Plastic deformation of particles

At the second and third stages, the processes involving plastic deformation of particles are developed. The smaller is particle size, the more efficient are these processes. Dispersion process is overlapped by the formation of secondary particles, while the rate of the latter process is comparable with dispersing rate thus, the surface area remains constant. Chemical reactions take place inside secondary aggregates at the contacts between particles. At the third stage, the crystallization of the products from the solid phase may occur, as well as its repeated amorphization, till some stationary state between these two is achieved. 

Fig. 13 Scheme of the proposed application of polyelectrolyte multilayer as removable templates. First wrinkles are formed by plastic deformation of the multilayer. The particles are deposited while the multilayer is in a glassy state and subsequently the multilayer is annealed... 

These differences were correlated with the size of the rubber particles in the systems the smaller the diameter of the dispersed phase (e.g. the lower the interparticular distance), the higher the benefits of a /3-nucleation (Fig. 25b). For the grades with the smallest particle sizes, it might be attributed to an easier plastic deformation of the matrix once the damage mechanisms initiated (by particle cavitation) as a result of the smaller matrix ligaments between the rubber phase. 

Considering a mass of ceramic powder about to be molded or pressed into shape, the forces necessary and the speeds possible are determined by mechanical properties of the diy powder, paste, or suspension. For any material, the elastic moduli for tension (Young s modulus), shear, and bulk compression are the mechanical properties of interest. These mechanical properties are schematically shown in Figure 12.1 with their defining equations. These moduli are mechanical characteristics of elastic materials in general and are applicable at relatively low applied forces for ceramic powders. At higher applied forces, nonlinear behavior results, comprising the flow of the ceramic powder particles over one another, plastic deformation of the particles, and rupture of... 

Errors are a result of the elastic and plastic nature of the ceramic particles themselves. Several other authors [81,82] have calculated the pressure distribution in cylindrical dies and other forms using finite element numerical methods. Bortzmeyer [81] has incorporated cohesion, elastic, and plastic deformation of the particles into finite element calculations for more complicated geometries, as shown in... 

In ABS, where particle size is much smaller than in HIPS, the particles are less effective as craze initiators and the fatigue fracture surface shows evidence of considerable localized plastic deformation of the matrix polymer as well as of cavitation and/or loss of adhesion of the rubber particles. 

Pressure sintering. Whereas solid-state sintering under normal conditions, dealt with so far, is based on the diffusion mechanism, during pressure sintering (hot pressing) the yield stress may be exceeded as a result of external pressure which results in plastic deformation of the particles. 

To achieve the goals of dry granulation as discussed above, it is necessary to induce plastic deformation of the powders of interest to facilitate bonding into a compact for subsequent milling into granules. While the theory of deformation is well understood for many materials (1), it is less well described for powders and even less for powders of molecular organic particles. 

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