Colloidal ceramics processing

For practical ceramic colloidal processing it is important to understand the relative importance of the interactions discussed below, how mutual combinations and combinations with other forces which occur during processing evolve. 

A part from EDM, a near net shaping process is very important when the final purpose is the obtainment of a complex geometry, and above all, complex porous architectures. Several techniques are available to realize ceramics with complex shape and/or tailored porous architecture and they are all based on ceramic colloidal processes (Lewis, 2000). Furthermore, water based near net-shaping is of major interest among the wet-based forming processes being more environmental friendly and low cost. 

FIG. 1.6 A schematic diagram of colloidal processing of ceramic specimens. The figure illustrates some of the ways in which a dispersion is densified and transformed into porous or compact films or bulk objects. (Adapted and modified from Brinker and Scherer 1990.)... 

In Section 13.2, we begin with a closer look at one of the applications we alluded to in Vignette 1.5 in Chapter 1 (colloidal processing of ceramics) in order to gain some perspective on how interparticle forces influence the structure of a dispersion. 

Lange FF, Luther EP (1994) Colloidal Processing of Structurally Reliable Si3N4. In Hoffmann MJ, Petzow G (eds) Tailoring of Mechanical Properties of Si3N4 Ceramics. NATO ASI Series E. Vol 276, Kluwer Acad Publ Dordrecht, p 3... 

In relatively recent years the term colloidal processing has been coined to describe processing technologies in which the colloidal properties of ceramic powders are exploited. J.A. Lewis [6] comprehensively reviews colloidal processing and its potential. 

Colloidal processing of ceramic membrane supports. General introduction... 

Hidber et al. [9] described the colloidal processing of wet-milled a-alumina suspensions by centrifugal casting from a 80 wt-% suspension at pH 4.3. The mean particle diameter of the a-alumina powder was 0.3 pm and the BET surface area 8.59 m /g. Nitric acid or ammonia was used for electrostatic stabilisation. Very dense ceramics could be obtained with relative densities up to 99.9%. 

This chapter is split in two parts. The first part will briefly treat the preparation of flat ceramic membrane supports by colloidal processing. In our laboratory, these supports are used to study stability and gas separation properties of microporous silica membranes because they are easy to prepare and demand less complex testing equipment. 

Windlass, H., Raj, P.M., Balaraman, D., Bhattacharya, S.K., and Tummala, R.R., Colloidal processing of polymer ceramic nanocomposites for integral capacitors, in Proceedings of the International Symposium on Advanced Packing Materials Processes, Properties, and Interfaces, IEEE, Piscataway, NJ, 2001. 

Since then, other colloidal oxide systems have been investigated in order to prepare ceramic mesoporous membranes designed for ultrafiltration. The preparation of an electronically conductive membrane from a Ru02 Ti02 mixed oxides sol and the application to an electro-ultrafiltration process [25,26], as well as the preparation of titania and zirconia ultrafiltration membranes [27], have been described following a colloidal process in which a partial destabilization of a metal oxide colloidal suspension is used to produce top layers with different pore size and pore volume in the mesoporous range. In agreement... 

Rosenholm, J.B. et al., Colloidal processing related to the properties of the ceramic pai ticles and the sintered ceramic body, in Proceedings of the International Workshop on Ceramic Intetfaces, Properties and Applications III, Smart, R.St.C and Nowotny, J. eds.. Institute of Materials Press, London, 1998, p. 433. 

Hackley, V.A., Colloidal processing of silicon nihide with poly(acrylic acid) 1. Adsorption and electrostatic interactions, J. Am. Ceram. Soc., 80, 2315, 1997. 

Ducker, W.A. et al.. Forces between alumina surfaces in salt solutions Non-DLVO forces and the implications for colloidal processing, J. Am. Ceram. Soc., 77, 437, 1994. 

Colloidal Processing In ceramics, a variation of slip-casting in which a stabilized colloidal dispersion of particles is poured into a mold for sintering. 

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