The influence of ammonium chloride (NH4Cl) on the rheological properties and sedimentation behavior of aqueous silica (SiO2) suspensions of varying solids volume fraction (φs) was studied. SiO2 suspensions with low NH4Cl concentration (≤0.05M, pH 5.2) exhibited Newtonian behavior and a constant settling velocity (U). The volume fraction dependence was well described by the Richardson-Zaki form, U = U0(1 - φs)n, where n = 4.63 and U0 = 1.0419 × 10-5 cm/s. At higher NH4Cl concentrations (0.07-2.0M, pH 5.2), suspensions exhibited shear thinning and more complicated sedimentation behavior due to their aggregated nature. For all suspensions studied, however, the apparent suspension viscosity, characteristic cluster size, and initial settling velocity were greatest at approx. 0.5M NH4Cl and exhibited a similar dependence on salt concentration. Above 0.5M NH4Cl, considerable restabilization was observed. This behavior cannot be explained by traditional DLVO theory.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of the American Ceramic Society|
|State||Published - 2000|
ASJC Scopus subject areas
- Ceramics and Composites
- Materials Chemistry