Electron microprobe method

In the present case, conditions are adjusted so that helium and silyl metal-carbonyl vapor (typically with a mole ratio of 30 1) have a total pressure of about 1 mmHg. Decomposition is very rapid on entering the furnace crystalline solids may form around the exit nozzle, while a matt grey or mirror-like thin film is deposited on a small plate about 5 mm from the nozzle. These thin films have been analyzed by X-ray powder and electron microprobe methods, and directly by atomic absorption spectroscopy (33,121, 187). 

The Fe " content in xenolith spinels is large and unlike garnet or pyroxenes can be measured reliably from electron microprobe methods (Wood and Virgo, 1989) and is useful for oxygen barometry of spinel peridotites (Wood et al, 1990 Ballhaus et al., 1991). Representative analyses from different peridotite facies are shown in Table 3. 

Using an electron microprobe method, it has been found that this element is concentrated in nodular lymphatic cells and is uniquely localized in the lysosomes of macrophages where it is associated with phos-... 

The silica loading and thickness in beads measured by electron microprobe method are shown in Figure 8 and Table 6. Table 7 summarizes the pore structure of fresh and aged catalysts (top 1 inch). The surface area and micropore volume of the aged catalyst was lower than that of the fresh catalyst, suggesting that silica has been preferentially deposited within the micropores of the catalyst, probably as a gaseous silica compound rather than as a particulate. 

Table 6 Silica loading and thickness in beads that were measured by electron microprobe method (from ref. 2)...

Electron Microprobe A.na.Iysis, Electron microprobe analysis (ema) is a technique based on x-ray fluorescence from atoms in the near-surface region of a material stimulated by a focused beam of high energy electrons (7—9,30). Essentially, this method is based on electron-induced x-ray emission as opposed to x-ray-induced x-ray emission, which forms the basis of conventional x-ray fluorescence (xrf) spectroscopy (31). The microprobe form of this x-ray fluorescence spectroscopy was first developed by Castaing in 1951 (32), and today is a mature technique. Primary beam electrons with energies of 10—30 keV are used and sample the material to a depth on the order of 1 pm. X-rays from all elements with the exception of H, He, and Li can be detected. 

Quantitative Electron-Probe Microanalysis. (V. D. Scott and G. Love, eds.) John Wiley Sons, New York, 1983. Taken from a short course on the electron microprobe for scientists working in the field. A thorough discussion of EDS and WDS is given, including experimental conditions and specimen requirements. The ZAF correction factors are treated extensively, and statistics, computer programs and Monte Carlo methods are explained in detail. Generally, a very useftd book. 

The characteristic feature of solid—solid reactions which controls, to some extent, the methods which can be applied to the investigation of their kinetics, is that the continuation of product formation requires the transportation of one or both reactants to a zone of interaction, perhaps through a coherent barrier layer of the product phase or as a monomolec-ular layer across surfaces. Since diffusion at phase boundaries may occur at temperatures appreciably below those required for bulk diffusion, the initial step in product formation may be rapidly completed on the attainment of reaction temperature. In such systems, there is no initial delay during nucleation and the initial processes, perhaps involving monomolec-ular films, are not readily identified. The subsequent growth of the product phase, the main reaction, is thereafter controlled by the diffusion of one or more species through the barrier layer. Microscopic observation is of little value where the phases present cannot be unambiguously identified and X-ray diffraction techniques are more fruitful. More recently, the considerable potential of electron microprobe analyses has been developed and exploited. 

Stoichiometric variations in compositions of a material and of surface layers can be revealed by AEM. Because a relatively small amount of scattering occurs through a thin HRTEM specimen, X-rays are generated from a volume that is considerably less than in the case of electron microprobe analysis (EPMA). For quantitative microanalysis, a ratio method for thin crystals (57) is used, given by the equation ... 

X-ray diffraction uses X-rays of known wavelengths to determine the lattice spacing in crystalline structures and therefore directly identify chemical compounds. This is in contrast to the other X-ray methods discussed in this chapter (XRF, electron microprobe analysis, PIXE) which determine concentrations of constituent elements in artifacts. Powder XRD, the simplest of the range of XRD methods, is the most widely applied method for structural identification of inorganic materials, and, in some cases, can also provide information about mechanical and thermal treatments during artifact manufacture. Cullity (1978) provides a detailed account of the method. 

Some of the disadvantages of the electron-probe method may be overcome, as in other methods, by the use of complementary techniques. Such techniques can complete the results obtained by electron microprobe. For instance, the introduction of a proton microprobe [39], which is much more sensitive (by two orders of magnitude) than the electron microprobe, and may be used with very good results in geochemical and cosmochemical studies. 

Recently, methods for quantitatively determining the chemical element composition of solid materials by x-ray emission spectroscopy using the electron microprobe have become available. A significant advantage of the electron microprobe, compared with methods for bulk analysis. Is Its capability for rapid analysis of many different mlcron-slze areas of a solid sample. Thus, In a relatively short time, we can obtain several hundred quantitative analyses of the chemical element content of a solid sample. These analyses usually will be different because sample homogeneity Is absent on the micron level. Thus, each chemical analysis Is a linear sum of the chemical elements In the subset of minerals present at that location. Generally, we expect the number of minerals present In a mlcron-slze spot to be less than the total number of minerals In the bulk sample. 

The accuracy of some isothermal techniques, particularly those that rely on observation of phases, is limited by the number of different compositions that are prepared. For example, if two samples are separated by a composition of 2at%, and one is single-phase while the other two-phase, dien formally the phase boundary can only be defined to within an accuracy of 2at%. This makes isothermal techniques more labour intensive than some of the non-isothermal methods. However, because it is now possible to directly determine compositions of phases by techniques such as electron microprobe analysis (EPMA), a substantially more quantitative exposition of the phase equilibria is possible. 

If mixing in each site is not ideal, would differ from the real equilibrium constant by the quotient of activity coefficients and hence may depend on composition. The measurement of the site occupancy (the fraction of Fe and Mg in each of Ml and M2 sites) is not trivial. There are two methods to determine the intracrystalline site distribution. One is by Mossbauer spectroscopy (MS), in which there are a pair of outer and smaller peaks, which are due to Fe in Ml site, and a pair of inner and larger peaks, which are due to Fe in M2 site (Figure 2-3). The ratio of Fe in Ml site to Fe in M2 site is assumed to be the area ratio of the pair of Ml peaks to the pair of M2 peaks. Using total Fe content from electron microprobe analysis, and the ratio from Mossbauer spectroscopy, Fe(Ml) and Fe(M2) concentrations can be obtained. 

After the experiment, the experimental charge is prepared for analysis of the diffusion component or species. The analytical methods include microbeam methods such as electron microprobe, ion microprobe, Rutherford backscatter-ing, and infrared microscope to measure the concentration profile, as well as bulk methods (such as mass spectrometry, infrared spectrometry, or weighing) to determine the total gain or loss of the diffusion component or species. Often, the analysis of the diffusion profile is the most difficult step in obtaining diffusivity. 

This method has been most widely used in (i) the °K- °Ar system, (ii) the U-Th-He system, (iii) the U-Pb dating of zircon, and (iv) the U-Th-Pb dating of monazite using electron microprobe measurements. The last is a developing method with large errors because of the low analytical precision and because isotopes are not measured. 

The amount and uniformity of the solid state reaction of halogen with TTF was probed by the electron microprobe technique. In this analytical method, low energy electron irradiation of a sample provides X-ray core level emissions, characteristic of the element and its relative concentration. Our initial analyses indicated a dramatic dependence of the halogen concentration with the energy of the electron beam. To probe this phenomenon further,... 

Although a number of secondary minerals have been predicted to form in weathered CCB materials, few have been positively identified by physical characterization methods. Secondary phases in CCB materials may be difficult or impossible to characterize due to their low abundance and small particle size. Conventional mineral identification methods such as X-ray diffraction (XRD) analysis fail to identify secondary phases that are less than 1-5% by weight of the CCB or are X-ray amorphous. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), coupled with energy dispersive spectroscopy (EDS), can often identify phases not seen by XRD. Additional analytical methods used to characterize trace secondary phases include infrared (IR) spectroscopy, electron microprobe (EMP) analysis, differential thermal analysis (DTA), and various synchrotron radiation techniques (e.g., micro-XRD, X-ray absorption near-eidge spectroscopy [XANES], X-ray absorption fine-structure [XAFSJ). 

Ultimately, all quantitative analytical methods rely upon standards, whose composition is determined by the classical techniques of wet chemical quantitative analysis. Obviously, the preferred techniques for analyzing art objects are nondestructive, such as x-ray fluorescence, neutron activation, electron microprobe (both dispersive and nondispersive techniques), and so forth. Emission spectrographic analysis is not suit-... 

The presence of small lead inclusions is easily established by using the x-ray modulation method on the microprobe. We believe that a lineal intercept analysis from pictures taken by this method is probably the most accurate if the electron microprobe is used. 

In on effort to establish the mechanism of coal flotation and thus establish the basis for an anthracite lithotype separation, some physical and chemical parameters for anthracite lithotype differentiation were determined. The electrokinetic properties were determined by streaming potential methods. Results indicated a difference in the characteristics of the lithotypes. Other physical and chemical analyses of the lithotypes were mode to establish parameters for further differentiation. Electron-microprobe x-ray, x-ray diffraction, x-ray fluorescent, infrared, and density analyses were made. Chemical analyses included proximate, ultimate, and sulfur measurements. The classification system used was a modification of the Stopes system for classifying lithotypes for humic coals. 

The partially oxidized mixed-valence complexes were generated by electrochemical methods. In the case of the BU4N salt (x = 0.29), the extent of oxidation was determined by elemental analysis, electron microprobe analysis, mass spectra and the X-ray structure analysis only elemental analysis was cited for the Et4N (x = —0.5) derivative. Upon reduction, the essentially planar anions exhibit the same Ni—S and S—C bond lengthening (see Table 4) as mentioned in Section 16.5.3.1. Based on the relative changes in the last two entries in the above table (then the only available data), Lindqvist et a/.184 185 suggested the redox process was centered on the metal. 

The thickness of the deposits was determined by the ball cratering method or SEM measurement of cross-sections. The elemental composition was determined by electron microprobe analysis with wavelength dispersive spectroscopy (EPMA-WDS) on a Camebax Cameca equipment and by X-ray photoelectron spectroscopy (XPS) on a VG Escalab MK2 apparatus... 

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