Shocks in dense clouds III. Dust processing and feedback effects in C-type shocks

Aims. We study the impact of grain-grain collisions in C-type shocks propagating in dense clouds (n(H) >= 10(4) cm(-3)) on the evolution of the dust size distribution, the shock dynamics and the release of chemical species into the gas phase such as SiO. Methods. Our shock code for transverse C-type shocks is extended to self-consistently couple the charge, dynamics and evolution of the size distributions of silicate and carbon grains with the shock dynamics. Dust processes included are sputtering in gas-grain collisions, vaporisation and shattering in grain-grain collisions. Results. Grain shattering and its feedback onto the dynamics of C-type shocks is found to be only significant at densities higher than similar to 10(5) cm(-3). Numerous small grains are produced in the shock through the fragmentation of large grains. C shocks are therefore shorter and warmer when shattering is included. Vaporisation is more efficient than sputtering at destroying grain cores. In particular, vaporisation destroys dust at low shock velocities where sputtering is inefficient (20-25 km s(-1)). Unlike sputtering, vaporisation produces SiO early in the shock, which may affect the SiO emission line profiles. All these effects are found to be negligible below a density of similar to 104 cm(-3).