The effect of surface modification of Si3N4 particle on the colloidal behav
ior and the rheological properties of aqueous Si3N4 suspensions under stead
y and oscillatory conditions are investigated in detail. Due to the decreas
e of the oxidizing level, the isoelectric point (IEP) of the modified parti
cle shifts to basic region gently. Attempts have been made to apply rheolog
ical models to the suspensions with various solid volume fraction (phi). Fo
r the as-received suspensions, the Sisco model provides the best fit in the
range of phi less than or equal to 0.30 while the Casson model in 0.35 les
s than or equal to phi less than or equal to 0.45. The shear behavior of mo
dified suspensions fits to Sisco model in the range of phi less than or equ
al to 0.40 and Casson model in 0.45 less than or equal to phi less than or
equal to 0.54. The rheological behavior of modified suspensions is improved
efficiently. The critical strain decreases and the linear viscoelastic reg
ime narrows continuously with increasing solid concentration. For the modif
ied suspensions, the linear viscoelastic regime broadens and the correspond
ing elastic modulus decreases sharply. With increasing solid concentration,
the characteristic frequency shifts toward lower frequencies and the suspe
nsion transforms from more viscous to more elastic. (C) 2001 Kluwer Academi
c Publishers.