Displacement of interface

The basic thesis of this paper, the displacement of interface states by strongly chemisorbed species, is also applicable to grain boundaries. 

Obviously, in an initial period of interaction of substances A and B when the ApBq layer is very thin, the number of the B atoms which could have diffused to interface 1 per unit time is considerably greater than the number of those atoms which could be combined in the ApBq compound by the surface A atoms. It should be noted that, in spite of the displacement of interface 1 in the course of reaction (1.1), the number of the A atoms per unit area of the surface of substance A bordering with the ApBq layer remains constant. As seen in Fig. 1.4, the number of the A atoms is the same in all sections of phase A by the vertical plane passing through the atomic sites. 

Fig. 2.4. Schematic diagram to explain one of the methods of determining the values of the chemical constants kQ in the reaction system A-ApBq-ArBs B. Axm = d] -d[, AyA3 = <2, -d. To simplify the figure, the displacement of interface 2 during layer formation is not shown.

FIG. 7 Log-log plots of the interface width (w ) versus the Monte Carlo time t, measured at different adsorption probabihties using channels of width L = 30. Data were obtained during the displacement of an A-poisoned phase by the reactive regime. From top to bottom the probabihties are 0.5192, 0.5202, 0.5211, 0.5215, and 0.5238. 

Similarly, in studies of lamellar interfaces the calculations using the central-force potentials predict correctly the order of energies for different interfaces but their ratios cannot be determined since the energy of the ordered twin is unphysically low, similarly as that of the SISF. Notwithstcinding, the situation is more complex in the case of interfaces. It has been demonstrated that the atomic structure of an ordered twin with APB type displacement is not predicted correctly in the framework of central-forces and that it is the formation of strong Ti-Ti covalent bonds across the interface which dominates the structure. This character of bonding in TiAl is likely to be even more important in more complex interfaces and it cannot be excluded that it affects directly dislocation cores. 

As indicated earlier, protective oxide scales typically have a PBR greater than unity and are, therefore, less dense than the metal from which they have formed. As a result, the formation of protective oxides invariably results in a local volume increase, or a stress-free oxidation strain" . If lateral growth occurs, then compressive stresses can build up, and these are intensified at convex and reduced at concave interfaces by the radial displacement of the scale due to outward cation diffusion (Fig. 7.7) . 

Marchello and Toor (M2) proposed a mixing model for transfer near a boundary which assumes that localized mixing occurs rather than gross displacement of the fluid elements. This model can be said to be a modified penetration-type model. Kishinevsky (K6-K8) assumed a surface-renewal mechanism with eddy diffusion rather than molecular diffusion controlling the transfer at the interface. 

A decisive factor for the physical behaviour of a composite is the adhesion efficiency at the boundaries between phases. In all theoretical models this adhesion is considered as perfect, assuming that the interfaces ensure continuity of stresses and displacements between phases, which should be different because of the proper nature of the constituents of composites. However, such conditions are hardly fulfilled in reality, leading to imperfect bonding between phases and variable adhesion between them. The introduction of the mesophase layer has as function to reconcile in a smooth way the differences on both sides of interfaces. 

A capillary system is said to be in a steady-state equilibrium position when the capillary forces are equal to the hydrostatic pressure force (Levich 1962). The heating of the capillary walls leads to a disturbance of the equilibrium and to a displacement of the meniscus, causing the liquid-vapor interface location to change as compared to an unheated wall. This process causes pressure differences due to capillarity and the hydrostatic pressures exiting the flow, which in turn causes the meniscus to return to the initial position. In order to realize the above-mentioned process in a continuous manner it is necessary to carry out continual heat transfer from the capillary walls to the liquid. In this case the position of the interface surface is invariable and the fluid flow is stationary. From the thermodynamical point of view the process in a heated capillary is similar to a process in a heat engine, which transforms heat into mechanical energy. 

The solution of Eqs. (11.15-11.17), subject to the conditions (11.24-11.26), determines the displacement of the interface in time, as well as the evolution of the velocity, pressure and temperature oscillations. 

Assuming that the temperature oscillations that are due to the displacement of the interface decrease far from Xf, the sign in front of Eq. (11.53) is positive for phase L and negative for phase G. 

By introducing surfactants, which lower the interfacial tension, it is possible to reduce the work necessary to deflocculate agglomerates. In liquid suspensions the introduction of an interfacial tension depressant facilitates wetting of the solid by the liquid and the displacement of adsorbed gases from the solid surface. Certain solids have adsorbed films whose adhesional forces are so great that they resist all mechanical efforts to displace them. Upon the addition of a surfactant, the Aims are displaced and a solid-liquid interface is achieved (1). 

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