What caused the unexpected results in my electrolysis of Iron Oxide?

[daniel350]

I for inquisitional purposes only recently attempted electrolysis of Iron to create Iron oxide. I used a car battery charger (12v, 2.7A) and two large (assumed iron) nails; a de-ionized water solution (200ml) with approx. 15g sea salt (claimed 99.995%).
After starting the reaction (outside with respiration), it appeared to be going well; however as time wore on (approx 15minutes), the solution turned clear, with large bubbles containing all the solutions previous red particulates.
Inquisitive, I watched it from afar, and saw it transition from the following colours: [clear, green, blue, grey]. I saw it stay this grey colour for the rest of its duration with large particles floating around, the froth on top had now grown to 2cm high, and was largely green and red (appeared as fine particles coating the bubbles).

To say the least, it looked disgusting. However I took my precautions with it, seeing as it was an unknown and without further investigation diluted and disposed of it. The submerged sections of the nails were a dark black and appeared to be what may have been solid iron; after 3 minutes however this dark black section became fully oxidized (rusted).

After seeing all these estranged results, it appeared that things had not gone to plan. :p
I theorized it to be a mix of Iron Hydroxide after using the search engine, (and turning up this which had some resemblance: http://webpages.charter.net/dawill/tmoranwms/Chem_FeOH.jpg - however less thick); and it appeared to be in too great a volume to be the zinc protective coatings that was on either nails.
And my theory for the green coloured bubbles/froth I could only see as electrolyzed chlorine gas that had not escaped.

Is anyone able to shed some light on these results, and perhaps confirm / destroy my theory's as what it may have been.
P.S: This is not for anything specific, I already have large amounts of FeO in storage, it was purely inquisitorial as stated above. (received some flak on another forum).

 

[corradini]

Funny you should mention it - I was just doing this yesterday, and just happened upon PF (for a totally different reason) today.

First of all -- seems someone's already spanked you, assuming you're making thermite. (A) I'm not going to (assume OR spank) but: (B) for anyone who's THINKING of doing it, please, PLEASE watch a bunch of YouTube videos first (including the guy who accidentally had his tiny pile of lit thermite spark off his full container, a few feet away, on his back porch). Thermite will melt through concrete. It gives off WHITE-hot molten iron.

I've done aluminum casting, and a 500g crucible of molten aluminum is hard to be NEAR, wearing welding gloves and a thick apron. And white-hot iron is A LOT hotter. You do NOT want to be ANYWHERE near a thermite reaction, even a little one. Think of it as an EXPLOSIVE, not just "powder that burns a lot". You will probably damage everything within at least 20 feet, including you. Again, it will MELT THROUGH concrete - if you're lucky. (Concrete has water trapped in it - so it'll possibly EXPLODE -- showering 2,500° molten iron into the air.)

That said - electrolysis of iron isn't a great way to go -- and your method has some drawbacks anyway. You don't want to use sea salt - you're making hydrogen and chlorine gas, and sodium hydroxide (lye). And - you've got galvanized nails - the zinc is going to be doing a bunch of other stuff - maybe Zn(OH)2? Also - you didn't mention polarity, as in, what happened at the cathode vs anode nail?

When I do this, it's to DE-rust tools. You hook the red (positive) to a sacrificial bit of iron (I use 'steel' wool), and the black (negative) to the object to be de-rusted. H2 comes off the anode (black); O2 off the cathode. The rust (ferric oxide) drops off the tool, leaving behind a black scale (which I seem to recall is ferrous oxide). The sacrificial cathode just rusts. And - a far better electrolyte is washing soda (sodium carbonate) - Arm & Hammer makes it, not too hard to find if you look around at drugstores and bigger groceries. Finally - a battery charger works much better than a battery. ;-)

There's an Instructable on it, and an article in the latest MAKE magazine (vol 17) on the technique.

That all said - if you want to produce rust - buy a sack of #0000 steel wool. Light it with a match. (Remove sack first.) Filter through a coffee filter w/ distilled water.

(Aluminum powder? Now that's harder. >;-)

 

[daniel350]

That said - electrolysis of iron isn't a great way to go -- and your method has some drawbacks anyway. You don't want to use sea salt - you're making hydrogen and chlorine gas, and sodium hydroxide (lye). And - you've got galvanized nails - the zinc is going to be doing a bunch of other stuff - maybe Zn(OH)2? Also - you didn't mention polarity, as in, what happened at the cathode vs anode nail?

Sorry, I forgot these details. And yes electrolysis was not a great way to go. I knew there would be some drawbacks with the galvanization. Would the most 'appropriate' reaction be:

2NaCl(aq) + 3Fe(s) + 3H₂O(l) > 2NaOH + H₂(g) + 2Fe(OH)₂(aq) + Cl₂(g) + FeO(aq)

Note: I am very tired when I wrote this up, it appears to be correctly balanced, but as far as theory goes, it could be all wrong.

I unfortunately cannot give results for the anode v cathode, as it was so long ago now, however a recent repeat of the experiment gave more 'traditional' or at least less complicated results. Anode v cathode in this result appeared indifferent by visual note as both nails appeared to have

...a black [coating]... ferrous oxide...

after removal from the experiment; and large amounts of gases forming on the surface around the nail during the experiment.
A filtered result of the solution aftermath gave Ferric Oxide (red iron oxide).

This may have been due to the larger container in which it was completed in (larger surface area, less chance of bubbles) and the fact I used the same nails from the previous experiment (they may have lost all of their galvanized protective layer).

And - a far better electrolyte is washing soda (sodium carbonate) - Arm & Hammer makes it, not too hard to find if you look around at drugstores and bigger groceries.

Are you referring to Na2CO3 or NaHCO3, or would there be no distinguishable difference.

Finally - a battery charger works much better than a battery. ;-)

I used a car battery charger (12v, 2.7A)

Or were you referring to something else?

I may be doing this experiment again soon, however with more appropriate recordings, and scientific method (last one was a bit scruffy). I also may conduct a few tests to check the presence of what else may be laying around in solution after ward's.

Other replies from different forums presumed these possibles of trace compounds:

Chlorine
Hydrogen
Sodium hypochlorite
Sodium hydroxide
Sodium chlorate
Iron hydroxide
Iron oxide(s)

Take your pick

 

[Gnosis]

...H2 comes off the anode (black); O2 off the cathode.

"Anode" refers to a positive potential, whereas "cathode" refers to a negative potential, in which case, your statement is reversed for the gases that are produced per the polarities you mentioned via anode and cathode. Electrolysis typically yields hydrogen from the negative potential and oxygen from the positive potential.

On several occasions via electrolysis, I’ve liberated full-sized plastic trash bags full of hydrogen and the negative terminal absolutely produces the hydrogen gas, which was verified when I released them and they quickly ascended up into the atmosphere.