Deposition of wood resin emulsion droplets on ceramic oxides

Abstract

The kinetics of deposition of wood resin emulsion droplets from aqueous dispersions onto Al₂O₃, ZrO₂, Cr₂O₃ and TiO₂ surfaces in stagnation point flow was studied using reflectometry. A semiquantitative measure for the amount deposited was obtained from theoretical mass transfer to the collector surfaces. Parameters investigated were electrolyte concentration and valence and pH (4.5 and 6.5). Electron spectroscopy for chemical analysis experiments showed that all oxide surfaces contained a very thin layer of hydrophobic impurities that covered a fraction of the surfaces. Taking the different isoelectric points into account, no qualitative differences between the oxides were observed. It is suggested that surface contamination affects the deposition process but its importance depends on the type of electrolyte used. For stable dispersions the initial rate of deposition was rate-determining, the rate remaining constant up to 50% or more of total deposition, depending on the electrolyte. The initial rate was a function of electrolyte concentration and decreased when the dispersion was made unstable by addition of electrolyte. Deposition could not be described in terms of the model for diffusion-controlled particle deposition developed by Dabros and van de Ven. The final amount deposited was a function of emulsion concentration, which is interpreted as a surface kinetic effect resulting from re-formation of droplets upon deposition.