Mechanical properties ceramic suspensions

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. 

In Chapter 12 of this book, the mechanical properties of ceramic suspensions, pastes, and diy ceramic powders are discussed. Ceramic suspension rheology is dependent on the viscosity of the solvent with polymeric additives, particle volume fraction, particle size distribution, particle morphology, and interparticle interaction energy. The interparticle forces play a veiy important role in determining the colloidal stability of the suspension. If a suspension... 

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... 

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

Considering a mass of ceramic powder about to be molded or pressed into shape, the forces necessary and the speeds possible are determined by mechanical properties of the diy powder, paste, or suspension. For any material, the elastic moduli for tension (Young s modulus), shear, and bulk compression are the mechanical properties of interest. These mechanical properties are schematically shown in Figure 12.1 with their defining equations. These moduli are mechanical characteristics of elastic materials in general and are applicable at relatively low applied forces for ceramic powders. At higher applied forces, nonlinear behavior results, comprising the flow of the ceramic powder particles over one another, plastic deformation of the particles, and rupture of... 

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. 

Correlations Between Suspension Formulation, Drying Parameters, Granule Structure, and Mechanical Properties of Spray Dried Ceramic Granules... 

Liu, Y. Huang, J. Yang, Effect of rheological properties of the suspension on the mechanical strength of A1203-Zr02 composites prepared by gelcasting. Ceramics International, 28, 159-164 (2002). 

Anionic polyelectrolytes are very effective deflocculating agents for suspensions of bariiun titanate. Properties of ceramic slip are affected by pH. In alkaline pH, interaction occurs through electrostatic mechanism. ... 

These relate mainly to the degree of purity of the powders and the nature of the particles surface. Purity depends on the source of the raw materials and the transformation processes that give rise to impurities (iron, heavy metals, salts, carbon, etc.). It will determine to a large extent the sintering reactivity, with the possible formation of a second intergranular phase and the final properties of the piece (mechanical, chemical, electric, etc.). The surface properties of the particles determine the mechanisms of species adsorption and dissolution. They will control the dispersion properties, homogenity and the rheological behavior of the suspensions and ceramic pastes (section 5.3). 

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