Tungsten current price was transformed yearly to its constant price since 1900, which is roughly decomposed into four components as trend, cycle, impact and random. The core prices, consisting of the trend and the cyc...Tungsten current price was transformed yearly to its constant price since 1900, which is roughly decomposed into four components as trend, cycle, impact and random. The core prices, consisting of the trend and the cycle, present regularities that a long-run cycle is embedded within two major cycles, and major cycle is composed of low-price period and high-price period, along with the rapid rise into a tower, and along with deep down into next trough; three sharply upward shocks occur by the events in a tower. Fluctuations in prices trend to slow cycles and expand the bands. It can be expected that tungsten price will highly stand over 17 a, and is is a advice that reducing production and restricting export maybe maintain a high price level.展开更多
A hydrometallurgical process for tungsten extraction and recovery from scheelite is reported.The technology includes leaching scheelite using phosphoric acid as chelating agent in nitric acid solutions,extracting tung...A hydrometallurgical process for tungsten extraction and recovery from scheelite is reported.The technology includes leaching scheelite using phosphoric acid as chelating agent in nitric acid solutions,extracting tungsten by solvent extraction and reusing leaching agent.In the leaching process,affecting factors,such as temperature,leaching time,nitric acid and dosage of phosphoric acid,were examined on recovery of tungsten.Results show that more than 97%of tungsten could be extracted under conditions of leaching temperature of 80-90°C,HNO3 concentration of 3.0-4.0 mol/L,liquild-to-soild ratio of 10:1,H3PO4 dosage of 3 stoichiometric ratio and leaching time of 3 h.Solvent extraction was then employed for the W recovery from the leachate with a organic system of 40%(v/v)N235,30%(v/v)TBP,and 30%sulfonated kerosene.Approximately 99.93%of W was extracted and ammonium tungstate solution containing 193 g/L W was obtained with a stripping rate of 98.10%under the optimized conditions.展开更多
Modeling is essential, significant and difficult for the quality and shaping control of arc welding process. A generalized rough set based modeling method was brought forward and a dynamic predictive model for pulsed ...Modeling is essential, significant and difficult for the quality and shaping control of arc welding process. A generalized rough set based modeling method was brought forward and a dynamic predictive model for pulsed gas tungsten arc welding (GTAW) was obtained by this modeling method. The results show that this modeling method can well acquire knowledge in welding and satisfy the real life application. In addition, the results of comparison between classic rough set model and back-propagation neural network model respectively are also satisfying.展开更多
The solubility of ammonium tungstate in a special hydrothermal condition is exploited to synthesize uniform microspheres of Ce-Cu-W-O oxides.Compared to their W-undoped counterparts,they possess more Ce^3+ and oxygen ...The solubility of ammonium tungstate in a special hydrothermal condition is exploited to synthesize uniform microspheres of Ce-Cu-W-O oxides.Compared to their W-undoped counterparts,they possess more Ce^3+ and oxygen vacancies,thereby promoting oxygen mobility.The formed rich WO3 surface can effectively provide acid sites,which is helpful for adsorption of vinyl chloride and interrupting the C-Cl bond.In addition,the presence of WO3 induces the formation of finer CuO nanoparticles with respect to the traditional coprecipitation method,thereby resulting in a better reducibility.Benefiting from both the enhanced acidity and reducibility,the Ce-Cu-W-O microspheres deliver excellent low-temperature vinyl chloride oxidation activity(a reaction rate of 2.01×10^-7 mol/(gcat·s)at 250℃)and high HCl selectivity.Moreover,subtle deactivation occurs after the three cycling activity tests,and a stable vinyl chloride conversion as well as mineralization are observed during the 72-h durability test at 300℃,which demonstrates good thermal stability.Our strategy can provide new insights into the design and synthesis of metal oxides for catalytic oxidation of chlorinated volatile organic compounds.展开更多
基金Project(2013ZK2001)supported by the Major Soft Science Program of Hunan Provice,ChinaProjects(1382ZD024,13BGL105)supported by the National Social Science Foundation of China
文摘Tungsten current price was transformed yearly to its constant price since 1900, which is roughly decomposed into four components as trend, cycle, impact and random. The core prices, consisting of the trend and the cycle, present regularities that a long-run cycle is embedded within two major cycles, and major cycle is composed of low-price period and high-price period, along with the rapid rise into a tower, and along with deep down into next trough; three sharply upward shocks occur by the events in a tower. Fluctuations in prices trend to slow cycles and expand the bands. It can be expected that tungsten price will highly stand over 17 a, and is is a advice that reducing production and restricting export maybe maintain a high price level.
基金Project(51334008) supported by the National Natural Science Foundation of China
文摘A hydrometallurgical process for tungsten extraction and recovery from scheelite is reported.The technology includes leaching scheelite using phosphoric acid as chelating agent in nitric acid solutions,extracting tungsten by solvent extraction and reusing leaching agent.In the leaching process,affecting factors,such as temperature,leaching time,nitric acid and dosage of phosphoric acid,were examined on recovery of tungsten.Results show that more than 97%of tungsten could be extracted under conditions of leaching temperature of 80-90°C,HNO3 concentration of 3.0-4.0 mol/L,liquild-to-soild ratio of 10:1,H3PO4 dosage of 3 stoichiometric ratio and leaching time of 3 h.Solvent extraction was then employed for the W recovery from the leachate with a organic system of 40%(v/v)N235,30%(v/v)TBP,and 30%sulfonated kerosene.Approximately 99.93%of W was extracted and ammonium tungstate solution containing 193 g/L W was obtained with a stripping rate of 98.10%under the optimized conditions.
基金The National Natural Science Foundation of China(No 60474036)
文摘Modeling is essential, significant and difficult for the quality and shaping control of arc welding process. A generalized rough set based modeling method was brought forward and a dynamic predictive model for pulsed gas tungsten arc welding (GTAW) was obtained by this modeling method. The results show that this modeling method can well acquire knowledge in welding and satisfy the real life application. In addition, the results of comparison between classic rough set model and back-propagation neural network model respectively are also satisfying.
文摘The solubility of ammonium tungstate in a special hydrothermal condition is exploited to synthesize uniform microspheres of Ce-Cu-W-O oxides.Compared to their W-undoped counterparts,they possess more Ce^3+ and oxygen vacancies,thereby promoting oxygen mobility.The formed rich WO3 surface can effectively provide acid sites,which is helpful for adsorption of vinyl chloride and interrupting the C-Cl bond.In addition,the presence of WO3 induces the formation of finer CuO nanoparticles with respect to the traditional coprecipitation method,thereby resulting in a better reducibility.Benefiting from both the enhanced acidity and reducibility,the Ce-Cu-W-O microspheres deliver excellent low-temperature vinyl chloride oxidation activity(a reaction rate of 2.01×10^-7 mol/(gcat·s)at 250℃)and high HCl selectivity.Moreover,subtle deactivation occurs after the three cycling activity tests,and a stable vinyl chloride conversion as well as mineralization are observed during the 72-h durability test at 300℃,which demonstrates good thermal stability.Our strategy can provide new insights into the design and synthesis of metal oxides for catalytic oxidation of chlorinated volatile organic compounds.
