Analysis microscopy, Analytical

A multifaceted characterization effort to stndy these materials as a function of thermal treatment has been undertaken. The techniques include BET surface area measurements. X-ray diffraction, chemisorption, scanning and high-resolution transmission electron microscopy, analytical electron microscopy, neutron activation analysis, atomic absorption spectroscopy, FTIR and isotopic tracer studies. The details of catalyst preparation have been previously... 

Other physical methods used in the investigation of N.a. structure are Hybridization (see), electron microscopy, analytical ultracentrifugation, CsQ density gradient centrifugation. X-ray diffraction analysis, infrared spectroscopy, optical rotatory dispersion, light scattering photometry and viscosity measurements. 

Quantitative X-ray analysis in analytical electron microscopy is now a most straightforward technique. Matrix (interelement) correction procedures based upon first principles physical models provide great flexibility in examining unknown samples of arbitrary composition. According to Castaing [251,252] ... 

Chemical composition by chemical analysis, spectrometry [Analytical spectroscopic methods ISO 6955 Fourier Transform Infrared Analysis (FT-IR) ASTM E1252], chromatography, microanalysis, microscopy, etc. Determination of molecular structures on the nano- and micro-scale, using diffractometry, micrography, spectroscopy, scattering and other methods [ASTM 5017 NMR of LLDPE]. 

Materials characterization techniques, ie, atomic and molecular identification and analysis, ate discussed ia articles the tides of which, for the most part, are descriptive of the analytical method. For example, both iaftared (it) and near iaftared analysis (nira) are described ia Infrared and raman SPECTROSCOPY. Nucleai magaetic resoaance (nmr) and electron spia resonance (esr) are discussed ia Magnetic spin resonance. Ultraviolet (uv) and visible (vis), absorption and emission, as well as Raman spectroscopy, circular dichroism (cd), etc are discussed ia Spectroscopy (see also Chemiluminescence Electho-analytical techniques It unoassay Mass specthot thy Microscopy Microwave technology Plasma technology and X-ray technology). 

The STEM instrument itself can produce highly focused high-intensity beams down to 2 A if a field-emission source is used. Such an instrument provides a higher spatial resolution compositional analysis than any other widely used technique, but to capitalize on this requires very thin samples, as stated above. EELS and EDS are the two composition techniques usually found on a STEM, but CL, and even AES are sometimes incorporated. In addition simultaneous crystallographic information can be provided by diffraction, as in the TEM, but with 100 times better spatial resolution. The combination of diffraction techniques and analysis techniques in a TEM or STEM is termed Analytical Electron Microscopy, AEM. A well-equipped analytical TEM or STEM costs well over 1,000,000. 

D. B. Williams. Practical Analytical Electron Microscopy in Materials Science. Verlag Chemie International, Weinheim, 1984. A good monograph discussing the use and applications of AEM, especially at intermediate voltages. The discussion on EDS is an excellent primer for using X-ray analysis on a TEM. 

Principles of Analytical Electron Microscopy (D. C. Joy, A. D. Romig, and J. I. Goldstein, eds.) Plenum Press, New York, 1986. Another book, more readily available, discussing all aspects of AEM. Approximately one-quarter of the book is devoted to EDS and a discussion of thin-film analysis in the TEM. 

The combined use of energy-dispersive X-ray spectroscopy and TEM/STEM is a routine method of analytical electron microscopy enabling both qualitative and quantitative chemical analysis of interfaces and interlayers with high lateral resolution. Reso-... 

Ultrafiltration utilizes membrane filters with small pore sizes ranging from O.OlS t to in order to collect small particles, to separate small particle sizes, or to obtain particle-free solutions for a variety of applications. Membrane filters are characterized by a smallness and uniformity of pore size difficult to achieve with cellulosic filters. They are further characterized by thinness, strength, flexibility, low absorption and adsorption, and a flat surface texture. These properties are useful for a variety of analytical procedures. In the analytical laboratory, ultrafiltration is especially useful for gravimetric analysis, optical microscopy, and X-ray fluorescence studies. 

Magonov, S., Atomic Force Microscopy in Analysis of Polymers, in Encyclopedia of Analytical Chemistry, Meyers, R.A., Ed., Wiley, New York, 2000. 

Price, D.M., Reading, M., Caswell, A., Hammiche, A., and PoUock, H.M., Micro-thermal analysis A new form of analytical microscopy, Microsc. Anal., 65, 17, 1998. 

The large size of CPOs allows their direct observation. For this purpose, scanning tunneling microscopy (STM) is the best method [32,34]. Electron microscopic analysis is used for phthalocyanine 3 and its derivatives however, most of the porphyrin derivatives are decomposed by electron beam irradiation. Presently, although only a limited number of researchers are able to perform atomic-scale resolution measurement, this powerful analytical method is expected to be used widely in the future. The author reported a summary of STM studies on porphyrins elsewhere [34]. 

Analytical electron microscopy permits structural and chemical analyses of catalyst areas nearly 1000 times smaller than those studied by conventional bulk analysis techniques. Quantitative x-ray analyses of bismuth molybdates are shown from lOnm diameter regions to better than 5% relative accuracy for the elements 61 and Mo. Digital x-ray images show qualitative 2-dimensional distributions of elements with a lateral spatial resolution of lOnm in supported Pd catalysts and ZSM-5 zeolites. Fine structure in CuLj 2 edges from electron energy loss spectroscopy indicate d>ether the copper is in the form of Cu metal or Cu oxide. These techniques should prove to be of great utility for the analysis of active phases, promoters, and poisons. 

Analytical electron microscopy (AEM) permits elemental and structural data to be obtained from volumes of catalyst material vastly smaller in size than the pellet or fluidized particle typically used in industrial processes. Figure 1 shows three levels of analysis for catalyst materials. Composite catalyst vehicles in the 0.1 to lOim size range can be chemically analyzed in bulk by techniques such as electron microprobe, XRD, AA, NMR,... 

Analysis of individual catalyst particles less than IMm in size requires an analytical tool that focuses electrons to a small probe on the specimen. Analytical electron microscopy is usually performed with either a dedicated scanning transmission electron microscope (STEM) or a conventional transmission electron microscope (TEM) with a STEM attachment. These instruments produce 1 to 50nm diameter electron probes that can be scanned across a thin specimen to form an image or stopped on an image feature to perform an analysis. In most cases, an electron beam current of about 1 nanoampere is required to produce an analytical signal in a reasonable time. 

Figure 1. Three levels of analysis for catalyst materials, a) bulk analysis of an entire catalyst pellet, b) surface analysis and depth profiling from the surface inward, c) analytical electron microscopy of individual catalyst particles too small for analysis by other techniques.

Analytical electron microscopy (AEM) can use several signals from the specimen to analyze volumes of catalyst material about a thousand times smaller than conventional techniques. X-ray emission spectroscopy (XES) is the most quantitative mode of chemical analyse in the AEM and is now also useful as a high resolution elemental mapping technique. Electron energy loss spectroscopy (EELS) vftiile not as well developed for quantitative analysis gives additional chemical information in the fine structure of the elemental absorption edges. EELS avoids the problem of spurious x-rays generated from areas of the spectrum remote from the analysis area. 

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