As an important mineral resource discovered and applied to writing tools since the15th century, graphite has unique physical and chemical properties, such as stable black color, good conductivity, lubricity and high temperature resistance, and is an ideal material for manufacturing pencil lead.
Clay is added to graphite as a binder to adjust the hardness and wear resistance of pencil lead. The content of clay directly affects the hardness of pencil lead: when the proportion of clay is high, pencil lead will be harder and lighter (such as H series pencils); Pencil lead, with high graphite content, is soft and dark when writing (such as B series pencils). Among them, 2B pencil is commonly used for daily writing and filling out answer sheets in exams because of its moderate hardness and obvious handwriting.
In addition, it is worth mentioning that the tiny marks left by the pencil when it is cut on the paper are essentially composed of multiple layers of graphene. Graphene is a two-dimensional nano-material with hexagonal honeycomb lattice structure formed by single-layer carbon atoms with sp2 hybrid orbitals, which has excellent conductivity and semiconductor characteristics with near zero band gap.
Although natural graphite is rich in graphene layers, it is difficult to peel off pure single-layer graphene structure in natural state due to technical limitations. Therefore, when you draw or write with a pencil, you actually leave a multi-layer graphene structure on the paper.