Atom transport

If samples of two metals widr polished faces are placed in contact then it is clear that atomic transport must occur in both directions until finally an alloy can be formed which has a composition showing die relative numbers of gram-atoms in each section. It is vety unlikely that the diffusion coefficients, of A in B and of B in A, will be equal. Therefore there will be formation of an increasingly substantial vacancy concentration in the metal in which diffusion occurs more rapidly. In fact, if chemically inert marker wires were placed at the original interface, they would be found to move progressively in the direction of slowest diffusion widr a parabolic relationship between the displacement distance and time. 

In all of the structures based upon hexagonal close-packed anions illustrated, continuous diffusion paths through empty sites can be traced, and a population of point defects is not mandatory to facilitate atom transport. 

Suppose that vacancy diffusion is the principal mechanism involved in atom transport. An expression for the fraction of vacancies in a pure crystal is [Eq. (2.6)]... 

Kinetics ofelectrodes and the role of electrons in atomic transport... 

Allnatt, A. R. Lidiard, A. B. Atomic Transport in Solids Cambridge University Press New York, 1993. 

The interpretation of this data on metals in terms of microscopic mechanisms of surface atom transport is not totally understood. The original papers[ 11] proposed that during surface transport the controlling process was adatom terrace diffusion between steps with the adatom concentration being that in local equilibrium with the atomic steps. This may indeed be the case, but in light of other experiments on adatom diffusion[13] and exchange processes at steps[14] the possibility of step attachment/detachment limited kinetics caimot be raled out. 

E. Torrontegui, S. Ibanez, X. Chen, A. Ruschhaupt, D. GuuLery-Odelin, and J. G. Muga. Fast atomic transport without vibrational heating. Phys. Rev. A, 83(1) 013415-013423(2011). 

We see from Figure 3-1 that edge dislocations possess a compressed region above, and a dilated region below the glide plane. Therefore, in the dilated area around the dislocation line, the transport coefficients will be larger than in the bulk crystal. Thus, dislocations can serve as fast diffusion pipes for atomic transport. 

Decomposition reactions are solid-gas reactions which do not involve diffusional transport through the solid. Their reaction rates are determined by surface kinetics and possibly pore diffusion. The assumption of local equilibrium is not valid. The course of an isothermal decomposition is schematically illustrated in Figure 15-15. There is often an induction period followed by a rapid increase in relative yield until, after the inflection point, the reaction eventually ceases (the yield will not always be 100%). Since atomic transport in crystals is normally not involved in these decomposition reactions, we shall restrict ourselves to a few comments only. 

Allnatt, A.R., Lidiard, A.B. (1993) Atomic Transport in Solids, Cambridge University Press, Cambridge... 

Chemical Kinetics of Solids covers a special part of solid state chemistry and physical chemistry. It has been written for graduate students and researchers who want to understand the physical chemistry of solid state processes in fair depth and to be able to apply the basic ideas to new (practical) situations. Chemical Kinetics of Solids requires the standard knowledge of kinetic textbooks and a sufficient chemical thermodynamics background. The fundamental statistical theory underlying the more or less phenomenological approach of this monograph can be found in a recent book by A. R. Allnatt and A.B. Lidiard Atomic Transport in Solids, which complements and deepens the theoretical sections. 

An analysis of the rate of elongation of a wire possessing a bamboo-type grain structure is given in Section 16.1.3. An essential aspect of the analysis is the assumption that the stress-induced atomic transport producing the elongation is diffusion-limited. Now, construct the main framework of a model for the same system in which the atomic transport is source-limited, as indicated below, and explain how the model works. 

These results support the hypothesis of etching by free radicals. Only under reaction conditions is it expected that there will be a mechanism for atomic transport resulting in Ostwald ripening, whereas in other environments only coalescence growth is anticipated. 

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