Colloidal ceramics particles

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

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. 

Evaporative decomposition erf solutions and spary pyrolysis have been found to be useful in the preparation of submicrometer oxide and non-oxide particles, including high temperature superconducting ceramics [819, 820], Allowing uniform aerosol droplets (titanium ethoxide in ethanol, for example) to react with a vapor (water, for example) to produce spherical colloidal particles with controllable sizes and size distributions [821-825] is an alternative vapor phase approach. Chemical vapor deposition techniques (CVD) have also been extended to the formation of ceramic particles [825]. 

Conventional routes to ceramics involve precipitation from solution, drying, size reduction by milling, and fusion. The availability of well-defined mono-dispersed particles in desired sizes is an essential requirement for the formation of advanced ceramics. The relationship between the density of ceramic materials and the sizes and packing of their parent particles has been examined theoretically and modeled experimentally [810]. Colloid and surface chemical methodologies have been developed for the reproducible formation of ceramic particles [809-812]. These methodologies have included (i) controlled precipitation from homogeneous solutions (ii) phase transformation (iii) evaporative deposition and decomposition and (iv) plasma- and laser-induced reactions. 

Sucrose, like other simple carbohydrates, is used as additive in mineral suspensions, concrete, and ceramics. The hygroscopic character of the carbohydrates and their ability to interact with colloidal inorganic particles and ions modifies the hydration phenomena within the suspensions, and consequently on the rheology of the medium and the kinetics (most often slowing down) of the... 

Apart from latexes, S-FFF has been used to fractionate and determine the size distribution of numerous industrial colloids including water-based titanium dioxide dispersions [6,171], carbon black dispersions [6],phthalocyanineblue [6], various silica sols [141,171,176], gold and silver sols [385], pigments, metal and ceramic particles, clay and a host of latexes [294]. Gold, palladium, silver and copper particles in the size range 0.3-15 pm were separated by steric-S-FFF and their size distributions determined in less than 12 min [69]. 

An aqueous colloidal suspension also has an osmotic pressure associated with both the double layer of the particles in solution and the structure of the particles. The osmotic pressure term for the structure is given in Section 11.6 for both ordered and random close packing. The osmotic pressure associated with the double layer surrounding the ceramic particles in aqueous solution is discussed here. 

Oc is the geometric constant for the shape of the ceramic particles and [1 + (Lg/a f] is the volume fraction correction for the adsorbed layer on the ceramic particles. Again, this equation is only good for colloidally stable suspensions. Fleer et al. [19] verified this equation for cubic particles with polytvinyl alcohol) adsorbed at the surface. For polymer solution concentrations (i.e., p) that give essentially monolayer coverage of the particle surface, the value of [1 + (LJaf] is nearly constant for a wide range of ceramic powder concentrations (Le., d>c)-... 

Commonly used enamels contain multiple ingredients. Typically silica, alumina and other metal oxides such as calcia arc the major ingredients. In addition, some organic additives such as dispersants and viscosity modifiers (e.g., polyvinyl alcohol) arc used to ensure that the starting slip consists of finely divided and dispersed particles in the submicron range in order to seal the pores on the end surfaces. The pores can be filled with very fine ceramic particles (Garcera and Gillot, 1986] or calcined colloidal silica... 

Rosenholm, J.B. et al., Colloidal properties related to the ceramic particles and the sintered body, in Ceramic Interfaces, R.St.C. Smart and J. Nowotny, Eds., lOM London, 433, 1998. 

Phosphorus-31 NMR was used by Burton et al, [20] to analyze polyphospha-zenes (dispersants) bound to the surface of alumina ceramic particles. The differences between the spectra of the inorganic polymer in solution and in colloidal suspensions were used to probe the chemical interaction with the alumina. Their P NMR results showed a small lower frequency shift associated with phosphazenes bound to alumina. Solution samples consistently displayed a broadening of the P resonance upon cumulative addition of alumina to the suspension, indicating some degree of chemical adsorption (Sec. II.E). However, Burton et al. pointed out that this lineshape difference might be mistaken as an artifact caused by the amount of solids present in the NMR sample. 

Refractory bodies of various types have been made from silica alone or by using silica as a binder for ceramic particles. Bergna (486) describes making transparent blocks similar to fused silica by hot pressing pure silica powder, made by spray. drying colloidal silica, at 1200 0 and 2000 psi for 5 min. 

Lyophobic (liquid-hating) colloids are those in which the liquid does not show affinity for the particle. The Gibbs free energy increases when the particles are distributed through the liquid so that if attractive forces exist between the particles, there will be a strong tendency for the particles to stick together when they come into contact. This system will be unstable and flocculation will result. A lyophobic colloid can, therefore, only be dispersed if the surface is treated in some way to cause a strong repulsion to exist between the particles. Suspensions of insoluble particles in a liquid (e.g., most ceramic particles dispersed in a liquid) are well-known examples of lyophobic colloids. We therefore need to understand the attractive forces that lead to flocculation and how they can be overcome by repulsive forces to produce colloids with the desired stability. 

Cerbelaud M, Videcoq A, Abelard P, Ferrando R (2009) Simulation of the heteroagglomeration between highly size-asymmetric ceramic particles. J Colloid Interface Sci 332 (2) 360-365. doi 10.1016/j.jcis.2008.11.063... 

Frey M.H., Payne D.A. Synthesis and processing of barium titanate ceramics from alkoxide solutions and monolithic gels. Chem. Mater. 1995 7 123-129 Fu X., Qutubuddin S. S)mlhesis of titania-coated sMca nanoparticles using a nonionic water-in-oil microemulsion. Colloids Surf. A 2001 179 65-70 Ganguli D. Sol-emulsion-gel synthesis of ceramic particles. Bull. Mater. Sd. 1999 22 221-226 GanguU D., Chatteijee M. Ceramic Powder Preparation A Handbook. Boston Kluwer Academic Publishers, 1997... 

Valentin C., Munoz M.C., Alarcdn J. Synthesis and characterization of vanadium-containing ZrSi04 solid solutions from gels. J. Sol-Gel Sci. Technol. 1999 15 221-230 Van Helden A.K., Jansen J.W., Vrij A. Preparation and characterization of spherical monodisperse silica dispersions in nonaqueous solvents. J. Colloid Interf. Sci. 1981 81 354-368 Woodhead J.L. Sol-gel processes to ceramic particles using inorganic precursors. J. Mater. Educ. 1984 6 887-925... 

Hashimoto T., Kamiya K., Nasu H. Strengthening of sol-gel-derived Si02 glass fibers by incorporating colloidal silica particles. J. Non-Cryst. Solids 1992 143 31-39 Hirano S., Hayashi T., Nosaki K., Kato K. Preparation of stoichiometric Cryst. lithium niobate fibers by sol-gel processing with metal alkoxides. J. Am. Ceram. Soc. 1989 72 707-709 Horikiri S., Tsuji K., Abe Y., Fukiu A., Ichiki E. US Patent 4,101,615 (1978)... 

Aburatani Y., Tsuru K., Hayakawa S., Osaka A. Mechanical property and microstructure of bioactive organic inorganic hybrids containing colloidal silica particles. J. Ceram. Soc. Jpn. 2003a 111 247 251... 

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