Graphite pressed pellet conductivity

High-purity graphite powder for DC-arc mixtures, or for pressed pellets for spark analysis, is also analyzed and guaranteed by manufacturers. In spark methods, the sample (if conductive) is often one of the two electrodes, and only a counter electrode is needed. Graphite electrodes are common, but metal counter electrodes, especially silver (to permit determination of carbon), are routinely employed in vacuum spark analysis. 

Arc nebulization can be used to produce an aerosol from a conducting solid sample. The aerosol is then introduced into the plasma for elemental or isotope ratio analysis. Powdered samples can be mixed with graphite and pressed to get a conducting pellet. The only matrix related interfering ions detected are ArC", ArO and Ar2". A precision of about 1% has been reported for isotope ratio determinations. 

The zinc-mercury oxide button cell (Fig. 23.8) uses a pellet of mercury oxide with a little graphite added to it for better conductivity as cathode. The anode of this battery is zinc powder (pressed or amalgamated). The electrolyte, a concentrated ZnO saturated potassium hydroxide solution, is on a cellulose felt. The following shows the simplified processes at the electrodes ... 

Propargylamine and aminoacetonitrile may be readily intercalated through acid-base interaction within the interslab spaces of a-M(H0P03)2 H2O (M = Zr, Sn) (75). Their subsequent thermal treatment (150-180°C for 24 h in air) or UV irradiation (550 W medium pressure Hg lamp for 11 days) results in polymerization of the guest molecules. However, if the photochemical reaction does not reduce the crystallinity of the initial materials, its extent is more limited, as observed by CP-MAS NMR spectroscopy. In all cases, these polymerized nanocomposites are insulators as pressed powder pellets (a < 10 S/cm). Heating these compounds to 300°C in argon turns them black and at temperature over 750°C the graphitization reaction leads to conductivities up to 1 S/cm. 

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