Surface phenomena

The antiozonant should possess adequate solubiUty and diffusivity characteristics (19). Siace ozone attack is a surface phenomenon, the antiozonant must migrate to the surface of the mbber to provide protection. The antiozonant should have no adverse effects on the mbber processiag characteristics, eg, mixing, fabrication, vulcanization, or physical properties. 

Surface Resistivity. Resistance is the measure of the conductivity of a material. Conductive materials have the abiUty to dissipate static charges. Therefore, resistance is a good measure of the abiUty of an object to dissipate a static charge. Since static electricity is primarily a surface phenomenon, the resistance along the surface of the object is of most interest. 

Adsorption (qv) is a phenomenon in which molecules in a fluid phase spontaneously concentrate on a sohd surface without any chemical change. The adsorbed molecules are bound to the surface by weak interactions between the sohd and gas, similar to condensation (van der Waals) forces. Because adsorption is a surface phenomenon, ah practical adsorbents possess large surface areas relative to their mass. 

Polyisobutylene and similar copolymers appear to "pack" well (density of 0.917 g/cm ) (86) and have fractional free volumes of 0.026 (vs 0.071 for polydimethylsiloxane). The efficient packing in PIB is attributed to the unoccupied volume in the system being largely at the intermolecular interfaces, and thus a polymer chain surface phenomenon. The thicker cross section of PIB chains results in less surface area per carbon atom. 

Retention of a given solids particle in the system is on the average veiy short, usually no more than a few seconds. This means that any process conducted in a pneumatic system cannot be diffusion-controlled. The reaction must be mainly a surface phenomenon, or the solids particles must be veiy small so that heat transfer and mass transfer from the interiors are essentially instantaneous. 

Adsorption of pollutant gases occurs when certain gases are selectively retained on the surface or in the pores or interstices of prepared solids. The process may be strictly a surface phenomenon with otily molecular forces involved, or it may be combined with a chemical reaction occurring... 

So far the structure of pure metals has been discussed with reference to bulk characteristics and continuous crystals. However, corrosion is essentially a surface phenomenon and it is necessary to consider how the structure and defects already described interact with free surfaces. At this stage it is convenient to consider only a film-free metal surface, although of course in most corrosion phenomena the presence of surface films is of the utmost importance. Furthermore, it is at free surfaces that the hard sphere model of metals... 

In general, adsorption is a surface phenomenon, where gas or liquid is concentrated on the surface of solid particles or fluid interfaces. There are many adsorption systems. 

The physical meaning of the parameter 2FNG/I is obvious It expresses the time required to form a monolayer of oxide ions on a surface with NG adsorption sites when the oxide ions are supplied at a rate I/2F. This proves that NEMCA is a surface phenomenon (not a bulk phenomenon and not a phenomenon at the tpb) taking place over the entire gas-exposed catalyst electrode surface. 

Since ozone attack on rubber is essentially a surface phenomenon, the test methods involve exposure of the rubber samples under static and/or dynamic strain, in a closed chamber at a constant temperature, to an atmosphere containing a given concentration of ozone. Cured test pieces are examined periodically for cracking. 

Because V-uptake is a surface phenomenon, we plotted (Fig. 1, b) the V adsorbed per unit area of zirconia (atoms nm 2) as a function of V atoms available in the AV solution (V atoms nm 2, referred to the ZrOa surface area). For ZV(a)pH2H-4 samples, up to 2.5 atoms nm-2, all the available V was adsorbed. As the available V increased further, uptake reached an extended plateau, corresponding to about 3 V atoms nm 2. By contrast, for ZV(a)pH1 samples, V-uptake progressively increased throughout the region of the available V. The maximum V-uptake was about 2.4 atoms nm 2. 

Adsorption, a surface phenomenon, is the basis of many gas or liquid mixture separation and purification methods. It is also the basis of adsorption chromatographic methods used for the analysis of complex mixtures. The knowledge of adsorption mechaiusms is useful in choosing the suitable systems providing optimum separation. 

Heterogeneous catalysis is by nature a surface phenomenon. An efficient catalytic system under reactive conditions demands a delicate energetic balance. For a catalytic reaction to occur, reactant molecules must adsorb on a surface, react, and... 

Ozone degradation is a surface phenomenon and hence a physical anti-ozonant must form a protective barrier. A chemical anti-ozonant can be added during polymer fabrication, but again it must diffuse to the surface. It must also provide a defence over the lifetime of the article. 

One way to control gaseous pollutants like SO2 and SO3 is to remove the gases from fuel exhaust systems by absorption into a liquid solution or by adsorption onto a solid material. Absorption involves dissolving the gas in a liquid while adsorption is a surface phenomenon. In each case, a subsequent chemical reaction can occur to further trap the pollutant. Lime and limestone are two solid materials that effectively attract sulfur dioxide gas to their surfaces. The ensuing chemical reaction converts the gaseous pollutant to a solid nontoxic substance that can be collected and disposed or used in another industry. 

It is perhaps useful to mentally picture the microwaves to travel through the waveguide like a water stream through a pipe. In reality, however, the transport is an electric phenomenon that occurs in a very thin layer of the waveguide s inside. The thickness of this layer is characterized by the skin depth parameter, 8, which depends on the used material and the frequency. For example, for the material copper and a frequency of 10 GHz the skin depth is 8 0.66 pm. While at the surface the amplitude of the electric field of the wave is maximal, at a depth of 8 the E is reduced by a factor e 1 0.37, and at a depth of a few 8 becomes negligibly small. Transmission of microwaves through a waveguide is essentially a surface phenomenon. 

However, in contrast to XPS, electrons are promoted into bound or continuum states and still provide partial screening to the excited atom, so that these absorption energies are less sensitive to relaxation effects. Shifts in absorption energies are thus often more easily detected than those in XPS BEs. Moreover, XANES is a bulk-sensitive technique, and avoids the ambiguities associated with XPS in attributing trends to a bulk vs. surface phenomenon. 

X-ray line broadening provides a quick but not always reliable estimate of the particle size. As Cohen [9] points out, the size thus determined is merely a ratio of two moments in the particle size distribution, equal to /. Both averages are weighted by the volume of the particles, and not by number or by surface area, as would be more meaningful for a surface phenomenon such as catalysis. Also, internal strain and instrumental factors contribute to broadening. 

When used in direct soil analysis, XRF suffers from the fact that it is largely a surface phenomenon. For this reason, only surface elements will be determined. However, because it is a surface phenomenon, it has been extensively used to study sorption on the surfaces of soil components. An extensive list of investigations using XRF to investigate various sorption mechanisms is given in the text by Sparks [33],... 

Deflagration Chemical reaction in which the output of heat is sufficient to enable the reaction to proceed and be accelerated without heat from another source a surface phenomenon in which reaction products flow away from the unreacted material along the surface at subsonic velocity. The result of a true deflagration under confinement is an explosion. 

Uptake is the process by which chemicals (either dissolved in water or sorbed onto sediment and/or suspended solids) are transferred into and onto an organism. For surfactants, this generally occurs in a series of steps a rapid initial step controlled by sorption, where the surface phenomenon is especially relevant then a diffusion step, when the chemical crosses biological barriers, and later steps when it is transported and distributed among the tissues and organs. 

Since sorption is primarily a surface phenomenon, its activity is a direct function of the surface area of the solid as well as the electrical forces active on that surface. Most organic chemicals are nonionic and therefore associate more readily with organic rather than with mineral particles in soils. Dispersed organic carbon found in soils has a very high surface-to-volume ratio. A small percentage of organic carbon can have a larger adsorptive capacity than the total of the mineral components. 

In a more restrictive sense, the term "ion exchange" is used to characterize the replacement of one adsorbed, readily exchangeable ion by another. This circumscription, used in soil science (Sposito, 1989), implies a surface phenomenon involving charged species in outer-sphere complexes or in the diffuse ion swarm. It is not possible to adhere rigorously to this conceptualization because the distinction between inner-sphere and outer-sphere complexation is characterized by a continuous transition, (e.g., H+ binding to humus). 

Hence, if the wire shrinkage would have been a surface phenomenon, as postulated, Eq. (29) still would be incorrect from the viewpoint of thermodynamics. Equations (27) or (28) are the only ones conforming to this science. Moreover, it is assumed in the derivation of Eq. (29) that v = 0.5. Most solids, especially metals, have v nearer to 0.3 than to 0.5. If v = 0,3 is substituted in Eq. (32), then W0 = 1.4 nr ys follows. 

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