Growth and characterization of model oxide catalysts

Oxide catalysts are frequently used to convert toxic species to environmentally benign molecules, and to prevent the formation of toxic species in the first place. In this paper, growth and characterization of model oxide systems employed in both approaches is discussed. An example of the former approach is the selective catalytic reduction (SCR) of NO emitted from power plants by NH₃, which employs tungsten and vanadium oxides supported on the anatase polymorph of TiO₂. To model SCR catalysts, epitaxial titanium, vanadium and tungsten oxide films were grown using molecular beam epitaxy and magnetron sputtering. Two different anatase orientations were grown on LaAlO₃ substrates and their interactions with vanadia were characterized. On LaAlO₃ (0 0 1), anatase exposed a (4 × 1) reconstructed (0 0 1) surface. Vanadia lifted the reconstruction and at 1 ML a (1 × 1) surface with mostly V⁵⁺ was observed. Continued V₂O₅ growth led to loss of order, but at high temperatures epitaxial VO₂ could be grown; vanadia behaved similarly on anatase films on LaAlO₃ (1 1 0). Results suggested that the monolayer is pseudomorphic with O adsorption oxidizing the surface V to 5+, since the anatase structure cannot accommodate more bulk oxygen, only a monolayer can be pseudomorphic and have only V⁵⁺. Thus the vanadia monolayer has unique structural and chemical properties that can help explain why vanadia monolayers on TiO₂ are much more active than bulk V₂O₅. For WO₃, a series of added row reconstructions were observed as the epitaxial films were reduced. The effect of these structures on surface chemistry was characterized by studying 1-propanol adsorption. The results indicated that the structure of the WO₃ surface did not alter its catalytic function but had a strong effect on reaction kinetics. As an example of a system where catalysts prevent the formation of toxic species, the reactivity of oxidized Pd surfaces used in CH₄ catalytic combustion were studied. An ordered PdO-like monolayer was found to be less reactive towards CO than adsorbed O on Pd. On the other hand, the PdO layer favored a lower activation energy C₃H₆ oxidation pathway. The results indicated that Pd oxidation reduces the sticking coefficient of reactive species but once molecules adsorb, the oxide surface can reduce the activation energy for subsequent reaction.     

High power diode single-end-pumped Nd:YVO4 laser

A fiber-coupled diode-single-end-pumped Nd:YVO₄ laser with an Nd:YVO₄ crystal of 0.3 at% doping concentration and 3×3×10 mm³ dimensions was reported. 14.850 W of continuous-wave output power in an M² factor of 1.12 was obtained under pump power of 27.365 W, with an optical conversion efficiency of 60.49%, and a slope efficiency of 64.5%.     

用反射法自动测量大尺寸样品的折射率分布

针对大尺寸样品的折射率分布测量,引入自动扫描装置和适时数据处理系统,研究出一种高灵敏度的智能化反射法折射率分布测量仪,可进行快速、自动、准确的折射率分布测量.经理论分析和实验研究提出了一套合理的实验数据处理方法.并具体介绍和详尽分析了实验装置,讨论了有关理论和实验误差,给出了消除各种误差的有效方法,最终得出较为理想的实验结果.     

基于悬臂梁调谐技术的光纤光栅无源振动监测

采用匹配光纤光栅设计了一种结构简单的振动信号无源监测装置.该装置利用悬臂梁调谐技术能够将微小振动信号转化为光电探测器可探测的光强信号,利用示波器实现实时监测.实验中对振幅为3mm的简谐振动信号进行了监测,测量结果与振动频率一致,可测量7～20Hz的振动,信噪比不低于14.9dB.监测频率受限是因为悬臂梁的性质,如采用金属材料或者采用齿轮组对转子进行减速,该装置可探测更高的频率.     

Controlling the gain shape of Er^3＋—doped fluorozirconate fibre amplifier by a coherent field

We proposed a four-level system to explore the quantum interference effects on optical amplification.We found that the gain of the probe.including positions and values of gain peaks,can be adjusted by changing the coherent field and the incoherent pumping.At the same time,we can also modify the absorption profile of electromagnetically induced transparency by the incoherent pump.The results provide a method to flatten the gain of Erbium-doped fibre amplifiers.     

风冷热泵冷热水机组动态过程仿真

本文给出了风冷热泵冷热水机组动态过程模型。系统的高、低压段被分成制冷剂侧、管壁、以及水或空气侧三个控制容积。针对每个控制容积建立了质量和能量平衡的微分方程。由于压缩机、热力膨胀阀阀体、以及四通换向阀具有较小的热惯性,因而采用稳态模型描述压缩过程、膨胀过程、以及内泄露过程。膨胀阀感温包中的制冷剂温度对于蒸发器出口温度的延迟用一阶惯性环节来描述。通过“预测-校正”和“自适应步长”方法实现系统仿真。仿真结果与测试数据吻合良好。     

磁性钴纳米晶的二维自组装

在两种表面活性剂存在下，采用高温醇还原，合成出单分散、平均颗粒尺寸为14±19nm，直径标准偏差小(～18%)的磁性金属Co纳米晶.利用x射线衍射、紫外吸收光谱、x射线光电子能谱及透射电子显微镜对其结构和表面价态进行了分析.并将磁性金属Co纳米晶自组织形成有序的二维(2D)六方紧密堆积结构. 关键词： Co纳米晶 单分散 自组装     

光照下meso-四(4-磺基苯基)卟啉(H_2TPPS)形成锌配合物的光-极谱研究

在氨性溶液中,光照射对ZnTPPS的形成影响很大。光-极谱试验表明:光电流(i_p)与浓度(c)间有以下的关系:对Zn(NH_3)_4~(2+),i_p∝C_((Zn)(NH_3)_4)~(2+)_~(1/2),对H_2TPPS,i_p∝C_(H_2TPPS),ZnTPPS络合物还原波的i_p不明显。本文对其差异性和光电流产生的原因做了初步探讨。     

Fundamental reactions in TiO2 nanocrystallite aqueous solutions studied by pulse radiolysis

Reactions of the hydrated electron, H atoms, 2-propanol, and methanol radicals with the TiO₂ nano-particles have been studied either directly or by competition kinetics. The radicals were produced by radiolysis of 2-propanol, t-butanol, or methanol aqueous solutions in acid pH's. The reactions involve electron injection to the conduction band. As expected, the t-butanol radical is inert towards TiO₂ under our conditions, while the other reducing radicals react with TiO₂. The reactivity decreases in the order: e_aq⁻>H>CH₃COHCH₃>CH₂OH. Two TiO₂ nanocrystallite sizes, with average diameters of 1.0 and 4.7 nm were compared. For equal concentrations (in terms of TiO₂ molecules), the rate of electron injection shows relatively little dependency on particle size. The rates of interfacial electron transfer and transfer coefficient are also reported.