N diffusivity

Model Phase boundary control (n) Diffusion control (171)... 

Denier van der Gon HAC, van Breemen N. Diffusion-controlled transport of methane from soil to atmosphere as mediated by rice plants. Biogeochemistry. 1993 21 177-190. 

Davies, C.N., Diffusion and Sedimentation of Aerosol Particles from Poiseuille Flow in Pipes, Aerosol Sci. 4 317-328 (1973). 

For many adsorbates, especially organic substances, the concept of semi-infinite linear diffusion can give us some ideas on the time necessary for an adsorbate to be adsorbed. The number of mols adsorbate, n, diffusing to a unit area of a surface per second, is proportional to the bulk concentration of adsorbate, c ... 

Plate 4.3 Microstructure of a Nb-N diffusion couple representative for annealing temperatures below about 1573 K (13U0°C) and nitrogen pressures above about 1 bar. Sample tilted for magnification of phase bands. Anodically oxidized. 

Figure 4.4 Microstructure of a V-N diffusion couple illustrating the general appearance of the phase band structure. Top right corner precipitation of metastable V(N) phase(s).

Plate 4.4 Two Ta-N diffusion couples above (top) and below (bottom) the eutectoid decomposition temperature of (5-TaN, v Upon cooling b-TaN, x decomposes into c-TaN and / -Ta2N. Polarized light. 

N diffuses into the structural pores of clinoptilolite 10 to 10 times faster than does CH4. Thus internal surfaces are kinetically selective for adsorption. Some clino samples are more effective at N2/CH4 separation than others and this property was correlated with the zeolite surface cation population. An incompletely exchanged clino containing doubly charged cations appears to be the most selective for N2. Using a computer-controlled pressure swing adsorption apparatus, several process variables were studied in multiple cycle experiments. These included feed composition and rates, and adsorber temperature, pressure and regeneration conditions. N2 diffusive flux reverses after about 60 seconds, but CH4 adsorption continues. This causes a decay in the observed N2/CH4 separation. Therefore, optimum process conditions include rapid adsorber pressurization and short adsorption/desorp-tion/regeneration cycles. 

Several recent studies7,9,10,23,26 have reported attempts to create silicon nitride by direct ammoniation of silica, usually as a spin-off of the integrated circuit technology research. Most of these studies agree that at temperatures about 1473 K up to 20 -25 % (w/w) nitrogen can be incorporated, but silicon nitride is seldom formed. The final product of this direct nitridation method is silicon-oxynitride (Si2N20) with residual silica. The nitridation is not restricted to the surface, but the N diffuses also into the bulk structure of the silica. No adequate mechanisms were presented to explain the observed reactions. 

When the above As are substituted into Eq. 9.29 or 9.30, we again end up with a linkage between experimental retention measurements (as reflected in R) and various electrical (n), diffusive (D), and thermal (a) properties of the components of interest. It is clear that species are separated on the basis of differences in these properties. For a particular sample we can, in theory, choose the property with the largest differences (the highest selectivity) between species, then apply the corresponding FFF subtechnique to that sample. 

Substitution of iron by nickel can be expected to order the Ni atoms at the corner positions since placement of a nickel atom (tigers1) at a face requires the eg orbital perpendicular to the N—Nif bond to be filled, thus preventing N atoms from occupying adjacent octahedral sites. (Occupancy would require antibonding Nif states to be populated.) Such an effect hinders N diffusion. In fact it was found... 

The diffiisivity versus composition has been investigated for 5-TiNi j, 5-HfNi j, and 5-NbNi j. A modified Boltzmann-Matano analysis, carried out on nitrogen diffusion profiles measured by EPMA, yielded a composition-dependent diffusion coefficient for N diffusion expressed as... 

All the samples possess BET surface areas considerably smaller than those calculated fi om CO adsorption data, pointing to very narrow micropores or obstructions of pore entrances that restrict N diffusion. Thus, differences between values of Sbet and Sco2 suggest prevalence of micropores over meso and macropoies in the Ugnocellulosic wastes and chars. The relative contribution of micropores to fite samples structures may be additionally inferred from the Scot/Sset tatio. Char samples present smaller ratios than the wastes, indicating decreases in the relative proportions of micropores owing to the thermal treatment. 

The diffusion potential must be estimated considering transport of both ions through the membrane. The interfering ion N" " diffuses from the right-hand side where its concentration is c r), to the left-hand side where it is zero. The situation... 

The reader should note that the microscale model is used to determine the nonzero terms in B, and thus for the following discussion B can be assumed to be known. Using matrix notation and the properties of the Wiener process (Gardiner, 2004), a symmetric N x N diffusion matrix D can be defined by... 

Enclosure with N Diffuse-Gray Surfaces—The Net Radiation Method.579... 

Consider an enclosure of N diffuse-gray, opaque surfaces, each surface being isothermal and having a uniform radiosity and irradiation. The radiative energy balance for the ith surface gives = A J - G,), where J = + p G = + (1- j)Gj. Combining these two equations to... 

Gollahalli, S. R., Khanna, T, and Prabhu, N. "Diffusion Flames of Gas Jets Issued From Circular and Elliptic Nozzles." Combustion Science and Technology 86 (1992) 267-88. 

As we did not detect N2 at the relatively low temperature of 323 K, atomic nitrogen is probably not formed. However, due to the high surface coverage of the various species (OH, NH2, NH, NO, N), diffusion may be impaired thereby hindering reconstruction to N2. 

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