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In dense molecular clouds, interstellar grains are covered by mantles of icedmolecules. The formation of the grain mantles has two important consequences:it removes species from the gas phase and promotes the synthesis of newmolecules on the grain surfaces. The composition of the mantle is a strongfunction of the environment which the cloud belongs to. Therefore, clouds inhigh-zeta galaxies, where conditions -like temperature, metallicity and cosmicrays flux- are different from those in the Milky Way, will have different grainmantles. In the last years, several authors have suggested that silicate grainsmight grow by accretion of silicon bearing species on smaller seeds. This wouldoccur simultaneously to the formation of the iced mantles and be greatlyaffected by its composition as a function of time. In this work, we present anumerical study of the grain mantle formation in high-zeta galaxies and wequantitatively address the possibility of silicate growth. We find that themantle thickness decreases with increasing redshift, from about 120 to 20layers for z varying from 0 to 8. Furthermore, the mantle composition is also astrong function of the cloud redshift, with the relative importance of CO, CO2,ammonia, methane and methanol highly varying with z. Finally, being Si-bearingspecies always a very minor component of the mantle, the formation of silicatesin molecular clouds is practically impossible.

The evolution of grain mantles and silicate dust growth at high redshift