In this paper Cu-WS2-graphite-WS2nanotube composites were fabricated by powder metallurgy hot pressing method.The effect of current polarity on the wear rates and contact voltage drops of the composites were investiga...In this paper Cu-WS2-graphite-WS2nanotube composites were fabricated by powder metallurgy hot pressing method.The effect of current polarity on the wear rates and contact voltage drops of the composites were investigated using a brush-on-slip ring tribometer rubbing against Cu-5 wt.%Ag alloy ring in air and vacuum,respectively.The worn surfaces of the composites were analyzed by scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy(XPS).Surface profile curves of the worn tracks were measured using the surface profiler.The results demonstrated that the current polarity has a significant effect on the wear rates and contact voltage drops of the composites in both air and vacuum conditions.Positive brush possesses a higher wear rate compared with the negative brush in the air atmosphere since the electrical field direction activates oxidation at the positive brush surface while inhibits oxidation at the negative brush surface.Except for the regular wear losses,the combined effect of molten metal bridge erosion and arc erosion cause the positive brush to lose extra material and the negative brush to gain extra material,so the positive brush shows a higher wear rate in the vacuum condition.The contact voltage drop of the positive brush is lower than that of the negative brush in the air atmosphere,but contrarily,the positive brush shows a higher contact voltage drop in the vacuum condition.展开更多
We reported the dielectric properties of CaCu3Ti4O12 in the temperature range from room temperature to 800℃ and the frequency range from 20 Hz to 10 MHz.Apart from the widely reported dielectric anomaly occurring aro...We reported the dielectric properties of CaCu3Ti4O12 in the temperature range from room temperature to 800℃ and the frequency range from 20 Hz to 10 MHz.Apart from the widely reported dielectric anomaly occurring around 200℃,three additional dielectric anomalies were found.The new anomalies are very sensitive to electrode sintering conditions and annealing atmospheres,indicating that they are dependent not only on the electrode-sample contact but also on oxygen vacancies.展开更多
ZnO nanorods prepared by a solution-phase method are annealed at different temperatures in oxygen ambient.The luminescence properties of the samples are investigated.In the same excitation condition,the photoluminesce...ZnO nanorods prepared by a solution-phase method are annealed at different temperatures in oxygen ambient.The luminescence properties of the samples are investigated.In the same excitation condition,the photoluminescence(PL) spectra of all samples show an ultraviolet(UV) emission and a broad strong visible emission band.The asymmetric visible emis-sion band of annealed samples has a red-shift as the annealing temperature increasing from 200 ℃ to 600 ℃ and it can be deconvoluted into two subband emissions centered at 535 nm(green emission) and 611 nm(orange-red emission) by Gaussian-fitting analysis.Analyses of PL excitation(PLE) spectra and PL spectra at different excitation wavelengths reveal that the green emission and the orange-red emission have a uniform initial state,which can be attributed to the electron transition from Zn interstitial(Zni) to oxygen vacancy(Vo) and oxygen interstitial(Oi),respectively.展开更多
In this paper, we presented a novel method for the facile and efficient one-pot synthesis of 2-arylbenzoxazoles, which were directly synthesized from 2-aminophenol and aldehydes catalyzed by hydrogen tetrachloroaurate...In this paper, we presented a novel method for the facile and efficient one-pot synthesis of 2-arylbenzoxazoles, which were directly synthesized from 2-aminophenol and aldehydes catalyzed by hydrogen tetrachloroaurate (HAuCl4·4H2O) under an oxygen atmosphere with anhydrous tetrahydrofuran (THF) as solvent or in solvent-free condition. The results show that this method could bring excellent yields as high as 96%. THF was proven to be the best choice among several solvents screened and the reaction was tolerated with a variety of aromatic aldehydes possessing electron-donating or withdrawing groups. The advantages of the present method lie in catalytic process using economic and environmentally benign dioxygen as oxidant.展开更多
基金supported by the Major Research Program of the National Natural Science Foundation of China(Grant No.91026018)the National Natural Science Foundation of China(Grant No.60979017)the Doctoral Fund of Ministry of Education of China(Grant No.20110111110015)
文摘In this paper Cu-WS2-graphite-WS2nanotube composites were fabricated by powder metallurgy hot pressing method.The effect of current polarity on the wear rates and contact voltage drops of the composites were investigated using a brush-on-slip ring tribometer rubbing against Cu-5 wt.%Ag alloy ring in air and vacuum,respectively.The worn surfaces of the composites were analyzed by scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy(XPS).Surface profile curves of the worn tracks were measured using the surface profiler.The results demonstrated that the current polarity has a significant effect on the wear rates and contact voltage drops of the composites in both air and vacuum conditions.Positive brush possesses a higher wear rate compared with the negative brush in the air atmosphere since the electrical field direction activates oxidation at the positive brush surface while inhibits oxidation at the negative brush surface.Except for the regular wear losses,the combined effect of molten metal bridge erosion and arc erosion cause the positive brush to lose extra material and the negative brush to gain extra material,so the positive brush shows a higher wear rate in the vacuum condition.The contact voltage drop of the positive brush is lower than that of the negative brush in the air atmosphere,but contrarily,the positive brush shows a higher contact voltage drop in the vacuum condition.
基金supported by the National Natural Science Foundation of China(11074001)
文摘We reported the dielectric properties of CaCu3Ti4O12 in the temperature range from room temperature to 800℃ and the frequency range from 20 Hz to 10 MHz.Apart from the widely reported dielectric anomaly occurring around 200℃,three additional dielectric anomalies were found.The new anomalies are very sensitive to electrode sintering conditions and annealing atmospheres,indicating that they are dependent not only on the electrode-sample contact but also on oxygen vacancies.
基金supported by the National Natural Science Foundation of China(Nos.60877029,10904109,60977035 and 60907021)the Natural Science Foundation of Tianjin(Nos.09JCYBJC01400 and 10SYSYJC28100)+1 种基金the Key Subject for Materials Physics and Chemistry of Tianjinthe Open Foundation of Key Laboratory of Luminescence and Optical Information of Ministry of Education(Nos.2010LOI02 and 2010LOI11)
文摘ZnO nanorods prepared by a solution-phase method are annealed at different temperatures in oxygen ambient.The luminescence properties of the samples are investigated.In the same excitation condition,the photoluminescence(PL) spectra of all samples show an ultraviolet(UV) emission and a broad strong visible emission band.The asymmetric visible emis-sion band of annealed samples has a red-shift as the annealing temperature increasing from 200 ℃ to 600 ℃ and it can be deconvoluted into two subband emissions centered at 535 nm(green emission) and 611 nm(orange-red emission) by Gaussian-fitting analysis.Analyses of PL excitation(PLE) spectra and PL spectra at different excitation wavelengths reveal that the green emission and the orange-red emission have a uniform initial state,which can be attributed to the electron transition from Zn interstitial(Zni) to oxygen vacancy(Vo) and oxygen interstitial(Oi),respectively.
基金Project supported by the Natural Science Foundation of Zhejiang Province (No. Y407168)the Opening Foundation of Zhejiang Provincial Top Key Discipline, China
文摘In this paper, we presented a novel method for the facile and efficient one-pot synthesis of 2-arylbenzoxazoles, which were directly synthesized from 2-aminophenol and aldehydes catalyzed by hydrogen tetrachloroaurate (HAuCl4·4H2O) under an oxygen atmosphere with anhydrous tetrahydrofuran (THF) as solvent or in solvent-free condition. The results show that this method could bring excellent yields as high as 96%. THF was proven to be the best choice among several solvents screened and the reaction was tolerated with a variety of aromatic aldehydes possessing electron-donating or withdrawing groups. The advantages of the present method lie in catalytic process using economic and environmentally benign dioxygen as oxidant.
