Oblique particle impact

Belloy et al. [36,38] investigated the oblique powder blasting, in which the jet of abrasive particles is directed to the masked workpiece at an angle different from normal incidence, which opens the way to new underetching effects and perspectives in the 3D microfabrication. A symmetrical shape is created if the abrasive particles impact the surface at normal incidence. An oblique particle impact, however, i.e. at an angle away from 90°, leads to the formation of an asymmetrical erosion profile. More material is removed in the... 

To give the particles the required momentum, they should be densely packed and rigid and have a well-defined narrow particle size distribution. Friable and oblique particles are not desirable because the penetration depth will increase if the particle characteristic is more variable (Hickey 2001). Studies have been performed with particles ranging from 20 to 40 J,m in size and 1.1 to 7.9 g/cm3 in density impacting human cadaver skin (Kendall et al. 2000). Velocities of up to 260 m/s were applied to particles of this size range. For many applications, smaller particles of about 1 to 4 j,m diameter may be required for an optimized delivery. To deliver particles of this size into the skin, higher densities and impact velocities are required. For this reason, gold particles are used as a carrier material for the delivery of plasmid DNA vaccines (Kendall et al. 2001). 

Fig. 5.8. Schematic illustration of (a) a profile of an oblique powder-blasted structure in glass using an eroding beam with an incidence angle different from 90° compared to normal impact, (b) The shape of the feature created dependent on directions of particle impact...

FIGURE 7.8 Comparison of the linear-spring, Mindlin s no-slip, and Mrndlin and Deresiewicz s models with the experimental data for oblique impact of a particle at different impact angles. (Reprinted from Chem. Eng. Sci., 59, Di Renzo, A. and Di Maio, RR, Comparison of contact-force models for the simulation of collisions in DEM-based granular flow codes, 525-541, Copyright 2004, with permission from Elsevier.)... 

Di Renzo and Di Maio [20] simulated oblique impact of a particle to a flat wall at different impact angles using the linear-spring, Mindlin s no-slip, and Mindlin and Deresiewicz s models. The comparison of the results to the experimental findings of Kharaz et al. [21] is shown in Figure 7.8. 

The deposition and adhesion of dust particles on cylindrical and spherical surfaces take place in a nonuniform manner. The number and diameter of deposited loess dust particles [291] are presented as functions of the angle of incidence on a cylindrical surface for various flow velocities in Fig. VI.20. The number and maximum size of the deposited particles fall as the angle rises from 0 to 90°. For a

flow velocity is minimal, so that the detachment of particles as a result of aerodynamic forces will be negligible. For close to 90°, the number of adhering particles falls sharply, since the oblique impact communicates a rotatory motion to the particles. 

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