From: dwilkins@means.net (Don Wilkins)
Newsgroups: sci.chem
Subject: Re: Fe3O4 question
Date: Wed, 08 Jan 1997 13:07:03 GMT

On Wed, 08 Jan 1997 01:50:19 GMT, kcd@insync.net (Casey Donovan)
wrote:

>thweatt@prairie.nodak.edu (Superdave the Wonderchemist) wrote:
>
>>Brad Brush (biomedic@wimsey.com) wrote:
>>> We have come upon a chemical that we cannot explain at our school. It
>>> is called Iron ferrosferric (natural magnetite), formula Fe3O4, one of
>>> the iron oxides.
>>> 
>>> The combining capacity of oxgyen is almost always -2 (except for
>>> peroxides). Iron has a capacity of 2 or 3. This does not come out to
>>> be a ratio with intact integers. How can I explain this? Thanks.
>>
>>As a simplification, think of it as a 1:1 mixture of FeO (Iron II) and 
>>Fe2O3 (Iron III) packed into a crystal such that the net stoichiometry is 
>>Fe3O4.
>>
>>To go any further, you should probably ask a geochemist or geologist.
>>
>>-Superdave The Wonderchemist
>
>You might also ask a metallurgist.  Magnetite is the oxide form
>(corrosion product) produced by steel in contact with severely
>limited amounts of moist atmospheric or dissolved oxygen.  If not
>removed by some mechanical action, it forms an impervious thin
>layer on the metal surface.  It's what keeps a steam boiler from
>quickly corroding into a pile of rust.
>
>BTW, it is magnetic, whereas Fe2O3 and (I think) FeO are not.
>This is a standard, though of course not definitive, test for its
>presence in a deposit.

Now let see if I have this straight. The gamma-Fe2O3 used in recording
tape is the figment of the manufacturers imagination.

Gamma-Fe2O3 is made by the oxidation of Fe3O4, retains the spinel
structure and is in fact magnetic. It changes to the non-magnetic
alpha-Fe2O3 at 600.

Nicht wahr


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