Self-Diffusion


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self-diffusion

[¦self di¦fyü·zhən]
(solid-state physics)
The spontaneous movement of an atom to a new site in a crystal of its own species.

Self-Diffusion

 

the special case of diffusion in a pure substance or a solution of constant composition where the substance’s own particles undergo diffusion. In self-diffusion, the atoms that participate in the diffusion movement have the same chemical properties but can differ in their physical characteristics—in the composition of their nuclei (see ISOTOPES). In the case of a difference in the isotopic composition of the substance, self-diffusion can be observed through the use of radioactive isotopes (see ISOTOPE TRACERS) or through analysis of the isotopic composition by means of mass spectrometers.

The change over time in the concentration of a given isotope in the volume of the substance under consideration is described by the usual equations for diffusion, and the rate of the process is characterized by the coefficient of self-diffusion (see DIFFUSION). When such forces as surface tension, gravity, elastic forces, or electrical forces act on a solid specimen for a long time, the diffusion displacements of the solid’s particles can result in a change in its shape or in other effects. These diffusion processes are evidenced in the joining together of two polished specimens of the same substance placed next to each other, in the sintering of powders, and in the stretching of a body under the action of a load suspended from it (diffusion creep). The study of the kinetics of these processes permits determination of the coefficient of self-diffusion of a substance.

References in periodicals archive ?
Using the asymptotes of [Delta]E([q.sup.2]) for small q, the total self-diffusion coefficient D = [D.sub.coll] + [D.sub.s-p] was found by the Eq 3.
The length of a weld line crack can be theoretically estimated through simple heat transfer analyses by combining the cooling profile through the thickness of the part with a calculation of instantaneous polymer self-diffusion rate.
The first was PS ([M.sub.w] = 270,000)-toluene self-diffusion coefficient data from Pickup and Blum (8) at low polymer concentration, which were converted to mutual diffusion coefficient using the method of Duda et al.
Also, a Curie temperature (770[degrees]C) was observed for self-diffusion in iron when the paramagnetic-ferromagnetic transition occurred [39], It is worthy to mention that the value of v in Fig.
In the absence of a chemical gradient, we call it self-diffusion coefficient.
In particular, it is well known that neutron irradiation leads to significant increase in the vacancies and interstitials concentrations and, as a result, to significant increase in the self-diffusion coefficient [11-22].
Moreover, the diffusion coefficient of ammonia in Table 1 can be compatible with the self-diffusion coefficient of ammonia in some porous solids: in silica from 300 to 500 K by QENS (2.5 x [10.sup.-6] to 2.0 x [10.sup.-5] [cm.sup.2]/s) and by PFG NMR (3 x [10.sup.-7] to 1.5 x [10.sup.-6] [cm.sup.2]/s) [18]; in H-ZSM5 in range from 1 x [10.sup.-7] to 2 x [10.sup.-5] [cm.sup.2]/s [17].
LeBihan, "Estimation of the effective self-diffusion tensor from the NMR spin echo," Journal of Magnetic Resonance, Series B, vol.
[31]; porosity, 37%; [D.sub.0], self-diffusion coefficients for Na and Cs from Savoye et al.
Then he examines defects in group IV semiconductors, self-diffusion experiments and their theoretical modeling as practical tools to deduce the nature and presence of native defects in group IV semiconductors, and defects in group IV carbides.
Wolverton, "First-principles calculation of self-diffusion coefficients," Physical Review Letters, vol.
DTI measurements are based on the assumption of a Gaussian displacement probability distribution of water molecules due to water self-diffusion, such as water in isotropic liquid media [10].