Colloidal ceramics

The production of fine particles that are either desirable (polymer colloids, ceramic precursors, etc.) or undesirable (soot, condensed matter from stack gases, etc.) involves chemical reactions, transport processes, thermodynamics, and physical processes of concern to the chemical engineer. The optimization and control of such processes and the assurance of the quality of the product requires an understanding of the fundamentals of microparticles. 

The methods as discussed above for controlling the stability of colloidal ceramic dispersions are summarised in Fig. 6.17. 

Fig. 6.17, Methods of stabilizing colloidal ceramic particles in liquids. (Redrawn from Pugh, Chap.

Van Houten [33] has shown that the maximum packing fraction obtained from the rheology of concentrated alumina suspensions is predictive for the maximum wet packing fraction that can be obtained in colloidal ceramic processing. 

Craig B.D. 1997. Interpenetrating Phase Ceramic/Polymer Composite Coatings. [LFF] Daniels M. 1999. Colloidal Ceramic Coatings with Silane Coupling Agents. [LFF]... 

Electrophoretic infiltration is a novel technique for the fabrication of fiber reinforced composites used by Kooner et al [234]. The technique involves arranging the fibers as one of the electrodes such that deposition of the colloidal ceramic occurs in the fiber preform. This method was investigated for the carbon fiber reinforced Si3N4 composite system and produced green composite microstruetures with good infiltration uniformity and fiber distribution, with hardly any macro defects. 

The volume of protein extract solution was adjusted to 5.0 ml with a phosphate reaction buffer consisting of 20 mM phosphates at pH 7.4 and then incubated with 5.0 mg ultra clean carbon/cellobiose core (0.5 ml of stock solution) at 4o C for 24 hours. The final colloid consisted of carbon ceramic particulates coated with a layer of cellobiose and a more superficial layer of adsorbed HIV proteins. These colloidal ceramic viral decoys were prepared for use by clearing unadsorbed material by ultrafiltration dialysis with a stir cell [Filtron, Northborough, MA] mounted with a 100 kd filter and flushed with 100 ml of sterile phosphate buffered saline (injection grade) at 4°C under a N2 pressure head of 10 psi. 

R. J. Pugh, Dispersion and Stability of Ceramic Powders, in Surface and Colloid Chemistry in Advanced Ceramics Processing, Marcel Dekker, New York, 1994, Chapter 4. 

Another approach is to use the LB film as a template to limit the size of growing colloids such as the Q-state semiconductors that have applications in nonlinear optical devices. Furlong and co-workers have successfully synthesized CdSe [186] and CdS [187] nanoparticles (<5 nm in radius) in Cd arachidate LB films. Finally, as a low-temperature ceramic process, LB films can be converted to oxide layers by UV and ozone treatment examples are polydimethylsiloxane films to make SiO [188] and Cd arachidate to make CdOjt [189]. 

In the process ia the center of Figure 17, complete hydrolysis is allowed to occur. Bases or acids are added to break up the precipitate iato small particles. Various reactions based on electrostatic iateractions at the surface of the particles take place the result is a colloidal solution. Organic binders are added to the solution and a physical gel is formed. The gel is then heat treated as before to form the ceramic membrane. 

Poly(vinyl alcohol) will function as a non-ionic surface active agent and is used in suspension polymerisation as a protective colloid. In many applications it serves as a binder and thickener is addition to an emulsifying agent. The polymer is also employed in adhesives, binders, paper sizing, paper coatings, textile sizing, ceramics, cosmetics and as a steel quenchant. 

Gregory, I., 1984b. Flocculation and filtration of colloidal particles. In Emergent process methods for high temperature ceramics, Eds. R.F. Dvais etai. Plenum Press, London p. 59. 

The elements are obtainable in a state of very high purity but some of their physical properties are nonetheless variable because of their dependence on mechanical history. Their colours (Cu reddish, Ag white and Au yellow) and sheen are so characteristic that the names of the metals are used to describe them. Gold can also be obtained in red, blue and violet colloidal forms by the addition of vtirious reducing agents to very dilute aqueous solutions of gold(III) chloride. A remarkably stable example is the Purple of Cassius , obtained by using SnCla as reductant, which not only provides a sensitive test for Au but is also used to colour glass and ceramics. Colloidal silver and copper are also obtainable but are less stable. 

Both silver (m.p. 962°C, b.p. 2212°C) and gold (m.p. 1065°C, b.p. 2807°C) have characteristic brilliant white and yellow colours in bulk but when finely divided are black or, in the case of gold, can be purple, ruby red or blue. Thus reduction of gold compounds by SnCl2 gives the colloid known as Purple of Cassius , which is used as a ceramic colorant. 

The solgel process uses a liquid reactive precursor material that is converted to the final product by chemical and thermal means. This precursor is prepared to form a colloidal suspension or solution (sol) which goes through a gelling stage (gel) followed by drying and consolidation. The process requires only moderate temperatures, in many cases less than half the conventional glass or ceramics... 

The formation of ordered two- and three-dimensional microstructuies in dispersions and in liquid systems has an influence on a broad range of products and processes. For example, microcapsules, vesicles, and liposomes can be used for controlled drug dehvery, for the contaimnent of inks and adhesives, and for the isolation of toxic wastes. In addition, surfactants continue to be important for enhanced oil recovery, ore beneficiation, and lubrication. Ceramic processing and sol-gel techniques for the fabrication of amorphous or ordered materials with special properties involve a rich variety of colloidal phenomena, ranging from the production of monodispersed particles with controlled surface chemistry to the thermodynamics and dynamics of formation of aggregates and microciystallites. 

The Group A emphases are those that inform the development of chemical literacy (DeBoer, 2000) and should be made available to all students (cf scientific literacy - (Roberts, 2007). These emphases all call for an imderstanding of a macro type of representation, so that learners appreciate what it is when they encounter a chemical phenomenon e.g. a solution, a colloid, a precipitate. This understanding would enable students to answer the question what is it and possibly what to do with it how to act when they encounter such a chemical phenomenon. These emphases also call for an understanding of the submicro type of representation, so that learners can qualitatively explain the nature of the macro phenomena that they encounter and hence be able to answer the question why is it as it is In order to explore these emphases, a chemistry curriculum would need to address a variety of contexts related to the three Group A emphases that have mearung in the everyday world. Pilot, Meijer and Bulte (2008) discuss three such contexts ceramic crockery, gluten-free bread and the bullet-proof vest. 

Surface and Colloid Chemistry in Advanced Ceramics Processing, edited by Robert... 

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