Surface Energy and Adsorption

G. A. Parks, Surface energy and adsorption at mineral/water interfaces an introduction, in M. F. Hochella and A. F. White, eds., Mineral-Water Interface Geochemistry, The Mineralogical Society of America, Washington, D. C (1990). 

Parks, G.A., Surface energy and adsorption at mineral-water interfaces An introduction, Rev. Miner, 23, 133, 1990. 

Surface Energies and Adsorption Energies for Water, Hydroxyl, Methanoic Acid, and Methylamine on Low Energy Pure Wollastonite Surfaces... 

B. Surface Energy and Free Energy Changes from Adsorption Studies... 

This type of fully local potential has some limited use, e.g., to consider adsorption in a slowly varying external potential. It fails, however, to describe the most important phenomena such as surface tension and adsorption at most types of interfaces. These phenomena reflect in a fundamental way the nonlocal interactions in the fluid. The most obvious nonlocality of the free energy arises due to the range of the attractive or soft interactions represented by the second term in the equation of state, —The corresponding potential energy can be obtained by the functional... 

Experimentally jB is found to be finite. The slope of the relative adsorption versus composition, which is also finite, is referred to as Henry s law for surfaces. For electronegative elements on metallic surfaces the surface activity becomes very high, often of the order of 103. This means that very small amounts of these elements have a large effect on the surface energy, and that the experimental determination of reliable surface energies needs systems of extreme purity. 

It involves the change of the internal surface energy upon adsorption of an infinitesimal amount of gas at constant temperature and total surface area. 

Figure 13.6 shows a schematic for IGC operation. Inverse, in this instance, refers to the observation that the powder is the unknown material, and the vapor that is injected into the column is known, which is inverse to the conditions that exist in traditional gas chromatography. After the initial injection of the known gas probe, the retention time and volume of the probe are measured as it passes through the packed powder bed. The gas probes range from a series of alkanes, which are nonpolar in nature, to polar probes such as chloroform and water. Using these different probes, the acid-base nature of the compound, specific surface energies of adsorption, and other thermodynamic properties are calculated. The governing equations for these calculations are based upon fundamental thermodynamic principles, and reveal a great deal of information about the surface of powder with a relatively simple experimental setup (Fig. 13.6). This technique has been applied to a number of different applications. IGC has been used to detect the following scenarios ...

WE shall now discuss a subject of great importance to the technology of fine particles—surface energy and the relation it bears to heat produced by particles on adsorption, wetting of particles, and other diverse phenomena which have found practical applications, such as flotation of ores and minerals. Information on this subject is still limited, but sufficient is known to permit explanation of the behavior of particulate matter. 

The chosen super cell for the Si(001)-(2 x 1) surface contains six layers of Si, each of which includes eight atoms as shown in Figure 15-l(b). The top surface layer is reconstructed via dimerization to lower down the surface energy and the bottom layer is saturated with hydrogen atoms. The cell parameters were taken from the crystal structure of silicon and the distance between the slabs was chosen to be about 26.0A. Upon C60 adsorption, the supercell contains 48 Si atoms and 16 hydrogen atoms in addition to 60 C atoms. 

Consider now that some adsorption of liquid vapours on the solid surface occurs (Figure 1,34.b), leading to a reduction of its surface energy by a quantity Aliquid surface). For the sake of clarity, we denote by cr< v and W the solid surface energy and the work of adhesion in the absence of adsorption, while pure solid/pure liquid/vapour system held at constant temperature, the solid surface is in equilibrium with a saturated vapour of the liquid at a partial pressure of Psat, the equilibrium values of [Pg.45]

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