Use of the Junction Between Two Solid Electrolytes for the Potentiometric Measurement of Gaseous Oxides

An exploratory study was carried out to elucidate the fabrication principles of a potentiometric SO2 sensor utilizing stabilized zirconia (solid electrolyte) and a metal sulfate (auxiliary phase). Among the MgO-, CaO-, Y303-stabilized zirconia (abbreviated as MSZ, CSZ, or YSZ) tested, only MSZ samples which contained 15 mole percent (mb) MgO and were partially stabilized gave a stable SO2 sensor by being attached with Li2SO4, whereas almost fully stabilized MSZ (15 mb MgO), partially stabilized MSZ (9 mb MgO), CSZ (11 mb CaO), or YSZ (8 mb Y303) gave a stable device only when attached with a mixed auxiliary phase of Li2SO4-MgO. These facts indicated an active role by MgO, either segregated from the stabilized zirconia or added intentionally, for the devices. It is estimated that, together with Li20 and Zr02, MgO is an essential component of the interfacial compound which acts as an ionic bridge between stabilized zirconia (0 -conductor) and auxiliary phase (Lit conductor). The electromotive force (EMF) response of each device to SO2 followed Nernst's equation well for a two-electron reaction per SO2 molecule, while the EMF dependence on oxygen concentration deviated slightly from the Nernstian behavior for the four-electron reduction of 02. Such behavior is discussed based on the sensing mechanism proposed. InfroductionIn recent years much effort has been directed to developing solid-state sensors for environmentally concerned gases such as SO2, C02, and NO. Particularly, solid electrolyte-based sensors have drawn great attention from their compactness, low cost, and capability of in situ monitoring. As for SO2 sensing, Maruyama et al.' disclosed a new type of solid-state SO2 sensor consisting of NASICON (Na3Zr3Si2PO,2, Na ionic conductor) and Na2SO4 (auxiliary phase), a type later classified as type 111.2.3 Although this sensor gave rather well-defined sensing behavior to SO2 in air, it possesses uncertainty about the stability of NASICON in S02-containing atmosphere, in addition to slow response kinetics. In an effort to replace NASICON by a more reliable solid electrolyte, we have found that a novel type III device utilizing MSZ and Li2SO4-based auxiliary phase shows excellent Nernst's responses to SO2 in air4" together with good long-term stability and good resistance to disturbance by the coexistence of CO2, NO, or NO2. This sensor is provided by combining an anion (02) conducting solid electrolyte with a cation (Lit) conducting auxiliary phase, unlike those type III sensors for which the main solid electrolytes and auxiliary phases have the same conducting ions or at least the conducting ions of the same sign.6-12 Such a device with heterojunction between anionic and cationic conductors has seldom been investigated so far.'3 It is considered that an intervening phase or ionic bridge must exist at the heterojunction interface for the device to achieve an electrochemical chain.In this study we aimed to collect more information regarding the heterojunction by inspecting the applicability of various kinds of st...

Section: Resultsmentioning

confidence: 99%

Construction and Working Mechanism of Sulfur Dioxide Sensor Utilizing Stabilized Zirconia and Metal Sulfate

Yan

Miura

Yamazoe

1996

“…The results obtained by Jorgensen (7, 8, I0), for instance, seem to confirm this effect, although other authors (14,15) did not find any influence of the external electric field on the oxidation kinetics. The reason for this probably lies in the difficulties both in measuring the potential difference at the growing oxide interfaces (16,17), and in…”

Section: Resultsmentioning

confidence: 99%

Sulfur Dioxide Gas Detection with Na2 SO 4 ‐ Li2 SO 4 ‐ Y 2 ( SO 4 ) 3 ‐ SiO2 Solid Electrolyte by a Solid Reference Electrode Method

Imanaka

Yamaguchi

Adachi

et al. 1987

The electromotive force (EMF) measurement for a Na2SO4-Li2SO4-Y2(SO4)3-SiO: solid electrolyte was performed both with NiSO4-NiO and CoSO4-Co304 solid reference SO2 electrodes. The measured EMF coincided well with the calculated EMF for a sulfur dioxide gas concentration from 30 ppm to 1% at 973 K. Good agreement between the measured and calculated EMF was also obtained for the SO: gas content from 100 ppm to 1%, at 923 K with the NiSO4-NiO electrode.ABSTRACT Results on the high temperature oxidation of nickel, as obtained when the metal is the anode of an electrochemical cell with yttria stabilized zirconia (YSZ) as the electrolyte, are presented. Three-electrode cyclic voltammetry was used to study oxide growth at the YSZ/Pt,,/(NiO)Ni interface by a cell system where sintered iron-wtlstite electrodes act both as reference and eounterelectrodes. The analysis of the voltammetric curve is carried out by considering that an oxygen producing charge transfer occurs at the YSZ/Pt~, interface and that the oxide grows under an external electric field which retards the oxidation kinetics. An approach for calculating the current/voltage curve of the growing oxide is also reported.

“…Bourhis and St. John (7) have shown that the catastrophic corrosion of superalloys containing Mo is due to fluxing by M003, which is formed at the scale-metal interface. Studies in this laboratory (3,8) have shown that all the Na~SO4 was converted to Na~CrO, much before the onset of catastrophic corrosion for superalloys containing Mo, and the onset of catastrophic corrosion was marked by the conversion of Na~CrO4 to Na~MoO4. The catastrophic corrosion was associated with the formation of a Na2MoO4--M003 melt.…”

Section: Introductionmentioning

confidence: 99%

“…Alkali-metal sulfates (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) have been extensively investigated as solid electrolytes for a sulfur dioxide gas detector. However, phase transformation of the sulfates occurs, resulting in gas permeation through the microcracks in the electrolyte.…”

mentioning

confidence: 99%

The Electrical and Thermal Properties of Sodium Sulfate Mixed with Lithium Sulfate, Yttrium Sulfate, and Silicon Dioxide

Imanaka

Yamaguchi

Adachi

et al. 1986

Sodium sulfate mixed with lithium sulfate, yttrium sulfate, and silicon dioxide was prepared. The thermal and electrical properties of its phases were investigated. The Na2SO4‐Li2SO4‐Y2false(SO4)3‐SiO2 samples are similar to the Na2SO4‐I phase (a high temperature phase), which is appreciably effective for Na+ ionic conduction. Phase transformation was considerably suppressed by mixing. Electromotive force (EMF) was measured, using Na2SO4‐Li2SO4‐Y2false(SO4)3‐SiO2 as a solid electrolyte, by constructing an SO2 gas concentration cell. The measured EMF's at 823 and 773 K were in fairly good accordance with the calculated EMF's for inlet SO2 gas concentration between 30 ppm and 1%, and 500 ppm and 0.5%, respectively.