Surfaces and Surface Roughness

From the materials point of view the surface of a solid can in a simple way be defined as a discontinuity in a lattice pattern. More precisely, a discontinuity in a lattice pattern is an interface. For example, the surface of a metal in a vacuum should be called the solid/ vacuum interface. The inner surface of a glass fish bowl filled with water should be called the glass/water interface. When we designate the interface simply as the surface of the solid we usually presume that what exists on the other side of the interfacial boundary has no effect on the solid at the interface. Sometimes this assumption is valid insofar as can be detected at other times the environment does affect the properties of the solid side of the interface. 

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Clearly geometrical factors relative to coke collection on metal surfaces have an important effect on coke formation. There is obviously a need to obtain more information relative to the flow patterns at or near the surface and surface roughness (and composition). Indirectly these factors would certainly affect the wettability of the surface with coke or coke precursors. 

Figure 8. AFM image of HTOZ and TZP surfaces and surface roughness derived from AFM observation.

The application of fundamentally new ECT (Russia patent Jf 2063025) has made it possible to provide high-efficiency defect control accompanied by detecting both small surface defects and more rough under-surface defects under non-magnetic metal layer of 7 mm thick, or surface defects under protection coatings, dye, corrosion, hermetic and other type of layer of 10 mm thick. 

For defect sizing by TOED, use of L waves involves a penalty in resolution of almost a factor of two at a given frequency because of difference in velocity as compared to shear waves and use of SV waves runs into difficulties because of the mode conversion problems. Further, problems due to couplant thickness variations, surface roughness affects, beam skewing and distortion problems in anisotropic welds can also be expected. On the contrary, SH waves are not affected... 

A number of refinements and applications are in the literature. Corrections may be made for discreteness of charge [36] or the excluded volume of the hydrated ions [19, 37]. The effects of surface roughness on the electrical double layer have been treated by several groups [38-41] by means of perturbative expansions and numerical analysis. Several geometries have been treated, including two eccentric spheres such as found in encapsulated proteins or drugs [42], and biconcave disks with elastic membranes to model red blood cells [43]. The double-layer repulsion between two spheres has been a topic of much attention due to its importance in colloidal stability. A new numeri-... 

In the context of the structural perturbations at fluid-solid interfaces, it is interesting to investigate the viscosity of thin liquid films. Eaily work on thin-film viscosity by Deijaguin and co-workers used a blow off technique to cause a liquid film to thin. This work showed elevated viscosities for some materials [98] and thin film viscosities lower than the bulk for others [99, 100]. Some controversial issues were raised particularly regarding surface roughness and contact angles in the experiments [101-103]. Entirely different types of data on clays caused Low [104] to conclude that the viscosity of interlayer water in clays is greater than that of bulk water. 

In the case of powders formed by grinding and particles formed by aggregation, surface roughness can be so extreme that, curiously, it can be treated by mathematical geometry (see Mandelbrot, Ref. 102 also Ref. 103). We can... 

The effect of surface roughness on contact angle was modeled by several authors about 50 years ago (42, 45, 63, 64]. The basic idea was to account for roughness through r, the ratio of the actual to projected area. Thus = rA. lj apparent and similarly for such that the Young equation (Eq.-X-18) becomes... 

Lin et al. [70, 71] have modeled the effect of surface roughness on the dependence of contact angles on drop size. Using two geometric models, concentric rings of cones and concentric conical crevices, they find that the effects of roughness may obscure the influence of line tension on the drop size variation of contact angle. Conversely, the presence of line tension may account for some of the drop size dependence of measured hysteresis. 

P. Meakin, Multiple Scattering of Waves in Random Media and Random Rough Surfaces, The Pennsylvania State University Press, State College, PA, 1985. 

Strongin D R, Carrazza J, Bare S R and Somoqai G A 1987 The importance of Cj sites and surface roughness in the ammonia synthesis reaction over iron J. Catal. 103 213... 

Guenther K FI, Wierer P G and Bennett J M 1984 Surface roughness measurements of low-scatter mirrors and roughness standards Appl. Opt. 23 3820... 

For primary insulation or cable jackets, high production rates are achieved by extmding a tube of resin with a larger internal diameter than the base wke and a thicker wall than the final insulation. The tube is then drawn down to the desked size. An operating temperature of 315—400°C is preferred, depending on holdup time. The surface roughness caused by melt fracture determines the upper limit of production rates under specific extmsion conditions (76). Corrosion-resistant metals should be used for all parts of the extmsion equipment that come in contact with the molten polymer (77). 

Convection Heat Transfer. Convective heat transfer occurs when heat is transferred from a soHd surface to a moving fluid owing to the temperature difference between the soHd and fluid. Convective heat transfer depends on several factors, such as temperature difference between soHd and fluid, fluid velocity, fluid thermal conductivity, turbulence level of the moving fluid, surface roughness of the soHd surface, etc. Owing to the complex nature of convective heat transfer, experimental tests are often needed to determine the convective heat-transfer performance of a given system. Such experimental data are often presented in the form of dimensionless correlations. 

Surface Finish. As well as influencing the rate of metal removal, electrolytes also affect the quality of surface finish obtained in ECM. Depending on the metal being machined, some electrolytes leave an etched finish. This finish results from the nonspecular reflection of light from crystal faces electrochemicaHy dissolved at different rates. Sodium chloride electrolyte tends to produce a kind of etched, matte finish when used for steels and nickel aHoys. A typical surface roughness average, Ra is about 1 ]lni. 

Particle Velocity on a. Surfa.ce. Smaller particles, those that are more irregular in shape and/or those that have a higher surface roughness, typically have a higher frictional drag on a hopper or chute surface. 

Years of development have led to a standardized system for objective evaluation of fabric hand (129). This, the Kawabata evaluation system (KES), consists of four basic testing machines a tensile and shear tester, a bending tester, a compression tester, and a surface tester for measuring friction and surface roughness. To complete the evaluation, fabric weight and thickness are determined. The measurements result in 16 different hand parameters or characteristic values, which have been correlated to appraisals of fabric hand by panels of experts (121). Translation formulas have also been developed based on required levels of each hand property for specific end uses (129). The properties include stiffness, smoothness, and fullness levels as well as the total hand value. In more recent years, abundant research has been documented concerning hand assessment (130—133). 

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