Surface reaction nonequilibrium adsorption

This reaction is actually slightly endothermic (A// = 88 kJ/mol), but the large net increase in entropy and the nonequilibrium nature of most CVD processes lead to significant tungsten deposition. As with the Ge example, the deposition mechanism involves adsorption steps and surface reactions. At low pressures and under conditions of excess hydrogen gas, the deposition rate follows the general form ... 

Here and f are the extents of adsorption reactions which imply an independent transport of each constituent to the Gibbs geometrical surface from the bulk phases b and b such that dnf = d + d Gibbs surface system model is used and the surface phase considered also contains parts of the homogeneous phases. Therefore no direct comparison between Eqs. (32) and (42) is possible. The last-mentioned equation cannot, however, be in contradiction to our assumptions because the regarded surface phase also contains homogeneous masses it represents instead an alternative way of extending the theory to nonequilibrium systems. 

The rates and mechanisms of sorption reactions at the mineral/water interface are critical in determining the mobility, speciation, and bioavailability of metals in aqueous and terrestrial environments. This chapter discusses nonequilibrium aspects of metal sorption at the mineral/water interface, with emphasis on confirmation of slow sorption mechanisms using molecular approaches. It is shown that there is often a continuum between sorption processes, viz, diffusion, sites of varying energy states, and nucleation of secondary phases. For example, recent molecular level in-situ studies have shown that metal adsorption and surface precipitation can occur simultaneously. 

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