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Melting of forsterite and spinel, with implications for the glass transition of Mg 2 SiO 4 liquid
Author(s) -
Richet Pascal,
Leclerc Franck,
Benoist Luc
Publication year - 1993
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/93gl01836
Subject(s) - forsterite , premelting , materials science , aluminosilicate , enthalpy , melting point , thermodynamics , spinel , entropy of fusion , glass transition , differential thermal analysis , magnesium , mineralogy , enthalpy of fusion , analytical chemistry (journal) , metallurgy , chemistry , catalysis , organic chemistry , composite material , physics , polymer , diffraction , optics
As determined by quantitative differential thermal analysis, the enthalpies of fusion of forsterite and spinel, are ΔH f = 142 ± 14 and 107 ± 11 kJ/mol at 2174 and 2408 K, respectively. Significant premelting has been observed for forsterite, beginning about 100 K below the congruent melting point. When heated in graphite crucibles, forsterite reacts with carbon and the products of reaction vaporize with an overall enthalpy of reaction of the order of 1600 kJ/mol. The configurational entropy of Mg 2 SiO 4 liquid decreases so rapidly with decreasing temperature that it would be almost zero at its nominal glass‐transition temperature as estimated by extrapolating viscosity data for magnesium aluminosilicate melts. Extreme cooling rates are thus needed in order to quench actual Mg 2 SiO 4 glasses having significant configurational entropies.