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

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.

Formation of chondrule analogs aboard the International Space Station

“…Recent crystallization experiments on Earth using laser heating of Mg 2 SiO 4 spherules which were levitated on a gas jet led to the formation of a dendritic microstructure, which is clearly different from the fabric observed here (Mishra et al. 2020). Consequently, the observed microstructure seems to be the result of crystallization in microgravity without any contact to sample chamber walls, which would imply that this feature probably cannot be observed in experiments on Earth.…”

“…2015; Mishra et al. 2020). Recent crystallization experiments on Earth using laser heating of Mg 2 SiO 4 spherules which were levitated on a gas jet led to the formation of a dendritic microstructure, which is clearly different from the fabric observed here (Mishra et al.…”

Reproduction Experiments of Radial Pyroxene Chondrules Using a Gas-jet Levitation System under Reduced Conditions

“…The wire method is unsuitable for accurately reproducing the crystallization process in the protoplanetary disk because the contact points between the starting materials and wires work as heterogeneous nucleation sites and facilitate crystallization. For this reason, levitation experiments have been conducted to simulate chondrule formation (Tsukamoto et al 1999;Nagashima et al 2006Nagashima et al , 2008Pack et al 2010;Mishra et al 2020;Shete et al 2021).…”

“…Chondrule formation took place under reducing conditions (e.g., Ebel & Grossman 2000;Grossman et al 2008;Tenner et al 2015;Villeneuve et al 2015), and some of the following levitation experiments simulated those conditions. Mishra et al (2020) conducted levitation experiments in a chamber filled with Ar gas under subatmospheric pressure and revealed that the latent heat of crystallization was removed more rapidly than under atmospheric conditions, resulting in faster cooling of the experimental samples that simulated chondrules. Consequently, this leads to smaller forsterite crystal sizes than under atmospheric conditions.…”