Deposition of Colloidal Zinc Sulfide on Glass Substrate

Abstract

The effect of colloidal forces involved in the deposition of spherical zinc sulfide colloidal particles on a packed bed of glass has been studied. Experiments were performed by pumping a suspension of monodisperse colloidal ZnS particles through a cylindrical plug of ground glass, and by continuous determination of the outgoing suspension concentration. The flux density of adhered particles,jexp(number of particles deposited per unit time and unit surface area of glass collector), decreased with both pH and ionic strength of the aqueous electrolyte solution. Qualitative explanation of the experiments has been given in terms of the total energy of interaction between the dispersed particles and the substrate, and between the particles themselves, computed from the extended DLVO theory, including acid–base interactions. The contributions to the total free energy of interaction were determined from the zeta potential and surface free energy of ZnS and glass, measured under different experimental conditions. It was found that at pH 4 (below the isoelectric point of ZnS) the efficiency of the deposition of ZnS on glass was maximum. At higher pH values the amount of ZnS deposited on glass clearly decreased. Increasing NaCl concentration at fixed pH (≥6) decreased the efficiency of the deposition. Adhesion experiments were also performed at pH 4 in the presence of increasing concentrations of CaCl2or La(NO3)3in the dispersion medium. In these cases, the rate of adhesion was qualitatively well correlated with the computed ZnS–glass interactions.