Ceramics Materials: Processes, Properties and Applications
Primarily an introduction to ceramic materials, this authoritative reference examines both traditional and "technical" ceramics and their respective properties and applications.
TABLE OF CONTENTS Ceramics Materials: Processes, Properties and Applications
Chapter 14: Sol-gel Methods and Optical Properties
Jean-Pierre Boilot, Jacques Mugnier
14.1 Physico-chemistry of gels
In standard methods of preparation of oxide-based materials (glasses and ceramics), the raw materials are crystalline powders (size of a few ?m). Ceramics are prepared through solid state reactions of powders and by high temperature of a granular agglomerate. Single crystals and glasses are generally obtained starting from a molten bath. In this case, the homogenity in liquid state facilitates the formation of the material, which does not involve long-distance atomic diffusion.
In sol-gel procedures [ [YOS 00]], the basic idea is simple: starting from a mixture of liquid molecular precursors, thus homogenous at the molecular scale, followed by the transformation of the liquid into a solid by a chemical reaction of inorganic polymerization at ambient temperature. The homogenous solid obtained is porous, amorphous and hardens at a low temperature, thus making glass or ceramic preparation possible, without going through fusion.
14.1.1 Sols and silica gels
Synthesis by the sol-gel method is generally done by using alkoxides having the formula M(OR) m, where M is an atom, very often metallic, and R an organic alkaline group C nH 2n+1. In alcoholic solution and in the presence of water, these alkoxide precursors undergo hydrolysis and condensation resulting in gelation. We will describe the reactions taking into account the specific case of tetraethoxysilane, Si(OC 2H 5) 4 or Si(OEt) 4, which constitutes a model system for inorganic polymerization [ [BRI 90]].
Hydrolysis is a...
Copyright ISTE Ltd. 2007 under license agreement with Books24x7
