Wr. Richmond et al., THE RELATIONSHIP BETWEEN PARTICLE AGGREGATION AND RHEOLOGY IN MIXED SILICA-TITANIA SUSPENSIONS, Chemical engineering journal, 71(1), 1998, pp. 67-75
The rheological behaviour of concentrated suspensions of coarse SiO2 p
articles containing various amounts of fine TiO2 has been studied usin
g a viscometer which prevents settling of the suspended material. At a
volume fraction of 0.468 the mixed SiO2/TiO2 suspensions exhibit shea
r thinning behaviour, with the yield stress and viscosity being strong
ly dependent on pH and the TiO2 content of the suspension. Four differ
ent TiO2 samples are investigated, each having different inorganic sur
face coatings. The TiO2 particles adsorb on the surface of the SiO2 pa
rticles and coat them, resulting in suspensions with isoelectric point
s corresponding to those of suspensions containing TiO2 alone. The cha
nges in yield stress as a function of pH are influenced by the TiO2 co
ntent of the suspension, and when the silica:TiO2 volume ratio is grea
ter than similar to 0.03, the yield stress vs pH curve resembles that
of a pure TiO2 suspension. The maximum yield stress is observed at a p
H corresponding to the isoelectric point of the TiO2 component, and at
this pH, networks of TiO2 aggregates can form. The formation and brea
kdown of these aggregates has been monitored in concentrated suspensio
ns using focused beam reflectance measurement (FBRM). FBRM results cle
arly demonstrate that increases in the yield stress of the suspensions
are accompanied by an increase in aggregate size. At a given pH, chan
ges in plastic viscosity with increasing TiO2 content in the suspensio
ns appear to result from an increase in the maximum packing density du
e to the corresponding change in the particle size distribution. (C) 1
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