Direct-current arc discharge

The decomposition is accomplished using electrically heated filaments, microwave plasma discharge, or direct-current arc discharge. Polycrystalline diamond is deposited as a thin, hard film. 

The TOF distribution for = 540 meV has been obtained in a completely different way. The helium plasma of a high-current arc discharge has been expanded through a small nozzle hole, giving directly a supersonic He(23S) beam of higher kinetic energy (see Section III.A.6). 

Alternating or direct current arcs and spark discharge are common methods of excitation for emission spectroscopic analysis of rare earth elements. Emission spectra of rare earth elements contain a large number of lines. The three arbitrary groups are (i) spectra of La, Eu, Yb, Lu and Y, (ii) more complicated spectra of Sm, Gd and Tm, (iii) even more complicated spectra of Ce, Nd, Pr, Tb, Dy and Er. Rare earths have been analyzed with spectrographs of high resolution and dispersion up to 2 A/mm. Some salient information is presented in Table 1.36. 

A number of electrical excitation-sources are available for emission spectroscopy. In most commercial spectrochemical instruments, more than one excitation source is contained in a single power-supply cabinet a typical combination may include a spark, a direct-current arc, and an alternating-current arc. A list of the various electrical excitation-sources, some of their characteristics, their approximate cost and the types of samples generally required is given in Table 11.1. Because of the actual or potential widespread use in emission spectroscopy, only the arc, spark, and inductively coupled plasma discharges will be described here in detail. 

Power supplies commonly used for arc welding can be used as an electric power supply for generating arc discharge. Either direct current (DC) or alternative current (AC) arc can evaporate carbon electrodes. The DC mode is almost exclu-... 

The direct introduction of atomic vapour into the AAS flame can also be seen as an equipment variation [148, 152], Here, the evaporation of the steel samples can be carried out with the help of the glow-discharge lamp [148] or an aerosol generator with a low current d.c.-arc discharge [152]. Another example is the combination of gas chromatography and AAS [92], where AAS is used as an element detector. 

Metallofullerenes can be synthesized typically in two ways similar to the s)mthesis of empty fullerenes, which involves the generation of a carbon-rich vapor or plasma in He or Ar gas atmosphere. The two methods have been routinely used to date for preparing macroscopic amounts of metallofullerenes the high-temperature laser vaporization or "laser-furnace method (Chai et al., 1991 Haufler et al., 1991 Ying et al., 1994) and the standard direct current (DC) arc discharge method (Haufler et al., 1990). Both methods simultaneously generate a mixture of hollow fullerenes (Ceo, C70, C76, C78, Cs4,...) together with metallofullerenes. The production of metallofullerenes can be followed by procedures to extract from soot and to separate/purify the metallofullerenes from the hollow fullerenes (see Sections 2.2, 3.1, and 3.2). 

The arc is an electrical discharge that must be triggered by an auxiliary self-ionising discharge. The direct-current electric arc (300 V, 20 A) is created between two solid electrodes. One of the electrodes contains the sample in powder form. This is compacted in a crater hollowed out in the end of the electrode consisting of a graphite rod (see Fig. 3.2). 

DC Arc Continuous, self-maintaining, direct-current discharge with low voltage and high current between sample and counter electrodes. powders, solids, residues 1000-6500... 

The temperature does not depend directly on the tube radius, but rather only on specific power w. The principal parameter of an arc discharge is the current. Assuming X const. = XT , the conductivity in the arc chaimel is proportional to crurent (Fridman Keimedy, 2004) ... 

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