Thick film miniaturized HCl gas sensor

Planar miniaturized HCl sensors were fabricated using thick films of the proton conducting solid electrolyte of strontium cerate doped with 10 mol% Nd2O3 interfaced with chloride ion conducting SrCl2. The proton conducting film was fabricated by screen-printing using an ink of the doped strontium cerate on an alumina substrate which was then fired at 1773 K. SEM and EDAX analysis showed that the film is dense and bonds closely to the substrate, although some reactions were observed at the interface between the strontium cerate film and the alumina substrate. Results from impedance spectroscopy showed that conductivity of the thick film is similar to that of bulk strontium cerate. SrCl2 was applied on the cerate film as a slurry from an aqueous solution which was then subsequently heated to 1153 K. Sensors based on forming an electrochemical chain with the two electrolytes showed fairly good HCI sensing properties in the 830-973 K temperature range. The emf values obtained were linear with respect to the logarithm of HCl concentration over a wide range (from several to 1000 ppm). The tubular sensors were also tested under similar conditions. The results given by film sensors are qualitatively comparable to the bulk tubular sensors, although not in complete quantitative agreement. (C) 2003 Elsevier B.V. All rights reserved.