engleski

Surface charge of gibbsite samples – 2 Questions and possible answers

We discuss the interfacial behaviour of α -Al2O3 basal planes in electrolyte solutions. The perfect, O-terminated, hydroxylated surface should consist of only doubly-coordinated hydroxyls (DCHs), i.e. a well-suited surface for the understanding of interfacial charging processes. Based on the popular MUSIC model these DCHs are not proton active over a wide pH range. The point of zero charge is expected at pH 6 and the surface potential should exhibit a plateau between pH 4.5 and 7.5. A wide range of data related to the interfacial charging of this plane have been obtained with various techniques including non-linear optics, atomic force microscopy, streaming potential and current measurements, colloid adsorption and contact angle titration. Most of these data show sharp points of zero charge below pH 5. In order to explain why the charging of these “ ideal” model systems is very different from those of corresponding particles we discuss the available data with respect to water ion adsorption.

α -Al2O3; electical interfacial layer; interfacial charging; MUSIC model; colloid adsorption

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