Graphite
C
Description
Graphite is one of the most stable allotropes of carbon at standard conditions. Unlike diamond, which is defined by a rigid 3D network, graphite is composed of stacked layers of carbon atoms. This structural difference makes it soft, opaque, and electrically conductive—properties that are rare for non-metals.
Crystallographic Structure
For physics modeling and visualization, graphite is the classic example of the Hexagonal Crystal System. It consists of "graphene" sheets—single layers of carbon atoms arranged in a honeycomb lattice.
- Lattice Parameters: a = b = 2.46 Å, c = 6.70 Å.
- Bonding: Carbon atoms within a layer are held together by strong covalent bonds ($sp^2$ hybridization), while the layers themselves are held together by weak van der Waals forces.
- Interplanar Spacing: The distance between layers is approximately 3.35 Å, which is much larger than the 1.42 Å distance between atoms within a layer.
- Symmetry: This layered arrangement allows the sheets to slide over one another easily, providing graphite’s characteristic "slippery" feel.
Properties
The behavior of graphite is highly anisotropic, meaning its physical properties differ significantly depending on whether you measure them parallel or perpendicular to its layers.
- Atomic Number: 6 (Carbon)
- Melting Point: ~3,600°C (Sublimes)
- Density: 2.26 g/cm³
- Hardness: 1–2 on the Mohs scale (extremely soft)
- Thermal Conductivity: High along the layers, low between them.
- Color: Steel gray to black with a metallic luster.
Applications
- Batteries & Electrodes: A critical anode material in Lithium-ion batteries and used as electrodes in electric arc furnaces for steelmaking.
- Dry Lubricants: Used in locks, hinges, and heavy machinery where liquid lubricants are impractical.
- Nuclear Reactors: Acts as a neutron moderator to slow down fast neutrons, helping to sustain a controlled nuclear chain reaction.
- Pencils: Mixed with clay to create "lead" (which contains no actual lead).
- Composite Materials: Reinforced graphite (carbon fiber) is used in high-performance sporting goods and aerospace components for its high strength-to-weight ratio.
Unit Cell Axes
a=2.46 b=2.46 c=6.7
Unit Cell Angles
α=90° β=90° γ=120°
Lattice Type
Primitive
Grid Expansion
Appearance
Coordination