Colloid 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... 

In the ceramic industry the rheology of clay suspensions plays a major role. Their colloidal properties are of especial significance in the process of slip-casting, in which a clay slurry is put in contact with a porous plaster mould, which sucks up the water to leave a solid form ready for firing, Here the suction provided by the porous mould in relation to the rate of flow of water through the clay matrix is important. The structure of the clay slurry, as determined by its degree of dispersion, has also to be controlled by suitable additives. 

Interfacial phenomena at metal oxide/water interfaces are fundamental to various phenomena in ceramic suspensions, such as dispersion, coagulation, coating, and viscous flow. The behavior of suspensions depends in large part on the electrical forces acting between particles, which in turn are affected directly by surface electrochemical reactions. Therefore, this chapter first reviews fundamental concepts and knowledge pertaining to electrochemical processes at metal oxide powder (ceramic powder)/aqueous solution interfaces. Colloidal stability and powder dispersion and packing are then discussed in terms of surface electrochemical properties and the particle-particle interaction in a ceramic suspension. Finally, several recent examples of colloid interfacial methods applied to the fabrication of advanced ceramic composites are introduced. 

Uses Binder, thickener, pigment/foam/filler stabilizer, dispersant, emulsifier, plasticizer, vise, control agent, sedimenting aid, and protective colloid in coatings, paints, resins, mining, batteries, insecticides, fungicides, herbicides, rubber, textiles, leather, ceramics, suspension polymerization, and pharmaceuticals Properties Gran. water-sol. nonionic 100% act. 

Saito N., Haneda H., Li D., Koumoto K. Characterization of zinc oxide micropatterns deposited on self-assembled monolayer template. J. Ceram. Soc. Jpn. 2002 110 386-390 Santos L.R.B., Santilli C.V., Pulcinelli S.H. Sol-gel transition in Sn02 colloidal suspensions viscoelastic properties. J. Non-Cryat. Solid 1999 247 153-157 Santos L.R.B., Craievich A.F., Santilli C.V., Pulcinelli S.H. Sol phase and sol-gel transition in Sn02 colloidal suspensions. J. Appl. Cryst. 2000 33 609-613 Sasaki T., Watanabe M., Michiue Y., Komatsu Y., Izumi F., Takeuchi S. Preparation of acid-base properties of a protonated titanate with the lepidocrocite-like layer structure. Chem. Mater. 1995 7 1001-1007... 

A suspension is a mixture which arises when solid particles are mixed optimally in a liquid. The suspended solid particles have a diameter of appr. 200-0.5 nm and the mixture is also called a colloidal dispersion . The liquid is the medium of dispersion. A clay suspension is suitable for the production of so-called hollow, non-rotation symmetrical articles, such as sanitary ware. Until the beginning of the 20th century these products were made by beating the clay into plaster of paris moulds, the so-called dies. Gradually people discovered not only the physically and chemical properties of suspensions but also how to change them and thus the technique of clay moulding developed and complicated shapes could be made. The science of colloid chemistry has been essential here. In the field of technical ceramics the moulding technique is also applied with other raw materials than clay. 

At this voliime fraction, the viscosity diverges because the shear stress is now given by the particle-particle contact in the tightly packed structure. As a result, we obtain a fluid with visco-elastic properties similar to polymeric solids. In ceramic processing, we extrude and press these pastes into green shapes. As a result, the rheology of ceramic pastes is of importance. The rheology of very concentrated suspensions is not particularly well developed, with the exception of model systems of monodisperse spheres. This section first discusses visco-elastic fluids and second the visco-elastic properties of ceramic pastes of monodisperse spheres. The material on visco-elastic fluids draws heavily from the book Colloidal Dispersions by Russel, Saville, and Schowalter [31]. 

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