Kinetics sintering

Another assumption is that the stress at the grain boundary is distributed so that atoms at the grain boundary eome out to the neek uniformly. Physically, this assumption is based on the fact that no pores form at the grain boundary even though atoms at the boundary are transported to the neck. Exner and Bross calculated a parabolic distribution of stress, compressive in the centre region and tensile in the surface region of the neck, for a two-wire model. 

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Sintering Kinetics of Supported Metals Perspectives from a Generalized Power Law Approach... 

Studies of sintering and redispersion of supported metal catalysts have been reviewed by several authors [M8] most of these reviews focus on early kinetic studies of sintering of supported metal catalysts using a simplified power law expression (SPLE). Unfortunately this crude approach does not permit sintering kinetics to be presented in a consistent way nor does it enable (1) useful extrapolation of the data to other conditions (2) useful quantitative comparisons between different studies, or (3) physically meaningful kinetic parameters to be obtained. The ultimate result has been confusion regarding the effects of reaction parameters such as atmosphere and temperature and of catalyst properties such as support promoters, etc., on sintering rates. 

In the light of the new approach to sintering kinetics and the well-defined data base available from this and the previous study [18], it is instructive to analyze the significance and functionality of each of the important kinetic parameters kg, and E. 

Since the introduction of a mathematical model for sintering by Kuczynski [12] numerous other models have been proposed. Reviews of these sintering kinetic models are given in references [13—19]. This description of sintering kinetics is organized into initial, intermediate, and final stage kinetic models. 

Effect of Particle Size Distribution on Sintering Kinetics... 

Solid state sintering was discussed previously in this chapter. The sintering kinetics depend upon the rate determining step, which can be either viscous flow, grain boundary diffusion, or lattice diffusion. These sintering kinetics are summarized in Tables 16.4 and 16.6 for the initial and intermediate stage and Section 16.3.2.3 for the final stage. 

Sintering in the real systems. The above considerations of the sintering kinetics have been derived from geometrically simple models. 

Sintering kinetics of model-suppoted catalysts are generally coielated by a GPLE of the form -d(D/Djj)/dt = kjCD/D -Dg /Dg) where m = 2. This result has important mechanistic implications since a number of fundamental processes such as emission of atoms frcnn crystallites, diffusion of adatoms on a support, collision of crystallites, w recmibination metal atoms may involve second-order processes. 

Based on quantitative GPLE treatments of sintering kinetics, it is possible to define effects of metal, metal dispersion, metal concentration, and support thermal stability ... 

Fuentes addressed the issue of deactivation kinetics in general [5], and of sintering kinetics in particular [6,7], and found an important discrepancy between experimental results and use of the PLE as a fitting tool. He observed that in most cases metallic dispersion reached a quasistationary plateau after an initial stage of fast changes in dispersion. That was at odds... 

C.H. Bartholomew, Sintering Kinetics of Supported Metals New Perspectives from a Unifying GPLE Treatment, Appl. Catal., 67 (1994) 1. 

D.L. Johnson and I.B. Cutler, Diffusion sintering, I initial stage modek and their applications to shrinkage of powder compacts, II intial sintering kinetics of alumina. /. Am. Ceram. Soc., 46 (1963) 541. 

Other possible areas of application of the periodic surfaces, or of disordered relatives of these, include structure of superconductors in the intermediate state (Shal nikov 1941), sintering kinetics (Hench and Ulrich 1984), fluid flow through porous media (e.g., Zick and Homsy 1982), the topology of spacetime at the scale of Planck length (Wheeler 1957), the structure of the prolamellar body in certain plastics (Gunning 1965), certain phase-segregated block copolymers (Thomas et al. 1986 Anderson and Thomas 1988)) semiconductor-... 

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