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

A second melting temperature occurs at a temperature T<sub>n+</sub> higher than T<sub>m</sub> 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 bo...

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Autores principales:	Robert F. Tournier, Michael I. Ojovan
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	melting enthalpy and entropy second melting temperature melting entropy reduction crystallization enthalpy reduction undercooling overheating Technology T Electrical engineering. Electronics. Nuclear engineering TK1-9971 Engineering (General). Civil engineering (General) TA1-2040 Microscopy QH201-278.5 Descriptive and experimental mechanics QC120-168.85
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spelling	oai:doaj.org-article:36ff50ba67b041c4b09f5964a22eb8bb2021-11-11T18:04:49ZPrediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations10.3390/ma142165091996-1944https://doaj.org/article/36ff50ba67b041c4b09f5964a22eb8bb2021-10-01T00:00:00Zhttps://www.mdpi.com/1996-1944/14/21/6509https://doaj.org/toc/1996-1944A second melting temperature occurs at a temperature T<sub>n+</sub> higher than T<sub>m</sub> 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<sub>n+</sub>. Recent MD simulations show full melting at T<sub>n+</sub> = 1.119T<sub>m</sub> for Zr, 1.126T<sub>m</sub> for Ag, 1.219T<sub>m</sub> for Fe and 1.354T<sub>m</sub> 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<sub>g</sub> and the nucleation temperatures T<sub>nG</sub> of glacial phases are successfully predicted below and above T<sub>m</sub>. The glass transition temperature T<sub>g</sub> increases with the heating rate up to T<sub>n+</sub>. Melting and crystallization of glacial phases occur with entropy and enthalpy reductions. A universal law relating T<sub>n+</sub> and T<sub>nG</sub> around T<sub>m</sub> shows that T<sub>nG</sub> cannot be higher than 1.293T<sub>m</sub> for T<sub>n+</sub>= 1.47T<sub>m</sub>. The enthalpies and entropies of glacial phases have singular values, corresponding to the increase of percolation thresholds with T<sub>g</sub> and T<sub>nG</sub> above the Scher and Zallen invariant at various heating and cooling rates. The G-phases are metastable up to T<sub>n+</sub> because the antibonds are broken by homogeneous nucleation of bonds.Robert F. TournierMichael I. OjovanMDPI AGarticlemelting enthalpy and entropysecond melting temperaturemelting entropy reductioncrystallization enthalpy reductionundercoolingoverheatingTechnologyTElectrical engineering. Electronics. Nuclear engineeringTK1-9971Engineering (General). Civil engineering (General)TA1-2040MicroscopyQH201-278.5Descriptive and experimental mechanicsQC120-168.85ENMaterials, Vol 14, Iss 6509, p 6509 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	melting enthalpy and entropy second melting temperature melting entropy reduction crystallization enthalpy reduction undercooling overheating Technology T Electrical engineering. Electronics. Nuclear engineering TK1-9971 Engineering (General). Civil engineering (General) TA1-2040 Microscopy QH201-278.5 Descriptive and experimental mechanics QC120-168.85
spellingShingle	melting enthalpy and entropy second melting temperature melting entropy reduction crystallization enthalpy reduction undercooling overheating Technology T Electrical engineering. Electronics. Nuclear engineering TK1-9971 Engineering (General). Civil engineering (General) TA1-2040 Microscopy QH201-278.5 Descriptive and experimental mechanics QC120-168.85 Robert F. Tournier Michael I. Ojovan Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations
description	A second melting temperature occurs at a temperature T<sub>n+</sub> higher than T<sub>m</sub> 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<sub>n+</sub>. Recent MD simulations show full melting at T<sub>n+</sub> = 1.119T<sub>m</sub> for Zr, 1.126T<sub>m</sub> for Ag, 1.219T<sub>m</sub> for Fe and 1.354T<sub>m</sub> 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<sub>g</sub> and the nucleation temperatures T<sub>nG</sub> of glacial phases are successfully predicted below and above T<sub>m</sub>. The glass transition temperature T<sub>g</sub> increases with the heating rate up to T<sub>n+</sub>. Melting and crystallization of glacial phases occur with entropy and enthalpy reductions. A universal law relating T<sub>n+</sub> and T<sub>nG</sub> around T<sub>m</sub> shows that T<sub>nG</sub> cannot be higher than 1.293T<sub>m</sub> for T<sub>n+</sub>= 1.47T<sub>m</sub>. The enthalpies and entropies of glacial phases have singular values, corresponding to the increase of percolation thresholds with T<sub>g</sub> and T<sub>nG</sub> above the Scher and Zallen invariant at various heating and cooling rates. The G-phases are metastable up to T<sub>n+</sub> because the antibonds are broken by homogeneous nucleation of bonds.
format	article
author	Robert F. Tournier Michael I. Ojovan
author_facet	Robert F. Tournier Michael I. Ojovan
author_sort	Robert F. Tournier
title	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_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_sort	prediction of second melting temperatures already observed in pure elements by molecular dynamics simulations
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/36ff50ba67b041c4b09f5964a22eb8bb
work_keys_str_mv	AT robertftournier predictionofsecondmeltingtemperaturesalreadyobservedinpureelementsbymoleculardynamicssimulations AT michaeliojovan predictionofsecondmeltingtemperaturesalreadyobservedinpureelementsbymoleculardynamicssimulations
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Prediction of Second Melting Temperatures Already Observed in Pure Elements by Molecular Dynamics Simulations

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