Thick film odor sensor with y-Fe_2O_3 semiconductor oxide

摘要

gamma-Fe_2O_3 is a n-type semiconductor oxide and it has been extensively studied as a gas sensing material. It is usually obtained by oxidizing Fe_3O_4 at 250 deg C, temperature confirmed by the DTA curve. gamma -Fe_2O_3 has a spinel type crystal structure with a lattice parameter of 8,3 A and can be expressed in the following form: Fe~(3+).[square _(1/3) .(Fe~(3+)_5/3]. O_4 where square: cation vacancy The gamma-Fe_2O_3 and Fe_3O_4 can be converted from one to the other by a reversible oxidation-reduction process in the gases atmosphere The microstructure of the gamma-Fe_2O_3 observed by scanning electron microscopy consist of columnar grains of 0.2-0,5 mu rn. a porosity of 57 percent and specific surface area of 16 m~2/g. The sensor is obtained by thick film technology. An alumina substrate was used. On one side of the substrate was screen-printed an interdigitated array electrode using a conductive Pd-Ag ink. A thick film heater by resistive ink was pasted on the other side of the substrate. The sensitive ink was prepared from gamma -Fe_2O_3 with a little amounts by TiO_2 and PdCl_2. The sensitive ink was screen-printed on the side with electrode of the substrate in a thickness of 50 mu m and heat treated at 380 deg C for 2 hours. The sensor was tested in a vacuum oven DUO-VAC. The electrical resistance in pure air was 1,8 MOMEGA and decrease in gases atmosphere. For 1000 ppm acetone, ethanol, cigarette's smoke, mercaptan, toluene the sensibilities were 93 percent, 89percent, 81percent. 75percent and 39percent, for 300 deg C working temperature. The response time 0f the sensor was 10 seconds.