Particles of a solid
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Understanding the Behavior of Particles in Solids
Redistribution of Particles during Solidification
During the solidification process, particles such as inclusions and equiaxed grains are either pushed or engulfed by the advancing freezing front. The redistribution of these particles within the solid is influenced by the forces acting on them and the flow dynamics within the liquid melt. Key parameters that govern this redistribution include the velocity of the freezing front and the interaction forces between the particles and the solid-liquid interface 157.
Interaction Between Particles and Solid-Liquid Interfaces
The interaction between particles and a solid-liquid interface is critical in determining whether particles are rejected or trapped by the solid. Experimental and theoretical studies have shown that there is a "critical velocity" for each type of particle. Below this velocity, particles are rejected, while above it, they are trapped within the solid. This behavior is influenced by the interfacial free energies between the particle, liquid, and solid phases. If the particle-solid interfacial free energy is higher than the sum of the particle-liquid and liquid-solid interfacial free energies, a short-range repulsion occurs, pushing the particle ahead of the interface 57.
Modeling Particle Behavior in Solid Mechanics
The consistent particle method (CPM), originally developed for fluid dynamics, has been adapted to address solid mechanics problems. This method uses a Lagrangian approach to simulate the motion of particles governed by mass conservation and dynamic equations. The CPM can handle complex scenarios such as shock wave propagation and large deformations, making it a versatile tool for studying particle behavior in solids .
Segregation and Mixing of Particles in Solids
In solid mixing processes, avoiding segregation is crucial, especially for free-flowing bulk solids with weak interparticle adhesive forces. The addition of liquids can reduce segregation by forming pendular liquid bridge networks, although it may also change the segregation mechanism. For instance, selective accumulation of water in hydrophilic components can lead to heteroagglomerates, degrading product quality. The Discrete Element Method (DEM) has been used to model these processes, showing that partial particle wetting improves mixing efficiency and liquid distribution .
Particle Packing and Rheological Properties
The packing characteristics of solid particles significantly affect the rheo-physical properties of cementitious suspensions. Non-colloidal particles, such as aggregates, interact mechanically, while colloidal particles, such as cementitious materials, are influenced by surface forces. The relative solid packing fraction ((\phi/\phi_m)) and the critical transition volume fraction ((\phi_c)) are key parameters. Properly optimizing particle packing can enhance the stability and performance of concrete by improving the particle lattice effect .
Conclusion
The behavior of particles in solids is a complex interplay of forces, velocities, and interfacial energies. Understanding these interactions is crucial for optimizing processes such as solidification, mixing, and the design of cementitious materials. Advanced modeling techniques like CPM and DEM provide valuable insights into these phenomena, enabling better control and enhancement of material properties.
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