Mechanical Properties of Dry Ceramic Powders

At low force, the powder particles remain fixed in position and the particles deform elastically. This takes place over a very small range of deformation for diy ceramic powders. This behavior is referred to as a compact body deformation. This deformation can be estimated from the elastic properties of the particles, the void fraction of the powder packing, and the nature of the liquid or binder occupying the voids [71]. 

With higher forces the friction between particles is overcome and the particles slide with respect to one another. This behavior is referred to as a plastic body deformation. The start of this particle movement 

After structural reorganization to rerrwve packing holes 

Comminution of agglomerates Ming the voids with fir e particles FIGURE 12.33 Behavior of a spray dried powder during die pressing. 

After the precedings movement is essentially complete, the particles themselves deform elastically and plastically. If the particles are 

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Mechanical Properties of Dry Ceramic Powders and Wet Ceramic Suspensions... 

In this chapter, we described the fundamentals of suspension iheol-ogy from dilute suspensions to concentrated suspensions. Attention has been paid to interparticle forces and the structure of the suspension because these things drastically influence suspension iheology. In addition, visco-elastic properties of concentrated suspensions including ceramic pastes have been discussed. Finally, the mechanical properties of dry ceramic powders have been discussed in terms of the dJoulomb yield criterion, which gives the stress necessary for flow (or deformation) of the powder. These mechanical prc rties will be used in the next chapter to predict the ease with vdiich dry powders, pastes, and suspensions can be made into green bodies by various techniques. 

In this chapter, we have described the colloid chemistiy of ceramic powders in suspension. Colloid stability is manipulated by electrostatic and steric means. The ramifications on processing have been discussed with emphasis on single-phase ceramic suspensions with a distribution of particle sizes and composites and their problems of component segregation due to density and particle size and shape. The next chapter will discuss the rheology of Uie ceramic suspensions and the mechanical behavior of dry ceramic powders to prepare the ground for ceramic green body formation. The rheology of ceramic suspensions depends on their colloidal properties. 

These mechanical properties are important in designing the equipment necessary to process the ceramic suspensions, pastes, and dry powders into ceramic green bodies. Each of the different raw materials... 

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