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- 2003 (2) (entfernen)
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- Englisch (2) (entfernen)
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- Amorphous carbon (1)
- Cathodic arc discharge (1)
- Nanotubes (1)
- Oxidation (1)
Single walled carbon nanotubes (SWNT) have been produced in an electric arc discharge by using a graphite rod as anode which is filled with a powder mixture of graphite and metallic catalysts like nickel and yttrium. The soot material containing approximately a third of SWNT was collected from the cathode region as a soft, voluminous material. The main by-products in this process are amorphous carbon and graphitic nanoparticles which have to be removed by an appropriate purification process. The as-produced soot material was purified by gas phase oxidation in air at 355 °C. The oxidation of amorphous carbon in air is advantageous against wet chemical methods because it is better controllable. Thermogravimetric analysis and electron microscopy were used to investigate the oxidation behavior of the different kinds of carbon. Oxidation of SWNT and amorphous carbon occurs simultaneously even at moderate temperatures, whereas amorphous carbon is more rapidly oxidized than SWNT. For optimizing the purification procedure by gas phase oxidation, kinetic studies were used to determine the oxidation time for each component in the soot at a given temperature. So it is possible to remove the amorphous carbon quantitatively with minimal losses of SWNT. But it was found that graphitic nanoparticles have the highest stability against oxidation and could therefore not be quantitatively removed by this method without the complete destruction of SWNT. Therefore, the electric arc discharge process has to be a controlled process for minimum production of graphitic nanoparticles to obtain a material with a high content of SWNT.
Effects of Heat Treatment on the Structure of Thermal Plasma Synthesized SiCN Composite Nanopowders
(2003)
SiCN composite nanopowders with different chemical composition and characteristics were synthesized by the RF induction plasma at atmospheric pressure. Frequently the as-produced powders exhibit a high degree of chemical disorder or structural defects. Because the composition and the microstructure of starting powders have a great influence on the properties of composite ceramics, the changes of chemical composition, crystallization, and morphology of the as-produced powders during heat treatment up to 1500 °C were investigated in detail.