Ni2SiO4-enthalphy of the olivine-spinel transition by solution calorimetry at 713°C

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Abstract

The high pressure spinel polymorph of Ni2SiO4 persists metastably at 713°C and atmospheric pressure. The enthalpy of the olivine-spinel transition was obtained by measuring the heats of solution of both polymorphs in a molten oxide solvent, 2PbO · B2O3, at that temperature. For Ni2SiO4 (ol) → Ni2SiO4, ΔH9860 = +1.4 ± 0.7 kcal/mol. The heat content increments, H986 - H297, were found to be: olivine, 25.73 ± 0.42 kcal/mol, and spinel, 25.39 ± 0.20 kcal/mol. The measured enthalpy of the transformation is consistent with the low slope of the phase boundary, π{variant}P/π{variant}T = ∼ 12 b/deg, observed by Akimoto and others. The entropy of the olivine-spinel transition in Ni2SiO4 is accordingly about a factor of three smaller in magnitude (ΔS = ∼ -1 cal/deg mol) than that for Co2SiO4, Fe2SiO4, Mg2SiO4 or Mg2GeO4 (ΔS = -3 to -3.5 cal/deg mol).

Original languageEnglish (US)
Pages (from-to)471-475
Number of pages5
JournalEarth and Planetary Science Letters
Volume19
Issue number4
DOIs
StatePublished - Aug 1973

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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