Physical chemistry of protoplanetary discs

This thesis presents a new assessment of the physical and chemical properties of crystalline grains widely observed in protoplanetary discs and in chondrite meteorites. We present new insights on the possible mechanisms that produced the observed crystalline grain distribution in protoplanetary discs and the bulk material which likely formed chondrites and the planets in our Solar System. We begin by presenting a comprehensive investigation of the thermodynamic behaviour of several astrophysically interesting crystalline phases, such as olivine and pyroxenes, as well as high refractory compounds and sulfides. Laboratory experiments show that the behaviour of most of these species deviate from the ideal with decreasing the temperature. Thus we introduce the regular solution model which we find to be a better approximation of the phases' behaviour especially outside the high temperature region, compared with the ideal solution model, which is widely used in astrophysics. An interesting new result is in the derived sequence of forsterite-enstatite-forsterite with lowering temperature, which differs from previous thermodynamic equilibrium calculations that show a sequence of forsterite-enstatite. Our 1D condensation sequence matches infrared observations of protoplanetary disc surfaces with increasing distance from the central star.