Void dissolution model

Although the void behavior is calculated through Stage 5, it is likely that the viscosity rises sufficiently high in Stage 4 so that the model assumptions are no longer valid. The void dissolution calculated in Stages 4 and 5 will therefore probably not occur in reality. 

The model framework for describing the void problem is schematically shown in Figure 6.3. It is, of course, a part of the complete description of the entire processing sequence and, as such, depends on the same material properties and process parameters. It is therefore intimately tied to both kinetics and viscosity models, of which there are many [3]. It is convenient to consider three phases of the void model void formation and stability at equilibrium, void growth or dissolution via diffusion, and void transport. 

For thick epoxy laminates processed in the autoclave, voids once formed and stabilized can only be removed by dissolution or by resin flow. Furthermore, resin gradients are deleterious to structural laminates. These two key phenomena make an understanding of resin transport vital to the development of any processing model. 

From such microbubble-dissolution measurements, Bemd (ref. 16,17) outlined a physical model to explain much of the dynamic behavior of film-stabilized microbubbles.- One problematic aspect of this dynamic behavior involved the question of how a gas nucleus can be surrounded by a relatively impermeable film and yet subsequently act to produce cavitation when a gas/water interface is needed to initiate cavitation. Bernd (ref. 16) explains that if the stabilized gas microbubble enters a low-pressure area, the gas within the microbubble will attempt to expand. The surfactant film may also elastically attempt to expand. The surfactant film will then be expanded until essentially the surface tension of the water alone acts to contract the microbubble, since the protective shell no longer acts. The film has either been ruptured upon expansion, or it has expanded until it is ineffectual. Thus the microbubble (i.e., gas nucleus) should be capable of expanding to form a cavitation void or acquire additional gas in the form of water vapor or from surrounding dissolved gas. In addition, Bernd points out that it is reasonable to expect a gas microbubble to acquire such an effective... 

In this paper we consider a pore scale model for crystal dissolution and precipitation processes. We follow the ideas in [3], where the corresponding macroscopic model was introduced. Let Q C (d > 1) denote the void region. This region is occupied by a fluid in which cations (Mi) and anions (M2) are dissolved. The boundary of Q has an internal part (IV ), which is the surface between the fluid and the porous matrix (grains), and an external part, which is the outer boundary of the domain. In a precipitation reaction,... 

This model assumes the transport of both anions (oxygen ions) and cations (metal) ions or then-respective vacancies. The anions diffuse to the metal surface with a resultant thickening of the film. Cation diffusion cause film dissolution and metal vacancies are created at the metal/film interface. When the rate of production of metal vacancies in the metal exceeds their rate of migration, the vacancies pile up at the metal/film interface and result in void craters. This is the process of pit incubation. At a certain critical size, the passive film suffers local collapse and the incubation period ends. The collapsed site dissolves much faster than at any other place and leads to pit growth. 

The absorber rod model will be completed by introducing the voiding of molten columns above the break elevation of the guide tube, and the dissolution of Zr by the Ag-In-Cd absorber material. 

Physical solubility appears to arise from the concept that a molten salt structure contains voids or so-called holes. Reiss et applying concepts from fluid mechanics, calculated an expression for the work necessary to create a spherical cavity in a real fluid. This work was then taken to represent the energy for the dissolution of a gas molecule in a liquid. Solubilities of noble gases, such as helium in benzene, appeared to satisfy the predictions from the model. 

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