Carbon fiber is very thin, strong crystalline filaments of carbon that are used to strengthen materials. It is also very flexible and can take a variety of shapes to support a structure. This flexibility is very important because it allows for a lot of freedom of movement inside the structure without having to worry about it collapsing or breaking. Carbon fiber is very popular because of its unique properties but the manufacturing process is expensive, which limits its use in many applications.
The carbonization of stabilized precursor fibers is a thermal reaction in which hydrogen, nitrogen, oxygen and other non-carbon elements are eliminated. The precursor fibers are drawn into long strands or a single filament. They are then heated to a high temperature in an inert environment. The atoms vibrate violently until most of the non-carbon atoms are removed and the result is carbonized fibers. This is called carbonization and it can be achieved using several different types of precursors.
Depending on the precursors and manufacturing processes, the microstructure of carbon fibers can vary. For example, Wick’s model for PAN carbon fibers suggests that the layer planes of a graphitic carbon crystal are stacked parallel to each other in regular hexagonal patterns and covalently bonded through sp2 bonding with very weak Van der Waals interactions between layers. In contrast, Watt and Johnson reported that PAN carbon fibers treated to 2,500 degC showed a turbostratic crystalline structure with layer planes stacked irregularly and haphazardly.