A technique for preparing perovskite type oxides was developed. By this technique, ultra fine particles of La 0.9 RE 0.1 MnO 3 (RE: Y, Ce, Pr, Sm, Gd,or Dy) with high surface area and single perovskite stru...A technique for preparing perovskite type oxides was developed. By this technique, ultra fine particles of La 0.9 RE 0.1 MnO 3 (RE: Y, Ce, Pr, Sm, Gd,or Dy) with high surface area and single perovskite structure were prepared, and the series of La 0.9 RE 0.1 MnO 3 catalysts were studied experimentally. The so prepared ultra fine particles exhibites high catalytic activity for CH 4 total oxidation. The ultra fine particles of La 0.9 RE 0.1 MnO 3 (except for La 0.9 Pr 0.1 MnO 3) prepared by this method are thermally much more stable than LaMnO 3. Of the La 0.9 RE 0.1 MnO 3 series, La 0.9 Y 0.1 MnO 3 is most thermally stable, and La 0.9 Y 0.1 MnO 3 or La 0.9 Gd 0.1 MnO 3 (varies with calcination temperature) exhibits the highest catalytic activity for total oxidation of methane. The specific surface area of La 0.9 Y 0.1 MnO 3 calcined at 1000 ℃ reaches 14.9 m 2·g -1 , while the specific surface area of LaMnO 3 calcined at the same temperature is only 1.8 m 2·g -1 .展开更多
Particle number and mass concentrations were measured in Beijing during the winter and summer periods in 2003, together with some other parameters including black carbon (BC) and meteorological conditions. Particle ma...Particle number and mass concentrations were measured in Beijing during the winter and summer periods in 2003, together with some other parameters including black carbon (BC) and meteorological conditions. Particle mass concentrations exhibited low seasonality, and the ratio of PM2.5/PM10 in winter was higher than that in summer. Particle number size distribution (PSD) was characterized by four modes and exhibited low seasonality. BC was well correlated with the number and mass concentrations of accumulation and coarse particles, indicating these size particles are related to anthropogenic activities. Particle mass and number concentrations (except ultra-fine and nucleation particles) followed well the trends of BC concentration for the majority of the day, indicating that most particles were associated with primary emissions. The diurnal number distributions of accumulation and coarse mode particles were characterized by two peaks.展开更多
Oxidative stress and hydroxyl radicals (·OH) play important roles in adverse health effects caused by inhalable ambient air particles (PM10). The ultra-fine fraction of PM10 has been hypothesized as one of the cr...Oxidative stress and hydroxyl radicals (·OH) play important roles in adverse health effects caused by inhalable ambient air particles (PM10). The ultra-fine fraction of PM10 has been hypothesized as one of the critical contributors to ·OH generation. Both in vivo and in vitro studies have shown that ultra-fine particles (UFPs) or nano-particles generate more ·OH than larger particles with identical mass and composition. Both the surface area and surface-adsorbed redox-active metals have been suggested as factors to determine the oxidative capacity of UFPs. In this study, the ·OH-generating capability of dif-ferent sizes of SiO2 particles was investigated in order to determine which factor influences particle-induced ·OH generation. The amount of ·OH generated in both acellular and cellular systems was quantified using a capillary electrophoresis method following exposure to SiO2 particles with diameters of 14, 100, and 500 nm. The amount of ·OH was strongly dependent on particle size, and a significant enhancement was observed only with 14 nm particles. Further studies indicated a close association between ·OH and iron ion concentration (R2 = 0.812, p<0.01). Washed particles, with their surface iron being removed, did not generate ·OH. The iron-containing leachate from these washings was able to enhance ·OH production as untreated particles did. Therefore, the presence of adsorbed iron on the surface of the SiO2 particles is presented as a possible mechanism of UPFs-induced ·OH generation. The SiO2 acted as an inert substrate, and the surface of ultra-fine SiO2 particles acted as a carrier for iron.展开更多
A conductive polymeric composite containing in situ ultra-fine metal particles is prepared by melt blending. Incorporation of elastomeric nano-particles and carbon nanotubes hinders the coalescing of metal particles a...A conductive polymeric composite containing in situ ultra-fine metal particles is prepared by melt blending. Incorporation of elastomeric nano-particles and carbon nanotubes hinders the coalescing of metal particles and causes a shift to the breakup direction in the breakup/coalescence equilibrium of metal particles. The prime metal particles （about 26 μm） are in situ converted into the ultra-fine metal particles （UFMP, about 932 nm）. The network of carbon nanotubes has been improved due to in situ ultra-fine metal particles and the percolation threshold of the composite with 1.96 vol% UFMP is only 0.25 vol% carbon nanotubes.展开更多
采用考虑颗粒脉动流动对气相湍流流动影响的大涡模拟(LES)研究气相湍流,采用直接模拟蒙特卡罗方法(DSMC)模拟颗粒间的碰撞。单颗粒运动满足牛顿第二定律,颗粒相和气相相间作用的双向耦合由牛顿第三定律确定,考虑超细颗粒间的van der Wa...采用考虑颗粒脉动流动对气相湍流流动影响的大涡模拟(LES)研究气相湍流,采用直接模拟蒙特卡罗方法(DSMC)模拟颗粒间的碰撞。单颗粒运动满足牛顿第二定律,颗粒相和气相相间作用的双向耦合由牛顿第三定律确定,考虑超细颗粒间的van der Waals作用力。数值模拟垂直管内超细颗粒气固两相流动,对颗粒相速度、浓度以及团聚物流动过程进行分析。展开更多
文摘A technique for preparing perovskite type oxides was developed. By this technique, ultra fine particles of La 0.9 RE 0.1 MnO 3 (RE: Y, Ce, Pr, Sm, Gd,or Dy) with high surface area and single perovskite structure were prepared, and the series of La 0.9 RE 0.1 MnO 3 catalysts were studied experimentally. The so prepared ultra fine particles exhibites high catalytic activity for CH 4 total oxidation. The ultra fine particles of La 0.9 RE 0.1 MnO 3 (except for La 0.9 Pr 0.1 MnO 3) prepared by this method are thermally much more stable than LaMnO 3. Of the La 0.9 RE 0.1 MnO 3 series, La 0.9 Y 0.1 MnO 3 is most thermally stable, and La 0.9 Y 0.1 MnO 3 or La 0.9 Gd 0.1 MnO 3 (varies with calcination temperature) exhibits the highest catalytic activity for total oxidation of methane. The specific surface area of La 0.9 Y 0.1 MnO 3 calcined at 1000 ℃ reaches 14.9 m 2·g -1 , while the specific surface area of LaMnO 3 calcined at the same temperature is only 1.8 m 2·g -1 .
文摘Particle number and mass concentrations were measured in Beijing during the winter and summer periods in 2003, together with some other parameters including black carbon (BC) and meteorological conditions. Particle mass concentrations exhibited low seasonality, and the ratio of PM2.5/PM10 in winter was higher than that in summer. Particle number size distribution (PSD) was characterized by four modes and exhibited low seasonality. BC was well correlated with the number and mass concentrations of accumulation and coarse particles, indicating these size particles are related to anthropogenic activities. Particle mass and number concentrations (except ultra-fine and nucleation particles) followed well the trends of BC concentration for the majority of the day, indicating that most particles were associated with primary emissions. The diurnal number distributions of accumulation and coarse mode particles were characterized by two peaks.
基金Supported by the National Basic Research Priorities Program (Grant No. 2002CB410802)the National Natural Science Foundation of China (Grant No. 20637020)
文摘Oxidative stress and hydroxyl radicals (·OH) play important roles in adverse health effects caused by inhalable ambient air particles (PM10). The ultra-fine fraction of PM10 has been hypothesized as one of the critical contributors to ·OH generation. Both in vivo and in vitro studies have shown that ultra-fine particles (UFPs) or nano-particles generate more ·OH than larger particles with identical mass and composition. Both the surface area and surface-adsorbed redox-active metals have been suggested as factors to determine the oxidative capacity of UFPs. In this study, the ·OH-generating capability of dif-ferent sizes of SiO2 particles was investigated in order to determine which factor influences particle-induced ·OH generation. The amount of ·OH generated in both acellular and cellular systems was quantified using a capillary electrophoresis method following exposure to SiO2 particles with diameters of 14, 100, and 500 nm. The amount of ·OH was strongly dependent on particle size, and a significant enhancement was observed only with 14 nm particles. Further studies indicated a close association between ·OH and iron ion concentration (R2 = 0.812, p<0.01). Washed particles, with their surface iron being removed, did not generate ·OH. The iron-containing leachate from these washings was able to enhance ·OH production as untreated particles did. Therefore, the presence of adsorbed iron on the surface of the SiO2 particles is presented as a possible mechanism of UPFs-induced ·OH generation. The SiO2 acted as an inert substrate, and the surface of ultra-fine SiO2 particles acted as a carrier for iron.
文摘A conductive polymeric composite containing in situ ultra-fine metal particles is prepared by melt blending. Incorporation of elastomeric nano-particles and carbon nanotubes hinders the coalescing of metal particles and causes a shift to the breakup direction in the breakup/coalescence equilibrium of metal particles. The prime metal particles （about 26 μm） are in situ converted into the ultra-fine metal particles （UFMP, about 932 nm）. The network of carbon nanotubes has been improved due to in situ ultra-fine metal particles and the percolation threshold of the composite with 1.96 vol% UFMP is only 0.25 vol% carbon nanotubes.
文摘采用考虑颗粒脉动流动对气相湍流流动影响的大涡模拟(LES)研究气相湍流,采用直接模拟蒙特卡罗方法(DSMC)模拟颗粒间的碰撞。单颗粒运动满足牛顿第二定律,颗粒相和气相相间作用的双向耦合由牛顿第三定律确定,考虑超细颗粒间的van der Waals作用力。数值模拟垂直管内超细颗粒气固两相流动,对颗粒相速度、浓度以及团聚物流动过程进行分析。
