Application of the method of images on electrostatic phenomena in aqueous Al 2O 3 and ZrO 2 suspensions

Abstract

A new solution for the Poisson equation for the diffuse part of the double layer around spherical particles will be presented. The numerical results are compared with the solution of the well-known DLVO theory. The range of the diffuse layer differs considerably in the two theories. Also, the inconsistent representation of the surface and diffuse layer charge in the DLVO theory do not occur in the new theory. Experimental zeta potential measurements were used to determine the charge of colloidal Al 2O 3 and ZrO 2 particles. It is shown that the calculated charge can be interpreted as a superposition of independent H + and OH − adsorption isotherms. The corresponding Langmuir adsorption isotherms are taken to model the zeta potential dependence on pH. In the vicinity of the isoelectric point the model fits well with the experimental data, but at higher ion concentrations considerable deviations occur. The deviations are discussed. Furthermore, the numerical results for the run of the potential in the diffuse part of the double layer were used to determine the electrostatic interaction potential between the particles in correlation with the zeta potential measurements. The corresponding total interaction potentials, including the van der Waals attraction, were taken to calculate the coagulation half-life for a suspension with a particle loading of 2 vol%. It is shown that stability against coagulation is maintained for Al 2O 3 particles in the pH region between 3.3 and 7 and for ZrO 2 only around pH 5. Stability against flocculation can be achieved in the pH regime between 4.5 and 7 for Al 2O 3, while the examined ZrO 2 particles are not stable against flocculation in aqueous suspensions.