Ceramic Suspension Rheology

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... 

FIGURE 12.2 Constitutive equations for ceramic suspension rheology. 

Ceramic Suspension Rheology son to the particle radius. This equation is given by... 

Bergstrom, L., and Sjostroum, E., Temperature-induced flocculation of concentrated ceramic suspensions rheological properties, J. Eur. Ceram. Soc., 19, 2117, 1999. 

Leo S, Tallon C, Franks GV (2014) Aqueous and nonaqueous colloidal processing of difficult-to-densify ceramics suspension rheology and particle packing. J Am Ceram Soc 97 3807-3817... 

Rheological methods are widely used to determine the properties of concentrated ceramic suspensions. Rheology can be used as an analysis method, e.g. when determining the optimal amount of dispersant from measurements of viscosity versus the amount of dispersant added. In addition, rheological measurements are often used for quality control in order to minimize the batch-to-batch variation before a ceramic suspension is processed further, e.g. spray dried or tape cast. The rheological behaviour can also be used as a direct process parameter, which should be appropriately adjusted to obtain the optimal green-body properties after forming. 

Binders in Ceramics, Powder Metallurgy, and Water-Based Coatings of Fluorescent Lamps. In coatings and ceramics appHcations, the suspension rheology needs to be modified to obtain a uniform dispersion of fine particles in the finished product. When PEO is used as a binder in aqueous suspensions, it is possible to remove PEO completely in less than 5 min by baking at temperatures of 400°C. This property has been successfully commercialized in several ceramic appHcations, in powder metallurgy, and in water-based coatings of fluorescent lamps (164—168). 

Unlike clay-based systems, modem ceramics require additives, termed binders, to provide the plasticity required for ductile-forming methods to be used. These organic additives serve to modify the rheological behavior of the ceramic suspensions and impart handling strength to the green, as-formed ceramic bodies. Their... 

Ceramic suspensions can also be deposited by dispensing or extrusion from a nozzle. While printing is a parallel process, i.e., many nozzles per color or substance are involved — say 128 or more, dispensing and extrusion processes usually use a single nozzle. The rheological properties of the ceramic suspensions are different from those of inkjet inks they may be much more viscous, i.e., contain a... 

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. 

All of the different rheological behaviors just discussed are observed in ceramic suspensions and so is time-dependent behavior. We need to know the rheological behavior of ceramic suspensions to predict how... 

This section on concentrated suspensions discusses the rheological behavior of sj tems which are colloidally stable and colloidally unstable suspensions. For stable sj tems, the rheology of sterically stabilized and electrostatically stabilized systems wiU be considered. For sterically stabilized suspensions, a hard sphere (or hard particle) model has been successfid. Concentrated suspensions in some cases behave rheologically like concentrated polymer solutions. For this reason, a discussion of the viscosity of concentrated polymer solutions is discussed next before a discussion of concentrated ceramic suspensions. 

Monodiefperse Spheres The rheology of concentrated ceramic suspensions is very important for good mold filling. For concentrated suspensions that are colloidally stable (by steric means, giving a hard sphere model), there is a particle volume fraction (i.e., = 0.63 for... 

The flow pattern of the powder mixture through the extruder influences the quality of the shaped article. The rheology of concentrated ceramic suspensions can be divided into four classes ideal plastic, Bingham, shear thinning, and shear thickening (dilant). 

Macromolecules are very important in the processing of powders into porous support layers. They are used to ensure the colloidal stability of ceramic suspensions, to control the rheology of suspensions and pastes, to avoid cracking... 

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