Rheological properties of aqueous silicon nitride suspensions

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.