Enhancement of diffusion

We have considered so far only disc-shaped microelectrodes, for which spherical diffusion can be applied, to a good approximation. Other forms have been used, mainly because they might be easier to fabricate. Most noted among these is the linear or strip niicroelec-trode, which is macroscopic in length but microscopic in width. The diffusion field at such electrodes can be approximated. satisfactorily by diffusion to a cylinder. The enhancement of diffusion is less than that... 

Vijayakumar M et al (1998) Electrostatic enhancement of diffusion-controlled protein-protein association comparison of theory and experiment on bamase and barstar. J Mol Biol 278(5) 1015-1024... 

The complex [Ru" L(H20)] (1 mM), at pH 5.3 exhibited the one electron reduction wave at -0.262 V (E/4-E3/4 = 57 mV) as shown in Figure 3A.a. Addition of sodium azide did not show any new reduction wave but only the enhancement of diffusion current along with shift in peak potential towards cathode (Figures 3A.b-c). The current enhancement was large at initial, but relatively less at higher concentrations. The plot of enhanced diffusion current vs [azide] confirmed the formation of monomeric complex and also the wave analysis indicated the electrode reactions were diffusion controlled lnd nearly reversible. This implies that the enhanced wave is totally new and multi-electron reduction wave characteristic of [Ru "L(N3)] which differs from one electron wave of aquo complex. 

Another class of adherends is that of thermoplastic polymers. In contrast to metal adherends, thermoplastics are not impenetrable and thus absorption effects can be expected in addition to adsorption phenomena. Hence, given sufficient conditions for preferential absorption, a considerable mass uptake by the thermoplastic can occur, potentially resulting in significant stoichiometric imbalances on the epoxy side. Apart from the driving force for absorption of molecules from the liquid epoxy formulation, it is the diffusivity of these molecules within the thermoplastic which plays a major role in the interdiffusion process. In particular, the diffusivity is affected by the mobility of the host molecules. Thus enhancement of diffusivity occurs in the glass transition region and at higher temperatures when intermolecular cooperative motion is activated. 

Recent work by Jones et al. [80] has shown an enhancement of diffusion due to vacancies formed by anodic polarization. He has once again suggested that vacancies formed at room temperature by anodic dissolution are implicated in dealloying, embrittlement, and stress corrosion cracking. Specifically, divacancies are the species that migrate to the dissolving interface and enhance diffusion at that site. Other authors [87] have also recently returned to the vacancy enhemced mechanism for dealloying and SCC. 

A marked enhancement of diffusivity with small stoichiometry deviations was observed at 800C. 

Materials of all types are often heat-treated to improve their properties. The phenomena that occur during a heat treatment almost always involve atomic diffusion. Often, an enhancement of diffusion rate is desired on occasion, measures are taken to reduce it. Heat-treating temperatures and times and/or cooling rates... 

Turkdogan E T, Grieveson P, Darken L S, Enhancement of diffusion-limited rates of vaporization of metals , J Phys Chem, 1963 67(8) 1647-1654. 

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