: Nitrogen oxides are among environmental pollutants that are very dangerous for human health. The main emission sources of nitrogen oxides are traort, oil and gas industries. Nitrogen oxides are poisonous and cause respiratory problems for humans. The detection of nitrogen oxides is also important in security applications because they are a good marker of explosives and narcotics. Metal oxide gas sensors can detect a wide range of flammable and toxic gases, including carbon monoxide, nitrogen oxides, methane, alcohols and hydrogen. These sensors have important advantages including simple structure, high sensitivity and low cost that makes them suitable for most of the gas analysis applications. The aim of this project was to fabricate and characterize nitrogen oxide sensors based on tin oxide semiconductor. Sensitive layer of the sensors were produced by paste casting and cold press methods. The fabrication process was repeated to study the effect of the process parameters on the sensing performance of the samples. The studied parameters include the amount of additive, sintering temperature and grain size. The microstructure of metal oxide powders and fabricated pellets were analyzed by SEM, DLS, BET and XRD tests. A simple sensor assembly was made for rapid testing of the samples. The assembly includes a micro-hotplate for adjusting the sensor temperature and two magnet electrodes for holding the sensing layer and measurement of its electrical resistance. An experimental setup was implemented to carry out the gas exposure tests in a safe manner. By this setup, nitrogen oxide is produced by thermal decomposition of lead nitrate powder. Many experiments were designed and carry out the measure the steady state and transient response of the fabricated gas sensors in test atmospheres. The effect of gas type, gas concentration and operating temperature on the sensor response were investigated experimentally. The results show that zinc oxide additive, sintering temperature and Pressure press have considerable effect on the sensing characteristics of tin oxide thick films. Sensors made with the same conditions were more sensitive at lower sintering temperatures. Keywords: Gas Detection, Metal Oxide Sensors, Tin Oxide, Nitrogen Oxides, Environmental Pollutants.
