Sintering theory

R.M. German. Sintering Theory and Practice. John Wiley Sons, New York, 1996. 

Note y = surface energy, D = volume diffusivity, Ds = surface diffusivity, Db = grain boundary diffusivity, ij = viscosity, b = Burgers vector, k = Boltzman s constant, p = density, S = width of grain boundary diffusion path, P = pressure, M = molecular weight, and 2 = atomic volume. Source From R. M. German, Sintering Theory and Practice (New York Wiley, 1996). Reprinted with permission of John Wiley Sons, Inc. 

Fusion and film formation of the polymeric particles during the coating process can be explained by the wet sintering theory for particles suspended in water, the capillary pressure theory for particle layers containing water in various degrees of saturation, and the dry sintering theory for dry particle layers. 

Equations for neck growth in the initial stage have been derived for each mechanism. While the neck growth equations were critical to the early development of sintering theory, their usefulness in practical sintering is limited. The predicted dependence of the... 

The rate of recrystallization by accretion is also dependent on the probability that two crystals are in the same region and can form a bridge. This is a function of how tightly packed the crystals are in the product. The coalescence frequency has been related to the average volume of the two crystals, although the surface area has also been used to refine sintering theory. However, these theories do not fit the experimental data. Our understanding of the process of accretion recrystallization in foods is still very poor. 

Exner, H.E. (1979) Principles of Single-Phase Sintering, in Reviews on Powder Metallurgy and Physical Ceramics 1, 1-251. Freund Pub. House, Tel-Aviv, Israel. Not just ceramics a very useful review. German, R.M. (1996) Sintering Theory and Practice. Wiley, New York. The standard reference. Not only concerned with ceramics. 

Matter transport through diffusion can be described in terms of the flux of atoms or the counterflow of vacancies. The approach based on the counterflow of vacancies driven by a vacancy concentration gradient has been used predominantly in the early development of sintering theory, which is discussed in this subsection first. More general approach based on the flux of atoms driven by a chemical potential gradient will be presented later. The following discussion is started with the mechanism of grain boundary diffusion. 

USEFULNESS AND UMITATIONS OF THE INITIAL STAGE SINTERING THEORY... 

German, R.M., Sintering Theory and Practice, John Wiley Sons, New York, 1996. Sarraute, S., Sorensen, O.T., and Hansen, E.R., Fabrication processes of magnetic and dielectric multilayer ceramics. Key Engineering Materials, Vol. 132-136, Pt. 2, 1151-1154, 1997. 

German RM. Sintering Theory and Practice. 1st ed. New York Willey. 1996, 568p. ISBN 978-0-471-05786-4... 

Traditional sintering theories are based on the kinetics of mass transport motivated by differential surface curvature as described by the Gibbs-Kelvin equation ... 

The above can be explained from fundamental sintering theory where the rates of densification are inversely related to the scale of the structure to sinter (the scaling law). Therefore, the small pores within the agglomerates disappear before the larger ones between them. 

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