Colloidal Filtration and (Simultaneous) Sedimentation of Alumina and Silica Suspensions: Influence of Aggregates

Abstract

Colloidal filtration and (simultaneous) sedimentation is studied for suspensions of alumina particles and monodisperse silica spheres. A comparison is made between stable suspensions and systems which are aggregated due to salt addition (silica) or absence of a deflocculant (alumina). From separate sedimentation experiments we conclude that the stable silica settles as an ordered particle array, that the unstable silica sediments as separate aggregates, and that aggregated alumina behaves as a densifying network. The filtration results show that settling of aggregates during filtration changes the filtration kinetics in accordance with our model for simultaneous filtration and sedimentation. Further, aggregates in suspension are shown to have little influence on the silica compact microstructure, whereas they clearly increase porosity and permeability of the alumina compact. We also find that for all suspensions porosities of compacts prepared by sedimentation are clearly larger then porosities of filter compacts. [

Particle size effects on colloidal processing of oxide powders

“…18 The densities of consolidated powder compacts were measured by the Archimedes method using kerosene. % A1 2 O 3 , 24.0 wt.…”

Effects of Ammonium Chloride on the Rheological Properties and Sedimentation Behavior of Aqueous Silica Suspensions

“…Above some critical volume fraction, known as the gel point ( g ), the clusters become overcrowded and an inhomogeneous space-filling network (or gel) forms, which may or may not sediment depending on its strength. 13 Philipse et al 14 have studied colloidal filtration of relatively dilute, aggregated silica suspensions and shown that simultaneous aggregate sedimentation leads to deviations from the known linear relationship between compact thickness and the square root of the filtration time as well as a decrease in process time. Carpineti et al 15 have studied fast, salt-induced colloidal aggregation phenomena, and shown that growth from dilute systems ceases because of sedimentation when clusters reach some maximum size.…”

Formation and liquid permeability of dense colloidal cube packings

“…To derive the √ t-scaling relation for growing packings in the experiments described in this study, we briefly review the derivation reported in Ref. [36]. We consider the situation as depicted in Fig.…”

“…Figure 4(a) shows a typical plot measured during the formation of a packing. Unlike for flow through a packing of constant thickness, the permeated mass through a growing packing does not grow linearly in time due to the increase of the hydrodynamic friction during packing formation [7,19,36]. From the derivation described in Appendix A, it follows that for a growing, incompressible and homogeneous packing, the permeated solvent mass W scales with the square root of the time t rather than with t according to…”

“…This result suggests that the packing is thicker than expected from packing formation by forced convection only. The deviation from the √ t-scaling relation has previously been related to the settling of the particles during packing formation [36]. Indeed, settling of both solid and hollow cubes is a process that occurs during packing formation, owing to their short gravitational lengths (approximately 24 nm for the solid cubes and 890 nm for the hollow cubes).…”