EDX spectra

Because of the limited energy resolution in EDX spectra an overlap of peaks can often occur, depending on the composition of the material to be analyzed. The situation is much improved in WDXS, for which the energy resolution is approximately 10 eV and better. This is demonstrated in Fig. 4.25, in which the WDX and EDX spectra recorded from BaTi03 are compared. Here, WDXS enables easy resolution of the Ba-La and Ti-Ka lines this is impossible by EDXS. In addition, for WDXS the... 

The procedure commonly used to quantify EDX spectra was originally outlined by Castaing [4.109], although for the general situation of investigating bulk materials. To a good approximation it can be assumed that the concentration Csp of an element present in an unknown sample is related to the concentration Cst of the same element in a standard specimen by... 

Figure 5.19. EDXS spectra corresponding to the images in Figure 5.18(a) and (b) respectively.

Fig. 12.13 SEM micrographs and EDX spectra of the SGA-Ca surface before and after soaking in SBF. The EDX spectra clearly show the evolution of the inorganic chemical composition on the surface from silicon and calcium oxide to a calcium phosphate.

EDX has, for instance, been used to determine the composition of individual particles in a bimetallic Pt-Pd catalyst on alumina. Electron micrographs show the presence of particles with diameters between 0.5 and 5 nm, while EDX spectra show the X-ray fluorescence peaks of Al, Pt and Pd of the individual particles and enable one to investigate whether all catalyst particles have the same compositions [10,22],... 

Figure 6. EDX spectra of a Pd filled PWHGM after smashed open to reveal its Pd.

Table IV. Normalized EM-EDX Spectra of Some "Pure" Minerals...

An experimental diffraction contrast image of model catalysts of Ag/alumina, prepared by evaporation, is shown in figure 5.5(a) at 200 kV. The corresponding EDX spectra from and off the metal particle are shown in figures 5.5(b) and (c), respectively. An HRTEM image of Pt/alumina at 400 kV in figure 5.6. 

Figure 5.5. (a) TEM image of Ag/alumina catalysts (b) and (c) are the EDX spectra from and off the catalyst particle, respectively, indicating the Ag metal and the support (sample on Cu-grid). 

Table 2 Semi-quantitative elemental analysis of sulphur on photo-sulphonated LDPE films obtained from the EDX spectra...

SEM of the treated films indicated a progressive change in the surface morphology, as seen in Fig. 17. After 5 min of reaction time (Fig. 17b), the surface appeared slightly smoother than that of the control sample (Fig. 17a), upon 10 min exposure (Fig. 17c) submicron-sized blisters appeared and at 30 min (Fig. 17d), the defects covered the entire surface and were of several micron in diameter. The EDX spectra substantiated the presence of sulphur on the treated films and its absence on the control. The results of this semi-quantitative elemental analysis of sulphur on the film surface, computed from the collective EDX spectra, are shown in Table 2. The tabulated results indicate that the relative concentration of sulphur in these films increases with an increase in the reaction time. 

Vanadium Porphyrin on EuY. SEM-EDX spectra of EuYV(p)AAAC are shown in Fig. 1. A sharp V Ka peak can be detected in the matrix (Fig. 1b) and only a small V Ka peak is observed in the zeolite (Fig.1a), indicating movement of vanadium from the zeolite to the gel after calcination. The large (8.45) V% reported in Table I may be due to V2O5 crystallites at the surface produced during calcination. Formation of vanadium is consistent with luminescence results obtained with these materials (10). 

In order to clarify the role of steaming on vanadium migration, the EuY component doped with V (EuYV) was calcined, prior to being mixed with the gel. The SEM-EDX spectra of the steamed sample, (EuYV(p)CAAAS), are illustrated in Fig. 3. Corresponding analytical data are given in Table I. 

Vanadium Porphyrin on AAA-alumina. SEM-EDX spectra of AAAV(p) EuYC are presented in Fig. 4. A small vanadium Ka peak at 4.96 kV can be observed for the zeolite particles (Fig. 4a) indicating that only small amounts of vanadium initially deposited on the matrix move to the zeolite during calcination, Fig. 4b. Eu K peaks seen for the gel are attributed to the presence of small EuY crystals embedded into the gel macroporous structure, Figure 4b. 

Figure 12. SEM/EDX spectra of (a) SiC>2 in EuYV(p)Si02C mixture (b) Y-AI2O3 in EuYV(n)-Y-Al2C>3C mixture, and (c) yAteOs in EuYV(p)-mixture...

Figure 13. SEM/EDX spectra of EuYV(p)-y-AI203CS mixture (a) zeolite (b) matrix.

Figures 3.5 and 3.6 show typical EDX spectra obtained from a sample of catalyst B after 1000 hours of use in a molten carbonate environment. Figure 3.5. shows the spectrum recorded from the nickel aggregate Figure 3.6. shows that recorded from the alumina support. Inspection of all the data reveals that up to and including 50 hours of operation, potassium covered both the support and the nickel areas of the catalyst. However, for catalysts discharged after 100 hours, potassium is associated primarily with the alumina support.

In EDX experiments on thick samples, for example in SEM, almost all the energy of the incident electron beam is consumed to produce X-rays and the number of atoms in a sample can be calculated from the X-ray intensities in the EDX spectra, by carrying out the ZAF calibration (Z = the atomic number effect A = the absorption effect and F = the fluorescence effect) [18]. However, HRTEM specimens are usually thin, 200nm or less. In this case, most electrons in the incident beam will pass through the specimen and the ZAF calibration cannot be done. In practice, we use some standard specimens (whose compositions are known) as references to obtain a relative composition of a target sample. 

Quantitative analysis of the chemical composition of the specimen by EDX relies on obtaining good EDX spectra with the intensities of all the emission lines being almost purely proportional to the concentration of the atoms in the sample. However, there are several technical problems that could affect the quality of an EDX spectrum. The most important one is the absorption problem. Absorption of X-rays can occur in various situations. For example, the X-rays may be absorbed by the specimen itself, by the sample near the examined area, by the specimen grid bars and so on. Therefore isolated particles and thin areas of the particles are always selected to collect the EDX spectra so that the absorption can be reduced to its lowest level. Even when the experimental conditions are well controlled, the... 

The ingress of electrolyte cations into the MOF framework was confirmed by scanning electron microscopy/energy-dispersive x-ray (EDX) analysis of electrochemically treated deposits of Cu-MOF. Results obtained after application of a reductive potential step to Cu-MOF crystals in contact with acetate buffers are shown in Figure 5.3. Here, EDX spectra for (a) pristine Cu-MOF and (b) Cu-MOF after application of a constant potential of-1.0 V for 10 min are shown. EDX spectra of original Cu-MOF crystals exhibits prominent Cu peaks at 1.0, 8.0, and 8.4 keV accompanied by a Si signal at 1.9 keV. After the electrolysis step, an additional Na peak at 1.1 keV appears. 

FIGU RE 5.3 EDX spectra recorded for a Cu-MOF deposit (a) before and (b) after application of a constant potential of-1.0 V during 10 min in contact with 0.50 M acetate buffer (pH 4.85). (From Domenech et al., 2006d. Electrochem. Commun. 8, 1830-1834, with permission.)... 

Fig. 11.3 EDX spectra of the nylon membrane impregnated with [bmimT[PF ], [bmim ][BF ] and [bmim [NTfj"]...

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