Sciencemadness Discussion Board

Platinum anode - odd reaction

elementcollector1 - 23-11-2012 at 17:34

My 1" Pt wire is doing something very strange. I taped it to a copper wire to act as anode, but every time I turn it on it creates several blackish-brown insoluble particles. This has happened in chloride solutions mainly, but I have not had the chance to test it with other anions.

hissingnoise - 24-11-2012 at 03:04

It's most likely that the particles are chips of copper oxide!
Taping the wires together won't form a secure connection and some surface oxidation will occur . . .

elementcollector1 - 28-11-2012 at 16:42

How resistant is platinum wire to chlorine, anyway? It should be immune, but still.

hissingnoise - 29-11-2012 at 02:55

Platinum is practically inert to chlorine . . .

Fleaker - 30-11-2012 at 19:23

Not so at all.

Bulk platinum might be (sheets, thick wire and the like), but I use Cl2/HCl to solvate platinum sponge every day.

elementcollector1 - 30-11-2012 at 19:33

Well, sponge is probably a bit more reactive than wire.
Still, this worries me, as I thought platinum was the ultimate anode; inert to just about anything but aqua regia...
I don't need it for anything but a chlorine-related anode, though. And an element sample. What does tarnished platinum look like?

kadriver - 3-12-2012 at 20:51

Quote: Originally posted by elementcollector1  
How resistant is platinum wire to chlorine, anyway? It should be immune, but still.


I use chlorine (HCl/clorox) to dissolve platinum from catalytic converter substrate. Chlorine will dissolve platinum, but only very slowly.

kadriver

kadriver - 3-12-2012 at 21:02

Quote: Originally posted by elementcollector1  
Well, sponge is probably a bit more reactive than wire.
Still, this worries me, as I thought platinum was the ultimate anode; inert to just about anything but aqua regia...
I don't need it for anything but a chlorine-related anode, though. And an element sample. What does tarnished platinum look like?


I was making some standard test solution by dissolving 100mg of pure platinum metal in hot aqua regia. The piece of platinum was about the size of a grain of rice.

It took me almost eight hours with multiple additions of fresh aqua regia and constant heat to get it to dissolve - even after all that there was still a tiny thread of the metal that remained undissolved.

Also, platinum will not discolor after being heated to redness or even bright yellow. It is one of the few metals that has this quality.

If one wants to prove a piece of platinum all you need to do is heat it until it glows bright yellow, then let it cool to room temp. If it is platinum, then it will look as if the a flame had never touched it.

kadriver