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Refinement of enthalpy measurement of MgSiO 3 perovskite and negative pressure‐temperature slopes for Perovskite‐forming reactions
Author(s) -
Akaogi Masaki,
Ito Eiji
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 - 10.1029/93gl01265
Subject(s) - periclase , enthalpy , thermodynamics , perovskite (structure) , ilmenite , spinel , materials science , mineralogy , calorimetry , bulk modulus , stishovite , chemistry , crystallography , high pressure , physics , metallurgy
Enthalpy for MgSiO 3 orthopyroxene‐perovskite transition at 298 K was measured by differential drop‐solution calorimetry. Based on four measurements of MgSiO 3 perovskite, the ΔH° 298 of 102.2±2.5 kJ/mol was more precisely determined than that in the previous study. The enthalpies of transitions from MgSiO 3 ilmenite to perovskite and from Mg 2 SiO 4 spinel to perovskite + periclase were calculated to be 43.2±5.0 and 86.1±3.6 kJ/mol, respectively. The boundaries of these transitions were calculated using the above data together with physical properties of relevant phases, including recently determined properties of perovskite: heat capacity, entropy, and temperature dependence of bulk modulus. The calculated P‐T slopes for the ilmenite‐perovskite transition and the spinel dissociation are −3.4±2 and −3±1 MPa/K, respectively. The latter slope may suggest that the upper and lower mantle convect separately but intermittent mixing occurs between them.