Full
ZHAO Fang (1982-), famale, Master, Associate Professor. E-mail: zhaofang19821106@163.com
Outline
La3+-doped SnO2 hollow micro/nanospheres were prepared by electrospray and calcination techniques with lanthanum nitrate, stannous chloride and polyvinylpyrrolidone (PVP) as raw materials. The formation mechanism of hollow structure was analyzed. The crystalline phase and micromorphology of the samples were examined by thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The microwave absorption properties of La3+-doped SnO2 were determined by a vector network analyzer. The results show that La3+-doped SnCl2/PVP precursor polymer appears smooth spheres with the diameters of 0.5-2.2 μm. The pure rutile structure of SnO2 forms at 600 ℃, and La3+ doping does not change the crystal structure. La3+-doped SnO2 micro/nanospheres appear to be a hollow structure, and the surfaces are made up of massive small particles. The optimum microwave absorption properties of La3+-doped SnO2 hollow micro/nanospheres with the matching thickness of 2 mm can be obtained when the doping ratio of La3+ is 0.6% (in mole). The minimum reflectivity can reach -29 dB at 11.1 GHz, and the frequency band with a reflectivity less than -10 dB is 10.0-13.0 GHz. When the doping ratio of La3+ is 0.6%, the minimum reflectivity of La3+-doped SnO2 hollow micro/nanospheres shifts to a low frequency as the matching thickness increases. The matching thickness is 4 mm at lower than 8 GHz, thus obtaining the optimum microwave absorption properties. The minimum reflectivity can reach -27 dB at 4.9 GHz, and the frequency band with a reflectivity less than -10 dB is 4.5-5.8 GHz.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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