engleski

Determination of Isoelectric Point of Silicon Nitride by Adhesion Method

Isoelectic point (i.e.p.) of silicon nitride is an important parameter in the technology of the fine ceramic production. The determination of its value may have problem, especially in nonaqueous media. For this purpose the adhesion method for i.e.p. determination was developed. In this paper the batch method was demonstrated. The kinetics of attachment of silicone nitride colloid particles on titanium collector beads was followed. The closed cylinders containing colloidal suspension of silicon nitride particles together with certain amount of titanium beads were rotated, and the silicon nitride colloid particle number concentration was measured as a function of time. From the experimental data the rate constants of attachment were determined by considering the reverse detachment process. The i.e.p. of titanium is at pH = 2, so that titanium surface was negatively charged in whole examined pH region. In the region where pH‹8 silicon nitride was positively charged which promoted the attachment. Above pH=8, both silicon nitride and titanium surface are negatively charged which significantly reduces the attachment rate. Theoretical rate constant in absence of interaction forces (kdiff) was calculated by considering the convection diffusion of colloid particles towards the moving beads. The velocity of titanium beads, with respect to the liquid suspension, was calculated taking into account gravitation, buoyancy and friction forces. The pH at which experimental rate constant coincides with the theoretical kdiff value was taken as the isoelectric point. The results were confirmed by independent electrokinetic measurements. Preliminary experiments in nonaqueous medium indicated the applicability of adhesion method also to these systems.

Isoelectric Point; adhesion; metal oxides; electrocinetics

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