Electron Probe Microanalysis Methods Research Articles

Electron Probe Microanalysis of Bromine in Minerals and Glasses with Correction for Spectral Interference from Aluminium, and Comparison with Microbeam Synchrotron X‐Ray Fluorescence Spectrometry

The strong spectral interference between Br‐ and Al‐induced X‐ray lines hampers the utilisation of electron probe microanalysis (EPMA) for measuring Br mass fractions in Al‐bearing minerals and glasses. Through measuring Br‐free Al‐bearing materials, we established an EPMA method to quantify the overlap from AlKα on BrLβ, which can be expressed as a linear function of the Al2O3 content. The count rate of the BrLβ peak signal was enhanced by high beam currents and long measurement times. Application of this EPMA method to Al‐ and Br‐bearing materials, such as sodalite and scapolite, and to five experimental glasses yielded Br mass fractions (in the range of 250–4000 μg g−1) that are consistent with those measured by microbeam synchrotron X‐ray fluorescence (μ‐SXRF) spectrometry. The EPMA method has an estimated detection limit of ~ 100–300 μg g−1. We propose that this method is useful for measuring Br mass fractions (hundreds to thousands of μg g−1) in Al‐bearing minerals and glasses, including those produced in Br‐doped experiments. In addition, the natural marialitic scapolite (ON70) from Mpwapwa (Tanzania) containing homogeneously distributed high mass fractions of Br (2058 ± 56 μg g−1) and Cl (1.98 ± 0.03% m/m) is an ideal reference material for future in situ analyses.

A new EPMA method for fast trace element analysis in simple matrices

It is well known that trace element sensitivity in electron probe microanalysis (EPMA) is limited by intrinsic random variation in the X-ray continuum background and weak signals at low concentrations. The continuum portion of the background is produced by deceleration of the electron beam by the Coulombic field of the specimen atoms. In addition to the continuum, the background also includes interferences from secondary emission lines, “holes” in the continuum from secondary Bragg diffraction, non-linear curvature of the wavelength-dispersive spectrometer (WDS) continuum and other background artifacts. Typically, the background must be characterized with sufficient precision (along with the peak intensity of the emission line of interest, to obtain the net intensity for subsequent quantification), to attain reasonable accuracy for quantification of the elements of interest. Traditionally we characterize these background intensities by measuring on either side of the emission line and interpolate the intensity underneath the peak to obtain the net intensity. Instead, by applying the mean atomic number (MAN) background calibration curve method proposed in this paper for the background intensity correction, such background measurement artifacts are avoided through identification of outliers within a set of standards. We divide the analytical uncertainty of the MAN background calibration between precision errors and accuracy errors. The precision errors of the MAN background calibration are smaller than direct background measurement, if the mean atomic number of the sample matrix is precisely known. For a simple matrix and a suitable blank standard, a high-precision blank correction can offset the accuracy component of the MAN uncertainty. Use of the blank-corrected-MAN background calibration can further improve our measurement precision for trace elements compared to traditional off-peak measurements because the background determination is not limited by continuum X-ray counting statistics. For trace element mapping of a simple matrix, the background variance due to major element heterogeneity is exceedingly small and high-precision two-dimensional background correction is possible.

Distributions of Sr and Fe and their influence on modification of hypoeutectic Al-Si alloy

The influence of cooling rate and Fe-containing phases on Sr-modification of Si phases in hypoeutectic Al-Si alloys, a problem with great industrial importance, was investigated. The microstructures of samples were examined using scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX). A new method of electron probe microanalysis (EPMA) map scanning was used to analyze the Sr distribution, which gave quantitative results covering more Si particles. EPMA map scanning, together with SEM with EDX, was also used in analyzing the distribution of Fe phases. Results show that Fe-containing phase was related to the unmodified Si particles in samples with partial modification failure and the plate-like Si phases in samples without modification failure. Such a relationship was further confirmed by the microstructure observation. In conclusion, a partial failure of Sr-modification can be caused by both slow cooling rate and Fe-containing phases.

Evaluation of P2O5 distribution inside the main clinker minerals by the application of EPMA method

The formation of Portland clinker phases has taken place in thermodynamically non-equilibrium state between macro-oxides CaO, SiO2, Al2O3, Fe2O3 and MgO from raw meal and P2O5 from bone meal. The paper deals with the study of clinker minerals as solid solutions with P2O5 during the clinkerization of raw mixture containing bone meal (BM). The ash of BM has contributed as a raw material to the formation of different clinker phases. Electron probe microanalysis (EPMA) method was used to determine the preferential distribution of P2O5 inside calcium silicate phases and its influence upon C2S/C3S ratio. Basing on these results, composition of solid solution of C2S and C3S was established.

Study of solar silicon multicrystals by SEM and EPMA methods

Multisilicon crystals grown from refined metallurgical silicon are studied by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The varieties of intergranular boundaries are revealed. Impurities are found to be contained in inclusions in multisilicon. The intergranular boundaries contain no impurities, and they do not concentrate the elements present in multisilicon. It is proved experimentally that, in the homogeneous areas of the crystal the lifetime of minor charge carriers is maximum, whereas its minimum value corresponds to the areas with numerous intergranular boundaries.

Range of homogeneity of the β-Al9Mn3Si phase of the Al – Mn – Si system at 823 K

The boundaries of the range of homogeneity of the β-Al9Mn3Si phase of the Al – Mn – Si system at 823 K are determined by the methods of electron probe microanalysis and scanning electron microscopy. It is shown that this phase has a narrow range of homogeneity with respect to manganese (24 – 26 at.%); the concentration of silicon in it varies from 3.7 to 18.5 at.%. The parameters of the crystal lattice of the compound are determined.

Microchemical and structural regular variability of apatites in “overbuilt” enamel and dentin of human molar teeth

The aim of a recent paper was to recognize the chemical and structural changes in apatites, which form both the enamel and the dentin of the human tooth. The aim was achieved by scrutinizing the linear elemental profiles along the cross-sections of human molar teeth. Essentially, the task was accomplished with the application of the Electron Probe Microanalysis method and with some additional studies by Micro-Raman spectrometry. All the trends in linear profiles were strictly determined. In the enamel zone they were either increasing or decreasing curves of exponential character. The direction of the investigations was to start with the tooth surface and move towards the dentin–enamel junction (DEJ). The results of the elemental studies were more visible when the detected material was divided, in an arbitrary way, into the prevailing “core” enamel (∼93.5% of the total mass) and the remaining “overbuilt” enamel. The material in the “core” enamel was fully stable, with clearly determined chemical and mechanical features. However, the case was totally different in the “overbuilt enamel”, with dynamic changes in the composition. In the “overbuilt” layer Ca, P, Cl and F profiles present the decaying distribution curves, whereas Mg, Na, K and CO 3 2− present the growing ones. Close to the surface of the tooth the mixture of hydroxy-, chlor- and fluor-apatite is formed, which is much more resistant than the rest of the enamel. On passing towards the DEJ, the apatite is enriched with Na, Mg and CO 3 2−. In this location, three of six phosphate groups were substituted with carbonate groups. Simultaneously, Mg is associated with the hydroxyl groups around the hexad axis. In this way, the mechanisms of exchange reactions were established. The crystallographic structures were proposed for new phases located close to DEJ. In the dentin zone, the variability of elemental profiles looks different, with the most characteristic changes occurring in Mg and Na concentrations. Mg content increases more and more when passing deeper in the dentin, while Na content decreases along this route. Na concentration reaches its maximum when it is very close to the DEJ zone. But the carbonate and phosphate spatial distributions inside the dentin refute the potential conclusions drawn from the studies of Mg and Na profiles.

η Phase Formation Mechanism at Cemented Carbide YG30/Steel 1045 Joints during Tungsten-Inert-Gas Arc Welding

Cemented carbide YG30 and steel 1045 were welded with various Ni-Fe-C filling alloys via the Cemented carbide YG30 and steel 1045 were welded with various Ni-Fe-C filling alloys via the tungsten-inert-gas (TIG) arc welding. η phase formation at the welding joints was investigated via scanning electronic microscope (SEM), transmission electronic microscope (TEM) coupled with selected diffraction, and electron probe microanalysis methods. η phases in three different morphologies were identified and they appeared to form in different mechanisms. The η phase formed at the heat-affected zone (HAZ) exhibited a similar size to that of WC particles and its formation was mainly attributed to the inter diffusion among W, C and Fe, Co, Ni in solid-state γ phase. The large-size η phase near the interface between YG30 and weld bead was due to the coarsening of tiny η grains in the liquid weld bead. The small-size η phase was formed via precipitation from the γ phase during cooling. The η phase formation could be controlled by optimization of C and/or Ni concentration in the filling alloys.

The influence of aluminum on the nickel and chromium diffusion into copper during the deposition and thermal treatment of gas-thermal coatings

The method of electron probe microanalysis is applied to analyze the distribution of elements over the diffusion layer obtained by the deposition on copper of gas-thermal coatings involving Al, Ni, Cr, Fe and subsequent thermal treatment. It is established that the penetration depth and concentration of the coating elements reach their maximal values in the case of the presence of an aluminum sublayer.

Assessment of porosity and structure of powder materials based on mechanically activated Ni-Fe-NaCl charges

Electron-probe microanalysis methods were used to study the formation of structure and the distribution of various components in high-porosity powder materials during heat treatment of compacts based on Ni-Fe-NaCl charges mechanically activated in fluid media. We confirmed the hypothesis that agglomerates are formed during mechanical activation of Ni-and Fe-based composite-particle charges in fluid media. A causal relationship was established between formation of structure in compacts and structure of the high-porosity powder material after heat treatment. A technique was proposed for determining the local porosity of the sintered high-porosity powder material. The structure of the high-porosity powder material was found to consist of large pores surrounded by powder material containing pores of smaller diameter.

Composition and mechanical properties of hard ceramic coating containing α-Al 2O 3 produced by microarc oxidation on Ti–6Al–4V alloy

Ceramic coatings with 1100–1600 HK 50 g hardness were deposited on Ti–6Al–4V alloy substrates using a microarc oxidation (MAO) technique, based on a dielectric barrier discharge created during anodic oxidation in an aqueous electrolyte. The influences of electrolyte concentration, deposition time and the cathodic to anodic current ratio Ic/Ia on phase composition and mechanical properties of the coatings have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis methods (EPMA), as well as microhardness measurement, direct pull-off and impact tests. The results show α-Al 2O 3 phase, which greatly improved the hardness of the coatings, can be obtained at high concentration of NaAlO 2 and its relative content increases with decreasing Ic/Ia ratio. The direct pull-off test and impact test results indicate that the films have the excellent adhesion with the substrate.

Inhibition of corrosion of mild steel by sodium n,n-diethyl dithiocarbamate in hydrochloric acid solution

The effect of sodium n,n-diethyl dithiocarbamate (SDEDTC) on the corrosion of mild steel in 0·5 mol L-1 HCl solution was studied using weight loss and potentiodynamic polarisation methods. Experimental data revealed that SDEDTC acted as an inhibitor in the acid environment and, furthermore, that the compound was a mixed type inhibitor, predominating as a cathodic inhibitor. It was found that the inhibition efficiency increased with an increase in SDEDTC concentration at temperatures in the range 303–333 K. The experimental data for the inhibitor fitted the Flory–Huggins adsorption isotherm and the El–Awady thermodynamic kinetic model. The corrosion inhibition mechanism of SDEDTC on mild steel in HCl solution was also investigated by infrared spectra and electron probe microanalysis methods. The process of inhibition is attributed to the formation of an adsorbed film on the metal surface, which protects the metal against corrosive agents.

Phase Diagram of the Ni ― Os System

Metallography, DTA, x-ray, and electron-probe microanalysis methods have been applied to alloys with four compositions in the cast and annealed states. A phase diagram has been constructed for the entire concentration range on the basis of these data together with published ones. The diagram is of peritectic type, and the peritectic temperature is 1500°C. The mutual solubilities of the components at that temperature are 13.3 at.% osmium in nickel and 13 at. % nickel in osmium. The solubility of osmium in nickel falls to 9.2 at. % when the temperature is reduced to 1200°C.

Phase identification of microfeatures using EPMA methods, especially high-resolution X-ray spectroscopy

Methods of electron-probe microanalysis (EPMA), with some input from scanning and transmission electron microscopy (SEM/TEM), are applied for the identification of micro-scale constituents in a solid matrix. The subject of the study is a magnesium alloy composite, which contains silicon carbide-based fibres made by a liquid metal infiltration process. Backscattered electron imaging of the composite in the SEM showed that during composite manufacture, fibres were chemically attacked by the metal, many of the fibres exhibiting three distinct grey levels, indicative of different reaction zones, and others appearing uniformly black. EPMA measurements showed that each region contained ∼12 wt.% oxygen and that penetration of the fibre by magnesium was accompanied by a reduction in the concentration of silicon and carbon. From studying the position and shape of specific X-ray lines it was shown that magnesium penetration involved a chemical reaction with silicon oxycarbide, established in earlier EPMA studies as one of the fibre constituents. Also, in the outermost region, aluminium in the alloy reacted with free carbon in the fibre to form aluminium carbide and with magnesium to produce a Mg–Al intermetallic. The composition of black fibres was quite different from the grey ones, with negligible silicon and only a small amount of aluminium. Oxygen levels in black fibres were consistent with complete oxidation, indicating these fibres were subjected, locally, to severe oxidising conditions during composite manufacture. In the metal matrix itself, particles of a mixed magnesium/aluminium oxide, silicon carbide and magnesium silicide were observed, the latter two phases forming as silicon and carbon were ejected from fibres.

Detection Limits of Grazing-Exit EPMA for Particle Analysis

In conventional electron probe microanalysis (EPMA), the electron-induced X-rays are measured at large take-off angles of about 45°. In the grazing exit EPMA (GE-EPMA) method, they are measured at small angles (< 1°). X-rays emitted from deep positions can not be detected at grazing exit angles due to refraction effects at sample-vacuum interface; therefore, it is possible to measure X-rays emitted only from near the surface with a low background. GE-EPMA is especially suitable for the analysis of particles deposited on a flat sample carrier. The detection limits of GE-EPMA were investigated for artificial particles (Al2O3, Fe2O3 and PbO2 , particle sizes: 1 ∼ 18 μm) deposited on flat sample carriers of Au thin films–Si wafers. The detection limits improved with decreasing exit angle. The detection limits for characteristic X-rays at an exit angle of approximately 1.1° were 2–4 times lower than at 45°. A minimum detection limit of ca. 0.1% was obtained for Al in small particles.

Morphology and structure of various phases at the bonding interface of Al/steel formed by explosive welding

The bonding interface of explosively-welded aluminium and steel in three explosive conditions have been investigated by using scanning electron microscopy, transmission electron microscopy, electron diffraction and electron probe microanalysis methods. The results show that all the interfaces have the shape of waves with curled front formed by process of superplasticity and some discontinuous reacted zones. They consist of amorphous and nano sized crystals and quasi-crystals as well as the compounds such as AlFe, Al2Fe, Al3Fe and Al6Fe with various shapes. The basal steel crystal near the interface has structure of martensite and perlite crystals which are deformed by the process of superplasticity. The size of reacted zone becomes large with increasing amount of explosive charge powder and separation of the driver Al plate from the basal steel plate.

Analysis of glass characteristics using optical and electrophysical methods

Glass parameters are studied using the methods of electron-probe microanalysis, Auger electron ellipsometry, and spectrophotometry. The optical and color parameters of tinted glasses are determined, and the state of their surface is studied.

Salt doping in electronprobe microanalysis

A new method of electronprobe microanalysis (EPMA) is suggested. It is based on creating ionic conductivity in frozen water solutions and in polymer films by doping them with a salt. This procedure is effective to prevent surface charging and allows imaging of nonconducting samples by scanning electron microscopy (SEM) as well as X-ray microanalysis. Specifically, this procedure makes it possible to perform EPMA of samples with xerogel matrices, which were used for molecular laser microprobe mass spectrometry analysis, and consequently to provide complex microprobe examination of samples.

Infrared Spectroscopy in Characterization of Metamorphic Garnets in Relation to other Techniques

For investigating the complex crystallochemical character of garnets occurring in multiply metamorphosed rock sequence of upper amphibolite-granulite facies, infrared spectroscopy has been found to offer some valuable clues as to the presence of OH-bands, unexpected in high P-T mineral phases. The investigation has been supplemented by EPMA (electron probe microanalysis) and X-ray diffraction method. IR studies of seven garnets from different areas of the Sittampundi (Tamil Nadu) metamorphic terrains reveal the presence of OH stretching components (around 3600 cm−1). A linear decrease in wavenumbers of IR bands in the 1000-450 cm−1 region is observed to be related with changes of cell-edges.

Tephra geochemistry: a discussion of some persistent analytical problems

Distal tephrochronological studies are reliant upon precise and accurate geochemical quantitation. This quantitation can involve difficulties not often encountered in more conventional petrology. Solving these problems is of particular importance in the Holocene (and Late Quaternary) of northwest Europe, where numerous tephra layers of Icelandic origin have been detected in peat bogs and lake and marine sediments. Electron probe microanalysis (EPMA) has proved the most applicable analytical technique when insufficient quantities of tephra are available for bulk analysis. Standard EPMA techniques require fine tuning to the tephra problem as the geochemical instability of glass is a common feature. In many previous studies, geochemical data of avoidably low quality have been produced, and little attention appears to have been directed to modification of EPMA methods. It is suggested that the 'black box' approach to geochemical analysis should be avoided by the consideration of several factors. These include minimization of sodium mobility during analysis, prevention and nonacceptance of low analytical totals, non-normalization of data, and making provision for the acceptable presentation and statistical treatment of data. Amongst tephrochronologists, these suggestions may not receive universal acceptance, but it is hoped that they will serve to promote further discussion on a much neglected topic. Until reliable analytical techniques are universally adopted, there is a real possibility that erroneous tephrochronologies will be established.