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Author

Gonghou Wang

Date of Award

10-1998

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Materials Science and Engineering

Supervisor

Patrick S. Nicholson

Abstract

The ionic stability of oxide particles in polar non-aqueous media is studied. Surface chemistry and interparticle forces are manipulated by controlling the acidity and ionic strength of the suspensions without dispersants. The acidity of ethanolic solution is determined using ion transfer functions, wherein the relationships between acidity, oxide particle-surface-charge, zeta-potential, stability and suspension rheological behaviour are established. The ionic stability of oxide particles in ethanol can be controlled by combination of potential determining ions and indifferent electrolyte to optimize the values of repulsive potential and repulsive force. It is shown oxide particles can be charge-stabilized, as in aqueous suspensions. The viscosity and flow curves for oxide/ethanol suspensions are acidity dependent. The flow curves of the suspensions follow the Casson model and the Casson yield value is used to evaluate their stability. Positive isoelectric point shifts were observed for alumina and magnesia in ethanol on increasing the solid concentration. However both dilute and concentrated aqueous suspensions of alumina give the same isoelectric point. Silica/ethanol suspensions are stable near the IEP. This result suggests the colloidal stability of silica in ethanol can not be explained exclusively by the ionic stability mechanism of DLVO theory. The discrepancy is believed due to a steric barrier consisting of a silicic acid gel network. The surface chemistry and rheological properties of alumina suspensions in EtOH and DMSO are strongly influenced by the ionic strength of the suspensions. Rheological measurements show the viscosity of the suspensions decreases with increasing salt concentration due to suppression of the second electroviscous effect. Solvent is found to have a marked influence on suspension rheology. The heterocoagulation behaviour of oxide-mixture/ethanol suspension systems is examined, elucidating the general principles underlying structure formation in mixed dispersions. It is demonstrated that the architecture of composites can be controlled by manipulation of the relative colloidal stability of the constituent primary particles.

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