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Sc metal chips and graphite

[5.92,93]

[email protected]

arc vaporization of graphite/Y2 03

[5.94]

[email protected]

laser vaporization of graphite/Y203

[5.65,94,95]

[email protected]

arc vaporization of La02/graphite electrode

[5.83]

[email protected]

arc vaporization of La02/graphite electrode

[5.83]

[email protected]

carbon arc using Scj03 packed electrode

[5.69,83,87,90,92]

[email protected]

arc vaporization

[5.69,87,90,92,94]

duction efficiency has been reported to increase in some cases if metal carbides, rather than oxides, are used to introduce the metal component into the vapor phase [5.96], The Sc-graphite electrodes are cured and carbonized at 1000°C for 5 h in vacuum (10~3 torr), and the rods are then further baked at 1200°C for 5 h at 10"5 torr. The composite rods are used as positive electrodes in a dc arc operating in an He atmosphere (50 torr). For quantitative studies, an anaerobic (air-free) production, sampling and solvent extraction method is used, whereby the carbon soot containing the endohedral metallofullerenes is produced in an He gas flow atmosphere (for example, 43 torr/1 s at 100 torr) [5.96]. A current density of ~2.4 A/mm2 is used between a pure graphite rod (negative electrode) and the composite rod (positive electrode). Solvent vapor (e.g., toluene) is introduced into the He gas stream that leaves the arc chamber. This allows the entrained fullerenes and the endohedrally doped fullerenes to be frozen in a downstream liquid nitrogen cold trap. After collection of the soot in the frozen solvent, the sample is kept in a dry nitrogen atmosphere. All sample handling for characterization measurements is done in a dry nitrogen atmo-

Fig. 5.10. Fast atom bombardment mass spectrum of the pyridine-soluble extract of the soot produced by arc vaporization of lanthanum-containing graphite electrodes. Evidence for [email protected] is clearly seen in this mass spectrum [5.11].

Fig. 5.10. Fast atom bombardment mass spectrum of the pyridine-soluble extract of the soot produced by arc vaporization of lanthanum-containing graphite electrodes. Evidence for [email protected] is clearly seen in this mass spectrum [5.11].

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