Abstract. This work investigates the annealing of silicate dust, the combustion of carbon dust and radial mixing of both dust species within protoplanetary disks. For this purpose the diffusion-transport-reaction equations of both dust species (including annealing of silicate and carbon combustion) are simultaneously solved with the equations for the global evolution of an α-disk within an one-zone, time-dependent numerical model. The protostar-disk system is assumed to be in a quiescent stage which corresponds with the class II phase of evolution of stardisk systems. The results suggest that the diffusive transport spreads the dust globally throughout the disk, and therefore provides an explanation for the existence of crystalline silicate and methane within the primordial bodies of the solar system.

Abstract. Protoplanetary disks as birth places of planets as well as of their host stars bear different element mixtures owing to the different chemical compositions of the environments where they are born. The chemical composition affects the structure and evolution of the disks, particularly the composition and abundance of the dust. In this work we perform one-zone model calculations of vertically selfgravitating protoplanetary accretion disks with the β-prescription for the viscosity with different element mixtures. The models consider the chemical equilibrium condensation of the most important dust species in the disk as well as annealing of interstellar silicate dust and combustion of carbon dust. Also a new inner boundary condition is introduced which avoids the unphysical decline of the surface density Σ of the frequently adopted no-torque (Σ = 0) condition. The main result of the model calculations is that with decreasing metallicity the disks become less opaque and hence colder as a consequence of the reduced dust-to-gas ratio. Further we give a rough estimate for the critical value of the metallicity below which the formation of terrestrial planets is inhibited.