Antilocalization in multiwalled carbon nanotubes

Positive magnetoresistance is measured in the low-magnetic fields in multiwalled carbon nanotubes, and interpreted as antilocalization in the weak-localization regime. The analysis shows that the weak antilocalization effect is related to the local interfacial electric field as a genuine property of the large curvature and multiwalls in the tubes. By fitting the positive magnetoresistance using the antilocalization theory, a set of scattering times in the tubes is obtained

Fullerene formation in acetylene/oxygen/argon/chlorine flames

The impact of Cl-2 addition on the fullerene formation in acetylene/oxygen/argon flat flames burning at low pressure was investigated. The quantities of C-60 and C-70 in the soot were determined by HPLC after extraction with toluene. Negative ion mass spectra were measured using chemical ionization by means of a CH4/N2O mixture. The chlorine containing species were identified by means of a precursor ion mass spectrum. The addition of 25% of Cl-2 led to a dramatic increase of fullerene formation; soot containing 7.7% of (C-60+C-70) was deposited in the combustion chamber. The mass spectra showed signals at the masses of C10H2, C11H8 and C12H10 for soot formed in flames with and without chlorine addition while peaks corresponding to the polycyclic aromatic hydrocarbons (PAH) C18H10, C22H12 and C24H12 could be observed only without chlorine addition. A positive role of thermally and photochemically unstable chlorinated intermediate species is suggested for the increase of fullerene formation. Copyright (C) 1996 Elsevier Science Lt

Calorimetric studies of solvates of C-60 and C-70 with aromatic solvents

To improve the understanding of the solution properties of C-60 and C-70 in aromatic solvents, binary systems of C-60 and C-70 with benzene, toluene, 1,2- and 1,3-dimethylbenzene, 1,2,4- and 1,3,5-trimethylbenzene, bromobenzene, and 1,2- and 1,3-dichlorobenzene were studied using differential scanning calorimetry, solution calorimetry, and thermogravimetry. Solid solvates with different compositions were identified in many of the systems. The solvates were characterized by composition and by the temperature and the enthalpy of the incongruent melting transition. Enthalpies of solution of C-60 in toluene, 1,2-dimethylbenzene 1,2- and 1,3-dichlorobenzene, and 1,2,4-trimethylbenzene and of C-70 in 1,2-dimethylbenzene and in 1,2- and 1,3-dichlorobenzene were determined. The formation-incongruent melting of solid solvates causes maxima in the temperature-solubility curves of fullerenes in aromatic solvents. Trends in solubility behavior of fullerenes were discussed in terms of thermodynamics of solution and solvate formation