Ultra-high temperature Soret effect in a silicate melt: SiO2 migration to cold side

Area of Science:

• Earth Sciences
• Materials Science
• Thermodynamics

Background:

• The Soret effect describes temperature gradient-driven diffusion in silicate melts, with SiO2 typically concentrating in hotter regions.
• This behavior has been extensively studied in earth sciences since the 1980s.

Purpose of the Study:

• To investigate the behavior of SiO2 diffusion in silicate melts at ultra-high temperatures.
• To determine if the Soret effect in silicate melts changes direction at extreme temperatures.

Main Methods:

• Experimental irradiation of aluminosilicate glass with a femtosecond laser to create localized temperature gradients.
• Non-equilibrium molecular dynamics (NEMD) simulations to model diffusion under temperature gradients.
• Molecular dynamics simulations to calculate molar volume and identify phase transitions.

Main Results:

• At temperatures above approximately 3060 K, SiO2 was observed to migrate to the colder region of the silicate melt.
• This high-temperature behavior was confirmed by NEMD simulations at an average temperature of 4000 K.
• At lower temperatures (2400 K), SiO2 migrated to the hotter region, consistent with previous studies.

Conclusions:

• The Soret effect in silicate melts exhibits a reversal at ultra-high temperatures (above ~3060 K), with SiO2 migrating to colder regions.
• This reversal may be linked to a discontinuous phase transition occurring around 3250 K at 500 MPa.
• The precise mechanism driving this high-temperature Soret effect reversal requires further elucidation.