The electrokinetic potential of glasses in aqueous electrolyte solutions

Abstract

Electrokinetic potentials of several glasses of well defined bulk composition in aqueous electrolyte solutions were computed from streaming current measurements. The composition of the bulk is reflected in the magnitude of the potential and in the shape of the curves relating the electrokinetic potential and the pH of the solution. No differences have been found between the crystalline and the vitreous state of silica. Addition of Al 2O 3 to the bulk results not in doping effects but rather in surface neutralization making the surface less acidic. Glasses with an appreciable amount of B 2O 3 have higher negative potentials at the same pH, and the derivatives of electrokinetic potential vs pH show them to belong to a different type of surface than vitreous or crystalline silica. Studies involving controlled pore glasses of various pore sizes have shown the importance of below-the-surface ionic penetration and/or adsorption in the pores in establishing the solid-movable liquid interfacial electrical equilibrium.