Rheology Control of Ceramic Slurries and Formation of Thin Layered Films by Coating

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Since the internal structure of sintered film of ceramics strongly depends on the geometrical distribution of particles and the interparticle attractions in slurry, it is important to control the rheological properties of ceramic slurries for formation of thin sintered film with high density. The study is designed to provide a new mechanism for rheology control of flocculated suspensions and preparation technique of rheology-controlled ceramic slurries. In the fundamental study of suspension rheology, associating polymers are introduced as rheology control agents. The associating polymers are hydrophilic long-chain molecules to which a small amount of hydrophobic groups is incorporated. In colloidal suspensions, the associating polymers act as flocculants by bridging mechanism. The flow of flocculated suspensions is Newtonian at very low shear rates. The liquidlike responses in the limit of zero shear rates imply that the polymer bridges are constantly forming, breaking, and re-forming … More in a quiescent state. The suspensions with polymer at relatively high concentrations are highly elastic even under large strains. The particles may be connected by bridges of interchain associations that are soft and flexible. In practical application, the PZT(lead zirconate titanate) slurries are prepared by the additions of surfactant and binder polymer. The sintered films of PZT at a thickness of about 10 μm are formed by formulating the slurries in which the particles are weakly flocculated by reversible bridging. In addition, by the use of rheologically controlled slurries, the multilayers of phosphor are formed on the plastic film by screen printing. On heating, the phosphor layers are transferred to the CRT panel. Because of smooth surface and high packing density, the sintered layer of phosphor gives the brightness comparable to that manufactured by conventional method. The rheology control of ceramic slurries by reversible bridging has great potential in formation of micropatterns of ceramics. Less