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

Autor:	J. M. McHale, Sankaran Sundaresan, Daniel M. Dabbs, Alexandra Navrotsky, Ilhan A. Aksay, K. Yürekli
Rok vydání:	1997
Předmět:	Chemistry General Chemical Engineering Spinel Configuration entropy Mineralogy Thermodynamics General Chemistry Calorimetry engineering.material Kinetic energy Gibbs free energy symbols.namesake Metastability Materials Chemistry engineering symbols Quartz Solid solution
Zdroj:	Chemistry of Materials. 9:3096-3100
ISSN:	1520-5002 0897-4756
DOI:	10.1021/cm970447f
Popis:	The addition of small amounts (2-10 wt %) of SiO2 to A-Al2O3 increases the temperature of heat treatment necessary for transformation to R-Al2O3 by100 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 a4O 2 - per mole basis) with respect to R-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, SiO2addition appears to provide mainly a kinetic hindrance to R-Al2O3 formation.
Databáze:	OpenAIRE
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