Deposition of colloidal zinc sulfide on glass substrate

The effect of colloidal forces involved in the deposition of spherical zinc sulfide colloidal particles on a packed bed of glass has been studied. Exp eriments were performed by pumping a suspension of monodisperse colloidal Z nS particles through a cylindrical plug of ground glass, and by continuous determination of the outgoing suspension concentration. The flux density of adhered particles, j(exp) (number of particles deposited per unit time and unit surface area of glass collector), decreased with both pH and ionic st rength of the aqueous electrolyte solution. Qualitative explanation of the experiments has been given in terms of the total energy of interaction betw een the dispersed particles and the substrate, and between the particles th emselves, computed from the extended DLVO theory, including acid-base inter actions. The contributions to the total free energy of interaction were det ermined from the zeta potential and surface free energy of ZnS and glass, m easured under different experimental conditions. It was found that at pH 4 (below the isoelectric point of ZnS) the efficiency of the deposition of Zn S on glass was maximum. At higher pH values the amount of ZnS deposited on glass clearly decreased. Increasing NaCl concentration at fixed pH (greater than or equal to 6) decreased the efficiency of the deposition. Adhesion e xperiments were also performed at pH 4 in the presence of increasing concen trations of CaCl2, or La(NO3)(3) in the dispersion medium. In these cases, the rate of adhesion was qualitatively well correlated with the computed Zn S-glass interactions. (C) 1999 Academic Press.