Normally Ti is etched using HCl before depositing the MnO2. However this method does use a lot of concentrated HCl and handles a lot of
nasty boiling acid.
Now, there's a way of etching Ti, that does not use HCl. Instead the Ti is submerged in boiling oxalic acid solution (mine was about 15%) and
connected up to the negative (yes, the negative) lead of a power supply (in this case 10V but that might not be optimal). The positive is connected to
a graphite rod, also suspended in the solution.
The solution begins to bubble and boil vigorously at the relatively small anode while the titanium cathode starts producing hydrogen and the solution
turns yellow on the surface of the titanium. After a while (like 2min in this
case) electricity is disconnected and the titanium is boiled for another few minutes. Apparrently the cathodic conditions reduce the titanium's
passivation layer and expose the bare metal, essentially activating it and allowing it to react with the acid.
I also tried hooking things up the other way round but that only resulted in some really gay looking rainbowy titanium (no offence intended).
Now, is this process any useful? It certainly is to me so I can conserve my HCl a bit and the etching bath is easier to store. Though I should add
that this process produces an oxalic acid aerosol, which is a bit harsh to breathe, so it's still not ideal.
Note: In the picture(s) the copper wire is also in the solution and I got away with it but it's definitely something to avoid. You can see a bit of a
redish deposition of copper (oops) on the etched Ti but that was easily wiped off and the electrode turned out fine.
[Edited on 1-8-2021 by BAV Chem] |