Influences of pretreatment temperature on the surface silylation of diatomaceous amorphous silica with trimethylchlorosilane

Diatomaceous amorphous silica samples were modified by silylation using trimethylchlorosilane (TMCS). The resultant materials were characterized by using thermogravimetry (TG), ¹H magic-angle spinning nuclear magnetic resonance (¹H MAS NMR), Fourier transform infrared spectroscopy (FTIR) and chemical analysis. The degree of silylation was found to increase with the increasing temperature of thermal pretreatment on diatomaceous silica prior to silylation. Increment of the pretreated temperature leads to stepwise removal of physisorbed water followed by the dehydration of capping water that H-bonded with the surface silanols, resulting in exposure of more and more isolated and H-bonded silanols previously covered by water molecules. Among these exposed silanols, isolated silanols show high activity for silylation reaction but H-bonded ones show poor activity. The maximum degree of surface attachment of TMCS grafted onto the diatomaceous silica (about 1.81 mmol TMCS groups per gram of silica) was shown in the sample pretreated at 1100 °C, in which the amount of exposed isolated silanols get the maximum. The fundamental information derived from this work is of significance in well understanding the surface silylation reaction of diatomaceous silica and providing useful information for related industrial production.     

Investigation of alkali borosilicate glass durability using tritium tracing, β-autoradiography, scanning electron microscopy and ion beam analysis

A Li-Na-containing borosilicate glass was submitted to aqueous corrosion in static mode in tritiated solutions of various pH at room temperature and 90 °C. Tritium counting, β-autoradiography, scanning electron microscopy (SEM) and ion beam analysis (IBA) techniques have been used to investigate the composition variations of the leached glass surfaces. In an acidic medium, the glass surface is covered by a thick hydrated silica layer; mobile elements like Li, Na and B and transition elements like Fe and Mo are strongly depleted. Near pH 7, relative enrichments of aluminium and iron are shown together with strong Li, Na and B depletions. In a basic medium, the glass surface exhibits iron and molybdenum enrichments whereas mobile elements seem to be kept at their nominal concentration level at the glass surface. The tritium activity and distribution on the leached glass surface is shown to depend strongly on the pH of the tritiated solutions. These observations are correlated with the observed changes of the surface morphology and chemistry characterized by IBA and SEM analysis. Elemental solubility versus pH of various chemical species have been calculated for comparison purpose with the experimental observations.     

Surface nitridation of a phosphate glass

Phosphate glass surfaces were nitrided by reacting them in dry ammonia at temperatures near the glass transition temperature (T_g) for up to 100 h. These treatments have significant effects on surface dependent glass properties. For example, the dissolution rate of a sodium-barium phosphate glass (T_g = 345°C) decreased by over an order of magnitude after 24 h in ammonia at T_g. X-ray photoelectron spectroscopic (XPS) analyses show that nitrogen in chemically incorporated into the glass structure at levels up to 3–5 at.%. Elemental depth profiles, obtained by XPS (for N) and by elastic recoil detection (ERD) analyses (for N and H), indicate that the surface oxynitrile layer extends to about 1 μm in depth. XPS analyses of in situ treated samples reveals the presence of several nitrogen species which affect the surface dependent properties by increasing the structural crosslink density of the glass surface.     

IBA and SIMS coupling to study glass alteration mechanisms

Alkali-alumino-borosilicate glasses have been synthesized by melting the stoichiometric corresponding powder mixtures and heating at 1100 °C in a platinum crucible. Electron microprobe analyses were then carried out in order to determine their initial composition. Glass samples were submitted to static aqueous leaching tests in deionized water during 1 month (surface/ratio = 0.3 cm⁻¹) at temperature of 96 °C. The leachates were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The leached samples were then characterized by ion beam analytical (IBA) methods: Rutherford backscattering and elastic recoil spectrometries (RBS and ERDA), proton-induced X-ray or gamma ray emission (PIXE and PIGE) and secondary ion mass spectrometry (SIMS). The role of the presence of one or several contained transition elements (Fe, Mo, and Nd) and the effect of their respective contents on the chemical durability of alkali-borosilicate glasses were investigated. This work outlines the fact that a competition may occur between congruent and selective dissolution. Both surface hydration thickness and mobile element depletion amplitude cannot be considered as the unique reliable glass durability indicators.     

Mass and bond density measurements for PECVD a-SiCx:H thin films using Fourier transform-infrared spectroscopy

The absolute concentration of chemical bonds in Plasma Enhanced Chemically Vapor Deposited (PECVD) a-SiC_x:H thin films have been determined via combining transmission Fourier-Transform Infra-red (FTIR) spectroscopy with X-ray Reflectivity (XRR) and Rutherford Backscattering (RBS) mass density and composition measurements. Specifically, we demonstrate in this paper that the integrated absorbance for the Si-C stretch in FTIR is linearly proportional to the mass density of PECVD a-SiC_x:H films as determined by XRR and RBS. This linear relationship allows us to accurately determine the IR absorption cross section for the Si-C stretch. Using these cross sections in combination with IR proportionality constants/cross sections published by other researchers, we demonstrate that mass densities in agreement with XRR and RBS can be calculated from the integrated absorbances of the Si-C, Si-H, and C-H stretches in FTIR spectra. From additional mass balance relationships, we further demonstrate that the full elemental and bond concentrations can be determined. This analysis reveals the presence of significant Si-Si and C-C bonding in the a-SiC_x:H films that was not clearly identified in previous FTIR investigations due to the low IR activity for these homopolar bonds. The bond and mass density calculations are demonstrated for both 3C-SiC and a-SiC_x:H thin films with mass density values ranging from 1 to 3.2 g/cm³.     

Gallium colloid formation during ion implantation of glass

Data are reported on the size and depth distribution of gallium colloids formed by gallium ion implantation at energies of 50 and 60 keV, and nominal doses up to 1.1 × 10¹⁷ ions/cm² into coverlip glass, float glass and white crown glass. Measurement techniques used to reveal colloid-induced changes include the wavelength dependence of optical reflectivity, transmission electron microscopy (TEM) and Rutherford backscattering (RBS). The reflectivity can be controlled by variations in ion dose, implant temperature and ion beam energy. The highest reflectivity is found after implants near 50°C and the level is extremely sensitive to the implant temperature. For controlled beam conditions, the reflectivity data are reproducible, despite there being variations in the colloid size and depth distributions as seen by TEM and RBS. The TEM data reveal that the depth distribution develops in two distinct regions, which at high concentration can precipitate into two layers of large colloids. Subsidiary experiments are reported to attempt to separate the effects of variations in the implant temperature and surface charging which influence the reflectivity, RBS and colloid formation.     

不同晶相WO3的热分解法制备及其光催化性能

以钨酸铵为钨源,硝酸为沉淀剂,首先通过沉淀法制备前驱体H2 WO4,随后采用热分解H2 WO4法合成六方及单斜晶相WO3催化剂.利用X射线衍射(XRD)、拉曼光谱、差热-热重(TG-DTA)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)及紫外-可见漫反射光谱(UV-Vis DRS)对H2 WO4向WO3转变过程中结构、形貌、组成及光学性质的变化进行研究.结果表明,热处理后前驱体发生如下相变过程:H2 WO4→六方相WO3→六方/单斜相WO3→单斜相WO3.此外,以罗丹明B为模拟污染物,考察不同晶相WO3的光催化活性,结果表明,六方相WO3具有更高的光催化性能,单斜相WO3的活性较低.     

Speciation of hydrogen in silica glass by 1H MAS NMR

The H-bearing species in silica glass melted quartz powder in hydrogen atmosphere have been investigated using high-resolution ¹H magicangle spinning nuclear magnetic resonance (¹H MAS NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and quadrupole mass spectrometry. The results show that molecular H₂, hydroxyl (OH) groups and hydride (SiH) groups are present in the glass. The physically dissolved molecular H₂ is represented by a broad NMR peak with the effects of strong H–H magnetic dipolar interactions. Isolated OH groups and hydrogen bonding OH groups in silica glass have been distinguished by the chemical shift of the ¹H NMR spectrum. The influence of E’ center on the ¹H MAS NMR spectrum are also analyzed.     

Influence of sputtering conditions and electron energy on XPS depth profiling of Ge in SiO2

Ge nanocluster formation in SiO₂ is of growing interest for new electronic applications. Ion beam synthesis using high‐energy Ge implantation connected with thermal annealing is one possible preparation method of such clusters. In addition to investigations of electrical and structural changes during the cluster formation process we also studied chemical changes in the samples using x‐ray photoelectron spectroscopy (XPS). This was done with low‐energy noble gas ion sputtering for depth profiling. Binding state information one can get from the XPS data by means of factor analysis (FA) in combination with other structural investigations. However, mixed bonding states probably created by ion beam damage during sputter erosion are dominating the results. It is shown, that by changing the experimental conditions (ion beam impact depth during sputtering, electron information depth during XPS measurement) these mixed states are influenced in an appropriate manner. It is concluded that useful chemical information on the behavior of the implanted Ge can be derived despite of the ion beam damage. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

影响化学机械抛光4H导电SiC晶片表面质量的关键参数研究

选用二氧化硅抛光液抛光4H导电SiC晶片表面,探究影响SiC晶片表面质量的关键参数,获得更高的去除效率和表面质量.实验结果表明,SiC表面的氧化是氢氧根离子和双氧水共同作用的结果.保持压力不变并增加氢氧根离子或双氧水的含量,SiC表面去除速率先增加后保持不变.在更大的压力下增加氢氧根离子的含量,SiC表面的抛光去除速率进一步增加.通过优化的抛光参数,SiC表面的抛光去除速率达到142 nm/h.进一步研究结果表明,保持化学机械抛光过程中氧化作用与机械作用相匹配,是获得高抛光效率和良好的表面质量的关键.表面缺陷检测仪(Candela)和原子力显微镜(AFM)的测试结果表明,SiC抛光片表面无划痕,粗糙度达到0.06 nm.外延后总缺陷密度小于1个/cm2,粗糙度达到0.16 nm.     

热丝辅助MW ECR CVD技术高速沉积高质量氢化非晶硅薄膜

氢化非晶硅薄膜具有优异的光电特性,在制备薄膜太阳能电池中有重要的应用.本文采用热丝辅助MWECR CVD技术,通过调整各种工艺参数,制备了高沉积速率(DR＞2.5nm/s)及高光敏性(σph/σD＞105)的氢化非晶硅薄膜.实验表明,在衬底表面温度的分布中,热丝辐射和离子轰击引起的温度对薄膜的光敏性影响较大;在薄膜沉积的最后几分钟适当加大H2稀释率,有利于薄膜光电特性的改善.     

Formation and behavior of surface layers on electron emission glasses

The thermochemical reduction of thin surface layers on multicomponent lead-silicate glasses is fundamental to their use in electron multiplier and microchannel plate devices. These surface layers can exhibit a specific conductivity as high as 10⁻² (Ω cm)⁻¹ and secondary electron yields up to 3.5. However, due to the complex processing used in the fabrication of the devices, a basic understanding of the chemical and structural surface characteristics responsible for these properties has not been established. Moreover, the effects of prolonged electron bombardment upon the chemical characteristics of the surface have not been extensively investigated, nor related to any associated degradation of the electron emission properties.

In this study, the clean fracture surfaces of these glasses were investigated. The effects of hydrogen reduction, chemical etching, and prolonged electron bombardment were determined. Ion-scattering spectroscopy (ISS) was used for its monolayer sensitivity, especially to alkali species, while secondary ion mass spectroscopy (SIMS) provided depth profiles. The hydrogen profile created by the reduction could also be obtained with SIMS. X-ray photoelectron spectroscopy (XPS) was employed selectively to examine changes in the oxidation state of the surface species.

It was found that the hydrogen reduction of these glasses creates a thin 20–50 nm silica-rich surface layer. The layer of reduced lead atoms is beneath this zone, and is visible to depths of the order 5 μm, but the hydrogen profiles which are found in these surfaces extend only 0.5 μm in depth. The electron bombardment of these surfaces leads to a decrease in concentration of alkali and lead in the surface monolayer, and to a change in the hydrogen profile. The cross-section for this bombardment-induced change in the surface composition correlates with the reported gain degradation in microchannel plate devices.     

Characterization of potash-glass corrosion in aqueous solution by ion beam and IR spectroscopy

In this work the corrosion processes of potash-glass surfaces in contact with aqueous solutions were studied using ion beam spectroscopic techniques, optical microscopy (OM) and Fourier transform infra-red (FTIR) spectroscopy. In order to follow the corrosion progress these surface studies were combined with the evaluation of the changes taking place in the aqueous solution. In particular, the hydrogen profiles obtained from the attacked surface region of glass were compared with the variation of pH values of the aqueous solutions, in order to extract information about the ion exchange processes. It is shown that pH values may also be a good parameter for studying corrosion kinetics in high humidity conditions. The two tests conditions explored (with and without stirring of the aqueous solution) proved to lead to different surface morphologies associated with different corrosion rates. Stirring results in a more fine grained and uniform morphology of the corrosion products and a higher corrosion rate.     

Sorption properties of silica gel with adsorbed copolymers of 4-vinylpyridine and styrene with respect to Cu(II), Pb(II) and Fe(III) ions

Abstract

A number of new organo-mineral composites in different mass ratios of organic and inorganic components were obtained by adsorption on the silica gel surface of 4-vinylpyridine–styrene copolymer. The fact of the copolymer immobilization on the silica gel surface was confirmed by Fourier transform infrared spectroscopy (FTIR) spectroscopy and thermogravimetry combined with mass-spectrometry analysis. Thermogravimetric analysis was employed for estimation of copolymers mass content in the composite obtained. It has been established that all the synthesized composites exhibit sorption activity toward traces of Cu (II), Pb (II) and Fe (III) ions in neutral aqueous medium.     

Rutherford backscattering investigation of the corrosion of borosilicate nuclear waste glass

The corrosion properties of several borosilicate nuclear waste glasses exposed to aqueous environments have been investigated using a combination of Rutherford backscattering (RBS) depth profiling and solution analysis. Using the technique of RBS, the concentration of individual elements in the glass can be quantitatively profiled within a 1–2 μm surface layer. All of the glass surfaces were corroded in distilled water at 90°C for times ranging from 0–28 days. The evolution and composition of the altered layer that formed on the glass surface was of particular interest, since this layer can be crucial in determining whether or not the remainder of the glass undergoes further rapid corrosion. Within the altered surface layer produced by the corrosion process, there was an enhancement in the concentrations of U, Ti, Sr, Nd, Gd, and Ca and a depletion of Na, Si, Cs, (and probably B) relative to the concentrations present in the bulk glass. The U concentration, for example, was often 3–4 times greater in the altered surface layer than in the bulk. The layer apparently forms due to a local reaction that results in the formation of insoluble complexes on the glass surface. A simple model of the corrosion process has been used to identify the most likely insoluble metal complex for each metal present in excess in the alteration layer. The mechanical and chemical stability of this layer are also discussed.     

Characterization of treated pbte surfaces by means of RHEED and RBS

Differently treated PbTe surfaces have been investigated by means of reflection high energy electron diffraction (RHEED) and Rutherford backscattering (RBS). It has been shown that chemical lap polishing followed by heat treatment is the best method to fulfil the requirements of the following epitaxy process concerning the absence of contaminations, the high structural surface perfection, and the flatness of the substrates. The influence of heat treatment on surface perfection, and chemical composition in the surface region has been investigated to determine the optimal conditions for the tempering step before epitaxy.     

Measuring surface forces to explore surface chemistry: Mica, sapphire and silica

In this paper measurements of the forces acting between two solid surfaces separated by a thin liquid film are discussed. By investigating these forces in a range of different liquids and solutions, it is possible to acquire an understanding of the surface properties of the solid material. The surface of mica has been studied extensively in this way, and the results obtained are reviewed to illustrate how the surface force measurements can give surface chemical information. Recent measurements on two other materials, sapphire and silica, which are of greater practical interest are also discussed.     

Methods of chemical and phase composition analysis of gallstones

This review presents the instrumental methods used for chemical and phase composition investigation of gallstones. A great body of data has been collected in the literature on the presence of elements and their concentrations, obtained by fluorescence microscopy, X-ray fluorescence spectroscopy, neutron activation analysis, proton (particle) induced X-ray emission, atomic absorption spectroscopy, high-resolution gamma-ray spectrometry, electron paramagnetic resonance. Structural methods—powder X-ray diffraction, infrared spectroscopy, Raman spectroscopy—provide information about organic and inorganic phases in gallstones. Stone morphology was studied at the macrolevel with optical microscopy. Results obtained by analytical scanning and transmission electron microscopy with X-ray energy dispersive spectrometry are discussed. The chemical composition and structure of gallstones determine the strategy of removing stone from the body and treatment of patients: surgery or dissolution in the body. Therefore one chapter of the review describes the potential of dissolution methods. Early diagnosis and appropriate treatment of the disease depend on the development of clinical methods for in vivo investigation, which gave grounds to present the main characteristics and potential of ultrasonography (ultrasound scanning), magnetic resonance imaging, and X-ray computed tomography.     

Chemistry of cultural glasses: the early medieval glasses of Monselice's hill (Padova, Italy)

To investigate the mechanisms of deterioration of historical glasses, under natural evolution, some early medieval glasses from the archaeological site of the Monselice's hill have been analysed. By an archaeological approach, developed at the Dipartimento di Scienze dell'Antichità, University of Padova, the glasses were dated between the VI and the beginning of the VII century and they were ascribed to the same artist or school. By a geological approach, developed at the Dipartimento di Mineralogia e Petrologia, University of Padova, it was found that some pieces of glasses, from the same archaeological site, were made of silica, rich in sodium and calcium, with iron and manganese. The composition was analogous the one of glasses produced during Roman empire, using `natron' (Na<sub>2</sub>CO<sub>3</sub>·NaHCO<sub>3</sub>·2H<sub>2</sub>O) as melting agent and glasses produced during medieval age, in the Mediterranean basin, using plant ash like `Salsola Kali' as melting agent. It was also found that there was a surface layer, with a special lamellar structure, easy to remove. The surface layer was found poor in alkali and alkaline-earth elements. By surface and microscopic analyses (optical microscopy, SEM-EDS, microRaman, XPS, SIMS and Mössbauer) it has been found that all the samples have a composition rich in silica, sodium and calcium except one that, unexpectedly, was rich in potassium and poorer in sodium. This sample, as composition, seems just like medieval glasses produced north of the Alps, using plant ash like ferns as melting agent. In all the samples the surface layers have less alkaline elements and the depletion goes to ten μm of depth. The extreme consequence of this depletion is the formation, in some samples, of an alteration layer, easy to remove, that the XPS analyses tell us it is made of very hydrated silica. The surface layers show a little accumulation of calcium. The calcium ion is also present in some birefringent crystal aggregates immersed in the glass that, in some samples, are around one mm large. These aggregates have a circular shape, with a nucleation centre in them. By microRaman spectroscopy it was found that the crystal aggregates are made of vateritic and calcitic calcium carbonate. By Mössbauer spectroscopy it was found that in the flat yellow coloured glasses, richer in iron, the Fe(III) species predominates. Instead in the pale green ones, poorer in iron, the Fe(II) prevails.