  We have applied the SRIM computer code to study the sputtering of some likely
astrophysical grain materials, and we have shown that selective embedding of
metallic projectiles offers a partial explanation of gas-phase depletions. We
show that supernova shockwaves sweep a significantly larger mass of
interstellar gas per unit time than the shockwaves generated by outflows in
star-forming regions. We apply our sputtering model to the bombardment levels
expected in a supernova shock, and show that net embedding may dominate over
net sputtering, leading to grain growth under some circumstances, particularly
when the bombarding gas is enriched with metals from the supernova progenitor
star. A combination of short cooling times and net embedding mean that it is
possible for a type II supernova to generate more dust that it destroys, and we
conclude that, in general, the sputtering process often leads to a
compositional change in the grain material rather than simply to grain erosion.
