Diamond may be
converted directly from a non-diamond carbon source in microseconds by a displacive
movement of atoms without diffusion, or synthesized catalytically in minutes by
reconstructive means with the transport of atoms. The diamond formation pressure and temperature are dependent on
the time scale and the structure of the carbon source. The instant conversion may occur with
zero-dimensional carbon (point-like sp0 atoms) by PVD,
one-dimensional carbon (line-like sp1 chains) by dynamite
detonation, or two-dimensional carbon (plane-like sp2 surface) by shock wave compaction. The timely synthesis may proceed with
two-dimensional (sp2) graphite (e.g., by puckering recrystallized flakes in a
molten catalyst, or with three-dimensional (sp3) diamond-like
molecules such as solute atoms in a molten catalyst (e.g., by temperature
gradient method), or caged atoms in methane molecules (e.g., by CVD).
The approximate
activation energies (E) for the major diamond synthesis methods may be
estimated from their reaction routes.
The threshold pressure and temperature for each of these synthesis
routine may be calculated based on the estimated activation energy. The results are summarized in the following
table.
C
Source State Method Route Time E(eV) P(Gpa) T(oC)
Plasma sp0 PVD Direct Instant 0.33 16 3500
Dynamite sp1 Explosion Direct Instant 0.25 12 2700
Graphite sp2 Shock Wave Direct Instant 0.17 8.1 1800
Graphite sp2 Puckering Catalytic Timely 0.13 6.2 1250
Solute sp3 Precipitation Catalytic Timely 0.13 6.2 1250
Methane sp3 Adjoining Catalytic Timely 0.09 4.3 800
Keywords: Diamond
Synthesis, Diamond Catalyst, PVD Diamond, CVD Diamond