Graphite and Its MicroStructure By Nathan Vincent Fleming

College is a very busy place. To succeed, many people need to forego the level of extracurricular activities and hobbies they have both before and after college - some students even choosing to forego friendship entirely. Balancing your free time, or more accurately not choosing what you've always known as a normal amount of free time over succeeding in your higher education, is perhaps the biggest struggle of the experience. However, for some the difference in lifestyle is much more notable - three short years ago, I was involved in a great many regular extracurricular activities, such as multiple yearly theatrical productions and regular community service, and I always had an abundance of friendships and hobbies to keep me busy. All considered though, I think the thing I'm most sad to "take a break from" is my artistic talents - if for no other reason than those talents slowly die if you don't regularly practice art! And no material is more important to art than simple pencil lead - graphite.

A close-up of a pencil's tip

The most important feature of graphite, and why it's such a good material for pencils, is its extreme brittleness. It crumbles so easily, in fact, that not only does it need to be wrapped in wood so as not to break unintentionally, it's typically mixed with clay to make it usable! Without the added clay, the pencil's graphite would sometimes crumble too quickly to be functionally useful. Interestingly, the clay actually hinders the process, even as it helps it - the graphite is what creates smudges on the paper, the clay only serves to make the markings lighter.

An illustration of graphite's layers

Graphite's brittle nature is due to its micro-structure. Carbon atoms in graphite only covalently bond to three other carbon atoms (as opposed to four in diamond), forming a "sheet" structure. While the individual bonds require a very high amount of energy to break, and the material has a very high melting and boiling point, graphite's sheets only contain weak bonds between them. This allows the layers to slide apart easily, leading to graphite's use as a writing implement.

Scanning tunneling microscope image of graphite, at 0.5 nm

The easy sliding of graphite layers has also led to its use as a lubricant, the material often best described as "slippery" (even in scientific papers). Scientists have had some trouble explaining why the material works as a lubricant, however; from what we know about material science, graphite should operate like a hard, brittle material, like a sort of "crumbly version of diamond". In many material applications, it's interestingly best described as a soft, malleable material, akin to a semisolid. This difference is also due to the micro-structure - in many ways, graphite works nothing like diamond, despite technically being a solid itself.

Natural Graphite

Graphite's micro-structure provides one more interesting material property. As previously mentioned, the atoms in graphite only form three bonds out of a possible four. This absent covalent bond makes graphite a good electrical conductor, and the material is often used to create components of circuits such as electrodes. Being a relatively cheap material, it's considered a valuable utility for these applications, and while it's too brittle to be used in any sort of wiring it's considered somewhat versatile as well.

Conclusion

Graphite's unique micro-structure gives it a number of interesting material properties, some of which continue to surprise scientists to this day. These unique properties have led to the material's utilization in some of our most important day-to-day activities.

References:

The website "Cult Pens"' article on "lead hardness", found at: http://www.cultpens.com/pencyclopedia/lead-hardness

All illustrations found at: https://en.wikipedia.org/wiki/Graphite (only a source for images)

The BBC's article on general carbon properties: http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/chemical_economics/nanochemistryrev2.shtml

Credits:

Created with images by COLORED PENCIL magazine - "DECEMBER CPM Art Challenge Photo "Pencils & Paper" #1312" • ToolManTimTaylor - "pencil"

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