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WO2 is the important intermediate product during the carbothermal reduction of WO3 to WC, and the systematical analysis of the reduction behavior of WO3 to WO2 has a significant role on the efficient preparation of WC. Reaction behavior of carbothermal reduction of WO3 to WO2 was investigated with adaptation of thermogravimetric (TG), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and thermodynamic calculation technologies. Influences of different parameters, such as reduction temperature, C/WO3 molar ratio, and reaction time, on the phase transition and morphological evolution during the process were considered. Results of non-isothermal reduction experiment from room temperature to 1200 ℃ showed that WO3 was preferentially reduced into WO2.72, then to WO2, and finally to metallic W. Phase transition law agreed well with thermodynamic theoretical calculation result. In the range of 1000 to 1050 ℃, with the increase of C/WO3 molar ratio, the relative content of WO2.72 in the reaction product gradually decreased, while that of WO2 increased. Single-phase WO2 can be prepared at the C/WO3 molar ratio of 1.1. However, when the C/WO3 molar ratio increased to 1.2, W formed due to the excess C. During the whole carbothermal reduction process, granular WO3 was first in contact with honeycomb activated carbon. As the increase of reaction time, heat transfer process began and then chemical reaction between the two reactants occurred to form columnar WO2.72. Subsequently, the columnar WO2.72 was further reduced into elliptical WO2. Based on experimental results, the optimal conditions for preparing well-dispersed WO2 were determined as follows: reduction temperature of 1050 ℃, C/WO3 molar ratio of 1.1, and reaction time of 90 min.
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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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