Oxide/solution interface: non-simple coulombic interactions supported by K+ ions

The paper reports determinations of the surface charge of zirconia suspensions in potassium nitrate. The analysis of charge vs. pH curves obtained when the conditioning of the oxide is performed at positive charges indicates that the interactions between the surface and the electrolyte are merely coulombic, other charge components being not appreciable. If the conditioning of the oxide is performed in the pH region where K+ is the counterion (negative charges) the electrification pattern is sensibly modified, the common intersection point of charge curves being shifted in the acid direction and the slope of the curves being much steeper. In the discussion, the above described phenomena are related to possible bulk ion-exchange mechanisms involving K+ ions.