A STUDY ON THE ADHESION OF CALCIUM-CARBONATE TO GLASS - ENERGY-BALANCE IN THE DEPOSITION PROCESS

This work describes an experimental investigation on the adhesion of i n situ synthesized calcite colloidal particles to rotating glass slide s. The relative importance of the hydrodynamic processes involved was analyzed by measuring the amount adhered as a function of both the tem perature and the rotation velocity. The adhesion was found to be tempe rature-dependent. At a given rotation speed of the slide, there exists a value of the temperature for which the adhesion is maximum. This va lue is lower, the higher the rotation speed. Comparison between experi mentally determined particle fluxes (number of particles adhered per u nit time and unit surface area of collector) and those calculated from Levich's theory (where laminar flow and absence of particle-collector repulsion are assumed) suggests that the hydrodynamic regime in the v icinity of the slide changes from laminar to turbulent when either the velocity or the temperature is increased above a certain critical val ue, corresponding to maximum adhesion. The effect of the electrolytes CaCl2 and MgCl2 on the adhesion was also studied in the range of conce ntrations between 0.7 and 70 mM. For fixed hydrodynamic conditions and temperature, the adhesion between the particle and the collector was found to be controlled by the interfacial interactions, including Lifs hitz-van der Weals (LW), electrostatic double layer (EL), and acid-bas e (AB). The calcite-solution and glass-solution interfaces were comple tely characterized by using electrophoresis, contact angle, and thin-l ayer wicking techniques, together with van Oss et al.'s model of inter facial thermodynamics. From these data the total energy of interaction between the particle and the substrate was computed using either the classical DLVO model (EL + LW) or the extended theory (EL + LW + AB) f or different electrolyte concentrations, and reasonably good agreement was found between the experimentally observed particle attachment and the predictions of the extended DLVO theory.