Resistive Heating of Graphite

In the Kratchmer and Huffman procedure, Qo is produced by the resistive heating of graphite at high temperatures in an inert atmosphere [92]. If the soot that is obtained is extracted with toluene, a mixture of compounds is obtained that consists of Qo, C , and smaller amounts of higher... 

We isolated the C7g-fraction from the toluene extract of the carbon produced through resistive heating of graphite under helium by methods previously described (11, 15) (i) the crude extract was separated... 

It was only in 1990 when the groups of W. Kratschmer and D. R. Huffman succeeded in isolating macroscopic amounts of the most abundant fuUerene C o by the arc evaporation of graphite or by resistance heating of graphite electrodes, respectively. In fact, their initial intention, too had been to produce in the laboratory substances that exist in interstellar dust, but at suitable conditions, their IR-spectra exhibited four sharp, characteristic signals that related to those predicted for the Ceo-molecule. Later on, C70 and the higher fullerenes were also obtained. 

Figure 2.20 The first synthesis providing larger amounts of fullerenes succeeded in an apparatus for resistance heating of graphite rods presented by Kratschmer et al. Its essential feature is the electrodes just touching each other in one point.

Fullerene C70 [115383-22-7] M 840.77. Purification procedures (a) This was purified from the soluble toluene extract (400mg) of the soot (Fullerite), formed from resistive heating of graphite, by adsorption on neutral alumina (lOOg, Brockmann I, 60 x 8cm). Elution with toluene/hexane (5 95 v/v) gives ca 250mg of quite pme Cgo- It has characteristic spectral properties (see below). Further elution with toluene/hexane (20 80... 

Other techniques involving resistive tube furnaces, induction furnaces, and even direct resistive heating of the components are available for graphitizing smaller pieces of material. These batch processes require much shorter graphitization cycle times. 

AAS are discontinuous, and an analysis cycle comprises the following four steps (1) The sample is introduced into the cold graphite furnace, (2) the solvent is evaporated at temperatures of around 100 °C, (3) the sample is ashed and any volatile sample constituents are removed by keeping the sample for ca. 1 min at 450—900 °C before (4) the temperature is rapidly increased to 2000—3000 °C to vaporise and atomise the sample in a very short interval (milliseconds to a few seconds). The entire cycle can be accomphshed in about 1 min due to the fast heating rates achieved by direct electrical (resistive) heating of the graphite furnace at currents of up to 400 A and a voltage in the order of 8 V (see Fig. 12.10). 

Electrothermal vaporisation Electrothermal vaporisation, analogous to the approach utilised in AAS, can be performed by resistive heating of sample devices such as boats, ribbons, rods, or tubes from graphite or a refractory element [46]. 

Weng BJ, Hwung JJ, Chen Cl, Hsu SE, Heat resistant composites of graphite fibre reinforced phosphate ceramics, Doyama M, Somiya S, Chang RPH, Kimura S, Kobayashi A, Umekawa S eds.. Composites Corrosion/Coating of Advanced Materials, Proc MRS Int Meeting on Advanced Materials 4, Materials Research Society, Tokyo, 135 140, 2-3 Jun 1998. 

The entire first SGI, including the SGs and pumps, was located in the center of the ship in an isolated RC. The three PWRs were aligned vertically in a plane perpendicular to the keel and were surrounded by a large water-filled steel shield tank. The biological shield located above the three PWRs was made of limonite concrete and a heat resistant composition of graphite and boron. 

Electrothermal Atomizers A significant improvement in sensitivity is achieved by using resistive heating in place of a flame. A typical electrothermal atomizer, also known as a graphite furnace, consists of a cylindrical graphite tube approximately... 

Gran plot a linearized form of a titration curve, (p. 293) graphite furnace an electrothermal atomizer that relies on resistive heating to atomize samples, (p. 414) gravimetry any method in which the signal is a mass or change in mass. (p. 233)... 

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