Synthesis of Carbynoid Structures by the Combustion Flame Method - Polyynes: Synthesis, Properties, and Applications - page 78

ablation of graphite or fullerene particles suspended in an organic solvent.
Recently, Cataldo [18,19] reported the production of a mixture of polyynes
having the general structure H-(C 2, 3, 4, 5, 6, 7, and 8, by

using an electric arc between two graphite electrodes submerged in a solvent
like decalin or acetonitrile. The interest in this technique lies in the fact that
the polyynes absorption band can be detected in any solvent (Cataldo also
used toluene, n-hexane, n-dodecane, acetonitrile, and a mixture of acetoni-
trile and water, 80:20). The formation of polyynes depends only on the
graphite electrodes and not on the nature of the solvent. Particularly, the
polyynes solution in decalin are stable in air for more than a week. This is
in contrast to the usual situation, where high instability and reactivity of
polyynes is encountered.
The synthesis of carbyne from graphite was first performed by
Kasatochkin et al. [20], Whittaker et al. [21] since 1970, Lagow et al. [22]
in 1995 and early in 2004 by Wakabayashi et al. [23]. In these techniques,
carbon vapor was produced either by evaporation of resistively heated
graphite rods or by laser ablation of graphite targets in a high vacuum
(10 7 Torr). The vapor, which consisted of carbon atoms and molecules,
was co-condensed with an excess of argon or neon gas on a substrate. The
energy of the ions impinging on the substrate varies within the range of
1.5-2 keV. The rate of films growth is very slow, typically

C) n -H, with n ¼

1 nm/min.
Microcrystalline carbyne of 10-100 nm size were obtained by this method.
The first attempt to produce carbyne from carbon by dynamic pressure
was by Litvinova et al. [24] in 1976, and then by Kleiman et al. [25] in 1984,
and Yamada et al. [26] in 1991. The principle of this method was based on
the pressure-temperature phase and transformation diagram of carbon. The
critical point, which has been estimated for transformations from graphite
to other solid phases (carbyne), is 0.2GPa/6800K [27]. Experiments were
performed with a starting material of amorphous acetylene black (>99%
pure, 45 nm average particle size) packed into a sample chamber of a cylin-
drical container to form a cylinder 40mm in height and 10mm in diameter.
Several carbyne polytypes with various carbon chain conjugation lengths
and bonding type were obtained. The carbyne crystals were surrounded by
tetragonal disordered diamond grains.
Kavan [28] and Kijima et al. [29] have used the electrochemical method
to synthesize carbyne. This technique may be realized by ''classical'' electro-
chemistry whereby the charge transfer reaction occurs at interface of a metal
electrode and liquid electrolyte solution. Electrons in reaction were supplied
either through redox active molecules or through an electrode, which
contacts an ionically conducting solid or liquid phase and the precursor.
In general, the structure and properties of electrochemical carbon may differ
considerably from those of usual pyrolytic carbons. The advantage of this
technique is the synthesis of carbyne at low (room) temperature. It was
shown that the best product was prepared by cathodic defluorination of
poly(tetrafluoroethylene) and some other perhalo-n-alkanes. The carbyne