Real-area factor

CI2 evolution reaction, 38 56 electrochemical desorption, 38 53-54 electrode kinetics, 38 55-56 factors that determine, 38 55 ketone reduction, 38 56-57 Langmuir adsorption isotherm, 38 52 recombination desorption, 38 53 surface reaction-order factor, 38 52 Temkin and Frumkin isotherm, 38 53 real-area factor, 38 57-58 regular heterogeneous catalysis, 38 10-16 anodic oxidation of ammonia, 38 13 binding energy quantification, 38 15-16 Haber-Bosch atrunonia synthesis, 38 12-13... 

The apparent surfaces of poly crystals, measured geometrically, are often 2—3 times smaller than the real area because the latter is relatively rough—it has hills and valleys that are invisible to unaided sight (see Fig. 7.32). Because various metals—and different samples of the same metal—may have different roughness factors ... 

There are some (Heinze, 1996) to whom the polaron explanation of the ionic introduction of electronic conductivity in organic compounds is specious The roughness factor of 400 would limit the degree of penetration of ions into the interstices of the polymer. However, Li+ or even CIOJ is of course much smaller than the test molecules (large dye molecules) which are generally used to probe the real area. Thus, one might conceive of a model of the polymer that is all fibers, the intercalation being all pervasive. It is obvious that an Li+ ion adsorbed on the surface of a fiber will promote an electron that may indeed be free to move under a field, i.e., to conduct. 

The maximum isosteric differential heat of adsorption interpolated from the heat-coverage plots. c The roughness factor is defined as the ratio of the experimental values of the weight of adsorbate required for monolayer coverage to that calculated for the same coverage of a geometrically planar surface. It can be interpreted as the ratio of the real area to the apparent area of the adsorbent. 

The apparent surface of polycrystals, measured geometrically, is often two to three times smaller than the real area, because the latter is relatively rough - even if its hills and valleys are invisible to unaided sight. Because various metals and different samples of the same metal may have different roughness factor and because the velocity of an electrode reaction has to be standardized to the real area, the roughness factor has to be determined.61,62... 

Figure 6. Tafel relations for the h.e.r. at Ni-Mo electroplated electrocatalysts at several temperature curves (1-4), 341, 319, 298, and 278 K, compared with behavior of metallic nickel (curve 5) (Real apparent area factor for Ni-Mo coated electrode 450 X ) electrolyte is 1.0 M aqueous KOH (from Ref. 46, see also Fig. 19).

The determination of the real surface area of the electrocatalysts is an important factor for the calculation of the important parameters in the electrochemical reactors. It has been noticed that the real surface area determined by the electrochemical methods depends on the method used and on the experimental conditions. The STM and similar techniques are quite expensive for this single purpose. It is possible to determine the real surface area by means of different electrochemical methods in the aqueous and non-aqueous solutions in the presence of a non-adsorbing electrolyte. The values of the roughness factor using the methods based on the Gouy-Chapman theory are dependent on the diffuse layer thickness via the electrolyte concentration or the solvent dielectric constant. In general, the methods for the determination of the real area are based on either the mass transfer processes under diffusion control, or the adsorption processes at the surface or the measurements of the differential capacitance in the double layer region [56],... 

It is an observed fact that a constant rate of volume-wear, unaffected by progressive change in the apparent area of contact during the course of wear, is one of the consistently characteristic types of wear behavior. For Eqn 13-21 to be a variant of Eqn 13-20 requires that the area factor remains constant. One way to realize this is by means of the plastic deformation model of the real contact area of asperities, in which case the expression equivalent to Eqn 13-21 is... 

The derivation of Eqns 13-29 implies that we know how to sum up the total wear volume and the total contact area. The format of Eqn 13-30 stems from Archard s analysis of the surface model described in Chapter 12, Section 12.2.1, where the relation between real area of contact and load as given by Eqn 12-9 reduces to A = W/P for the case of plastic deformation of asperities. Other relations between real area of contact and load and other models for the formation of wear particles will give other expressions for wear, as discussed by Archard [6]. The quantity Z, which we have termed the effectivity factor, is designated as a... 

Question by Professor S. Bahadur, Iowa State University The viscoelastic effect in deformation reported by you is similar to what has been known for a long time in wood. As such the deformation values in loading and unloading are different. Have you given any consideration how these results could be factored into the adhesion theory of friction which has as one of its components the real area of contact ... 

The effect of roughness of the solid surface is to increase the actual area of contact between solid and liquid and also that of the unwetted solid per unit geometric area. The roughness factor, r, is defined as the real area of the solid divided by this geometrical area described by a boundary. Wenzel therefore proposed that Young s Eqn. 1 be modified as... 

These decompositions into more elementary factors are purely virtual ones. They do not imply the existence of real areas or true ions in the systems. A force may exist independent of any surface... 

The different slopes allow the deduction of the geometrical structure which is defined as the ratio between real junction area and the projection of the real junction area on the substrate. This area factor (4 - 8)- in structured junctions decreases with duration of heat treatment and with increasing reverse potential due to a smoothing effect of the space charge region (figures 19e and 19f). 

Contact angle hysteresis results from surface roughness and/or surface heterogeneity which is the case with all real surfaces, in particular with leaf surfaces that are covered with microcrystalline wax. Surface roughness may be expressed by a factor r, r = Real area/Projected area... 

Depending upon these factors, the Intensity of contact which Is intimately related to friction, is defined. It has been pointed out by Bowden and Tabor that the area of real contact Is usually much smaller than the nominal area on account of the presence of surface roughness and that the determination of the real area is of fundamental Importance In tribology. This Is undoubtedly justified, considering the fact that the failure of adhesion occurs at the real area of contact. The real area has been regarded as the key parameter in the description of the intensity of contact. 

For elastic contacts, it has been shown that the real area increases proportionately with the normal load by a process involving contact of a larger number of asperities, in such a way that the mean area per contact is constant. The nominal pressure governs the penetration of surfaces and consequently the ratio of the real area to the nominal area of contact. As long as the normal load is kept constant, it follows that the real area is independent of the nominal area. A detailed analysis of the influence of the factors considered in this section upon the penetration of surfaces and the real area of contact is available in the aforementioned works. 

The real behavior of a gas essentially depends on how far away the actual pressure and temperature are from the thermodynamic critical point and not on the absolute values of pressure or temperature of the gas. The assumption that a gas behaves ideally (Z = 1) may lead to significant errors in the sizing of safety valves. Basically, the required cross-sectional area of the valve seat is rather underestimated if a too small real gas factor is assumed. 

Unlike the deformation models where the friction scales with the apparent contact area, the adhesion models assume that the friction is proportional to the real area of contact. The direct measurement of the real area of contact is generally impracticable and it is normal to resort to analytical models or computer simulations.Surfaces are invariably rough and the type and scale of the surface topography as well as the deformation characteristics of the solids control the real contact area. Some of the topographical factors were introduced in Section 23.3.1.2 for elastic bodies. At the simplest level the contact area for elastic contacts can be considered as arising from the contact of many spherical asperities of radius with a plane. For one asperity the contact area A is given by ... 

Eq. (2-6), but also adversely affects surface film formation. Figure 17-2 shows the relation between protection current density and steaming velocity. Factor Fj relates to undisturbed film formation. The influence of flow is not very great in this case. Factor F2 represents the real case where surface films are damaged by abrasion [15]. The protection current density can rise to about 0.4 A m at uncoated areas. 

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