Fe3O4 vs iron filings

[apathyboy]

Is there an easy way to separate or even differentiate fine iron filings from Fe3O4 powder? Whenever I have encountered fine iron filings, they are black from a coating of oxidation, so visually they are almost identical, and of course both are magnetic, so separating them that way is likewise impossible. I thought of using the differing densities, but fine powders take forever to settle out of suspension, and I do not have access to a centrifuge.
Thanks in advance

P.S. just for clarification, I'm producing the iron oxide from large iron filings submerged in a salt water solution

[jfk]

Is rust magnetic? Can't say that I know ...but if it is that could be one way.

[totenkov]

No rust is not magnetic :rolleyes:. You can seperate the filings by running a magnet over the pile a few times.

[Lewis]

and of course both are magnetic

He seems to think otherwise...

Magnetic or not, if the metal and its oxide are powdered together, the oxide particles are going to stick to the elemental iron.

[Cobalt.45]

Fe3O4 is in fact magnetic.

A procedure is shown here:http://www.physicsforums.com/showthread.php?t=103373
for making it from steel wool.

[apathyboy]

Cobalt is correct, Fe3O4 is magnetic. If you want a cheap giggle at a fellow forum member, google "lodestone" or "magnetite" :rolleyes:

-Lewis
Yes, you are correct, which is why I mixed the powder up in alcohol and used a magnet to pull out the powder, it didn't leave anything behind, whereas a separate powdered non magnetic material would have been left in suspension. Whatever I have, it's entirely magnetic

I just thought of another possible fix

If anyone knows a quick and thorough way to convert my mystery powder (if it is indeed Fe3O4) to the more common Fe2O3, that would work too, as any residual magnetism would only be explainable by metallic iron left in the powder. I googled a bit, but the refs I found were all for going the other way, from red oxide to black. Apparently the black oxide will form a passivating coating, and most people are trying to *prevent* rust.

[SilverMatch]

Fe3O4 is used as a coating on steel by gunsmiths to prevent oxidation in a process called bluing.
I've heard that Fe3O4 can be reduced to iron by using ascorbic acid, or possibly by EDTA - but I'm not sure how these chemicals will effect the rust that you already have.
In essence Fe3O4 is really just molecules of FeO and Fe2O3 within the same structure, so pure rust can probably be produced by further oxidation. I would give chlorine bleach a try.
If rust powder is all you're looking for, though, there are far easier ways to make it than to mess with filings of iron in a solution of salt and water. A quick search of the forum will give you plenty of options.

[Cobalt.45]

While there's good reasons to make some chems, iron oxide- red or black- is just so damn cheap to buy that not many bother.

I go through quite a bit as a burn enhancer in rocket fuel. I wouldn't want to have to make it, although like I said, there are reasons one might want to...

Which begs the question: What are you up to, apathyboy???:cool:

[apathyboy]

Well, the obvious, thermite, and possibly as a catalyst in KNSU rocket propellant.
And the reason I was looking to produce it from iron filings is I know a couple sources of large quantities (~50 pounds) of iron filings for free, as opposed to buying it directly, or buying the other stuff to make it, like NBK's fertilizer method
All my method takes is a bit of time and some 1 gallon ice cream containers, and could produce literally hundreds of pounds for free. The caveat being making it work of course :p

[Cobalt.45]

You can hit up the local machine shop for their brake lathe turnings.

I use them as is after screening for fountains.

I had to train them not to toss their cigarette buts, etc. into the collection bin, though.

[Killy]

If you need lots of Fe2o3, the best method is electrolisys, I know that because before I mess with grinding rust steel, covering it with salt water etc. in one word I got only total crap,
but electrolisys rocks.
All you need is transformator, cup, wires and iron product, but that method is surely in detail somewhere on the forum.

[6.22E23]

Fe3O4 is strongly magnetic (hence the mineralogical name of magnetite), and Fe2O3 is weakly magnetic. Fe2O3 is, however, magnetic enough to be used in recording tape. Very little Fe2O3 will be attracted to a magnet, so the method will separate the raw Iron from the Oxide.

You didn't mention the source of your Iron; if it's from grinding operations, it's probably already oxidized to Fe3O4; the sparks are the Iron oxidizing (burning) in air. Depending on the wheel grit, feed rate, etc. you may get complete oxidation or not. If it's not complete, you will have a passivation layer on top of the iron you are trying to oxidize (more on this later). If you mill the raw material to a finer powder, you not only remove the magnetite but increase the surface area availble for oxidation.

Ah yes, the oxidation step... Remember, you need Oxygen. Just immersing the Iron is not enough. Get an aquarium pump and aerate the mix. Keep it warm (10 degrees doubles reaction rates) but not too warm or the dissolved Oxygen will be too low. The chloride just helps speed the rusting process (just take a look at the steel shelves holding the muiatic acid at the hardware store). It's still gonna take days.

Once you get your mixed Iron Oxide, how will you know the composition? For a stoichiometric thermite mixture, you will have to do some kind of analysis.

My biggest question is why you are going through this when you can get Iron Oxide for about a dollar a pound? The Aluminium you need for 50 pounds of iron will cost much more than the oxides, not to mention having a known composition.