Iron carbide: an ancient advanced material.

Iron carbide ranks amongst the oldest materials known to mankind. As a matter of fact, the combination of iron and carbon was discovered even before the pure metal and what ancient cultures named “iron” was, in reality, an iron/iron carbide composite. The presence of 6.7 wt% C in Fe 3 C in fact changes its properties dramatically: iron carbide is ceramiclike in mechanical behavior and chemically much more inert than pure iron. The so-called “meteorite iron” is rich in Cohenite, cannot be forged, and is apparently “noble” (does not corrode, even on long time scales and in contact with oxygen and water). The presence of Fe 3 C was confi rmed, for example, in ancient Damascene steel, [ 1 ] a 2500-year-old material largely used for swords and daggers due to its very special properties (e.g., superior hardness and lightness), which originates in the modern view from reinforcing the metallic iron with ceramic nanofi llers, more specifi cally iron carbide nanofi bers enwrapped in carbon nanotubes. All of these properties, mechanical and magnetic, as well as the chemical inertness, plus the property that iron is rather sustainable and nontoxic, can open new interest in this material in the form of nanostructures, either as pure iron carbide or in combination with second-phase carbon. Until now, nanosized iron carbide has been mainly observed as a side product in the synthesis of carbon structures, where metallic iron is used as a catalyst, for example, in chemical vapor deposition (CVD) [ 2 ] and pyrolysis processes [ 3 ] during the synthesis of carbon nanotubes. At a time when the literature presents countless procedures for the production of a plethora of nanoparticles and nanostructures (ranging from physical to chemical approaches, in water or solventless, by using a hard template or soft matter), it is surprising that a synthetic pathway to produce basic Fe 3 C nanoparticles in a reproducible, simple, and fast manner is still missing. Iron carbide nanoparticles would indeed be suitable for a variety of applications, from biomedicine (e.g., as a magnetically guided transporter for drugs [ 4 ] or as a contrast agent for magnetic resonance imaging [ 5 ] ) to electronics (e.g.,