NA2O-AL2O3 SYSTEM - ACTIVITY OF NA2O IN (ALPHA + BETA)-ALUMINA AND (BETA + BETA'')-ALUMINA

The activity of Na2O in a biphasic mixture of (alpha + beta)-alumina has been measured in the temperature range of 700 to 1100 K using the solid-state galvanic cell: Pt, CO2/(1:1) + O2/Na2CO3/(alpha + beta)-alumina//(Y2O3)ZrO2//In + In2O3, Ta, Pt Similarly, the activity of Na2O in a (beta + beta'')-alumina two-phase mixture has been measured between 700 and 1100 K employing the galvanic cell: Pt, CO2/(1:1) + O2/Na2CO3/(beta + beta'')-alumina//(Y2O3)ZrO2//In + In2O3, Ta, Pt The reversible electromotive force (emf) of both the cells was found to vary linearly with temperature over the entire temperature range of measurement. From the measured reversible emf and auxiliary thermodynamic data for In2O3, Na2O, CO2 and Na2CO3 reported in the literature, the temperature dependence of the logarithm of activity of Na2O in (alpha + beta)-alumina is obtained: log a(Na2O)(alpha + beta) = 1. 85 - 14,750/T(K) (+/- 0.015) (700 less-than-or-equal-to T less-than-or-equal-to 1100) For (beta + beta'')-alumina, log a(Na2O)(beta + beta'') = 3.9 - 13,000/T(K) (+/-0.015) (700 less-than-or-equal-to T less-than-or-equal-t 1100)