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Iron Carbide Fe3C; also known as Cementite |
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Iron carbide , Fe3C in chemical
short-hand, is also known as "cementite".
It is a chemical compound of iron and carbon. Iron
carbide is normally classified as a "ceramic", i.e. it is hard, brittle and an insulator.
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Considering that carbon steel is what it is because of cementite, I was amazed
how little information I found about the stuff. Its lattice type and so is known, of course (see below) but not much else. |
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| Crystal cell of iron carbide Fe3C |
| The green spheres symbolize iron atoms, the small black spheres at the intersection of the thick blue lines
(symbolizing bonding) symbolize the carbon atoms. The cuboid symbolizes the elementary unit cell of the crystal.
| | Source: after Wikipedia |
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Here is a HRTEM picture of a cementite particle in steel. |
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| HRTEM picture of a cementite precipitate in an iron matrix |
| Source: Picture from Eyüp Duman's PhD thesis: "Druckabhängigkeit der Invar-typischen
Instabilitäten von Fe3C- (Zementit) Partikeln", Universität Duisburg-Essen: 2006; thanks for letting
me use it. |
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Cementite is not found as a mineral in nature, except in iron meteorites. Then
it is called cohenite after the German mineralogist Emil Cohen who first described it. |
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Cementite is rather hard (HV = 800) and brittle. It is magnetic
like iron but looses its magnetism at a Curie temperature of 215 oC (424 oF).
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It appears that cementite has no major uses by itself. |
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© H. Föll (Iron, Steel and Swords script)
With frame
Magnetism