https://hal-insu.archives-ouvertes.fr/insu-03748858Le Losq, CharlesCharlesLe LosqNeuville, Daniel R.Daniel R.NeuvilleIPGP - Institut de Physique du Globe de Paris - INSU - CNRS - Institut national des sciences de l'Univers - UPD7 - Université Paris Diderot - Paris 7 - UR - Université de La Réunion - IPG Paris - Institut de Physique du Globe de Paris - CNRS - Centre National de la Recherche ScientifiqueMolecular structure, configurational entropy and viscosity of silicate melts: Link through the Adam and Gibbs theory of viscous flowHAL CCSD2017ViscosityEntropyGlassMeltSilicateRaman spectroscopy[SDU] Sciences of the Universe [physics]POTHIER, Nathalie2022-08-10 09:14:302023-02-04 03:10:522022-08-10 09:14:30enJournal articles10.1016/j.jnoncrysol.2017.02.0101The Adam and Gibbs theory depicts the viscous flow of silicate melts as governed by the cooperative re-arrangement of molecular sub-systems. Considering that such subsystems involve the silicate Q<SUP>n</SUP> units (n = number of bridging oxygens), this study presents a model that links the Q<SUP>n</SUP> unit fractions to the melt configurational entropy at the glass transition temperature T<SUB>g</SUB>, S<SUP>conf</SUP>(T<SUB>g</SUB>), and finally, to its viscosity η. With 13 adjustable parameters, the model reproduces η and T<SUB>g</SUB> of melts in the Na<SUB>2</SUB>O-K<SUB>2</SUB>O-SiO<SUB>2</SUB> system (60 ≤ [SiO<SUB>2</SUB>] ≤ 100 mol%) with 1σ standard deviations of 0.18 log unit and 10.6°, respectively. <P />The model helps understanding the links between the melt chemical composition, structure, S<SUP>conf</SUP> and η. For instance, small compositional changes in highly polymerized melts generate important changes in their S<SUP>conf</SUP>(T<SUB>g</SUB>) because of an excess of entropy generated by mixing Si between Q<SUP>4</SUP> and Q<SUP>3</SUP> units. Changing the melt silica concentration affects the Q<SUP>n</SUP> unit distribution, this resulting in non-linear changes in the topological contribution to S<SUP>conf</SUP>(T<SUB>g</SUB>). The model also indicates that, at [SiO<SUB>2</SUB>] ≥ 60 mol%, the mixed alkali effect has negligible impact on the silicate glass Q<SUP>n</SUP> unit distribution, as corroborated by Raman spectroscopy data on mixed Na-K tri- and tetrasilicate glasses. Such model may be critical to link the melt structure to its physical and thermodynamic properties, but its refinement requires further high-quality quantitative structural data on silicate and aluminosilicate melts.