Abstract

Since the properties of a ceramic green body and compact 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 ceramic manufacturing. Macroscopically, the rheological properties of a suspension are the key parameters that influence the behaviour during the shaping process. The rheological behaviour of aqueous suspensions of nanosized fumed silica (DEGUSSA, Aerosil OX50) with different amounts of OX50 (10 to 50 wt.%) was measured over a pH-range from 1 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 solid content of the suspensions. Since the rheological behaviour of the suspensions could not be explained by the zeta -Potential measured for OX50, the suspensions were investigated by means of so-called cryo-SEM characterization. A droplet of the suspension is quench-frozen in subcooled nitrogen (-210 degreesC), prepared and the water is sublimed at -90 degreesC. Thus it was possible to visualize the agglomerate structure of the primary OX50-particles within the suspensions.