Sputtering of interstellar grains in shock processes

Using experimental results and an empirical formula describing the sputtering yield of low-energy light ions, the erosion rates of nonthermal sputtering induced by supernova shock waves eroding graphite or silicate grains are calculated. It is found that graphite and silicate grains are almost equally destroyed at shock velocities greater than about 70 km/sec. At lower velocities graphite is preferentially eroded. This finding seems to be inconsistent with the recent attempt by Seab and Shull (1983) to explain observations showing that some stars near three supernova remnants exhibit a strong 2200-A hump and normal or high far-ultraviolet extinction.