Molecular dynamics simulation of the Soret effect in a CaSiO₃ glass melt

Abstract

The mole fraction distributions of CaO and SiO 2 under a temperature gradient in a CaSiO 3 melt were calculated by molecular dynamics. The temperatures at the cold and hot ends of the gradient were 1800 and 2200 K, respectively, in the simulation. We used two sets of potential parameters proposed by Matsui et al. and Seo et al. The simulation results obtained with the two potentials indicate that the mole fraction of CaO in the cold region was higher than that in the hot region, and the mole fraction of SiO 2 in the hot region was higher than that in the cold region. This is qualitatively consistent with previous experimental results obtained by laser local heating inside a CaSiO 3 glass [Shimizu et al., Optics letters, 36, 21612163(2010)].©2017 The Ceramic Society of Japan. All rights reserved.Key-words : Soret effect, Silicate melt, Glass melt, Molecular dynamics [Received August 31, 2016; Accepted January 10, 2017] Temperature gradient-driven diffusion in multi-component systems is called the Soret effect. Although it has been over 150 years since this phenomenon was discovered, 1),2) the mechanism of the Soret effect is still controversial. There have been several approaches to predict Soret coefficients, which indicate whether the components diffuse toward the hot or cold regions and the separation degree of the components between the hot and cold regions.3) The Soret effect is currently an area of interest in nonequilibrium thermodynamics.The Soret effect in multicomponent silicate melts that contain more than two oxides has been investigated in the field of earth science, 4)8) and two important conclusions were drawn. First, the SiO 2 component concentrates in the hot region. 4),5) Second, heavier isotopes concentrate in the cold region more than lighter isotopes. 6)8) Our group has investigated the Soret effect in twocomponent silicate glass melts with a laser irradiation method. In a CaSiO 3 glass melt, Ca concentrated in the cold region, and Si and O concentrated in the hot region, 9) suggesting that CaO concentrated in the cold region and SiO 2 concentrated in the hot region. However, the factors determining the diffusion direction and separation degree have not been fully elucidated. It is also important to elucidate these factors for the glass industry because the spatial homogeneity of glass composition is important for optical and thermally stable glass. In industrial glass-melting tanks 10) and glass-melting crucibles, temperature gradients induce the Soret effect, which could cause the spatial inhomogeneity of the glass composition. Furthermore, laser irradiation during laser welding 11) and laser cutting 12) of glasses would also induce the Soret effect because optical absorption at the small focal spot causes a steep temperature gradient. Determining the main factors involved in the Soret effect may enable us to avoid or predict the inhomogeneity in glass tanks and damage caused by laser irradiation.Molecular dynamics (MD) is a powerful tool for investigating the factors that dominate the S...

Role of partial molar enthalpy of oxides on Soret effect in high-temperature CaO–SiO2 melts

“…The simulation method was similar to that in our previous report 20 , but the details had some differences. We employed the potential proposed by Seo 21 .…”

Compositional design for SrTiO₃ crystal precipitation from spinodal-type borosilicate glass containing large amounts of TiO₂

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Soret effect in binary glass-forming oxide melts: theory and its verification

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