I use electrolysis for rust removal and electroplating. I notice that when one of the electrodes is a closed tube or has other topological holes with a sufficiently large height:diameter ratio, the inside surface does not react.
My hypothesis is that current is not flowing through these surfaces because I didn't pay attention in the electromagnetism part of Physics 1 in high school, and karma has finally caught up with me 25 years later.
My questions are:
What is going on here? I vaguely remember something about Michael Faraday. Am I on the right track?
More importantly, how can I induce a reaction on the inside surface? Will running the opposite electrode through the hole work?
Here is a video of the effect: https://youtu.be/H6TrLn8TkS8
|Reaction visible on outer surface||Calm, quiet inner surface|
I don't think the setup details are that important, since the context here is physics not chemistry. However, for completeness, an example setup:
- electrolyte is sodium bicarbonate and distilled water
- both electrodes are mild carbon steel
- cathode is a square tube
- width of electrodes and distance between them is pretty much the same order of magnitude as the diameter of the tube, lengths of electrodes are one higher order
- typically running 5-10A at 12-20V
- electrolyte temperature held around 100-130F