Experiments to understand crystallization of levitated high temperature silicate melt droplets under low vacuum conditions

Biswajit Mishra,Atul Srivastava,Pratikkumar Manvar,S Karagadde,Kaushik Choudhury

doi:10.1038/s41598-020-77965-4

Biswajit Mishra, Atul Srivastava + Show 3 more

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https://doi.org/10.1038/s41598-020-77965-4

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Journal: Scientific Reports	Publication Date: Dec 1, 2020
Citations: 4	License type: open-access

Affiliation: Indian Institute of Technology Bombay

Abstract

We report experiments on crystallization of highly undercooled forsterite melt droplets under atmospheric and sub-atmospheric pressure conditions. Experiments have been conducted under non-contact conditions using the principles of aero-dynamic levitation. Real time dynamics of solidification, along with the transient evolution of surface textures, have been recorded using high speed camera for three cooling rates. These images have been matched with the time-tagged temperature data to understand the effect of pressure conditions and cooling rates on the crystallization dynamics. Compared to normal pressure, relatively higher levels of undercooling could be achieved under sub-atmospheric conditions. Results showed a strong dependence of surface textures on pressure conditions. For any externally employed cooling rate, relatively small length scale morphological textures were observed under sub-atmospheric conditions, in comparison to those achieved under ambient conditions. The observed trends have been explained on the basis of influence of pressure conditions on recalescence phenomenon and the rate at which latent heat of crystallization gets dissipated from the volume of the molten droplet. Sub-atmospheric experiments have also been performed to reproduce one of the classical chondrule textures, namely the rim + dendrite double structure. Possible formation conditions of this double structure have been discussed vis-à-vis those reported in the limited literature. To the best of our knowledge, the reported study is one of the first attempts to reproduce chondrules-like textures from highly undercooled forsterite melt droplets under sub-atmospheric non-contact conditions.

Highlights

We report experiments on crystallization of highly undercooled forsterite melt droplets under atmospheric and sub-atmospheric pressure conditions
A direct comparison of surface textures of the samples crystallized under sub-atmospheric conditions was made with those achieved under normal pressure conditions
The observed trends were explained on the basis of difference in the rates at which the latent heat of crystallization gets dissipated from the volume of the molten droplet under the varying pressure conditions

Summary

Introduction

We report experiments on crystallization of highly undercooled forsterite melt droplets under atmospheric and sub-atmospheric pressure conditions. Real time dynamics of solidification, along with the transient evolution of surface textures, have been recorded using high speed camera for three cooling rates These images have been matched with the timetagged temperature data to understand the effect of pressure conditions and cooling rates on the crystallization dynamics. To the best of our knowledge, the reported study is one of the first attempts to reproduce chondrules-like textures from highly undercooled forsterite melt droplets under sub-atmospheric non-contact conditions. One section of the astronomical society argues that crystallization took place under low cooling rates Motivated by these studies, a considerable number of experiments have been performed under such conditions[11,12,13] with an intent to reproduce some of the commonly encountered chondrule textures, for instance as reported in Ref.[14]. Theoretical analysis of similar problems pertaining to solidification of semi-transparent melt particles for various applications have been reported[25,26,27,28]

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