Electrokinetics and rheology of silicon nitride suspensions

Results of electrokinetic and rheological measurements of silicon nitride suspensions are presented. The surface modification of Si3N4 powders with fluoric acid strongly influences the surface charge of the powders in aqueous suspension (indicated by acoustophoretic measurements). For example the isoelectric point of the Si3N4 powder SN E10 (UBE) is shifted from pH equal 5,9 for the as-received powder to pH equal 8,5 for the same powder treated with fluoric acid. The oxygen content of this powder is reduced from 1,26 to 0,67 weight percent. Furthermore the influence of PVA-binder on the surface charge and the viscosity of aqueous Si3N4 suspensions is investigated.