<b>Determination of surface charge density of α-alumina by Acid - base titration</b>

Abstract

The surface charge density ( s o ) of colloidal alpha alumina suspended in various 1:1 electrolytes was measured using acid-base titration. An autotitrator capable of dispensing accurately 25 ± 0.1 m L of titrant was used. The pH and temperature in the titration cell were monitored using single junction electrodes and platinum resistance thermometers, respectively. A constant supply of nitrogen gas in the cell was used to maintain inert conditions. The whole set up was interfaced with a computer for easy data acquisition. It was observed that the material exhibits a point of zero charge (PZC), this occurred at pH of 7.8 ± 0.1, 7.6 ± 0.2, 8.5 ± 0.1, 8.3 ± 0.1 for NaCl, NaNO 3 , CsCl and CsNO 3 systems, respectively. It was also observed that below PZC, s o increases with increase in electrolyte concentration (C o ) whereas above PZC, s o decreases with increase in C o . It was concluded that s o of this material is a function of pH and C o and that its polarity can be varied through zero by varying these parameters. KEY WORDS: Alumina, Surface charge density, Acid-base titration, Point of zero charge Bull. Chem. Soc. Ethiop. 2007 , 21(1), 117-128.