Effects of Polyelectrolyte as a Dispersant on Slip Casting of Ceramic Slurries

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It is desirable in slip casting to prepare concentrated slurries whilst retaining fluidity. A polyelectrolyte as a dispersant is effective for thickening of the slurries and that polymer have a characteristic function in fluidizing slurries, other than that dispersion and stabilization. The flow point refers to the least amount of a medium (the thickening limit) required for a definite amount of powder of a start to flow. The fluidity of the slurries in the vicinity of the thickening limit was affected by a kind of dispersant, the concentration and molecular weight of dispersants and the solid loading in the slurries. The dispersion accompanied by fluidization and the limit of thickening should be related to the structure of the length extension of dispersant (the conformation of dispersant) in the adsorption layr on the ceramic particles and also to the interaction among such solid particles in the concentrated slurry. A polyelectrolyte dispersant has electrostatic effect and an addit … More ional steric effect since the polymer expands in the adsorption layr thereby exceeding the effective distance that the van der Waals attraction force operates over.An average shell volume occupied in the adsorption layr on alumina by a polyacrylic acid ammonium salts molecule (PAA) defined as the average area occupied by an adsorped PAA on alumina multiplied by the average thickness of the water layr at the limit of thickening, has been calculated from the adsorbed amount of PAA and from the flow points of alumina in the presence of PAA of different molecular weights. A steric effect of the PAA dispersant on the dispersion of alumina resulted in a flow with no yield stress. This was due to the change of the extension of PAA in the adsorption shell from a sphere to an ellopsoid with a long axis which exceeded the effective distance that the van der Waals attraction force reaches at a molecular weight for the PAA of between 10,000-20,000.It was also developed the determination method of polyelectrolyte and discussed the effects of pH changes on the conformation changes for polymers in the slurries, the adsorbed amount of polymers and the dispersion accompanied by fluidization in the presence of dispersant. Less