Displacement s. Migration

Displacement s. Migration, Rearrangement, Replacement, Substitution Disproportionation s. Comproportionation Distannoxanes, reactions, review 21, 684 suppl. 24 Disulfides... 

Displacement s. Migration, Rearrangement, Replacement, Substitution Disproportionation... 

Bakewell, 0. (2011) Conceptualizing Displacement and Migration Processes, Conditions, and Categories. Pp. 14-28 in K. Koser and S. Martin (eds.). The Migration-Displacement Nexus Patterns, Processes, and Policies. New York Berghahn Books. 

If the source of water is relatively unlimited (long-term flooding), the downward migrating water will displace air from the pores and migrate according to Darcy s... 

Equation 8.29 can be used to obtain another approximation for f by employing an estimated value of (cos 0). To estimate this quantity, consider an atom that has just exchanged with a vacancy there is a probability l/z that the vacancy s next exchange will be with the same atom and, therefore, the probability that cos = —1 is l/z or (cos0 = —l/z. If the vacancy separates from the particular atom, that particular atom cannot migrate until it obtains another (or the same) vacancy as a neighbor the contribution to (cos 0) from these displacements will be small compared to —l/z, and therefore Eq. 8.29 can be written... 

Thus, a 2-D separation can be seen as 1-D displacement operating in two dimensions. The 2-D TLC separation is of no interest if selection of the two mobile phases is not appropriate. With this in mind, displacement in either direction can be either selective or non-selective. A combination of two selective displacements in 2-D TLC will lead to the application of different separating mechanisms in each direction. As an extreme, if the solvent combinations are the same (ST1 =. S T2 SVi = Sv2) or very similar (ST1. S T2 SW1 SW2), the compounds to be separated will be poorly resolved or even unresolved, and as a result a diagonal pattern will be obtained. In such circumstances, a slight increase in resolution might occur, because of an increase by a factor of V2 in the distance of migration of the zone (4). 

The Kirkendall effect arises from the different values of the self-diffusion coefficients of the components of a substitutional solid solution, determined by Matano s method. Matano s interface is defined by the condition that as much of the diffusing atoms have migrated away from the one side as have entered the other. If DA = DB, its position coincides with the initial interface between phases A and B. If I)A f DB, it displaces into the side of a faster diffusant (see Fig. 1.22c). Note that KirkendalFs discovery only relates to disordered phases. It was indeed a discovery since at that time most reseachers considered the relation l)A = DB to hold for any solid solution of substitutional type. KirkendalFs experiments showed that in fact this is not always the case. 

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