Behaviour of clay and oxide suspensions: surface chemistry, surface force, microstructure, and rheology inter-relationships

Pek Ing Au

    Research output: ThesisDoctoral Thesis

    1025 Downloads (Pure)

    Abstract

    [Truncated] Surface chemistry conditions such as pH and ionic strength, are known to alter the underlying particle interaction configuration and microstructure which in turn controlling the rheological properties of colloidal dispersions. Hence the knowledge and understanding of the relationship between surface chemistry-microstructure-rheology of colloidal dispersion is essential allowinga more accurate control of properties for the industrial needs. The present study aims to develop an in-depth understanding particularly on the yield stress and microstructure of isotropically charged oxides and anisotropically charged clay particles under the effect of changing surface chemistry. The yield stress measures the strength of the particle network. Clay slurries from different sources or deposits often display different rheological and surface charge properties. Inthis body of work, the differences in yield stress-pH behaviour and microstructure were used toidentify the important factors responsible for the variation in rheological behaviour. The possible governing factors of clay rheology are the effect of impurities, crystallinity, swelling nature, particle shape and size, ionic strength, and structural recovery.

    The first part of the thesis focuses on the characterisation and evaluation of the properties and behaviour of isotropically charged oxides including alumina, titania, zirconia and silica. The particle size and shape were revealed to be important controlling parameters of the aggregate structure and rheological behaviour of oxide suspensions. The predominant stacking of plateswas observed for platelet alumina. The size polydispersed spherical alumina particles formed small and compact aggregates with insignificant inter-aggregate void spaces. On the contrary, the relatively size monodispersed titania and zirconia particles formed large compact aggregates with large inter-aggregate porosity. Interestingly, the microstructure of oxides was found to be independent of the surface chemistry condition. Excellent correlation between zeta potential-pHand yield stress-pH data was obtained. The variation of yield stress with pH was therefore a result of the changing interparticle force. An experimental and computational study of fragmentation process of polymer-bridged silica flocs was also conducted addressing the effectof shear rate. Experimental characterisation via particle size distribution and microstructural analysis as a function of shearing time revealed that pure fragmentation with negligible reaggregation occurred under both uniform and high shear conditions. The temporal evolutionof size density function was compared with that obtained via population balance modelling. A good agreement between experimental and simulated results was observed supporting the experimental outcomes.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    • The University of Western Australia
    Award date21 Jun 2016
    Publication statusUnpublished - 2016

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