Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Rust, Steel, Heat, and Magnetism
Name: Dan
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A

We rusted some steel wool with bleach and vinegar as catalyst. We removed the wool and drained the liquid through a coffee filter. We tested the dried residue, which was no longer magnetic. We then heated it in a spoon over a candle flame, which turned it black. It was magnetic again. What was the process that "remagnetized" it?

Probably what you did is drive off some of the oxygen from the rust (hematite or goethite) turning it into magnetite, which is black and magnetic. The balanced chemical reaction starting with goethite would be:

12 FeO(OH) --> 4 Fe3O4 + 6 H2O + O2

That is the most realistic, since rust is generally hydrated. The reaction is a little easier to balance from hematite:

6 Fe2O3 --> 4 Fe3O4 + O2

Richard Barrans, Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming

Some oxides of iron are non-magnetic, others are magnetic. Fe2O3 . nH2O (red rust) is definitely non-magnetic. "Magnetite" mineral is an iron oxide about like hematite, something like Fe2O3 . FeO. (aka Fe3O4) FeO is blackish not red, and the mixes tend to be gray-black too.

Your residue lost all water and a little oxygen and maybe also recrystallized while in the solid state, to a form more appropriate to its new composition. . Check out whether your estimated peak temperature, in degrees K, was more than 1/3 to 1/2 of the melting point of Fe3O4, also in degK. If so some recrystallization should be able to occur on the molecular level, though perhaps not to crystals large enough to be visible.

It is possible the gasses in the candle flame helped chemically, not just thermally, with some of the oxygen removal. If the flame wrapped around the spoon on all sides, it might create an oxygen-depleted or reducing atmosphere in the spoon. Carbon monoxide, unburned wax fumes, and soot are all reducing agents for the conversion of Fe2O3 to Fe3O4.

Jim Swenson

Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory