Collision breeding

Several theories have been proposed to explain secondary nucieation. These theories fall into two categories—one traces the origin of the secondary nuclei to the parent crystal—that include (1) initial or dust breeding (2) needle breeding and (3) collision breeding. Secondary nuclei can also originate from the solute in the liquid phase and the theories that take this into account include (1) impurity concentration gradient nucieation and (2) nucieation due to fluid shear. 

Garabedian, H. and Strickland-Constable, R.F. (1972) Collision breeding of crystal nuclei sodium chlorate. Journal of Crystal Growth, 13/14, 506-509. 

Two types of secondary nudeation are exemplified collision breeding and surface breeding. 

In order to achieve breakdown, electrons (either from the air or from the body) must be accelerated to a sufficient velocity to ionize the air and breed more electrons by any one of several processes. In an actual gas, however, some of the kinetic energy of the electrons is lost in collisions with air molecules without resulting in ionization. This combined effect has been expressed in terms of the Townsend ionization coefficient. As a body becomes smaller, its curvature increases and the electric field intensity drops off more rapidly with distance from the surface consequently, to accelerate electrons a given amount, the body surface field intensity must be higher than for a flat surface. Actually, because of increased attenuation resulting from the increased distance that an electron must travel through air to achieve a given acceleration, the required surface intensity must increase even faster. 

Macroabrasion, usually called collision or attrition breeding, causes rounding of edges and corners. It can be an industrial problem, but it has a clear mechanism, and can often be controlled with suitable choices of mixing impellers and other parameters. 

So far, we have discussed the extension of classical perturbation theory to the collision probability model and the generalization of perturbation theory to arbitrary characteristics in steady-state but subcritical systems having a source. Even this is not the most general characterization we might require of a reactor. We are, in addition, concerned to compute arbitrary ratios in a critical system. These might (typically) be the breeding ratio, although several others are of interest. 

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