Preparation and Characterization of CeO_2-Y_2O_3 Binary-Oxides and Their CO_2 Gas-Sensing Properties

摘要

A CeO_2-Y_2O_3 binary oxide powder was prepared by the sol gel method using citric acid 10% aqueous solution as chelating agent, at 70℃, under constant stirring. The molar ratio for oxides was CeO_2/Y_2O_3 = 4:1. Ethylene glycol was added to promote the citrate polymerization by the polyesterification reaction. The citric acid ethylene glycol ratio was fixed at 2:1. The gel resulted was calcined at 800℃ for 2 hours. For the sensor fabrication, a disc of 4 mm diameter and 1 mm thickness was prepared by pressing of CeO_2-Y_2O_3 powder at 10 tons force/cm~2 and sintered at 1100℃ for 6 hours. The circular gold electrodes with φ 1 mm were deposited on both faces of the disc by e-beam evaporation in the conditions: P = 10~(-5) Torr, current 8 mA, time 60 s. The thickness of the gold electrodes 0.7 μm was determined with white light interferometric microscopy. For the powder oxides the X-ray diffraction analysis evidenced CeO_2 phase with a cubic structure (lattice parameter a = b = c = 5.409 A). The crystallites size calculated with Scherrer formula for the powder calcined at 800℃ was 107,3 nm for the (111) peak. For the Y_2O_3 phase, a cubic structure was identified with a lattice parameter a = b = c = 10.616 A and a crystallites size 22.6 nm. BET analysis revealed a specific area of 3.13 m~2/g, a pores size of 8.93 A and a pores volume of 1,066 × 10~(-3) cm~3/g. The sensor was exposed to 0-5000 ppm CO_2 and the voltage was measured in climatic conditions at 20℃ temperature, relative humidity of 40% and 80% respectively. The sensor sensitivity was 0.3 μV/ppm and the response time was less than 30 seconds. Also, the electronic signal conditioning of the sensing element was presented.