Evaporation of Fe and FeS dust in the active stage of the primordial solar nebula, and Fe/S fractionation

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The evaporation kinetics of troilite and metallic iron was applied to evaporation of dust particles moving toward the protosun in the turbulent solar nebula. In the calculations, it was assumed that dust particles do not grow by collision, evaporated gas and residual dust are not separated, and dust particles move only radially along the midplane or the surface of the nebula. It was found that evaporation of metallic iron would occur almost in equilibrium both along the midplane and the surface. Troilite could survive to higher temperature than the equilibrium evaporation temperature due to its evaporation kinetics. However, the kinetic effects are not so large, and the incongruent evaporation of troilite is also regarded to occur roughly in equilibrium. The timescales for evaporation of metallic iron and troilite were compared with the timescales for drifts along r-and z-directions and that for coagulation to understand general aspects of the effect of evaporation kinetics. Since the temperature of the surface is lower than that of the midplane, dust particle at the surface can get closer to the sun than those at the midplane. This can cause Fe/S fractionation in a wide range of the nebula if effective solid-gas separation occurred.
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