Natural Carbynes,Including Chaoite, on Earth, in Meteorites, Comets, Circumstellar and Interstellar Dust - Polyynes: Synthesis, Properties, and Applications - page 337

when randomly frozen-in defects are incorporated in the lattice [40].
The positive slope of the equilibrium graphite diamond reaction in the

carbon P-T diagram will cause diamond to become increasingly sensitive to
''melting'' and vitrification by decompression towards higher temperatures.
When at some pressure the melting curve of a mineral intersects its glass-
transition curve, isothermal decompression below T g will then cross the
vitrification curve where the crystal will directly vitrify without melting [41].
An ''extreme-disordered amorphous carbon'' due to first-order solid-
state hexagonal graphite and cubic diamond amorphization (''melting'')
yields the EDAC phase field (Figure 16.2) that is also reached by ultra-fast
quenching of a carbon melt or vapor. When quenching was the controlling
parameter, deep metastable eutectic behavior at T<T g might favor a
specific carbon form, for example, chaoite, as a quenched-melt metastable
solid. Amorphous solids formed anywhere within the EDAC field will
experience thermal annealing either during initial heat dissipation of the
very formation process or during post-formation heat treatment. In both

,

FIGURE 16.2 The proposed ''extreme disordered amorphous carbon'' field defined
by low-pressure diamond ''melting'' and ''melting'' superheated graphite in the
previously modified [27,68] high-temperature/low-pressure region of the carbon
phase diagram.