Cobalt spinel via solution combustion synthesis as an ammonia sensing material

Nano-crystalline cobalt oxide (Co3O4) was prepared by solution combustion synthesis (SCS) and used as ammonia sensing material. The obtained powder was characterized by laser granulometry, thermal analysis, X-ray diffraction, X-ray Photoelectron Spectroscopy, nitrogen adsorption (B.E.T -Brunnauer, Emmet, Teller- technique), Raman spectroscopy, field emission scanning electron microscopy and transmission 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’s response (R) was defined as the ratio between the impedance of the film under gas exposure at the equilibrium and the impedance under dry air and was measured in the range 150°C – 250°C under 1 – 50 ppm of NH3. 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 also determined. Best results were obtained at 225°C, with R equal to 1.83 under 50 ppm exposure to NH3.