School of Chemistry - Theses

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End date: 1999 × Subject: adsorption × Subject: dispersing agents × Subject: electric properties ×

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    Adsorption of polyphosphate dispersants onto oxide surfaces
    Simmons, Jennifer Carol ( 1993)
    The production of high-performance advanced material products based on controlled colloidal dispersions has received increased attention in recent times. In many cases, the mechanical strength of the final product relies on a homogenous microstructure resulting from a well-dispersed slurry. This may be achieved by the addition of dispersing agents to the colloidal dispersion. Inorganic dispersions offer greater durability than many of the organic compounds currently available. Polyphosphate dispersants are thought to act through electrostatic stablization, however the exact method of their action is unclear. The adsorption of polyphosphates onto colloidal zirconia (ZrO2) and titania (TiO2) particles has been studied as a function of chain length and pH. Adsorption isotherms and electroacoustic measurements have been used to study the adsorption process. Isotherms showed "high-affinity" type behavior. The extent of adsorption increased in each case as the pH decreased. Adsorption onto both oxide surfaces increased in the order P1 < P2 < P-5, where the subscript refers to the number of phosphate units in the chain. The shape of the adsorption isotherms indicated that the polyphosphates were adsorbed in a flat configuration in the plane of the surface. Electroacoustic results showed on a molar basis that the longer chain polyphosphates are more efficient at shifting the isoelectric point of the oxides. This was attributed to the greater specific adsorption of these molecules. The results of this study were consistent with an adsorption mechanism that is electrostatic in nature.