Low-Temperature Crystallization of Amorphous Silicate in Astrophysical Environments - Astrophysics > Earth and Planetary AstrophysicsReportar como inadecuado




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Abstract: We construct a theoretical model for low-temperature crystallization ofamorphous silicate grains induced by exothermic chemical reactions. As a firststep, the model is applied to the annealing experiments, in which the samplesare 1 amorphous silicate grains and 2 amorphous silicate grains coveredwith an amorphous carbon layer. We derive the activation energies ofcrystallization for amorphous silicate and amorphous carbon from the analysisof the experiments. Furthermore, we apply the model to the experiment oflow-temperature crystallization of amorphous silicate core covered with anamorphous carbon layer containing reactive molecules. We clarify the conditionsof low-temperature crystallization due to exothermic chemical reactions. Next,we formulate the crystallization conditions so as to be applicable toastrophysical environments. We show that the present crystallization mechanismis characterized by two quantities: the stored energy density Q in a grain andthe duration of the chemical reactions \tau . The crystallization conditionsare given by Q > Q {min} and \tau < \tau {cool} regardless of details of thereactions and grain structure, where \tau {cool} is the cooling timescale ofthe grains heated by exothermic reactions, and Q {min} is minimum stored energydensity determined by the activation energy of crystallization. Our resultssuggest that silicate crystallization occurs in wider astrophysical conditionsthan hitherto considered.



Autor: Kyoko. K. Tanaka, Tetsuo Yamamoto, Hiroshi Kimura

Fuente: https://arxiv.org/







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