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The Behavior of Zeta Potential of Silica Suspensions

Zeta potential, also known as electrokinetic potential, is one of the most relevant parameters controlling the rheological behavior of ceramic suspensions. It is the potential difference across phase boundaries between solids and liquids. Its measurement is frequently used in coagulation (aggregation) and dispersion processes in several applications, such as colloidal processing of ceramic pastes and slurries, water purification, paints and cosmetics.

In this paper, the authors discussed the behavior of zeta potential versus pH, in the vicinity and away from the isoelectric point (IEP), presented by suspensions of several silica raw materials of different crystal structures and specific surface area. The chosen silica powdered raw materials for this study were two crystalline polymorphs of silica (α-quartz and α-cristobalite), as well as vitreous silica. And it was observed that for pH values below the isoelectric point (IEP), the positive value of zeta potential of water suspensions of α-quartz and α-cristobalite, experienced a sudden steep increase with the increase in specific surface area of the powders. For pH values above the IEP, the zeta potential values of crystalline forms of silica (α-quartz and α-cristobalite) got gradually more negative with the increase in pH. Conversely in the case of vitreous silica, for pH values above 6, there was a steep change towards more negative values of zeta potential than those presented by quartz and cristobalite.

In conclusion, through this work, it was possible to identify different behaviors of the zeta potential versus pH for silica samples, crystalline or vitreous, which was found remarkably different from pH values below and above the IEP. And understanding how the zeta potential varies with crystalline and vitreous character and its dependence on powder surface area of silica raw materials would help to predict and control the rheological behavior of the silica slips. In this manner, the stabilization and destabilization of these ceramic materials under colloidal processing can be considerably facilitated.

Article by José Antonio Alves Júnior and João Baptista Baldo, from Universidade Federal de São Carlos, São Carlos, Brazil.

Full access: http://mrw.so/vja34
Image by Geoff Whiteway, from Flickr-cc.


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