Transcript Prezentace aplikace PowerPoint

Forms of Carbon
Diamond
•
•
•
Covalent crystals: C, Si, Ge, SiC
Strong sp3s bonds form tetrahedral
structure
Face Centered Cubic lattice (fcc)
– 8 C atoms at the vertices of the cube,
6 C atoms in the face center, and
4
more within the unit cell
– Each C is tetrahedrally bonded to four
others
– All C-C bonds 1.54 Ǻ
•
Properties
– Extremely hard
• Strong rigid structure (macromolecule)
– Insulator
• No delocalized e– (p bonds)
– High index of refraction and strong
dispersion of light
Diamond film (CVD)
Diamond
Graphite
•
Parallel sheets of graphene
– Hexagonal, aromatic, “benzene” ring
arrays
– sp2s bonds stronger than in diamond
•
Delocalized p e– between sheets
– Covalent-metal bond
•
•
•
Van der Walls forces between sheets
Randomly oriented graphite grains
Properties
– Anisotropic
– Electrical conductivity along sheets
• Graphene: zero gap semi-conductor
– Soft, greasy and lubricating
– Strong absorption of light
• On p e–
Graphite
Fullerene
•
•
•
•
Richard Buckminster Fuller (1895 - 1993)
Bulk solid state: Fullerite
Closed cage C molecule
Pentagons in hexagonal structure
– Isolated Pentagon Rule IPR (stress)
– Spheroidal curvature
– Admixture of sp3 hybridization
•
C60
– Diameter 7 Ǻ
• With e 10 Ǻ, cavity 4 Ǻ
– Hexagons (20)
• Single bonds (red) 1.40 Ǻ
• Double bonds (yellow) 1.46 Ǻ
– Pentagons (12)
• Single
– Delocalized p e–
• Mostly outside the cage
• Higher density on double bonds
– Influence of sp3 and curvature
• Decreases with increasing n in Cn
Nanotube
•
Cylindrical C nanostructure
– Graphene sheets wrapped into a cylinder
• Armchair (1), zigzag (2), chiral (3)
– sometimes capped by fullerene-like
structure
– Diameter: 1 to several nm
– Length: 101 mm
•
Single-walled carbon nanotubes SWCNT
– Bundles (ropes) of tens SWCNT stuck in
triangular lattice
•
1
Multi-walled carbon nanotubes MWCNT
– Few to few tens of concentric cylinders
• Spacing close to graphite 3.35 Ǻ
•
Toughest materials ever known
2
– High elastic modulus of graphene sheets
3
Forms of Carbon
sp2
sp2
pure sp2
pure sp3