Isolated graphite crystallites, recognizable by their
characteristic geometric shapes and Raman spectra, are occasionally
precipitated on suddenly cooled samples:
Triangular crystallites precipitated from tungsten-doped
nickel:
Splattering carbon-saturated molten nickel against a glowing
tungsten filament produces a surprising feature. Notice the small
equilateral triangle on the left end of the otherwise gnarly nickel lump.
Close
view of the crystallite. Raman analysis reveals graphite in the triangle.
X-ray microanalysis reveals a high concentration of tungsten, which appears to
be the magic ingredient that makes the crystals triangular, rather than
hexagonal.
Hexagonal crystallites precipitated from iron:
This nearly hexagonal graphite crystallite swiftly
precipitated from iron is more typical than the triangular
crystallite shown above.
This
small crystallite, visible to the upper left of the larger crystallite, at left,
seems to be biting into the iron surface. The tendency of small graphene
molecules to spontaneously curve to reduce edge energy has been noted in the
fullerene literature[2].
