Abstract
The isoelectric point (IEP) of a typical carbon black in aqueous solutions is increased from pH 4.5 to ~ ̊ 11.5 by prior graphitization in N 2 or Ar at temperatures up to 2700°C. The high IEP of the graphitized carbon surface decreases slowly to pH 4.5 or lower by storing at ambient temperature or by rapidly pre-heating in oxygen at 370°C. The pH IEP, as measured by microelectrophoresis, of graphitized carbon was found to be sensitive to the electrolytes present, with H + ions giving the highest IEP. It is postulated that H + ions are strongly adsorbed as part of the process of reduction of water by the graphitized carbon and partial surface oxidation of the solid.
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