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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Hematite posted by unclestu on January 19, 2011 at 16:07:27:
This is one of the two paramagnetic oxides of Iron, the other being ferrosoferric oxide (Fe3O4). Ferrous oxide (FeO) apparently lacks magnetic properties.
Hematite is the naturally occurring mineral form of ferric oxide, and one of the primary iron ores. It occurs in both massive and crystalline forms, in colors ranging from black to metallic gray to rusty red. Finely ground, and embedded in a ceramic matrix, it is known as "ferrite," and is used to make permanent magnets (for speakers and motors, among other applications). Nonmagnetized ferrite is used in inductor and electromagnet cores, and in the "beads" you clamp over cables to keep EMI/RFI out of sensitive equipment. Ferric oxide was the first compound to be used in the coating of magnetic recording tape.
The ferric oxide used in ferrofluids is ground extremely fine, to nanoparticle size, and the particles are coated with a surfactant (to keep them from clumping together) and colloidally suspended in an oil. In the voice coil gap of a dynamic tweeter, the particles align with the flux lines of the permanent magnet pole piece to bring them "closer" to the alternating field of the voice coil, slightly improving efficiency. The oil helps damp and cool the voice coil, somewhat reducing its maximum excursion (and thus lowering its impedance peak) at fs.
Ferrosoferric oxide occurs naturally as the mineral Magnetite, which in its naturally magnetized form is Lodestone. It likewise occurs in both massive and crystalline forms. Also an important ore of iron, its main electromagnetic industrial application seems to be in electrophotographic toners. I can find no information about its use in magnetic recording, permanent magnets, or ferrofluids.
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Follow Ups
- Ferric oxide (Fe2o3) - caspian@peak.org 14:31:06 01/21/11 (2)
- A.K.A. Rust NT - Alpha Al 17:16:34 01/21/11 (1)
- It never sleeps..... nt - bartc 21:46:49 01/21/11 (0)