Optical diagnostics of carbon arc and induction plasmas

In this article, the analysis of optical diagnostics of plasma parameters of carbon arc and induction thermal plasma in the process of fullerene synthesis is presented. The effect of carbon concentration on vibrational temperatures of C-2 radicals was investigated. The molecular vibrational temperatures of C-2. calculated from the emission intensities are in the range of 5000-10500 K.Progress in Advanced Materials and Processes, 5th Conference of the Yugoslav-Materials-Research-Society (Yu-MRS 2003), Sep 15-19, 2003, Herceg Novi, Yugoslavi

The processing of Mg-Ti for hydrogen storage; mechanical milling and plasma synthesis

A study was carried out into the processing of Mg-10 vol.% Ti powder mixture for hydrogen storage purposes. Two processing routes were evaluated; mechanical milling and plasma synthesis. Mechanical milling, carried out with a high speed planetary mill, yielded a particulate structure made up of large Mg agglomerates, 90-100 mu m, with embedded Ti fragments of approx. 1 mu m in size with a uniform distribution. Mg agglomerates were made up of coherently diffracting volumes that were less than SO nm in size. Plasma processing was carried out with an RF plasma torch of 25-27 kW applied power, the powder mixtures fed with 1-3 g/min axially into the torch. The mixture Mg-10 vol.% Ti after plasma processing comprised Mg powders which were extremely fine, <100 nm. Ti occurred as separate particles mixed with Mg nanopowders. The powders had a coherently diffracting volumes that were comparable to the size of the particles themselves indicating that the plasma processing yields relatively defect free crystals. The formation of the nano-size particulate structures is evaluated with regard to their possible implications on the hydrogenation of Mg-Ti alloys. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved

Comparative analysis of carbon plasma in arc and RF reactors

Results on studies of molecular spectra emitted in the initial stages of fullerene formation during the processing of graphite powder in induction RF reactor and evaporation of graphite electrodes in arc reactor are presented in this paper. It was found that C-2 radicals were dominant molecular species in both plasmas. C-2 radicals have an important role in the process of fullerene synthesis. The rotational-vibrational temperatures of C-2 and CN species were calculated by fitting the experimental spectra to the simulated ones. The results of optical emission study of C-2 radicals generated in carbon arc plasma have shown that rotational temperature of C-2 species depends on carbon concentration and current intensity significantly. The optical emission study of induction RF plasma and SEM analysis of graphite powder before and after plasma treatment have shown that evaporation of the processed graphite powder depends on feed rate and composition of gas phase significantly. Based on the obtained results, it was concluded that in the plasma region CN radicals could be formed by the reaction of C-2 species with atomic nitrogen at smaller loads. At larger feed rate of graphite powder, CN species were produced by surface reaction of the hot carbon particles with nitrogen atoms. The presence of nitrogen in induction RF plasma reduces the fullerene yield significantly. The fullerene yield obtained in two different reactors was: 13% in arc reactor and 4.1% in induction RF reactor. However, the fullerene production rate was higher in induction RIF reactor-6.4 g/h versus 1.7 g/h in arc reactor.22nd Summer School and International Symposium on the Physics of Ionized Gases, Aug 23-27, 2004, Tara Natl Pk, Yugoslavi

Comparative analysis of carbon plasma in arc and RF reactors

Results on studies of molecular spectra emitted in the initial stages of fullerene formation during the processing of graphite powder in induction RF reactor and evaporation of graphite electrodes in arc reactor are presented in this paper. It was found that C-2 radicals were dominant molecular species in both plasmas. C-2 radicals have an important role in the process of fullerene synthesis. The rotational-vibrational temperatures of C-2 and CN species were calculated by fitting the experimental spectra to the simulated ones. The results of optical emission study of C-2 radicals generated in carbon arc plasma have shown that rotational temperature of C-2 species depends on carbon concentration and current intensity significantly. The optical emission study of induction RF plasma and SEM analysis of graphite powder before and after plasma treatment have shown that evaporation of the processed graphite powder depends on feed rate and composition of gas phase significantly. Based on the obtained results, it was concluded that in the plasma region CN radicals could be formed by the reaction of C-2 species with atomic nitrogen at smaller loads. At larger feed rate of graphite powder, CN species were produced by surface reaction of the hot carbon particles with nitrogen atoms. The presence of nitrogen in induction RF plasma reduces the fullerene yield significantly. The fullerene yield obtained in two different reactors was: 13% in arc reactor and 4.1% in induction RF reactor. However, the fullerene production rate was higher in induction RIF reactor-6.4 g/h versus 1.7 g/h in arc reactor.22nd Summer School and International Symposium on the Physics of Ionized Gases, Aug 23-27, 2004, Tara Natl Pk, Yugoslavi

Influence of carbon concentration and rotational temperature on fullerene yield in RF reactor

In this paper, report on fullerene formation in a radio-frequency (RF) thermal plasma reactor has been presented. In order to determine the degree of evaporation of the graphite precursor used, analysis of SEM micrographs of deposited soot in different parts of RF reactor has been made. It was found that the degree of graphite evaporation and fullerene yield varied depending on the distance from the plasma torch nozzle. Carbon concentration and rotational temperature of C-2 radicals in plasma flame have been calculated as well. The concentration of C-2 radicals in plasma flame, which participated in fullerene formation, was in the range of (1.75-3.88)- 10(20) m(-3).Recent Developments in Advanced Materials and Processes, 7th Conference of the Yugoslav-Materials-Research-Society (Yu-MRS), Sep 12-16, 2005, Herceg Novi, Montenegr

Optical emission study of RF thermal plasma during fullerene synthesis

Results on studies of molecular spectra emitted in the initial stages of fullerene synthesis during processing of graphite powder in RF thermal plasma conditions are presented in this work. CN-usually present in carbon plasmas-and C-2 were found as dominant molecular species. The role of CN radicals on the fullerene formation was discussed in detail. Intensities of CN and C-2 lines were studied against the composition of gas phase and the feed rate of graphite powder. The rotational-vibrational temperatures of CN species were calculated by fitting the experimental spectra to the simulated ones. It was concluded that in the plasma region CN radicals could be formed by the reaction Of C-2 with atomic nitrogen at smaller loads. This reaction lowered the yield of fullerenes. At larger loads, C2 formation was decreased due to lower temperature of the particles compared to smaller load. The CN radicals were produced by the surface reaction of the hot carbon particles with nitrogen atoms. Results confirmed that for effective fullerene synthesis, the nitrogen content of the precursors and the plasma gases should be minimized

Efficient synthesis of fullerenes in RF thermal plasma reactor

Formation of fullerene soot was studied in an inductively coupled, radiofrequency (RF) thermal plasma reactor. A previously developed kinetic model of fullerene formation was applied to determine synthesis conditions leading to high fullerene yield. The experimental results verified the kinetic model. Maximum yield of 4.1% was obtained in particular conditions. It corresponded to a fullerene production rate of 6.4 g h(-1). (C) 2003 Elsevier B.V. All rights reserved

Comparative process analysis of fullerene production by the arc and the radio-frequency discharge methods

In this work, comparative analysis of processes in carbon arc and radio frequency (RF) plasma during fullerene synthesis has been presented. The kinetic model of fullerene formation developed earlier has been verified in both types of plasma reactors. The fullerene yield depended on carbon concentration, velocity of plasma flame and rotational temperature of C(2) radicals predominantly. When mean rotational temperature of C(2) radicals was 3000 K, the fullerene yield was the highest regardless of the type of used reactor. The zone of fullerene formation is larger significantly in RF plasma reactor compared to arc reactor