In our laboratory, two types of sensors using solid state electrolyte have been developed. These sensors can measure NOx in real time; one of these sensors is for controlling the denitrification process in the boiler exhaust, and the other is for monitoring NOx in the atmosphere.

1. The sensor for monitoring NOx in the boiler exhaust

For the denitrification process of the boiler exhaust, the contact catalytic reduction method using ammonia or urea has been mainly used. But an ammonia injection process utilizing the sensor which has superior features including, quick response, lower running cost, etc. is expected to achive more effective denitrification than the previous method; moreover it can dispense with an expensive continuous analyzer.

In our laboratory, some kinds of solid state electrolytes, that is, stabilized zirconia, NASICON, silver composites and solid polymer electrolytes (SPE), were evaluated for the selection of the most appropriate material, and obtained lots of information on the basic properties of these materials for the said purpose. Especially, the sensor using the stabilized zirconia has high sensitivity to both NO and NO2, and is expected to be applicable for practical use.

2. The sensor for monitoring NOx in the atmosphere

A potentiostatic electrolysis NOx sensor, an application of SPE; which has high sensitivity has been developed; it has been confirmed that this sensor can detect NOx in the atomosphere up to the order of 0.01 ppm. This sensor is so small that it can be integrated in a portable instrument, which has the merit of monitoring atmosphere at any place in real time. The major features of the sensor are as follows.

* Small size & weight : 24 mm dia. × 50 mm. 20 g (weight)

* resolution : NO: 0.1 ppm , NO2: 0.01 ppm

* linearity : ≦± 5 %FS

* reproducibility : ≦± 5 %FS

* response time : ≦ 20 sec (90% r esponse time)