Investigations towards the use of Gd0.7Ca0.3CoOx as membrane in an exhaustgas sensor for NOx

Application of a material with the nominal composition Gd0.7Ca0.3CoOx is co nsidered for use as membrane material in an exhaust gas sensor for NOx. SEM -EDX and XRD measurements revealed that after sintering at 1200 degreesC in air, three co-existing phases are present: (Gd0.6Ca0.4)(2)CoOx (60 vol,%), GdCoO3 (26 vol.%) and CoO, Catalytic activities were investigated using te mperature-programmed reaction (TPR). Whereas the composite Gd0.7Ca0.3CoOx s hows no catalytic activity towards NO, reduction, as required in the target ed application, the single phase components (Gd0.6Ca0.4)(2)CoOx and GdCoO3, were found both to be active. The permeation rates exhibited by the compos ite material, at 1000 degreesC, are considered too low for real application of this material. Oxygen permeation rates through perovskite-structured Gd CoO3-delta and (Gd0.6Ca0.4)(2)CoO4-delta, having the K2NiF4-structure, were found to be below the range of detection (< 10(-11) mol/cm(2) s). <(c)> 20 01 Elsevier Science B.V. All rights reserved.