Interaction Forces Between Alumina Surfaces in Magnesium Chloride Solutions

The surface forces between alumina colloidal sphere and alumina flat surface in magnesium chloride solutions were measured by an atomic force microscope. The forces between alumina surfaces were measured as a function of surface separation, salt concentration, and pH. Experimental decay lengths for the repulsive electric double layer interaction were in good agreement with the theoretical Debye lengths in the range of 0.000lmol/L to 0.0lmol/L. The Debye length decreased with the increasing of the salt concentrations due to the compression of the electric double layer. No attractive force could be detected in the pH range between 3.64 and 9.09, and the zeta potential was always positive, which strongly verified the existence of the specific adsorption. The short-ranged non-DLVO forces were observed in the magnesium chloride solutions at pH 9.52. Magnesium ions took the form of Mg(OH)+ and Mg2 (OH)3+ to form the adsorption layer, which changed into precipitation layer with the rise of pH, the thickness was estimated as 5nm.