Determining Extremely Low Sodium Activities at Elevated Temperatures

Abstract

The electrochemical determination of extremely low sodium activities may be affected by electronic transference through the electrolyte as far as potentiometric measurements using a cell with a sodium ion conducting solid electrolyte are concerned. Until now, this source of error has been ignored in the literature. Therefore, a new experimental approach has been developed which is based on the reproducible transformation of the sodium activity into an oxygen potential. The latter is measured by means of an oxygen concentration cell under conditions that definitely exclude any impact of electronic transference. The feasibility of the measuring technique has been demonstrated for the heterogeneous phase system NaSi y O 2yϩ0.5 /SiO 2 (y ϭ 1.5). As a result, the standard Gibbs energy of formation of NaSi 1.5 O 3.5 has been obtained to be ͑350-800°C͒ ⌬ f G NaSi 1.5 O 3.5 o (kJ/mol) ϭ Ϫ1697.787 Ϯ 24.16 ϩ (339.512 Ϯ 26.69) ϫ 10 Ϫ3 T/K which appears reasonable from a comparison with data known in the literature on Na 2 SiO 3 .

Electrochemical CO2Separation through an Alkali-Carbonate-Based Membrane

“…Electronic conduction parameters p ⊕ and p for yttria-stabilized zirconia (YSZ) and variously doped ceria (DC) according to a critical assessment of literature data. [25][26][27][28][29][30][31][32] increases. In detail the behavior depends on the magnitudes of the electronic conduction parameters a ⊕ , a , p ⊕ and p of the electrolytes.…”

“…with: [32] It is in the nature of an efficient permeation process that the gradient of the CO 2 partial pressure is as high as possible. On the other hand, this gradient has to be maintained by means of a minimum of technical measures.…”