Naturally-occurring magnetite (Fe3O4) has, of course, been of interest to navagators since the invention of the magnetic compass. Nano-magnetite particles have long been very important to the recording industry, from magnetic tape recorders to computer hard disks. More recently with help from magnetic nanoparticles, ferrofluids (like the spiky brown blob suspended in the Figure at left by a white-colored magnet) are showing promise for non-invasive repair of blood vessels and location-targeted delivery of drugs. Whoa! Nano-magnetite in model form can even be used to make cool wallpaper designs e.g. by using the right-click options menu on the figure below to remove perspective from image.
If you instead look closely while rotating the model, you may note that some of the iron atoms have 4 nearest-neighbor oxygens (in a "di-valent" tetrahedral arrangement), while the remainder of the irons have six bonds to oxygens (in a "tri-valent" octahedral arrangement). All oxygens have four bonds, three to tri-valent irons and one to a di-valent iron. Can you estimate the fraction of the iron atoms that are divalent, either by counting or from the information given above?
Below find a faceted ferro-fluid nanomagnetite particle.
The closeup below shows steps on its surface, control of which is likely to be quite important for surface reactions and bonding. Can the surface of such steps be seen on the model above? Pay particular attention to their size, recognizing that iron atoms will show up much more strongly in transmitted electron images than do oxygens, since iron nuclei have so much more electrostatic charge (26 versus 8 protons). Hint: Contrast in the image may be coming from planes comprised of which one of the two iron valence types mentioned above?
