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Slowness surface

Various plastics and other nonmetallics also provide excellent compatibiHty, low friction, low wear, and good scoring resistance. Their appHcation is usually limited to slow surface speeds, however, where their low thermal conductivity does not lead to overheating. [Pg.1]

Great care must, therefore, be exercised in attaching theoretical significance to experimentally determined values of A and E. The identification of an activation energy with a particular slow surface reaction requires perhaps greater knowledge of the specialized conditions prevailing at the interface than is often available or assumptions that cannot be demonstrated. [Pg.97]

Cu9ln4 and Cu2Se. They performed electrodeposition potentiostatically at room temperature on Ti or Ni rotating disk electrodes from acidic, citrate-buffered solutions. It was shown that the formation of crystalline definite compounds is correlated with a slow surface process, which induced a plateau on the polarization curves. The use of citrate ions was found to shift the copper deposition potential in the negative direction, lower the plateau current, and slow down the interfacial reactions. [Pg.117]

Phase densities differ by a Phase densities differ by only about 10%. factor of 100-10,000 1. Viscosity in both phases is Liquid phase viscosity moderate, solid low. phase rigid. Phase separation is rapid Phase separation is slow surface-tension and complete. effects prevent completion. Countercurrent contacting is Countercurrent contacting is slow and quick and efficient. imperfect. ... [Pg.3]

The reaction may be characterized by slow surface kinetics, leading to shortening of the plateau. Compare, for example, ferricyanide reduction and copper deposition at a rotating disk (shown in Fig. 3a and b). [Pg.252]

The AC data of Hillman and co-workers (Li et al., 1992) showed a marked dependence on both geometry and convection effects. By using a thin ring electrode of thickness 0,025 cm and diameter 0,8 cm, results showing both simple Warburg behaviour and, in rotation, the underlying slow surface kinetics can be obtained. [Pg.169]

EELS has been used to study the kinetics of relatively slow surface reactions, such as the hydrogen-deuterium exchange in benzene adsorbed on platinum [54], In... [Pg.240]

The standard calorimetric reaction of tris(hydroxymethyl) aminomethane (THAM) neutralization with HC1 was used in several initial experiments to determine both precision and accuracy for the data acquisition and reduction process. Three to five minutes were allowed between acid additions, since this same time frame was used for all later suspension titrations in order to minimize the effects of slow surface reactions which occur during a titration (9,29,30). The amount of acid added in each experiment was varied to generate heat changes of 40-400 mj (typical heat changes observed in our adsorption studies with goethite suspensions). [Pg.145]

In the absence of sensitizer, neither graft nor homopolymerization was induced by irradiation at 366nm. However, irradiation by a low pressure mercury lamp through a quartz plate(the glass plate(c) in Figure 1 was replaced by a quartz plate.) induces slow surface grafting sensitized by acetone. [Pg.228]

The cell potential is simply the work that can be accomplished by the electrons produced in the SOFC, and this potential decreases from the equilibrium value due to losses in the electrodes and the electrolyte. For YSZ electrolytes, the losses are purely ohmic and are equal to the product of the current and the electrolyte resistance. Within the electrodes, the losses are more complex. While there can be an ohmic component, most of the losses are associated with diffusion (both of gas-phase molecules to the TPB and of ions within the electrode) and slow surface kinetics. For example, concentration gradients for either O2 (in the cathode) or H2 (in the anode) can change the concentrations at the electrolyte interface,which in turn establish the cell potential. Similarly, slow surface kinetics could result in the surface at the electrolyte interface not being in equilibrium with the gas phase. [Pg.610]

In the simplest version of a surface reaction, the rate of termination of the chain reaction by reaction of R on a surface should be proportional to D, the square of the vessel diameter We will also leave this calculation for a homework problem, but the imphcations are profound for a chain reaction. When the vessel size increases, the rate of a chain reaction can increase drastically, from a slow surface-quenched process in small vessels to very fast process whose only quenching steps are homogeneous reactions. [Pg.407]

In principle, silica growth kinetics may be controlled by (1) slow release of monomer via alkoxide hydrolysis in the particle-free reverse micelles, (2) slow surface reaction of monomer addition to the growing particle, and (3) slow transport processes as determined by the dynamics of intermicellar mass transfer. There is strong experimental evidence to support the view that the rate of silica growth in the microemulsion environment is controlled by the rate of hydrolysis of TEOS (23,24,29). Silica growth kinetics can be analyzed in terms of the overall hydrolysis and condensation reactions ... [Pg.180]

Fig. 11.1. Slowness surfaces, k/w, for nickel. The representation is in k-space, and only the outermost slowness surface in any direction is displayed (courtesy of... Fig. 11.1. Slowness surfaces, k/w, for nickel. The representation is in k-space, and only the outermost slowness surface in any direction is displayed (courtesy of...
The solution to the Christoffel equation for a given material can be plotted in k-space as surfaces of k/w. These are known as slowness surfaces, because they represent the reciprocal of phase velocity. Figure 11.1 is a representation of slowness surfaces of nickel in three-dimensional k-space. Because longitudinal waves have the greatest velocity and therefore... [Pg.229]

Fig. 11.2. Section through the nickel slowness surfaces of Fig. 11.1 in an 001 plane. Fig. 11.2. Section through the nickel slowness surfaces of Fig. 11.1 in an 001 plane.
Snell s law of refraction may be solved graphically using slowness surfaces. It may be expressed as the requirement that the tangential component of the k-vector be conserved across a refracting interface. This is illustrated for waves in water incident on an (001) GaAs surface in Fig. 11.3. The slowness surfaces... [Pg.233]

Let us consider in more detail, using the above concepts, how a photocorrosion process occurs under the illumination of a semiconductor. Suppose that electron transitions at the interface between the semiconductor and solution do not take place in darkness in a certain potential range (the semiconductor behaves like an ideally polarizable electrode). This range is confined to the potentials of decomposition of the semiconductor and/or solution. The steady state potential of a semiconductor is usually determined in this case by chemisorption processes (e.g., of oxygen) or, which is the same in the language of the physics of semiconductor surface, by charging of slow surface states. It is these processes that determine the steady state band bending. [Pg.288]

The expected greater size of protein-polysaccharide complexes can reduce the diffusion rate of the adsorbing species towards the interface. This effect is especially important for small monomeric proteins. In addition, Ganzevles and co-workers (2006) have suggested that the diffusion of protein in the complexes may not solely be responsible for the slow surface tension decay. Rather, the gradual dissociation (and subsequent adsorption) of protein from complexes, when they are in close proximity to the interface, could also contribute to the behaviour. [Pg.268]

The rates of uptake of molybdenum, tellurium, and rubidium oxide vapors by substrates of calcium ferrite and a clay loam have been measured in air over a temperature range of 900° to 1500°C. and a partial pressure range of about 10r7 to 10 atm. The measured rates of uptake of molybdenum and tellurium oxide vapors by molten calcium ferrite and of rubidium oxide vapor by both molten clay loam and calcium ferrite were controlled by the rates of diffusion of the oxide vapors through the air. The measured rates of uptake of molybdenum and tellurium oxide vapors by molten clay loam were controlled by a combination of a slow surface reaction and slow diffusion of the condensate into the substrate. [Pg.43]

T = 1400° C.9 MoOs vapor concentration = 22.4 figrams/liter (total MoOs partial pressure = 1.3 X 10 l atm.). The large dashed line indicates the uptake of MoOs as calculated by use of the simple diffusion model (D = 9.25 X 10 cm.91 sec.). Small dashed line indicates the uptake of MoOs as calculated by the complex model combining a slow surface reaction with diffusion within the particle (a = 4 X 10 5, D =... [Pg.66]

Test of Uptake Model Based on a Slow Surface Reaction Combined with Diffusion within the Particle. Since the simple diffusion model is inadequate to describe the uptake behavior of the molybdenum and tellurium oxide vapors by the clay loam particles, a more complex model is required, in which the effects of a slow surface reaction and of diffusion of the condensed vapor into the particle are combined. Consider the condensation of a vapor at the surface of a substrate (of any geometry) and the passage by diffusion of the condensed vapor through a thin surface layer into the body of the substrate. The change in concentration of solute per unit volume in the surface layer caused by vapor condensa-... [Pg.67]

The rate determining step need not always be, as in this case, one of the reduction steps. Thus at low overpotential, slow surface diffusion was rate determining for the deposition of copper.7... [Pg.5]

To compose equations for adsorption of the 02 molecules with an allowance for the slow surface mobility of adsorbed particles along a surface. Compose the similar equations for adsorption of the CO molecules at low temperatures, when the surface mobility of adsorbed molecules needed be taken into account. [Pg.452]


See other pages where Slowness surface is mentioned: [Pg.662]    [Pg.1989]    [Pg.106]    [Pg.78]    [Pg.745]    [Pg.230]    [Pg.137]    [Pg.217]    [Pg.98]    [Pg.230]    [Pg.231]    [Pg.233]    [Pg.234]    [Pg.235]    [Pg.241]    [Pg.254]    [Pg.76]    [Pg.18]    [Pg.116]    [Pg.206]    [Pg.212]    [Pg.396]   
See also in sourсe #XX -- [ Pg.229 ]




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