Metastability of Spinel-type Solid Solutions in the SiO2-Al2O3 System

J. M. McHale, K. Yürekli, D. M. Dabbs, A. Navrotsky, Sankaran Sundaresan, Ilhan A. Aksay

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The addition of small amounts (2-10 wt %) of SiO2 to γ-Al2O3 increases the temperature of heat treatment necessary for transformation to α-Al2O3 by ∼100 K. We have studied this system using high-temperature solution calorimetry in molten 2PbO·B2O3 at 1043 K. Our results indicate that the spinel-type Al2O3-SiO2 solid solutions with 2-10 wt % SiO2 are always energetically metastable by 30-35 kJ·mol-1 (on a 4 O2- per mole basis) with respect to α-Al2O3 and quartz. Calculation of the maximum configurational entropy of the solid solutions allowed determination of the likely most negative value of the Gibbs free energy of the materials. The solid solutions are somewhat entropy stabilized, but still thermodynamically metastable by >10 kJ·mol-1 at 1400 K. Therefore, SiO2 addition appears to provide mainly a kinetic hindrance to α-Al2O3 formation.

Original languageEnglish (US)
Pages (from-to)3096-3100
Number of pages5
JournalChemistry of Materials
Issue number12
StatePublished - Dec 1997

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • General Chemical Engineering
  • Materials Chemistry


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