Microstructure consolidated suspensions

Surface area of a powder increases geometrically with decreasing particle size, so that the volume fraction of the outermost layer of ions on the surface increase significantly, which has a significant effect on properties of the powder. With the development of nanotechnology, it is readily to synthesize powders with nanosized particles (1-100 nm). Therefore, characterization of surface properties becomes more and more important. Specifically for ceramics or transparent ceramics, the consolidation of fine ceramic powders with liquid suspensions to produce more uniform green bodies has been shown to play an important role in the fabrication ceramics, especially when special or complex structures are required. Because the quality of microstructure of the consolidated body is determined by the dispersion behavior of the powder and the interaction between the particles in the suspension, which is closely related to the surface properties of the particles, controlling the physical and chemical properties of particles is a critical to ceramics fabrication. 

The structure of the suspension and the compression rheological properties determine much of the consolidation behaviour. Colloidally stable, dilute suspensions of monodisperse spherical particles are well described by the relationships described above. The effect of the shape of the particles and the particle concentration can be accounted for by multiplying the expression given in equation (9.22) by suitable factors. For flocculated suspensions, the situation is much more complex. The attractive interparticle forces can produce a cohesive network of particles, which will resist consolidation depending on its strength. Because flocculation generally affects the suspension microstructure, the permeability will change. 

Hirata Y., Onoue K. and Tanaka Y., 2003. Effects of pH and concentration of aqueous alumina suspensions on pressure filtration rate and green microstructure of consolidated powder cake, J. Ceram. Soc. Jpn., Ill, 93-99. 

The structure of the consolidated colloid formed is actually more complex than the arrangements illustrated in Fig. 4.33. The microstructures of nearly mono-disperse Si02 particles shown in Fig. 4.34 indicate that the difference in structure formed from the stable suspension and the unstable suspension is not controlled by the way in which the individual particles arrange themselves in the sediment but rather the way they group themselves to form densely packed multiparticle units called domains (52). Figure 4.34c shows that the domains in a consolidated... 

Figure 4.34 Microstructures of particle domains formed by centrifugal consolidation of Si02 colloidal suspensions at (A) = 0 mV, (B) = 68 mV and (C) I = 110 mV. The average particle diameter is 0.7 p,m. (From Ref. 52.)...

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