IRON

ARTHUR B. ELLIS, NATIONAL SCIENCE FOUNDATION

In the course of learning and teaching chemistry, I have come to appreciate the value of "teachable moments" that spark interest and curiosity. In my experience, there are many compelling teachable moments associated with the element iron. I'd like to share with you some of my favorite pedagogical "irons in the fire."

People of all ages are fascinated by magnetism, and iron is the quintessential magnetic material. Whether it is the attraction of a magnet to various surfaces, the ability to arrange filings into patterns, or the use of a wire-wound nail as an electromagnet to pick up paper clips, you can't help but be mesmerized by iron. If you value flexibility and advertising capability in a magnet, the refrigerator magnet is worthy of admiration. The refrigerator magnet consists of particles of an oxide of iron embedded in a polymer matrix to make a composite material.

Iron appears in some unexpected places. If you haven't attempted to find iron in food, try this experiment with Total cereal, which has reduced iron as an ingredient: Pour the cereal into a bowl, grind it up, mix the finely powdered cereal around with a magnet, and voilà! Small iron particles appear on the magnet.

Why do we need iron in our bodies? Iron is an essential part of our physiology. Myoglobin and hemoglobin, for instance, are iron-containing proteins that store and transport the oxygen that keeps us alive.

	MAGNETIC A 3-cm drop of ferrofluid, a suspension of magnetite in oil, placed on a glass slide. Under the slide is a yellow Post-it and seven circular magnets. © FELICE FRANKEL, FROM "ENVISIONING SCIENCE"

Iron intrigues us both as an element and through its many chemical incarnations. Its facile transformation into rust is an archetypal chemical conversion with enormous economic implications. Although the slow conversion of iron to iron oxide lacks excitement, the conversion of iron oxide back to iron can be extraordinarily dramatic. The thermite reaction, wherein iron oxide reacts with aluminum to produce aluminum oxide and molten iron, is one of the most spectacular in chemistry.

Of all of iron's compounds, my favorite is magnetite, Fe₃O₄. This compound is the basis for one of the most astounding demonstrations I have seen in science: the response of a ferrofluid to a strong magnet. A common ferrofluid comprises nanoscale particles of magnetite suspended in a liquid. When a magnet is brought up to a black quiescent puddle of ferrofluid, the liquid suddenly seems to come to life: The placid surface of the puddle erupts into spikes as suspended nanoscale particles of magnetite relocate themselves in the magnetic field and drag the liquid along for the ride. Ferrofluids are used to dampen unwanted resonances in loudspeakers and to create seals for high-speed computer disc drives. There is even experimental work in which drugs are combined with ferrofluids so that their physiological location can be controlled with magnets.

Although samples of ferrofluids are commercially available, the awestruck response of many viewers to them prompted my coworkers and me to develop a simple, robust synthesis so that others could enjoy preparing these materials. As a series of movies on our website demonstrates (http://www.mrsec.wisc.edu/edetc/cineplex/ff/index.html), some simple manipulations that combine ferric chloride, ferrous chloride, aqueous ammonia, and a surfactant--none of which will show a response to a common magnet--produce a magnet-responsive ferrofluid in less than an hour.

Our search to optimize the preparation and properties of ferrofluids is emblematic of humankind's efforts to place iron in service to civilization. The Iron Age, for example, marked a passage from alchemy to chemistry as our ancestors "ironed out" physical and chemical modifications of the element's properties. From the Industrial Age to the present, our many uses of steel have been enabled by purposeful choices of impurity atoms and informed by increasingly sophisticated synthetic and characterization methods. A lovely recent high-tech example of the use of iron was devel- oped through the tools of nanotechnology. Scientists at IBM used the tip of a scanning probe microscope to position 48 iron atoms to form a ring. As the ring--dubbed a "quantum corral"--was completed, a magnificent circular wave pattern appeared, allowing the direct visualization of the quantum behavior of electrons (http://www.almaden.ibm.com/vis/stm/corral.html).

And what of the future? There are no ironclad guarantees, of course, but its abundance and chemical versatility make me confident that iron will continue to provide a mother lode of opportunities in science and technology, as well as many more teachable moments!

Arthur B. Ellis is director of the Division of Chemistry at the National Science Foundation. He is on detail from the University of Wisconsin, Madison, where he is Meloche-Bascom Professor of Chemistry. Opinions expressed are the author's and may or may not reflect those of NSF.

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