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Interstellar grains are swept up, and betatron accelerated, by supernova-generated shock waves in the interstellar medium and are subject to destructive processing. The degree of destruction is determined by the relative gas-grain and grain-grain velocities, which lead to sputtering of the grain surface and grain disruption (deformation, vaporization and shattering). The threshold pressure for grain shattering in grain-grain collisions is of order 100 kbar, considerably lower than that for vaporization which is of order 5 Mbar. Therefore, collisions between grains will readily shatter large grains into smaller fragments with sizes ranging down to molecules. We have used new algorithms for the destructive processes (Tielens et al. \,1994, Ap.J.,431 ,321; Jones et al. \,1994, Ap.J.,433 ,797) and have modeled the shattering that occurs in grain-grain collisions (Jones and Tielens 1994, in The Cold Universe, p35). We present new data for the shattering of grains in interstellar shocks and discuss the importance of this process for the dust size distribution and the evolution of dust in the interstellar medium.
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