Adsorption of block copolymers in nanoporous alumina

We have studied the adsorption of end-attaching block copolymer chains inside the cylindrical pores of nanoporous alumina. Highly asymmetric PS-PEO block copolymers, with a small PEO anchoring block and a long PS dangling block, were allowed to adsorb onto porous alumina substrates with an average pore diameter of ∼200 nm from toluene solution. The adsorption process was monitored using FTIR spectroscopy, whereas depth profile analysis was performed by means of XPS and Ar⁺ ion sputtering. It is found that the PS-PEO adsorption kinetics in porous alumina are ∼4 orders of magnitude slower than the corresponding case of a flat alumina substrate. It appears that chains adsorbed near the pore entrance early on tend to form a barrier for chains entering the pore at later times, thereby slowing down the adsorption process significantly. This effect is much more pronounced for large chains whose dimensions are comparable with the pore diameter. The equilibrium adsorbance value is also affected by chain size due to the additional entropic penalty associated with chain confinement, the adsorbance falling substantially when the chain dimensions become comparable with the pore diameter. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1676–1682, 2010     

固体多核 NMR 研究 Mo/Hβ-Al2O3 催化剂在烯烃歧化反应中的积炭

 采用固体多核 13C, 27Al 及 29Si MAS NMR 结合吸附气体 Xe 后的 129Xe NMR, 详细研究了乙烯和 2-丁烯歧化生成丙烯反应过程中 6%Mo/Hβ-Al2O3 催化剂上积炭的类型和落位. 结果表明, 积炭以饱和烷烃为主, 并随着反应的进行生成更多的支链烷烃, 积炭主要分布在 Hβ 分子筛上, 并主要落位在分子筛的交叉孔道处.     

透明陶瓷透光性能的影响因素

 研究了影响激光透明陶瓷透光性能的主要因素,讨论了陶瓷内部气孔和杂质颗粒等散射粒子、晶界结构中晶界折射率与晶粒折射率的差异以及晶界表面粗糙度等因素对陶瓷透光性能的影响,并定量分析了激光陶瓷透过率随气孔尺寸、气孔率、晶粒相对晶界折射率以及晶界表面粗糙度的变化关系。结果表明： 陶瓷的透过率随着气孔率的减小而增大,但透过率随气孔尺寸的增大而呈现出周期性振荡,且当气孔尺寸与入射光波长可比拟时,陶瓷的透过率会明显降低;在晶界结构中,晶界的折射率与晶粒的折射率相差越小,陶瓷的透过率就越高;晶界表面粗糙度越大,透过率越低。然而,晶界折射率不同于晶粒折射率,这使得其陶瓷透过率降低的程度比对晶界表面粗糙度的影响明显得多。在陶瓷制备过程中,需要重点排除尺寸与入射波长可比拟的气孔, 以抑制晶界结构中第二相的产生。     

Electrical and thermal properties of lead titanate glass ceramics

Glass samples with composition of (50−X)PbO-(25+X)TiO₂-25B₂O₃ (where X=0, 5, 10 and 12.5 mol%) were prepared using conventional quenching technique. The glass transition temperature, T_g and crystallization temperature T_c were determined from the DTA. These glass samples were converted to glass ceramics by following two stage heat treatment schedule. The glass ceramic samples were characterized by XRD, SEM and dielectric constant measurements. The XRD results revealed the formation of ferroelectric lead titanate (PT) as a major crystalline phase in the glass ceramics. The density increases and the CTE decreases for all glass ceramics with increase in X (mol%). This may be attributed to increase in PT phase. The SEM results which show rounded crystallites of lead titanate, also supports other results. Hysteresis loops observed at room temperature confirms the ferroelectric nature of glass ceramics. The optimized glass ceramic sample exhibits high dielectric constant which is of technical importance.     

Effect of environment and heat treatment on the optical properties of RF-sputtered SnO2 thin films

Thin films of SnO₂ were deposited by RF-magnetron sputtering on quartz substrates at room temperature in an environment of Ar and O₂. The XRD pattern shows amorphous nature of the as-deposited films. The optical properties were studied using the reflectance and transmittance spectra. The estimated optical band gap (E_g) values increase from 4.15 to 4.3 eV as the Ar gas content decreases in the process gas environment. The refractive index exhibits an oscillatory behavior that is strongly dependent on the sputtering gas environment. The Urbach energy is found to decrease with increase in band gap. The band gap is found to decrease on annealing the film. The role of oxygen defects is explored in explaining the variation of optical parameters.     

X-ray photoelectron spectroscopy of Sm-doped CaO-MgO-Al2O3-SiO2 glasses and glass ceramics

Sm³⁺ doped CaO-MgO-Al₂O₃-SiO₂ glass and glass ceramics have been prepared. The diopside crystal (CaMgSi₂O₆) was identified in the glass ceramics by X-ray diffraction analysis. X-ray photoelectron spectra of the glass and glass ceramics were measured by a monochromatised Al-Kα XPS instrument. Sm 3d core level spectra for the Sm doped samples showed that Sm ions are predominantly in the Sm (III) state in glass and glass ceramics. The O 1s core spectra could be fitted by summing the contributions from bridging oxygen (BO) and non bridging oxygen (NBO) for samarium undoped glass, BO, NBO and Si-O-Sm for the doped glass. The O 1s XPS spectrum of undoped glass ceramics was curve fitted with BO and NBO in glass phase, as well as SiOSi, SiOMg and SiOCa in diopside. In addition to the five components above mentioned, SiOSm in diopside also appeared in O 1s XPS spectra of samarium doped glass ceramics. According to the fitting results, we demonstrate that the Sm₂O₃ exist in glass network as a glass modifier. After heat treatment, nearly all the Sm³⁺ existed in diopside phase as the substitution for Ca²⁺.     

Ultrasound-assisted anodization of aluminum in oxalic acid

Porous anodic alumina is an important nanoscale template for fabrication of various nanostructures. We report a new ultrasound-assisted anodization process in oxalic acid. Under the continuous irradiation of ultrasound, the one-step-anodized sample has a smooth and clean surface, and two-step-anodization brings ordered porous anodic alumina with higher growth rate of 52 μm/h. The ultrasound applied during the anodization can clean the surface and enhance the nanopore growth since it can accelerate the oxide dissolving on the electrolyte/oxide interface. The ultrasound-assisted anodization may be utilized for other anodizations.     

Preparation and characterization of manganese and cobalt based semiconducting ceramics

The spinel phases Mn_3-x Co _x O₄ are prepared directly and at low temperature (600-700°C) by means of thermal decomposition of mixed oxalate salt precursors in air or controlled atmosphere. The powders so obtained when sintered at 1200°C behave as semiconducting or insulating ceramics, depending on their cobalt content. The electrical properties of these ceramics have been found to be related to the distribution and valencies of the cations in the spinel structure. The study of their crystalline structure and stability, complemented by electrical measurements have permitted us to distinguish two types of compounds. The first type includes those given by Mn_3-x Co _x O₄ with 0 < x < 1. These are stable at high temperature, have a tetragonal structure and are insulators. The cation distributions for them can be deduced from that of hausmannite as given by Mn²⁺ [Mn³⁺ ₂]O₄, by substituting Mn²⁺ ions with Co²⁺ ions. The second type of compounds correspond to the cubic phases and occur for 1 < x < 3. These are unstable at high temperature and show a lower resistivity (e.g. 360 ° cm) which is of particular interest for their application in the design of negative temperature coefficient (N.T.C.) thermistor components.     

Adsorption of benzene on the V2O5/γ-Al2O3 catalyst

Adsorption of benzene on the V₂O₅/-Al₂O₃ catalysts was studied in the temperature interval from 443 to 493 K and at partial pressures of the adsorbate ranging from 1 to 400 Pa. The adsorption isotherms were plotted. The isosteric heats and various entropy characteristics of adsorption were determined. Mobility of benzene in the adsorption layer is restricted compared to the model of ideal dimeric gas. The adsorbed amounts of benzene and chlorobenzene are compared.     

Cr－Ag／γ－Al_2O_3催化剂在CO氧化反应中Ag的助催化作用

Ｃｒ－Ａｇ／γ－Ａｌ_２Ｏ_３催化剂在ＣＯ氧化反应中Ａｇ的助催化作用陈平，朱波，钟依均，罗孟飞，李少华，吴红丽（杭州大学催化研究所杭州３１００２８）（杭州大学中心实验室杭州）关键词氧化铬，氧化银，氧化铝，负载催化剂，还原特性，一氧化碳，氧化活性催化燃烧...