| With the rapid development of nonatechnology, nonamaterials for gas sensing applications become more widespread. Nowadaysα-Fe2O3 has been used as the third kind gas-sensing materials and gained wide application after the development of ZnO and SnO2 nanomaterials, which has high stability and selectivity. In this dissertation, a-Fe2O3 nano-poeder were synthesised by two methods, and carried on the ingredient doping. On the basis of measurements and characterizations of a-Fe2O3-based nano-powders and gas sensitive sensors, the correlativity between the synthesis and structre of powders and the characters of sensors studied in detail and the sensitive mechanism was discussed. The main conclusions can be drawn as follows:a-Fe2O3 nano-powders were made by chemistry precipitation and ultrasonic chemistry with raw materials of FeCl3 6H2O and NaOH. The experiment results showed that the a-Fe2O3 nano-powders made by two methods are of high purity with its size of 20-40nm. During the process of chemistry precipitation various sintering temperatures were used. When they were sintered at 300℃and 400℃, few by-products of y-Fe2O3 can be detected. The average diameters ofα-Fe2O3 powder were 32nm and 37nm at 500℃and 600℃,respectively. When they were sintered at 400℃for 2h and then 600℃for 0.5h, ellipsoidal-shapedα-Fe2O3 nano-powders were uniform distributed with size of 28nm, and no other impurities were found. The influence of shock power in ultrasonic chemistry on nano-powders was studied. As the shock power increases, the size of nano-powders decreases, uniform dispersion and spherical liked nano-powders with size of 20nm were obtained as the shock power reaches 81W.Based on the preparation ofα-Fe2O3 nano-powders,doping experiments were performed. By changing the concentration Sn4+,Mg2+,Ce4+ and Zr4+. respectively the doped were successfull,Tabricated. With the help of XRD,SEM and TEM. the results showed that Fe3+ has partial replaced by Sn4+,Mg2+ and Ce4+. which changes the crystal structure. Additionly, the size of a-Fe2O3 nano-powders were decreased. However, Zr4+ did not enter in the crystal ofα-Fe2O3, thus resulting the formation of ZrO2 and a-Fe2O3. The dopedα-Fe2O3 nano-powders were made by changing the concentration of ZrO2 and Y2O3 using ultrasonic chemistry method. Results showed that Y3+ enter into the crysral of a-Fe2O3, and coexistence of Zr4+ and found. The nano-powders show three morphology:rod-like,spiudle-shaped and spherical-shape.The CH4 gas-sensor properties of a-Fe2O3 doped nano-powders were studied. Among all the investigated materials, can be achieved that gas sensing ofα-Fe2O3 doped nano-poeders containing Sn4+ or Ce4+ is superior to that ofα-Fe2O3 doped nano-powders containing Zr4+ and Mg2+. When the concentration of CH4 1000ppm reaches 6.4 for doping 7mol% Ce4+ doped nao-powders. The response and recovery time for 5mol% Sn4+ doped nao-powders are 18s and 21s, respectively under the condition of 1000ppm CH4. Two phase doping ofα-Fe2O3 nano-powder increased the sensitivity of the methane gas, which reaches 9.6 for 5mol% ZrO2 and 10mol% Y2O3 doped nano-powders at 1000ppm CH4. The response-recovery time of all was around reach 20s in the atomosphere of CH4. |
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