X-Ray Spectroscopy by Shatendra K. Sharma


115a9c9489b191a-261x361.jpeg Author Shatendra K. Sharma
Isbn 9789533079677
File size 20MB
Year 2011
Pages 289
Language English
File format PDF
Category physics



 

X-RAY SPECTROSCOPY Edited by Shatendra K. Sharma X-Ray Spectroscopy Edited by Shatendra K. Sharma Published by InTech Janeza Trdine 9, 51000 Rijeka, Croatia Copyright © 2011 InTech All chapters are Open Access distributed under the Creative Commons Attribution 3.0 license, which allows users to download, copy and build upon published articles even for commercial purposes, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. After this work has been published by InTech, authors have the right to republish it, in whole or part, in any publication of which they are the author, and to make other personal use of the work. Any republication, referencing or personal use of the work must explicitly identify the original source. As for readers, this license allows users to download, copy and build upon published chapters even for commercial purposes, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. Notice Statements and opinions expressed in the chapters are these of the individual contributors and not necessarily those of the editors or publisher. No responsibility is accepted for the accuracy of information contained in the published chapters. The publisher assumes no responsibility for any damage or injury to persons or property arising out of the use of any materials, instructions, methods or ideas contained in the book. Publishing Process Manager Anja Filipovic Technical Editor Teodora Smiljanic Cover Designer InTech Design Team First published January, 2012 Printed in Croatia A free online edition of this book is available at www.intechopen.com Additional hard copies can be obtained from [email protected] X-Ray Spectroscopy, Edited by Shatendra K. Sharma p. cm. ISBN 978-953-307-967-7 Contents Preface IX Part 1 XRF Processes and Techniques 1 Chapter 1 X-Ray Spectroscopy Tools for the Characterization of Nanoparticles 3 Murid Hussain, Guido Saracco and Nunzio Russo Chapter 2 A Practical Application of X-Ray Spectroscopy in Ti-Al-N and Cr-Al-N Thin Films Leonid Ipaz, William Aperador, Julio Caicedo, Joan Esteve and Gustavo Zambrano Chapter 3 High Resolution X-Ray Spectroscopy with Compound Semiconductor Detectors and Digital Pulse Processing Systems Leonardo Abbene and Gaetano Gerardi Chapter 4 Analysis of the K Satellite Lines in X-Ray Emission Spectra 65 M. Torres Deluigi and J. Díaz-Luque Chapter 5 Application of Wavelength Dispersive X-Ray Spectroscopy in X-Ray Trace Element Analytical Techniques Matjaž Kavčič 21 39 81 Part 2 Characterization and Analytical Applications of X-Rays Chapter 6 The Use of Electron Probe MicroAnalysis to Determine the Thickness of Thin Films in Materials Science 101 Frédéric Christien, Edouard Ferchaud, Pawel Nowakowski and Marion Allart 99 VI Contents Chapter 7 Chemical Quantification of Mo-S, W-Si and Ti-V by Energy Dispersive X-Ray Spectroscopy 119 Carlos Angeles-Chavez, Jose Antonio Toledo-Antonio and Maria Antonia Cortes-Jacome Chapter 8 Quantification in X-Ray Fluorescence Spectrometry Rafał Sitko and Beata Zawisza Chapter 9 The Interaction of High Brightness X-Rays with Clusters or Bio-Molecules Kengo Moribayashi 137 163 Chapter 10 Employing Soft X-Rays in Experimental Astrochemistry Sergio Pilling and Diana P. P. Andrade 185 Chapter 11 X-Ray Analysis on Ceramic Materials Deposited by Sputtering and Reactive Sputtering for Sensing Applications 219 Rossana Gazia, Angelica Chiodoni, Edvige Celasco, Stefano Bianco and Pietro Mandracci Chapter 12 Application of Stopped-Flow and Time-Resolved X-Ray Absorption Spectroscopy to the Study of Metalloproteins Molecular Mechanisms 245 Moran Grossman and Irit Sagi Chapter 13 Nanoscale Chemical Analysis in Various Interfaces with Energy Dispersive X-Ray Spectroscopy and Transmission Electron Microscopy 265 Seiichiro Ii Preface Since Roentgen’s discovery in 1885, x-rays have been employed as a diagnostic tool, first in medical sciences, followed by physics, material and engineering sciences, and today almost in every field. The applications of x-rays are versatile even in those areas where they were least expected to have use just ten years back. The material characterization using x-rays is a well explored field since the beginning of the 20th century. Many processes have been standardized and are fast and compact enough to give instant results. Over the years, the production techniques and design of such instruments have also changed a lot from Crook’s tube to synchrotron and to x-ray lasers. Today, the x-ray based instruments have attained the status of simple and fast analytical tools that are used in characterization of materials of biological, physical, chemical, archeological, geological, and material science. The processes of x-ray emission are well studied, and new applications of x-ray as a tool are being explored and developed every day. The progress in detector instrumentation and data acquisition techniques over past few decades has enhanced the precision and the speed of characterization using x-rays. The present book is a collection of contributions from the authors who are expert researchers in their fields involving x-ray processes and techniques. The book has been divided into two sections. The first section is on XRF Processes and Techniques, with chapters on the study and investigations related to x-ray emission processes, instrumentation, data acquisition, spectra, and analysis techniques. The second section is dedicated to the Characterization and Analytical Applications of X-Rays, and includes the chapters related to the x-ray spectroscopic techniques for analysis of material, nanoparticles, and thin films. Shatendra K. Sharma Professor and Director University Science Instrumentation Centre Jawaharlal Nehru University New Delhi India Part 1 XRF Processes and Techniques 1 X-Ray Spectroscopy Tools for the Characterization of Nanoparticles Murid Hussain, Guido Saracco and Nunzio Russo Politecnico di Torino Italy 1. Introduction Photocatalysts are solids that can promote reactions in the presence of light without being consumed in the overall reaction (Bhatkhande et al., 2001), and they are invariably semiconductors. A good photocatalyst should be photoactive, able to utilize visible and/or near UV light, biologically and chemically inert, photostable, inexpensive and non-toxic. For a semiconductor to be photochemically active as a sensitizer for the aforementioned reaction, the redox potential of the photogenerated valence band hole should be sufficiently positive to generate OH• radicals that can subsequently oxidize the organic pollutant. The redox potential of the photogenerated conductance band electron must be sufficiently negative to be able to reduce the adsorbed O2 to a superoxide. TiO2, ZnO, WO3, CdS, ZnS, SrTiO3, SnO2 and Fe2O3 can be used as photocatalysts. TiO2 is an ideal photocatalyst for several reasons (Bhatkhande et al., 2001; Fujishima et al., 2000, 2006; Mills & Hunte, 1997; Park et al., 1999; Peral et al., 1997; Periyat et al., 2008). It is relatively cheap, highly stable from a chemical point of view and easily available. Moreover, its photogenerated holes are highly oxidizing, and the photogenerated electrons are sufficiently reducing to produce superoxides from dioxygen groups. TiO2 promotes ambient temperature oxidation of most indoor air pollutants and does not need any chemical additives. It has also been widely accepted and exploited as an efficient technology to kill bacteria. Volatile organic compounds (VOCs) are considered to be as some of the most important anthropogenic pollutants generated in urban and industrial areas (Avila et al., 1998). VOCs are widely used in (and produced by) both industrial and domestic activities since they are ubiquitous chemicals that are used as industrial cleaning and degreasing solvents (Wang et al., 2007). VOCs come from many well-known indoor sources, including cooking and tobacco smoke, building materials, furnishings, dry cleaning agents, paints, glues, cosmetics, textiles, plastics, polishes, disinfectants, household insecticides, and combustion sources (Jo et al., 2004; Wang et al., 2007; Witte et al., 2008). Moreover, ethylene (C2H4) is an odorless and colorless gas which exists in nature and is generated by human activities as a petrochemical derivative, from transport engine exhausts, and from thermal power plants (Saltveit, 1999). However, it is produced naturally by plant tissues and biomass fermentation and occurs along the food chain, in packages, in storage chambers, and in large commercial refrigerators (Martinez-Romero et al., 2007). The effect of ethylene on fruit ripening and vegetable senescence is of significant interest for the 4 X-Ray Spectroscopy scientific community. During the postharvest storage of fruit and vegetables, ethylene can induce negative effects, such as senescence, overripening, accelerated quality loss, increased fruit pathogen susceptibility, and physiological disorders. Fruit, vegetables, and flowers have ethylene receptors on their surface. Their actuation promotes ethylene production by the fruit itself and accelerates its ripening and aging (Kartheuser & Boonaert, 2007). Thus, the prevention of postharvest ethylene action is an important goal. Conventional as well as commercial techniques and technologies are used to control the action of ethylene, e. g. ethylene scavengers, especially the potassium permanganate (KMnO4) oxidizer. However, KMnO4 cannot be used in contact with food products due to its high toxicity. Ozone (O3) is also an alternative oxidant, but it is highly unstable and decomposes into O2 in a very short time. Carbons and zeolites are used as ethylene adsorbers and they play a key role in the control of ethylene. This technique only transfers the ethylene to another phase rather than destroying it. Hence, additional disposal or handling steps are needed. New, safe and clean chemical technologies and processes for VOC and ethylene (generated by fruit) abatement are currently being developed (Hussain et al., 2010, 2011a, 2011b, Toma et al., 2006). Conventionally, VOC pollutants are removed by air purifiers that employ filters to remove particulate matter or use sorption materials (e.g. granular activated carbon) to adsorb the VOC molecules. These techniques also transfer the contaminants to another phase instead of destroying them and hence, additional disposal or handling steps are again needed. Moreover, all these sequestration techniques have inherent limitations, and none of them is decisively cost effective. Therefore, there is great demand for a more cost effective and environmentally friendly process that is capable of eliminating VOCs from gas streams, for example photochemical degradation, UV photolysis and photo-oxidation in the presence of some oxidants such as ozone. The photocatalytic oxidation (PCO) of VOCs is a very attractive and promising alternative technology for air purification. It has been demonstrated that organics can be oxidized to carbon dioxide, water and simple mineral acids at low temperatures on TiO2 catalysts in the presence of UV or near-UV illumination. PCO requires a low temperature and pressure, employs inexpensive semiconducting catalysts, and is suitable for the oxidation of a wide range of organics. Some researchers (Augugliaro et al., 1999; Kumar et al., 2005) have already focused on this promising technique, and a great deal of beneficial advancement has been made in the field of VOC abatement. The performance of semiconducting photocatalyst depends above all on its nature and morphology. Most of the studies have shown that the photocatalytic activity of titanium dioxide is influenced to a great extent by the crystalline form, although controversial results have also been reported in the literature. Some authors have stated that anatase works better than rutile (Zuo et al., 2006), others have found the best photocatalytic activity for rutile (Watson et al., 2003), and some others have detected synergistic effects in the photocatalytic activity for anatase–rutile mixed phases (Bacsa & Kiwi, 1998). It has recently been demonstrated that photo-activity towards organic degradation depends on the phase composition and on the oxidizing agent; for example, when the performance of different crystalline forms was compared, it was discovered that rutile shows the highest photocatalytic activity with H2O2, whereas anatase shows the highest with O2 (Testino et al., 2007). It has also been found that photoformed OH species, as well as O2− and O3− anion radicals, play a significant role as a key active species in the complete photocatalytic oxidation of ethylene with oxygen into carbon dioxide and water (Kumar et al., 2005). X-Ray Spectroscopy Tools for the Characterization of Nanoparticles 5 Therefore, in this chapter we have focused in particular on the synthesis of titania nanoparticles (TNP) at a large scale by controlling the optimized operating conditions and using a special passive mixer or vortex reactor (VR) to achieve TNPs with a high surface area and a mixed crystalline phase with more anatase and small amounts of rutile in order to obtain the synergistic effect that occurs between anatase and rutile. These TNPs were characterized and compared with TiO2, synthesized by the solution combustion (TSC) method, and commercially available TiO2 by Degussa P-25 and Aldrich. X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques were used to screen the best candidate with the best characteristics for the above mentioned catalytic applications. 2. Titania synthesis and optimization by means of the XRD technique Many processes can be employed to produce titanium dioxide particles, e. g. flame aerosol synthesis, hydrothermal synthesis, and sol–gel synthesis (Hussain et al., 2010). Flame aerosol synthesis offers the main advantage of being easily scalable to the industrial level, but also suffers from all the disadvantages of high temperature synthesis. Hydrothermal synthesis is instead particularly interesting as it directly produces a crystalline powder, without the need of a final calcination step, which is necessary in the sol–gel process. However, a lack of knowledge on the chemical equilibria of the species in solution and on the kinetics of the nucleation and growth of the different phases makes it difficult to control the overall process. Therefore, at the moment, the sol–gel process is the most common and promising at a lab scale. Although the sol–gel process has been known for almost a century and some of the most important aspects have been clarified, there is still room for improvement as far as individuating the synthesis conditions that result in a powder with improved properties, compared with the commercial products that are currently available, is concerned. Furthermore, upscaling the process from the laboratory to the industrial scale is still a complex and difficult to solve problem. Mixing plays an important role, but its effects are usually underestimated, as can be seen by the qualitative statements (e.g. add drop wise or mix vigorously) that are generally used to define ideal mixing conditions. In our previous studies, TNPs were synthesized at a large scale (2 L gel), and the optimized operating parameters were controlled using the vortex reactor (VR) (Hussain et al., 2010, 2011a). Titanium tetra-isopropoxide (TTIP: Sigma–Aldrich) was used as a precursor in these studies, because of its very rapid hydrolysis kinetics. Two solutions of TTIP in isopropyl alcohol and of water (Milli-Q) in isopropyl alcohol were prepared separately under a nitrogen flux to control the alkoxide reactivity with humidity. Hydrochloric acid (HCl: Sigma–Aldrich) was added to the second solution as a hydrolysis catalyst and deagglomeration agent. The TTIP/isopropanol concentration was taken equal to 1 M to obtain the maximum TiO2 (1 M), whereas the water and hydrochloric acid concentrations were chosen in order to result in a water-to-precursor ratio, W= [H2O]/[TTIP], equal to four, and an acid-to-precursor ratio, H= [H+]/[TTIP], equal to 0.5. The two TTIP and water solutions in isopropyl alcohol were stored in two identical vessels, then pressurized at 2 bars with analytical grade nitrogen, and eventually fed and mixed in the VR. The inlet flow rates were kept equal to 100 mL/min by using two rotameters. This inlet flow rate guarantees very fast mixing, and induces the formation of very fine particle. Equal volumes of reactant solutions (i.e. 1 L) were mixed at equal flow rates at 28 ◦C and then, for both configurations, the solutions exiting the VR were collected in a beaker thermostated at 28 ◦C and gently 6 X-Ray Spectroscopy stirred. The TTIP conversion into TiO2 through hydrolysis and condensation can be summarized in the following overall chemical reaction: Ti(OC3H7)4 +4H2O → TiO2 +2H2O + 4C3H7OH It is well known that a very fast chemical reaction is characterized by an equilibrium that is completely shifted towards the products, and that TiO2 is a thermodynamically very stable substance which results in an almost 100% yield. The reaction product (i.e. gel) was dried in three different ways; dried by a rotavapor, directly in an oven, and in an oven after filtration. The resulting dried powders were eventually calcined at 400 ◦C for 3 h. TSC was synthesized by following the procedure reported in (Sivalingam et al., 2003), but with modified precursors and ratios. TTIP was used as the precursor, glycine/urea as the fuel, at stoichiometric as well as non-stoichiometric ratios, and 400/500 ◦C was adopted as the combustion temperature. After the combustion reaction, the samples were calcined at 400 ◦C for 3 h. Different commercial TiO2 were purchased from Sigma–Aldrich and Aerosil for comparison purposes. The TNPs were dried according to three different commercial processes in order to find the best method. After drying and before calcination, the powder is mainly amorphous and no distinct peak can be observed, as shown in Fig. 1 (Hussain et al., 2010). However, after calcination at 400 ◦C for 3 h, the main crystalline form was anatase (denoted as “A”) and rutile (denoted as “R”) was present to a lower extent (Fig. 1). The optimal drying condition was found by drying in a rotavapor, this resulted in an anatase-to-rutile ratio of 80:20. Details and a comparison with the other drying conditions are reported in Table 1. Compared to TNP, TSC showed a greater rutile phase in all the cases shown in Fig. 2. However, TSC (glycine, 500 ◦C, 1:1) and TSC (urea, 500 ◦C, 1:3) were comparatively better in this category, as shown in Table 1. Fig. 3 shows the XRD patterns of three different commercial TiO2. The TiO2 by Aldrich (anatase) showed a pure anatase phase whereas the TiO2 by Aldrich (technical) had a mixed phase. Degussa P 25 also showed mixed anatase and rutile phases. Fig. 1. XRD patterns of different dried TNPs showing the anatase and rutile phases X-Ray Spectroscopy Tools for the Characterization of Nanoparticles 7 In order to determine the different polymorphs, XRD patterns were recorded on an X’Pert Phillips diffractomer using Cu K radiation, in the following conditions: range = (10–90◦) 2θ; step size 2θ = 0.02. Moreover, quantification of the anatase:rutile phases was performed on the basis of the X’Pert database library (Hussain et al., 2010). Fig. 2. XRD patterns of different titania synthesized by the solution combustion method (TSC) showing the anatase and rutile phases Fig. 3. XRD patterns of different commercial titania showing the anatase and rutile phases 8 X-Ray Spectroscopy Sample Anatase:Rutile (%) TNP (rotavapor dried and calcined) 80:20 TNP (filtered, dried and calcined) 71:29 TNP (oven dried and calcined) 69:31 TSC (glycine, 400 oC, 1:1) 55:45 TSC (glycine, 500 oC, 1:1) 60:40 TSC (urea, 500 oC, 1:3) 61:39 TSC (urea, 500 oC, 1:1) 58:42 TiO2 commercial (aldrich, technical) 80:20 TiO2 commercial (aldrich, anatase) 100:0 TiO2 commercial (degussa P 25) 70:30 Table 1. Crystalline phases of different TiO2 obtained by means of XRD It is generally accepted that anatase demonstrates a higher activity than rutile, for most photocatalytic reaction systems, and this enhancement in photoactivity has been ascribed to the fact that the Fermi level of anatase is higher than that of rutile (Porkodi & Arokiamary, 2007). The precursors and the preparation method both affect the physicochemical properties of the specimen. In recent years, Degussa P 25 TiO2 has set the standard for photoreactivity in environmental VOC applications. Degussa P 25 is a non-porous 70:30% (anatase to rutile) material. Despite the presence of the rutile phase, this material has proved to be even more reactive than pure anatase (Bhatkhande et al., 2001). Therefore, a mixed anatase–rutile phase seems to be preferable to enable some synergistic effects for photocatalytic reactions since the conduction band electron of the anatase partly jumps to the less positive rutile part, thus reducing the recombination rate of the electrons and the positive holes in the anatase part. The synthesized TNP is characterized by a similar anatase–rutile mixture. Fig. 4(a) (Hussain et al., 2011a) shows the effect of calcination temperatures at a specific moderate calcination time (3 h) on the TNP by XRD patterns in order to establish the optimized calcination temperature. It was found that when the calcination temperature was below 500 ◦C, the TNP sample dominantly displayed the anatase phase with just small amounts of rutile. The synthesized TNP was dried in a rotary evaporator and this process was followed by complete water evaporation at 150 ◦C in an oven before calcination. Just after drying, the powder was mainly amorphous and no distinct peak was found, as shown in Fig. 4(b), although there were some very low intensity peaks at 2θ = 38.47, 44.7, 65.0 and 78.2, which were due to the aluminum sample holder. These aluminum sample holder peaks can also be observed in other samples, as shown in Fig. 4. The effect of calcination times on the characteristics of TNP is shown in Fig. 4(b); these data indicate that even the longer calcination time (7 h) has no significant effect on the TNP and the main phase remains anatase with low amounts of rutile. Therefore, the effect of calcination times at 400 ◦C is not so severe. X-Ray Spectroscopy Tools for the Characterization of Nanoparticles 9 Fig. 4. XRD patterns of TNP at different calcinations (a) temperatures and (b) times 3. Synthesis confirmation of optimized TNP with EDX analysis The elemental composition of TNPs was checked by EDX analysis equipping a highresolution FE-SEM instrument (LEO 1525). Figure 5 shows the EDX analysis of the optimized TNP (dried by rotavapor and calcined at 400 oC for 3 h). This figure demonstrates that the main components are O and Ti with small amounts of Cl impurity. This Cl impurity originated from the HCl that was added during the synthesis and it is usually favorable for the photocatalytic reaction (Hussain et al., 2011b). Fig. 5. EDX analysis of TNP 10 X-Ray Spectroscopy 4. Photocatalytic reaction All the ethylene, propylene, and toluene photocatalytic degradation tests were performed in a Pyrex glass reactor with a total volume of 2 L. The experimental setup of the photocatalysis reaction includes a Pyrex glass reactor (transparent to UV light), connectors, mass flow controllers (MFC, Bronkhorst high tech), and a UV lamp (Osram ULTRAVITALUX 300W. This lamp has a mixture of UVA light ranging from 320–400 nm and UVB light with a 290–320 nm wavelength which produces 13.6 and 3.0 W radiations, respectively; it is ozone-free and the radiations are produced by a mixture of quartz burner and a tungsten wire filament, as mentioned in the manufacturer’s indications). The set up also has gas cylinders (1000ppm ethylene/propylene/toluene), a gas chromatograph (Varian CP3800) equipped with a capillary column (CP7381) and a flame ionization detector (FID) with a patented ceramic flame tip for ultimate peak shape and sensitivity, which was used for the gas analysis of the products (Hussain et al., 2010, 2011a, 2011b). 4.1 Screening of the best photocatalyst for ethylene photodegradation The calcined TiO2 photocatalyst sample was spread homogeneously, by hand, on a support placed inside the Pyrex glass reactor. An initial humidity of 60% was supplied to the photocatalyst to initiate the photocatalytic reaction. The VOC (ethylene, propylene or toluene) was continuously flushed in the reactor, with the help of the MFC, at a constant flow rate of 100 mL/min. After achieving equilibrium in the peak intensity, the UV light was turned on, the reaction products were analyzed by GC, and the conversion was calculated. The reaction experiments were repeated twice and the results showed reproducibility. PCO of the ethylene over TNP was performed at ambient temperature and compared with different TSC and commercial TiO2 photocatalysts. The important feature of this reaction is the use of air instead of conventional oxygen. In this situation, the required oxygen for the photocatalytic reaction is obtained from the air, leading towards the commercialization step. Fig. 6 shows the percentage conversion of ethylene as a function of time (Hussain et al., 2010). The TNP showed significantly higher conversion than all the other samples. Degussa P 25 showed comparable results. Even the 100% anatase commercial TiO2 showed very low conversion in this reaction. Obviously, TSC synthesized in different ways using urea and glycine were also not suitable for this application. The TNP was active for 6 h of reaction time, unlike degussa P 25, which started to deactivate at this time. This deactivation of degussa P 25 is due to its inferior properties. Moreover, the TNP showed higher activity and better stability because of its superior properties. The main superior characteristic of TNP in ethylene photodegradation is that it has a main anatase phase with limited rutile (Table 1). The photocatalyst become active when photons of a certain wavelength hit the surface, which promotes electrons from the valence band and transfers them to the conductance band (Bhatkhande et al., 2001). This leaves positive holes in the valence band, and these react with the hydroxylated surface to produce OH• radicals, which are the most active oxidizing agents. In the absence of suitable electron and hole scavengers, the stored energy is dissipated, within a few nanoseconds, by recombination. If a suitable scavenger or a surface defect state is available to trap the electron or hole, their recombination is prevented and a subsequent redox reaction may occur. In TNP, which is similar to degussa P 25, the conduction band electron of the anatase part jumps to the less positive rutile part, thus reducing the rate of recombination of the electrons and positive holes in the anatase part. X-Ray Spectroscopy Tools for the Characterization of Nanoparticles 11 Fig. 6. Ethylene photodegradation over different titania photocatalysts with the illumination time 4.2 Optimization of photocatalyst for ethylene photodegradation The PCO of ethylene was performed at ambient temperature over TNPs calcined at different calcination temperatures and times (Fig. 7) in order to check the catalytic performance of the developed TNP material (Hussain et al., 2011a). Air was again used instead of conventional oxygen in order to obtain more representative data for practical application conditions, in view of commercialization. After a preliminary saturation of the sample under an ethylene flow, conversion did not occur in the dark in any of the experiments, even in the presence of a catalyst or in the presence of UV light and the absence of a catalyst. Therefore, it can be concluded that the reaction results reported hereafter are only induced photocatalytically. Figs. 7(a) and 7(b) show the percentage conversion of ethylene as a function of illumination time. A steady-state conversion is reached after approximately 6 h of illumination for all the samples. This rather long time is necessary because of the type of experimental apparatus that has been employed; on the one hand because of fluid-dynamic reasons and on the other hand to make the surface of the sample reach a steady, equilibrium coverage value. The CO and CO2 measurements of the outlet gases demonstrated that ethylene oxidizes completely to CO2, and only traces of CO are observable. The TNP sample at the highest calcination temperature (700 ◦C) showed the worst performance, as can be observed in Fig. 7(a). However, the highest conversion was obtained for TNP calcined at 400 ◦C for 3 h. As expected, all the other sample preparation conditions resulted in a lower catalytic activity. In other words, the TNP sample at the highest calcination time (7 h), also showed the lowest

Author Shatendra K. Sharma Isbn 9789533079677 File size 20MB Year 2011 Pages 289 Language English File format PDF Category Physics Book Description: FacebookTwitterGoogle+TumblrDiggMySpaceShare This book consists of selected chapters on the recent applications of x-ray spectroscopy that are of great interest to the scientists and engineers working in the fields of material science, physics, chemistry, astrophysics, astrochemistry, instrumentation, and techniques of x-ray based characterization. The book covers some basic principles of satellite x-rays as characterization tools for chemical properties and the physics of detectors and x-ray spectrometer. The techniques like EDXRF, WDXRF, EPMA, satellites, micro-beam analysis, particle induced XRF, and matrix effects are discussed. The characterization of thin films and ceramic materials using x-rays is also covered. The chapters have been grouped into two major sections based upon the techniques and applications. Contents Preface Part 1 XRF Processes and Techniques 1 X-Ray Spectroscopy Tools for the Characterization of Nanoparticles 2 A Practical Application of X-Ray Spectroscopy in Ti-AI-N and Cr-AI-N Thin Films 3 High Resolution X-Ray Spectroscopy with Compound Semiconductor Detectors and Digital Pulse Processing Systems 4 Analysis of the ? Satellite Lines in X-Ray Emission Spectra 5 Application of Wavelength Dispersive X-Ray Spectroscopy in X-Ray Trace Element Analytical Techniques Part 2 Characterization and Analytical Applications of X-Rays 6 The Use of Electron Probe MicroAnalysis to Determine the Thickness of Thin Films in Materials Science 7 Chemical Quantification of Mo-S, W-Si and Ti-V by Energy Dispersive X-Ray Spectroscopy 8 Quantification in X-Ray Fluorescence Spectrometry 9 The Interaction of High Brightness X-Rays with Clusters or Bio-Molecules 10 Employing Soft X-Rays in Experimental Astrochemistry 11 X-Ray Analysis on Ceramic Materials Deposited by Sputtering and Reactive Sputtering for Sensing Applications 12 Application of Stopped-Flow and Time-Resolved X-Ray Absorption Spectroscopy to the Study of Metalloproteins Molecular Mechanisms 13 Nanoscale Chemical Analysis in Various Interfaces with Energy Dispersive X-Ray Spectroscopy and Transmission Electron Microscop     Download (20MB) An Introduction To Beam Physics Electromagnetic Radiation in Analysis and Design of Organic Materials Microwave Materials and Applications, 2 Volume Set Radiation Detection and Measurement, 4 edition Electron Backscatter Diffraction in Materials Science Load more posts

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