COLLOIDAL PROCESSING OF A VERY FINE BATIO3 POWDER - EFFECT OF PARTICLE INTERACTIONS ON THE SUSPENSION PROPERTIES, CONSOLIDATION, AND SINTERING BEHAVIOR

The relation between the suspension state and the rheological properti es, the consolidation, and packing of a very fine (nanosized) BaTiO3 p owder has been investigated, The BaTiO3 powder was suspended in a nona queous medium by adsorbing fatty acids and a polymeric dispersant, pol y(12-hydroxy stearic acid), (PHS), at the BaTiO3/decane interface, Cal culated interparticle energies imply that the suspension with PHS adso rbed is colloidally stable, while the suspensions with oleic and octan oic acid can be characterized as weakly and strongly flocculated, resp ectively, Analysis of settling experiments and rheological measurement s at high concentrations confirmed these characteristics, Pressure fil tration resulted in nearly identical green body densities in spite of the differences in colloidal properties, but the preliminary sintering experiments and microstructural characterization showed that the stro ngly flocculated suspension displays a significantly retarded sinterab ility compared to the colloidally stable and the weakly flocculated su spensions, The absence of a correlation between green density and sint ering behavior was explained by considering both the volume taken by t he adsorbed fatty acids and the PHS polymer-which can be substantial f or nanosized powders-and the state of the suspension, While a decrease in the thickness of adsorbed surfactant or polymer layer will enable a higher particle packing density, such a thin adsorbed layer results in a more strongly flocculated suspension which will resist dense pack ing, Hence, it is suggested that the green bodies of the colloidally s table and the weakly flocculated suspensions correspond to a relativel y homogeneous, but loosely packed, green body microstructure, The stro ngly flocculated suspension results in a green body with a more inhomo geneous microstructure.