When many people think about the strength of graphite, they tend to imagine the brittleness of a typical #2 pencil, and they assume that it is very weak. However, quite the opposite is true! Due to the hexagonal honeycomb lattice of the material’s molecular structure, the material is actually quite strong.
On the molecular level, the difference between graphite and a diamond, one of the strongest and hardest materials on earth, is essentially one single carbon atom, and of course, the lattice that is formed from the resulting configuration.
In a diamond, the carbon atoms are arranged tetrahedrally, where each carbon atom is attached to four other carbon atoms — forming a unique diamond lattice. When it comes to graphite however, the carbon atoms are arranged planar-triangularly, where each carbon atom is attached to three carbon atoms — forming a planar hexagonal honeycomb lattice. While this difference in molecular structure may seem modesty insignificant, it is enough to make to two carbon-based materials distinguishably different. The biggest difference between the two materials, besides obviously the color, the hardness and the density, is with regards to their electrical conductivities. One is very conductive and the other is not. Diamonds do not conduct electricity. However, due to these configurations, both materials are great conductors of heat and both materials are very, very strong.
While graphite doesn’t come close to the strength of most high-strength steels, it should be noted that a mild A36 grade is only 2-4x times stronger (in compressive strength) than most synthetic grades of graphite (400-600 MPa versus 100-300 MPa). However, one thing that should be considered here is that graphite is usually 4-5x times lighter than any A36 grade of steel. So there is a trade-off that should be noted with regards to the strength-to-weight ratio.
This strength-to-weight ration makes graphite a wonderful solution when it comes to an array of consumer products. For example, carbon reinforced plastics and carbon reinforced alloys have become quite popular in today’s fishing rods, pool cues, golf clubs, tennis rackets, baseball bats, and even bicycle frames. Sports cars have often used carbon reinforced plastics and carbon reinforced fiberglass for their main body panels to give it strength and reduce its overall weight.
And most recently, it was discovered that Boeing has been using carbon reinforced plastics and carbon reinforced composites for their fuselages (aircraft bodies and frames). According to Boeing, their transition to carbon fiber has offered a weight savings of roughly 20% compared to that of their conventional aluminum based designs [41]. Boeing engineers have stated that they have been using these materials for more than 10 years now (in more than 565 airplanes), and to date they have not replaced a single composite floor beam [42]. Another benefit in using these carbon reinforced materials is that it saves time and money when it comes to the assembly. Boeing stated that “a single piece of carbon fiber structure of the fuselage has eliminated 1,500 sheets of aluminum and has saved them 40,000-50,000 fasteners per section” [42].
Companies like BMW are now teaming up with Boeing to continue development on these carbon fiber products because they will likely be the future of ground and air transportation.[42]
Sources
[41] Hale, Justin. “Boeing 787, From The Ground Up.” The Boeing Company. Online Article
(2006). Accessed 1 May 2017. http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_06/article_04_2.html
[42] “Boeing, Carbon Fiber and Engineering the Future of Aviation.” Engineering.com.
Online Article (12 December 2013). Accessed 1 May 2017. http://www.engineering.com/DesignerEdge/DesignerEdgeArticles/ArticleID/6810/Boeing-Carbon-Fiber-and-Engineering-the-Future-of-Aviation.aspx
