Structural investigations of copper doped B2O3-Bi2O3 glasses with high bismuth oxide content

Raman and infrared spectroscopy have been employed to investigate the 99.5%[xB₂O₃(1−x)Bi₂O₃]0.5%CuO glasses with different Bi/B nominal ratios (0.07?x?0.625) in order to obtain information about the competitive role of B₂O₃ and Bi₂O₃ in the formation of the glass network. The glass samples have been prepared by melting at 1100 °C and rapidly cooling at room temperature. In order to relax the structure, to improve the local order and to develop crystalline phases the glass samples were kept at 575 °C for 10 h. The influence of both Bi₂O₃ and CuO on the vitreous B₂O₃ network as well as the local order changes around bismuth and boron atoms in as prepared and heat treated samples was studied. Structural modifications occurring in heat treated samples compared to the untreated glasses have been observed.     

A new class of infrared transmitting glass-ceramics based on controlled nucleation and growth of alkali halide in a sulphide based glass matrix

Oxides-based glass-ceramics have been intensively studied and while they exhibit exceptional thermo-mechanical properties, their transparency in the infrared is limited to the 3 μm region. In this paper we describe a new type of glass-ceramics which are transparent up to 11 μm and based on the controlled nucleation and crystallization of cesium chloride sub-micron particles inside a Ge-Sb-S glass matrix. The evolution of the optical transmission versus annealing time and temperature has been investigated. Observations under scanning electronic microscopy as well as X-ray diffraction indicate that the crystalline phase is a primitive cubic cell with a parameter slightly inferior to that of pure CsCl and that the grain sizes are about 100 nm. A preliminary test on fracture propagation shows a much better resistance of glass-ceramics to cracks than the corresponding pure glass matrix.     

Bridging, non-bridging and free (O) oxygen in Na2O-SiO2 glasses: An X-ray Photoelectron Spectroscopic (XPS) and Nuclear Magnetic Resonance (NMR) study

High resolution Na 1s, O 1s and Si 2p core level XPS spectra of six Na₂O-SiO₂ glasses ranging in composition from 100 to 45 mol % SiO₂ have been collected using the Kratos Ultra Axis instrument with its unique charge compensation system. The O 1s spectra for the glasses are well resolved so that bridging oxygen (BO, Si-O-Si) and non-bridging oxygen (NBO, Na-O-Si) signals can be accurately fitted and quantified without resorting to constraints or assumptions. The same samples were analysed by ²⁹Si MAS NMR to obtain Q-species abundances from which BO and NBO proportions were calculated. Similar BO:NBO ratios were obtained by both methods over the entire compositional range studied. They are also consistent with most previous XPS and NMR results for glasses containing more than ~ 65 mol % SiO₂. Our XPS and NMR experimental results, however, differ somewhat from previously published XPS and NMR results for glasses containing less than about 65 mol % SiO₂.Na is mobile in the X-ray beam and mobility causes BO:NBO ratios to increase with time of exposure. Na mobility here has been circumvented to yield reliable BO:NBO ratios of the glasses. The ratios are lower than previously reported in XPS studies and are similar to ratios obtained from our ²⁹Si MAS NMR results on the same glasses. The XPS and ²⁹Si MAS NMR results also indicate the presence of a third oxygen species in sodic glasses. As has been proposed for CaSiO₃ glass and for sodic and potassic glasses containing La, we suggest that O²⁻ is present in sodic glasses at small concentrations. The O²⁻ content correlates with increased soda content and may be associated with, and instrumental in development of, three dimensional percolation channels in the glasses. The XPS O 1s line width of the BO peak is broader than the NBO peak, indicating more than one contribution to the BO peak. As observed in crystalline Na metasilicate and Na disilicate, BO of Na-silicate glasses may be of two types, one arising from BO bridging two Si atoms, and the second BO signal arising from BO bonded not only to two Si atoms but also to Na.     

Preparation and optical properties of titania-doped hybrid polymer via anhydrous sol-gel process

Incorporation of metal alkoxides (Ti, Zr, etc.) for tuning the optical properties of silica glasses by the sol-gel process is of significant interest for optical applications. In this paper, we report an anhydrous sol-gel process for preparation of photosensitive titania-doped hybrid glassy polymer with good homogeneity and high doping concentration (TiO₂ up to 40 mol%). The process consists of two steps: in the first step methacryloxypropyltrimethoxysilane (MPS) is hydrolyzed by boric acid through ligand exchange reaction (OH↔OR) under anhydrous conditions; and in the second step dimethyldimethoxysilane (DMDMS), diphenyldimethoxysilane (DPhDMS) and titanium ethoxide (TET) were added to condense with the silanols formed in the first step. The optical properties of the synthesized hybrid polymer were studied, and results showed that the hybrid material has low OH absorption, low optical losses (0.45 dB/cm at 1550 nm and 0.16 dB/cm at 1310 nm respectively), and good thermo-optical linearity with tuneable refractive index. The effect of TiO₂ doping in reducing the OH concentration of the hybrid material was observed, and the mechanism for this effect is discussed.     

RF measurements of a C-band cavity beam position monitor

RF cold test of a novel C-band cavity beam position monitor (PBM) to be used in the SDUVFEL Test Facility is described.The test results are presented and some characteristics discussed.The main parameters obtained are in reasonable agreement with the analytical estimations.Effective suppression of the common mode has been demonstrated.The position sensitivity over the test region of±0.5 mm is about -21.58 dB/10 μm for the TM110 mode and is linear in the central region of the BPM cavity.     

Stochastic resonance in surface catalytic oxidation of carbon monoxide induced by colored noise

Noise is generally considered as a disadvanta-geous factor, which would smear weak signals, there-fore, people always try to reduce its influence. How-ever, recent studies show that, for a nonlinear system, under certain circumstances, noise can enhance sys-tem抯 response to a signal. At specific noise intensity, the response of a system to a weak signal may reach its maximum, which is called 搒tochastic resonance?(SR). The concept of SR was originally put forward by Benzi and his collaborat…     

非恒温CO表面催化氧化体系双随机共振

当考虑化学反应热、热传导和热辐射的影响时, Pt(110)/CO+O2表面催化氧化体系温度出现时空变化. 以衬底温度为控制参数, 通过计算机模拟, 研究了衬底温度噪声对该非恒温表面反应体系振荡动力学行为的影响. 研究发现, 温度噪声可以诱导体系双随机共振现象, 而且增大衬底温度可以使体系共振行为由双随机共振变为单随机共振. 这表明体系可以利用温度噪声加强其反应振荡, 并对其具有双重选择性, 人们可以通过改变衬底温度大小来控制体系的共振行为.     

铂单晶电极表面下不可逆反应动力学(III)

在本系列研究论文Ⅰ[1]和Ⅱ[2]报导的结果基础上，进一步发展动力学数据解析方法．通过改变反应体系的温度，首次获得甲酸在Pt（100），Pt（110），Pt（111）电极上直接氧化反应的表观活化Gibbs自由能（△G≠0）．在实验选定的标准状态下，即0．0V／SCE、298．15K和1．013×105Pa下，来算得到。还发现传递系数β在实验温度范围（283．15～303．15K）不随温度变化，但随电极表面原子排列结构变化，大小次序与△G≠0的变化一致．     

Na(110)和Na2O(111)表面弛豫的研究

We have studied the relaxation of Na(110) and Na_2O(111) surfaces with LEED, and found that the best agreement between theory and experiment in such a structure, the surface layer distance d=0.291±0.01 nm (contracted 0.34%±0.01 nm) [for Na(110)]; and the three atomic surface layer distances d_1=0.117±0.01 nm (expanded 4.63%±0.01 nm), d_2=0.161±0.01 nm(expanded 0.063%±0.01 nm) and d_3=0.086±0.01 nm (expanded 0.75%±0.01 nm) [for Na_2O(111)].     

Search for highly resolved electron spin resonance spectra of the transient radical in radical polymerization

The detection of highly resolved spectra in electron spin resonance (ESR) measurements of radical polymerization is presented. Well‐resolved ESR spectra of the propagating radical were detected in the radical polymerization of several vinyl monomers with a specially designed cavity and cell. More highly resolved ESR spectra of the propagating radicals of vinyl and diene compounds were observed with aconventional spectrometer without the specially designed cavity and cell. On the basis of the ESR spectra, propagation rate constants and dynamic behavior of propagating radicals are discussed. Moreover, the application of time‐resolved ESR spectroscopy to research on the initiation process in radical polymerization is shown. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 269–285, 2002