Iron oxide reduction

[chrismohr]

Here are my general questions about rust: 1) The melting point of iron is around 2750 F. But at what temperature can small or nano-sized iron oxide flakes "melt" when they are released into the air? 2) When this happens, at approximately what temperature can iron oxide reduction to iron begin to take place? Are there relatively simple ways for to make iron oxide reduce to iron or does this happen only when the temperature exceeds 2750 F (iron's melting point)? 3) At what temperature can small or nano-sized rust flakes reduce to iron and turn into small spheres? Are iron-rich microspheres a byproduct of regular fires at under 2200 F or are they unique to super-hot fires above 2750 F? Thank you!

[studiot]

Don't you also require carbon as well as heat to reduce iron oxides to iron?

 

Iron will burn if you heat it hard enough, so I don't think heat alone will do it.

[John Cuthber]

1

Iron forms a number of oxides, the one you will get by heating it in air until it melts (Fe3O4 and/ or Fe2O3) will melt at about 1500 C

The melting point isn't strongly affected by particle size so it doesn't matter if it's nanoparticulate or not.

2

it doesn't.

As pointed out, you need a reducing agent and a lack of air.

You can do this below the melting point of iron.

In fact, you can do it in solution in water, but not easily.

3 in general, they won't reduce to the metal.

If the flame is hot enough, they will melt and become roughly spherical at about 1500C

 

It would help if you explained why you are asking.

Also, science uses C or K not F.

[Macaday]

1) the T_m of Fe₂0₃ Haematite is 1838 K and for Fe₃O₄ Magnetite is 1867 K. The melting point of a substance is only dependant on the temperature not on the environment.

2) the reduction of Iron can take place in the presence of CO as it does in the blast furnace (800 - 1050^oC) so the formation of iron micro spheres in the system could depend on the flue gas composition; as the formation of Iron would only happen with sufficient CO. Excess O₂ would result in the oxidation of the iron formed back to Iron oxide

[Enthalpy]

I wouldn't be surprised if the "iron-rich microsphere" produced by fires were iron oxides mixed with other solids. These would still qualify as iron-rich.

 

But could we reduce iron oxides at heat in vacuum? Concentrated sunlight can make up to 5900K theoretically, and the top of an oxide heap needs no other mechanical support. That would cost vacuum but save coal - cleaner, probably not cheaper.

 

Or copper, nickel, cobalt, molybdenum, tin, lead, which seem easier.