Sensitive glasslike sol–gel materials suitable for environmental light sensors

New sol–gel based sensitive materials able to detect moderate doses of UV, Vis and near IR radiations have been designed, prepared and characterised. These glasslike detectors are respectively composed by four different sols of inorganic and hybrid organic–inorganic silica matrixes. The sols were prepared from alkoxide (TEOS) and alkylalkoxide (GLYMO) precursors with molar ratios 1:0, 1:1, 1:4 and 0:1, respectively. All the sols were doped with an organic photochromic dye (spiropyran). The detectors characterisation was carried out by means of exposures to natural light under different light intensities (100–3000 lx). The highest sensitivity against the light radiation was found for sols with molar ratio TEOS:GLYMO of 1:1. The time response of detectors is found at about 10 min and their life time is roughly 4 months at least. Moreover, the detectors show good optical reversibility. These sensitive glasslike materials have been designed to be applied for preservation of historical goods. They can detect and evaluate dangerous light doses for the proper conservation conditions of historical materials, which are sensitive or moderately sensitive against light radiation (<600 lx).     

Effects of silica sol on ion exchange membranes: Electrochemical characterization of anion exchange membranes in electrodialysis of silica sol containing-solutions

The fouling potential of the negatively charged silica sol in electrodialysis (ED) by adsorption on the surface of an anion exchange membrane was investigated. Since the fouling potential is related to the physical and electrochemical properties of the silica sol and anion exchange membranes, it is important to characterize the properties of silica sol and membranes. The surface charge of silica sol was investigated by the electrophoretic mobility and its isoelectric point was determined as pH 3. The commercial anion exchange membranes were characterized in terms of exchange capacity, water content, the zeta potential and the electrochemical properties of the membranes using impedance spectroscopy to predict the effects on the electrodialysis performances. Among the characterized properties, exchange capacity and some electrochemical properties of the anion exchange membranes were rather improved after ED experiments. In the electrodialysis of solution containing silica sol, deposition of the silica sol did not decrease the desalting performance of the anion exchange membranes because of loosely packed cake layer on the membrane surface.     

THE INFLUENCE OF SILANE COUPLING AGENT COMPOSITION ON THE SURFACE CHARACTERIZATION OF FIBER AND ON FIBER-MATRIX INTERFACIAL SHEAR STRENGTH

It is well known that the fiber-matrix interface in many composites has a profound influence on composite performance. The objective of this study is to understand the influence of composition and concentration of coupling agent on interface strength by coating E-glass fibers with solutions containing a mixture of hydrolyzed propyl trimethoxysilane (PTMS) and γ-aminopropyl trimethoxysilane (APS). The failure behavior and strength of the fiber-matrix interface were assessed by the single-fiber fragmentation test (SFFT), while the structure of silane coupling agent was studied in terms of its thickness by ellipsometry, its morphology by atomic force microscopy, its chemical composition by diffuse reflectance infrared Fourier transform (DRIFT), and its wettability by contact angle measurement. Deposition of 4.5 ×10 -3 mol/L solution of coupling agent in water resulted in a heterogeneous surface with irregular morphology. The SFFT results suggest that the amount of adhesion between the glass fiber and epoxy is dependent not only on the type of coupling agent but also on the composition of the coupling agent mixture. As the concentration of APS in the mixture increased, the extent of interfacial bonding between the fiber and matrix increased and the mode of failure changed. For the APS coated glass epoxy system, matrix cracks were formed perpendicular to the fiber axis in addition to a sheath of debonded interface region along the fiber axis.     

Identification of Sulfur‐Containing Impurities in Biodiesel Produced From Brown Grease

Fatty acid methyl esters (FAME) from waste grease usually contain higher concentrations of sulfur (S) than allowed to meet the specified quality standard for biodiesel (<15 ppm). Brown grease lipid‐derived FAME was produced and fractionated by two passes through a wiped‐film evaporator (WFE) to produce three fractions: (1) a 120 °C pass distillate, (2) a 170 °C pass distillate, and (3) a heavy residue. Solid phase extraction (SPE) was used to concentrate the S species from the distillate fractions so that they could be detected by a gas chromatography–pulsed flame photometric detector (GC–PFPD) and GC–mass spectrometry (MS). The ethyl acetate and methanol (MeOH) fractions obtained by SPE of the 120 °C WFE distillate and methyl tert‐butyl ether and acetone fractions obtained by SPE of the 170 °C WFE distillate had the highest concentration of S and were, therefore, the best candidates for GC–PFPD analysis. GC–PFPD methods were developed to separate the S species adequately enough for those peaks to be analyzed by GC–MS which matched fragmentation patterns identified by the MS chemical library as tetrahydrothiophenes, dithiolanes, and thiophenes. MS fragmentation patterns were used to identify other, larger, S‐bearing species as sulfides and disulfides cross‐linking between two FAME molecules. The results obtained from this study provide a foundation for developing effective purification methods to remove S‐containing impurities from waste grease‐derived biodiesel.     

Growth and stability of Ga2O3 nanospheres

Gallium oxide thin films were prepared by thermal evaporation and deposition of Ga₂O₃ on NaCl(001) cleavage planes at varying substrate temperatures, oxygen pressures and deposition rates. The structure of the so-prepared thin films was checked by Transmission Electron Microscopy and Selected Area Diffraction and also characterized by X-ray Photoelectron Spectroscopy and Atomic Force Microscopy, both in the as-deposited state and after different oxidative and reductive treatments. The substrate temperature proved to be most crucial for the structure of the gallium oxide films, ranging from low-contrast amorphous structures at low substrate temperatures (298 K) to nanosphere structures at higher temperatures (580 K). The stability of the films was found to be mainly determined by the interaction of substrate temperature and deposition rate. Crystalline β-Ga₂O₃ structures were obtained after oxidative, reductive and annealing treatments at and beyond 773 K suggesting that the crystallization is mainly a thermal annealing effect.     

真伪天麻二维相关红外光谱法的鉴别研究

本文采用红外光谱法并结合二维相关(Two-Dimensional Correlation Spectroscopy)分析技术,对药用天麻和伪品天麻(芭蕉芋)进行了无损快速鉴别研究。天麻和芭蕉芋在外观上很相似,都是成椭圆或扁卵圆形的块茎,皱缩而稍弯曲,并且在一维谱图上差别很细微,而在二维谱图上显示出较大的差别。在800～1500cm~(-1)波段范围内,天麻在同步图上有二个较强的自动峰,分别在1237cm~(-1)和1415cm~(-1)附近,而芭蕉芋有四个较强的自动峰,在1024、1055、1194、1225cm~(-1)附近,1400cm~(-1)处也有相关峰,但是较微弱,二维相关谱可以提高谱图的分辨率,增加谱图的识别能力,可用于药材真伪品的鉴别。该法快速、准确,为客观评价中药材的来源提供了一种新的方法和手段。     

Microwave plasma enhanced chemical vapor deposition diamond synthesis from high carbon content source

To synthesize diamond films by microwave plasma enhanced chemical vapor deposition (MPECVD), the methane concentration (CH₄/H₂)plays a crucial role. It is well-known that there always exists a critical methane concentration (≤0.6%) only below which a good quality diamond film can be obtained. In this study, however, the phenomena of diamond synthesis resulting from high carbon concentration conditions were observed. The molten metals, e.g., Ag, Cu, were used as the deposition substrates on which crystalline diamonds can be achieved from a methane content of CH₄/H₂≥6% or even from solid carbon sources. These results suggest that there may exist a low methane content boundary layer (<0.6%) in the proximity of molten metal surface on which suitable species, CH, CH⁺, H_α and H_β are composed for the diamond nucleation and growth similar to the condition as in the conventional low methane contents. The molten metal inclines to dissolve other forms of carbonaceous materials other than diamond, and thus keeps a much higher steady supply of carbon atoms that enhances the quality as well as the growth rate of the forming diamonds. Received: 23 June 2001 / Accepted: 23 July 2001     

Ga_(1-x)In_xAs_ySb_(1-y)/GaSb LPE生长及其性质研究

报导了在n型(100)GaSb衬底上,温度为520—530℃时,用液相外延的方法实现了组分在0≤x≤0.19,0≤y≤0.14范围内的Ga_(1-x)In_xAs_ySb_(1-y)四元合金半导体的生长。X射线双晶衍射,电子探针及光学显微镜的观察和分析测试表明:所得外延层的表面形貌和界面特性优良,组分分布和层厚均匀,晶格匹配及单晶性能良好。对外延层表面的氧化情况使用Auger能谱仪进行测试分析。另外,对生长中存在的一些问题进行了讨论。     

气体浓度计现状,原理和试验

本文介绍了排放气体组分浓度分析仪的原理和国内外该仪器的性能指标.国内分析仪器厂在引进国外技术后已能提供符合需要的成套分析系统.我们实验室对用富里叶光谱仪用于浓度检测作了可行性试验,证实可以一次取得各组分浓度数据.对 CO 和 CH 国内能提供标准样气的组分得到的标准曲线,精度优于5%.