Papers by Author: Kwang Soo Yoo

Abstract: Thick-film CO2 sensors were fabricated using a sodium super ionic conductor (NASICON: Na1+xZr2SixP3-xO12) with a series of Li2CO3-BaCO3 auxiliary phases. The powder of a precursor of NASICON with high purity was synthesized by a sol-gel process. Using the NASICON paste, an electrolyte was prepared on the alumina substrate through screen printing and then sintered at 1000°C for 5 hours. The resulted NASICON thick film was characterized by XRD and FESEM. Within a wide range of CO2 volume ratio concentration from 1,000 to 10,000 ppm, the output of the sensor showed a good electromotive force (EMF) response that was very close to the theoretical value. The sensor attached with a binary carbonate auxiliary phase Li2CO3-BaCO3 (1:2) showed fairly good CO2 sensing properties at 470°C.

Abstract: The ultrasonic spray pyrolysis method and proper heat treatments were applied in order to synthesize La0.8Sr0.2CrO3 (LSC) which is one of promising materials for separator in soild oxide fuel cell in this study. LSC powders that were sprayed at 800oC, heat-treated at 900oC for 5 hrs, ball-milled and finally heat-treated again at 1200oC for 20 hrs showed the average diameter of 0.3 *m and narrow size distribution to find particles above 0.5 *m hardly. In addition, the synthesizing temperature of LSC powders in ultrasonic spray pyrolysis method was 100
lower than conventional ball milling and drying method. Therefore the proper combination of heat treatment and milling process after spray pyrolysis was found to be very critical in synthesizing fine and uniform LSC powders. Finally, the sintering properties of these LSC powders were analyzed and compared with those of conventional ones.