A Highly Selective Room Temperature NH3 Gas Sensor based on Nanocrystalline a-Fe2O3

Nanocrystalline a-Fe2O3 powder was synthesized by simple, inexpensive sol-gel method. The obtained powder was calcined at 700 0C in air atmosphere for 2 hours. The structural and morphological properties of calcined powder were studied by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) respectively. Thermal properties of dried gel were studied by Thermogravimetric Analysis/Differential Scanning Calorimetry (TGA/DSC). The XRD pattern of the powder confirmed the a-Fe2O3 (hematite) phase of iron oxide with average crystalline size of 30.87 nm calculated from Scherrer equation. The FESEM images showed uniform wormlike morphology of a-Fe2O3 powder. TGA result indicated that a-Fe2O3 is thermodynamically stable. Room temperature NH3 sensing characteristics of a-Fe2O3 were studied for various concentration levels (250-2500 ppm) of NH3 at various humid conditions. The sensor based on a-Fe2O3 exhibited good selectivity and excellent sensitivity (S=92) towards 1000 ppm of NH3 with quick response of 4 sec and fast recovery of 9 sec. Room temperature sensing mechanism is also discussed

Characterizations of Ultrasonically Prepared Nanostructured ZnO powder and NH3 Sensing Performance of its Thick Film Sensor

AbstractIn the present investigation nanostructured ZnO powder was prepared using ultrasonic atomization method. An aqueous solution of Zn (NO3)2 *6H2O was atomised using ultrasonic atomizer. The prepared nanostructured ZnO powder was collected using a simple but novel trapping system. The powder was characterized using XRD, TEM, SEM and EDAX. Nanostructured thick-film sensors of this powder were prepared by using the simple screen printing technique. The gas sensing performance of this film was tested. The sensor was found to be most sensitive to NH3