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Surface diffusivity

An alternative defining equation for surface diffusion coefficient Ds is that the surface flux Js is Js = - Ds dT/dx. Show what the dimensions of Js must be. [Pg.157]

It was commented that surface viscosities seem to correspond to anomalously high bulk liquid viscosities. Discuss whether the same comment applies to surface diffusion coefficients. [Pg.157]

Protein adsorption has been studied with a variety of techniques such as ellipsome-try [107,108], ESCA [109], surface forces measurements [102], total internal reflection fluorescence (TIRE) [103,110], electron microscopy [111], and electrokinetic measurement of latex particles [112,113] and capillaries [114], The TIRE technique has recently been adapted to observe surface diffusion [106] and orientation [IIS] in adsorbed layers. These experiments point toward the significant influence of the protein-surface interaction on the adsorption characteristics [105,108,110]. A very important interaction is due to the hydrophobic interaction between parts of the protein and polymeric surfaces [18], although often electrostatic interactions are also influential [ 116]. Protein desorption can be affected by altering the pH [117] or by the introduction of a complexing agent [118]. [Pg.404]

It is known that even condensed films must have surface diffusional mobility Rideal and Tadayon [64] found that stearic acid films transferred from one surface to another by a process that seemed to involve surface diffusion to the occasional points of contact between the solids. Such transfer, of course, is observed in actual friction experiments in that an uncoated rider quickly acquires a layer of boundary lubricant from the surface over which it is passed [46]. However, there is little quantitative information available about actual surface diffusion coefficients. One value that may be relevant is that of Ross and Good [65] for butane on Spheron 6, which, for a monolayer, was about 5 x 10 cm /sec. If the average junction is about 10 cm in size, this would also be about the average distance that a film molecule would have to migrate, and the time required would be about 10 sec. This rate of Junctions passing each other corresponds to a sliding speed of 100 cm/sec so that the usual speeds of 0.01 cm/sec should not be too fast for pressurized film formation. See Ref. 62 for a study of another mechanism for surface mobility, that of evaporative hopping. [Pg.450]

The state of an adsorbate is often described as mobile or localized, usually in connection with adsorption models and analyses of adsorption entropies (see Section XVII-3C). A more direct criterion is, in analogy to that of the fluidity of a bulk phase, the degree of mobility as reflected by the surface diffusion coefficient. This may be estimated from the dielectric relaxation time Resing [115] gives values of the diffusion coefficient for adsorbed water ranging from near bulk liquids values (lO cm /sec) to as low as 10 cm /sec. [Pg.589]

One might expect the frequency factor A for desorption to be around 10 sec (note Eq. XVII-2). Much smaller values are sometimes found, as in the case of the desorption of Cs from Ni surfaces [133], for which the adsorption lifetime obeyed the equation r = 1.7x 10 exp(3300// r) sec R in calories per mole per degree Kelvin). A suggested explanation was that surface diffusion must occur to desorption sites for desorption to occur. Conversely, A factors in the range of lO sec have been observed and can be accounted for in terms of strong surface orientational forces [134]. [Pg.709]

Mobility of this second kind is illustrated in Fig. XVIII-14, which shows NO molecules diffusing around on terraces with intervals of being trapped at steps. Surface diffusion can be seen in field emission microscopy (FEM) and can be measured by observing the growth rate of patches or fluctuations in emission from a small area [136,138] (see Section V111-2C), field ion microscopy [138], Auger and work function measurements, and laser-induced desorption... [Pg.709]

The sequence of events in a surface-catalyzed reaction comprises (1) diffusion of reactants to the surface (usually considered to be fast) (2) adsorption of the reactants on the surface (slow if activated) (3) surface diffusion of reactants to active sites (if the adsorption is mobile) (4) reaction of the adsorbed species (often rate-determining) (5) desorption of the reaction products (often slow) and (6) diffusion of the products away from the surface. Processes 1 and 6 may be rate-determining where one is dealing with a porous catalyst [197]. The situation is illustrated in Fig. XVIII-22 (see also Ref. 198 notice in the figure the variety of processes that may be present). [Pg.720]

Linderoth T R, Florsch S, Laesgaard E, Stensgaard i and Besenbacher F 1997 Surface diffusion of Pt on Pt(110) Arrhenius behavior of iong ]umps Phys. Rev. Lett. 78 4978... [Pg.317]

Dunphy J C, Sautet P, Ogietree D F, Dabbousi O and Saimeron M B 1993 Scanning-tunneiing-microscopy study of the surface diffusion of suifur on Re(OOOI) Phys. Rev. B 47 2320... [Pg.317]

George S M, DeSantoio A M and Haii R B 1985 Surface diffusion of hydrogen on Ni(IOO) studied using iaser-induced thermai desorption Surf. Sol. 159 L425... [Pg.317]

Schultz K A and Seebauer E G 1992 Surface diffusion of Sb on Ge(111) monitored quantitatively with optical second harmonic microscopy J. Chem. Phys. 97 6958-67... [Pg.1304]

Zhu X D, Rasing T H and Shen Y R 1988 Surface diffusion of CO on Ni(111) studied by diffraction of optical second-harmonic generation off a monolayer grating Phys. Rev. Lett. 61 2883-5... [Pg.1304]

Jaklevic R C and Elie L 1988 Scanning-tunnelling-microscope observation of surface diffusion on an atomic scale Au on Au(111) Rhys. Rev. Lett. 60 120... [Pg.1721]

Figure C2.11.6. The classic two-particle sintering model illustrating material transport and neck growtli at tire particle contacts resulting in coarsening (left) and densification (right) during sintering. Surface diffusion (a), evaporation-condensation (b), and volume diffusion (c) contribute to coarsening, while volume diffusion (d), grain boundary diffusion (e), solution-precipitation (f), and dislocation motion (g) contribute to densification. Figure C2.11.6. The classic two-particle sintering model illustrating material transport and neck growtli at tire particle contacts resulting in coarsening (left) and densification (right) during sintering. Surface diffusion (a), evaporation-condensation (b), and volume diffusion (c) contribute to coarsening, while volume diffusion (d), grain boundary diffusion (e), solution-precipitation (f), and dislocation motion (g) contribute to densification.
The incorporation of surface diffusion into a model of transport in a porous medium is quite straightforward, since the surface diffusion fluxes simply combine additively with the diffusion fluxes in the gaseous phase. [Pg.62]

It is therefore reasonable to go ahead with the construction of models for the gaseous phase diffusion without considering surface diffusion, though of course it must be incorporated before the models are used predictively. [Pg.62]

The literature of surface diffusion is now quite extensive. A review of the basic ideas, with reference to many of the earlier papers, is given by Dacey [44], and a good selection of references including more recent work can be found in Aris [45]... [Pg.62]

The flux N (a,w) is the Sum of contributions from a gaseous phase flux and a flux due to surface diffusion. The surface diffusion contribution is given by equation (7.7) or, more generally, by the corresponding relation which follows from equation (7.5). For the gaseous phase contribution Feng and Stewart assume flux relations of the dusty gas form, (5.1)- ... [Pg.71]

The disposable parameters in these equations are the permeability 0, the surface diffusion factor y, the tortuosity function . (a) (which also... [Pg.74]

Since the void fraction distribution is independently measurable, the only remaining adjustable parameters are the A, so when surface diffusion is negligible equations (8.23) provide a completely predictive flux model. Unfortunately the assumption that (a) is independent of a is unlikely to be realistic, since the proportion of dead end pores will usually increase rapidly with decreasing pore radius. [Pg.75]


See other pages where Surface diffusivity is mentioned: [Pg.258]    [Pg.295]    [Pg.545]    [Pg.560]    [Pg.571]    [Pg.652]    [Pg.710]    [Pg.711]    [Pg.711]    [Pg.1298]    [Pg.1304]    [Pg.2768]    [Pg.2926]    [Pg.2929]    [Pg.59]    [Pg.59]    [Pg.59]    [Pg.59]    [Pg.61]    [Pg.62]    [Pg.62]    [Pg.73]    [Pg.74]    [Pg.78]    [Pg.194]    [Pg.196]   
See also in sourсe #XX -- [ Pg.93 ]

See also in sourсe #XX -- [ Pg.148 ]




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Activation energy for surface diffusion

Activation energy surface diffusion

Adion surface diffusion

Adsorption Entropy on Heterogeneous Surfaces with Surface Diffusion

Adsorption surface diffusion

Alterations in Surface Films, Diffusion and Dissociation

Combined surface exchange/diffusion

Combined surface exchange/diffusion process

Competitive surface diffusion

Contributions of diffuse layer sorption and surface complexation

Dealloying surface diffusion

Density functional theory surface diffusion

Diffuse double layer ionic surface excesses

Diffuse layer model adsorption, 378 surface

Diffuse layer model metal surface complexation constants

Diffuse radiating surface

Diffuse reflectance laser flash-photolysis surface studies

Diffuse reflectance techniques, surface

Diffuse reflectance techniques, surface photochemistry studies

Diffuse surface

Diffuse surface

Diffuse temperature-programmed surface

Diffusion -hardened surfaces

Diffusion Boundary Layer Near the Surface of a Drop (Bubble)

Diffusion Boundary Layer Near the Surface of a Particle

Diffusion at surfaces

Diffusion coefficient from surface

Diffusion effects, surface

Diffusion electrode surface

Diffusion flat surface

Diffusion from permeate/membrane surface

Diffusion lateral surface

Diffusion length, surface

Diffusion ocean surface

Diffusion on surfaces

Diffusion on the Surface of a Micelle

Diffusion surface barriers

Diffusion surface evolution

Diffusion surface relaxation

Diffusion surface resistance

Diffusion surface transport

Diffusion surface treatments

Diffusion to surface

Diffusion vs. Surface Controlled Deposition

Diffusion with catalytic surface reaction

Diffusion with surface resistance

Diffusion, and surface exchange coefficients

Diffusion, bulk surface

Diffusion, definition surface

Diffusion, surface deterioration

Diffusion-convection layer near electrode surface

Diffusion-limited surface reaction

Effective surface diffusivity

Electrode surfaces diffusion-convection layer

Electrode surfaces reactant diffusion process

Electrodeposition surface diffusion

Flattening of Free Surfaces by Surface Diffusion

Gray diffuse surface

H and O surface diffusion

Homogenous surface diffusion model

Hydrogen Surface Diffusion on Homogeneous Metal Surfaces

Isothermal micropore pore-surface diffusion models

Lattice Diffusion from Particle Surfaces

Macropores, surface diffusion

Mass diffusion with catalytic surface reaction

Materials surface: diffusion

Maxwell-Stefan surface diffusion

Maxwell-Stefan surface diffusivities

Measurement of Diffusion and Surface Exchange Coefficients

Mechanisms of Surface Diffusion

Mesopores surface diffusion

Non-equilibrium surface forces of diffusion-electrical nature in

Photochemistry studies, surface, diffuse

Platinum electrodes surface diffusion

Pore Diffusion Resistance Combined with Surface Kinetics

Pore-surface diffusion model

Proton surface diffusion

Qualitative observations of vacancy-induced surface diffusion

Selective adsorption-surface diffusion

Selective surface diffusion membrane

Self-diffusion surface structure sensitivity

Self-diffusion, surface

Separation with Surface Diffusion and Capillary Condensation

Siliceous surface, variable-temperature diffuse reflectance Fourier transform

Silver surface diffusion

Sintering surface diffusion

Slow surface diffusion

Solid surfaces diffusion

Solid-state diffusion, surface evolution

Sorption processes surface diffusion

Specular and diffuse surfaces

Steady-state mass diffusion with catalytic surface reaction

Superficial velocity surface diffusion

Surface Diffusion Constant

Surface Diffusion and Entropy of Adsorbate

Surface Diffusion and Phase Formation

Surface Diffusion from Particle Surfaces

Surface Diffusion in Liquid-Filled Pores

Surface Reaction and Diffusion-Controlled Crack Growth

Surface and bulk diffusion of active particles

Surface chain diffusion

Surface charge density diffuse double layer

Surface charge diffusion

Surface complexation models diffuse layer model

Surface conditions, pure diffusion control

Surface density, diffuse double

Surface density, diffuse double layer

Surface diffusion

Surface diffusion

Surface diffusion 556 Subject

Surface diffusion Diffusivity

Surface diffusion Diffusivity

Surface diffusion Temperature dependence

Surface diffusion and capillary condensation

Surface diffusion and reactions

Surface diffusion anisotropic

Surface diffusion coefficients

Surface diffusion distance

Surface diffusion dynamics

Surface diffusion electrocatalysts

Surface diffusion exchange mechanisms

Surface diffusion jump lengths

Surface diffusion measurement

Surface diffusion mechanism

Surface diffusion model

Surface diffusion nature

Surface diffusion of ad-atoms

Surface diffusion of oxygen species on supported metal catalysts

Surface diffusion of reactant

Surface diffusion on metals

Surface diffusion parameters, table

Surface diffusion preexponential factor

Surface diffusion process

Surface diffusion random-walk analysis

Surface diffusion rate controlled proces

Surface diffusion rates, measurement

Surface diffusion rates, measurement applications

Surface diffusion rates, measurement principles

Surface diffusion rates, measurement theory

Surface diffusion separation

Surface diffusion separation types

Surface diffusion statistics

Surface diffusion vacancies

Surface diffusion, alumina

Surface diffusion, rapid alloying, microcluster

Surface diffusion/reaction coupling

Surface evolution by solid-state diffusion

Surface phenomena diffusion

Surface self-diffusion coefficient

Surface-diffusion-mediated deposition

Surfaces diffuse, grey

The relationship between diffusion constant and specific surface

The role of vacancies in surface diffusion

Thermal activation surface diffusion

Thermal surface diffusion

Transport coefficients surface diffusion coefficient

Transport mechanism, membranes surface diffusion

Transport mechanisms surface diffusion

Underground Storage of Helium Diffusion through a Spherical Surface

Vacancy-induced surface diffusion

With surface diffusion

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