| Summary: | 碩士 === 逢甲大學 === 材料科學所 === 99 === In this research, crystalline and amorphous WO3-x nanopowder was produced by gas condensation (i.e., GC) and spray pyrolysis (SP) methods. For GC method, commercial tungsten oxide powder was used as the precursor and, by controlling partial pressure of helium and oxygen, amorphous W5O14, crystalline W19O55 and WO3 nanoparticles can be prepared. For SP method, ammonium tungstate para pentahydrate was used as the precursor and, by controlling pyrolysis temperature, amorphous W5O14 and crystalline WO3 nanoparticles can be obtained. Both GC and SP powder was analyzed by TGA, XRD, XPS, FESEM, HRTEM, in-situ XRD and BET to reveal their fundamental structure, composition and surface morphology. Besides, the as–prepared powder was used to prepare MOS gas sensing device and their gas sensing performances were investigated.
Experimental results showed that the particles were consisted of amorphous and crystalline structures. GC powder was octahedron-shaped particles, ranged from 7-60 nm, and exhibited rough surface. The SP powder, however, were smooth and solid spheres with a particle size ranged from 371 to 392 nm.
Gas sensing results showed that the optimum operating temperatures ranged from 75 to 125 oC, with a sensitivity ranged from 3 to 323. Among all the samples, W5O14 powder prepared by GC method exhibited the best gas sensing performance. When tested under 11 ppm NO2 concentration at a temperature of 75 oC, the highest sensitivity of 323 can be observed.
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