Transport properties of sealants for high-temperature electrochemical applications: RO-BaO-SiO(2) (R = Mg, Zn) glass-ceramics


The electrical properties and oxygen permeability of glass-ceramics 55SiO(2)-27BaO-18MgO, 55SiO(2)-27BaO-18ZnO and 50SiO(2)-30BaO-20ZnO (%mol), which possess thermal expansion compatible with that of yttria-stabilized zirconia (YSZ) solid electrolytes, were studied between 600 and 950 degrees C in various atmospheres. The ion transference numbers, determined by the modified electromotive force (e.m.f.) technique under oxygen partial pressure gradients of 21 kPa/(1-8) x 10(2) Pa and 21 kPa/(1 x 10(-18)-2 x 10(-12)) Pa, are close to unity both under oxidizing and reducing conditions. The electronic contribution to the total conductivity increases slightly on increasing temperature, but is lower than 2% and 7% for the Zn- and Mg-containing compositions, respectively. The conductivity values measured by impedance spectroscopy vary in the range (1.4-7.8) x 10(-6) S/cm at 950 degrees C under both oxidizing and reducing conditions, with activation energies of 122-154 kJ/mol and a minor increase in H(2)-containing atmospheres, indicating possible proton intercalation. In agreement with the electrical measurements which indicate rather insulating properties of the glass-ceramics, the oxygen permeation fluxes through sintered sealants and through sealed YSZ/glass-ceramics/YSZ cells are very low, in spite of an increase of 15-40% during 200-230 h under a gradient of air/H(2)-H(2)O-N(2) due to slow microstructural changes. (c) 2005 Elsevier Ltd. All rights reserved.




Materials Science


Pascual, MJ; Kharton, VV; Tsipis, E; Yaremchenko, AA; Lara, C; Duran, A; Frade, JR

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