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Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations

A second melting temperature occurs at a temperature T(n+) higher than T(m) in glass-forming melts after heating them from their glassy state. The melting entropy is reduced or increased depending on the thermal history and on the presence of antibonds or bonds up to T(n+). Recent MD simulations sho...

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Autores principales: Tournier, Robert F., Ojovan, Michael I.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2021
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8585396/
https://www.ncbi.nlm.nih.gov/pubmed/34772033
http://dx.doi.org/10.3390/ma14216509
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author Tournier, Robert F.
Ojovan, Michael I.
author_facet Tournier, Robert F.
Ojovan, Michael I.
author_sort Tournier, Robert F.
collection PubMed
description A second melting temperature occurs at a temperature T(n+) higher than T(m) in glass-forming melts after heating them from their glassy state. The melting entropy is reduced or increased depending on the thermal history and on the presence of antibonds or bonds up to T(n+). Recent MD simulations show full melting at T(n+) = 1.119T(m) for Zr, 1.126T(m) for Ag, 1.219T(m) for Fe and 1.354T(m) for Cu. The non-classical homogeneous nucleation model applied to liquid elements is based on the increase of the Lindemann coefficient with the heating rate. The glass transition at T(g) and the nucleation temperatures T(nG) of glacial phases are successfully predicted below and above T(m). The glass transition temperature T(g) increases with the heating rate up to T(n+). Melting and crystallization of glacial phases occur with entropy and enthalpy reductions. A universal law relating T(n+) and T(nG) around T(m) shows that T(nG) cannot be higher than 1.293T(m) for T(n+)= 1.47T(m). The enthalpies and entropies of glacial phases have singular values, corresponding to the increase of percolation thresholds with T(g) and T(nG) above the Scher and Zallen invariant at various heating and cooling rates. The G-phases are metastable up to T(n+) because the antibonds are broken by homogeneous nucleation of bonds.
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spelling pubmed-85853962021-11-12 Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations Tournier, Robert F. Ojovan, Michael I. Materials (Basel) Article A second melting temperature occurs at a temperature T(n+) higher than T(m) in glass-forming melts after heating them from their glassy state. The melting entropy is reduced or increased depending on the thermal history and on the presence of antibonds or bonds up to T(n+). Recent MD simulations show full melting at T(n+) = 1.119T(m) for Zr, 1.126T(m) for Ag, 1.219T(m) for Fe and 1.354T(m) for Cu. The non-classical homogeneous nucleation model applied to liquid elements is based on the increase of the Lindemann coefficient with the heating rate. The glass transition at T(g) and the nucleation temperatures T(nG) of glacial phases are successfully predicted below and above T(m). The glass transition temperature T(g) increases with the heating rate up to T(n+). Melting and crystallization of glacial phases occur with entropy and enthalpy reductions. A universal law relating T(n+) and T(nG) around T(m) shows that T(nG) cannot be higher than 1.293T(m) for T(n+)= 1.47T(m). The enthalpies and entropies of glacial phases have singular values, corresponding to the increase of percolation thresholds with T(g) and T(nG) above the Scher and Zallen invariant at various heating and cooling rates. The G-phases are metastable up to T(n+) because the antibonds are broken by homogeneous nucleation of bonds. MDPI 2021-10-29 /pmc/articles/PMC8585396/ /pubmed/34772033 http://dx.doi.org/10.3390/ma14216509 Text en © 2021 by the authors. https://creativecommons.org/licenses/by/4.0/Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Tournier, Robert F.
Ojovan, Michael I.
Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations
title Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations
title_full Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations
title_fullStr Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations
title_full_unstemmed Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations
title_short Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations
title_sort prediction of second melting temperatures already observed in pure elements by molecular dynamics simulations
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8585396/
https://www.ncbi.nlm.nih.gov/pubmed/34772033
http://dx.doi.org/10.3390/ma14216509
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