Bi/Bi2O3 sensor for quantitation of dissolved oxygen in molten salts

Huiping Zheng,Danyu Jiang,Jinfeng Xia,Hongqiang Nian,Guohong Zhou,Qiang Li

doi:10.1007/s40145-017-0250-4

Abstract

To quantify the oxygen content in molten salts, we examined the performance of an yttria-stabilized zirconia solid electrolyte oxygen sensor with a Bi/Bi2O3 reference electrode, focusing on its output accuracy. When the above sensor was tested in a flow of gas with known oxygen partial pressure, p_{O_2}, a linear relationship between lgp_{O_2} and the electromotive force (EMF) was observed, and the correlation slope exhibited a positive deviation from Nernstian behavior. EMF measurements performed in molten NaCl–KCl indicated that the oxygen content of this salt mixture increased with increasing oxygen partial pressure in the covering gas, in agreement with Henry’s law. Moreover, the EMF exhibited a linear decrease with increasing melt temperature of molten NaCl–KCl, in agreement with the theoretical model. Finally, a relationship between the structure of molten NaCl–KCl and its oxygen diffusion behavior was established. As a result, the developed sensor was demonstrated to be well suited for determining the oxygen content of molten salts.

Highlights

Molten salts remain liquid in a wide temperature range, exhibiting stability at high temperatures, low vapor pressure, ability to dissolve numerous inorganic and organic compounds, low viscosity, and high heat capacity per unit volume [1,2], being broadly utilized as engineering fluids with a wide range of applications, e.g., catalytic medium for coal gasification, waste oxidation, sensible heat storage, and molten salt reactors [3,4,5,6]
The oxygen content of molten salts exposed to covering gases with different oxygen partial pressures and its temperature dependence were measured using a Bi/Bi2O3 sensor
The electromotive force (EMF) of the Bi/Bi2O3 sensor in the molten salt mixture was measured at 973 K for covering gases with different oxygen contents (i.e., high-purity N2 (99.999%, 200 vppm O2) and N2+O2 (0.5, 1.0, and 2.5 vol%)) and at different temperatures (973–1073 K) in a covering gas of high-purity N2/200 vppm O2

Summary

Introduction

Molten salts remain liquid in a wide temperature range, exhibiting stability at high temperatures, low vapor pressure, ability to dissolve numerous inorganic and organic compounds, low viscosity (due to ions being mutually independent), and high heat capacity per unit volume [1,2], being broadly utilized as engineering fluids with a wide range of applications, e.g., catalytic medium for coal gasification, waste oxidation, sensible heat storage, and molten salt reactors [3,4,5,6]. The development of the above mentioned technologies increases the requirements placed on the composition and properties of molten salts, such as the content of. Volkovic et al [17] developed a novel sensitive method for determining oxygen solubility in molten carbonates and carbonate-based melts, revealing that measurements at various partial pressures of oxygen allowed the determination of www.springer.com/journal/40145. J Adv Ceram 2018, 7(1): 1–4 predominant oxygen species in the melt and examining the applicability of Henry’s law to this system. Phongikaroon et al [18] used a high-speed digital camera to analyze oxygen bubble distributions in LiCl–KCl melts at 723 K produced at different sparging rates. The oxygen content of molten salts exposed to covering gases with different oxygen partial pressures and its temperature dependence were measured using a Bi/Bi2O3 sensor

Experimental

Results and discussion

Conclusions