Ceramics-Silikáty 56, (1) 1 - 8 (2012)

Physicochemical properties of colloid zirconia aqueous sol, used as a binder in the investment casting industry, were thoroughly determined. The size of the particles was determined by dynamic light scattering, and the zeta potential of the particles was measured by microelectrophoresis. The average size of the particles was 13 nm and the zeta potential was positive, equal to 30 mV. The size distribution of particles deposited on mica surface was also determined using AFM measurements. The wetting properties of the binder suspension were determined for the paraffin/air interface using the shape analysis of pendant and sessile drops. The perfluorononanoic acid (PFNA), an anionic surfactant, the non-ionic fluorinated surfactants Zonyl FSO-100 and Rokafenol RN8, and the mixtures of the surfactants were studied. Our investigations showed that the Zonyl-FSO surfactant and its mixture with Rokafenol effectively reduced the dynamic contact angle from the initial value of 94^o to the value of 30^o. Such low contact angles represent an essential improvement of zirconia binder wettability, thus widen the range of applicability in investment casting of finely shaped details.