Particle segregation phenomena occurring during the slip casting process

Homogenous microstructures are important to improve the reliability of the final ceramic products. This target is usually hindered by particle segregation phenomena that occur during colloidal processing when the suspended powders present significant differences in average particle size. In the present work binary suspensions have been prepared by mixing fumed silica (D50=0.07 μm), with coarser silica powders (P600, D50=2.2 μm and P10, D50=19 μm) in different proportions. The effects of milling time, average particle size, proportion of the components in the mixtures and total solids volume fraction on the extent of particle segregation that occurs during unidirectional slip casting were evaluated. Particle size distribution analysis and scanning electron microscopy revealed that successive layers of fine/coarse/fine particles have been successively deposited during casting. The extension of segregation was dependent upon particles’ size ratio, total solids volume fraction and milling time. It could be concluded that the clogging effect of the cake by the fine particles was the main mechanism responsible for particle segregation.