Pores vacancy model

Cairns-Smith is careful enough to concede that the first hypothetical informationcarrying material was not of necessity a clay mineral however, the basic features of the model can best be demonstrated using different clay species. Thus, for example, clays could have crystallized out in sandstone pores from solutions containing products derived from weathering. The result would have been clay layers, which could have been separated and transported further by external influences replication under similar conditions would have followed. Such crystallization processes would have also involved errors, such as defects, vacancies, and the incorporation of other ions or atoms these inorganic mutations would have been passed on, i.e., they would have been incorporated into the next sheet to be formed. 

Thus, contributions include accounting for adsorbent heterogeneity [Valenzuela et al., AIChE J., 34, 397 (1988)] and excluded pore-volume effects [Myers, in Rodrigues et al., gen. refs.]. Several activity coefficient models have been developed to account for nonideal adsorbate-adsorbate interactions including a spreading pressure-dependent activity coefficient model [e.g., Talu and Zwiebel, AIChE h 32> 1263 (1986)] and a vacancy solution theory [Suwanayuen and Danner, AIChE J., 26, 68, 76 (1980)]. 

Considering the obtained experimental data, it is possible to propose a model of the formation of a porous structure of the films of zirconia-based solid electrolytes. The model assumes the formation of pores and submicropores when vacancies, which are trapped during sputtering of the solid-electrolyte films (the sputtering temperature was Tf < 0.3Tmeit), pass to sinks and then condense [2,3,4,5], The sinks are boundaries between the crystallites forming the film structure. 

The adsorption of gas mixtures has been extensively studied. For example, Wendland et al. [64] applied the Bom—Green—Yvon approach using a coarse grained density to study the adsorption of subcritical Lennard-Jones fluids. In a subsequent paper, they tested their equations with simulated adsorption isotherms of several model mixtures [65]. They compared the adsorption of model gases with an equal molecular size but different adsorption potentials. They discussed the stmcture of the adsorbed phase, adsorption isotherms, and selectivity curves. Based on the vacancy solution theory [66], Nguyen and Do [67] developed a new technique for predicting the multicomponent adsorption equihbria of supercritical fluids in microporous carbons. They concluded that the degree of adsorption enhancement, due to the proximity of the pore... 

Figure 10.14 (a) Tetrakaidecahedron model of intermediate-stage sintering, b) Expanded view of one of the cylindrical pore channels. The vacancies can diffuse down the grain boundary (dashed arrow) or through the bulk (solid arrows). Note that in both cases the vacancies are annihilated at the grain boundaries. 

Volume diffusion. In this model, the vacancy source is the pore surface of radius pp and the sink is the spherical surface of radius / , where R s> Pp (Fig. 10.15a). By solving the flux equation, subject to the appropriate boundary conditions, it can be shown that (see App. lOD)... 

In the simplest model for representing the elimination of porosity in a solid. Fig. 3.11, volume diffusion takes place by means of lattice defects, in particular, vacancies. Pores play the role of vacancy sources, and grain boundaries act as vacancy sinks. The key point in this mechanism is that a... 

All voids described so far have been formed at, or released from, the metal-oxide interface. Birchenal has discussed the formation and growth of voids within the oxide scale by condensation of vacancies. For this to occur anions must be removed in some way and he has suggested creep and slip in the anion lattice as possible mechanisms. More recently, Cox has used a sensitive porosimeter as well as special metallographic techniques to study strings of voids formed in zirconium oxide as a result of recrystallisation—the work is discussed in more detail below. Although Birchenal s model predicted greater deviations from the parabolic rate law than were in fact found, the phenomenon of pore growth within the scale seems to be real and it is as well to keep the implications for anion movement in mind. 

Bobeth M, Gutkin M, Pompe W and Romanov A E (1998), Modelling of vacancy diffusion and pore formation during parabolic oxide growth , Phys Stat Sol (a), 165, 165-184. 

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