High-purity silica glass components can be produced powder technologically with a sintering temperature as low as 1250 °C using nanosized filmed silica powders. Due to the low bulk density of nanosized powders only suspension-based shaping techniques can be used. Since the properties of a green body and the sintered component produced thereof are strongly influenced by the properties of the suspension used, controlling structure and properties of a suspension is a very important issue in powder manufacturing of glasses. Macroscopically, the rheological properties of a suspension are the key parameters that influence the behavior during shaping process. The rheological behavior of aqueous suspensions of nanosized fumed silica (DEGUSSA, Aerosil OX50/A380) with different solids content (10 to 50 wt %) was measured over a pH-range from 3 to 13 by means of rotational viscosimetry. A distinct maximum of the viscosity was observed for a pH of about 7 to 8, independent of the solids content of the suspensions. Since the rheological behavior of the suspensions could not be explained by the ζ-potential measured for OX50, the suspensions were investigated by means of Low-Temperature-SEM (LTSEM) or cryogenic SEM (Cryo-SEM) to visualize the agglomerate structure of the particles within the suspension.
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