Migration of Voids

The present analysis shows that the thermal deconsolidation of thermoplastic matrix composites is primarily attributable to two essential factors. One is the decompaction behavior of the fiber network, and the other is the elasticity of the matrix melt. The decompaction of fiber network produces the driving force for void growth, and the elasticity of the matrix melt enables the matrix melt to carry the traction. Other phenomena, such as migration of voids and reconsolidation may also appear in a thermal deconsolidation process. These issues will be discussed in a future work. 

It is shown in the present chapter that the apparent migration of voids during thermal deconsolidation is not really due to the movement of voids. Instead, it is actually a process of void formation and closure. Reconsolidation is another event associated with the migration of voids. In addition to the requirement that the temperature of the matrix must be sufficiently high so that the melt is in a fully liquid state, whether or not reconsolidation takes place also depends on the ratio of the external load to the compressibility of the fiber reinforcement in the second run of compression. An adequate external load is the sufficient condition for the suppression of deconsolidation and the realization of reconsolidation, but it may also result in a considerable squeezed flow of matrix, which should be carefully considered to keep a balance between the two events. 

From a molecular point of view inside a catalyst particle, diffusion may be considered to occur by three different modes molecular, Knudsen, and surface. Molecular diffusion is the result of molecular encounters (collisions) in the void space (pores) of the particle. Knudsen diffusion is the result of molecular collisions with the walls of the pores. Molecular diffusion tends to dominate in relatively large pores at high P, and Knudsen diffusion tends to dominate in small pores at low P. Surface diffusion results from the migration of adsorbed species along the surface of the pore because of a gradient in surface concentration. 

Readers will understand that we are loading our case in favor of a reticulated polyurethane as the material of choice. Figure 1.8 qualitatively speaks to a structure that is conducive to the migration of a developing hepatic colony. The void volume... 

The velocity factor, k e, as defined in Eq. (8), serves as a peak locator and can be used for the evaluation of various separation parameters such as selectivity and resolution [1,4], The velocity factor can either be positive or negative when the electrophoretic migration of the analyte is co- or counterdirectional to the EOF, respectively. For this reason, and since k e is void of thermodynamic or any other kind of fundamental significance, the velocity factor finds very limited applications. 

During the period of the current decay, there are two competitive processes, densification to form the barrier layer and dissolution of barrier layer to form the porous layer. Under the high electrical field strength (constant voltage mode), the densification of the aluminium oxide films is favoured for process durations shorter than 3700 s. When the constant voltage was kept for a long anodisation time (beyond 10900 s), the dissolution of the aluminium oxide film becomes more dominant. Thus, the film could be contaminated by inward migration of the electrolyte into the film or by formation of micro-voids. 

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