Aa. Zaman et al., RHEOLOGICAL BEHAVIOR OF HIGHLY CONCENTRATED AQUEOUS SILICA SUSPENSIONS IN THE PRESENCE OF SODIUM-NITRATE AND POLYETHYLENE OXIDE, Journal of rheology, 40(6), 1996, pp. 1191-1210
The shear flow properties of aqueous silica suspensions at different S
olids loading in the presence of polyethylene oxide (PEG) and added sa
lt (NaNO3) have been investigated. Particular attention is given to th
e evaluation of the role of electrolyte concentration, pH, and polymer
concentration in viscosity reduction. The variation of the rheologica
l properties with shear rate, solids loading, particle size, pH, elect
rolyte concentration, PEO concentration, and its molecular weight are
discussed. The viscosity of the silica suspension was determined to be
a decreasing function of the particle diameter and at 54% volume, the
effect of particle size was scaled using Peclet number and relative v
iscosity of the suspension (hard sphere scaling). The flow properties
of silica suspensions are highly affected by the pH of the suspending
media and concentration of the added salt. At a fixed electrolyte conc
entration, the viscosity decreases by increasing pH, reaches a minimum
, and then increases with further increase in pH. At a fixed pH level,
the same behavior was observed for viscosity as a function of electro
lyte concentration. The effect of the electrolyte concentration is mor
e significant at lower shear rates. It is shown that the rheological p
roperties of silica suspensions are strongly affected by the concentra
tion of the added polymer and its molecular weight. For each sample, t
here is a critical amount of polymer that must be added before low vis
cosities result. There is a nearly linear relation between the critica
l polymer concentration and volume fraction of the particles. The resu
lts of this work provide useful information for selection of a proper
pH range, electrolyte concentration, and optimum polymer concentration
to control the viscosity behavior of highly concentrated silica slurr
ies. (C) 1996 Society of Rheology.