Optimizing the rheological behavior of silicon nitride aqueous suspensions

This work focuses on the optimization of the rheological behaviors of the Si3N4 aqueous suspensions by changing the kind and concentration of dispersant, pH value of dispersing medium and other process parameters. Zeta potentials, sedimentation and rheological behavior measurements have been carried out to prepare a well dispersed, uniform and concentrated Si3N4 aqueous suspension. The isoelectric point of Si3N4 powders is at the pH value of 4.2 and the value of Zeta potential is up to its maximum near pH 11. A good agreement between sedimentation and electrophoresis tests is found which identifies the optimum pH value for promising dispersion. Na2SiO3 is an efficient dispersant which increases Zeta potentials in magnitude and improves the fluidity of Si3N4 suspensions effectively. The optimum concentration of dispersant is in the range of 1.0 to 1.2 wt%, which is independent on the solids volume fraction of slips. A ball milling of 8 h helps to improve the fluidity of suspensions while longer milling is detrimental.