Kinetic Processes in Ceramics and Glasses

Let us first consider the liquid-solid phase transformation. At the melting point (or more appropriately, fusion point for a solidification process), liquid and solid are in equilibrium with each other. At equilibrium, we know that the free energy change for the liquid-solid transition must be zero. We can modify Eq. (2.11) for this situation 

If we assume that the entropy and enthalpy are relatively independent of temperature, we can drop the subscript m on temperature in Eq. (3.32), thereby obtaining a more general relationship between the entropy and enthalpy of fusion as a function of temperature. Substitution of this modified form of Eq. (3.32) into Eq. (3.31) gives the following relation for the free energy  

This expression will be very useful in the discussion of nucleation and growth kinetics. 

In the nucleation step, there must be sites upon which the crystals can form. This is similar to seeding the clouds to cause water to precipitate (rain). There are two sources for these nucleating particles homogeneous and heterogeneous agents. 

Work with a neighbor. Consider Eq. (3.34), which describes the free energy change associated with the homogeneous nucleation of a solid, spherical particle of radius, r, from a parent liquid phase  

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Obviously, all these structure-sensitive factors influence the reaction kinetics in practical applications to such systems as refractories, ceramics, cement, glass, luminescent materials, semiconductors, catalysts, and pigments. The reactivity of the raw mixes of the constituents, the effects of calcination or burning conditions, and the various types of diffusing species in the course of solid reactions influence the quality of the final product. From an industrial viewpoint the reactions in ionic solid systems have a universal importance. This is so vast a field that for an illustration of this significance an arbitrary selection is necessary. It is hoped, however, that the examples discussed will convey the impact of the reactivity of ionic solids on modern industrial processes and products. 

Liquid infiltration into dry porous materials occurs due to capillary action. The mechanism of infiltrating liquids into porous bodies has been studied by many researches in the fields of soil physics, chemistry, powder technology and powder metallurgy [Carman, 1956 Semlak Rhines, 1958]. However, the processes and kinetics of liquid infiltration into a powdered preform are rather complex and have not been completely understood. Based on Darcy s fundamental principle and the Kozeny-Carman equation, Semlak Rhines (1958) and Yokota et al. (1980) have developed infiltration rate equations for porous glass and metal bodies. These rate equations can be used to describe the kinetics of liquid infiltration in porous ceramics preforms, but... 

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