Sorption surfaces

Three differing capacities of a pump for the gases which can be pumped result from the size of the three surfaces (baffle, condensation surface at the outside of the second stage and sorption surface at the inside of the second stage). In the design of a cryopump, a mean gas composition (air) is assumed which naturally does not apply to all vacuum processes (sputtering processes, for example. See 2.1.9.6 Partial Regeneration ). 

Fuller et al. (2002) used EXAFS to study the sorption/surface precipitation of U(VI) to hydroxyapatites used in permeable reactive... 

Salts can affect sorption of organic compounds by displacing cations from the soil ion exchange matrix, by changing the activity of the sorbate in solution, and by changing the charge density associated with the soil sorption surface (Hamaker and Thompson, 1972). Salt effects are most important for basic sorbates in the cation state, where an increase in salinity can significantly lower the sorption coefficient. Salt effects are least important for neutral compounds, which may show either increases or decreases in sorption as salinity increases. 

Surface charge results from the sorption (surface complex formation) reaction itself. 

S. J. Gregg, K. S. W. Sing, Ad.sorption, Surface Area and Porosity, Academic Press, Lx>ndon, 1982. 

Previous work described in the literature [1,2,4] suggests that iron carbide is a necessary constituent of an active FT catalyst and hence it is reasonable to believe that the carbide surface area should correlate with catalyst activity. The actual surface area of the carbide phase on a FT catalyst is difficult to measure, because the carbide surface is covered with CH which is reactive in the presence of H2 [1,2]. This makes the accuracy of H2 chemisorption, one potential method, uncertain. Since CHx covers all the carbide particles and since it is unclear whether H2 would measure CHx surface area, iron carbide surface area, or react with the CHx, the accuracy of H2 chemisorption is uncertain. In addition, the extreme air sensitivity of the catalyst, and the inherent wax build up on any catalyst that has been reacted in synthesis gas, makes potential sorption surface-measurement difficult since it requires removing wax from the pores of the catalyst in an oxygen free environment before a meaningful sorption experiment. But if the carbide particles all grow from the magnetite and are similar in particle size, then the total amount of carbide as seen by a bulk technique such as x-ray diffraction may also be used as a measure of the active phase. 

The most promising is the application of the Taylor-vortex column with Taylor-Couette flow. Sorption of hydrophobic organic compounds can lead to under estimation of actual removal efficiency of wastewater treatment, as weU as cross-contamination of the batches of the effluent due to release ofthe sorbed solute molecules. This is supported by the results ofthe laboratory studies, along with the ease ofthe potential scale-up. The critical part in the context ofthe removal of organic compounds from wastewater(s) is the material of the inner cylinder. The surface of the inner cylinder provides a potential sorption surface for hydrophobic organic molecules. Since the PTFE price could be prohibitive for the scale-up, stainless steel, or other materials should be explored as replacements for potential industrial applications. 

The surface defines the interface between a mineral and its surroundings. In a dynamic context, reactions that occur between apatites and the environments in which they exist take place at or through their surfaces. This includes, but is not restricted to, crystal growth, dissolution, and surface-mediated reactions such as sorption, surface complexation, and catalysis (Hochella and White 1990). Because this interface is partly defined by the nature of the environment around the crystal, the properties, structure and chemistry of the crystal surface are always different than those of the bulk, and can be quite varied depending on the environment. For example, the crystal surface of apatite may have very different characteristics in contact with an aqueous solution as opposed to a polymerized silicate melt. 

The other principal controls on heavy metal availability proposed previously are the layer silicates, organic matter, and carbonates. Where the controls for a given process are not understood, numerous hypotheses are to be expected. The previous explanations of heavy metal sorption by the layer silicates include surface sorption, surface complex ion formation, lattice penetration, and ion exchange. The mechanisms of heavy... 

The vapor density of dieldrin over a Gila silt loam (0.6% om) increases with the concentration in the soil (Fig. 4.5) and at soil concentrations of only 100 ppm gives a vapor density essentially equal to that of the pure compound. As would be expected, vapor density over the soil increases with temperature. The effect of soil water content on the vapor density of dieldrin over the same sod has been reported and from Figure 4.6 it is clear that a dry sod results in a dramatic reduction in vapor density. In discussing sorption of gases on sod (see Physical chemical properties. Chapter 2) it was suggested that this effect resulted from water displacing the compound from the more polar sorption surfaces (e.g., clays) and it can be seen that this transition occurs quite abruptly. The effect of composition on the vapor density of dieldrin over soil is illustrated by the data in Table 4.7. ... 

Although there is an immense amount of literature concerned with adsorption phenomena at electrodes, few practical applications of electrodes as sorption surfaces are reported for the recovery of chemicals, as occurs in the classical adsorption process. Electrosorption, however, could be an alternative means of separation of small quantities of organics and other species from effluent streams. High surface-area adsorbent electrodes would clearly be required. The technique has been demonstrated in the adsorption of P-naphthol onto a packed bed of glassy carbon spheres [95], and cyclic electrosorption was experimentally demonstrated. 

Temperature-dependent NMR spectra of monolayers of CgDe on a-BN were measured at 52.7 MHz from 80 to 293 K. Below 225 K, the largely different linewidths of the singlet spectra recorded appear to be mainly determined by the adsorbent particle morphology (averaging of the nuclear quadrupole interaction upon surface diffusion). Above 225 K, the linewidths are considered to be dominated by isotropic molecular reorientation motions [56] also compare [57]. Graphitic a-BN is used as sorbent layer on sorption surfaces for cooling traps and cryopumps [58]. 

Electric double layer (EDL) theory can account for the effect of surface charge on sorption. Surface charge (a) and electric potential... 

Mass sorption, surface washing, and surface concentration monitoring were three experimental techniques compared. ... 

GAS SORPTION - SURFACE AREA AND PORE SIZE DETERMINATION... 

Table 2. Nitrogen Sorption Surface Areas and Mean Pore Diameters of Bridged Polysilsesquioxanes Before and After Treatment with an...

Mehra and Jackson [1959] showed, for a wide range of soil clays, that the sum of planar sorption surface of expandable 2 1 layer silicates and the mica unit-cell interlayer surface (as measured by potassium content), when corrected to exclude quartz, chlorite, and kaolinite in mixed clays, is constant within the experimental error of about 2%. 

Mehra, O. P., and M. L. Jackson, 1959. Constancy of the sum of mica unit cell potassium surface and interlayer sorption surface in vermiculite-illite clays. Soil Sci. Soc. Am. Proc. 23 101-105. 

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