| 摘要 |
PROBLEM TO BE SOLVED: To enhance the dependence of the concentration of CO of a CO sensor by adding Ir in a specific unit in terms of a metal to SnO2 as a gas-sensitive material for the CO sensor. SOLUTION: A sintered compact (a chip-shaped sintered compact or a thick- film sintered compact formed on an insulating substrate) which uses SnO2 as a gas-sensitive material is sintered, e.g. at a temp. of 500 to 850 deg.C. After that, the sintered compact is impregnated with the solution of an Ir compound in such a way that the addition amount of Ir to the SnO2 becomes 5 to 500μg/g SnO2 in terms of a metal. Then, the impregnated Ir compound is decomposed by thermal decomposition, hydrogen reduction or the like, and the Ir is added to the SnO2. At this time, the temperature of the thermal decomposition is set, e.g. at a temp. of about 500 to 850 deg.C. When the Ir at 5μg/g SnO2 or higher is added, the dependenceαon the concentration of Co of a Co sensor is increased. When the addition amount of the Ir is increased, a sensor resistance Rs is increased. The addition amount of the Ir is set at 500μg/g SnO2 or lower, and a resistance value Rs which is suitable for practical use is obtained. In addition, when an Ir-Pt composite catalyst is added, the dependence on humidity of the CO sensor can be suppressed.
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