Phase high-stress

If there is particle—particle interaction, as is the case for flocculated systems, the viscosity is higher than in the absence of flocculation. Furthermore, a flocculated dispersion is shear thinning and possibly thixotropic because the floccules break down to the individual particles when shear stress is appHed. Considered in terms of the Mooney equation, at low shear rates in a flocculated system some continuous phase is trapped between the particles in the floccules. This effectively increases the internal phase volume and hence the viscosity of the system. Under sufficiently high stress, the floccules break up, reducing the effective internal phase volume and the viscosity. If, as is commonly the case, the extent of floccule separation increases with shearing time, the system is thixotropic as well as shear thinning. 

Crazing. This develops in such amorphous plastics as acrylics, PVCs, PS, and PCs as creep deformation enters the rupture phase. Crazes start sooner under high stress levels. Crazing occurs in crystalline plastics, but in those its onset is not readily visible. It also occurs in most fiber-reinforced plastics, at the time-dependent knee in the stress-strain curve. 

Pneumatic conveying systems and in particular dilute phase conveying systems are known to create a high stress on particulate solids leading to significant attrition. In contrast to fluidized beds, it is not the material loss which is the main problem. Depending on the application, problems may rather occur in a number of different areas. Attrition may, for example,... 

H-H interaction due to the lattice expansion becomes important and the hydride phase (P phase) nucleates and grows. The hydrogen concentration in the hydride phase is often found to be H M = 1. The volume expansion between the coexisting a- and P-phases corresponds in many cases to 10-20% ofthe metal lattice. Therefore, at the phase boundary high stress is built up and often leads to decrepitation of brittle host metals such as intermetaiiic compounds. The final hydride is a powder with a typical particle size of 10-100 pm (Figure 5.24). 

When production of submicrometer droplet size is aimed at, the continuous-phase shear stress and disperse-phase flux have to match the need for small droplet (i.e., high shear stress and low disperse-phase flux) with the need for a reliable system productivity (i.e., high disperse-phase flux). 

High stresses Established cracks Propagation phase Time/temp. dependence due to dieological properties... 

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