The Stability of β ‐ Al2 O 3 ( Na2 O  · 11Al2 O 3 )  in Oxygen Atmospheres

Abstract

The sodium oxide activity in the a-A1203 + ~-A1203 coexistence was determined between 823 and 1198 K by relating measured values of the electromotive force of cells of the type Pt[M, MX2, NamX[~-and a-AI~O~[M', M'nO[Pt and the Gibbs energy change of the cell reaction which can be written as M + 2Na~X + taM'nO = mNa20(~) + MX2 + mnM' where X refers to halide or sulfide anion. The dependence of activity, aNa~o, On temperature, T (K), is 16,400 log aNglO = --+ 3.60 (823--~-T --1198 K) * Electrochemical Society Active aMember.

Alkaline Earth Effects on the Reaction of Sodium with Aluminum Oxide

“…Since the diffusion of sodium metal atoms in aluminum oxide is very unlikely, sodium must be in its oxidized state prior to penetrating the arc tube and forming beta alumina at spinel particles. In the case of calcium, the best thermodynamic data available for beta alumina (13) and calcium hexaaluminate (14) indicate that, in the presence of aluminum oxide, calcium hexaaluminate is a more stable compound. Therefore, in a HPS lamp, aluminum oxide is more likely to be reduced by sodium vapor than calcium hexaaluminate or, for that matter, magnesium aluminate spinel.…”

The Determination of Gibbs Energy of the Exchange Reaction of Iodides Using Beta‐Alumina Solid Electrolytes

“…The enthalpy changes for these transformation could be estimated from Eq. [3], [4], and [5]. These were calculated to be 1.85 -+ 1.25 kJ/mo] at 369.6 K and 6.77 -+ 0.72 k J/tool at 422.4 K. The enthalpies of transformation reported in the literature (13) are 2.59 kJ/mol at 371 K for Na and 6.150 kJ/mol at 420 K for AgI.…”

“…and E/V -+0.00044 = 2.46506 (-+0.00077) -5.3566 (-+0.0145) • 10 -4 • (T/K) (422.4 < T < 647 K) [5] Table Ii List of experimental results…”

“…Therefore, Eq. [19] is given by-EF = RT in a~a(meas) [20]Using Eq [3],[4],[5]. and [19], Na activity in the Ag + AgI + NaI is expressed by log aNa = 1.6002 -ll,973/(T/K) (309<T<369.6K) [21] log aNa = 1.8622 -12,070~(T/K) (369.6 < T < 422.4 K) [22] and log as~ = 2.6997 -12,424/(T/K) (422.4<T<647K) [23] Standard state of Na was taken as a solid in Eq.…”

“…Comparison of the various determinations of the Ha activities in No reference electrodes. July 1986 Mo,Na(s,1) l~"-aluminal NaI + Ag + AgI,Mo The EMF's were represented by E/V • 0.00075 = 2.37566 (-+0.00620) -3.1751 (-+0.1834) • 10 -4 x (T/K) (309 < T < 369.6 K) [3]E/V • 0.00053 = 2.39487 (-+0.00672) -3.6948 (-+0.1700) x 10 -4 • (T/K) (369.6 < T < 422.4 K[4] and E/V -+ 0.00044 = 2.46506 (• -5.3566 (-+0.0145) • 10 -4 x (T/K) (422.4 < T < 647 K)[5] …”