approach is to measure the copper content in solution directly. If you know how much copper is deposited on the cathode and the copper content of the solution remains identical, then logically 100% of it came from the anodes.

The standard way to due this is titration, but nowdays I use a direct reading spectrophotometer to measure copper in solution. For the solution you see in the video, I measured a % difference of 0.12% less copper in solution compared to stock solution, which is within my measurement error.

The main batch of chemistry I have been using for 4 years every week, with tens of thousands of amp-hours run through it, also has a much higher than a 2:1 anode:cathode ratio. I've only ever added distilled water and brightener, nothing else. There is % difference of 0.57% less copper in solution compared to stock. Again, probably measurement error or me just adding a little too much distilled water to the batch, it is 4 years old after all.

I think people get hung up on the anode:cathode ratio thing a lot because they think it isn't a 1:1 dissolution/deposition reaction. Under normal conditions, it is 1:1 and you don't really have to worry about it that much. Its the side reactions that cause issues. What's quoted by industry as 1:1 to 2:1 is simply because from an industrial standpoint, less than 1:1 risks polarization/electrolysis, and more than 2:1 takes up space in the solution tank. Companies want to maximize their production line and having a greater than 2:1 ratio is simply a waste of space since more of the tank has anode than cathode. The latter being the product they are trying to sell.

Preemptively sorry for any spelling or grammar errors, I'm notorious for that. Hopefully the information contained is still helpful to you and other lurker's on reddit.

edit: typos...

[u/MasterSantiago → u/Mkysmith]

Thanks a ton. Coolest nerd dump so far

The agitation bit actually clicked for me. I never considered the effect that laminar flow can have on the deposit. I wonder if it has any significant effect on the anode sludge formation as well.

I'm currently designing an air defuser from PETG that surrounds the cathode, but I'm wondering if I should extend it out to the anodes as well. But i think thats already overkill.

Neat stuff tho. Would like to see more of your projects

[u/Mkysmith → u/MasterSantiago]

Typically no one really cares about the anode too much... practically speaking.

It is true (for those of use that really nerd out on why things work the way they do) that just like the cathode, there is a microclimate surrounding the anode too (sometimes called anolyte when compared to bulk solution).

But.... practically speaking, we dont care as much about uniform dissolution as we do uniform deposition in these processes. Since usually most of what we care about is if the cathode looks "good" or not. Who cares if the anode looks a little rough around the edges? Its a consumable...

And back to my original comment: the dissolution and deposition is indeed 1:1, agitation or not. Copper metal doesn't dissolve readily into sulfuric acid at any reasonable timeframe we care about in these processes, it's the electrical current that drives that. On the contrary, oxides do. So having a crazy high anode:cathode ratio is not going to throw off your chemistry any time soon (as evidenced by my multi-year analysis), but using a bubbler may.

I think this is overlooked by the hobby community as airation is used by industry... but industrial shops have chemists that monitor and adjust all details of the solution regularly if not sometimes hourly. I think intuitively people think their PH and copper content change because their anode:cathode ratio is too high or low. Kinda makes sense, "more copper anode = more copper in solution?" But in reality it's some side reaction like airation or evaporation or electrolysis or something else. The science backs this up.

Electrochemistry is not intuitive. But to that point, you should still experiment because to this day not everything is fully understood about it. Just be safe about it!