Resistive Oxygen Gas Sensors Using Cerium Oxide Nanosized Powder
- PDF / 2,648,266 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 91 Downloads / 220 Views
A3.2.1/K4.2.1
Resistive Oxygen Gas Sensors Using Cerium Oxide Nanosized Powder Norimitsu Murayama, Noriya Izu, Woosuck Shin, and Ichiro Matsubara National Institute of Advanced Industrial Science and Technology, Nagoya 463-8560, Japan, ABSTRACT Cerium oxide nanosized powder was synthesized by modified precipitation method. The precipitate, which was formed from the addition of NH4OH to Ce(NO3)3 aqueous solution, and was filtered. The obtained gel was mixed with carbon powder with a particle size of about 20 nm by a mechanically rotating mixer. The mixture was dried at 343 K in air. The carbon powder was burned out by heat treatment at 1173 K in air for 4 h, resulting in the formation of CeO2 powder with a size of 50 nm. A thick film was formed on an alumina substrate by screen printing, and was fired at 1373 K. The thick film had porous structure and the grain size was about 120 nm. The resistance of the thick film was almost proportional to P(O2)1/6, where P(O2) is oxygen partial pressure, in the P(O2) range from 10-13 to 105 Pa at 1073 and 1173 K. The response time (t90) was 23 and 7 ms at 1023 K when P(O2) changed from 65 to 25 kPa and 25 to 65 kPa, respectively. The reason for this result was explained on the basis of surface reaction of cerium oxide grain. INTRODUCTION Emission control regulations for two-wheeled vehicles have been tightened globally. The electrical fuel injection (EFI) control system will be introduced to two-wheel vehicles as well as to four-wheel vehicles. Another future technology in EFI control system is controlling each cylinder during combustion for reducing emission and improving efficiency [1]. Assuming a four-cylinder motor with a fuel injection for every cylinder running at 3000 rpm, then the motor control system injects fuel 100 times per second. To make the every cylinder balanced, the sensor should measure oxygen partial pressure at least below 10 ms. In order to develop such new EFI control systems, we need oxygen gas sensors with small size, fast response and low cost. Resistive oxygen gas sensors are promising candidates for responding to such specifications. They can be easily miniaturized because they have thick film structure. The subject to be solved is shortening response time. The operating principle of resistive oxygen gas sensors is that the electrical conductivity of oxide semiconductor changes with the amounts of oxygen deficiency [2]. From the principle, large diffusion coefficient for oxygen vacancy in oxide semiconductor and/or small grain size of oxide semiconductor result in decreasing the response time. Cerium oxide (CeO2) is suitable material for the sensors, since it has large diffusion coefficient for oxygen vacancy [3]. Several works about CeO2 resistive oxygen sensors have been reported. [4-10] In our previous work [7], it was confirmed that the response time decreased with decreasing grain size using cerium oxide nanosized powder prepared by mist pyrolysis method. And it was found that the response time when oxygen partial pressure suddenly changes from a
Data Loading...
