Hues, Luke Lovejoy, in, 2008 10.2.6 Energy dispersive X-ray spectroscopyEnergy dispersive X-ray analysis 32 (EDS or EDX) is an X-ray fluorescence technique in which the excitation source used to generate the core vacancy, see Figure 10.1-2, is typically a beam of energetic electrons, commonly from a scanning electron microscope (SEM). The energies of the resulting X-ray fluorescence photons is determined in the same manner as in TXRF, typically with an SiLi detector and detection limits are on the order of 0.1–1 atomic%.

It is a fast, non-destructive analytical technique that is relatively inexpensive and readily adapted to most SEM instruments. EDS is quite useful in the analysis of particulate and other localized forms of contamination. Images of the contamination distribution may be obtained by monitoring the detected X-ray intensity at an energy characteristic of a particular element, as a function of the scanned electron beam position. However, it must be remembered that the high-energy electrons generates X-ray at a considerable depth into the sample 33 (up to 3–5 μm) and the X-rays have an escape depth well beyond this thickness. This is particularly true if a normal (perpendicular to the surface) electron beam is used. Therefore, when analyzing small particles, e.g. ∼0.2 μm in diameter or less on a SiO 2 film, the majority of the analytical signal is generated from the underlying film and the particle may be misidentified as a silica particle.

Pratima Bajpai, in, 2018 Scanning Electron Microscopy With Elemental AnalysisSEM with energy dispersive X-ray analysis (EDAX) is a very useful tool for qualitative and semiquantitative analysis of elements with atomic numbers of 13 or higher (aluminum and heavier) on the surface of paper. Electrons have very little penetrating power, so only the surface is characterized. It is very useful for looking at element distributions on the surface or through the thickness of paper if cross sections are made.When elements are bombarded with electrons, they give off X-rays at frequencies (measured in energy units of electron volts) characteristic to the element.

Energy-dispersive X-ray spectroscopy (also known as EDS, EDX, or EDXA) is a powerful technique that enables the user to analyze the elemental composition of a desired sample. The major operating principle that allows EDS to function is the capacity of high energy electromagnetic radiation (X-rays) to eject 'core' electrons (electrons that are. Introduction to Energy Dispersive X-ray Spectrometry (EDS) Please visit our website for more information at Prepared by Emil.

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With proper calibration, the number of X-rays given off shows the relative amount of that material. Fig. 2.22 shows an analysis of a 3M Post-it note from 1987 (before most mills went to alkaline papermaking). HANS-JURGEN SEIFERT. TAMARA JANTZEN, in, 2008 IV.2.2.2 Cu–Mg–Zn systemExperimental investigations by energy-dispersive X-ray analysis were carried out on ternary Cu–Mg–Zn alloys to provide missing data on the copper solubilities in the Mg–Zn phases 98Lia2. Ternary solubilities are described in the literature for only the Laves phases C15 (MgCu 2), C14 (MgZn 2) and C36 (Mg 2CuZn 3) along the quasibinary section MgCu 2–MgZn 2.These phases were modelled by Cu–Zn exchange, Mg(Cu 1– xZn x).

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The weak tendency for antistructure atom formation (copper and zinc on the magnesium sublattice and magnesium on the Cu–Zn sublattice) was interpolated between the binary boundary systems. The Gibbs free energies of the three Laves phases were optimised along the quasibinary join MgCu 2–MgZn 2 using the published liquidus, solidus and enthalpy of mixing data. The binary intermetallic phases MgZn, Mg2Zn3 and Mg2Zn11 were modelled to have Cu–Zn exchange on one sublattice. The corresponding parameters were adjusted to reproduce the copper solubility measurements obtaned by three of three of the present authors and co-workers 98Lia2.

Jayakumar, A.K. Tyagi, in, 2012 5.7 CharacterizationChemical composition has been determined by energy-dispersive X-ray analysis using a focused electron beam. Phase purity and the structure of the samples were analysed using Cu Kα radiation by using a Philips diffractometer (model PW 1071) fitted with a graphite crystal monochromator. The lattice parameters of the compounds were extracted by Rietveld refinement of the XRD data by using the program Fullprof. DC magnetization measurements as a function of field were performed using an EG&G Princeton Applied Research vibrating sample magnetometer (model 4500). X-ray photoelectron spectroscopy (XPS) measurements were performed using an Escalab MK2 spectrometer equipped with an Al Kα (1486.6 eV) source.

The C1s peak set at 284.6 eV was used as reference. For morphological and high-resolution electron microscopy (HRTEM) studies, a high-resolution transmission electron microscope, Hitachi HF-3000F, operated at 300 kV and JEOL, fast TEM 2010HR was used. The TEM specimens were prepared by placing a drop of the suspended particles on carbon-coated Cu grids. The increasing use of HRTEM, energy dispersive X-ray analysis (EDX) and EELS techniques is revealing that precipitation is more complex than that which might be expected from equilibrium conditions. In continuous cast slab, not only may some of the larger precipitates be cored in terms of the major microalloying additions but, depending on location in the slab, and therefore cooling rate, others may be more complex, consisting of two or more phases. Several different morphologies have been identified in Nb-Ti-V microalloyed steels ( Raison, 1982; Chen et al., 1987; Houghton et al., 1982).

Some examples are shown in Fig. 6.2, the ‘dendritic’ types are found mainly at grain boundaries whereas the ‘star’ morphology ( Fig. 6.3) is more common in the grain interiors or in locations closer to the centre of the slab where cooling and solidification structures are markedly different from those near the slab surface ( Figs 6.3a and b) ( Couch, 2001). Given the thermal history of the slab, these morphologies have yet to be explained in any detail and are believed to be a consequence of micro-segregation during solidification. It seems likely that the size of the particles found can only have formed in the interdendritic liquid during the later stages of solidification ( Raison, 1982; Chen et al., 1987). As the solidification sequences depend on steel composition ( Davies and Strangwood, 2009), particularly for carbon contents between the peritectic, 0.04%C, where solidification begins as δ-ferrite, and C contents greater than approximately 0.09%C when austenite forms first, significant differences in the size, composition and morphology of precipitates can be anticipated. The resulting size, type and distribution can then be important factors in the development of the austenite grain structure during reheating of the slab prior to rolling.

The diffusion distances for the microalloying elements for typical slab reheating temperatures and times are small in relation to the interdendrite spacing, which is of the order of 100s of microns where microsegregation of Nb, etc., is found. Hence, the austenite is likely to remain inhomogeneous. An example is shown in Fig. 6.4 taken from the study by Couch (2001), and this illustrates that microsegregated regions of high Nb present in the slab are not entirely eliminated even after times considerably longer than would be used for commercial slab reheating before rolling. The consequences of this type of study have yet to be explored fully but would have implications for the development of austenite grain structure before rolling; should this grain size be too large (of the order of 500 μm and above) or the initial rolling reductions too small, little or no grain refinement is possible unless impracticably large rolling reductions are made ( Cuddy, 1984).

Similar considerations may apply to some of the newer thin slab casting direct charging processes being studied as alternative lower energy (‘greener’) approaches to steel production, the work of Baker and co-workers ( Li et al., 2007; Wilson et al., 2009) being relevant in this context. Anne Julbe, in, 2007 3.1 Static characterization methodsScanning electron microscopy (SEM), coupled with energy dispersive X-ray analysis, is the most classical method used to study zeolite membranes. It gives access to the homogeneity, morphology, adhesion, infiltration and thickness of the zeolite layer.

Crystal sizes can be also evaluated (the length of crystal boundaries influences the permeation properties). HR-TEM and coupled analysis are useful to study the zeolite structure and composition, also within the pores of the support 109. Atomic force microscopy can also be used to study the growth of zeolite films.

X-ray diffraction, including grazing incidence XRD, is needed to study the crystalline phases and the orientation of zeolite crystals grown on supports.Gas adsorption (N 2, Kr) can be used to estimate the relative quantity of zeolite deposited on the support (BET- or Langmuir equation). When a dense substrate is used, ellipsometry gives the film thickness and void volume fraction. Absorption spectroscopies, such as FTIR, are adapted to study the membrane material short range structure.The novel extension of fluorescent confocal optical microscopy (FCOM) has also to be underlined as a qualitative, non-destructive, three-dimensional imaging tool, to view polycrystalline features of MFI membranes. The coupling of this technique with simultaneous reflectance and SEM provides a critical link between the grain structure of MFI membranes and the more qualitative FCOM images.

The selective adsorption of large dye molecules (diameter-tuned) within the grain boundaries throughout the membrane thickness, allows to evidence “quantitatively” non-zeolite pores 184. Neikov, Nikolay A. Yefimov, in, 2019 Energy-Dispersive SpectrometryEnergy-dispersive X-ray spectroscopy, sometimes called energy-dispersive X-ray analysis or energy-dispersive X-ray microanalysis, is based on the measurement of the energy of characteristic X-ray emissions of excited specimens under study.

To stimulate the emission, a high-energy beam of charged particles such as electrons or protons, or a beam of X-rays, is focused into the observable specimen. At rest, an atom within the sample contains a ground state (or unexcited electrons) in discrete energy levels or electron shells bound to the nucleus.

The incident beam may excite an electron in an inner shell, ejecting it from the shell, while creating an electron hole that is filled by an electron from a higher-energy shell. The difference in energy between the higher-energy shell and the lower-energy shell may be released in the form of an X-ray. The number and energy of the X-rays emitted from a specimen can be measured by an energy-dispersive spectrometer that allows us to define the elemental composition of the specimen.The EDS apparatus includes four primary components: the excitative source (electron beam or X-ray beam), the X-ray detector, the pulse processor, and the analyzer.

An excitative electron beam is used in electron microscopes, scanning electron microscopes, and scanning transmission electron microscopes. The X-ray beam excitation is used in X-ray fluorescence spectrometers. A detector is used to convert X-ray energy into voltage signals; this information is sent to a pulse processor, which measures the signals and passes them onto an analyzer for data display and analysis. The most common detector now is the Si(Li) detector cooled to cryogenic temperatures with liquid nitrogen; however, newer systems are often equipped with silicon drift detectors with Peltier cooling systems. Several observations can be made from Table 15.3. 1.Fe content is very high at the interface and drops to  2 wt% within 100 μm. The presence of a small amount of Fe in the rest of the coating implies that Fe ions have diffused in the coating and are likely to form their own compounds.

This suggests the passivation layer is rich in Fe minerals. 2.Mg, K, P, and O contents, except for an abnormal jump in K content at 300 μm, taper off at distances beyond 100 μm. This abnormality in K may be due to the fact that the measurement was right on the grain containing K at that point.

The presence of these elements all along the surface of the coating indicates that MgKPO 4 6H 2O, which is Ceramicrete, forms the major part of the coating. 3.Mg and P contents are high compared to the concentration of K. Mg is high because an excessive amount of MgO/Mg(OH) 2, more than stoichiometrically needed to form MgKPO 4 6H 2O, was added in the coating composition to provide better stability and strength to the coating and to promote faster reaction.

The higher content of P compared to K indicates that there are phosphate forms other than MgKPO 4 6H 2O. They may be iron or magnesium phosphates. 4.The higher content of P and also the presence of Fe at locations  100 μm suggests that, apart from forming the Ceramicrete phase, there may be iron phosphate phases forming in the coating. This will be investigated using Raman spectroscopy data in subsequent sections. 5.Si seems to accumulate at  200 μm and is very low in the rest of the coating.

As has been discussed earlier in Chapter 14, Si forms phosphosilicate amorphous phases, which seem to have accumulated at that distance.The most general observation, however, is that within 100 μm, the concentration of all elements changes with respect to the distance from the substrate, and they taper off beyond 100 μm. This implies that the phases within the passivation layers may be different from the topcoat.

To gain a better insight into the passivation layer, further EDX analysis was done within the first 30 μm, and is discussed in the next section. Apart from the coating material elements (Mg, K, P, O, Ca, Si), impurity elements of initial reagents such as Na, S, and Cl were present, which we have not listed in Table 15.4.

Several conclusions can be drawn from the data in this table: 1.Consistent with the earlier observation made in Table 15.3, the content of Fe in the passivation layer is very high, decreases rapidly away from the substrate, and diffuses in the topcoat. 2.Potassium content is comparatively lower in the passivation layer than in the topcoat. 3.The same is observed for phosphorus.

Even when calculated in molar fraction, it is still higher than the molar fraction of K, implying phases other than MgKPO 4 6H 2O are formed. 4.Silicon content is much higher in the topcoat compared to its concentration in the passivation layer. This means Si does not significantly enter the passivation layer. 5.There is no signficant trend in the Mg content, but it is much lower than in the topcoat.These general observations reinforce the theoretical conclusions drawn in Section 15.3 that the passivation layer is composed of mainly iron oxide and phosphate minerals, such as FeOOH and FePO 4, and the topcoat consists of MgKPO 4 6H 2O. A small amount of Mg found in the passivation layer might be forming a newberyite phase, but at the same time, due to the low content of K, a MgKPO 4 6H 2O phase, if formed, may not be prominent. The high content of silicon in the topcoat suggests that it forms either phosphosilicate complexes or stays as wollastonite that reinforces the topcoat structure. More direct evidence of some of these conclusions were drawn using Raman spectroscopy.

Ahmad Fauzi Ismail. Takeshi Matsuura, in, 2019 3.3.4 Energy Dispersive X-Ray SpectroscopyEnergy-dispersive X-ray spectroscopy (EDS, EDX, or XEDS), sometimes called energy dispersive X-ray analysis (EDXA) or energy dispersive X-ray microanalysis (EDXMA), is an analytical technique used for the elemental analysis or chemical characterization of a sample.

The EDS analysis can be used to determine the elemental composition of individual points or to map out the lateral distribution of elements from the imaged area. It can also be used to obtain compositional information on quasi-bulk specimens (low SEM magnification, high accelerating voltage) or on specific particles, morphologies, or isolated areas on filters or within deposits. The EDS has an analytical capability that can be coupled with several applications including SEM, TEM, and scanning transmission electron microscopy (STEM). Beverly et al. 42 demonstrated that EDS, combined with XPS, FTIR, and SEM, is a valuable diagnostic tool for the analysis of polymeric RO membrane failure and provides valuable information to aid the manufacturers in designing better membranes for RO.

Interaction of an electron beam with a sample target produces a variety of emissions, including x-rays. An energy-dispersive (EDS) detector is used to separate the characteristic x-rays of different elements into an energy spectrum, and EDS system software is used to analyze the energy spectrum in order to determine the abundance of specific elements. EDS can be used to find the chemical composition of materials down to a spot size of a few microns, and to create element composition maps over a much broader raster area. Together, these capabilities provide fundamental compositional information for a wide variety of materials.

How it Works - EDS

EDS systems are typically integrated into either an SEM or EPMA instrument. EDS systems include a sensitive x-ray detector, a liquid nitrogen dewar for cooling, and software to collect and analyze energy spectra. The detector is mounted in the sample chamber of the main instrument at the end of a long arm, which is itself cooled by liquid nitrogen. The most common detectors are made of Si(Li) crystals that operate at low voltages to improve sensitivity, but recent advances in detector technology make availabale so-called 'silicon drift detectors' that operate at higher count rates without liquid nitrogen cooling.

An EDS detector contains a crystal that absorbs the energy of incoming x-rays by ionization, yielding free electrons in the crystal that become conductive and produce an electrical charge bias. The x-ray absorption thus converts the energy of individual x-rays into electrical voltages of proportional size; the electrical pulses correspond to the characteristic x-rays of the element.

Strengths

• When used in 'spot' mode, a user can acquire a full elemental spectrum in only a few seconds. Supporting software makes it possible to readily identify peaks, which makes EDS a great survey tool to quickly identify unknown phases prior to quantitative analysis.
• EDS can be used in semi-quantitative mode to determine chemical composition by peak-height ratio relative to a standard.

Limitations

• There are energy peak overlaps among different elements, particularly those corresponding to x-rays generated by emission from different energy-level shells (K, L and M) in different elements. For example, there are close overlaps of Mn-K_α and Cr-K_β, or Ti-K_α and various L lines in Ba. Particularly at higher energies, individual peaks may correspond to several different elements; in this case, the user can apply deconvolution methods to try peak separation, or simply consider which elements make 'most sense' given the known context of the sample.
• Because the wavelength-dispersive (WDS) method is more precise and capable of detecting lower elemental abundances, EDS is less commonly used for actual chemical analysis although improvements in detector resolution make EDS a reliable and precise alternative.
• EDS cannot detect the lightest elements, typically below the atomic number of Na for detectors equipped with a Be window. Polymer-based thin windows allow for detection of light elements, depending on the instrument and operating conditions.

Results

A typical EDS spectrum is portrayed as a plot of x-ray counts vs. energy (in keV). Energy peaks correspond to the various elements in the sample. Generally they are narrow and readily resolved, but many elements yield multiple peaks. For example, iron commonly shows strong K_α and K_β peaks. Elements in low abundance will generate x-ray peaks that may not be resolvable from the background radiation.

References

• Severin, Kenneth P., 2004, Energy Dispersive Spectrometry of Common Rock Forming Minerals. Kluwer Academic Publishers, 225 p.--Highly recommended reference book of representative EDS spectra of the rock-forming minerals, as well as practical tips for spectral acquisition and interpretation.
• Goldstein, J. (2003) Scanning electron microscopy and x-ray microanalysis. Kluwer Adacemic/Plenum Pulbishers, 689 p.
• Reimer, L. (1998) Scanning electron microscopy : physics of image formation and microanalysis. Springer, 527 p.
• Egerton, R. F. (2005) Physical principles of electron microscopy : an introduction to TEM, SEM, and AEM. Springer, 202.
• Clarke, A. R. (2002) Microscopy techniques for materials science. CRC Press (electronic resource)

Related Links

• Petroglyph--An atlas of images using electron microscope, backscattered electron images, element maps, energy dispersive x-ray spectra, and petrographic microscope-- Eric Chrisensen, Brigham Young University

Teaching Activities

• Argast, Anne and Tennis, Clarence F., III, 2004, A web resource for the study of alkali feldspars and perthitic textures using light microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy, Journal of Geoscience Education 52, no. 3, p. 213-217.