Ammonia selective sensors based on cobalt spinel prepared by combustion synthesis.

Nano-crystalline cobalt spinel was prepared by combustion synthesis and used as ammonia sensing material. After synthesis, the powder was calcined at 600 °C for 4 h and characterized by thermal analysis, X-ray diffraction, Raman spectroscopy, X-ray Photoelectron Spectroscopy, nitrogen adsorption (B.E.T, Brunauer, Emmet, Teller and B.J.H., Barrett, Joyner, Halenda techniques), H 2 temperature programmed reduction, H 2 O adsorption and field emission scanning electron microscopy. Sensors were screen-printed onto α-alumina substrates with platinum interdigitated electrodes and fired at 700 °C for 1 h in air, after drying overnight. The sensor response was measured in the range 150 °C–250 °C under 1–50 ppm of NH 3. Best results were obtained at 225 °C, with R (the ratio between the impedance of the film under gas exposure at the equilibrium and the impedance under dry air) equal to 1.83 under 50 ppm NH 3. Response time and recovery time (e.g., the times taken by the sensor to attain 90% of total impedance change from its initial impedance value) were determined, together with cross-sensitivity tests towards CH 4 , CO, N 2 O, humidity, O 3, CO 2 and NO 2 at the best operating temperature. • Nano-crystalline Co 3 O 4 powder was synthesized by combustion synthesis. • Sensors were screen-printed with the prepared powder. • Thick films could selectively detect 1 ppm ammonia concentration at 225 °C. • Both response and recovery times of the sensor were reasonably fast (few minutes). [ABSTRACT FROM AUTHOR]