Subsurface Region of a Solid

A very important characteristic of the subsurface region is the surface concentration of the atoms. For alloys, it is customary to speak of the surface segregation of the component whose surface concentration exceeds the bulk one. With an increase in the distance from the surface, the local concentrations of the particles tend to their bulk values. This also relates to the other characteristics of particle distribution determining short- and long-range orders, which in the subsurface region can have a great anisotropy. 

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The simplest model of the condensed phase is represented by the lattice-gas model [50]. It reflects two major features of the any species in the condensed phase, viz., their characteristic volume and species interactions. The volume of a crystalline solid is characterized by its natural lattice. With a good approximation, one can consider that the subsurface region of a solid is... 

When particle impacts with a solid surface, the atoms of the surface layer undergo crystal lattice deformation, and then form an atom pileup on the outlet of the impacted region. With the increase of the collision time, more craters present on the solid surface, and amorphous transition of silicon and a few crystal grains can be found in the subsurface. 

Adsorption is the net accumulation of matter on the sohd phase at the interface with an aqueous solution or gaseous phase. In this process, the solid surface is the adsorbent and the matter that accumulates is the adsorbate. Adsorption also may be defined as the excess concentration of a chemical at the subsurface solid interface compared to that in the bulk solution, or the gaseous phase, regardless of the nature of the interface region or the interaction between the adsorbate and the sohd surface that causes the excess. Surface adsorption is due to interactions between electrical charges, or nonionized functional groups, on mineral and organic constituents. 

Cations held on external surfaces are immediately accessible to (subsurface) water. Once removed from the solid phase, they move to a region of reduced concentration. This movement is conholled by diffusion, and the diffusion coefficient (D) can be calculated using the equation described by Nye and Tinker (1977) ... 

In any evaluation of a remediation scheme utilizing surfactants, the effect of dose on HOC distribution coefficients must be quantified. Very often, only one coefficient value for HOC partitioning to sorbed surfactants has been reported in the literature, presumably because the experimental data covers only the sorption regions where the surfactant molecule interactions dominate at the surface (Nayyar et al., 1994 Park and Jaffe, 1993). However, all of the characteristic sorption regions will develop during an in-situ SEAR application as the surfactant front (i.e., mass transfer zone) advances through the porous medium. Therefore, the relative role ofregional HOC partition coefficients to sorbed surfactant should be considered in any remediation process. Finally, the porosity or solid volume fraction for the particular subsurface system must be taken into account when surfactant sorption is quantified. 

In certain environments, localized anomalously low concentrations of soil O2 have been used by exploration geologists to indicate the presence of a large body of chemically reduced metal sulfides in the subsurface. Oxidation of sulfide minerals during weathering and soil formation draws down soil gas po below regional average. Oxidation of sulfide minerals generates solid and aqueous-phase oxidation products (i.e., sulfate... 

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