Crystalline solids self-diffusion

The change in the two-state distribution is easily monitored by a convenient one-wavelength measurement of the neutral form fluorescence, and this can be used for probing the membrane. The fairly large differences in wavelengths of excitation (300 nm), fluorescence of the neutral form (360 nm), and fluorescence of the anion form (480 nm) makes the fluorescence free from spectral interference. The variation of the P form fluorescence intensity with temperature showed a maximum at phase-transition temperatures (Tc) for both DMPC (23°C) (Fig. 2) and DPPC (42°C) membranes (Fig. 3). Figures 2 and 3 show a very nice correspondence of this variation with DPH fluorescence polarization and self-diffusion rate [93] of 22Na+. The coexistence of solid gel and fluid liquid-crystalline phases at Tc and the consequent imperfection of the membrane [93] result in a redistribution of... 

Diffusion of atoms or ions in crystalline solids can occur by at least three possible mechanisms, as shown schematically in Figure 2.7. In some solids, transport proceeds primarily by the vacancy mechanism, in which an atom jumps into an adjacent, energetically equivalent vacant lattice site. The vacancy mechanism is generally much slower than the interstitial mechanism (discussed below). Nonetheless, it is thought to be responsible for self-diffusion in all pure metals and for most substitutional alloys (Shewmon, 1989). 

Fig. 2.18. Arrhenius plots of various relevant diffusion constants for Ni/Hf and Co/Zr diffusion couples. The upper dashed and solid line are based on tracer diffusion data for Ni and Co in crystalline a-Zr [2.38,28]. The lower curve is for self diffusion of a-Zr [2.103], The open squares are Co tracer diffusion data in amorphous Co89Zru [2.28], Solid circles are the interdiffusion constant D obtained by SSAR on Ni/Hf diffusion couples [2.79], Open circles, upward triangles, downward triangles, and diamonds are interdiffusion constants obtained from studies of SSAR in Co/Zr diffusion couples [2.28]. The latter data were determined from RBS studies and direct cross-sectional TEM observation of the thickness of the amorphous layer. The downward arrows indicate an upper bound for the intrinsic diffusion constant of Zr in the amorphous layer during SSAR...

Sabioni ACS, Huntz AM, Phihbert J, Lesage B (1992) Relation between the oxidation growth rate of chromia scales and self-diffusion in Cr203. J Mater Sci 27 4782-4790 Sabioni ACS, Zanotto E, Millot F, Fuller H (1998) Oxygen self-diffusion in a cordierite glass. J Non-Crystalline Solids 242 177-182... 

Behr W, Haase A, Reichenauer G et al (1998) Self and transport diffusion of fluids in Si02 alcogels studied by NMR pulsed gradient spin echo and NMR imaging. Journal of Non-Crystalline Solids 225 91-95... 

Figure 7.4 shows an initial nonuniform distribution of element i in a medium of j. Atoms of species i diffuse from the region of high concentration to the region of low concentration and establish a more imiform concentration distribution of the species. Self-diffusion also takes place in a relatively pure crystalline solid material controlled by a process known as vacancy mechanism or the hopping process. The ion transport in crystalline electrolyte is controlled by this vacancy diffusion or hopping diffusion mechanism. In this... 

M. Nastar, V. Y. Dobretsov, and G. Martin, Self-consistent formulation of configurational kinetics close to equilibrium the phenomenological coefficients for diffusion in crystalline solids, Phil. Mag. A, vol. 80, p. 155, 2000. 

Systems composed of solid polymers and of low-molecular-mass active compounds find several practical and advanced applications. Recent studies have suggested that a simple method to reduce diffusivity of active molecules in the solid state and to prevent their self-aggregation consists of the formation of co-crystals with suitable polymer hosts. The formation of co-crystalline phases with SPS appears to be particularly efficient and versatile. 

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