DEVELOPMENT OF SHORT-RANGE REPULSIVE POTENTIALS IN AQUEOUS, SILICON-NITRIDE SLURRIES

The properties of aqueous, dispersed, silicon nitride slurries, with a n isoelectric point of pH 5.5, can be changed with additions of NH4Cl. At pH 10 the effect of adding NH4Cl is similar to that suggested by D LVO theory; namely, for concentrations greater-than-or-equal-to 0.5M, the viscosity vs shear rate behavior, the elastic modulus, and the rel ative packing density are identical to those for slurries prepared at the isoelectric point. On the other hand, the effect of salt on disper sed slurries prepared at pH 2 differs from the behavior implied by cla ssic DLVO theory; i.e., measurement of the same properties showed that the attractive interparticle potential was much weaker relative to th at produced at the isoelectric point. As previously reported for alumi na slurries, the results suggest that a short-range, repulsive interpa rticle potential is developed in salt-added slurries prepared at pH 2 which prevents attractive particles in the slurry from touching and ai ds particle packing. The same short-range potential apparently is not developed with salt additions at pH 10. The difference between silicon nitride and alumina slurries is apparent when the slurries are consol idated. Bodies consolidated from any silicon nitride slurry are elasti c (i.e., they fracture before they flow) unlike salt-added alumina slu rries, which are plastic.